The Molecular Imaging Program (MIP) of the National Cancer Institute is charged with the task of developing chemical probes specific to pathways associated with the development, growth and treatment of cancer. Radionuclide-labeled compounds are an important subset of such agents. Successfully developed radionuclide-labeled compounds offer the ultimate prospect of PET, SPECT and planar imaging in human subjects for medical diagnostic and management purposes, and equally powerful applications in basic science when used for probe validation in small laboratory animals. The MIP radionuclide instrumentation group supports this basic science mission by exploring and implementing new radionuclide imaging technologies that improve or advance the state of MIP small animal imaging. Development work carried out by the RIG and its (essential) collaborators is based on the notion of directed exploration where technological opportunities are examined at the research level (panel A, Figure 1) but with a particular systems level goal in mind (panel B, Figure 1). Figure 1. (A): Research areas in imaging system development: (B): current focused systems level development project: dual gamma camera planar projection imaging system for single photon, high-speed dynamic whole body bio-distribution studies in mice. To illustrate this parallelism, work is now underway in the RIG in each of the areas shown in Figure 1A: LaBr3 slab and NaI(Tl) pixelated detector modules and support electronics development (CIT-NIH/RIG);evaluation of a new, modular DAQ system (Thomas Jefferson National Accelerator Facility (JLAB), Newport News, VA/RIG);creation of a high speed data processing interface using both centroid event positioning and advanced Maximum Likelihood (ML) positioning (RIG/CIT);and evaluation of a commercial system (Nuclear Mac) for image display and analysis (RIG/CIT). Each of these sub-system projects are evaluated in light of the current systems level goal of creating a dual planar gamma camera device for imaging mice while at the same time providing information in each technical area for potential use in our next systems level development project. For example, one of the detector modules (M1 or M2 in Figure 1B) will be comprised of a rectangular pixelated NaI(Tl) array coupled to two side-by-side Hamamatsu H8500 position-sensitive photomultiplier tubes (PSPMTs, panel A, Figure2). Initial imaging results obtained with this combination (panel B, Figure 2) required full use of the JLAB DAQ, CIT developed electronics and RIG-developed data processing software for acquisition and analysis of these data. Figure 2. (A): NaI(Tl) detector module and supporting electronics (CIT/RIG);(B): early 511 keV field flood image from this 19 x 42 (43mm x 94 mm) pixel module. Note clear identification of the 2 mm x 2 mm pixels in the gap between the two side-by-side PSPMTs. A custom collimator has been designed for this array where each pixel has its own individual collimator hole. We plan to continue this exploratory work with the goal of turning over the completed dual gamma camera system to MIP scientists , followed by a review of accrued technical findings and designation of the next systems level project.
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