| 5951. |
- Persson, Eva, et al.
(författare)
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Quantification of myocardial hypoperfusion with 99m Tc-sestamibi in patients undergoing prolonged coronary artery balloon occlusion.
- 2002
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Ingår i: Nuclear Medicine Communications. - 1473-5628. ; 23:3, s. 219-228
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Tidskriftsartikel (refereegranskat)abstract
- SUMMARY: Percutaneous transluminal coronary angioplasty provides an excellent opportunity to investigate the location and quantity of hypoperfusion during sudden complete occlusion of one of the major coronary arteries. Thirty-five patients referred for elective percutaneous transluminal coronary angioplasty were injected intravenously with 99mTc-sestamibi during balloon inflation. To visualize and quantify the hypoperfused region, a map of perfusion was constructed from that occlusion study and from the control study performed on the following day. Patients were divided into groups according to proximal or distal occlusion within each of the three coronary arteries. The region of myocardium supplied by each coronary artery varied in location and extended outside the typical borders for all arteries, but most prominently for the left circumflex coronary artery. The quantities of hypoperfusion varied within each artery group, but the average hypoperfusion was greater for the left anterior descending coronary artery than for either the right coronary artery or the left circumflex coronary artery. It is concluded that the quantities of hypoperfusion were highly variable within each artery group. Occlusion of the left anterior descending coronary artery was associated with the largest ischaemic region. The area of hypoperfusion extended outside the typical borders, most prominently for the left circumflex coronary artery.
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| 5952. |
- Persson, Emilia
(författare)
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Validation and clinical implementation of an MRI-only prostate cancer radiotherapy workflow
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The radiotherapy workflow for prostate cancer is associated with systematic uncertainty stemming from the registration between the computed tomography (CT) and magnetic resonance (MR) images. A radiotherapy workflow based solely on MR imaging (MRI), called an MRI-only workflow, has been suggested as a means of eliminating this uncer¬tainty. The aim of the work presented in this thesis was to validate and clinically implement an MRI-only workflow for prostate cancer.Several aspects of the implementation of an MRI-only workflow have been investigated in the work presented in this thesis. In the registration process between MR and CT images using fiducial markers, the observer bias was found to displace the estimated target position by up to 3 mm, compared to the clinical baseline. The delineated prostate volume was, on average, 18% smaller in the MRI-only delineation procedure than in dual-modality delineation. If this difference is not accounted for, a reduction in the treated volume could arise in the implementation of an MRI-only workflow. Both registration and target delineation uncertainties manifest as systematic deviations for each patient in the dual-modality workflow, which are elimi¬nated in an MRI-only workflow. MRI-only treatment planning employing the synthetic CT (sCT)-generation software MriPlannerTM, was validated in a multi-centre/multi-vendor study. The method was found to be robust for a variety of MRI vendors, magnetic field strengths, prescriptions and treatment planning strategies. In the spring of 2017, the first MRI-only-based treatment in Sweden using this software was delivered in a clinical study in Lund. A total of 39 patients were treated in this study using a prospective implementation approach together with an MRI-only workflow. Using a new single-sequence strategy, image registration between different image volumes was eliminated. One patient was excluded due to obesity. CT imaging was included in the workflow for quality assurance (QA) purposes. Acceptance criteria for dose calculations were confirmed within a 2% dose deviation and 98% gamma pass rate. Fiducial marker identification was successfully performed with 100% detection accuracy using MR images. Patient set-up verification was performed, and was within 2 mm of the CT-based set-up verification for most patients. In the clinical use of an MRI-only workflow there will be no need for CT imaging. An sCT QA method using cone beam CT (CBCT) images was developed to completely remove the need for CT imaging in a clinical MRI-only workflow. CBCT images successfully replaced the CT images in the suggested QA method for sCT images. In conclusion, the work presented in this thesis demonstrates that an MRI-only workflow for radiotherapy of prostate cancer can be clinically implemented.
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| 5953. |
- Persson, Jonas, et al.
