| Part ? Evaluation of lumbar intervertebral disc degeneration using histogram analysis of T2 and T2* mapping Purpose: This study was to evaluate the feasibility of histogram analysis of T2 and T2* mapping on grading lumbar intervertebral disc degeneration(IVDD),characterizing microstructural heterogeneity of discs,and identifying low back pain(LBP)patients from healthy subjects.Materials and Methods: A total of 394 lumbar intervertebral discs were collected from 61 patients with chronic nonspecific LBP and 20 healthy volunteers who underwent routine lumbar MRI and axial T2 mapping and T2* mapping.All lumbar intervertebral discs were classified into grades ?-? according to the Pfirrmann grade.Then,the T2 and T2* histogram parameters of discs were obtained via the post-processing software,including mean,median,5th,10 th,25th,75 th,90th,95 th percentiles,standard deviation,kurtosis,skewness and entropy.The ratio of the area of the red zone on T2* color map to total cross sectional area of the intervertebral disc(i.e.,red zone ratio)was calculated.The correlations between histogram-derived parameters based on T2 and T2* values and Pfirrmann grade as well as between red zone ratio and Pfirrmann grade were calculated.The differences of histogram-derived parameters and red zone ratio between LBP patients and healthy people were statistically analyzed.Results: The inter-observer agreements for Pfirrmann grade of 394 lumbar intervertebral discs were excellent(Radiologist 1: ?=0.847,p<0.001;Radiologist 2: ?=0.834,p<0.001),and the intra-observer agreement was good(?=0.715,p<0.001).The consistency of the measured T2 and T2* histogram parameters was excellent,with intraclass correlation coefficient(ICC)ranging from 0.901-0.992 and 95% confidence intervals(CIs)ranging from 0.878-0.994.Each histogram-derived parameter had a statistically significant relationship with Pfirrmann grade(p<0.001)and had a diagnostic value for distinguishing normal(grade I and II)and degenerative(grade III-?)intervertebral discs,with area under the curve(AUC)ranging from 0.605-0.880(p<0.001).The bright red zone on T2* color maps of intervertebral discs displayed as a separated peak relative to the rest of voxels in the histograms.The mean area ratio of red zone over the corresponding disc was 9.889%6.606 and ranged from 0.517% to 30.598%.The red zone ratio was highly related to Pfirrmann grade(r=-0.708,p<0.001)and capable of to distinguish between normal and degenerative discs(AUC=0.884,p<0.001).The correlation coefficient r and AUC of the red zone ratio were higher than that of all histogram parameters.All histogram-derived parameters and red zone ratio were not statistically different between LBP patients and healthy people(p=0.130-0.777).Conclusion: Histogram analysis of T2 and T2* value is an effective tool for the detection and grading of IVDD.But its ability of LBP identification and diagnosis needs further studies.Identification of the red zone may provide a new breakthrough in research of disc degeneration initiation and generate new hypotheses in the anatomical and histological studies of lumbar intervertebral discs.Part ? Quantitative distinction between the nucleus pulposus and annulus fibrosus using a Gaussian-fitted histogram analysis of T2 relaxation times Purpose:To explore if Gaussian-fitted histogram analysis of T2 relaxation times can effectively distinguish the nucleus pulposus(NP)from the annulus fibrosus(AF)and detect intervertebral disc degeneration(IVDD).Materials and Methods: A total of 394 lumbar intervertebral discs were collected from 61 patients with chronic nonspecific low back pain(LBP)and 20 healthy volunteers.All discs were classified into grades ?-? according to the Pfirrmann grade.First,the post-processing software automatically generated the mean and standard deviation(SD)of T2 values for the AF(Mean1,SD1)and NP(Mean2,SD2)as well as 200-binned histograms containing individual voxel values and their corresponding frequencies.Then,a home-written MATLAB script was used to generate T2 value histograms and Gaussian fitting curves of the AF and NP based on 200 sets of voxel values and frequencies.Four features of the two fitted lines were extracted,including ?1 and W1 for the AF as well as ?2 and W2 for the NP(?: Gaussian mean;W: full width of half maximum).Additionally,the parameter reflecting the distinction between the AF and NP(??= ?2?1)was calculated.The correlations between all parameters and Pfirrmann grade were calculated.The differences of all parameters between LBP patients and healthy subjects were statistically analyzed.Results: The inter-observer agreements for Pfirrmann grade of 394 lumbar intervertebral discs were excellent(Radiologist 1: ?=0.847,p<0.001;Radiologist 2: ?=0.834,p<0.001),and the intra-observer agreement was good(?=0.715,p<0.001).All the T2 histograms of the AF and NP could be fitted to an independent Gaussian peak.Gaussian-fitted quantitative T2-based distributions of the AF and NP were clearly separable in the intact healthy discs(grade ? and ?).With degeneration severity(grade III-V),the peak values of the NP gradually decreased and shifted towards the peak values of the AF.Eventually the two fitted lines overlapped with the peak AF values exceeding those of the NP(?1>?2).The consistency of all quantitative parameters was excellent with ICC ranging from 0.919-0.979.Mean1,SD1,and W1 of AF had no statistical correlation with Pfirrmann grade(p=0.202-0.911),and ?1 had low correlation with Pfirrmann grade(r=0.108,p= 0.032).Mean2(r=-0.630),SD2(r=-0.422)and W2(r=-0.652)of NP were moderately correlated with Pfirrmann grade(p<0.001),and ?2(r=-0.714)and ??