| 1. |
- Chesnut, Randall, et al.
(författare)
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A management algorithm for adult patients with both brain oxygen and intracranial pressure monitoring : the Seattle International Severe Traumatic Brain Injury Consensus Conference (SIBICC)
- 2020
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Ingår i: Intensive Care Medicine. - : Springer. - 0342-4642 .- 1432-1238. ; 46:5, s. 919-929
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Tidskriftsartikel (refereegranskat)abstract
- Background: Current guidelines for the treatment of adult severe traumatic brain injury (sTBI) consist of high-quality evidence reports, but they are no longer accompanied by management protocols, as these require expert opinion to bridge the gap between published evidence and patient care. We aimed to establish a modern sTBI protocol for adult patients with both intracranial pressure (ICP) and brain oxygen monitors in place.Methods: Our consensus working group consisted of 42 experienced and actively practicing sTBI opinion leaders from six continents. Having previously established a protocol for the treatment of patients with ICP monitoring alone, we addressed patients who have a brain oxygen monitor in addition to an ICP monitor. The management protocols were developed through a Delphi-method-based consensus approach and were finalized at an in-person meeting.Results: We established three distinct treatment protocols, each with three tiers whereby higher tiers involve therapies with higher risk. One protocol addresses the management of ICP elevation when brain oxygenation is normal. A second addresses management of brain hypoxia with normal ICP. The third protocol addresses the situation when both intracranial hypertension and brain hypoxia are present. The panel considered issues pertaining to blood transfusion and ventilator management when designing the different algorithms.Conclusions: These protocols are intended to assist clinicians in the management of patients with both ICP and brain oxygen monitors but they do not reflect either a standard-of-care or a substitute for thoughtful individualized management. These protocols should be used in conjunction with recommendations for basic care, management of critical neuroworsening and weaning treatment recently published in conjunction with the Seattle International Brain Injury Consensus Conference.
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| 2. |
- Chesnut, Randall M., et al.
(författare)
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Perceived Utility of Intracranial Pressure Monitoring in Traumatic Brain Injury : A Seattle International Brain Injury Consensus Conference Consensus-Based Analysis and Recommendations
- 2023
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Ingår i: Neurosurgery. - : Oxford University Press. - 0148-396X .- 1524-4040. ; 93:2, s. 399-408
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Intracranial pressure (ICP) monitoring is widely practiced, but the indications are incompletely developed, and guidelines are poorly followed. OBJECTIVE: To study the monitoring practices of an established expert panel (the clinical working group from the Seattle International Brain Injury Consensus Conference effort) to examine the match between monitoring guidelines and their clinical decision-making and offer guidance for clinicians considering monitor insertion.METHODS: We polled the 42 Seattle International Brain Injury Consensus Conference panel members' ICP monitoring decisions for virtual patients, using matrices of presenting signs (Glasgow Coma Scale [GCS] total or GCS motor, pupillary examination, and computed tomography diagnosis). Monitor insertion decisions were yes, no, or unsure (traffic light approach). We analyzed their responses for weighting of the presenting signs in decision-making using univariate regression.RESULTS: Heatmaps constructed from the choices of 41 panel members revealed wider ICP monitor use than predicted by guidelines. Clinical examination (GCS) was by far the most important characteristic and differed from guidelines in being nonlinear. The modified Marshall computed tomography classification was second and pupils third. We constructed a heatmap and listed the main clinical determinants representing 80% ICP monitor insertion consensus for our recommendations.CONCLUSION: Candidacy for ICP monitoring exceeds published indicators for monitor insertion, suggesting the clinical perception that the value of ICP data is greater than simply detecting and monitoring severe intracranial hypertension. Monitor insertion heatmaps are offered as potential guidance for ICP monitor insertion and to stimulate research into what actually drives monitor insertion in unconstrained, real-world conditions.
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| 3. |
- Edefell, Ellen, et al.
(författare)
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Digging deep into a GAC filter – Temporal and spatial profiling of adsorbed organic micropollutants
- 2022
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Ingår i: Water Research. - : Elsevier BV. - 0043-1354 .- 1879-2448. ; 218
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Tidskriftsartikel (refereegranskat)abstract
- A large pilot-scale granular activated carbon (GAC) filter was operated downstream in a full-scale wastewater treatment plant to remove organic micropollutants. To describe the spatial and temporal developments of micropollutant adsorption profiles in the GAC filter, micropollutants were extracted from GAC media taken at various filter depths and number of treated bed volumes. At a low number of treated bed volumes (2600 BVs), most micropollutants were adsorbed in the top layers of the filter. At increasing number of treated bed volumes (7300–15,500 BVs), the adsorption front for micropollutants progressed through the filter bed at varying rates, with sulfamethoxazole, fluconazole, and PFOS reaching the bottom layer before carbamazepine and other well-adsorbing micropollutants, such as propranolol and citalopram. Higher amounts of adsorbed micropollutants in the bottom layer of the filter bed resulted in decreased removal efficiencies in the treated wastewater. Mass estimations indicated biodegradation for certain micropollutants, such as naproxen, diclofenac, and sulfamethoxazole. A temporary increase in the concentration of the insecticide imidacloprid could be detected in the filter indicating that extraction of adsorbed micropollutants could provide an opportunity for backtracking of loading patterns.
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| 4. |
- Hawryluk, Gregory W. J., et al.
(författare)
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A management algorithm for patients with intracranial pressure monitoring : the Seattle International Severe Traumatic Brain Injury Consensus Conference (SIBICC)
- 2019
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Ingår i: Intensive Care Medicine. - : Springer. - 0342-4642 .- 1432-1238. ; 45:12, s. 1783-1794
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Tidskriftsartikel (refereegranskat)abstract
- Background: Management algorithms for adult severe traumatic brain injury (sTBI) were omitted in later editions of the Brain Trauma Foundation's sTBI Management Guidelines, as they were not evidence-based.Methods: We used a Delphi-method-based consensus approach to address management of sTBI patients undergoing intracranial pressure (ICP) monitoring. Forty-two experienced, clinically active sTBI specialists from six continents comprised the panel. Eight surveys iterated queries and comments. An in-person meeting included whole- and small-group discussions and blinded voting. Consensus required 80% agreement. We developed heatmaps based on a traffic-light model where panelists' decision tendencies were the focus of recommendations.Results: We provide comprehensive algorithms for ICP-monitor-based adult sTBI management. Consensus established 18 interventions as fundamental and ten treatments not to be used. We provide a three-tier algorithm for treating elevated ICP. Treatments within a tier are considered empirically equivalent. Higher tiers involve higher risk therapies. Tiers 1, 2, and 3 include 10, 4, and 3 interventions, respectively. We include inter-tier considerations, and recommendations for critical neuroworsening to assist the recognition and treatment of declining patients. Novel elements include guidance for autoregulation-based ICP treatment based on MAP Challenge results, and two heatmaps to guide (1) ICP-monitor removal and (2) consideration of sedation holidays for neurological examination.Conclusions: Our modern and comprehensive sTBI-management protocol is designed to assist clinicians managing sTBI patients monitored with ICP-monitors alone. Consensus-based (class III evidence), it provides management recommendations based on combined expert opinion. It reflects neither a standard-of-care nor a substitute for thoughtful individualized management.
