Matthew D. Walker

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PURPOSE Psychogenic nonepileptic seizures (PNES) continue to represent a serious diagnostic challenge for neurologists. Video-electroencephalography (EEG) studies have provided detailed knowledge of the spectrum of visible PNES manifestations. However, little is known about how patients or seizure witnesses experience PNES, although many diagnoses in(More)
Longitudinal measurements of dopamine (DA) uptake and turnover in transgenic rodents may be critical when developing disease-modifying therapies for Parkinson's disease (PD). We demonstrate methodology for such measurements using [(18)F]fluoro-3,4-dihydroxyphenyl-L-alanine ([(18)F]FDOPA) positron emission tomography (PET). The method was applied to(More)
Iterative image reconstruction methods such as ordered-subset expectation maximization (OSEM) are widely used in PET. Reconstructions via OSEM are however reported to be biased for low-count data. We investigated this and considered the impact for dynamic PET. Patient listmode data were acquired in [(11)C]DASB and [(15)O]H(2)O scans on the HRRT brain PET(More)
This study aimed to derive accurate estimates of regional cerebral blood flow (rCBF) from noisy dynamic [¹⁵O]H₂O PET images acquired on the high-resolution research tomograph, while retaining as much as possible the high spatial resolution of this brain scanner (2-3 mm) in parametric maps of rCBF. The PET autoradiographic method and generalized linear(More)
Positron emission tomography (PET) is generally considered to be a quantitative imaging modality, allowing assessment of regional differences in radiotracer accumulation and the derivation of quantitative physiological information. Due to the increasing complexity of PET technology, the quantitative accuracy of PET images has to be continually reassessed if(More)
BACKGROUND A major risk-factor for developing Parkinson's disease (PD) is genetic variability in leucine-rich repeat kinase 2 (LRRK2), most notably the p.G2019S mutation. Examination of the effects of this mutation is necessary to determine the etiology of PD and to guide therapeutic development. OBJECTIVE Assess the behavioral consequences of LRRK2(More)
The precision of biological parameter estimates derived from dynamic PET data can be limited by the number of acquired coincidence events (prompts and randoms). These numbers are affected by the injected activity (A(0)). The benefits of optimizing A(0) were assessed using a new model of data variance which is formulated as a function of A(0). Seven cancer(More)
This paper proposes a new algorithm that extracts color correction parameters from pairs of images and enables the perceived illumination of one image to be imposed on the other. The algorithm does not rely upon prior assumptions regarding illumination constancy and operates between images that can be significantly different in content. The work derives(More)
OBJECTIVE Epileptic seizures, syncope, and psychogenic nonepileptic seizures (PNES) account for over 90% of presentations with transient loss of consciousness (TLOC). The patient's history is crucial for the diagnosis, but the diagnostic value of individual semiologic features is limited. This study explores the diagnostic potential of a comprehensive(More)