Ultra-short echo time MR imaging in assessing cartilage endplate damage and relationship between its lesion and disc degeneration for chronic low back pain patients

Abstract

Objective: To investigate the feasibility of ultra-short echo time (UTE) magnetic resonance imaging (MRI) in the assessment of cartilage endplate (CEP) damage and further evaluate the relationship between total endplate score (TEPS) and lumbar intervertebral disc (IVD) degeneration for chronic low back pain patients.

Materials and methods: IVD were measured in 35 patients using UTE imaging at 3T MR. Subtracted UTE images between short and long TEs were obtained to depict anatomy of CEP. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated to assess the image quality quantitatively. A new grading criterion for endplate damage evaluation was developed based on Rajasekaran.S grading system in this study. Two radiologists were employed to evaluate CEP and bony vertebral endplates (VEP) using this new grading criterion and assess TEPS, independently. Cohen's kappa analysis was applied to evaluate the inter-observer agreement of endplate damage assessment between two radiologists, and the Kendall's TAU-B analysis was employed to determine the relationship between TEPS and IVD degeneration evaluated with Pfirrmann grading.

Results: Well structural CEP was depicted on subtracted UTE images and confirmed by high SNR (33.06±2.92) and CNR values (9.4±2.08). Qualified subtracted UTE images were used by two radiologists to evaluate the degree of CEP and VEP damage. Excellent inter-observer agreement was confirmed by high value in Cohen's kappa test (0.839, P < 0.001). Ensured by this, 138 endplates from 69 IVDs of 35 patients were classified into six grades based on the new grading criterion and TEPS of each endplate was calculated. In addition, the degeneration degree of IVDs were classified into five grades. Finally, using Kendall's TAU-B analysis, significant relationship was obtained between endplate damage related TEPS and IVD degeneration (r = 0.864, P < 0.001).

Conclusion: Ensured by high image quality, UTE imaging might be considered an effective tool to assess CEP damage. Additionally, further calculated TEPS has shown strong positive association with IVD degeneration, suggesting that the severity of endplate damage is highly linked with the degree of IVD degeneration.

Keywords: Bony vertebral endplate; Cartilage endplate; Chronic low back pain; Disc degeneration; Magnetic resonance imaging; Pfirrmann grade; Total endplate score; Ultra-short echo time.

Fig. 1

Subtracting a 3D ultrashort Echo Time (UTE) image acquired at short TE of 0.03 ms (a) by the one acquired at long TE of 6 ms (b), a resultant subtracted 3D UTE image (c) of a lumbar spine with relatively normal cartilage endplate (CEP) is presented at sagittal view. Well structural CEP (denoted by white arrow) is hyperintense as well as adjacent hypointense vertebral endplate. The effect of nucleus pulposus, annulus fibrosus was removed after image subtraction

Fig. 2

Representative images of ROIs in cartilaginous endplate (CEP), disc, and background in 25-year-old male volunteer. Mid sagittal image of subtracted ultra-short echo time images. ROI of CEP was drawn using freehand technique. In this image, ROI 1 is located on inferior CEP of L3 and 22 mm² in area. ROI of disk (ROI 2) was circle and 8 mm² in area. ROI of background (ROI 3) was circle and 9 mm² in area

Fig. 3

On the subtracted 3D UTE images, representative endplate images at each grade are shown. a: grade I, normal cartilage endplate (CEP) and bony vertebral endplate (VEP). b: grade II, CEP local thinning (denoted by white arrow). c: grade III, focal sunken of CEP (white arrow), complete continuity and VEP was not involved. d,e: grade IV and V, the defect of CEP and VEP can be observed (white arrow), adjacent to normal CEP and VEP. f: grade VI, CEP and VEP almost defected completely (white arrow), with obvious collapse of the disc