Evaluation of the prostate cancer and its metastases in the [68Ga]Ga-PSMA PET/CT images: deep learning method vs. conventional PET/CT processing.

PURPOSE: This study demonstrates the feasibility and benefits of using a deep learning-based approach for attenuation correction in [68Ga]Ga-PSMA PET scans. METHODS: A dataset of 700 prostate cancer patients (mean age: 67.6 ± 5.9 years, range: 45-85 years) who underwent [68Ga]Ga-PSMA PET/computed tomography was collected. A deep learning model was trained to perform attenuation correction on these images. Quantitative accuracy was assessed using clinical data from 92 patients, comparing the deep learning-based attenuation correction (DLAC) to computed tomography-based PET attenuation correction (PET-CTAC) using mean error, mean absolute error, and root mean square error based on standard uptake value. Clinical evaluation was conducted by three specialists who performed a blinded assessment of lesion detectability and overall image quality in a subset of 50 subjects, comparing DLAC and PET-CTAC images. RESULTS: The DLAC model yielded mean error, mean absolute error, and root mean square error values of -0.007 ± 0.032, 0.08 ± 0.033, and 0.252 ± 125 standard uptake value, respectively. Regarding lesion detection and image quality, DLAC showed superior performance in 16 of the 50 cases, while in 56% of the cases, the images generated by DLAC and PET-CTAC were found to have closely comparable quality and lesion detectability. CONCLUSION: This study highlights significant improvements in image quality and lesion detection capabilities through the integration of DLAC in [68Ga]Ga-PSMA PET imaging. This innovative approach not only addresses challenges such as bladder radioactivity but also represents a promising method to minimize patient radiation exposure by integrating low-dose computed tomography and DLAC, ultimately improving diagnostic accuracy and patient outcomes.

A crying liver: a scan pattern mimicking spontaneous perforation of the biliary ducts.

A 2-month-old infant was referred for hepatobiliary scintigraphy due to ascites of unknown cause. The top differential diagnosis was spontaneous perforation of the biliary ducts. Delayed images up to 4 hours were against this diagnosis showing normal distribution of the radiotracer throughout the bowel. However, on delayed images, the scan showed mild tracer retention in the ascites confirmed by SPECT/CT images. Surprisingly, the exploratory abdominal surgery revealed an intact hepatobiliary system, pointing toward other possible etiologies. Second-review surgery was performed due to uncontrolled progressive ascites showing congestive hepatopathy and biliary leak from the hepatic surface suggestive of the "crying liver".

Unusual presentation of lumbar chordoma on bone scintigraphy in a young patient.

Chordoma is a rare bone cancer which arises from undifferentiated notochordal remnants in the axial skeleton. It generally has slow-growing and locally aggressive behavior. This tumor is usually diagnosed by CT and MRI modalities and the role of SPECT/CT is still debated. It shows reduced or normal uptake of radioisotope on bone scanning and increased tracer uptake is infrequently reported. Here we present a 33-year-old man with complaint of low back pain and numbness of his right leg. The whole body bone scan showed relatively uniform radiotracer activity throughout the skeleton. A focal increased uptake in the second lumbar vertebra was noted on SPECT/CT images. SPECT/CT also demonstrated multiple lytic lesions in lumbar vertebrae. The lesions were proven to be chordoma on biopsy. Lumbar chordoma could be one of the differential diagnoses for lytic lesions of the vertebrae which show absent or minimal tracer uptake on bone scintigraphy and SPECT/CT imaging. Our case was unusual as the patient was very young for chordoma diagnosis and bone scan showed increased uptake adjacent to the involved vertebral lesion detected by SPECT/CT.