Robert W. Pyzalski

Whole-body positron emission tomography in patients with HIV-1 infection.

Positron emission tomography with fluorine-18-deoxyglucose (FDG-PET) detects active lymphoid tissues during HIV-1 infection in man. We used FDG-PET to study anatomical correlates of HIV-1 infection in man. Whole-body FDG-PET images from 15 patients with HIV-1 showed distinct lymphoid tissue activation in the head and neck during acute disease, a generalised pattern of peripheral lymph-node activation at mid-stages, and involvement of abdominal lymph nodes during late disease. Unexpectedly, HIV-1 progression was evident by distinct anatomical correlates, suggesting that lymphoid tissues are engaged in a predictable sequence. Understanding the anatomy of HIV-1 infection could encourage use of surgical or radiological interventions to supplement chemotherapy.

Memory relationships between MRI volumes and resting PET metabolism of medial temporal lobe structures

Prior studies of temporal lobe epilepsy (TLE) patients showed that MRI volumes and resting PET scan measures of temporal lobe structures were related to memory. Weintrob and colleagues [Ann. Neurol. 2002;51:442-7] reported that PET glucose uptake in the left perirhinal cortex predicted verbal paired associate (PA) learning, whereas MRI volume of the left hippocampus did not. We investigated whether MRI volumes could account for memory functioning if both PET and volumes were from the same region in 18 TLE patients. Volumes and glucose uptake of the hippocampus and parahippocampal gyrus (PHG) were compared with WMS-III performance. Significant correlations were observed between hippocampal volumes and PA and Logical Memory (LM) Percent Retention, but not between memory and PHG volumes or any PET measures. Multiple regression revealed that hippocampal volumes, but not PHG volumes or PET, significantly predicted PA and LM retention scores. These findings suggest that hippocampal volumes provide unique information regarding memory.

A Controlled Quantitative MRI Volumetric Investigation of Hippocampal Contributions to Immediate and Delayed Memory Performance

MRI volumetric TLE studies show inconsistent evidence of hippocampal involvement in memory. Prior studies have not dissociated hippocampal and temporal lobe contributions to memory. We measured hippocampal and temporal lobe volumes and immediate/delayed memory performances in 64 TLE patients. Regression was used to dissociate hippocampal from temporal lobe contributions to memory. Results revealed reliable evidence for dominant hippocampal involvement in delayed verbal recall across three separate measures and less consistent evidence for nondominant hippocampal involvement. The findings point to a consistent relationship of dominant hippocampal volumes to delayed verbal recall but no involvement of the temporal lobe or nondominant hippocampus in memory.

Memory for famous faces and the temporal pole: functional imaging findings in temporal lobe epilepsy.

The ability to recognize, name, and provide information about famous persons is deficient in patients with temporal lobe epilepsy (TLE), although the neural basis for these deficits is not well understood. We examined the relationship of resting metabolism of the temporal poles, as determined by [18F] fluorodeoxyglucose positron emission tomography, to performance on a task of famous face recognition, naming, and generation of semantic information in 12 patients with TLE. Correlations between metabolic measures of the temporal poles and performance on the Famous Faces Task revealed strong relationships between all aspects of the Famous Faces Task and the left temporal pole, whereas Famous Faces Task correlations with the right temporal pole were not significant. These findings indicate that the left temporal pole is associated with lexical and semantic retrieval of knowledge of famous persons in patients with TLE. Further study appears warranted to elucidate the networks involved in semantic knowledge for famous faces.

Discordance between accumulation of C-14 deoxyglucose and T1–201 in reperfused myocardium

Radiolabeled deoxyglucose (FDG) has been advocated as a marker of viability of reperfused myocardium during acute infarction. However, data for such recommendation are few. We investigated cardiac deposition of C-14 deoxyglucose (C-14 DG) and of Thallium -201 (Tl-201) in rabbits subjected to coronary occlusion (15, 30, 60 or greater than 100 min) and reperfusion (75 min and 24 h). Measured myocardial concentrations of C-14 DG and Tl-201 in macroautoradiograms were quantitatively correlated in a 24 h reperfusion group with presence of myocardial necrosis evaluated by light microscopy. The major finding in this investigation was that with 30 min or 60 min of ischemia followed by reperfusion there were myocardial regions with significant hypoperfusion (Tl-201) and histologic necrosis. However, in the same myocardial areas, the deposition of C-14 DG was not correlated with the extent of necrosis (r = 0.27). Also, the deposition of C-14 DG in acute myocardial infarction was higher than that of Tl-201 (P = 0.05 by paired T test and by nonparametric Wilcoxons test). It was also demonstrated that when the occlusion time was varied (15-130 min) and early reperfusion was provided for 75 min or omitted altogether, the myocardial accumulation of Tl-201 was variable and that myocardial sequestration of C-14 DG was higher than perfusion in central and peripheral portions of the area-at-risk. These observations do not support a role for the use of radiolabeled deoxyglucose for the detection of myocardial viability in recently infarcted cardiac muscle.