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| 5. |
- Roberts, Sigrid C, et al.
(författare)
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Arginase plays a pivotal role in polyamine precursor metabolism in Leishmania. Characterization of gene deletion mutants.
- 2004
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Ingår i: J Biol Chem. - 0021-9258. ; 279:22, s. 23668-78
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Tidskriftsartikel (refereegranskat)abstract
- The polyamine pathway of protozoan parasites has been successfully targeted in anti-parasitic therapies and is significantly different from that of the mammalian host. To gain knowledge into the metabolic routes by which parasites synthesize polyamines and their precursors, the arginase gene was cloned from Leishmania mexicana, and Deltaarg null mutants were created by double targeted gene replacement and characterized. The ARG sequence exhibited significant homology to ARG proteins from other organisms and predicted a peroxisomal targeting signal (PTS-1) that steers proteins to the glycosome, an organelle unique to Leishmania and related parasites. ARG was subsequently demonstrated to be present in the glycosome, whereas the polyamine biosynthetic enzymes, in contrast, were shown to be cytosolic. The Deltaarg knockouts expressed no ARG activity, lacked an intracellular ornithine pool, and were auxotrophic for ornithine or polyamines. The ability of the Deltaarg null mutants to proliferate could be restored by pharmacological supplementation, either with low putrescine or high ornithine or spermidine concentrations, or by complementation with an arginase episome. Transfection of an arg construct lacking the PTS-1 directed the synthesis of an arg that mislocalized to the cytosol and notably also complemented the genetic lesion and restored polyamine prototrophy to the Deltaarg parasites. This molecular, biochemical, and genetic dissection of ARG function in L. mexicana promastigotes establishes: (i) that the enzyme is essential for parasite viability; (ii) that Leishmania, unlike mammalian cells, expresses only one ARG activity; (iii) that the sole vital function of ARG is to provide polyamine precursors for the parasite; and (iv) that ARG is present in the glycosome, but this subcellular milieu is not essential for its role in polyamine biosynthesis.
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| 6. |
- Sarigul, Buse, et al.
(författare)
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Prognostication and Goals of Care Decisions in Severe Traumatic Brain Injury : A Survey of The Seattle International Severe Traumatic Brain Injury Consensus Conference Working Group
- 2023
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Ingår i: Journal of Neurotrauma. - : Mary Ann Liebert. - 0897-7151 .- 1557-9042. ; 40:15-16, s. 1707-1717
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Tidskriftsartikel (refereegranskat)abstract
- Best practice guidelines have advanced severe traumatic brain injury (TBI) care; however, there is little that currently informs goals of care decisions and processes despite their importance and frequency. Panelists from the Seattle International severe traumatic Brain Injury Consensus Conference (SIBICC) participated in a survey consisting of 24 questions. Questions queried use of prognostic calculators, variability in and responsibility for goals of care decisions, and acceptability of neurological outcomes, as well as putative means of improving decisions that might limit care. A total of 97.6% of the 42 SIBICC panelists completed the survey. Responses to most questions were highly variable. Overall, panelists reported infrequent use of prognostic calculators, and observed variability in patient prognostication and goals of care decisions. They felt that it would be beneficial for physicians to improve consensus on what constitutes an acceptable neurological outcome as well as what chance of achieving that outcome is acceptable. Panelists felt that the public should help to define what constitutes a good outcome and expressed some support for a "nihilism guard." More than 50% of panelists felt that if it was certain to be permanent, a vegetative state or lower severe disability would justify a withdrawal of care decision, whereas 15% felt that upper severe disability justified such a decision. Whether conceptualizing an ideal or existing prognostic calculator to predict death or an unacceptable outcome, on average a 64-69% chance of a poor outcome was felt to justify treatment withdrawal. These results demonstrate important variability in goals of care decision making and a desire to reduce this variability. Our panel of recognized TBI experts opined on the neurological outcomes and chances of those outcomes that might prompt consideration of care withdrawal; however, imprecision of prognostication and existing prognostication tools is a significant impediment to standardizing the approach to care-limiting decisions.
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| 7. |
- Andreasson, Ingrid, et al.
(författare)
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Functional outcome after corrective osteotomy for malunion of the distal radius: a randomised, controlled, double-blind trial
- 2020
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Ingår i: International Orthopaedics. - : Springer Science and Business Media LLC. - 0341-2695 .- 1432-5195. ; 44:7, s. 1353-1365
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Tidskriftsartikel (refereegranskat)abstract
- Purpose The purpose of this randomised, controlled, double-blind trial was to evaluate functional outcome during the first year after corrective osteotomy for malunited distal radius fractures, with or without filling the osteotomy void. Method Patients were randomised to receive a HydroSet bone substitute or no graft. Cortical contact was maintained and stabilisation of the osteotomy was carried out with a DiPhos R- or RM Plate. To evaluate subjective functional outcome, the Patient-Rated Wrist Evaluation (PRWE), the Quick Disabilities of the Arm, Shoulder and Hand Questionnaire (Q-DASH), the Canadian Occupational Performance Measure (COPM) and the RAND-36 were used. Moreover, range of motion and grip strength were measured by blinded evaluators. Evaluations were made pre-operatively and three, six and 12 months post-operatively. Results There were no significant differences between the groups at any time point post-operatively with respect to any of the PROMs that were used or range of motion or grip strength (p> 0.05). In both groups, there was a significant improvement at the 12-month follow-up compared with pre-operatively for the PRWE, the Q-DASH and the COPM satisfaction scores. The RAND-36 revealed no significant differences except for two domains, in which there was an improvement in the treatment group (p< 0.05). For grip strength and for range of motion in all movement directions, except dorsal extension, there was a significant improvement in both groups (p< 0.05). Conclusion There is no significant difference in functional outcome during the first year after corrective open-wedge distal radius osteotomy, where cortical contact is maintained, regardless of whether or not bone substitute to fill the void is used.
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| 8. |
- Andreasson, Ingrid, et al.
