Quantitative assessment of atherosclerotic plaques on (18)F-FDG PET/MRI: comparison with a PET/CT hybrid system.

PURPOSE: PET with (18)F-FDG has the potential to assess vascular macrophage metabolism. (18)F-FDG is most often used in combination with contrast-enhanced CT to localize increased metabolism to specific arterial lesions. Novel (18)F-FDG PET/MRI hybrid imaging shows high potential for the combined evaluation of atherosclerotic plaques, due to the superior morphological conspicuity of plaque lesions. The purpose of this study was to evaluate the reliability and accuracy of (18)F-FDG PET/MRI uptake quantification compared to PET/CT as a reference standard in patients with carotid atherosclerotic plaques. METHODS: The study group comprised 34 consecutive oncological patients with carotid plaques who underwent both PET/CT and PET/MRI with (18)F-FDG on the same day. The presence of atherosclerotic plaques was confirmed by 3 T MRI scans. Maximum standardized uptake values (SUVmax) for carotid plaque lesions and the average SUV of the blood pool within the adjacent internal jugular vein were determined and target-to-blood ratios (TBRs, plaque to blood pool) were calculated. RESULTS: Atherosclerotic lesions with maximum colocalized focal FDG uptake were assessed in each patient. SUVmax values of carotid plaque lesions were significantly lower on PET/MRI than on PET/CT (2.3 ± 0.6 vs. 3.1 ± 0.6; P < 0.01), but were significantly correlated between PET/CT and PET/MRI (Spearman's r = 0.67, P < 0.01). In contrast, TBRmax values of plaque lesions were similar on PET/MRI and on PET/CT (2.2 ± 0.3 vs. 2.2 ± 0.3; P = 0.4), and again were significantly correlated between PET/MRI and PET/CT (Spearman's r = 0.73, P < 0.01). Considering the increasing trend in SUVmax and TBRmax values from early to delayed imaging time-points on PET/CT and PET/MRI, respectively, with continuous clearance of radioactivity from the blood, a slight underestimation of TBRmax values may also be expected with PET/MRI compared with PET/CT. CONCLUSION: SUVmax and TBRmax values are widely accepted reference parameters for estimation of the radioactivity of atherosclerotic plaques on PET/CT. However, due to a systematic underestimation of SUVmax and TBRmax with PET/MRI, the optimal cut-off values indicating the presence of inflamed plaque tissue need to be newly defined for PET/MRI.

Real-time sonoelastography of salivary glands for diagnosis and functional assessment of primary Sjögren's syndrome.

The purpose of this study was to investigate the value of real-time sonoelastography (RTS) of salivary glands for the diagnosis and assessment of glandular damage in primary Sjögren's syndrome (pSS). After institutional review board approval, 45 pSS patients, 24 sicca patients and 11 healthy controls were investigated prospectively. Questionnaires were completed and Saxon and Schirmer tests and routine blood tests carried out in all patients. All patients underwent B-mode ultrasonography and RTS of parotid and submandibular glands. Abnormal findings were graded from 0 to 48 and from 0 to 16, respectively. Sialoscintigraphy was done according to a routine protocol; scoring ranged from 0 to 12. Statistical analysis comprised receiver operating characteristic curve and multivariate regression analysis. Patients with pSS had higher B-mode (median score = 25 [range: 2-44] vs. 9 [1-20], p < 0.001) and RTS (6.5 [2-13] versus 4 [1-9], p < 0.001) scores than controls with sicca syndrome, yielding areas under the curve of 0.83 and 0.85 (p < 0.05 each), respectively for pSS diagnosis. In cases with an inconclusive B-mode ultrasonography result, RTS (cutoff score: ≥ 6) led to a sensitive (66.7%) and specific (85.7%) classification of patients and sicca controls. In multivariate regression analysis, RTS (regression coefficient = -0.48, p = 0.005), but not B-mode ultrasonography, reflected impaired salivary gland function according to the Saxon test, whereas none of the subjective measures of dryness or discomfort were related to ultrasonography results. B-mode and RTS results were both associated with sialoscintigraphy scores (regression coefficient = 0.66, p < 0.001, and regression coefficient = 0.55, p = 0.001, respectively). Reproducibility of B-mode ultrasonography and RTS was good, with intra-class correlation coefficients of 0.93 (95% confidence interval: 0.57-0.98) and 0.93 (95% confidence interval: 0.79-0.98), respectively. In summary, RTS might be a useful adjunct to B-mode ultrasonography for diagnosis and assessment of salivary gland impairment in primary Sjögren's syndrome.