Improving image quality for I-123 whole body images using medium-energy vs. low-energy collimators

Objectives Several studies have shown improvement in I-123 image quality utilizing a medium-energy collimator as opposed to the traditional low-energy collimator in phantom studies performed several weeks apart. We wanted to put the theory to clinical practice by comparing the two collimators using actual patient scans collected back-to-back in order to reduce as many variants as possible.

Methods Previously published research has shown that the small amount of photons with energies above 400 keV present in I-123 is just enough to degrade image quality due to septal penetration. Upon obtaining patient permission, two (2) twenty-four hour delayed I-123 whole body images were acquired on two patients using exactly the same parameters except for the collimator being exchanged out. The first scan utilized a low-energy high resolution (LEHR) collimator as per department protocol. The repeat scan followed immediately after changing to a medium-energy general purpose (MEGP) collimator. The whole body images were displayed side by side and presented to our radiologists and technologists in a blinded fashion for image quality evaluation.

Results All of our radiologists and technologists found the images acquired with the MEGP collimator to be of a much better quality, demonstrating improved contrast and resolution over those acquired with the LEHR collimator. This was achieved without altering any other parameters in our current protocol for I-123 whole body imaging.

Conclusions Using a MEGP collimator greatly improves the image quality of the whole body scan. As a result of this comparison, the protocol for imaging I-123 radiopharmaceuticals has been modified to utilize the MEGP collimator instead of the LEHR