Line-source experiments were conducted to assess the performance of a gamma-camera equipped with a specially designed 511-keV collimator for the planar imaging of positron emitters. The results were compared with the camera performance with routinely used collimators and radionuclides (thallium-201, technetium-99m and gallium-67). With positron emitters, scatter contributed less to the widening of the line spread function than with radionuclides emitting lower photon energies. These observations can be explained by the relative deterioration in the discrimination power of the gamma-camera to reject scattered radiation at low energies. Planar 511-keV imaging may provide relevant clinical information, as we showed by fluorodeoxyglucose studies in a patient with a myocardial infarction and in a patient with a malignant lymphoma. It is concluded that positron emitters can be effectively applied for planar imaging with the generally available gamma-cameras. This study implies that radiotracers developed for positron emission tomography may find a place in the practice of conventional nuclear medicine.

Abstract. An X-ray crystal structure analysis of 9,9a-dihydro-1,9,9-trimethyl-2-methylene-3,10-diketo-9a-mercapto-piperazino[ 1,2-a]indole (1) shows a boat conformation for the piperazinedione ring in this compound. This observation supports the previously suggested Zn' + chelate 3 as an intermediate in the conversion of 1 into 2. Crystals of 1 are monoclinic, a = 12.751 (7) A, b = 7.439 (2) A, c = 15.324(15) A, p = 98.73 (6)"; space group: P2,/n, 2 = 4. In solution at room temperature 1 dimerizes to 4 with loss of one molecule of H,S.

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