Serial PET studies of human cerebral malignancy with [1-11C]putrescine and [1-11C]2-deoxy-D-glucose

Serial PET measurements of [1-11C]putrescine ([11C]PUT) uptake and glucose metabolic rate (GMR) using [1-11C]2-deoxy-D-glucose ([11C]2DG) were made on eight human subjects with a radiological and, in most cases, pathological diagnosis of primary or metastatic brain tumor. Blood-to-brain influx constants (Ki) were calculated for [11C]PUT. Tumor uptake of 11C after [11C]PUT injection was unidirectional peaking at 15 min. The mean +/- s.d. Kis for [11C]PUT for tumor and normal brain tissue were 0.78 +/- 0.045 and 0.024 +/- 0.007 ml cc-1 min-1, respectively (average of ratio, 3.11) whereas the ratio of GMR for tumor and normal brain tissue was 1.2 +/- 0.5. The mean Ki for four active, high grade astrocytomas was 0.098 +/- 0.030 in contrast to 0.027 +/- 0.008 ml cc-1 min-1 for two patients with low grade astrocytoma. Active high grade astrocytomas also showed marked CT contrast enhancement and regional glucose hypermetabolism. In one subject with brain metastases, both [11C]PUT and GMR correlated with a declining clinical picture in repeated studies over a 4-mo period. PET studies with [11C]PUT provide a better signal:noise ratio than GMR measurements, are useful for locating small glycolytically hypometabolic tumors and, when used in longitudinal studies in a single subject, appear to provide an index of degree of malignancy.