"Low Dose MR" Dixon Technique for Imaging FDG PET-MR Lymphoma.

Introduction Hybrid PET-MR is a relatively new imaging modality with its major strength being the MR component offering superior soft tissue contrast. While PET/MRI offers the inherent advantage of reduced radiation dose, it has been shown to result in a markedly prolonged examination time becoming a challenge in children and sick patients. "Low dose MRI" is a term used in the nuclear medicine community to describe fast acquired PET-MR scan protocols that rely heavily on PET images for diagnosis. In this study, we sought to determine if the Dixon sequences obtained for attenuation correction could be used as a diagnostic sequence for interpreting PET-MRI lymphoma cases, potentially reducing scan time. Materials and Methods We retrospectively identified 40 patients who underwent 88 FDG PET-MR body imaging studies for staging or restaging lymphoma. A radiologist and nuclear medicine physician initially reviewed top of the head to mid thigh PET images, attenuation correction coronal Dixon MRI sequences, and PET-MR fusion with Dixon sequence. The same physicians reviewed the PET images, multi-sequence MR including the attenuation correction Dixon, and multi-sequence PET-MR fusion images The lesions were further characterized based on their imaging characteristics, size, SUVmax, and malignant potency. A consensus read followed. Results All patients were adults with an average study age of 43.8 years. Our study consisted of 40 females and 48 males out of which 7 were for staging and 81 were for re-staging. All patients had systemic lymphoma. Thirty-seven of the studies had active lymph nodes on Dixon PET-MR that agreed with multi-sequence PET-MR which identified 33 positive cases (89.1%) having an average SUV 10.2 ± 7.74 SD. Four Dixon PET-MR cases did not detect lesions, with an average SUV 2.3 ± 0.55 SD, which was read as minimal residual activity. Multi-sequence MR identified 11 patients with enlarged lymph nodes without FDG uptake, which were not seen on Dixon MR. All 5 studies with bones lesions were detected by Dixon PET-MR as well as 2 soft tissue organ lesions. Multi-sequence MR identified 1 patient with non-active, healed bone lesion. Fifty-five of these studies were true negatives. Compared to multi-sequence PET-MR, Dixon PET-MR demonstrated 89.2% sensitivity, 100% specificity with no false positive studies. Conclusion The present study investigated the diagnostic potential of a fast protocol for integrated PET/MRI used for dedicated tumor staging of patients with lymphoma. In this retrospective study, Dixon PET-MR was shown to be sensitive and specific compared to multi-sequence PET-MR in the detection of lymphoma. The low number of these cases not detected had minimally active lymph nodes that resolved on subsequent imaging and probably were not clinically important.

Frequency and distribution of incidental findings deemed appropriate for S modifier designation on low-dose CT in a lung cancer screening program.

PURPOSE: To describe the frequency, distribution and reporting patterns of incidental findings receiving the Lung-RADS S modifier on low-dose chest computed tomography (CT) among lung cancer screening participants. METHODS: This retrospective investigation included 581 individuals who received baseline low-dose chest CT for lung cancer screening between October 2013 and June 2017 at a single center. Incidental findings resulting in assignment of Lung-RADS S modifier were recorded as were incidental abnormalities detailed within the body of the radiology report only. A subset of 60 randomly selected CTs was reviewed by a second (blinded) radiologist to evaluate inter-rater variability of Lung-RADS reporting. RESULTS: A total of 261 (45%) participants received the Lung-RADS S modifier on baseline CT with 369 incidental findings indicated as potentially clinically significant. Coronary artery calcification was most commonly reported, accounting for 182 of the 369 (49%) findings. An additional 141 incidentalomas of the same types as these 369 findings were described in reports but were not labelled with the S modifier. Therefore, as high as 69% (402 of 581) of participants could have received the S modifier if reporting was uniform. Inter-radiologist concordance of S modifier reporting in a subset of 60 participants was poor (42% agreement, kappa = 0.2). CONCLUSIONS: Incidental findings are commonly identified on chest CT for lung cancer screening, yet reporting of the S modifier within Lung-RADS is inconsistent. Specific guidelines are necessary to better define potentially clinically significant abnormalities and to improve reporting uniformity.