Performance evaluation of a clinical SPECT system with multifocal collimator for brain studies

Single-photon emission computed tomography (SPECT) is an indispensable examination for evaluating brain function to diagnose dementia. During head examination, the collimator makes contact with the shoulders, which often causes the patient discomfort. A new multifocal high-resolution collimator (SMARTZOOM high resolution and extended [SZHRX]) can maintain image quality, even when there is distance between the patient and the collimator. Therefore, it may be a useful tool to prevent patient discomfort during head imaging.

In this study, we evaluated spatial resolution, sensitivity, uniformity, and %contrast in several basic experiments using different phantoms to clarify the image quality of the multifocal collimator.

We used ^99mTc and ¹²³I nuclides, which were sealed in several phantoms and imaged using SZHRX. The rotation radius for SZHRX was varied from 24-34.5 cm. For comparison, low-energy high-resolution (LEHR) and low-medium energy general purpose (LMEGP) images were acquired with a rotation radius of 14 cm. Spatial resolution, sensitivity, uniformity, and %contrast were calculated from the images obtained using each phantom and collimator.

For both ^99mTc and ¹²³I, the wider the radius of rotation, the larger the full-width half maximum (FWHM) of SZHRX. The FWHM of SZHRX was larger than that of LEHR, and the FWHM of SZHRX was smaller than that of LMEGP. The sensitivity of SZHRX increased as the distance increased, regardless of nuclides. For ^99mTc, SZHRX had higher sensitivity than LEHR. The sensitivity of SZHRX for ¹²³I was lower than that of LMEGP at short distances, with the same sensitivity at a radius of rotation of 26-28 cm. The coefficient of variation (CV) of ^99mTc for SZHRX was lower than that for LEHR, and the further the distance, the lower the CV. For ¹²³I, the CVs of SZHRX and LMEGP were comparable. The %contrast of SZHRX worsened as the rotation radius increased. For ^99mTc, the %contrast of SZHRX was lower than that of LEHR. For ¹²³I, the %contrast of SZHRX and LMEGP were comparable.

It is possible to acquire images with high spatial resolution and uniformity, even if the rotation radius is widened by the use of SZHRX. The image quality of SZHRX obtained in this study will be helpful for future clinical applications.