Photon penetration and scatter in micro-pinhole imaging: a Monte Carlo investigation.
Pinhole SPECT is rapidly gaining popularity for imaging laboratory animals using gamma-emitting molecules. Penetration and scattering of gamma radiation in the pinhole edge material can account for a significant fraction of the total number of photons detected, particularly if the pinholes have small diameters. This study characterizes the effects of penetration and scatter with micro-pinholes made of lead, tungsten, gold and platinum. Monte Carlo simulations are performed for 1-125 (27-35 keV) and Tc-99m (140 keV) point sources with pinhole diameters ranging from 50 to 500 microm. The simulations account for the effects of photo-electric interaction, Rayleigh scattering, Compton scattering, ionization, bremsstrahlung and electron multiple scattering. As a typical example, in the case of a Tc-99m point source and pinholes with a diameter of 300 microm in gold or platinum, approximately 55% of the photons detected resulted from penetration and approximately 3% from scatter. For pinhole diameters ranging from 100 to 500 microm, the penetration fraction for tungsten and lead was approx a factor of 1.0 to 1.6 higher and the scatter fraction was 1.0 to 1.8 times higher than in case of gold or platinum. Using I-125 instead of Tc-99m decreases the penetration fraction by a factor ranging from 3 to 11 and the scatter fraction by a factor ranging from 12 to 40. For all materials studied, the total amounts of penetrated and scattered photons changed approximately linearly with respect to the pinhole diameter.
van der Have
Frans
F
Image Sciences Institute, UMC Utrecht STR 5.203, Universiteitsweg 100. 3584 CG Utrecht, The Netherlands. f.vanderhave@azu.nl
Beekman
Freek J
FJ
D004583:Electrons; D006046:Gold; D007091:Image Processing, Computer-Assisted; D007477:Ions; D007854:Lead; D015233:Models, Statistical; D008962:Models, Theoretical; D009010:Monte Carlo Method; D017785:Photons; D010984:Platinum; D012542:Scattering, Radiation; D013667:Technetium / Q000378:metabolism; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*; D014414:Tungsten
D007477:Ions; D007854:Lead; D010984:Platinum; D013667:Technetium; D006046:Gold; D014414:Tungsten