非对称回波的最小二乘估算法迭代水脂分离技术评估腰椎间盘退行性改变的研究

Study of iterative Dixon water-fat separation with echo asymmetric and least-squares estimation for evaluation of intervertebral disc degeneration

目的定量分析磁共振非对称回波的最小二乘估算法迭代水脂分离技术（IDEAL）提供的多组参数，以实现安全无创、客观准确地观测椎间盘的退变程度；及时预测早期退变，提高影像检查的图像质量，缩短检查时间，提供个性化的影像检查方案，从而实现精准医疗。方法自愿参与本试验的志愿者40例，其中男性23例、女性17例，年龄20～84岁，平均年龄（53．4±16．5）岁。全部志愿者接受磁共振腰椎检查，检查序列包括矢状位T2FSE、矢状位T1FSE、轴位T2 FSE，矢状位T2FSE压脂和矢状位T2 IDEAL序列。依据Pfirrmann分级标准对全部200个腰椎间盘进行I级～V级评分。利用IDEAL序列同相位图像和反相位图像，测量并计算每个腰椎间盘的水信号分数（WSF）。采用统计学方法分析不同Pfirrmann评分组之间WSF的差异性。在T2FSE压脂及IDEAL序列脂肪抑制正中矢状面图像上，对同一水平椎体（L3）及背景噪声区分别设置同样大小的感兴趣区，测量椎体信号强度的平均值和背景信号强度的标准差，计算两种序列图像的信噪比（SNR），采用统计学方法比较两种序列的图像质量优劣。结果全部200个腰椎问盘中，Pfirrmann评分39个为I级，42个为II级，27个为III级，53个为IV级，39个为V级。T2FSE压脂图像的SNR为（11．42±6．17）dB，IDEAL技术脂肪抑制图像的SNR为（20．63±9．44）dB，两者差异有统计学意义（P〈0．05）。各组椎问盘WSF随Pfirrmann评分的升高而降低，且除IV级组和V级组之间差异无统计学意义（P〉0．05），其余各组间差异均有统计学意义（P（0．05）。结论IDEAL脂肪抑制图像的SNR明显高于T2 FSE压脂图像，其图像质量更佳。依据IDEAL技术计算得到的WSF可定量分析腰椎间盘的退变程度，该技术安全无创、客观准确，尤其对椎间盘的早期退变更为敏感。

Objective To analyze quantitatively the multiple parameters of iterative Dixon water-fat separation with echo asymmetric and least-squares estimation （IDEAL） MR imaging sequence, in order to realize safe, noninvasive and accurate observation of intervertebral disc degeneration, and to predict early degeneration in time, improve image quality, and to realize precision medical treatment by providing personalized examinations and optimized imaging protocols. Methods A total of 40 volunteers, 23 males and 17 females, with 20-84 years of age （mean （53.4±16.5） years）, were participated in our study to accept lumbar spine MRI examination, including sequences of OSAG T2 FSE, OSAG TI FSE, OAX T2 FSE, OSAG T2 FSE FS and OSAG IDEAL T2. Lumbar intervertebral disc degeneration was evaluated by Pfirrmann classification. The water signal fraction （WSF） of each disc was measured and calculated accurately with IDEAL in phase and IDEAL out phase images. The differences between Pfirrmann grade and WSF were analyzed statistically. The signal-to-noise ratio （SNR） measurements were carried out on equal size region of interest （ROI） from the same levels of vertebral body （L3） and background zone of T2 FSE FS and T2 IDEAL water image mid-sagittal planes, respectively, and the average value of vertebral body signal strength and the standard deviation of background signal were measured. SNRs of the two sequences were calculated, and the image qualities were compared statistically. Results Of all 200 lumbar discs that measured using Pfirrmann classification, 39 discs were classified as Pfirrmann grade I, 42 as grade II, 27 as grade III, 53 as grade IV, and 39 as grade V. The SNR of T2 FSE FS images was （11.42±6.17） dB, while that of the IDEAL water images was （20.63±9.44） dB, and there was a statistically significant difference between them （P〈0.05）. The WSF decreased along with the increase of Pfirrmann grade. The significant differences of WSF were found in all grades （P〈 0.05） except for the grade IV and V （P〉0.05）. Conclusions The S.NR of the IDEAL water images is significantly higher than that of T2 FSE FS images, which bring about better image quality. The WSF calculated based on the IDEAL in phase and IDEAL out phase images will make possible the quantitative, noninvasive and accurate analysis of lumbar disc degeneration, especially on the early stage of disc degeneration.