多次激发平面回波扩散加权成像在颅底成像中的应用

Application of multi-shot echo planar imaging diffusion weighted imaging in the skull base

目的探讨不同激发次数和图像空间采样重建算法(image reconstruction using image-space sampling,IRIS)对颅底多次激发平面回波扩散加权成像(multi-shot echo planar imaging diffusion weighted imaging,MS-EPI DWI)图像质量的影响。材料与方法招募健康志愿者49例,年龄(42.00±19.39)岁,所有受试者均行常规单激发平面回波扩散加权成像(single-shot echo planar imaging diffusion weighted imaging,SS-EPI DWI)序列和基于IRIS的MS-EPI DWI序列(激发次数分别为8、6、4、2)。测量计算两侧小脑和脑干脑桥的表观扩散系数(apparent diffusion coefficient,ADC)、信噪比(signal to noise ratio,SNR)、对比噪声比(contrast to noise ratio,CNR)。两位观察者采用五分评分法对图像质量进行评价。采用Kappa检验评价两位观察者评分的一致性。使用Friedman检验MS-EPI DWI序列不同激发次数ADC、SNR、CNR及主观评分与SS-EPI DWI序列的差异性。若差异具有统计学意义,进行后续多重比较并对P值做Bonferroni校正。结果两位观察者主观评分一致性良好(Kappa=0.795、0.871、0.782、0.880、0.847)。MS-EPI DWI序列不同激发次数间比较,两侧小脑ADC差异无统计学意义(P>0.05),其余数据差异均有统计学意义(P<0.05)。与SS-EPI DWI序列相比,当激发次数为8时,MS-EPI DWI序列左脑桥脑干处ADC小于SS-EPI DWI序列(P<0.05);当激发次数为4、2时两侧脑桥脑干ADC小于SS-EPI DWI序列(P<0.05);当激发次数为8、6、2时,MS-EPI DWI序列两侧小脑和脑桥脑干SNR、CNR及主观评分均大于SS-EPI DWI序列;其中当激发次数为6时,左侧小脑和脑桥脑干SNR、CNR和右侧小脑SNR、CNR,右侧脑桥脑干SNR及主观评分较SS-EPI DWI序列差异均有统计学意义(P<0.05)。结论与SS-EPI DWI序列相比,基于IRIS的MS-EPI DWI序列具有SNR较高、几何畸变小等优势。对于颅底部成像,临床推荐使用MS-EPI DWI序列激发次数为6次。

Objective:To explore the performance of image reconstruction using image-space sampling(IRIS)-based multi-shot echo planar imaging diffusion weighted imaging(MS-EPI DWI)for the skull base region.Materials and Methods:Forty-nine volunteerss were recruited,with an average age of(42.00±19.39)years old.All subjects underwent conventional single-shot echo planar imaging diffusion weighted imaging(SS-EPI DWI)and IRIS-based multiple-shot diffusion-weighted imaging(8,6,4,and 2 shots,respectively).The apparent diffusion coefficient(ADC)values,signal to noise ratio(SNR)and contrast to noise ratio(CNR)of bilateral cerebellum,brainstem and pons were measured or calculated.A five-point scoring method was used by two observers to subjectively evaluate the image quality.The Kappa test was adopted to evaluate the consistency of the scores by the two observers.The differences of ADC,SNR,CNR and subjective scores among MS-EPI DWI with different number of shots and SS-EPI DWI were analyzed using Friedman test.If the differences were statistically significant,subsequent multiple comparisons were performed with Bonferroni correction for P values.Results:The scores by the two observers were in good agreement(Kappa=0.795,0.871,0.782,0.880,0.847).Compared with different shot times of MS-EPI DWI,there was no significant difference in ADC between the two sides of the cerebellum,and there was statistical difference in the rest of the data(P<0.05).Compared with the SS-EPI DWI sequence,when the number of shots was 8,the ADC in the left brainstem and pons was smaller than that in the SS-EPI DWI(P<0.05),and when the number of shots was 4 and 2,the ADC in the bilateral brainstem and pons was smaller than that in the SS-EPI DWI(P<0.05).When the number of shots was 8,6,and 2,the SNR,CNR and subjective scores of both sides of the cerebellum and pons and brain stem of MS-EPI DWI were higher than those of SS-EPI DWI.When the number of shots was 6,the SNR and CNR of the left cerebellum and pontine stem,the SNR and CNR of the right cerebellum,the SNR of the right pontine stem and subjective scores were significantly different from those of SS-EPI DWI(P<0.05).Conclusions:Compared with SS-EPI DWI,MS-EPI DWI based on IRIS that showed higher SNR and lower geometric distortion compared with SS-EPI DWI.MS-EPI DWI shots 6 is recommended for clinical skull base between imaging time and image quality.