  The nuclides inhaled during nuclear accidents usually cause internal
contamination of the lungs with low activity. Although a parallel-hole imaging
system, which is widely used in medical gamma cameras, has a high resolution
and good image quality, owing to its extremely low detection efficiency, it
remains difficult to obtain images of inhaled lung contamination. In this
study, the Monte Carlo method was used to study the internal lung contamination
imaging using the MPA-MURA coded-aperture collimator. The imaging system
consisted of an adult male lung model, with a mosaicked, pattern-centered, and
anti-symmetric MURA coded-aperture collimator model and a CsI(Tl) detector
model. The MLEM decoding algorithm was used to reconstruct the internal
contamination image, and the complementary imaging method was used to reduce
the number of artifacts. The full width at half maximum of the I-131 point
source image reconstructed by the mosaicked, pattern-centered, and
anti-symmetric Modified uniformly redundant array (MPA-MURA) coded-aperture
imaging reached 2.51 mm, and the signal-to-noise ratio of the simplified
respiratory tract source (I-131) image reconstructed through MPA-MURA
coded-aperture imaging was 3.98 dB. Although the spatial resolution of MPA-MURA
coded aperture imaging is not as good as that of parallel-hole imaging, the
detection efficiency of PMA-MURA coded-aperture imaging is two orders of
magnitude higher than that of parallel hole collimator imaging. Considering the
low activity level of internal lung contamination caused by nuclear accidents,
PMA-MURA coded-aperture imaging has significant potential for the development
of lung contamination imaging.
