Variable Refocusing Flip Angle Single-Shot Imaging for Sedation-Free Fast Brain MRI.

R Jabarkheel,U Yousaf,A.M Loening,S.S Vasanawala,E Tong,V Taviani,K.W Yeom,E.H Lee,Michael Iv,T.M Cullen,G.A Grant,S.J Holdsworth

doi:10.3174/ajnr.a6616

R Jabarkheel, U Yousaf + Show 10 more

Open Access

https://doi.org/10.3174/ajnr.a6616

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Abstract

Conventional single-shot FSE commonly used for fast MRI may be suboptimal for brain evaluation due to poor image contrast, SNR, or image blurring. We investigated the clinical performance of variable refocusing flip angle single-shot FSE, a variation of single-shot FSE with lower radiofrequency energy deposition and potentially faster acquisition time, as an alternative approach to fast brain MR imaging. We retrospectively compared half-Fourier single-shot FSE with half- and full-Fourier variable refocusing flip angle single-shot FSE in 30 children. Three readers reviewed images for motion artifacts, image sharpness at the brain-fluid interface, and image sharpness/tissue contrast at gray-white differentiation on a modified 5-point Likert scale. Two readers also evaluated full-Fourier variable refocusing flip angle single-shot FSE against T2-FSE for brain lesion detectability in 38 children. Variable refocusing flip angle single-shot FSE sequences showed more motion artifacts (P < .001). Variable refocusing flip angle single-shot FSE sequences scored higher regarding image sharpness at brain-fluid interfaces (P < .001) and gray-white differentiation (P < .001). Acquisition times for half- and full-Fourier variable refocusing flip angle single-shot FSE were faster than for single-shot FSE (P < .001) with a 53% and 47% reduction, respectively. Intermodality agreement between full-Fourier variable refocusing flip angle single-shot FSE and T2-FSE findings was near-perfect (κ = 0.90, κ = 0.95), with an 8% discordance rate for ground truth lesion detection. Variable refocusing flip angle single-shot FSE achieved 2× faster scan times than single-shot FSE with improved image sharpness at brain-fluid interfaces and gray-white differentiation. Such improvements are likely attributed to a combination of improved contrast, spatial resolution, SNR, and reduced T2-decay associated with blurring. While variable refocusing flip angle single-shot FSE may be a useful alternative to single-shot FSE and, potentially, T2-FSE when faster scan times are desired, motion artifacts were more common in variable refocusing flip angle single-shot FSE, and, thus, they remain an important consideration before clinical implementation.

Highlights

MethodsWe retrospectively compared half-Fourier single-shot FSE with half- and full-Fourier variable refocusing flip angle single-shot FSE in 30 children
BACKGROUND AND PURPOSEConventional single-shot FSE commonly used for fast MRI may be suboptimal for brain evaluation due to poor image contrast, SNR, or image blurring
While variable refocusing flip angle single-shot FSE may be a useful alternative to single-shot FSE and, potentially, T2-FSE when faster scan times are desired, motion artifacts were more common in variable refocusing flip angle single-shot FSE, and, they remain an important consideration before clinical implementation

Summary

Methods

We retrospectively compared half-Fourier single-shot FSE with half- and full-Fourier variable refocusing flip angle single-shot FSE in 30 children. Two readers evaluated full-Fourier variable refocusing flip angle single-shot FSE against T2-FSE for brain lesion detectability in 38 children. Clinical characteristics of patients who had SSFSE and vrfSSFSE images are listed in On-line Table 1. Subjects Undergoing T2-FSE and Full-Fourier vrfSSFSE We retrospectively identified 38 consecutive children who had undergone back-to-back T2-FSE and full-Fourier vrfSSFSE scans at 3T MR imaging in October 2016 as part of a qualityassurance project. SSFSE parameters were the following: FOV 1⁄4 18–22 cm (adjusted to each patient’s anatomy), array coil spatial sensitivity encoding parallel imaging factor 1⁄4 2, half-Fourier with homodyne reconstruction, effective TE = 86 ms, matrix 1⁄4 256 Â 256, and bandwidth 1⁄4 83 kHz. Contiguous, 4-mm-thick slices with interleaved section ordering were used.

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