Anne Bol

Neuronal ceroid-lipofuscinosis: preferential metabolic alterations in thalamus and posterior association cortex demonstrated by PET.

Regional brain glucose utilisation was investigated with positron emission tomography (PET) and fluorodeoxyglucose (FDG) in four siblings with neuronal ceroid-lipofuscinosis. A consistent pattern was found, namely a decrease of glucose utilisation in all grey structures but more marked at the level of the thalamus and posterior association cortex. The severity of metabolic anomalies was correlated with the degree of clinical impairment and with disease duration; they were the most severe in the oldest patient, who was also the most affected clinically, intermediate in two others, and minimal in the subject with the shortest period of development of the disease. These observations suggest that PET is useful for the definition of anatomical targets of metabolic diseases and for the investigation of their pathophysiology.

Assessment Of Scatter In Two PET Scanners With And Without Interplane Septa

Removal of interplane septa increases the sensitivity of multi-ring positron tomographs at the cost of an increase in the scatter fraction (SF) and randoms. We have Bssessed SF both experimentally and theoretically for two commercial tomographs: CTI 931/08-12 and CTI 953B with and without interplane septa. Monte Carlo simulations were undertaken using the GEANT package from CERN. SFs were calculated for various source geometries as a function of energy discrimination. For a line source at the center of a 21.6 cm diameter scattering cylinder (6.4 liters) in the 931/08-12 with a 250 keV threshold, the measured (calculated) SF in the whole field of view (FOV) are 15% (14%) for the sum of all direct and cross planes and 45% (46%) for the sum of all 64 planes, with and without septa, respectively. At 350 keV, the corresponding values are 12% (11%) and 35% (37%). respectively. For the 953B with the same source geometry and a threshold set at 380 keV, the measured (calculated) SF in a 40 cm FOV, is 14 % (15%) and 46% (46%). for the sum of all planes up to the third coincidence order (i.e. 100 sinograms or axial lines of response (LORS)). When varying the energy discrimination threshold. the agreement is not as good and may be due to the sharp threshold model used in the simulation.

Methodological Issues in Regional Myocardial Perfusion Imaging with Positron Emission Tomography

Positron emission tomography (PET) is currently the only technique available that permits the quantification of regional myocardial blood flow in vivo. Absolute PET measurements of nutrient tissue flow and flow reserve1 have contributed significantly to the understanding of the mechanisms of various cardiac disorders such as ischemic heart disease, cardiac hypertrophy or microcirculatory disorders.2 However these quantitative measurements are demanding and are currently performed adequately in a limited number of laboratories with particular expertise in instrumentation and tracer modelling. This chapter deals with several aspects of PET methodology in the evaluation of myocardial perfusion.

A simplified blood sampling scheme in FDG-PET studies

Quantitative measurement of brain glucose metabolism with positron emission tomography (PET) and fluorodeoxyglucose (FDG) involves arterial blood sampling to estimate the delivery of radioactivity to the brain. Usually, for an intra-venous bolus injection of 30 sec duration, an optimal manual sampling requires more than 25 blood samples since a frequency of 1 sample every 5 sec or less is necessary to determine the peak activity in arterial plasma during the first 2 minutes after injection. In the present work, 13 standardized sampling times were shown to be sufficient to accurately define the input curve. This standardized input curve was subsequently fitted by a polynomial function for its rising part and by spectral analysis for its decreasing part. Using the measured, the standardized as well as the fitted input curves, the regional cerebral metabolic rate for glucose (rCMRGlc) was estimated in 32 cerebral regions of interest (ROIs) in 20 normal volunteers. Metabolic values were obtained by both the autoradiographic method (ARG) and the kinetic analysis of dynamic data (DYN). Comparison of rCMRGlc values obtained with the measured and the fitted input curves showed that both procedures gave consistent results, with a maximal relative error in mean rCMRGlc of about 1% in ARG and 2% in DYN studies. This input curve fitting technique which was not dependent on the peak time occurrence, allowed an accurate determination of the input curve shape from reduced sampling schemes.

Assessment of Myocardial Perfusion by PET

Several tracer approaches have been proposed for the assessment of myocardial perfusion with positron emission tomography (PET) in the clinical setting. These include nitrogen-13 (13N) labelled ammonia, oxygen-15 (15O) labelled water, rubidium-82 (82Rb) and potassium-38 (38K). These tracers require a local cyclotron for production, except for 82Rb which may be delivered directly to the patient from an on-site generator. There are two specific clinical applications of PET that have been proposed for the evaluation of patients with coronary artery disease (CAD) [1-3]. The first is the noninvasive detection of CAD and estimation of the severity of the disease. This is performed using a PET perfusion agent at rest and during pharmacologic vasodilation. A unique application of PET is the noninvasive calculation of absolute regional myocardial perfusion at rest and during vasodilation in humans using [15O]water or [13N]ammonia. However, most centers rely on the qualitative interpretation of 82Rb or [13N]ammonia images for the detection of CAD and the assessment of its severity. The second clinical application of PET is the assessment of myocardial viability in CAD patients with left ventricular dysfunction. The most common approach is to determine whether metabolic activity assessed by 2-[18F]fluoro-2-deoxy-D-glucose ([18F]FDG) is preserved in regions with reduced perfusion, thus indicating tissue viability.

Myocardial blood flow quantitation with positron emission tomography

Dynamic Positron Emission Tomography (PET) with the use of appropriate tracers is the only technique available thus far that permits quantitation of regional myocardial blood flow (MBF) in absolute terms, i.e. ml/min/g of tissue. This review discusses some of the contributions of PET measurements of MBF to the understanding of the pathophysiology of coronary artery disease.