Chitra Saxena

Longitudinal noninvasive PET-based β cell mass estimates in a spontaneous diabetes rat model

Diabetes results from an absolute or relative reduction in pancreatic beta cell mass (BCM) leading to insufficient insulin secretion and hyperglycemia. Measurement of insulin secretory capacity is currently used as a surrogate measure of BCM. However, serum insulin concentrations provide an imprecise index of BCM, and no reliable noninvasive measure of BCM is currently available. Type 2 vesicular monoamine transporters (VMAT2) are expressed in human islet beta cells, as well as in tissues of the CNS. [11C]Dihydrotetrabenazine ([11C]DTBZ) binds specifically to VMAT2 and is a radioligand currently used in clinical imaging of the brain. Here we report the use of [11C]DTBZ to estimate BCM in a rodent model of spontaneous type 1 diabetes (the BB-DP rat). In longitudinal PET studies of the BB-DP rat, we found a significant decline in pancreatic uptake of [11C]DTBZ that anticipated the loss of glycemic control. Based on comparison of standardized uptake values (SUVs) of [11C]DTBZ and blood glucose concentrations, loss of more than 65% of the original SUV correlated significantly with the development of persistent hyperglycemia. These studies suggest that PET-based quantitation of VMAT2 receptors provides a noninvasive measurement of BCM that could be used to study the pathogenesis of diabetes and to monitor therapeutic interventions.

F-18 FDG PET imaging of chronic traumatic brain injury in boxers: a statistical parametric analysis

PurposeThe participation in concussive susceptible sports such as boxing may cause chronic traumatic brain injury. The objective of this study was to determine whether there are unique patterns of reduced brain glucose metabolism in professional and amateur boxers. MethodWe compared the fluorine-18 fluorodeoxyglucose (F-18 FDG) PET brain scans of boxers (group) (N=19) with those of controls (group) (N=7) using both statistical parametric mapping and region of interest analysis. ResultsBoxers showed decreased F-18 FDG uptake by 8–15% in the following brain areas: posterior cingulate cortex, parieto–occipito, frontal lobes (Brocas area) bilaterally, and the cerebellum (P<0.005) as compared with controls. ConclusionOur results suggest that F-18 FDG PET scans of boxers suspected of chronic traumatic brain injury show unique patterns of hypometabolism, and that these patterns may reflect the mechanisms of repeated traumatic brain injury unique to boxers.

18Fluoro-deoxyglucose positron emission tomography evaluation of benign versus malignant osteochondromas: preliminary observations.

Objective: To determine the contribution of 18fluoro-deoxyglucose positron emission tomography (18FDG PET) in distinguishing benign from malignant osteochondromas. Materials and Methods: From 2000 to 2004, 10 patients (4 females, 6 males, 12 to 64 years old) with osteochondromas were referred for whole body PET by clinicians for metabolic evaluation before planned surgery for pain or cosmesis. Two PET readers and 1 pathologist, blinded to their diagnoses and imaging studies (except for radiographs), correlated results post surgery. The PET average and maximum standard uptake value (SUV) generated by computer for Regions of Interest and correlated with radiographs, were based on axial 3.37 mm thick, 3×3 mm pixel images. Since SUVs vary from site to site depending on scanning devices and techniques, a 2.0 maximum cutoff SUV separated benign and malignant osteochondromas based on our standard protocols and specific equipment (Siemens Ecat Exact Knoxville, Tenn) used with our prior oncological studies. Results: Results showed that no definitive statistical conclusions could be drawn due to the small number of patients involved, but they were, nevertheless, deemed promising. Conclusions: The 18FDG whole body PET aided the identification of malignant osteochondromas, their local recurrence and metastases by both displaying and quantifying their metabolic activity. Although the current study is limited by a small cohort, which precludes statistical analysis, additional experience with PET analysis of osteochondromas may further support its value as a physiological parameter supplementing anatomically based imaging modalities most often used for their evaluation.