(författare)
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Long-term outcomes of corrective osteotomy for malunited fractures of the distal radius
- 2020
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Ingår i: Journal of Plastic Surgery and Hand Surgery. - : Medical Journals Sweden AB. - 2000-656X .- 2000-6764. ; 54:2, s. 94-100
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Tidskriftsartikel (refereegranskat)abstract
- The aim was to investigate the long-term outcome after corrective osteotomy for malunion of distal radius fractures. Radiological findings, function, activity performance, pain, health-related quality of life and self-efficacy were studied. Evaluation of 37 patients 3-10 years after osteotomy fixated with a volar plate. Conventional radiographs were taken. Grip strength and range of motion were evaluated. Scores from the Patient Rated Wrist Evaluation (PRWE) were compared with normative values. The RAND-36 was used for evaluation of health-related quality of life and the General Self-Efficacy scale (S-GSE) for self-efficacy. Radial height, volar tilt, and ulnar variance improved postoperatively. In the long term, the corrections were maintained. Radiographs showed significantly more advanced osteoarthritis. Mean grip strength was 31 kg (SD 13) 89%, and range of motion varied between 80% and 95% compared to the uninjured side. The median PRWE was 12 points (0-99). The study group experienced higher levels of pain than reference values. There was a moderate correlation between the PRWE and volar tilt (rs = 0.453, p = .006) and grip strength (rs = 0.40, p = .014). At long-term follow-up functional outcome after a corrective osteotomy is generally good, but patients may experience some degree of pain. Corrective osteotomy might be considered for patients with a poor functional outcome after a distal radius fracture.
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| 9. |
- Dance, D, et al.
(författare)
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Breast dosimetry using high-resolution voxel phantoms
- 2005
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Ingår i: Radiation Protection Dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 359-363
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Tidskriftsartikel (refereegranskat)abstract
- A computer model of X-ray mammography has been developed, which uses quasi-realistic high-resolution voxel phantoms to simulate the breast. The phantoms have 400 μm voxels and simulate the three-dimensional distributions of adipose and fibroglandular tissues, Cooper's ligaments, ducts and skin and allow the estimation of dose to individual tissues. Calculations of the incident air kerma to mean glandular dose conversion factor, g, were made using a Mo/Mo spectrum at 28 kV for eight phantoms in the thickness range 40-80 mm and of varying glandularity. The values differed from standard tabulations used for breast dosimetry by up to 43%, because of the different spatial distribution of glandular tissue within the breast. To study this further, additional voxel phantoms were constructed, which gave variations of between 9 and 59% compared with standard values. For accurate breast dosimetry, it is therefore very important to take the distribution of glandular tissues into account. © The Author 2005. Published by Oxford University Press. All rights reserved.
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| 10. |
- Elden, Helen, 1959, et al.
(författare)
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Postpartum septic symphysitis, a rare condition with possible long-term consequences: a cohort study with long-term follow-up
- 2021
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Ingår i: BMC Pregnancy and Childbirth. - : Springer Science and Business Media LLC. - 1471-2393. ; 21:1
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Tidskriftsartikel (refereegranskat)abstract
- Background Postpartum septic symphysitis (PPSS) is defined as acute onset of severe pain around the symphysis, restricted movement, fever, and elevated inflammatory parameters. It is a rare but serious condition requiring urgent diagnosis and treatment. The aim of this study was to describe the incidence, symptoms, diagnosis, treatment, and long-term follow-up of PPSS. Methods This follow-up study included 19 out of 21 women diagnosed with PPSS from 1989 to 2017 at one tertiary care hospital in Sweden. Clinical data were retrieved from hospital records and compared to those retrieved from a regional registry. Women completed a postal questionnaire, and those who reported lumbopelvic pain (LPP) were offered a clinical examination. Results 1) PPSS was diagnosed after a normal postpartum period of 24 to 50 h by blood tests (n = 19/19), ultrasonography (n = 9 /19), computer tomography (n = 8/19) or magnetic resonance imaging (n = 16/19) Treatment included aspiration of symphyseal abscesses, i.v. antibiotics and different physiotherapeutic interventions. Women with PPSS more frequently were primiparous (n = 14/19, p = 0.001), had an instrumental delivery (n = 14/19, p = 0.003), longer time of active labour (p = 0.01) and second stage of labour (p = 0.001) than women in the regional registry. 2) Ten out of 19 (52%) women reported LPP at follow-up. These women more often suffered impaired function related to LPP (Pelvic Girdle Questionnaire, 27 versus 0, p < 0.0001), a poorer health-related quality of life (EuroQol-5 dimensions p = 0.001 and EuroQol-visual analogue scale, 65 mm versus 84 mm, p = 0.022) and higher levels of anxiety and depression (Hospital Anxiety Depression Scale (HADS) HADS-Anxiety, 7 versus 2, p = 0.010; and HADS-Depression, 1 versus 0, p = 0.028) than women with no pain. 3). Of the eight women who were clinically assessed, one had lumbar pain and seven had pelvic girdle pain (PGP). Conclusions In the largest cohort of patients with PPSS to date, primiparas and women with instrumental vaginal delivery were overrepresented, indicating that first and complicated deliveries might be risk factors. Approximately half of the women reported PGP at follow-up, with considerable consequences affecting health-related quality of life and function decades after delivery. Prospective multicentre studies are needed to establish risk factors, long-term consequences, and adequate treatment for this rare pregnancy complication.
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| 11. |
- Hedenius, Martina, et al.
(författare)
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Enhanced Recognition Memory after Incidental Encoding in Children with Developmental Dyslexia
- 2013
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8:5, s. e63998-
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Tidskriftsartikel (refereegranskat)abstract
- Developmental dyslexia (DD) has previously been associated with a number of cognitive deficits. Little attention has been directed to cognitive functions that remain intact in the disorder, though the investigation and identification of such strengths might be useful for developing new, and improving current, therapeutical interventions. In this study, an old/new recognition memory paradigm was used to examine previously untested aspects of declarative memory in children with DD and typically developing control children. The DD group was not only not impaired at the task, but actually showed superior recognition memory, as compared to the control children. These findings complement previous reports of enhanced cognition in other domains (e. g., visuo-spatial processing) in DD. Possible underlying mechanisms for the observed DD advantage in declarative memory, and the possibility of compensation by this system for reading deficits in dyslexia, are discussed.
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| 12. |
- Hedenius, Martina, et al.
