Abstract
Objectives The purpose of a parallel-hole collimator in a scintillation camera system is to
transmit only those photons that have an emission angle close to the direction of
the hole. This makes it possible to receive spatial information about the origin of
the emission, that is, radioactivity decay. The dimension, shape, and intrahole thickness
determine the spatial resolution and, by a tradeoff, sensitivity. The composition
of the collimator material also plays an important role in determining a proper collimator.
In this study, we compared tungsten alloys as a potential collimator material replacement
for the conventional lead antimony material used in most of the current camera systems.
Materials and Methods Monte Carlo simulations of a commercial scintillation camera system with low energy
high resolution (LEHR), medium-energy (ME), and high-energy (HE) collimators of lead,
tungsten, and tungsten-based alloy were simulated for different I-131, Lu-177, I-123,
and Tc-99m sources, and a Deluxe rod phantom using the SIMIND Monte Carlo code. Planar
images were analyzed regarding spatial resolution, image contrast in a cold source
case, and system sensitivity for each collimator configuration. The hole dimensions
for the three collimators were those specified in the vendor's datasheet.
Results Using Pb, W, and tungsten alloy (Wolfmet) as collimator materials, the full width
at half maximum (FWHM) measures for total counts (T) for LEHR with Tc-99m source (6.9,
6.8, and 6.8 mm), for ME with Lu-177 source (11.7, 11.5, and 11.6 mm), and for HE
with I-131 (6.2, 13.1, and 13.1 mm) were obtained, and the system sensitivities were
calculated as 89.9, 86.1, and 89.8 cpsT/MBq with Tc-99m source; 42.7, 17.4, and 20.9 cpsT/MBq with Lu-177 source; and 40.1, 69.7, and 77.4 cpsT/MBq with I-131 source. The collimators of tungsten and tungsten alloy (97.0% W, 1.5%
Fe, 1.5% Ni) provided better spatial resolution and improved image contrast when compared
with conventional lead-based collimators. This was due to lower septal penetration.
Conclusion The results suggest that development of a new set of ME and HE tungsten and tungsten
alloy collimators could improve imaging of I-131, Lu-177, and I-123.
Keywords
collimator - gamma camera - planar imaging - SIMIND - tungsten - spatial resolution
- Wolfmet
