Comparison between enhanced susceptibility-weighted angiography and time of flight sequences in the detection of arterial occlusion in acute ischemic stroke.

PURPOSE: Optimizing the MRI protocol in acute ischemic stroke remains a challenging issue. In this field, susceptibility-weighted sequences have proved their superiority over T2*. Besides the strengthened susceptibility effect, enhanced susceptibility-weighted angiography (eSWAN) sequence provides also a time-of-flight (TOF) effect, allowing the exploration of the intracranial arterial circulation. The objective of our study was to compare eSWAN and 3D TOF, considered as the reference, in the detection of arterial occlusion in acute stroke. METHODS: Patients who underwent MRI between March and July 2014 for suspected acute stroke with an acute ischemic lesion on diffusion-weighted imaging (DWI) were prospectively included in this study. eSWAN and TOF images were analyzed under double-blind conditions by a junior radiologist and a senior neuroradiologist for the detection of arterial occlusion. eSWAN images were assessed in order to estimate the inter-observer agreement. After a consensus, eSWAN and TOF data were compared to calculate inter-modality agreement. RESULTS: Thirty-four patients were included. Inter-observer agreement was excellent (kappa: 0.96) for eSWAN detection of occlusion. After consensus, comparison between TOF and eSWAN showed substantial agreement (kappa: 0.71). eSWAN provided better detection of distal occlusions, but poorer performance for detection of siphon occlusions. CONCLUSIONS: Shortest echoes eSWAN images enabled detection of arterial occlusion with substantial agreement with TOF images. The susceptibility vessel sign associated with the TOF effect improved the identification of distal occlusions. In acute stroke protocol, eSWAN may represent a valuable alternative to T2* and TOF sequences.

Cervical Spinal Cord DTI Is Improved by Reduced FOV with Specific Balance between the Number of Diffusion Gradient Directions and Averages.

BACKGROUND AND PURPOSE: Reduced-FOV DTI is promising for exploring the cervical spinal cord, but the optimal set of parameters needs to be clarified. We hypothesized that the number of excitations should be favored over the number of diffusion gradient directions regarding the strong orientation of the cord in a single rostrocaudal axis. MATERIALS AND METHODS: Fifteen healthy individuals underwent cervical spinal cord MR imaging at 3T, including an anatomic 3D-Multi-Echo Recombined Gradient Echo, high-resolution full-FOV DTI with a NEX of 3 and 20 diffusion gradient directions and 5 sets of reduced-FOV DTIs differently balanced in terms of NEX/number of diffusion gradient directions: (NEX/number of diffusion gradient directions = 3/20, 5/16, 7/12, 9/9, and 12/6). Each DTI sequence lasted 4 minutes 30 seconds, an acceptable duration, to cover C1-C4 in the axial plane. Fractional anisotropy maps and tractograms were reconstructed. Qualitatively, 2 radiologists rated the DTI sets blinded to the sequence. Quantitatively, we compared distortions, SNR, variance of fractional anisotropy values, and numbers of detected fibers. RESULTS: Qualitatively, reduced-FOV DTI sequences with a NEX of ≥5 were significantly better rated than the full-FOV DTI and the reduced-FOV DTI with low NEX (N = 3) and a high number of diffusion gradient directions (D = 20). Quantitatively, the best trade-off was reached by the reduced-FOV DTI with a NEX of 9 and 9 diffusion gradient directions, which provided significantly fewer artifacts, higher SNR on trace at b = 750 s/mm2 and an increased number of fibers tracked while maintaining similar fractional anisotropy values and dispersion. CONCLUSIONS: Optimized reduced-FOV DTI improves spinal cord imaging. The best compromise was obtained with a NEX of 9 and 9 diffusion gradient directions, which emphasizes the need for increasing the NEX at the expense of the number of diffusion gradient directions for spinal cord DTI contrary to brain DTI.