Collimator choice in cardiac SPECT with I-123-labeled tracers.

BACKGROUND: Septal penetration of high-energy photons may degrade the quality of single photon emission computed tomography (SPECT) of the heart with iodine 123-labeled tracers. We investigated the impact of collimator choice on cardiac SPECT with I-123. METHODS AND RESULTS: SPECT of a thoracic phantom containing I-123 solution was performed with a low-energy high-resolution (LEHR) collimator, special LEHR (SLEHR) collimator, and medium-energy (ME) collimator, and the cavity-to-myocardium contrast, wall thickness, and defect contrast were compared among the collimators. For all indices, use of the SLEHR collimator yielded the best results. Comparison between the LEHR and ME collimators revealed that the cavity-to-myocardium contrast and contrast for large defects were better with the ME collimator, whereas wall thickness and contrast for small defects were similar. Scatter correction by the triple-energy window method improved the indices examined; however, the superiority of the SLEHR collimator was still observed after correction. CONCLUSIONS: Collimator choice substantially influences the quality of cardiac SPECT with I-123-labeled agents, and an appropriate collimator needs to be selected in consideration of septal penetration and spatial resolution.

Effect of collimator choice on quantitative assessment of cardiac iodine 123 MIBG uptake.

BACKGROUND: Quantitative accuracy in iodine 123 studies may be impaired by septal penetration. We evaluated the effect of collimator choice on estimation of the heart-to-mediastinum (H/M) ratio in cardiac I-123 metaiodobenzylguanidine (MIBG) imaging. METHODS AND RESULTS: A low-energy high-resolution (LEHR) collimator, special LEHR (SLEHR) collimator, and medium-energy (ME) collimator were used. In experiments in which a phantom of simple geometry was used, the use of the LEHR collimator provided the lowest contrast accuracy, suggesting the effect of septal penetration. Thoracic phantom studies demonstrated contamination of heart and mediastinum counts by lung and liver activities, which was greatest with the LEHR collimator and least with the ME collimator. In 8 patients anterior chest views were acquired successively with the three collimators after I-123 MIBG injection. H/M ratios were significantly higher with the SLEHR collimator than with the LEHR collimator and were still higher with the ME collimator. The difference in H/M ratios between the LEHR and ME collimators showed a high positive correlation with the lung-to-mediastinum ratio. CONCLUSIONS: Collimator choice substantially influences estimation of the H/M ratios in cardiac I-123 MIBG imaging. The use of an ME collimator provides high quantitative accuracy and may enhance reliability in the evaluation of cardiac sympathetic nerve function.