The expression of prostate-specific membrane antigen (PSMA) is increased in prostate cancer. Recently, 68 Ga-PSMA (Glu-NH-CO-NH-Lys-(Ahx)-[ 68 Ga(HBED-CC)]) was developed as a PSMA ligand. The aim of this study was to investigate the detection rate of 68 Ga-PSMA PET/CT in patients with biochemical recurrence after radical prostatectomy. Methods: Two hundred forty-eight of 393 patients were evaluable for a retrospective analysis. Median prostate-specific antigen (PSA) level was 1.99 ng/mL (range, 0.2-59.4 ng/mL). All patients underwent contrast-enhanced PET/CT after injection of 155 ± 27 MBq of 68 Ga-PSMA ligand. The detection rates were correlated with PSA level and PSA kinetics. The influence of antihormonal treatment, primary Gleason score, and contribution of PET and morphologic imaging to the final diagnosis were assessed. Results: Two hundred twenty-two (89.5%) patients showed pathologic findings in 68 Ga-PSMA ligand PET/CT. The detection rates were 96.8%, 93.0%, 72.7%, and 57.9% for PSA levels of $2, 1 to ,2, 0.5 to ,1, and 0.2 to ,0.5 ng/mL, respectively. Whereas detection rates increased with a higher PSA velocity (81.8%, 82.4%, 92.1%, and 100% in ,1, 1 to ,2, 2 to ,5, and $5 ng/mL/y, respectively), no significant association could be found for PSA doubling time (82.7%, 96.2%, and 90.7% in .6, 4-6, and ,4 mo, respectively). 68 Ga-PSMA ligand PET (as compared with CT) exclusively provided pathologic findings in 81 (32.7%) patients. In 61 (24.6%) patients, it exclusively identified additional involved regions. In higher Gleason score (#7 vs. $8), detection efficacy was significantly increased (P 5 0.0190). No significant difference in detection efficacy was present regarding antiandrogen therapy (P 5 0.0783). Conclusion: Hybrid 68 Ga-PSMA ligand PET/CT shows substantially higher detection rates than reported for other imaging modalities. Most importantly, it reveals a high number of positive findings in the clinically important range of low PSA values (,0.5 ng/mL), which in many cases can substantially influence the further clinical management.

Attenuation correction (AC) of whole-body PET data in combined PET/MRI tomographs is expected to be a technical challenge. In this study, a potential solution based on a segmented attenuation map is proposed and evaluated in clinical PET/CT cases. Methods: Segmentation of the attenuation map into 4 classes (background, lungs, fat, and soft tissue) was hypothesized to be sufficient for AC purposes. The segmentation was applied to CT-based attenuation maps from 18 F-FDG PET/CT oncologic examinations of 35 patients with 52 18 F-FDG-avid lesions in the lungs (n 5 15), bones (n 5 21), and neck (n 5 16). The standardized uptake values (SUVs) of the lesions were determined from PET images reconstructed with nonsegmented and segmented attenuation maps, and an experienced observer interpreted both PET images with no knowledge of the attenuation map status. The feasibility of the method was also evaluated with 2 patients who underwent both PET/CT and MRI. Results: The use of a segmented attenuation map resulted in average SUV changes of 8% 6 3% (mean 6 SD) for bone lesions, 4% 6 2% for neck lesions, and 2% 6 3% for lung lesions. The largest SUV change was 13.1%, for a lesion in the pelvic bone. There were no differences in the clinical interpretations made by the experienced observer with both types of attenuation maps. Conclusion: A segmented attenuation map with 4 classes derived from CT data had only a small effect on the SUVs of 18 F-FDGavid lesions and did not change the interpretation for any patient. This approach appears to be practical and valid for MRI-based AC.Key Words: instrumentation; PET/CT; PET/MRI; attenuation correction J Nucl Med 2009; 50:520-526 DOI: 10.2967/jnumed.108.054726 Int he same way in which PET/CT has been shown to be a powerful multimodality imaging tool, there are compelling reasons for combining PET and MRI. PET/MRI would have the following advantages: improved soft-tissue contrast; the possibility of performing truly simultaneous instead of sequential acquisitions; and the availability of sophisticated MRI sequences, such as diffusion and perfusion imaging, functional MRI, and MR spectroscopy, which can add important information. Moreover, the use of PET/MRI would result in a significant decrease in radiation exposure, which is of foremost importance for serial follow-up and pediatric imaging.Thus, a combined PET/MRI scanner would provide an alternative to a combined PET/CT scanner for whole-body oncologic imaging (1,2); improved accuracy could be achieved in the detection, staging, and characterization of several cancers (3-10). Moreover, the combination of PETand MRI is perfectly suited to neurologic imaging and offers new possibilities for cardiovascular imaging (11,12). Consequently, much research effort is being directed toward the development of combined imaging devices, and the initial results are promising (13-18).However, a still-unsolved technical challenge for combined whole-body PET/MRI is the correction of attenuation and scatter in the PET data (19). For this purpose, an...

In patients with intermediate to high risk prostate cancer preoperative lymph node staging with (68)Ga-PSMA-PET proved to be superior to standard routine imaging. Thus it has the potential to replace current standard imaging for this indication if confirmed by prospective studies.