Axial Spondyloarthritis: Dual-Energy Virtual Noncalcium CT in the Detection of Bone Marrow Edema in the Sacroiliac Joints.

Purpose To determine the diagnostic performance of dual-energy virtual noncalcium (VNCa) CT in the detection of bone marrow edema in study participants with sacroiliitis associated with axial spondyloarthritis. Materials and Methods In this prospective study, 47 consecutive participants (mean age, 27 years; age range, 14-41 years [28 male; mean age, 24 years; age range, 14-37 years] [19 female; mean age, 29 years; age range, 17-41 years]) underwent dual-energy CT and 3.0-T MRI between April 2016 and December 2017. Two independent readers visually evaluated all sacroiliac joints for the presence of abnormal marrow attenuation on dual-energy VNCa images using a four-point classification system (0, no edema; 1, mild edema; 2, moderate edema; 3, severe edema). CT numbers on VNCa images were determined with region-of-interest-based quantitative analysis. MRI was the reference standard for presence of bone marrow edema. Results Sensitivity, specificity, and accuracy of readers 1 and 2, respectively, in the identification of bone edema at CT were 87% and 93% (48 and 51 of 55), 94% and 91% (32 and 31 of 34), and 90% and 92% (80 and 82 of 89). Interobserver agreement was excellent (κ = 0.81). CT numbers from VNCa images increased from no edema to severe edema (P < .001). The area under the receiver operating characteristic curve was 0.93 for reader 1 and 0.91 for reader 2 in differentiation of the presence of bone marrow edema from no edema. A cutoff value of -33 HU derived from reader 1 yielded overall sensitivity, specificity, and accuracy of 90% (49 of 55), 83% (28 of 34), and 87% (77 of 89) in the detection of any extent of edema in the sacroiliac joints. Conclusion Dual-energy VNCa CT images had excellent diagnostic performance in evaluation of the extent of bone marrow edema in study participants with sacroiliitis associated with axial spondyloarthritis. © RSNA, 2018 See also the editorial by Guggenberger in this issue.

Effects of contrast agent on water suppression and shimming of kidney single-volume proton MR spectroscopy at 3.0T.

RATIONALE AND OBJECTIVES: The aim of this study was to determine whether the administration of gadolinium diethylenetriamine penta-acetic acid (Gd-DTPA) significantly affects shimming and water suppression on kidney magnetic resonance spectroscopic prescanning and whether the impact of shimming and water suppression is changed with time after intravenous administration on a 3.0-T system. METHODS: Forty patients (two patients were excluded from analysis because of motion) were examined before and after the administration of Gd-DTPA (the interval between the right and left kidneys was approximately 40 seconds). Regions of interest were carefully positioned in the region of the corresponding location of both kidneys separately. Line widths (full width at half maximum) and water suppression were obtained. A paired t test for comparison of means was used. In addition, repeat measurements with a shorter time interval (obtained 120-130 seconds after the injection) and a longer time interval (obtained 150-160 seconds after the injection) were performed in five patients in the same regions of interest of the right kidney. Sequential ¹H magnetic resonance spectroscopic prescanning in the same region of interest was performed in one patient. RESULTS: The left kidney had slightly better shimming and water suppression effects than the right kidney after contrast agent administration (all P values < .01). The limiting resolution of both shimming and water suppression effects was decreased on enhanced images in both kidneys (all P values < .01). The longer time interval group had better shimming and water suppression effects than the shorter time interval group (all P values < .01). After the administration of Gd-DTPA in one patient, sequential values of shimming and water suppression in the right and left kidneys, respectively, were 13 Hz and 97% and 12 Hz and 97% prior to the examination, 34 Hz and 86% and 30 Hz and 88% at 5 minutes, 32 Hz and 89% and 27 Hz and 90% at 10 minutes, 28 Hz and 91% and 24 Hz and 91% at 15 minutes, and 24 Hz and 92% and 20 Hz and 92% at 25 minutes. CONCLUSIONS: Gd-DTPA exerts adverse effects on water suppression and shimming, both of which show a trend of becoming well gradually with time extension after the injection of Gd-DTPA. This phenomenon limits the diagnostic use of kidney magnetic resonance spectroscopy performed immediately after contrast-enhanced magnetic resonance imaging.

Grading of rabbit skeletal muscle trauma by diffusion tensor imaging and tractography on magnetic resonance imaging.

OBJECTIVE: To distinguish the edema, injury, or rupture in the traumatic skeletal muscle fiber in vivo using diffusion tensor imaging (DTI) and tractography on magnetic resonance imaging (MRI). METHODS: The skeletal muscle trauma models were made in 4 rabbits (eight hindlimbs) by iron discus (weight 1.0 kg, diameter 6 cm) falling down vertically from 45 cm height to rabbits' thighs. Conventional sequences and two-dimensional (2D) diffusion-weighted (DW) spin-echo (SE) echo planar imaging (EPI) sequence with fat suppression (b = 600 s/mm2) were performed on 1. 5T MRI scanner. The grading of edema, injury, and fiber rupture in the damaged muscle were made according to their histopathological views, which was consistent with the images. The mean apparent diffusion coefficient (ADC) values and fractional anisotropy (FA) values were measured from the region of interests (ROIs) of all groups on 2D DW images used for tractography. Analysis of variance test was performed to analyze all data. RESULTS: ADC values of the areas in normal muscle, edema muscle, injury muscle, and ruptured muscle were (6.12 +/- 1.34) x 10(-3), (6.38 +/- 1.30) x 10(-3), (8.06 +/- 0.97) x 10(-3), and (9.57 +/- 0.93) x 10(-3) mm2/s, respectively. There was significant difference among groups (P < 0.001), but no difference between edema muscle and normal muscle group (P > 0.05). The FA values of normal muscle, edema muscle, injury muscle, and ruptured muscle were 0.42 +/- 0.12, 0.36 +/- 0.12, 0.26 +/- 0.09, 0.12 +/- 0.08, respectively, with a significant difference among groups (P < 0.001). In the edema muscle, the tracking cross-fiber could be seen but it decreased slightly. In the injury muscle, the tracking fiber decreased markedly. In the ruptured muscle, the transverse-orientation tracking fiber vanished, yet some interrupted longitudinal-orientation tracking fiber could be found. CONCLUSION: The edema, injury, and rupture of muscle fiber in rabbit damaged skeletal muscle can be verified according to the ADC and the FA on DTI and tractography.