(r=-0.751)were highly correlated with Pfirrmann grade(p<0.001).All AF parameters had low AUC for identifying degeneration grades or cannot distinguish adjacent grades(AUC=0.501-0.766),while all NP parameters and ?? had relatively high AUC to distinguish adjacent Pfirrmann grades.?2 generated a higher AUC than Mean2(p=0.004;0.016;0.003,respectively)for differentiating grade I and II,II and ?,and ? and ?.The AUC of ?? were higher than those of ?2 for distinguishing grade II and ?,? and ?,and ? and ?,but the differences were not statistically significant(p>0.05).W2 generated higher AUC than SD2(p=0.008;0.002;0.000,respectively)for differentiating grade I and II,II and ?,? and ?.The combination of ?2,W2 and ?? resulted in a statistically significant improvement versus the combination of Mean2+SD2 for differentiating grade I and II,II and ?,? and ?(p=0.048;0.000;0.000,respectively).All the quantitative parameters showed no significant difference between the LBP group and the normal control group(p=0.084-0.978).Conclusion: The present study applied a Gaussian-fitted histogram analysis on T2 relaxation time.This method enabled quantitative distinction between the NP and AF.Furthermore,Gaussian-fitted histogram parameters were better than conventional mean or SD in diagnosing and grading IVDD,especially the ?? reflecting the distinction between the AF and NP.Part ? Histogram analysis of T2 mapping and T2* mapping of lumbar facet joint osteoarthritis and its relationship with intervertebral disc degeneration Purpose:The aim of this study was to explore the feasibility of histogram analysis of T2 and T2* values on grading lumbar facet joint osteoarthritis(FJOA)and to examine the correlation between the FJOA and intervertebral disc degeneration(IVDD).Materials and Methods: A total of 394 lumbar intervertebral discs and 788 facet joints were collected from 61 patients with chronic nonspecific low back pain(LBP)and 20 healthy volunteers who underwent routine lumbar MR imaging as well as axial T2 mapping and T2* mapping.All discs and facet joints were classified,respectively,according to the Pfirrmann and Weishaupt grade and grouped by age.The degeneration rate in each age group was calculated as: Degeneration rate = the number of abnormal counts/ the total counts.Then the T2 and T2* histogram parameters of facet joints were obtained through the post-processing software.The correlations between histogram parameters based on T2 and T2* values of facet joints and Weishaupt grade and the ability of histogram parameters to distinguish between normal and degenerated facet joints were calculated.The degeneration rate of lumbar intervertebral discs and facet joints in different age groups were compared.The correlation of histogram parameters and degeneration grades between the anterior intervertebral disc and posterior two facet joints in each three-joint complex were statistically analyzed.Results: The inter-observer agreements for Weishaupt grade of 788 lumbar facet joints(radiologist 1: ?=0.422,p<0.001;radiologist 2: ?=0.454,p<0.001)and the intra-observer agreement(?=0.405,p<0.001)were moderate.22 subjects with 109 intervertebral discs and 218 facet joints were divided into the age of 20-29 group,18 subjects with 87 discs and 174 facet joints in the age of 30-39 group,16 subjects with 80 discs and 160 facet joints in the age of 40-49 group,13 subjects with 59 discs and 118 facet joints in the 50-59 years group,and 12 subjects with 59 discs and 118 facet joints in the 60-69 years group.The degeneration rate of the intervertebral discs for 5 successive age groups was 15.60%,22.99%,56.25%,93.22% and 94.92%,the degeneration rate of the facet joints for those age groups was 36.7%,39.08%,43.75%,64.41% and 73.73%.Only the reliability of the mean,median,5th,10 th,25th,and 75 th percentile of T2 value was good(ICC=0.777-0.875),and the agreement of the other parameters was low to medium(ICC=0.158-0.684).Only the mean,median,5th,10 th,25th,75 th percentile,skewness,kurtosis of T2 values and the mean of T2* values had low correlations with Weishaupt grade(|r|=0.072-0.246,p<0.05).Only the mean,median,5th,10 th,25th,75 th percentile,skewness and kurtosis of T2 values had diagnostic value for distinguishing normal(Weishaupt 0 and 1)and degenerative(Weishaupt 2 and 3)facet joints(AUC=0.546-0.620).The correlations of degenerative grades between the anterior disc and the posterior facet joints were low(Left: Kendall's tau-b=0.256,p<0.001;Right: Kendall's tau-b=0.300,p<0.001),the correlation of degenerative grades between the posterior two facet joints was moderate(Kendall's tau-b=0.541,p<0.001).The 10 th percentile(p=0.045)of T2 value,mean(p=0.004),75 th percentile(p=0.015),90 th percentile(p=0.044)and entropy(p=0.001)of T2* values were significantly different between LBP group and the normal control group.Conclusions: The current results showed that the degeneration rate of the facet joint was higher than that of lumbar intervertebral disc under the age of 39 years.The results suggested that the anterior intervertebral disc and the posterior two facet joints in each three-joint complex may have a mutual influence,but the correlation between the two facet joints was stronger.The feasibility of histogram analysis of T2 and T2* values on grading FJOA was still controversial.The mean,75 th,90th percentile and entropy of T2* value and 10 th percentile of T2 value have diagnostic value for distinguishing LBP patients from healthy subjects. |
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