(författare)
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Grammar predicts procedural learning and consolidation deficits in children with Specific Language Impairment
- 2011
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Ingår i: Research in Developmental Disabilities. - : Elsevier. - 0891-4222 .- 1873-3379. ; 32:6, s. 2362-2375
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Tidskriftsartikel (refereegranskat)abstract
- The Procedural Deficit Hypothesis (PDH) posits that Specific Language Impairment (SLI) can be largely explained by abnormalities of brain structures that subserve procedural memory. The PDH predicts impairments of procedural memory itself, and that such impairments underlie the grammatical deficits observed in the disorder. Previous studies have indeed reported procedural learning impairments in SLI, and have found that these are associated with grammatical difficulties. The present study extends this research by examining consolidation and longer-term procedural sequence learning in children with SLI. The Alternating Serial Reaction Time (ASRT) task was given to children with SLI and typically developing (TD) children in an initial learning session and an average of three days later to test for consolidation and longer-term learning. Although both groups showed evidence of initial sequence learning, only the TD children showed clear signs of consolidation, even though the two groups did not differ in longer-term learning. When the children were re-categorized on the basis of grammar deficits rather than broader language deficits, a clearer pattern emerged. Whereas both the grammar impaired and normal grammar groups showed evidence of initial sequence learning, only those with normal grammar showed consolidation and longer-term learning. Indeed, the grammar-impaired group appeared to lose any sequence knowledge gained during the initial testing session. These findings held even when controlling for vocabulary or a broad non-grammatical language measure, neither of which were associated with procedural memory. When grammar was examined as a continuous variable over all children, the same relationships between procedural memory and grammar, but not vocabulary or the broader language measure, were observed. Overall, the findings support and further specify the PDH. They suggest that consolidation and longer-term procedural learning are impaired in SLI, but that these impairments are specifically tied to the grammatical deficits in the disorder. The possibility that consolidation and longer-term learning are problematic in the disorder suggests a locus of potential study for therapeutic approaches. In sum, this study clarifies our understanding of the underlying deficits in SLI, and suggests avenues for further research.
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| 13. |
- Hedenius, Martina, 1970-, et al.
(författare)
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Impaired implicit sequence learning in children with developmental dyslexia
- 2013
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Ingår i: Research in Developmental Disabilities. - : Elsevier. - 0891-4222 .- 1873-3379. ; 34:11, s. 3924-3935
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Tidskriftsartikel (refereegranskat)abstract
- It has been proposed that an impairment of procedural memory underlies a range of linguistic, cognitive and motor impairments observed in developmental dyslexia (DD). However, studies designed to test this hypothesis using the implicit sequence learning paradigm have yielded inconsistent results. A fundamental aspect of procedural learning is that it takes place over an extended time-period that may be divided into distinct stages based on both behavioural characteristics and neural correlates of performance. Yet, no study of implicit sequence learning in children with DD has included learning stages beyond a single practice session. The present study was designed to fill this important gap by extending the investigation to include the effects of overnight consolidation as well as those of further practice on a subsequent day. The results suggest that the most pronounced procedural learning impairment in DD may emerge only after extended practice, in learning stages beyond a single practice session.
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| 14. |
- Hedenius, Martina
(författare)
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Procedural and Declarative Memory in Children with Developmental Disorders of Language and Literacy
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The procedural deficit hypothesis (PDH) posits that a range of language, cognitive and motor impairments associated with specific language impairment (SLI) and developmental dyslexia (DD) may be explained by an underlying domain-general dysfunction of the procedural memory system. In contrast, declarative memory is hypothesized to remain intact and to play a compensatory role in the two disorders. The studies in the present thesis were designed to test this hypothesis.Study I examined non-language procedural memory, specifically implicit sequence learning, in children with SLI. It was shown that children with poor performance on tests of grammar were impaired at consolidation of procedural memory compared to children with normal grammar. These findings support the PDH and are line with previous studies suggesting a link between grammar processing and procedural memory.In Study II, the same implicit sequence learning paradigm was used to test procedural memory in children with DD. The DD group showed a learning profile that was similar to that of children with SLI in Study I, with a significant impairment emerging late in learning, after extended practice and including an overnight interval. Further analyses suggested that the DD impairment may not be related to overnight consolidation but to the effects of further practice beyond the initial practice session. In contrast to the predictions of the PDH, the sequence learning deficit was unrelated to phonological processing skills as assessed with a nonword repetition task.Study III examined declarative memory in DD. The performance of the DD group was found to be not only intact, but even enhanced, compared to that of the control children. The results encourage further studies on the potential of declarative memory to compensate for the reading problems in DD.In sum, the results lend partial support for the PDH and suggest further refinements to the theory. Collectively, the studies emphasize the importance of going beyond a narrow focus on language learning and memory functions in the characterization of the two disorders. Such a broader cognitive, motor and language approach may inform the development of future clinical and pedagogical assessment and intervention practices for SLI and DD.
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| 15. |
- Hunt, R, et al.
(författare)
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Calculation of the properties of digital mammograms using a computer simulation
- 2005
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Ingår i: Radiation Protection Dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 395-398
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Tidskriftsartikel (refereegranskat)abstract
- A Mote Carlo computer model of mammography has been developed to study and optimise the performance of digital mammographic systems. The program uses high-resolution voxel phantoms to model the breast, which simulate the adipose and fibroglandular tissues, Cooper's ligaments, ducts and skin in three dimensions. The model calculates the dose to each tissue, and also the quantities such as energy imparted to image pixels, noise per image pixel and scatter-to-primary (S/P) ratios. It allows studies of the dependence of image properties on breast structure and on position within the image. The program has been calibrated by calculating and measuring the pixel values and noise for a digital mammographic system. The thicknesses of two components of this system were unknown, and were adjusted to obtain a good agreement between measurement and calculation. The utility of the program is demonstrated with the calculations of the variation of the S/P ratio with and without a grid, and of the image contrast across the image of a 50-mm-thick breast phantom. © The Author 2005. Published by Oxford University Press. All rights reserved.
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| 16. |
- Hunt, R, et al.
(författare)
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Monte Carlo simulation of a mammographic test phantom
- 2005
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Ingår i: Radiation Protection Dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 432-435
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Tidskriftsartikel (refereegranskat)abstract
- A test phantom, including a wide range of mammographic tissue equivalent materials and test details, was imaged on a digital mammographic system. In order to quantify the effect of scatter on the contrast obtained for the test details, calculations of the scatter-to-primary ratio (S/P) have been made using a Monte Carlo simulation of the digital mammographic imaging chain, grid and test phantom. The results show that the S/P values corresponding to the imaging conditions used were in the range 0.084-0.126. Calculated and measured pixel values in different regions of the image were compared as a validation of the model and showed excellent agreement. The results indicate the potential of Monte Carlo methods in the image quality-patient dose process optimisation, especially in the assessment of imaging conditions not available on standard mammographic units. © The Author 2005. Published by Oxford University Press. All rights reserved.
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| 17. |
- Kalland, Kristine, et al.
