Abstract:
Objective To implement physical corrections in semiquantitative Co-SPECT to improve image resolution and contrast, along with the capability for image semiquantitation. And to evaluate the image performance using 18F-FDG PET/CT as the reference standard.
Methods Full physical corrections included attenuation correction, scatter correction, and spatially dependent point-spread functions. Point sources in a cross shape and a standard National Electrical Manufacturers Association phantom were utilized to verify image resolution and contrast, as well as the accuracy in measuring 18F activity concentration. In the patient study, 13 males and 2 females with histologically confirmed thoracic carcinomas were included. All patients were subjected to 18F-FDG Co-SPECT/CT scan followed by 18F-FDG PET/CT scan. The functional parameters SUVmax, SUVmean, SULpeak and MTV from semiquantitative Co-SPECT and PET were analyzed.
Results In the phantom study, the image resolution of Co-SPECT improved. The mean image resolution improved from (13.1±1.2) mm to (9.5±0.8) mm in the in-plane direction(7.4±0.4)mm for PET and from (13.5±1.1) mm to(9.8±0.7) mm in the axial direction(7.6±0.5) mm for PET, whereas the image contrast improved from 1.79 to 6.32(6.69 for PET). In the patient study, paired t-test showed that the functional parameters of quantitative Co-SPECT(i.e., SUVmax, SUVmean, SULpeak and MTV) significantly differed from those of PET(t=3.16, 3.90, 3.92, 3.98, respectively; all P<0.0025). Conversely, the correlations of SUVmax, SUVmean, SULpeak, and MTV from semiquantitative Co-SPECT were highly correlated overall with those from PET(r=0.8218, 0.8390, 0.8171 and 0.8791, respectively). Measurements remained stable whereas the threshold adjustment of SUVmax and SUV for SUVmean and MTV determination did not further change the correlations with PET(r=0.8103–0.8801).
Conclusion Adding physical corrections to Co-SPECT images can significantly improve image resolution and contrast to reveal smaller tumor lesions, as well as the capability to semiquantify functional parameters such as PET/CT.