| 11. |
- Fredenberg, Erik, PhD, 1979-, et al.
(författare)
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A low-absorption x-ray energy filter for small-scale applications
- 2009
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Ingår i: Optics Express. - : The Optical Society. - 1094-4087. ; 17:14, s. 11388-11398
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Tidskriftsartikel (refereegranskat)abstract
- We present an experimental and theoretical evaluation of an x-ray energy filter based on the chromatic properties of a prism-array lens (PAL). It is intended for small-scale applications such as medical imaging. The PAL approximates a Fresnel lens and allows for high efficiency compared to filters based on ordinary refractive lenses, however at the cost of a lower energy resolution. Geometrical optics was found to provide a good approximation for the performance of a flawless lens, but a field-propagation model was used for quantitative predictions. The model predicted a 0.29 ΔE/E energy resolution and an intensity gain of 6.5 for a silicon PAL at 23.5 keV. Measurements with an x-ray tube showed good agreement with the model in energy resolution and peak energy, but a blurred focal line contributed to a 29% gain reduction. We believe the blurring to be caused mainly by lens imperfections, in particular at the periphery of the lens.
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| 12. |
- Fredenberg, Erik, PhD, 1979-, et al.
(författare)
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A Tunable Energy Filter for Medical X-Ray Imaging
- 2008
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Ingår i: X-Ray Optics and Instrumentation. - : Hindawi. - 1687-7632 .- 1687-7640. ; 2008
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Tidskriftsartikel (refereegranskat)abstract
- A multiprism lens (MPL) is a refractive X-ray lens, and its chromatic properties can be employed in an energy filtering setup to obtain a narrow tunable X-ray spectrum. We present the first evaluation of such a filter for medical X-ray imaging. The experimental setup yields a 6.6 gain of flux at 20 keV, and we demonstrate tunability by altering the energy spectrum to center also around 17 and 23 keV. All measurements are found to agree well with ray-tracing and a proposed geometrical model. Compared to a model mammography system with absorption filtering, the experimental MPL filter reduces dose 13–25% for 3–7 cm breasts if the spectrum is centered around the optimal energy. Additionally, the resolution is improved 2.5 times for a 5 cm breast. The scan time is increased 3 times but can be reduced with a slightly decreased energy filtering and resolution.
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| 13. |
- Baumann, Pia, et al.
(författare)
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Stereotactic body radiotherapy for medically inoperable patients with stage I non-small cell lung cancer - a first report of toxicity related to COPD/CVD in a non-randomized prospective phase II study.
- 2008
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Ingår i: Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology. - : Elsevier BV. - 0167-8140 .- 1879-0887. ; 88:3, s. 359-67
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND AND AIMS: In a retrospective study using stereotactic body radiotherapy (SBRT) in medically inoperable patients with stage I NSCLC we previously reported a local control rate of 88% utilizing a median dose of 15Gyx3. This report records the toxicity encountered in a prospective phase II trial, and its relation to coexisting chronic obstructive pulmonary disease (COPD) and cardio vascular disease (CVD). MATERIAL AND METHODS: Sixty patients were entered in the study between August 2003 and September 2005. Fifty-seven patients (T1 65%, T2 35%) with a median age of 75 years (59-87 years) were evaluable. The baseline mean FEV1% was 64% and median Karnofsky index was 80. A total dose of 45Gy was delivered in three fractions at the 67% isodose of the PTV. Clinical, pulmonary and radiological evaluations were made at 6 weeks, 3, 6, 9, 12, 18, and 36 months post-SBRT. Toxicity was graded according to CTC v2.0 and performance status was graded according to the Karnofsky scale. RESULTS: At a median follow-up of 23 months, 2 patients had relapsed locally. No grade 4 or 5 toxicity was reported. Grade 3 toxicity was seen in 12 patients (21%). There was no significant decline of FEV1% during follow-up. Low grade pneumonitis developed to the same extent in the CVD 3/17 (18%) and COPD 7/40 (18%) groups. The incidence of fibrosis was 9/17 (53%) and pleural effusions was 8/17 (47%) in the CVD group compared with 13/40 (33%) and 5/40 (13%) in the COPD group. CONCLUSION: SBRT for stage I NSCLC patients who are medically inoperable because of COPD and CVD results in a favourable local control rate with a low incidence of grade 3 and no grade 4 or 5 toxicity.