Rate of 6‐[18F]fluorodopa uptake decline in striatal subregions in Parkinson's disease

Rate of decline in 6‐L‐[18F]fluorodopa (FDOPA) uptake within the striatum has been reported as showing regional differences in Parkinsons disease (PD).

Localization of Trapping of 6-[18F] Fluoro-L-m-tyrosine, an Aromatic L-Amino Acid Decarboxylase Tracer for PET

The purpose of this study was to address four major questions regarding 6‐FMT, a noncatecholic PET tracer for AAAD: 1) Where is the specific uptake of 6‐FMT? 2) Why does it accumulate where and to the degree that it does? 3) How does its uptake differ from that of fluoroDOPA globally? and 4) Does its regional uptake differ significantly from that of fluoroDOPA? High‐resolution PET scans were obtained in three rhesus monkeys using 6‐FMT and in two of them using fluoroDOPA. Anatomic distribution was analyzed visually and quantitative uptake of 6‐FMT was compared with published regional decarboxylase activity and monoamine neurotransmitter concentrations. In addition to high uptake in the dopamine‐rich striatal nuclei, there was specific uptake of 6‐FMT in brain regions which have little dopaminergic innervation but which have other amines in significant concentration. 6‐FMT uptake correlated best with regional AAAD activity (r = 0.97). It correlated slightly less well with the sum of catecholamine and indolamine neurotransmitter concentrations, but does not correlate with dopamine concentration. The uptake of 6‐FMT is greater than that of fluoroDOPA, with only slight differences in their regional distributions. Radiolabeled analogs of DOPA are often implicitly or explicitly regarded as tracers for presynaptic dopaminergic function. However, localization of these tracers more broadly includes many regions with relatively high concentrations of norepinephrine and serotonin. This may be especially important in diseases or experimental states in which dopaminergic neurons are selectively reduced, and may allow for the study of nondopaminergic neuronal systems in vivo with this tracer. Synapse 34:111–123, 1999.

Noninvasive mapping of regional response to segmental allergen challenge using magnetic resonance imaging and [F-18]fluorodeoxyglucose positron emission tomography

Magnetic resonance (MR) and positron emission tomography (PET) imaging techniques were coregistered to demonstrate regional ventilation and inflammation in the lung for in vivo, noninvasive evaluation of regional lung function associated with allergic inflammation. Four Brown Norway rats were imaged pre‐ and post segmental allergen challenge using respiratory‐gated He‐3 magnetic resonance imaging (MRI) to visualize ventilation, T1‐weighted proton MRI to depict inflammatory infiltrate, and [F‐18]fluorodeoxyglucose‐PET to detect regional glucose metabolism by inflammatory cells. Segmental allergen challenges were delivered and the pre‐ and postchallenge lung as well as the contralateral lung were compared. Coregistration of the imaging results demonstrated that regions of ventilation defects, inflammatory infiltrate, and increased glucose metabolism correlated well with the site of allergen challenge delivery and inflammatory cell recruitment, as confirmed by histology. This method demonstrates that fusion of functional and anatomic PET and MRI image data may be useful to elucidate the functional correlates of inflammatory processes in the lungs. Magn Reson Med 53:1243–1250, 2005.

Potential of magnetization transfer MRI for target volume definition in patients with non-small-cell lung cancer.

To develop a magnetization transfer (MT) module in conjunction with a single‐shot MRI readout technique and to investigate the MT phenomenon in non‐small‐cell lung cancer (NSCLC) as an adjunct for radiation therapy planning.

Comparison of 2D and 3D PET for cerebral FDG in human subjects

The authors compared 12 pairs of cerebral [/sup 18/F]-fluoro-deoxyglucose (FDG) 2D/3D image sets from a GE/Advance PET scanner, incorporating the actual corrections used on human subjects. Differences in resolution consistent with other published values were found. There is a significant difference in axial resolution between 2D and 3D, and the authors focused on this as it is a scanner feature that cannot be readily changed. Previously published values for spatial axial resolution in 2D and 3D modes were used to model the differential axial smoothing at each image voxel. This model was applied to the 2D FDG images, and the resulting smoothed data indicate the published differences in axial resolution between 2D and 3D modes can account for 30-40% of the differences between these image sets. The authors then investigated the effect this difference might have on analysis typically performed on human FDG data. A phantom containing spherical hot- and cool-spots in a warm background to mimic a typical human cerebral FDG PET scan was scanned for a variety of time durations (30, 15, 5, 1 min). Only for the 1-minute frame (total counts 2D:6M, 3D:30M) is there an advantage to using 3D mode; for the longer frames which are more typical of a human FDG protocol, the reliability for extracting regions-of-interest is the same for either mode while 2D mode shows better quantitative accuracy.