(författare)
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Discovery, optimization and biodistribution of an Affibody molecule for imaging of CD69
- 2021
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Due to the wide scale of inflammatory processes in different types of disease, more sensitive and specific biomarkers are required to improve prevention and treatment. Cluster of differentiation 69 (CD69) is one of the earliest cell surface proteins expressed by activated leukocytes. Here we characterize and optimize potential new imaging probes, Affibody molecules targeting CD69 for imaging of activated immune cells. Analysis of candidates isolated in a previously performed selection from a Z variant E. coli library to the recombinant extracellular domain of human CD69, identified one cross-reactive Z variant with affinity to murine and human CD69. Affinity maturation was performed by randomization of the primary Z variant, followed by selections from the library. The resulting Z variants were evaluated for affinity towards human and murine CD69 and thermal stability. The in vivo biodistribution was assessed by SPECT/CT in rats following conjugation of the Z variants by a DOTA chelator and radiolabeling with Indium-111. A primary Z variant with a K-d of approximately 50 nM affinity to human and murine CD69 was identified. Affinity maturation generated 5 additional Z variants with improved or similar affinity. All clones exhibited suitable stability. Radiolabeling and in vivo biodistribution in rat demonstrated rapid renal clearance for all variants, while the background uptake and washout varied. The variant Z(CD69:4) had the highest affinity for human and murine CD69 (34 nM) as well as the lowest in vivo background binding. In summary, we describe the discovery, optimization and evaluation of novel Affibody molecules with affinity for CD69. Affibody molecule Z(CD69:4) is suitable for further development for imaging of activated immune cells.
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| 5954. |
- Persson, Jonas, et al.
(författare)
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Imaging Fatigue of Interference Control Reveals the Neural Basis of Executive Resource Depletion
- 2013
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Ingår i: Journal of cognitive neuroscience. - : MIT Press - Journals. - 0898-929X .- 1530-8898. ; 25:3, s. 338-351
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Tidskriftsartikel (refereegranskat)abstract
- Executive control coordinates, prioritizes, and selects task-relevant representations under conditions of conflict. Behavioral evidence has documented that executive resources are separable, finite, and can be temporarily depleted; however, the neural basis for such resource limits are largely unknown. Here, we investigate the neural correlates underlying the fatigue or depletion of interference control, an executive process hypothesized to mediate competition among competing memory representations. Using a pre/post continuous acquisition fMRI design, we demonstrate that, compared with a nondepletion control group, the depletion group showed a fatigue-induced performance deficit that was specific to interference control and accompanied by a left-to-right shift in the network of active regions. Specifically, we observed decreased BOLD signal in the left inferior frontal gyrus (IFG), striatum, and the cerebellum, along with a corresponding increase in right hemisphere regions including the IFG, insular, and temporal cortex. Depletion-related changes in activation magnitude correlated with behavioral changes, suggesting that decreased recruitment of task-relevant regions, including left IFG, contributes to impaired interference control. These results provide new evidence about the brain dynamics of "process-specific" fatigue and suggest that depletion may pose a significant limitation on the cognitive and neural resources available for executive control.
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| 5955. |
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| 5956. |
- Persson, Johan K, et al.
(författare)
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Ultrasound nucleolysis: an in vitro study.
- 2002
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Ingår i: Ultrasound in Medicine and Biology. - 0301-5629. ; 28:9, s. 1189-1197
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Tidskriftsartikel (refereegranskat)abstract
- Thermal intradiscal therapy for chronic low back pain, using a catheter inserted into the intervertebral disc, is becoming more popular in the treatment of low back pain. The aim of this study was to investigate the possibility of heating the nucleus pulposus of the intervertebral disc with high-intensity focused ultrasound (US) or HIFU. Two specific situations were considered, invasive transducers that would be in contact with the annulus fibrosus of the disc, and noninvasive transducers that could be used externally. Theoretical simulations were performed to find the optimal parameters of US transducers and then experimental studies were done using transducers made to these specifications. These experiments confirmed that it was possible to heat the discs with HIFU. Two orthogonal transducers resulted in a superior temperature distribution than using just one transducer. It is, therefore, feasible to consider thermal treatment of the nucleus pulposus of the disc using noninvasive US. (E-mail: Johan.Persson@ort.lu.se)
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| 5957. |
- Persson, Jonas, et al.
