B J Kemp1, F S Prato, R L Nicholson, L Reese. 1. Department of Nuclear Medicine and Magnetic Resonance, St. Joseph's Health Centre, London, Ontario, Canada.
Abstract
UNLABELLED: Transmission images of relatively high resolution as compared to SPECT are needed for brain SPECT quantification to provide skull thickness, attenuation coefficients and anatomical correlation. Consequently, a technique to acquire transmission CT images with a SPECT system by using a collimated line source positioned at the focal line of a fanbeam collimator (FBC) has been developed. METHODS: Computer simulations that model the transmission imaging system optimized the system resolution and tested the validity of a equation for the geometric efficiency of the line source collimator (LSC). Based on the computer simulations, a LSC was constructed with tantalum septa 100 mm long, 0.5 mm thick and spaced 1.0 mm apart. A 600-mm focal length FBC was used. Experiments were conducted to measure the system resolution and to determine the effect of the LSC on the amount of detected scatter. RESULTS: The simulations showed that without a LSC the transmission images have a longitudinal resolution (LR) characterized by the resolutions of the FBC (depth-dependent, approximately 8 mm FWHM at 150 mm) and the detector (approximately 4 mm). However, with an optimally designed LSC, the contribution of the FBC to the system resolution can be made negligible, creating a system with a LR that is comparable to the detector resolution and independent of object depth. Resolution experiments conducted with a lucite rod phantom showed that the LR and TR are better than 4.8 mm and confirmed the results of the computer simulations. CONCLUSION: Brain transmission images of relatively high isotropic resolution can be obtained using a SPECT system, a FBC and an optimized LSC.
UNLABELLED: Transmission images of relatively high resolution as compared to SPECT are needed for brain SPECT quantification to provide skull thickness, attenuation coefficients and anatomical correlation. Consequently, a technique to acquire transmission CT images with a SPECT system by using a collimated line source positioned at the focal line of a fanbeam collimator (FBC) has been developed. METHODS: Computer simulations that model the transmission imaging system optimized the system resolution and tested the validity of a equation for the geometric efficiency of the line source collimator (LSC). Based on the computer simulations, a LSC was constructed with tantalum septa 100 mm long, 0.5 mm thick and spaced 1.0 mm apart. A 600-mm focal length FBC was used. Experiments were conducted to measure the system resolution and to determine the effect of the LSC on the amount of detected scatter. RESULTS: The simulations showed that without a LSC the transmission images have a longitudinal resolution (LR) characterized by the resolutions of the FBC (depth-dependent, approximately 8 mm FWHM at 150 mm) and the detector (approximately 4 mm). However, with an optimally designed LSC, the contribution of the FBC to the system resolution can be made negligible, creating a system with a LR that is comparable to the detector resolution and independent of object depth. Resolution experiments conducted with a lucite rod phantom showed that the LR and TR are better than 4.8 mm and confirmed the results of the computer simulations. CONCLUSION: Brain transmission images of relatively high isotropic resolution can be obtained using a SPECT system, a FBC and an optimized LSC.
Authors: Tomislav Bokulić; Brendan Vastenhouw; Hugo W A M de Jong; Alice J van Dongen; Peter P van Rijk; Freek J Beekman Journal: Eur J Nucl Med Mol Imaging Date: 2004-03-18 Impact factor: 9.236