Improved image quality of I-123 MIBG with medium energy collimators

Objectives To optimize image quality of ¹²³I MIBG scans by using Medium Energy (ME) Collimators to reduce high-energy photon septal penetration.

Methods In addition to the 159 KeV gamma ray, ¹²³I has a small abundance of energies above 500 KeV that can compromise the image quality of MIBG studies because of septal penetration. Using a low energy ultra high resolution collimator (LEUHR) and ME we obtained and compared SPECT and planar images of the Data Spectrum SPECT phantom filled with ¹²³I. These studies were acquired at a count level comparable to clinical MIBG images, 24K counts per view for SPECT and 300K counts for planar imaging. Also we evaluated the sensitivity of the two collimators at 0 and 10cm using the NEMA protocol.

Results The image quality for both SPECT and planar ¹²³I images using the ME collimators was determined to be substantially better than when using the LEUHR collimators. The septal thickness of ME collimators is much thicker than for the LEUHR collimators (1.14 vs 0.13mm). This significantly reduces the septal penetration of the high energy gamma rays, leading to a marked improvement in image quality. The sensitivity for the ME collimators did not change with distance (323cpm/μCi), as opposed to the LEUHR collimators (226 and 208cpm/μCi for 0 and 10cm, respectively). This variation and sensitivity for the LEUHR is again due to the presence of high energy photons.

Conclusions Use of the ME collimators substantially improves the quality ¹²³I images of both planar and SPECT. We recommend ME collimators routinely be used for ¹²³I MIBG imaging.