High contrast cartilaginous endplate imaging in spine using three dimensional dual-inversion recovery prepared ultrashort echo time (3D DIR-UTE) sequence

Abstract

Purpose: To investigate the feasibility and application of a novel imaging technique, a three-dimensional dual adiabatic inversion recovery prepared ultrashort echo time (3D DIR-UTE) sequence, for high contrast assessment of cartilaginous endplate (CEP) imaging with head-to-head comparisons between other UTE imaging techniques.

Method: The DIR-UTE sequence employs two narrow-band adiabatic full passage (AFP) pulses to suppress signals from long T₂ water (e.g., nucleus pulposus (NP)) and bone marrow fat (BMF) independently, followed by multispoke UTE acquisition to detect signals from the CEP with short T₂ relaxation times. The DIR-UTE sequence, in addition to three other UTE sequences namely, an IR-prepared and fat-saturated UTE (IR-FS-UTE), a T₁-weighted and fat-saturated UTE sequence (T_1w-FS-UTE), and a fat-saturated UTE (FS-UTE) was used for MR imaging on a 3 T scanner to image six asymptomatic volunteers, six patients with low back pain, as well as a human cadaveric specimen. The contrast-to-noise ratio of the CEP relative to the adjacent structures-specifically the NP and BMF-was then compared from the acquired images across the different UTE sequences.

Results: For asymptomatic volunteers, the DIR-UTE sequence showed significantly higher contrast-to-noise ratio values between the CEP and BMF (CNR_CEP-BMF) (19.9 ± 3.0) and between the CEP and NP (CNR_CEP-NP) (23.1 ± 1.7) compared to IR-FS-UTE (CNR_CEP-BMF: 17.3 ± 1.2 and CNR_CEP-NP: 19.1 ± 1.8), T_1w-FS-UTE (CNR_CEP-BMF: 9.0 ± 2.7 and CNR_CEP-NP: 10.4 ± 3.5), and FS-UTE (CNR_CEP-BMF: 7.7 ± 2.2 and CNR_CEP-NP: 5.8 ± 2.4) for asymptomatic volunteers (all P-values < 0.001). For the spine sample and patients with low back pain, the DIR-UTE technique detected abnormalities such as irregularities and focal defects in the CEP regions.

Conclusion: The 3D DIR-UTE sequence is able to provide high-contrast volumetric CEP imaging for human spines on a clinical 3 T scanner.

Keywords: Cartilaginous endplate; Dual adiabatic inversion recovery; High contrast; Low back pain; UTE.

Fig. 1

Sequence diagram for four different UTE techniques, including DIR-UTE (A) IR-FS-UTE (B) T_1w-FS-UTE (C), and FS-UTE (C). The DIR-UTE sequence utilizes two AFP pulses to invert long T₂ water (e.g., NP) and BMF with center frequencies of 0 and -440 Hz, respectively (A). The IR-FS-UTE sequence employs an AFP pulse for inverting long NP while the FatSat module is utilized to improve CEP contrast against BMF (B). The FatSat module is applied for fat suppression in both T_1w-FS-UTE and FS-UTE sequences (C). The multispoke acquisition strategy is employed in all UTE sequences to reduce the total scan time. A slab selective half pulse is utilized for signal excitation in each spoke (D). The 3D Cones trajectory enables efficient k-space coverage for all UTE scans (E)

Fig. 2

Lumbar spine imaging for two asymptomatic volunteers. Images from a 32-year-old asymptomatic male subject are shown in (A—E) while (F—J) correspond to images obtained from a 38-year-old asymptomatic male volunteer. The clinical fat suppressed T_2w-FSE sequence shown in (A and F) fails to capture CEP signals owing to its long TE relative to the CEP’s short T₂ relaxation. The DIR-UTE (B and G) provides the best contrast in comparison to other UTE imaging techniques, including IR-FS-UTE (C and H), T_1w-FS-UTE (D and I), and FS-UTE (E and J), between CEP and BMF and between CEP and NP. Panel B shows representative ROIs of CEP, NP and BMF to calculate CEP CNRs

Fig. 3

The clinical T_2w- and T_1w-FSE (A and B) as well as DIR-UTE (C) imaging for an ex vivo spine sample from an 87-year-old female donor. There is a CEP fracture with herniation of NP through the focal defect as indicated on the DIR-UTE image with an orange arrow

Fig. 4

Representative lumbar spine imaging from a 40-year-old male patient with low back pain. While the CEP region is completely invisible in the clinical fat suppressed T_2w-FSE (A) it is well highlighted in the DIR-UTE (B) IR-FS-UTE (C) and T_1w-FS-UTE (D). Regular FS-UTE (E) is able to capture the CEP signal, but has relatively low contrast of the CEP region compared to the other UTE imaging techniques. The NP regions of degenerated discs (indicated by arrows) exhibit stronger signals than those in normal discs for the DIR-UTE, IR-FS-UTE, and T_1w-FS-UTE, which can be attributed to the shortened T₁ relaxation due to dehydration in NP

Fig. 5

The clinical T_1w-FSE (A) PDw-UTE (B) and DIR-UTE (C) images from a 37-year-old male with known PsA. Yellow line in (A) on the clinical image indicates the cross-section plane for coronal slice in DIR-UTE image. The CEP irregularities as marked by arrows are depicted in the coronal DIR-UTE image (C). The DIR-UTE image obtained from another asymptomatic subject (24-year-old male) (D) is used for comparison where the CEP region shows continuous and bright signal

Fig. 6

The clinical T_1w-FSE (A) PDw-UTE (B) and DIR-UTE (C) images from a 51-year-old male patient with PsA. The CEP irregularities are clearly seen on the inferior endplates at L2, L3, and L4 with the DIR-UTE sequence. These CEP irregularities are associated with bony endplate remodeling shown in the PDw-UTE bone image and were caused by Schmorl’s nodes