John N. Aarsvold

Modular Scintillation Cameras: A Progress Report

Modular scintillation cameras are gamma cameras with relatively small crystal faces, a small number of photomultiplier tubes (PMTs), and independent processing electronics. Our prototypical module has a 10 cm square crystal face, four PMTs, and digital processing electronics. Scintillation event information is transferred to images by mapping digitized PMT response combinations to optimal position estimates of event locations. In our prototype, a look-up table is used to perform this mapping. To encode scintillation event information more effectively, we use nonlinear compression of each of the PMT signals. Also introduced are logarithmic matched filtering and likelihood windowing, two processing techniques that result from exploitations of the Poisson model of the distribution of photopeak events. Logarithmic matched filtering is a method of obtaining estimates of mean detector response functions having greater accuracy than that indicated by the digitization of the PMT responses. Likelihood windowing is the utilization of a likelihood threshold, rather than the familiar energy window, as a discriminant of photopeak and scatter events. We have implemented each of the above on our prototypical module. Performance characteristics of this module include energy resolution of 10% full width at half maximum (FWHM) at 140 keV and spatial resolution of better than 4mm FWHM over 90% of the crystal.

Preliminary Results from Simulations of Tomographic Imaging Using Multiple-Pinhole Coded Apertures

The use of multiple-pinhole coded apertures in single-photon emission computed tomographic (SPECT) systems makes possible SPECT geometries that image from multiple directions simultaneously and that have greater photon-collection efficiencies than conventional SPECT systems. However, the multiplexing of data that results from the use of such apertures is not well understood and, therefore, is not always optimally decoded. Presented in this paper are results from a simulation study of multiple-pinhole coded-aperture systems having pinholes that are uniformly spaced and of uniform width. Five apertures representing varying degrees of multiplexing are considered, and the results presented are in the form of pictorial displays that make possible qualitative comparisons of images from the five imaging systems. Shown are representations of the Hoffman brain phantom determined following singular value decompositions of the system matrices and reconstructions of simulated SPECT data using a Monte Carlo algorithm and prior information.

Applications of Statistical Decision Theory in Nuclear Medicine

Over the last several years, Bayesian decision and estimation theory has become a central theme in the nuclear medicine research program at the University of Arizona. We have used concepts from this theory for image reconstruction, evaluation and optimization of imaging systems, position arithmetic in scintillation cameras, and in decision making in the operating room. In this paper, a brief review of Bayesian theory is given, followed by a survey of all of these applications, with emphasis on points of commonality among them.

The Design and Implementation of Modular SPECT Imaging Systems

This paper describes a small, digital, modular gamma camera that can be used individually as a small organ, planar imaging system or can be combined to create modular single-photon emission computed tomography (SPECT) systems that contain no moving parts. We describe two systems currently under design: a cardiac imager capable of multi-slice, two-dimensional SPECT, and a full three-dimensional brain imager. Finally, we present a two-dimensional tomographic image generated by a prototypical modular camera SPECT system.

The quality field of view of a discovery 530c

The quality field of view (QFOV) of a GE Healthcare Discovery NM 530c cardiac single-photon emission computed tomograph (D530c) is the volume representing the intersection of the 19 conic volumes defined by the systems 19 pinhole/detectorarray pairs. Here are reported phantom experiments conducted to investigate and characterize aspects of the D530c QFOV.