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J Nucl Med. 2008; 49 (Supplement 1):120P
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Instrumentation & Data Analysis: Instrumentation

Pre-Clinical Imaging

A fillable micro-lesion detection phantom with zero wall effect

Frank DiFilippo1, Sven Gallo1 and Ryan Klatte2

1 Nuclear Medicine; 2 Biomedical Engineering, Cleveland Clinic, Cleveland, Ohio

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Objectives: A basic problem with lesion detection phantoms having fillable spheres is that the sphere walls cause a region of zero activity between the lesion and background chambers. This problem is especially acute for small spheres, where the wall volume is much larger than the internal volume, preventing accurate characterization of small animal scanners.

Methods: The micro-lesion phantom uses superposition to avoid the wall effect. The phantom is designed to be rotated in-place to switch the locations of separate sphere and background chambers. Data are acquired in two phases, and the sinograms are summed afterwards to produce the desired sphere-to-background ratio. The phantom is fabricated by stereolithography and has interchangeable fillable spheres of 1.25 to 3.0 mm diameter (1 to 14 µL volume). The phantom is designed to maintain constant attenuation, scatter, and count rate between the two scan phases.

Results: As expected, micro-SPECT images of the phantom show no region of zero activity around the spheres. Lesion detectability is assessed versus sphere diameter and sphere-to-background ratio by inspecting multiple images produced by variable downsampling of the two sinograms prior to summing and reconstruction. Mass measurements during phantom preparation validate the accuracy of the micro-liter syringes used to fill the spheres.

Conclusions: This micro-phantom allows lesion detection performance of small animal scanners to be evaluated while avoiding errors due to the wall effect. Although existing phantoms adequately characterize spatial resolution and uniformity, this new phantom provides a valuable task-based test that better reflects a scanner's capabilities for cancer research and other applications.

Research Support: NIH grant R21-CA124406





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