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| 14. |
- Cronqvist, Mats
(författare)
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Results and complications of endovascular neurointerventions in intracranial aneurysms and arteriovenous malformations, evaluated by conventional angiography and diffusion-perfusion MRI
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Aims - To describe and evaluate the efficacy and safety of intra-arterial fibrinolysis and the clinical outcome in SAH patients with thromboembolic complications during endovascular coiling of a ruptured aneurysm. (Paper I) - To describe the use and feasibility of magnetic resonance imaging (MRI), especially diffusion and perfusion imaging, in three patients treated endovascularly for various cerebrovascular disorders. (Paper II) - To evaluate treatment safety as well as complication frequency and management in endovascular coiling of ruptured and unruptured intracranial aneurysms using MR diffusion and perfusion imaging. (Paper III). - To evaluate treatment safety in patients with cerebral arteriovenous malformations and to correlate the anatomical results with regard to complications and clinical outcome using MRI, including diffusion-weighted (DWI) and perfusion imaging (PI). (Paper IV).
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| 15. |
- Wang, Chunliang, 1980-, et al.
(författare)
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Coronary artery segmentation and skeletonization based on competing fuzzy connectedness tree
- 2007
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Ingår i: Medical Image Computing and Computer-Assisted Intervention – MICCAI 2007. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 9783540757566 - 9783540757573 ; , s. 311-318
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Konferensbidrag (refereegranskat)abstract
- We propose a new segmentation algorithm based on competing fuzzy connectedness theory, which is then used for visualizing coronary arteries in 3D CT angiography (CTA) images. The major difference compared to other fuzzy connectedness algorithms is that an additional data structure, the connectedness tree, is constructed at the same time as the seeds propagate. In preliminary evaluations, accurate result have been achieved with very limited user interaction. In addition to improving computational speed and segmentation results, the fuzzy connectedness tree algorithm also includes automated extraction of the vessel centerlines, which is a promising approach for creating curved plane reformat (CPR) images along arteries’ long axes.
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| 16. |
- Fredenberg, Erik, 1979-, et al.
(författare)
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An efficient pre-object collimator based on an x-ray lens
- 2009
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Ingår i: Medical physics (Lancaster). - : Wiley. - 0094-2405. ; 36:2, s. 626-633
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Tidskriftsartikel (refereegranskat)abstract
- A multiprism lens (MPL) is a refractive x-ray lens with one-dimensional focusing properties. If used as a pre-object collimator in a scanning system for medical x-ray imaging, it reduces the divergence of the radiation and improves on photon economy compared to a slit collimator. Potential advantages include shorter acquisition times, a reduced tube loading, or improved resolution. We present the first images acquired with a MPL in a prototype for a scanning mammography system. The lens showed a gain of flux of 1.32 compared to a slit collimator at equal resolution, or a gain in resolution of 1.31–1.44 at equal flux. We expect the gain of flux in a clinical setup with an optimized MPL and a custom-made absorption filter to reach 1.67, or 1.45–1.54 gain in resolution.
