| Background:T1 ρ and T2* relaxation times are capable of providing information about early biochemical changes in intervertebral disk degeneration (IVDD). The purpose of this study was to analyze the relationship between T1 ρ, T2* relaxation time and Pfirrmann grade, intervertebral disc levels and patient age, and compare T1 ρ and T2* mapping in IVDD with reference to Pfirrmann grade. Material/Methods:Subjects:Lumbar sagittal T2-weighted, T1 ρ and T2* relaxation MRI were performed at 3.0T in 42 subjects covering discs L1-L2 to L5-S1.Inclusion criteria were patients with single or recurrent episodes of low back pain, and radiologic screening and conventional MRI confirmation of no other spine diseases except disc degeneration. Exclusion criteria were a body mass index greater than 25, spinal malignancy, spine fractures, spinal infection, lumbar scoliosis. sacroiliac arthritis, rheumatoid arthritis, metabolic bone disease, previous spine surgery or interventional treatment, and contraindications for MR imaging. This prospective study was approved by the institute research ethics committee, and written informed consent was obtained from each participant prior to the study.MR Imaging:MRI was performed in the morning for all subjects to reduce the potential influence of diurnal variation in intervertebral disks. All MRI examinations were performed by a 3.0T scanner (Achieva, Philips Healthcare, Best, the Netherlands) and a dedicated 15-channel SENSE spine coil. To guarantee the same in-plane and out-of-plane resolution for better comparability between the T1 ρ and T2* sequences, the following parameters were kept consistent:field of view=220mm, matrix=432x432, slice thickness=5mm. slices=9, voxel size=0.57x0.57x5.00mm3. First, conventional sagittal T2-weighted images were acquired by using a turbo spin echo (TSE) sequence with the following parameters:TR/TE=2500ms/90ms, flip angle=90°, field of view=220mm, NSA=2, and scan time=1min40s. Next, a series of sagittal T1 ρ and T2* quantification sequences were performed. The T1 ρ-weighted images were obtained with a 3D balanced fast field echo (b-FFE) sequence with the following parameters:TR/TE= 4.8 ms/2.4 ms, flip angle= 50°. NSA=1. Five subsequent T1 ρ-weighted scans were performed with spin lock durations of 0,10.20. 30. and 40 ms. spin-lock frequency of 500Hz, and with scan time of 1 min 9 s for each scan. The T2* relaxation time measurements were acquired by a fast field echo (FFE) sequence with the following parameters:TR/TEs=310ms/5.1:10.0; 14.9:19.8: 24.7ms. Hip angle=25°. NSA=4. and acquisition time=2min46s.Image Post-processing and Analysis:Two radiologists independently assessed the five lumbar discs in each subject on the mid-sagittal T2-weighted images according to the Pfirrmann grading system. The T1 ρ-weighted images were fitted on a pixel by pixel basis to the exponentially decaying Tip function to generate a T1 ρ relaxation map. and the T2*-weighed image analyses were conducted by using Image J software. Regions of interest (ROls) were set manually on the T1 ρ and T2* mappings with reference to the T2 images. The ROIs were drawn on the NP, anterior annulus fibrosus (AAF) and posterior annulus fibrosus (PAF). Values of AAF and PAF were averaged as the value for annulus fibrosus (AF). The ROI sizes for NP were 10-55 mm2, while the ROI sizes for AF were 10-45 mm2. All the measurements were performed twice by a single observer with an interval of four weeks, and the average of the twice as the final value.Statistical Analysis:All statistical analysis was performed by PASW Statistics software,P<0.05 was considered statistically significant. The intraclass correlation coefficients (ICC) with 95% confidence intervals (95%CIs) was used to assess the reproducibility in two measurements of T1 ρ and T2* relaxation times. The differences of T1 ρ，T2* relaxation times between NP and AF were tested using the Wilcoxon signed rank test, as well as between AAF and PAF. Kruskal-Wallis test were applied to compare the difference in age, disc levels, various disc degeneration grades and T1 ρ, T2 values of NP and AF. Associations between T1 ρ, T2* relaxation times and Pfirrmann grade, disc segments and patient age were tested using Spearman rank correlation. Results:1. A total of 42 subjects (30 men,12 women; rang,21-80 years; mean age,44.2 years) with 210 intervertebral lumbar disks from L1-2 to L5-S1 were included in this study. There were 41 in Pfirrmann grade I.68 in Pfirrmann grade Ⅱ.53 in Pfirrmann grade III,41 in Pfirrmann grade IV, and 7 in Pfirrmann grade V.2. The reproducibility between the two measurements was excellent (ICC=0.909-0.969). The ICC of NP was 0.955. the ICC of AAF was 0.932 and the ICC of PAF was 0.955 in T1 ρ Mapping. The ICC of NP was 0.955. the ICC of AAF was 0.932 and the ICC of PAF was 0.913 in T1 ρMapping. The ICC of NP was 0.969, the ICC of AAF was 0.937 and the ICC of PAF was 0.909 in T2* Mapping.3. T1 ρ relaxation