(författare)
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Similar outcome of femoral neck fractures treated with Pinloc or Hansson Pins: 1-year data from a multicenter randomized clinical study on 439 patients
- 2019
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Ingår i: Acta Orthopaedica. - : Medical Journals Sweden AB. - 1745-3674 .- 1745-3682. ; 90:6, s. 542-546
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Tidskriftsartikel (refereegranskat)abstract
- Background and purpose - There are few reports on the efficiency of the Hansson Pinloc System (Pinloc) for fixation of femoral neck fractures. We compare Pinloc with the commonly used Hansson Pin System in a randomized clinical trial. The primary outcome measure is non-union or avascular necrosis within 2 years. We now report fracture failures and reoperations within the first year. Patients and methods - Between May 2014 and February 2017, 439 patients were included in the study. They were above 50 years of age and treated for a femoral neck fracture at 9 orthopedic departments in Sweden. They were randomized to either Pinloc or Hansson pins. The fractures were grouped as (a) non-displaced regardless of age, (b) displaced in patients < 70 years, or (c) >= 70 years old, but deemed unfit to undergo arthroplasty. Follow-up with radiographs and outpatient visits were at 3 and 12 months. Failure was defined as early displacement/non-union, symptomatic segmental collapse, or deep infection. Results - 1-year mortality was 11%. Of the 325 undisplaced fractures, 12% (21/169) Pinloc and 13% (20/156) Hansson pin patients had a failure during the first year. The reoperation frequencies were 10% (16/169) and 8% (13/156) respectively. For the 75 patients 50-69 years old with displaced fractures, 11/39 failures occurred in the Pinloc group and 11/36 in the Hansson group, and 8/39 versus 9/36 patients were reoperated. Among those 39 patients >= 70 years old, 7/21 failures occurred in the Pinloc group and 4/18 in the Hansson group. Reoperation frequencies were 4/21 for Pinloc and 3/18 for the Hansson pin patients. No statistically significant differences were found in any of the outcomes between the Pinloc and Hansson groups. Interpretation - We found no advantages with Pinloc regarding failure or reoperation frequencies in this 1-year follow-up.
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| 18. |
- Koch, Felix-Sebastian, 1977-, et al.
(författare)
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Data and analysis script for infant and adult eye movement in an adapted ocular-motor serial reaction time task assessing procedural memory
- 2020
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Ingår i: Data in Brief. - : ELSEVIER. - 2352-3409. ; 29
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Tidskriftsartikel (refereegranskat)abstract
- This article provides a description of eye movement data collected during an ocular-motor serial reaction time task. Raw gaze data files for 63 infants and 24 adults along with the data processing and analysis script for extracting saccade latencies, summarizing participants performance, and testing statistical differences, are hosted on Open Science Framework (OSF). Files (in Matlab format) available for download allow for replication of the results reported in "Procedural memory in infancy: Evidence from implicit sequence learning in an eye-tracking paradigm" [1]. (C) 2020 The Authors. Published by Elsevier Inc.
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| 19. |
- Koch, Felix-Sebastian, et al.
(författare)
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Procedural memory in infancy: Evidence from implicit sequence learning in an eye-tracking paradigm
- 2020
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Ingår i: Journal of experimental child psychology (Print). - : ELSEVIER SCIENCE INC. - 0022-0965 .- 1096-0457. ; 191
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Tidskriftsartikel (refereegranskat)abstract
- Procedural memory underpins the learning of skills and habits. It is often tested in children and adults with sequence learning on the serial reaction time (SRT) task, which involves manual motor control. However, due to infants slowly developing control of motor actions, most procedures that require motor control cannot be examined in infancy. Here, we investigated procedural memory using an SRT task adapted for infants. During the task, images appeared at one of three locations on a screen, with the location order following a five-item recurring sequence. Three blocks of recurring sequences were followed by a random-order fourth block and finally another block of recurring sequences. Eye movement data were collected for infants (n = 35) and adults (n = 31). Reaction time was indexed by calculating the saccade latencies for orienting to each image as it appeared. The entire protocol took less than 3 min. Sequence learning in the SRT task can be operationalized as an increase in latencies in the random block as compared with the preceding and following sequence blocks. This pattern was observed in both the infants and adults. This study is the first to report learning in an SRT task in infants as young as 9 months. This SRT protocol is a promising procedure for measuring procedural memory in infants. (C) 2019 Elsevier Inc. All rights reserved.
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| 20. |
- Lauten, Alexander, et al.
(författare)
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Percutaneous Left-Ventricular Support With the Impella-2.5-Assist Device in Acute Cardiogenic Shock Results of the Impella-EUROSHOCK-Registry
- 2013
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Ingår i: Circulation Heart Failure. - 1941-3289 .- 1941-3297. ; 6:1, s. 23-30
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Tidskriftsartikel (refereegranskat)abstract
- Background-Acute cardiogenic shock after myocardial infarction is associated with high in-hospital mortality attributable to persisting low-cardiac output. The Impella-EUROSHOCK-registry evaluates the safety and efficacy of the Impella-2.5-percutaneous left-ventricular assist device in patients with cardiogenic shock after acute myocardial infarction. Methods and Results-This multicenter registry retrospectively included 120 patients (63.6 +/- 12.2 years; 81.7% male) with cardiogenic shock from acute myocardial infarction receiving temporary circulatory support with the Impella-2.5-percutaneous left-ventricular assist device. The primary end point evaluated mortality at 30 days. The secondary end point analyzed the change of plasma lactate after the institution of hemodynamic support, and the rate of early major adverse cardiac and cerebrovascular events as well as long-term survival. Thirty-day mortality was 64.2% in the study population. After Impella-2.5-percutaneous left-ventricular assist device implantation, lactate levels decreased from 5.8 +/- 5.0 mmol/L to 4.7 +/- 5.4 mmol/L (P=0.28) and 2.5 +/- 2.6 mmol/L (P=0.023) at 24 and 48 hours, respectively. Early major adverse cardiac and cerebrovascular events were reported in 18 (15%) patients. Major bleeding at the vascular access site, hemolysis, and pericardial tamponade occurred in 34 (28.6%), 9 (7.5%), and 2 (1.7%) patients, respectively. The parameters of age >65 and lactate level >3.8 mmol/L at admission were identified as predictors of 30-day mortality. After 317 +/- 526 days of follow-up, survival was 28.3%. Conclusions-In patients with acute cardiogenic shock from acute myocardial infarction, Impella 2.5-treatment is feasible and results in a reduction of lactate levels, suggesting improved organ perfusion. However, 30-day mortality remains high in these patients. This likely reflects the last-resort character of Impella-2.5-application in selected patients with a poor hemodynamic profile and a greater imminent risk of death. Carefully conducted randomized controlled trials are necessary to evaluate the efficacy of Impella-2.5-support in this high-risk patient group.
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| 21. |
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| 22. |
- Pavlov, Michael, et al.
(författare)
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Estimation of peptide elongation times from ribosome profiling spectra
- 2021
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Ingår i: Nucleic Acids Research. - : Oxford University Press. - 0305-1048 .- 1362-4962. ; 49:9, s. 5124-5142
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Tidskriftsartikel (refereegranskat)abstract
- Ribosome profiling spectra bear rich information on translation control and dynamics. Yet, due to technical biases in library generation, extracting quantitative measures of discrete translation events has remained elusive. Using maximum likelihood statistics and data set from Escherichia coli we develop a robust method for neutralizing technical biases (e.g. base specific RNase preferences in ribosome-protected mRNA fragments (RPF) generation), which allows for correct estimation of translation times at single codon resolution. Furthermore, we validated the method with available datasets from E. coli treated with antibiotic to inhibit isoleucyl-tRNA synthetase, and two datasets from Saccharomyces cerevisiae treated with two RNases with distinct cleavage signatures. We demonstrate that our approach accounts for RNase cleavage preferences and provides bias-corrected translation times estimates. Our approach provides a solution to the long-standing problem of extracting reliable information about peptide elongation times from highly noisy and technically biased ribosome profiling spectra.