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| 17. |
- Jönsson, Lena M
(författare)
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Internal Dosimetry Development and Evaluation of Methods and Models
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Radionuclide therapy requires patient-specific planning of the absorbed dose to target volumes, in most cases tumours, in order to achieve an expected biological effect, taking into account that the absorbed doses to normal organs and tissues should be kept as low as reasonably achievable. Therefore, the calculation of absorbed doses has to be as accurate as possible. The accuracy depends on the methods used for activity quantification and on how well the dosimetric model describes the organs and tissues in the particular patient. This thesis presents new methodologies developed to investigate the accuracy of internal dosimetry. The main focus was on the use of detailed biokinetic data from animals combined with Monte Carlo simulations using anthropomorphic phantoms on macro level, and applied in the development and refinement of an intestinal dosimetry model on a small-scale level. A novel approach is the generation of Monte Carlo simulated scintillation camera images of a computer patient using a radionuclide biodistribution obtained from an experimental animal study. The accuracy of the activity quantification based on planar scintillation camera imaging was investigated and in particular the corrections for attenuation and scatter with the presence of activity in overlapping tissues. The absorbed doses were calculated using phantom-specific dose factors (S values) and were compared with absorbed doses calculated from standard MIRD-phantom-based S values. The results demonstrate the potential inaccuracy of the calculated absorbed dose to an individual patient when using dose factors based on the MIRD phantom. A dosimetry model for the small intestine was developed and refined in order to obtain a more accurate model and dose factors. Previous dosimetry models of the small intestine have been limited to calculating the absorbed dose to the intestinal wall from activity in the contents only. The work in this thesis included Monte Carlo calculations of dose factors for the radiation sensitive crypt cells as target organ. The activity in the contents as well as in the intestinal wall was taken into account, and dose factors were calculated for both self-dose and cross-dose from surrounding parts of the small intestine. Calculations of the absorbed dose to the crypt cells for a realistic activity distribution are presented and compared with results from the general absorbed dose calculation. It is evident from the results in this thesis that improvements are necessary in the quantification procedure, as well as further development of more realistic, small-scale anatomy models.
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| 18. |
- Knutsson, Linda
(författare)
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Optimisation and Validation of Dynamic Susceptibility Contrast MRI Perfusion Measurements
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The studies presented in this thesis concern the optimisation and evaluation of the dynamic susceptibility contrast magnetic resonance imaging (DSC-MRI) technique for the assessment of perfusion-related parameters of the brain, such as cerebral blood flow (CBF), cerebral blood volume (CBV) and mean transit time (MTT). Several methodological factors influence these measurements, for example, contrast-agent administration, arterial input function (AIF) registration, choice of deconvolution algorithm and the choice of pulse-sequence parameters. In the first study, a comparison of two different deconvolution techniques was made, i.e., one based on the fast Fourier transform (FT) and the other on singular value decomposition (SVD). The primary result of this study was that CBF estimates obtained by FT-based deconvolution were lower than the CBF values resulting from SVD-based deconvolution. This is in agreement with the results presented in previous publications, demonstrating that the use of FT-based deconvolution underestimates high blood-flow rates (at short MTT). In the second study, perfusion parameters were calculated from simulated data corresponding to different experimental conditions. For example, variations in signal-to-noise ratio (SNR), temporal resolution, AIF shape, signal drop and cut-off level in the truncated SVD deconvolution were investigated. The main conclusions were that the echo time requires optimisation to ensure sufficient signal drop in combination with reasonable baseline SNR, and that a broad input function can lead to underestimation of the CBF. Regional AIFs (rAIFs) were the subject of the third investigation. By using factor analysis of dynamic studies in combination with principal component analysis, rAIFs were obtained and the CBF was calculated by using the rAIF located closest to each tissue voxel. The conclusions drawn from the study were that the use of rAIFs reduced dispersion effects which can lead to CBF underestimation. In the fourth study, CBF was measured in absolute terms in 20 volunteers using Xe-133 SPECT and DSC-MRI. An AIF time-integral correction was introduced in order to improve the absolute CBF quantification in DSC-MRI. Average whole-brain estimates as well as regional CBF values in grey matter (GM) and white matter (WM) were obtained, and the results from the two modalities were compared. For the whole-brain average, the linear relationship was found to be CBF(MRI)=2.4?CBF(Xe)-7.9 [CBF given in units of ml/(min 100 g)], with a correlation coefficient of r=0.76.
