Background [18F]-Fluorodeoxyglucose (FDG) positron emission tomography–computed tomography (PET/CT) may sometimes be suboptimal for imaging gastric adenocarcinoma. The recently introduced [68Ga]Ga-FAPI-04 (FAPI) PET/CT targets tumor stroma and has shown considerable potential in evaluating the extent of disease in a variety of tumors. Methods We performed a head-to-head prospective comparison of FAPI and FDG PET/CT in the same group of 13 patients with gastric adenocarcinoma who presented for either initial staging (n = 10) or restaging (n = 3) of disease. Lesion detection and maximum standardized uptake value (SUVmax) were compared between the two types of radiotracers. Results All ten primary gastric tumors were FAPI-positive (100% detection rate), whereas only five were also FDG-positive (50%). SUVmax was not significantly different, but the tumor-to-background ratio was higher for FAPI (mean, median, and range of 4.5, 3.2, and 0.8–9.7 for FDG and 12.9, 11.9, and 2.2–23.9 for FAPI, P = 0.007). The level of detection of regional lymph node involvement was comparable. FAPI showed a superior detection rate for peritoneal carcinomatosis (100% vs. none). Two patients with widespread peritoneal carcinomatosis underwent a follow-up FAPI scan after chemotherapy: one showed partial remission and the other showed progressive disease. Conclusions The findings of this pilot study suggest that FAPI PET/CT outperforms FDG PET/CT in detecting both primary gastric adenocarcinoma and peritoneal carcinomatosis from gastric cancer. FAPI PET/CT also shows promise for monitoring response to treatment in patients with peritoneal carcinomatosis from gastric cancer; however, larger trials are needed to validate these preliminary findings.

PET/CT is an accurate technique in the detection of pelvic recurrence after surgical removal of rectal cancer.

Ga-Prostate Specific Membrane Antigen (Ga-PSMA), a positron emission tomography (PET) tracer that was recently introduce for imaging of prostate cancer, may accumulate in other solid tumors including Hepatocellular Carcinoma (HCC). The aim of the study was to assess the potential role of Ga-PSMA PET-Computed Tomography (CT) for imaging of HCC. A prospective pilot study in seven patients with HCC with 41 liver lesions: 37 suspected malignant lesions (tumor lesions) and 4 regenerative nodules. For each liver lesion, uptake of Ga-PSMA andF-FDG uptake were measured [standard uptake value (SUV) and lesion-to-liver background ratios (TBR-SUV)], and correlated with dynamic characteristics (HU and TBR-HU) obtained on contrast enhanced CT data. Immunohistochemistry staining of PSMA in the tumor tissue was analyzed in samples obtained from 5 patients with HCC and compared to control samples from 3 patients with prostate cancer. Thirty-six of the 37 tumor lesions and none of the regenerative nodules showed increasedGa-PSMA uptake while only 10 lesions were F-FDG avid. Based on contrast enhancement, tumor lesions were categorized into 27 homogeneously enhancing lesions, nine lesions with "mosaic" enhancement composed of enhancing and non-enhancing regions in the same lesion and a single non-enhancing lesion, the latter being the only non-Ga-PSMA avid lesion. Using the Mann-Whitney test, Ga-PSMA uptake was found significantly higher in enhancing tumor areas compared to non-enhancing areas and in contrast,F-FDG uptake was higher in non-enhancing areas, P<0.001 for both. Ga-PSMA uptake (TBR SUV) was found to correlate with vascularity (TBR-HU) (Spearman r=0.866, p<0.001). Immunohistochemistry showed intense intra-tumoral microvessel staining for PSMA in HCC, in contrast with cytoplasmic and membranous staining, mainly in the luminal border, in prostate cancer samples. In two of the study patients Ga-PSMA PET-CT identified unexpected extrahepatic metastases. Four regenerative liver nodules showed no increased uptake of either of the PET tracers.Ga-PSMA PET-CT is superior to F-FDG PET-CT in imaging patients with HCC. HCC lesions are more commonly hypervascular taking upGa-PSMA in tumoral micro-vessels. Ga-PSMA PET-CT is a potential novel modality for imaging patients with HCC.

To evaluate the presence of (a) a focus of high signal intensity in the center of an osseous lesion (bull's-eye) as a negative discriminator for metastasis and (b) a rim of high signal intensity around an osseous lesion (halo) as a positive discriminator, a retrospective study was performed in 47 patients with osseous lesions suspect for metastatic disease who underwent magnetic resonance (MR) imaging of the pelvis. The findings in 17 patients with proved osseous metastasis were compared with those in 30 patients not believed to have metastatic disease; T1- and T2-weighted MR images were evaluated. The bull's-eye sign was found to be a specific indicator of normal hematopoietic marrow (sensitivity, 95%; specificity, 99.5%). The halo sign and diffuse signal hyperintensity were a strong indicator of metastatic disease (sensitivity, 75%; specificity, 99.5%). These results suggest that use of the bull's-eye sign as a discriminator of benign disease and use of the halo sign as a discriminator of metastasis help characterize suspect areas of marrow lesions.

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