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| 23. |
- Sandborg, Michael, et al.
(författare)
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Comparison of clinical and physical measures of image quality in chest and pelvis computed radiography at different tube voltages
- 2006
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Ingår i: Medical Physics. - : Wiley. - 0094-2405. ; 33:11, s. 4169-4175
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this work was to study the dependence of image quality in digital chest and pelvis radiography on tube voltage, and to explore correlations between clinical and physical measures of image quality. The effect on image quality of tube voltage in these two examinations was assessed using two methods. The first method relies on radiologists' observations of images of an anthropomorphic phantom, and the second method was based on computer modeling of the imaging system using an anthropomorphic voxel phantom. The tube voltage was varied within a broad range (50-150 kV), including those values typically used with screen-film radiography. The tube charge was altered so that the same effective dose was achieved for each projection. Two x-ray units were employed using a computed radiography (CR) image detector with standard tube filtration and antiscatter device. Clinical image quality was assessed by a group of radiologists using a visual grading analysis (VGA) technique based on the revised CEC image criteria. Physical image quality was derived from a Monte Carlo computer model in terms of the signal-to-noise ratio, SNR, of anatomical structures corresponding to the image criteria. Both the VGAS (visual grading analysis score) and SNR decrease with increasing tube voltage in both chest PA and pelvis AP examinations, indicating superior performance if lower tube voltages are employed. Hence, a positive correlation between clinical and physical measures of image quality was found. The pros and cons of using lower tube voltages with CR digital radiography than typically used in analog screen-film radiography are discussed, as well as the relevance of using VGAS and quantum-noise SNR as measures of image quality in pelvis and chest radiography.
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| 24. |
- Svalkvist, Angelica, et al.
(författare)
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Investigation of the effect of varying scatter-to-primary ratios on nodule contrast in chest tomosynthesis
- 2011
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Ingår i: Medical Imaging 2011. - : SPIE - International Society for Optical Engineering. - 9780819485038 ; 7961
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The primary aim of the present work was to analyze the effects of varying scatter-to-primary ratios on the appearance of simulated nodules in chest tomosynthesis section images. Monte Carlo simulations of the chest tomosynthesis system GE Definium 8000 VolumeRAD (GE Healthcare, Chalfont St. Giles, UK) were used to investigate the variation of scatter-to-primary ratios between different angular projections. The simulations were based on a voxel phantom created from CT images of an anthropomorphic chest phantom. An artificial nodule was inserted at 80 different positions in the simulated phantom images, using five different approaches for the scatter-to-primary ratios in the insertion process. One approach included individual determination of the scatter-to primary-ratio for each projection image and nodule location, while the other four approaches were using mean value, median value and zero degree projection value of the scatter-to-primary ratios at each nodule position as well as using a constant scatter-to-primary ratio of 0.5 for all nodule positions. The results indicate that the scatter-to-primary ratios vary up to a factor of 10 between the different angular tomosynthesis projections (±15°). However, the error in the resulting nodule contrast introduced by not taking all variations into account is in general smaller than 10 %.
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| 25. |
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| 26. |
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| 27. |
- Ullman, Gustaf, et al.
(författare)
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A Monte Carlo-based model for simulation of digital chest tomosynthesis
- 2010
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Ingår i: Radiation Protection Dosimetry. - Oxford : Oxford University Press. - 0144-8420 .- 1742-3406. ; 139:1-3, s. 159-163
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this work was to calculate synthetic digital chest tomosynthesis projections using a computer simulation model based on the Monte Carlo method. An anthropomorphic chest phantom was scanned in a computed tomography scanner, segmented and included in the computer model to allow for simulation of realistic high-resolution X-ray images. The input parameters to the model were adapted to correspond to the VolumeRAD chest tomosynthesis system from GE Healthcare. Sixty tomosynthesis projections were calculated with projection angles ranging from +15 to −15°. The images from primary photons were calculated using an analytical model of the anti-scatter grid and a pre-calculated detector response function. The contributions from scattered photons were calculated using an in-house Monte Carlo-based model employing a number of variance reduction techniques such as the collision density estimator. Tomographic section images were reconstructed by transferring the simulated projections into the VolumeRAD system. The reconstruction was performed for three types of images using: (i) noise-free primary projections, (ii) primary projections including contributions from scattered photons and (iii) projections as in (ii) with added correlated noise. The simulated section images were compared with corresponding section images from projections taken with the real, anthropomorphic phantom from which the digital voxel phantom was originally created. The present article describes a work in progress aiming towards developing a model intended for optimisation of chest tomosynthesis, allowing for simulation of both existing and future chest tomosynthesis systems.
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| 28. |
- Ullman, Gustaf, et al.
(författare)
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A search for optimal x‐ray spectra in iodine contrast media mammography
- 2005
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Ingår i: Physics in medicine and biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 50:13, s. 3143-3152
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this work was to search for the optimal x-ray tube voltage and anode–filter combination in digital iodine contrast media mammography. In the optimization, two entities were of interest: the average glandular dose, AGD, and the signal-to-noise ratio, SNR, for detection of diluted iodine contrast medium. The optimum is defined as the technique maximizing the figure of merit, SNR2/AGD. A Monte Carlo computer program was used which simulates the transport of photons from the x-ray tube through the compression plate, breast, breast support plate, anti-scatter grid and image detector. It computes the AGD and the SNR of an iodine detail inside the compressed breast. The breast thickness was varied between 2 and 8 cm with 10–90% glandularity. The tube voltage was varied between 20 and 55 kV for each anode material (Rh, Mo and W) in combination with either 25 µm Rh or 0.05–0.5 mm Cu added filtration. The x-ray spectra were calculated with MCNP4C (Monte Carlo N-Particle Transport Code System, version 4C). A CsI scintillator was used as the image detector. The results for Rh/0.3mmCu, Mo/0.3mmCu and W/0.3mmCu were similar. For all breast thicknesses, a maximum in the figure of merit was found at approximately 45 kV for the Rh/Cu, Mo/Cu and W/Cu combinations. The corresponding results for the Rh/Rh combination gave a figure of merit that was typically lower and more slowly varying with tube voltage. For a 4 cm breast at 45 kV, the SNR2/AGD was 3.5 times higher for the Rh/0.3mmCu combination compared with the Rh/Rh combination. The difference is even larger for thicker breasts. The SNR2/AGD increases slowly with increasing Cu-filter thickness. We conclude that tube voltages between 41 and 55 kV and added Cu-filtration will result in significant dose advantage in digital iodine contrast media mammography compared to using the Rh/Rh anode/filter combination at 25–32 kV.
