Purpose
To prospectively compare the ability of F-18-PSMA-1007 PET/CT and whole-body MRI (WBMRI) with DWI to detect prostate cancer (PCa) lesions and assess their local stage. Additionally, to evaluate the correlation between PSMA uptake on PET/CT and PSMA expression as assessed by immunohistochemistry.

Methods
Men with newly diagnosed unfavourable intermediate or high-risk PCa underwent F-18-PSMA-1007 PET/CT and WBMRI with DWI before robot-assisted laparoscopic prostatectomy. Diagnostic accuracy for intraprostatic tumour localization, seminal vesicle invasion (SVI), and extraprostatic extension (EPE) was evaluated using whole-mount prostatectomy specimens as the reference standard. SUVmax was compared with immunohistochemical PSMA staining intensity quantified using QuPath software.

Results
19 patients with 39 intraprostatic lesions in histopathology were included. The overall lesion detection rates for PET/CT were 84.6% and 82.1% for two independent readers, compared to 74.4% and 46.2% for MRI readers. The detection rates of index lesions were 94.7% for PET/CT and 74.0-84.0% for MRI, whereas those of non-index lesions were 70.0-75.0% for PET/CT and 20.0-65.0% for MRI. For detecting EPE, AUC values were 0.500-0.591 for PET/CT and 0.648-0.682 for MRI. For detecting SVI, AUC values ranged from 0.629 to 0.700 across both modalities. SUVmax showed a weak correlation with immunohistochemical expression of PSMA multiplied by lesion diameter (Spearman's rho = 0.427, p = 0.013). Lesion diameters measured using 30% and 40% of SUVmax, as well as prostate SUVbackground x2, showed the closest agreement with histopathological measurements.

Conclusion
F-18-PSMA-1007 PET/CT demonstrated high sensitivity in localizing intraprostatic carcinoma lesions but seemed inferior to WBMRI in detecting EPE. PSMA uptake appears to depend on both PSMA expression and lesion size. These findings highlight the complementary roles of PET/CT and MRI in the detection and tumor staging of PCa.