18F-FDG PET-MRI with T1 MOLLI mapping to detect systemic sclerosis bowel inflammation and fibrosis

Abstract

BackgroundSystemic sclerosis-associated gastrointestinal tract involvement (SSc-GIT) is an independent predictor of 2-year mortality in early SSc. Availability of non-invasive investigations will facilitate early diagnosis and monitoring. HypothesisWe investigate the role of 18F-FDG-PET-MRI in SSc-GIT, hypothesizing that i) higher bowel FDG-PET uptake, a surrogate biomarker for inflammation, distinguishes healthy bowel from inflamed SSc-GIT; ii) MRI T1-MOLLI mapping, a surrogate biomarker for cardiac fibrosis, distinguishes healthy bowel from fibrotic SSc-GIT. MethodsIn this prospective study, 16 SSc patients and 15 healthy controls were recruited. All SSc patients and 5 controls underwent PET-MRI (with T1-MOLLI mapping) on a Siemens 3T mMR; 10 controls underwent MRI without PET. Manual segmentation of the large and small bowels was performed jointly by two trained analysts in order to report T1 and PET values. Control dataset was used to assess normal healthy range. Mean T1 values, mean Tissue-to-Background (TBR) PET values, as well as amount of supposedly abnormal bowel (measured using the healthy ranges) was compared using Student’s t-test and Cohen’s d effect size. ResultsMean T1 values in large (1113 ± 182 ms vs 856 ± 176 ms; p-value < 0.001) and small bowel (1331 ± 239 ms vs 1169 ± 118 ms; p = 0.02) were higher in SSc patients than controls. 87.5% of the SSc patients’ bowel had at least a grade 3 segmental FDG-PET uptake, while no controls showed more than a grade 2 segmental uptake. Patients had higher large bowel mean PET TBR (1.12 ± 0.22) than controls (0.82 ± 0.20, p = 0.02). Using PET and T1 thresholds defined using the control PET-MR data, the percentage of supposedly healthy (non-fibrotic and non-inflamed) tissue was significantly lower in SSc patients (81.1 ± 13.1%) than controls (95.7 ± 3.1%, p = 0.03) for the large bowel. ConclusionOur novel study of FDG-PET-MRI in SSc-GIT demonstrated promising results in non-invasively evaluating concurrently bowel inflammation and fibrosis.