Improved image resolution on thoracic carcinomas by quantitative ¹⁸F-FDG coincidence SPECT/CT in comparison to ¹⁸F-FDG PET/CT

Currently, ¹⁸F-FDG coincidence SPECT (Co-SPECT)/CT scan still serves as an important tool for diagnosis, staging, and evaluation of cancer treatment in developing countries. We implemented full physical corrections (FPC) to Co-SPECT (quantitative Co-SPECT) to improve the image resolution and contrast along with the capability for image quantitation. FPC included attenuation, scatter, resolution recovery, and noise reduction. A standard NEMA phantom filled with 10:1 F-18 activity concentration ratio in spheres and background was utilized to evaluate image performance. Subsequently, 15 patients with histologically confirmed thoracic carcinomas were included to undergo a ¹⁸F-FDG Co-SPECT/CT scan followed by a ¹⁸F-FDG PET/CT scan. Functional parameters as SUVmax, SUVmean, SULpeak, and MTV from both quantitative Co-SPECT and PET were analyzed. Image resolution of Co-SPECT for NEMA phantom was improved to reveal the smallest sphere from a diameter of 28 mm to 22 mm (17 mm for PET). The image contrast was enhanced from 1.7 to 6.32 (6.69 for PET) with slightly degraded uniformity in background (3.1% vs. 6.7%) (5.6% for PET). Patients' SUVmax, SUVmean, SULpeak, and MTV measured from quantitative Co-SPECT were overall highly correlated with those from PET (r=0.82–0.88). Adjustment of the threshold of SUVmax and SUV to determine SUVmean and MTV did not further change the correlations with PET (r=0.81–0.88). Adding full physical corrections to Co-SPECT images can significantly improve image resolution and contrast to reveal smaller tumor lesions along with the capability to quantify functional parameters like PET/CT.