Performance characteristics of a 511-keV collimator for imaging positron emitters with a standard gamma-camera

Abstract

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.

Steps Forward in the Assessment of Myocardial Viability in Left Ventricular Dysfunction

“…9 More recently, however, these distinctions have blurred with the advent of high-energy collimators for SPECT imaging of positrons, 10,11 allowing the potential for the more widely available SPECT imaging technique to assess metabolic activity with 18 FDG. Because PET technology is not widely available, and because on the basis of its expense and nonuniform reimbursement in this era of cost containment it is unlikely to be as available as SPECT in the future, the ability of SPECT imaging to assess regional metabolic activity in states of LV dysfunction is potentially of great interest.…”

Is planar thallium-201/fluorine-18 fluorodeoxyglucose imaging a reasonable clinical alternative to positron emission tomographic myocardial viability scanning?

“…The limiting factors in this exercise include adequate camera head shielding, electronics capable of detecting the 511-keV annihilation photons and a collimator design rigorous enough to minimise septal penetration without a severe degradation of image resolution. Following successful in vitro studies, several groups including our own have been able to obtain clinically acceptable myocardial FDG images [9,10,12]. These studies use identical activities of 18F-FDG to those required for formal myocardial viability studies, and by adding thallium-201 [or technetium-99m methoxyisobutylisonitrile (MIBI)] as the myocardial perfusion tracer have the potential to perform a metabolically equivalent evaluation to the PET technique.…”

“…This has led several research groups to modify conventional gamma cameras to allow them to image the 511-keV photons of 18F-FDG [9][10][11][12][13], as was done for rubidium-81 myocardial perfusion scans in the mid 1970s, when planar scintillation cameras were fitted with pin-hole collimators [14,15]. The limiting factors in this exercise include adequate camera head shielding, electronics capable of detecting the 511-keV annihilation photons and a collimator design rigorous enough to minimise septal penetration without a severe degradation of image resolution.…”

A Parallel-Cone Collimator for High-Energy SPECT

“…The strategy used to optimize parallel-hole collimators for high-energy applications is to increase septal thickness and length to limit septal penetration. Over the years, several high-energy collimators have been designed to accommodate photon energies of 200-511 keV, including the special high-energy all-purpose collimator (8), the ultra-high-energy collimator (9), and the more common highenergy general-purpose (HEGP) collimator. In general, increasing the septal thickness will decrease the amount of penetrated photons, but it will also decrease the system sensitivity.…”