Dixon Imaging of Bone stress injury of knee- comparison to conventional Intermediate-weighted MR imaging

Objectives: Dixon sequence is a chemical shift-based MR sequence that produces four sets of images (water only, fat only, in-phase, and out-of-phase) images and is currently being used in various musculoskeletal applications. The aim of this study was to test the sensitivity of detection and determine the extent of the lesion on the Dixon imaging versus conventional proton density weighted (PDW) imaging in the domain of bone stress injury (BSI) and obtain inter-reader performance. Methods: In this retrospective cross-sectional study, 32 consecutive BSI were compared on conventional imaging versus different Dixon images in terms of area of bone marrow edema, inter-trabecular fracture detection and fracture conspicuity. Inter-reader reliability was also evaluated. p<0.05 was considered statistically significant. Results: The Dixon imaging showed excellent quality except two cases with some motion degradation. BSI detection on Dixon water image is equivalent to the routine fat suppressed fluid sensitive intermediate weighted sequence. BSI area on water image is not significantly different from the intertrabecular lesion area on opposed-phase imaging (p=0.9531). The opposed-phase images detected more number of fractures than the water, PDW, & in-phase images (p<0.0001, =0.0008, and <0.0001, respectively) with superior fracture conspicuity than the water, PDW, & in-phase images (p value <0.0001, =0.0085, and =0.0035, respectively). Fair to moderate inter-reader agreement was seen. Conclusions: Dixon imaging is as sensitive as conventional fat suppressed fluid sensitive imaging of the knee for the identification of bone bruise with superior detection and improved characterization of the intertrabecular fractures. Advances in knowledge: In the domain of bone stress injury (BSI), Dixon opposed-phase MR images detect more number of fractures with better conspicuity than water-only, PDW, and in-phase images.

Characterization of Intervertebral Disc Changes in Asymptomatic Individuals with Distinct Physical Activity Histories Using Three Different Quantitative MRI Techniques

(1) Background: Assessments of intervertebral disc (IVD) changes, and IVD tissue adaptations due to physical activity, for example, remains challenging. Newer magnetic resonance imaging techniques can quantify detailed features of the IVD, where T2-mapping and T2-weighted (T2w) and Dixon imaging are potential candidates. Yet, their relative utility has not been examined. The performances of these techniques were investigated to characterize IVD differences in asymptomatic individuals with distinct physical activity histories. (2) Methods: In total, 101 participants (54 women) aged 25–35 years with distinct physical activity histories but without histories of spinal disease were included. T11/12 to L5/S1 IVDs were examined with sagittal T2-mapping, T2w and Dixon imaging. (3) Results: T2-mapping differentiated Pfirrmann grade-1 from all other grades (p < 0.001). Most importantly, T2-mapping was able to characterize IVD differences in individuals with different training histories (p < 0.005). Dixon displayed weak correlations with the Pfirrmann scale, but presented significantly higher water content in the IVDs of the long-distance runners (p < 0.005). (4) Conclusions: Findings suggested that T2-mapping best reflects IVD differences in asymptomatic individuals with distinct physical activity histories changes. Dixon characterized new aspects of IVD, probably associated with IVD hypertrophy. This complementary information may help us to better understand the biological function of the disc.