Next-generation 5-min Knee MRI with Combined Simultaneous Multislice and Parallel Imaging Acceleration: Ready for Prime Time?

Purpose: To compare traditional twofold parallel imaging (PI)- and novel fourfold simultaneous multislice (SMS)-PI-accelerated two-dimensional (2D) fast spin-echo (FSE) magnetic resonance imaging (MRI) of the knee for the detection of internal derangement.

Methods and Materials: Following institutional review board approval and informed consent, 25 symptomatic patients (12 women, 13 men; age 44 years [range: 18–64 years]) prospectively underwent 1.5-T MRI of the knee including a 2-fold PI-accelerated 5-minute 2D FSE MRI protocol and a fourfold SMS-PI-accelerated 5-minute 2D FSE MRI protocol with higher spatial resolution, higher anatomical coverage, smaller interslicer gaps, improved suppression of vascular flow artifacts, and stronger and more homogeneous fat suppression (FS). Both protocols included sagittal proton density (PD), sagittal PDFS, coronal T1, coronal T2FS, and axial PDFS sequences. Two musculoskeletal radiologists independently assessed image contrast, noise, artifacts, structural visibility, and abnormalities. Nonparametric comparison, κ agreement, and interchangeability tests were applied.

Results: The interreader reliability (κ = 0.681) was good. The 5-minute SMS-PI MRI of the knee had better image contrast (p < 0.001), less noise (p < 0.001), better structural visibility (p < 0.001), and no flow or aliasing artifacts (p = 0.657). There was unidirectional interchangeability in favor of SMS-PI MRI for the diagnosis of meniscal tears and cartilage defects, and bidirectional interchangeability for anterior cruciate and collateral ligament tears, tendon tears, bone marrow edema pattern, and fractures.

Conclusion: Combined, fourfold-accelerated SMS-PI 2D FSE enables artifact-free 5-minute MRI of the knee with higher image quality, better visibility of anatomical structures, and possibly better detectability of cartilage defects and meniscal tears than twofold accelerated 5-minute 2D FSE MRI of the knee.