time ranged from 73.8 to 235.1ms for NP, and from 55.7 to 173.8 ms for AF, while T2* relaxation times ranged from 9.6 to 185.8 ms for NP, and from 12.0 to 52.7 ms for AF. The difference in T1 ρ and T2* values between NP and AF were highly significant (both P<0.001), and the difference in T1 ρ and T2* values between AAF and PAF were also highly significant (both P<0.01). The trends of increasing age and disc levels with increasing Pfirrmann grades were significant (P< 0.01).4. T1 ρ and T2* values versus Pfirrmann grade. From Pfirrmann grade I to grade V, the mean and standard deviation of ± values were 177.3 ± 36.0ms,172.2± 31.9ms.128.8 ± 30.1ms,105.7 ± 21.5ms,99.1 ± 12.2ms for NP, while the mean and standard deviation of T2* values were 85.8±43.7ms、64.6±28.0ms、42.7±14.6ms、 33.9±12.1ms,26.1±11.2ms for NP. The mean and standard deviation of ±values were 117.4±21.3ms、120.5±18.2ms、03.7±20.0ms、97.9±15.2ms、81.5± 14.4ms for AF. while the mean and standard deviation of T2* values were 32.3±9.4ms、 28.1±8.1ms、27.2±6.3ms、25.3±6.2ms、22.3±4.4ms for AF. The trends of decreasing T1 ρ and T2* values with increasing Pfirrmann grade were significant (P<0.001). The Kruskal-Wallis test showed a significant difference in Tip and T2* relaxation times of NP and AF among the Pfirrmann grade groups (P<0.01). For both T1 ρ and T2* relaxation times in the NPs. a significant difference was found between Pfirrmann grade Ⅱ and Pfirrmann grades greater than II (P<0.001). especially between Pfirrmann grade βⅡ and Ⅲ. and the difference was not statistically significant between Pfirrmann grade Ⅰ and Ⅱ (P>0.05). nor between Pfirrmann grade IV and V (P>0.05). For AFs. the T1 ρ values also showed Pfirrmann grade Ⅱ was significantly different from Pfirrmann grades higher than II (P.001), particularly notable between Pfirrmann grades II and III; the T2* values demonstrated significant difference between Pfirrmann grade I and all the other grades (P<0.05). Spearman correlation analysis demonstrated that Pfirrmann grades were inversely significantly correlated with both T1 ρ and T2* values in the NP (r=-0.69, P<0.001; r=-0.56, P<0.001) and AF(r=-0.45, P<0.001; r=-0.26, P<0.001).5. Pfirrmann grade,T1 ρ and T2* values versus age. From Pfirrmann grade I to grade V, the mean and standard deviation of ages of the patients were 29.1 ± 5.3 year, 39.8 ± 10.7 year,51.5 ± 13.6 year,55.2 ± 13.6 year,54.5 ± 11.0 year. The trends of increasing age with increasing Pfirrmann grades was significant (r=0.645, P<0.001). Ages were inversely significantly correlated with both T1 ρ and T2* values in the NP (r=-0.45, P<0.001; r=-0.51, P<0.001) and AF (r=-0.28, P<0.001; r=-0.31, PO.001).6. Pfirrmann grade,T1 ρ and T2* values versus disc levels. From disc level L1/2 to L5S1, the mean and standard deviation of Tip values were 161.8±42.5ms、 159.8±42.8ms,146.6±41.9ms,129.0±37.3msand 136.7±37.8ms, while the mean and standard deviation of T2* values were 43.8±19.1ms,51.3±24.9ms,52.7±27.9ms、 61.3±43.4ms and 68.5±36.8ms for NP. The mean and standard deviation of T1 ρ values were 116.2±21.2ms,117.2±20.4ms,112.8±20.5ms,102.9±20.5ms and 100.7± 19.4ms, while the mean and standard deviation of T2* values were 24.2±7.9ms, 26.4±8.0ms,29.0±7.9ms.29.7±7.5ms and 29.7±6.6ms for AF. From disc level L1/2 to L5S1, the Pfirrmann grades were 2.2±0.9,2.3±1.0,2.6±1.1,3.0±1.3 and2.6±1.1. The Kruskal-Wallis test showed a significant difference in T1 ρ and T2* relaxation times of NP and AF among the different disc levels (PO.01), but not when comparing between L4/5 and L5/S1. Disc levels were negatively correlated with T1 ρ values in the both NP and AF (r=-0.27, P<0.001; r=-0.31, P<0.001). However, disc levels were positively correlated with T2* values in the both NP and AF (r=0.21, P<0.001; r=0.32, P<0.001).Conclusions:1. Both T1p and T2* relaxation time in NP and AF decreased with the increase of Pfirrmann grade. T1ρ relaxation time might be sensitive to the change of proteoglycan.And the T2* relaxation time might not only be sensitive to GAG content, but also collagen integrity. Reduced proteoglycan content of the NP could lead to reduced water content.2. T1ρ、T2*mapping may be able to distinguish between Pfirrmann grades II and III, and the difference was not statistically significant between Pfirrmann grade IV and V.3. T1ρ was more sensitive than T2* mapping in the judgment of Pfirrmann grade, but T2* mapping was more sensitive than T1ρ in the early judgment of the degeneration of the AF.4. T1ρ, T2* Mapping were able to reflect the impact of age on lumbar disc degeneration, and both methodologies displayed roughly comparable performance.5. There are different effects on T1ρ and T2* relaxation time of stress direction and anatomical site.In conclusion, T1ρ T2* relaxation time measurements quantitatively reflect changes in IVDD composition and evaluate age-related disk degeneration. T1ρ and T2* mapping displayed roughly comparable performance. |
PDF Full Text Request