Program Information
Quantitative Small-Animal SPECT Without Scatter Correction Using High-Purity Germanium Detectors
A Gearhart1*, T Peterson1 , L Johnson2 , (1) Vanderbilt University, Nashville, TN, (2) University of Pennsylvania, Philadelphia, PA
Presentations
SU-C-201-2 (Sunday, July 12, 2015) 1:00 PM - 1:55 PM Room: 201
Purpose: To evaluate the impact of the exceptional energy resolution of germanium detectors for preclinical SPECT in comparison to conventional detectors.
Methods: A cylindrical water phantom was created in GATE with a spherical Tc-99m source in the center. Sixty-four projections over 360 degrees using a pinhole collimator were simulated. The same phantom was simulated using air instead of water to establish the true reconstructed voxel intensity without attenuation. Attenuation correction based on the Chang method was performed on MLEM reconstructed images from the water phantom to determine a quantitative measure of the effectiveness of the attenuation correction. Similarly, a NEMA phantom was simulated, and the effectiveness of the attenuation correction was evaluated. Both simulations were carried out using both NaI detectors with an energy resolution of 10% FWHM and Ge detectors with an energy resolution of 1%.
Results: Analysis shows that attenuation correction without scatter correction using germanium detectors can reconstruct a small spherical source to within 3.5%. Scatter analysis showed that for standard sized objects in a preclinical scanner, a NaI detector has a scatter-to-primary ratio between 7% and 12.5% compared to between 0.8% and 1.5% for a Ge detector. Preliminary results from line profiles through the NEMA phantom suggest that applying attenuation correction without scatter correction provides acceptable results for the Ge detectors but overestimates the phantom activity using NaI detectors. Due to the decreased scatter, we believe that the spillover ratio for the air and water cylinders in the NEMA phantom will be lower using germanium detectors compared to NaI detectors.
Conclusion: This work indicates that the superior energy resolution of germanium detectors allows for less scattered photons to be included within the energy window compared to traditional SPECT detectors. This may allow for quantitative SPECT without implementing scatter correction, reducing uncertainties introduced by scatter correction algorithms.
Funding Support, Disclosures, and Conflict of Interest: Funding provided by NIH/NIBIB grant R01EB013677 Todd Peterson, Ph.D., has had a research contract with PHDs Co., Knoxville, TN
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