(författare)
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Longitudinal structure – function correlates in elderly reveal MTL dysfunction with cognitive decline
- 2012
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Ingår i: Cerebral Cortex. - New York, NY : Oxford University Press (OUP). - 1047-3211 .- 1460-2199. ; 22:10, s. 2297-2304
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Tidskriftsartikel (refereegranskat)abstract
- By integrating behavioral measures and imaging data, previous investigations have explored the relationship between biological markers of aging and cognitive functions. Evidence from functional and structural neuroimaging has revealed that hippocampal volume and activation patterns in the medial temporal lobe (MTL) may predict cognitive performance in old age. Most past demonstrations of age-related differences in brain structure–function were based on cross-sectional comparisons. Here, the relationship between 6-year intraindividual change in functional magnetic resonance imaging (fMRI) signal and change in memory performance over 2 decades was examined. Correlations between intraindividual change in fMRI signal during episodic encoding and change in memory performance measured outside of scanning were used as an estimate for relating brain–behavior changes. The results revealed a positive relationship between activation change in the hippocampus (HC) and change in memory performance, reflecting reduced hippocampal activation in participants with declining performance. Using a similar analytic approach as for the functional data, we found that individuals with declining performance had reduced HC volume compared with individuals with intact performance. These observations provide a strong link between cognitive change in older adults and MTL structure and function and thus provide insights into brain correlates of individual variability in aging trajectories.
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| 5958. |
- Persson, Jonas, et al.
(författare)
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Sex differences in volume and structural covariance of the anterior and posterior hippocampus
- 2014
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Ingår i: NeuroImage. - : Elsevier BV. - 1053-8119 .- 1095-9572. ; :99, s. 215-25
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Tidskriftsartikel (refereegranskat)abstract
- Sex differences in episodic and spatial memory are frequently observed, suggesting that there may be sex-related structural differences in the hippocampus (HC). Earlier findings are inconsistent, possibly due to a known variability along the hippocampal longitudinal axis. Here, we assessed potential sex differences in hippocampal volume and structural covariance with the rest of the brain in young men and women (N=76), considering the anterior (aHC) and posterior (pHC) hippocampus separately. Women exhibited a larger pHC than men adjusted for brain size. Using partial least squares, we identified two significant patterns of structural covariance of the aHC and pHC. The first included brain areas that covaried positively and negatively in volume with both the aHC and pHC in men, but showed greater covariance with the aHC than pHC in women. The second pattern revealed distinct structural covariance of the aHC and pHC that showed a clear difference between men and women: in men the pHC showed reliable structural covariance with the medial and lateral parietal lobes and the prefrontal cortex, whereas in women the aHC showed reliable structural covariance with the anterior temporal lobe bilaterally. This pattern converges with resting state functional connectivity of the aHC and pHC and suggests that these hippocampal sections interact with different brain regions, consistent with a division of labor with regards to episodic and spatial memory. Our findings lend support to a division of the HC into an anterior and posterior part and identify sex as a potential moderating factor when investigating hippocampal structure and connectivity.
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| 5959. |
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| 5960. |
- Persson, Mats, et al.
(författare)
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A Framework for Evaluating Threshold Variation Compensation Methods in Photon Counting Spectral CT
- 2012
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Ingår i: IEEE Transactions on Medical Imaging. - 0278-0062 .- 1558-254X. ; 31:10, s. 1861-1874
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Tidskriftsartikel (refereegranskat)abstract
- One of the challenges in the development of photon counting spectral computed tomography (CT) detectors is that the location of the energy thresholds tends to vary among detector elements. If not compensated for, this threshold variation leads to ring artifacts in the reconstructed images. In this paper, a framework is presented for the systematic comparison of different methods of compensating for inhomogeneities among detector elements in photon counting CT with multiple energy bins. Furthermore, we propose the use of an affine minimum mean square error estimator, calibrated against transmission measurements on different combinations of two materials, for inhomogeneity compensation. Using the framework developed here, this method is compared to two other compensation schemes, flatfielding using an air scan and signal-to-thickness calibration using a step wedge calibrator, in a simulation study. The results show that for all but the lowest studied level of threshold spread, the proposed method is superior to signal-to-thickness calibration, which in turn is superior to flatfielding. We also demonstrate that the effects of threshold variation can be countered to a large extent by substructuring each detector element into depth segments.
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