Positron Emission Tomography (PET)

A key issue in functional neuroimaging is the amount of variability produced by individual differences in anatomical and functional patterns of activation. This variability affects summed images created when responses are averaged across subjects as well as comparisons between groups of subjects.In this report, functional-anatomical variability was explored at two different levels. The first level addressed whether responses defined in one group of subjects would replicate in a second subject group performing the same tasks.

1. Data from a series of positron emission tomography (PET) experiments were analyzed with two goals. The first goal was to determine whether there were reliable differences in prefrontal cortex activation across two different speech production tasks. Such differences are important in determining functional subdivisions within prefrontal cortex. The second goal was to determine whether there were any gender differences across the two speech production tasks. 2.

Across three experiments, PET scans were obtained while subjects performed different word-stem completion and FIXATION control tasks designed to study the functional anatomy of memory retrieval. During each of three different word-stem completion scans, word-stem cues were visually presented in uppercase letters. The RECALL task required explicit retrieval of study words presented prior to the PET scan. The PRIMING task addressed the implicit effects of the prior study words without requiring intentional recall.

Nine previous positron emission tomography (PET) studies of human visual information processing were reanalyzed to determine the consistency of blood flow changes during a wide variety of active tasks relative to passive viewing of the same stimulus array. Consistent modulations were found in the early visual cortex, probably including area 17, and these modulations could reflect selective mechanisms. Blood flow decreases were found in some auditory and somatosensory areas, but did not appear to reflect a broad suppression of subcortical input.

Nine positron emission tomography (PET) studies of human visual information processing were reanalyzed to determine the consistency across experiments of blood flow increases during active tasks relative to passive viewing of the same stimulus array. No consistent blood flow increases were found in cerebral cortex outside of the visual system, but increases were seen in the thalamus and cerebellum.

The potential structural similarity of technetium-99m-labeled glucaric acid (99mTc-glucarate) to that of fructose suggests that this agent may enter cells by a sugar transport system. Studies with LLC-PK1 cells demonstrated inhibition of 99mTc-glucarate uptake by fructose, confirming this potential relationship. Since anaerobic metabolism can use either glucose or fructose, we hypothesized that 99mTc-glucarate may concentrate in areas of acute ischemic injury.

Glucose utilization studies using high resolution positron emission tomography and tissue oxygenation measurements using microelectrode techniques were carried out in nude mice bearing oncogene-transformed (Rat1pEJ6.6 and REFpneoMYCrasEpool) cell line tumours and a non-transformed (Rat1) cell line tumour to determine the correlation between glucose utilization, tissue oxygenation and tumour growth rate. Control measurements were performed in the subcutis of tumour-free animals.

In this article, we show that 1) computed tomographic (CT)-guided stereotactic infusion of an excitotoxin into the striatum of a nonhuman primate provides a useful neuropathologic and behavioral model for Huntington's disease. 2) High-resolution positron emission tomography (PET) can be used to image the decreased glucose utilization and the preservation of dopaminergic terminals in the lesioned striatum by using 2-fluoro-deoxy-D-glucose (2FDG) and N-(C-11)-methyl-2-beta-carbomethoxy-3-beta-phenyl tropane (CPT) as tracers.

Monkeys were treated on two regimens of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) injections to achieve dopamine fiber degeneration of differing severities. A rapid treatment regimen produced a severe parkinsonian syndrome, whereas an intermittent regimen did not cause locomotor symptoms to appear up to 25 weeks. High resolution PET scanning of dopamine nerve terminals revealed that the specific binding of the dopamine transporter [11C]-WIN 35,428 ([11C]-CFT) was diminished by 94% (caudate nucleus) and by 93% (putamen) in the symptomatic monkey.

PET has inherently high resolution and excellent contrast imaging and accurately measures radioactivity concentrations in vivo. When combined with specific immunological targeting it might provide a highly specific and sensitive radioimmunoscintigraphic tool. To investigate this we injected 124I-labeled MAb MX35 or MAb MH99 monoclonal antibodies (doses 200-400 mu Ci) intravenously into nude rats bearing subcutaneous human ovarian cancer xenografts (SK-OV-7 and SK-OV-3 cell lines). A melanoma cell line (SK-MEL-30) was used as a control tumor.