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| 29. |
- Ullman, Gustaf, et al.
(författare)
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Calculation of images from an anthropomorphic chest phantom using Monte Carlo methods
- 2006
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Ingår i: Proceedings of SPIE. - : SPIE.
-
Konferensbidrag (refereegranskat)abstract
- Monte Carlo (MC) computer simulation of chest x-ray imaging systems has hitherto been performed using anthropomorphic phantoms with too large (3 mm) voxel sizes. The aim for this work was to develop and use a Monte Carlo computer program to compute projection x-ray images of a high-resolution anthropomorphic voxel phantom for visual clinical image quality evaluation and dose-optimization. An Alderson anthropomorphic chest phantom was imaged in a CT-scanner and reconstructed with isotropic voxels of 0.7 mm. The phantom was segmented and included in a Monte Carlo computer program using the collision density estimator to derive the energies imparted to the detector per unit area of each pixel by scattered photons. The image due to primary photons was calculated analytically including a pre-calculated detector response function. Attenuation and scatter of x-rays in the phantom, grid and image detector was considered. Imaging conditions (tube voltage, anti-scatter device) were varied and the images compared to a real computed radiography (Fuji FCR 9501) image. Four imaging systems were simulated (two tube voltages 81 kV and 141 kV using either a grid with ratio 10 or a 30 cm air gap). The effect of scattered radiation on the visibility of thoracic vertebrae against the heart and lungs is demonstrated. The simplicity in changing the imaging conditions will allow us not only to produce images of existing imaging systems, but also of hypothetical, future imaging systems. We conclude that the calculated images of the high-resolution voxel phantom are suitable for human detection experiments of low-contrast lesions.
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| 30. |
- Ullman, Gustav, et al.
(författare)
-
Comparison of clinical and physical measures of image quality in chest PA and pelvis AP views at varying tube voltages
- 2004
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Image quality in digital chest PA and pelvis AP was assessed using two different methods; one based on observations of images of an anthropomorphic phantom, one based on computer modelling using an anthropomorphic voxel phantom. The tube voltage was varied within a broad range (50-150 kV), including those values typically used with screen-film radiography. The tube charge was altered so that approximately the same effective dose was achieved in the modelled patient (anthropomorphic phantom). Two x-ray units were employed using a digital image detector (computed radiography, CR, system) with standard tube filtration and anti-scatter device. Clinical image quality was assessed by a group of radiologists using a visual grading analysis (VGA) technique based on the revised CEC image criteria. Physical image quality was derived from the computer model in terms of the signal-to-noise ratio, SNR for fixed effective dose in the voxel phantom. The computer model uses Monte Carlo simulations of the patient and complete imaging system. Both the VGAS (visual grading analysis score) and SNR increase with decreasing tube voltage in both chest PA and pelvis AP examinations, indicating superior performance if lower tube voltages than used today are employed in digital radiology. A positive correlation between clinical and physical measures of image quality was found. The pros and cons of using lower tube voltages with CR digital radiography than typically used in analogue screen-film radiography are discussed as well as the relevance of using VGAS and quantum noise SNR as measures of image quality.
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| 31. |
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| 32. |
- Ullman, Gustaf, et al.
(författare)
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Distributions of scatter to primary ratios and signal to noise ratios per pixel in digital chest imaging
- 2005
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 355-358
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of this work was to calculate distributions of scatter-to-primary ratios (s/p) and signal-to-noise ratios per pixel (SNRp) in chest images. Such distributions may provide useful information on how physical image quality (contrast, SNR) is distributed over the posterior/anterior (PA) chest image. A Monte Carlo computer program was used for the calculations, including a model of both the patient (voxel phantom) and the imaging system (X-ray tube, anti-scatter grid and image detector). The calculations were performed for three PA thicknesses 20, 24 and 28 cm. For a 24 cm patient, the s/p varies between 0.5 in the lung to 2.5 behind the spine and heart. The corresponding variation of the SNRp is a factor of 3, with the highest values in the lung. Increasing the patient thickness from 20 to 28 cm increases the s/p by a factor of 2.2 behind the spine and heart.
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| 33. |
- Ullman, Gustav, et al.
(författare)
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Distributions of scatter-to-primary ratios in chest PA radiography using grid or air gap for scatter-rejection
- 2004
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The aim for this work was to calculate distributions of scatter-to-primary ratios (εs/εp) and signal-to-noise ratios per pixel (SNRp) for a large set of imaging systems with either grid or air gap for scatter rejection. Grids with ratio 8-16 and air gap length 20 and 40 cm were used. The tube voltage was varied between 90-150 kV and three patient thickness between 20-28 cm were tested in order to compare scatter-rejections techniques for different conditions. Distributions of this sort may provide useful information on how physical image quality (contrast, SNR) is distributed over the chest PA image. A Monte Carlo computer program was used for the calculations, including a model of both the patient (voxel phantom) and the imaging system. The mean value of the εs/εp is 0.39 in the hilar region and 1.72 in the lower mediastinal region. For a 28 cm patient, the corresponding values are 0.42 in the hilar region and 2.58 in the lower mediastinal region. The grid with ratio 16 is the most efficient scatter rejection technique in all regions except the hilar region. In the hilar region, the most efficient technique is the 40 cm air gap.
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| 34. |
- Ullman, Gustav, et al.
(författare)
-
Implementation of pathologies in the Monte Carlo model in chest and breast imaging
- 2003
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The Monte Carlo simulation model of the chest and breast imaging systems including a voxelised model of the patient are used to compute measures of image quality and patient absorbed dose. It is important that the model computes measures of image quality of pathological details that are similar in size, composition and position as real pathological details in typical chest and breast images. Moreover, the other partners of the co-coordinated research project will produce hybrid images with pathological details and have these images assessed by a group of radiologist. The model will then be used to study to what extent variations in clinical image quality can be explained by variations in physical image quality, for example signal-to-noise ratio. This report summarizes the selection of pathological details to include in the model of chest and breast imaging systems.
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| 35. |
- Ullman, Gustav, et al.
