The Quantitative Study Of Magnetizaton Transfer Ratio In Lumbar Intervertebral Disc Degeneration

Objective: To evaluate the study value of magnetization transfer ratio(MTR) in disk degeneration by measuring the values of the nucleuspulposus(NP) and the annulus fibrosus(AF),and to correlating，a gradingsystem for lumber disk degeneration（improved Pfirrmann grade）.Methods:77patients with degenerative lumbar disc(male,32cases;female,45cases) and19healthy volunteers(male,15cases; female,4cases) were chosen. A total of96cases(male,47cases, female49cases; meanage,43.3±16.5years; range,12～78years). All the subjects were performedwith1.5-T MR scanner(Siemens, Avanto). Firstly, The lumbar intervertebraldiscs were scanned by the proton density sequence on the sagittal for twice,and one of the twice was added the MT. Secondly, From the lumbar1-2discto the lumbar5-sacral1disc, the proton density sequence was used on thelevel that parallel to the disc for twice, and one of the twice was added the MT,which were marked to Mo and the other to Ms. Thus the MTR values of NPand AF were measured【MTR=（Mo-Ms）/Mo】. At the same time, the lumbardiscs of96cases were scanned by MRI conventional sequences, and weregraded from1to8by the improved Pfirrmann grading method. Lastly, thecorrelativity was analyzed between the improved Pfirrmann grade and theMTR values of nucleus pulposus and annulus fibrosus. The MTR valueswere compared for healthy volunteers with age-matched patients.Results:1Descriptive statistical analysis1.1The MTR values of NP and AFThe MTR values of NP and AF showed a normal distribution（P＜0.01）. The mean of MTR values of NP was7.48%. The mean of MTRvalues of AF was10.96%. This observation corroborates a previous study showing that collagen constitutes70%of the dry weight of the AF andonly20%of the dry weight of the NP. The observed NP saturationappeared to be unproportionally high when compared with the AFsaturation. Statistics the MTR values according the improved Pfirrmanngrading method and draw the chart. The MTR values of NP graduallyincreased with the improved Pfirrmann grading method, but it was notobvious in the AF.1.2The distribution of improved Pfirrmann grading method and ageThe improved Pfirrmann grading method and age showed a normaldistribution（P＜0.01）.1.3The differences between male with femaleThe male accounted for about49%of the sample size and the female51%. The MTR values of NP of male was7.00±2.74%and the female was7.94±2.74%;/The MTR values of AF of male was11.25±2.86%and thefemale was10.69±2.72%. The difference was not significant by the singlesample T-test(P=.653/P=0.645).2The correlativity between the improved T2Pfirrmann grade and the MTRvalues of NP and AF.Because the MTR values of NP and AF showed a normal distribution,the Pearson correlation analysis was used. The statistically significant positivecorrelation between the MTR value of NP and the improved Pfirrmann gradecan be found in the condition that P＜0.01and the Pearson correlationcoefficient was0.201(P=0.000). But the statistically significant between theMTR value of AF and the improved Pfirrmann grade was notstrong(P=0.049). The correlation between the MTR values of the NP and themodified Pifrrmann grade correlation description that the collagen of NP wasrelated to the disc degeneration.3The correlativity between age and the MTR values of NP and AFBecause all of them showed a normal distribution, the Pearsoncorrelation analysis was used. The statistically significant positive correlationbetween the MTR value and age can be found, and the Pearson correlation coefficient was0.177(P=0.000). but the MTR value of AF was not relatedto age(P=0.465).4The difference between the healthy volunteers and the age-matchedpatients.There was弄significant difference of the MTR values and the improvedPfirrmann grade in the disc of L1-2、L2-3、L3-4、L5-S1. The significantdifference in the disc of L4-5can be found.5MTR ImageGreater signal saturation in the AF was observed after the application ofthe1.5kHz off-resonance saturation pulse. The significant signal saturation ofthe AF compartment was best visualized in the subtraction (difference) imageshown in the same figure, in which the anterior and posterior AF bothdemonstrates higher signal reduction compared with the NP. And the mapclear visualization of the IVD’s AF compartment, along with excellentdemarcation between the AF and NP compartments. The young’s IVDs haveclear distinction between the AF with high MTR and the NP with lowMTR.In contrast,the IVDs of the older subject no longer exhibit a cleardemarcation between the NP and the AF compartments.Conclusion: The study further proved that the degeneration of disc isrelated to the change of collagen,and mainly ralated to the collagen of thenucleus. This observation may suggest a possible increase in absolute collagencontent，in addition to increased collagen relative density.In summary，magnetization transfer MRI of the disc may serve as a noninvasive diagnostictool for disc degeneration，in addition to other MRI techniques specific tocollagen content.