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Cheng J.-C.K.,University of British Columbia | Cheng J.-C.K.,Washington University in St. Louis | Blinder S.,Pacific Parkinsons Research Center | Rahmim A.,Johns Hopkins University | Sossi V.,University of British Columbia
IEEE Transactions on Nuclear Science | Year: 2010

We describe a scatter calibration technique which improves the quantitative accuracy of the positron emission tomography data in specific scanning conditions: i.e., scans with high random fraction (RF) and/or low number of counts. Such a situation is often encountered in dynamic imaging on scanners with a large number of lines-of-response (LOR) such as the high resolution research tomograph (HRRT). In this paper, we first describe how high RFs and low number of counts affect the scatter scaling process. We then demonstrate experimentally, with phantom studies, the bias in the scatter estimate introduced by the commonly used tail-fitting technique employed in the single scatter simulation (SSS) method. A significant bias in scatter fraction (SF) was found for frames which contain a RF higher than 50% and/or with a number of counts less than 20 M. Finally, we present a new scatter scaling technique which compensates this bias. The scatter calibration technique is based on using the scatter estimate obtained from a reference frame, in which the bias due to high RFs and low number of counts is minimized, to calibrate the scatter in each dynamic frame. The calibration also separately accounts for the change in SF due to the pulse pile-up effect. A much more consistent and accurate SF value was assigned to each segment of the scatter sinogram thus leading to a more quantitative reconstructed image with a better axial uniformity after the scatter calibration. The new calibration technique was tested with phantom, monkey, and human data and was found to significantly improve the quantitative aspect of the early frames: such improvement is expected to positively affect the feasibility of rather novel image analysis methods, such as determination of image derived input function. © 2010 IEEE. Source


Harris M.A.,University of British Columbia | Harris M.A.,Occupational Cancer Research Center | Tsui J.K.,University of British Columbia | Tsui J.K.,Pacific Parkinsons Research Center | And 3 more authors.
Movement Disorders | Year: 2012

The ultimate causes of idiopathic Parkinson's disease (PD) are not fully known, but environmental and occupational causes are suspected. Postencephalitic parkinsonism has been linked to influenza, and other viral infections have also been suspected to relate to PD. We estimated the relationship between PD and both infections and possible vectors of infection (i.e., animal and human) in a population-based, case-control study in British Columbia, Canada. We recruited 403 cases detected by their use of antiparkinsonian medications and 405 controls from the registrants of the provincial universal health insurance plan. Severe influenza was associated with PD (odds ratio [OR]: 2.01; 95% confidence interval [CI]: 1.16-3.48), although this effect was attenuated when reports were restricted to those occurring 10 or more years before diagnosis. Childhood illnesses were inversely associated with PD, particularly red measles (OR: 0.65; 95% CI: 0.48-0.90). Several animal exposures were associated with PD, with statistically significant effects for cats (OR: 2.06; 95% CI: 1.09-3.92) and cattle (OR: 2.23; 95% CI: 1.22-4.09). Influenza infection may be associated with PD. The inverse relationships with childhood infections may suggest an increased risk with subclinical or asymptomatic childhood infections. Occupational exposure to animals may increase risk through transmission of infections or may indicate exposure to another agent of interest (e.g., bacterial endotoxin). © 2012 Movement Disorder Society. Source


Klyuzhin I.S.,University of British Columbia | Dinelle K.,Pacific Parkinsons Research Center | Sossi V.,University of British Columbia
IEEE Nuclear Science Symposium Conference Record | Year: 2012

PET and SPECT images are traditionally reconstructed using voxel grids. In situations where non-rigid motion correction is required, meshes are believed to be better suited than voxels for image reconstruction. With meshes, deformations can be modeled explicitly by changing the coordinates of the mesh nodes. Previously proposed approaches to mesh-based image reconstruction relied either on computing the projection of mesh polyhedrons onto the detector planes, or computing the length-of-intersection between the polyhedrons and the lines-of-response. © 2011 IEEE. Source


Sossi V.,University of British Columbia | De La Fuente-Fernandez R.,Pacific Parkinsons Research Center | Nandhagopal R.,Pacific Parkinsons Research Center | Schulzer M.,Pacific Parkinsons Research Center | And 4 more authors.
Movement Disorders | Year: 2010

Increase in dopamine (DA) turnover was found to occur early in symptomatic Parkinson's disease (PD) and to be functionally related to the dopamine transporter (DAT). The objectives of this study were to examine changes in DA turnover in the asymptomatic PD phase; to compare them with changes in other dopaminergic markers, and to investigate a possible relationship between DAT and DA turnover. Eight subjects from families at increased risk of PD due to LRRK2 mutation were investigated. Positron emission tomography imaging was performed with: 18F-fluorodopa to determine the effective DA distribution volume (EDV), the inverse of DA turnover, and the DA uptake rate Kocc, a marker of DA synthesis and storage; 11C-methylphenidate (MP, a DAT marker) and 11C-dihydrotetrabenazine (DTBZ, a VMAT2 marker) to estimate the binding potentials BPND_MP and BPND_DTBZ. On average, EDV showed the largest reduction from age-matched control values (42%) followed by BPND_MP (23%) and BPND_DTBZ (17%), whereas Kocc remained in the normal range for all subjects. No correlation was found between EDV and any other marker. DA turnover was found to be elevated in asymptomatic mutation carriers at increased risk of PD. Such change was determined to be larger than and statistically independent from changes observed with the other markers. These results support a compensatory role of increased DA turnover in presymptomatic disease and indicate that at this stage, in contrast to the symptomatic PD phase, increased turnover is not related to DAT. © 2010 Movement Disorder Society. Source


Lee G.,University of British Columbia | Byram A.C.,University of British Columbia | Owen A.M.,University of Western Ontario | Ribary U.,Simon Fraser University | And 5 more authors.
Canadian Journal of Neurological Sciences | Year: 2015

Background: Acquired brain injury is a critical public health and socioeconomic problem in Canada, leaving many patients in vegetative, minimally conscious, or locked-in states, unresponsive and unable to communicate. Recent advances in neuroimaging research have demonstrated residual consciousness in a few exemplary patients with acquired brain injury, suggesting potential misdiagnosis and changes in prognosis. Such progress, in parallel with research using multimodal brain imaging technologies in recent years, has promising implications for clinical translation, notwithstanding the many challenges that impact health care and policy development. This study explored the perspectives of Canadian professionals with expertise either in neuroimaging research, disorders of consciousness, or both, on the potential clinical applications and implications of imaging technology. Methods: Twenty-two professionals from designated communities of neuroimaging researchers, ethicists, lawyers, and practitioners participated in semistructured interviews. Data were analyzed for emergent themes. Results: The five most dominant themes were: (1) validation and calibration of the methods; (2) informed consent; (3) burdens on the health care system; (4) implications for the Canadian health care system; and (5) possibilities for improved prognosis. Conclusions: Movement of neuroimaging from research into clinical care for acquired brain injury will require careful consideration of legal and ethical issues alongside research reliability, responsible distribution of health care resources, and the interaction of technological capabilities with patient outcome. Copyright © The Canadian Journal of Neurological Sciences Inc. 2015. Source

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