(författare)
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On the extent of quantum noise limitation in digital chest radiography
- 2004
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The aim for this work was to study to what extent the detection of nodules is quantum noise limited, based on the combined results from a nodule-detection clinical trial and a Monte Carlo computational model of a digital chest imaging system. The Monte Carlo computer program computes measures of physical image quality such as image contrast, C and signalto-noise ratio, SNR for nodules of any size. A computed radiography (CR) imaging system used simulated. The patient anterior-posterior thickness was 25 cm and nodules with diameters between 1-40 mm were included. The image contrast and SNR was calculated for 1600 (40x40) positions in the chest image and averaged over five anatomical regions of interest (lateral pulmonary, retrocardial, hilar, lower- and upper mediastinal regions). Threshold contrasts for each region, Cth, corresponding to Az=0.80 for detecting a 10 mm nodule, were deduced from the clinical trial. A threshold is also used for the quantum noise signal-to-noise ratio, SNRth. The model computes the diameter of a disk-shaped object that is required to comply with the two criteria: SNR≥SNRth and C≥Cth. A system is said to be quantum noise limited when the nodule size required to fulfil both criteria is not limited by the contrast but by the SNR. The required nodule diameter is largest in the hilar region (25 mm) and smallest in the lateral pulmonary region (11 mm). When the threshold SNRth=25 is used, the lower mediastinal region is quantum noise limited already at low speed classes (S>100). The hilar region is never quantum noise limited at realistic speed classes (S<1000). The accuracy of this model will be tested in the future by more sophisticated modelling of anatomical background and noise in the SNR-expression.
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| 36. |
- Ullman, Gustav, et al.
(författare)
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Optimisation of chest radiology by computer modelling of image quality measures and patient effective dose
- 2004
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A set of modelled computed radiography (CR) systems are compared with a reference system. Calculations are performed, which compares the effective dose and a set of figures of merit corresponding to the image quality of both the modelled systems and the reference system. For a nodule with soft tissue corresponding, the signal-to-noise ratio, SNR, is found to decrease with increasing tube voltage. On the other hand, the ratio of the contrast of the nodule compared to the contrast of a rib (nodule-to-rib contrast-ratio) is found to increase with increasing tube voltage.
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| 37. |
- Ullman, Gustaf, 1977-
(författare)
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Quantifying image quality in diagnostic radiology using simulation of the imaging system and model observers
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Accurate measures of both clinical image quality and patient radiation risk are needed for successful optimisation of medical imaging with ionising radiation. Optimisation in diagnostic radiology means finding the image acquisition technique that maximises the perceived information content and minimises the radiation risk or keeps it at a reasonably low level. The assessment of image quality depends on the diagnostic task and may in addition to system and quantum noise also be hampered by overlying projected anatomy.The main objective of this thesis is to develop methods for assessment of image quality in simulations of projection radiography. In this thesis, image quality is quantified by modelling the whole x‐ray imaging system including the x‐ray tube, patient, anti‐scatter device, image detector and the observer. This is accomplished by using Monte Carlo (MC) simulation methods that allow simultaneous estimates of measures of image quality and patient dose. Measures of image quality include the signal‐to‐noise‐ratio, SNR, of pathologic lesions and radiation risk is estimated by using organ doses to calculate the effective dose. Based on high‐resolution anthropomorphic phantoms, synthetic radiographs were calculated and used for assessing image quality with model‐observers (Laguerre‐Gauss (LG) Hotelling observer) that mimic real, human observers. Breast and particularly chest imaging were selected as study cases as these are particularly challenging for the radiologists.In chest imaging the optimal tube voltage in detecting lung lesions was investigated in terms of their SNR and the contrast of the lesions relative to the ribs. It was found that the choice of tube voltage depends on whether SNR of the lesion or the interfering projected anatomy (i.e. the ribs) is most important for detection. The Laguerre‐Gauss (LG) Hotelling observer is influenced by the projected anatomical background and includes this into its figure‐of‐merit, SNRhot,LG. The LG‐observer was found to be a better model of the radiologist than the ideal observer that only includes the quantum noise in its analysis. The measures of image quality derived from our model are found to correlate relatively well with the radiologist’s assessment of image quality. Therefore MC simulations can be a valuable and an efficient tool in the search for dose‐efficient imaging systems and image acquisition schemes.
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| 38. |
- Ullman, Gustaf, 1977-, et al.
(författare)
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The influence of patient thickness and imaging system on patient dose and physical image quality in digital chest imaging
- 2005
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Ingår i: Radiation Protection Dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 294-297
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of this work was to study the influence of patient thickness, tube voltage and image detector on patient dose, contrast and ideal observer signal-to-noise ratio (SNRI), for pathological details positioned at different regions in the image in posterior-anterior (PA) chest radiology. A Monte Carlo computational model was used to compute measures of physical image quality (contrast, SNRI) and patient effective dose, E. Two metastasis-like details positioned in the central right lung and right lung near the spine, respectively, were studied. The tube voltage was varied between 100 and 150 kV and the patient thickness between 20 and 28 cm. Both, a computed radiography (CR) system and a direct radiography (DR) system, were investigated. The DR system provides both lower doses and better image quality compared with the CR system. The SNRI2/E is ∼2.9 times higher for the DR system compared with the CR system. © The Author 2005. Published by Oxford University Press. All rights reserved.
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| 39. |
- Ullman, Gustaf, et al.
(författare)
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Towards optimization in digital chest radiography using Monte Carlo modelling
- 2006
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Ingår i: Physics in medicine and biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 51:11, s. 2729-2743
-
Tidskriftsartikel (refereegranskat)abstract
- A Monte Carlo based computer model of the x-ray imaging system was used to investigate how various image quality parameters of interest in chest PA radiography and the effective dose E vary with tube voltage (90–150 kV), additional copper filtration (0–0.5 mm), anti-scatter method (grid ratios 8–16 and air gap lengths 20–40 cm) and patient thickness (20–28 cm) in a computed radiography (CR) system. Calculated quantities were normalized to a fixed value of air kerma (5.0 µGy) at the automatic exposure control chambers. Soft-tissue nodules were positioned at different locations in the anatomy and calcifications in the apical region. The signal-to-noise ratio, SNR, of the nodules and the nodule contrast relative to the contrast of bone (C/CB) as well as relative to the dynamic range in the image (Crel) were used as image quality measures. In all anatomical regions, except in the densest regions in the thickest patients, the air gap technique provides higher SNR and contrast ratios than the grid technique and at a lower effective dose E. Choice of tube voltage depends on whether quantum noise (SNR) or the contrast ratios are most relevant for the diagnostic task. SNR increases with decreasing tube voltage while C/CB increases with increasing tube voltage.
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| 40. |
- Ullman, Gustav, et al.
(författare)
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Validation of Voxman Monte Carlo code and calibration for digital systems
- 2003
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The objective of this work was to test the Monte Carlo model ‘Voxman’ against measurements on x-ray systems in the clinic. X-ray transmission experiments are performed to test of the accuracy of the Monte Carlo photon transport. Experiments were also performed with an image plate (CR) system in the clinic to compare the measured pixel values with calculated pixel values. Measurements were also performed with the automatic exposure control (AEC) chambers used in Linköping and Motala. The purpose for those measurements was to choose a normalisation of the entrance surface dose.
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