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The use of relaxometry measurements in synthetic MR in assessing the lumbar intervertebral disk degeneration in patients with chronic low back pain1Beijing Hospital, Beijing, China, 2GE Healthcare, Beijing, China
Synopsis
Our purpose was to verify the use of synthetic MR in quantitative analysis of lumbar intervertebral disk degeneration in patients with chronic low back pain. Twenty-four patients underwent MR examination including conventional T2map and synthetic MR. Our results showed strong correlations between the two techniques. These absolute parameters obtained can reflect the intervertebral disk degeneration grades quantitatively. Synthetic MR is efficient and reproducible in the assessment of disk degeneration.
Introduction
The intervertebral disk (IVD) degeneration is thought to be the main cause of chronic low back pain.1,2 T2 relaxometry that may reflect the composition of IVD,3 is a promising technique for quantitative evaluation of IVD degeneration. The convention approach of multi-echo spin echo sequence, termed Carr-Purcell-Meiboom-Gill (CPMG) T2 mapping is usually time consuming and faces practical challenges.4 Synthetic MR is a novel imaging technique that offers time efficient measurement of relaxation weighted imaging as well as mapping.5,6 This study aims to verify the use of Synthetic MR in T2 mapping as compared to conventional CPMG-T2 mapping, and to explore the feasibility of grading IVD degeneration based on quantitative maps acquired from Synthetic MR.Methods
Twenty-four patients with chronic low back pain were enrolled in this study (6 men and 18 women; mean age, 43 years; range, 24–78 years), ethical approval and consent forms were obtained. All patients underwent routine lumbar MRI exam, CPMG T2 mapping, and synthetic MR (MAGnetic resonance imaging Compilation, MAGiC) on a 3.0T MRI scanner (Signa Pioneer, GE Healthcare, Milwaukee, USA). Identical slices, with FOV of 280*280 mm, matrix of 320*256, were prescribed for both CMPG T2 mapping and MAGiC. The other imaging parameters for MAGiC were: TR = 4243ms, and TE = 17/93ms. T2 map from CPMG-T2 mapping were generated from CartiGram package (Advanced Workstation 4.6), and the relaxation maps from MAGiC were generated automatically. An elliptic ROI in the midsagittal section on T2WI, was manually drawn on the inner portion of each lumbar disk with about 80% areas of the nucleus pulposus and inner annulus fibrosus, which appeared hyperintense on T2WI. Two experienced radilogists measured the results respectively, and the measurements were repeated after one week. The degree of disk degeneration was assessed based on T2-weighted images according to the Pfirrmann classification by two experienced radiologists. The correlation between the two T2 measurements was assessed by the Pearson correlation test. PD, T1, T2 values of MAGiC and the different grades of the IVDs were analyzed by one-way ANOVA testing. Intra- and inter-observer agreement of measurement was assessed using intraclass correlation (ICC). Moreover, ROC curves were used to test the sensitivity and specificity of CPMG and MAGiC measures for assessing Pfirrmann grading.Results
In total, a total of 120 lumbar discs were recorded. Representative images of a patient are shown in Figure 1, along with illustration of the placement of ROIs. T2 measurements from CPMG-T2 and MAGiC showed strong correlations with statistical significance (r = 0.962, p < 0.01, Figure 2). Figure 3 shows the relaxometry measurements with different grades: T1 and T2 values decrease as Pfirrmann grades increases except for grade V; significant differences of T1 and T2 were observed among grades I-IV (p < 0.05). PD values showed significant differences among grade I/II, grade III, and grade IV/V (p < 0.05). The ICC for intra- and inter-observer agreement was 0.979 and 0.982 for PD, 0.986 and 0.974 for T1, and 0.967 and 0.952 for T2. There was no significant difference between the AUC of CPMG and MAGiC measures (p > 0.05), shown in Figure 4.Discussion
In this study, a strong correlation was found between T2 measurements from CPMG and MAGiC, and the T1, T2 and PD values observed were in line with those of previous reports.4,6,7 It has been reported that decreased disc water content and proteoglycan loss may lead to decreased T1 and T2 values.3,7-10 It was found that T1 and T2 values decreased as Pfirrmann grades increased except for grade V. There was no significant difference in T1 and T2 values between grades IV and V, which might suggest that morphological change instead of content change underlies between IV and V. There is also no significant difference in PD values respectively between grades I and II, gradesIV and V. This finding reflects that T1 and T2 could offer a more sensitive measurement to differentiate IVDs degeneration stages than PD. The high ICC value in the inter- and intra-observer analysis also supports the reproducibility of the measurements used.Conclusion
The quantitative relaxometry measures obtained using synthetic MR may be used for assessing the level of lumbar intervertebral disk degeneration.Acknowledgements
No acknowledgement found.References
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