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| 19. |
- van Westen, Danielle
(författare)
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MRI at 3 T of brain functions and fibre tracts adjacent to intracranial tumors
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aims of the studies were: to evaluate the spatial resolution of fMRI at 3 T by studying fingersomatotopy in area 3 b of the primary sensory area (Paper 1); to investigate the potential of fMRI at 3T as a clinical tool for preoperative evaluation of patients with intracranial tumors (Paper 2); to investigate the effect of glioma resection on the spatial extent of fMRI activation as compared to the normal within-subject variability (Paper 3); to determine whether the apparent diffusion coefficient (ADC) and fractional anisotropy (FA) can distinguish tumor-infiltrated edema of gliomas from pure edema of meningiomas and metastases (Paper 4). Results: Strict somatotopic organisation in the primary sensory cortex was shown in the group average; at the subject level the thumb was located laterally, anteriorly and inferiorly to the little finger in 94 % of subjects (Paper 1). The sensorimotor and language areas close to intracranial tumors were identified in 95 % of patients. Paradigm effectiveness ranged from 79 to 95 %. The median quality of the activation maps was high. fMRI contributed to the decision to operate, the surgical approach and the extent of the resection in 9, 13 and 12 patients, respectively (Paper 2). BOLD activation obtained from fMRI with motor, sensory and language stimulation pre- and postoperatively in glioma patients yielded differences in the spatial extent similar to those obtained from repeated examinations in healthy controls (Paper 3). Values and lesion-to-brain ratios of ADC and FA in peritumoral edema did not differ between high grade gliomas, meningiomas and metastases (Paper 4). Conclusions: Our results suggest that the spatial resolution of fMRI using a clinical protocol is adequate for localisation of the sensory representation of a finger (Paper 1). Preoperative fMRI for mapping of motor, sensory and language functions at 3 T is feasible and contributes to neurosurgical decision making (Paper 2). Longitudinal pre- and postoperative fMRI studies may be performed in patients with gliomas without concerns for potential effects of the decreased tumor volume on the BOLD effect as a possible source of error (Paper 3). Values and lesion-to-brain ratios of ADC and FA may not be useful to distinguish pure edema from tumor-infiltrated edema in peritumoral areas with T2-signal changes (Paper 4).
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| 20. |
- Toporski, Jacek, et al.
(författare)
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High-dose iodine-131-metaiodobenzylguanidine with haploidentical stem cell transplantation and posttransplant immunotherapy in children with relapsed/refractory neuroblastoma.
- 2009
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Ingår i: Biology of Blood and Marrow Transplantation. - : Elsevier BV. - 1083-8791. ; 15:9, s. 1077-1085
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Tidskriftsartikel (refereegranskat)abstract
- We evaluated the feasibility and efficacy of using high-dose iodine-131-metaiodobenzylguanidine ((131)I-MIBG) followed by reduced-intensity conditioning (RIC) and transplantation of T cell-depleted haploidentical peripheral blood stem cells (designated haplo-SCT) to treat relapsing/refractory neuroblastoma (RRNB). Five RRNB patients were enrolled: 4 with relapse (3 after autologous SCT) and 1 with induction therapy failure. The preparative regimen included high-dose (131)I-MIBG on day -20, followed by fludarabine (Flu), thiotepa, and melphalan (Mel) from day -8 to -1. Granulocyte-colony stimulating factor (G-CSF)-mobilized, T cell-depleted haploidentical paternal stem cells were infused on day 0 together with cultured donor mesenchymal stem cells. A single dose of rituximab was given on day +1. After cessation of short immunosuppression (mycophenolate, OKT3), 4 children received donor lymphocyte infusion (DLI). (131)I-MIBG infusion and RIC were well tolerated. All patients engrafted. No primary acute graft-versus-host disease (aGVHD) was observed. Four children developed aGVHD after DLI and were successfully treated. Analysis of immunologic recovery showed fast reappearance of potentially immunocompetent natural killer (NK) and T cells, which might have acted as effector cells responsible for the graft-versus-tumor (GVT) effect. Two children are alive and well, with no evidence of disease 40 and 42 months after transplantation. One patient experienced late progression with new bone lesions (sternum) 38 months after haplo-SCT, and is being treated with local irradiation and reinstituted DLI. One patient rejected the graft, was rescued with autologous backup, and died of progressive disease 5 months after transplantation. Another child relapsed 7 months after transplantation and died 5 months later. High-dose (131)I-MIBG followed by RIC and haplo-SCT for RRNB is feasible and promising, because 2 of 5 children on that regimen achieved long-lasting remission. Further studies are needed to evaluate targeted therapy and immune-mediated tumor control in high-risk neuroblastoma.
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