3092
Prospective Evaluation of Wave-CAIPI Susceptibility-Weighted Imaging (SWI) Compared to Conventional 3D SWI in a Clinical Setting1Radiology, Massachusetts General Hospital (MGH), Boston, MA, United States, 2Athinoula A. Martinos Center for Biomedical Imaging, Boston, MA, Charlestown, MA, United States, 3Siemens Healthineers, Shenzhen, China, 4Siemens Medical Solutions, San Francisco, CA, United States, 5Siemens Healthineers, Erlangen, Germany
Synopsis
We present the first large-scale evaluation of Wave-CAIPI susceptibility-weighted imaging (Wave-SWI) for clinical brain imaging. Wave-SWI was compared to conventional SWI in 107 patients undergoing 3T MRI for a range of indications in both inpatient and outpatient settings. Two neuroradiologists assessed the images in individual and head-to-head comparisons, and found no significant difference between the two sequences for detection of microhemorrhages, visualization of pathology and normal anatomy, and overall diagnostic quality, despite a nearly 5-fold decrease in acquisition time using Wave-SWI. Broader application of highly-accelerated 3D imaging may improve utilization of MRI resources while reducing motion artifacts and patient anxiety.
Introduction
Susceptibility-weighted imaging (SWI) is widely applied in clinical brain imaging due to its exquisite sensitivity for the detection and characterization of blood products, superior to that of conventional T2*-weighted gradient-echo imaging.1 However, conventional 3D SWI is associated with long acquisition times, which may contribute to greater motion artifacts and patient anxiety.2-4 Wave-CAIPI (controlled aliasing in parallel imaging) enables highly accelerated 3D imaging with negligible g-factor penalty 5 and may facilitate broader application of SWI, especially in motion-prone patients (e.g., children, the elderly, and the critically ill). The goal of this study was to evaluate the image quality and diagnostic performance of Wave-SWI compared to conventional SWI in a prospective trial of patients undergoing brain MRI for a broad range of clinical indications.Methods
Study Design
This study was approved by the Institutional Review Board (IRB) and was Health Insurance Portability and Accountability Act (HIPAA) compliant. Consecutive patients (n=107, age 60.1 ± 16.6 years) undergoing clinical brain MRI were prospectively enrolled, encompassing a range of indications in both inpatient and outpatient settings. The most common indications were brain tumor (n=34), altered mental status (n=13), intracranial hemorrhage (n=13), and stroke (n=10). In addition to the clinical protocol, all scans included a conventional SWI and ultrafast Wave-SWI sequence (detailed below). The order of these two sequences was randomly assigned, and the standard SWI was used as the reference standard.
MRI Protocol
MRI was performed on two clinical 3T MRI scanners (MAGNETOM Prisma and MAGNETOM Skyra; Siemens Healthcare GmbH, Erlangen, Germany) using 20 or 32-channel multiarray receiver head coils chosen to accommodate head size and patient comfort. The prototype Wave-SWI and standard SWI sequences were resolution-matched (in-plane voxel size=0.9×0.9 mm, slice thickness=1.8 mm). Acquisition time (AT) was 5 min for standard SWI (GRAPPA R=2). Wave-SWI was performed using 6-fold acceleration (AT=1 min 40 sec) on the 20-channel coil, and 9-fold acceleration (AT=1 min) on the 32-channel coil to take advantage of the increased SNR provided by the higher coil density.
Imaging evaluation
Two blinded neuroradiologists independently reviewed all images for clinical pathology, including the number of cerebral microbleeds (<5 mm) when present. For abnormal studies, Wave-SWI and standard SWI were compared side-by-side (e.g., Figure 1) for visualization of pathology, visualization of normal anatomic structures, noise (central and peripheral), artifacts, and overall diagnostic quality. A predefined 5-point scale was used, where positive numbers favored Wave-SWI and negative numbers favored standard SWI: 0 indicated equivalence, ±1 indicated that one sequence was preferred but the difference did not affect the final diagnosis, and ±2 indicated that one sequence was preferred and the difference would impact the final diagnosis. Discrepancies were adjudicated by a third blinded reader.
Statistical Analysis
The Wilcoxon signed-rank test was used to compare the difference between the two sequences for each variable. Proportions of agreement between readers were reported with the weighted Cohen kappa coefficient. P values <0.05 were considered statistically significant. All statistical calculations were performed using R version 3.4.3.
Results
There was no difference in the number of microhemorrhages detected using Wave-SWI versus standard SWI (p>0.05, kappa=0.73) (Figure 2) or the number of studies that were considered non-diagnostic (p>0.05, kappa=0.44). In the accompanying balloon plot (Figure 3), the size and color of each circle indicates the number of cases receiving a given score. There was no difference between the two sequences for visualization of pathology, visualization of normal anatomy, image noise in the periphery of the brain, or overall diagnostic quality (all p>0.05, kappa=0.42 to 0.59). Wave-SWI images had slightly fewer artifacts (p=0.04) and slightly increased image noise within the central brain compared to standard SWI (p<0.001). However, there were no cases where these differences impacted the final clinical diagnosis.Discussion and Conclusions
Highly-accelerated Wave-CAIPI SWI provides comparable performance to standard SWI across a range of clinical pathologies, with an approximate 5-fold reduction in acquisition time. Artifacts were more prevalent using the standard SWI sequence, likely due to the longer acquisition time resulting in greater motion sensitivity. Central image noise was slightly more conspicuous in Wave-SWI, presumably due to 1/√R related SNR loss at high acceleration factors; however, there were no cases where this difference impacted the clinical diagnosis, and there was no difference in the radiologists’ evaluation of overall diagnostic quality between the two sequences. The findings support clinical application of Wave-SWI over conventional SWI for routine clinical brain imaging on 3T scanners. Broader application of highly-accelerated 3D imaging may improve utilization of MRI resources, and reduce the number of motion artifacts and nondiagnostic exams, while improving patient comfort and reducing anxiety.Acknowledgements
No acknowledgement found.References
1. Nandigam RN, Viswanathan A, Delgado P, Skehan ME, Smith EE, Rosand J, Greenberg SM, Dickerson BC. MR imaging detection of cerebral microbleeds: effect of susceptibility-weighted imaging, section thickness, and field strength. AJNR Am J Neuroradiol. 2009 Feb;30(2):338-43.
2. Havsteen I, Ohlhues A, Madsen KH, Nybing JD, Christensen H, Christensen A. Are Movement Artifacts in Magnetic Resonance Imaging a Real Problem?-A Narrative Review. Front Neurol. 2017;8:232. eCollection 2017.
3. Savalia NK, Agres PF, Chan MY, Feczko EJ, Kennedy KM, Wig GS. Motion-related artifacts in structural brain images revealed with independent estimates of in-scanner head motion. Hum Brain Mapp. 2017;38(1):472-492.
4. Ooi MB, Krueger S, Thomas WJ, Swaminathan SV, Brown TR. Prospective real-time correction for arbitrary head motion using active markers. Magn Reson Med. 2009;62(4):943-54.
5. Bilgic B, Gagoski BA, Cauley SF, Fan AP, Polimeni JR, Grant PE, Wald LL, Setsompop K. Wave-CAIPI for highly accelerated 3D imaging. Magn Reson Med. 2015 Jun;73(6):2152-62.
Figures
