High contrast cartilaginous endplate imaging using a 3D adiabatic inversion‐recovery‐prepared fat‐saturated ultrashort echo time (3D IR‐FS‐UTE) sequence

Abstract

Ultrashort echo time (UTE) sequences can image tissues with transverse T 2 /T 2 * relaxations too short to be efficiently observed on routine clinical MRI sequences, such as the vertebral body cartilaginous endplate (CEP). Here, we describe a 3D adiabatic inversion-recovery-prepared fat-saturated ultrashort echo time (3D IR-FS-UTE) sequence to highlight the CEP of vertebral bodies in comparison to the intervertebral disc (IVD) and bone marrow fat (BF) at 3 T. The IR-FS-UTE sequence used a 3D UTE sequence combined with an adiabatic IR preparation pulse centered in the middle of the water and fat peaks, while a fat saturation module was used to suppress the signal from fat. A slab-selective half pulse was used for signal excitation, and a 3D center-out cones trajectory was used for more efficient data sampling. The 3D IR-FS-UTE sequence was applied to an ex vivo human spine sample, as well as the spines of six healthy volunteers and of three patients with back pain. Bright continuous lines representing signal from CEP were found in healthy IVDs. The measured contrast-to-noise ratio was 18.5 ± 4.9 between the CEP and BF, and 20.3 ± 4.15 between the CEP and IVD for the six volunteers. Abnormal IVDs showed CEP discontinuity or irregularity in the sample and patient studies. In conclusion, the proposed 3D IR-FS-UTE sequence is feasible for imaging the vertebral body's CEP in vivo with high contrast. K E Y W O R D Sadiabatic inversion recovery, cartilaginous endplate, ultrashort echo time | INTRODUCTIONLow back pain is the most common cause of disability in all ages and both sexes, 1 presenting with high incidence and high recurrence rates. 2 A multifactorial problem, low back pain may be associated with degenerative disc disease, vertebral body fractures, spondylolysis, spondylolisthesis, facet joint disorders, and instability. 3 The cartilaginous endplate (CEP), a thin layer of hyaline cartilage between the vertebral body and the Abbreviations: AF, anulus fibrosus; BF, bone marrow fat; CEP, cartilaginous endplate; CNR, contrast-to-noise ratio; CT, computed tomography; FA, flip angle; FS, fat saturated; FSE, fast spinecho; IR, inversion recovery; IVD, intervertebral disc; NP, nucleus pulposus; ROI, region of interest; T1w, T 1 weighted; T E , echo time; T I , time of inversion recovery; T R , repetition time; UTE, ultrashort echo time; VFA, variable flip angle; VERSE, variable-rate selective excitation; μCT, micro-computed tomography.

High-Contrast Lumbar Spinal Bone Imaging Using a 3D Slab-Selective UTE Sequence

“…UTE MRI has been very useful to image the cartilaginous endplate (CEP). We have recently developed a new inversion recovery-prepared and fat-saturated UTE (IR-FS-UTE) sequence to highlight the CEP signal (30). However, in this study, a proton density-weighted UTE sequence (flip angle = 1°) was used for bone imaging.…”

“…Thus, the signal intensity of CEP is actually similar to that of other long T 2 soft tissues and, as a result, we don't expect that CEP signal would affect vertebral bone imaging. In addition, we would suggest using a highly T 1 -weighted UTE sequence (e.g., an increased excitation flip angle (e.g., 15°) in the UTE sequence) to image CEP as the CEP has a much shorter T 1 than the nucleus pulposus (30).…”

Ultrashort Echo Time Magnetic Resonance Imaging Techniques: Met and Unmet Needs in Musculoskeletal Imaging

“…Figure 5b-d shows conventional and IR-FS-UTE imaging of the lumbar spine of a 38-year-old male patient. 25 A small incipient Schmorl's node on the vertebral body superior endplate is seen with further detailed characterization of a preserved thin CEP. As expected, this could not be identified on the clinical sequences.…”

“…Figure 5a shows the IR-FS-UTE contrast mechanism to highlight short-T2 signal with efficient suppression of long-T2 water and fat. [25][26][27] The IR-FS-UTE sequence uses a long adiabatic inversion pulse to invert the longitudinal magnetizations of long-T2 tissues such as the nucleus pulposus (NP) in the vertebral disk. A chemical shift-based fat saturation module is used to further suppress fat signal.…”

“…Of the various morphological imaging techniques, adiabatic IRbased approaches, including single IR-UTE, [15][16][17][18][19][20] dual-IR-UTE, [21][22][23] double-IR-UTE, 24 IR-FS-UTE, [25][26][27] and STAIR-UTE, [28][29][30] appear to provide more uniform suppression of long-T2 water and fat signals. This is attributable to the insensitivity of adiabatic pulses to B1 and B0 inhomogeneities.…”