To compare the effect of different β values on the semi-quantitative accuracy and image quality of ⁶⁸Ga-prostate specific membrane antigen (PSMA) PET/CT imaging after partial volume effect correction (PVC).

In the model experiment, image reconstruction was carried out based on block sequential regularized expectation maximization algorithm (BSREMA) with the range of β values from 100 to 1 000. Recovery coefficient (RC), contrast recovery (CR) and background variability (BV) were measured to evaluate semi-quantitative accuracy and image quality. In the clinical study, image data of 21 prostate cancer patients (age 45-78 years) who underwent ⁶⁸Ga-PSMA PET/CT examination in the First Hospital of Shanxi Medical University from March 2019 to February 2020 were retrospectively collected. A total of 29 abdominal imaging positive lymph nodes were divided into the small lymph node group (diameter <10 mm; n=12) and the large lymph node group (10 mm≤diameter≤30 mm; n=17). SUV parameters including SUV_max, SUV_mean and peak of SUV (SUV_peak) and the influence of different β values on the SUV parameters were evaluated. The signal to noise ratio (SNR) and subjective scores were used to evaluate image quality. Independent-sample t test, Kappa test and Pearson correlation analysis were used to analyze data.

The model experiment showed that CR, RC and BV decreased with the increase of β values. The image quality, image clarity, lesion significance, and total image scores given by nuclear medicine physicians showed strong consistency (Kappa values: 0.65-0.87, P values: 0.026-0.043). The small lymph node group had the highest score (13 and 14) with β value of 600, while the large lymph node group had the highest score (13 and 14) with β value of 700. SNR of the two groups increased steadily within β values from 100 to 600 (t values: 2.49-8.99, P values: 0.023-0.038). When the β value was higher than 600, SNR of the small lymph node group reached a plateau (t values: 1.28-2.00, P values: 0.072-0.098), while the SNR of the large lymph node group continued to increase (t values: 2.98-4.63, P values: 0.012-0.029). Before PVC, there were significant negative correlations between SUV parameters and β values (r values: from -0.94 to -0.64, P values: 0.039-0.046). After PVC, it was found that SUV_mean and SUV_max still had significant negative correlation with β values (r values: from -0.78 to -0.68, P values: 0.035-0.042), while the SUV_peak showed no significant correlation with β values (r values: -0.22, -0.28, P values: 0.069, 0.126).

Based on subjective scores and semi-quantitative indicators, ⁶⁸Ga-PSMA PET/CT is superior to select β values of 600 and 700 for image reconstruction based on BSREMA. The SUV_peak of small lesions is stable after PVC and the clinical value should be explored in further.

Prostatic neoplasms; Prostate-specific membrane antigen; Isotope labeling; Gallium radioisotopes; Positron-emission tomography; Tomography, X-ray computed; Image processing, computer-assisted