Deep learning-based magnetic resonance imaging reconstruction for improving the image quality of reduced-field-of-view diffusionweighted imaging of the pancreas

BACKGROUND It has been reported that deep learning-based reconstruction(DLR)can reduce image noise and artifacts,thereby improving the signal-to-noise ratio and image sharpness.However,no previous studies have evaluated the efficacy of DLR in improving image quality in reduced-field-of-view(reduced-FOV)diffusionweighted imaging(DWI)[field-of-view optimized and constrained undistorted single-shot(FOCUS)]of the pancreas.We hypothesized that a combination of these techniques would improve DWI image quality without prolonging the scan time but would influence the apparent diffusion coefficient calculation.AIM To evaluate the efficacy of DLR for image quality improvement of FOCUS of the pancreas.METHODS This was a retrospective study evaluated 37 patients with pancreatic cystic lesions who underwent magnetic resonance imaging between August 2021 and October 2021.We evaluated three types of FOCUS examinations:FOCUS with DLR(FOCUS-DLR+),FOCUS without DLR(FOCUS-DLR−),and conventional FOCUS(FOCUS-conv).The three types of FOCUS and their apparent diffusion coefficient(ADC)maps were compared qualitatively and quantitatively.RESULTS FOCUS-DLR+(3.62,average score of two radiologists)showed significantly better qualitative scores for image noise than FOCUS-DLR−(2.62)and FOCUS-conv(2.88)(P<0.05).Furthermore,FOCUS-DLR+showed the highest contrast ratio and 600 s/mm^(2)(0.72±0.08 and 0.68±0.08)and FOCUS-DLR−showed the highest CR between cystic lesions and the pancreatic parenchyma for the b-values of 0 and 600 s/mm2(0.62±0.21 and 0.62±0.21)(P<0.05),respectively.FOCUS-DLR+provided significantly higher ADCs of the pancreas and lesion(1.44±0.24 and 3.00±0.66)compared to FOCUS-DLR−(1.39±0.22 and 2.86±0.61)and significantly lower ADCs compared to FOCUS-conv(1.84±0.45 and 3.32±0.70)(P<0.05),respectively.CONCLUSION This study evaluated the efficacy of DLR for image quality improvement in reduced-FOV DWI of the pancreas.DLR can significantly denoise images without prolonging the scan time or decreasing the spatial resolution.The denoising level of DWI can be controlled to make the images appear more natural to the human eye.However,this study revealed that DLR did not ameliorate pancreatic distortion.Additionally,physicians should pay attention to the interpretation of ADCs after DLR application because ADCs are significantly changed by DLR.

小视野DWI在中轴型脊柱关节炎定量评估中的价值

[目的]探讨小视野弥散加权成像(r-FOV DWI)在中轴型脊柱关节炎定量评估中的应用价值。[方法]前瞻性收集2019年11月至2021年11月间因慢性腰痛、临床怀疑中轴型脊柱关节炎同时行小视野和全视野DWI成像者112例。首先,2名研究者对DWI图像质量进行主、客观评价,主观评估包括图像解剖细节、变形、伪影、整体图像质量的评分,客观评估包括图像信噪比和对比噪声比。然后,相同2名研究者分别在小视野和全视野DWI上测量3组(活动组、非活动组和对照组)的表观扩散系数(ADC)值,评价观察者间的测量一致性,比较ADC值有无差异。绘制两种技术ADC值受试者工作特征曲线并比较曲线下面积(AUC)。[结果]最终纳入102例,根据国际脊柱关节炎协会(ASAS)MRI工作组诊断标准分为3组,其中活动组32例、非活动组29例、对照组41例。小视野DWI图像的主观评分高于全视野DWI[4(3~4)vs.3(3~3),P<0.05];小视野DWI图像的客观评分高于全视野DWI信噪比:6.58(5.05~10.38)vs.4.46(2.37~10.04)对比噪声比:2.04(-1.14~8.29)vs.0.97(-8.19~7.12);P<0.05。两名观察者测量的组间一致性0.60~0.74(ICC相关系数);活动组、非活动组和对照组的ADC值均具有显著差异(P<0.05),小视野DWI测量的ADC值高于全视野DWI。非活动组vs.对照组AUC结果显示,全视野DWI在非活动组vs.对照组中优于小视野DWI,其他组别(病变组vs.对照组、活动组vs.非活动组)两种DWI技术没有统计学差异(P<0.05)。[结论]小视野DWI可用于中轴型脊柱关节炎的定量评估,且其图像主观评分和信噪比较全视野DWI高。

Flexible reduced field of view magnetic resonance imaging based on single-shot spatiotemporally encoded technique

In many ultrafast imaging applications, the reduced field-of-view（r FOV） technique is often used to enhance the spatial resolution and field inhomogeneity immunity of the images. The stationary-phase characteristic of the spatiotemporallyencoded（SPEN） method offers an inherent applicability to r FOV imaging. In this study, a flexible r FOV imaging method is presented and the superiority of the SPEN approach in r FOV imaging is demonstrated. The proposed method is validated with phantom and in vivo rat experiments, including cardiac imaging and contrast-enhanced perfusion imaging. For comparison, the echo planar imaging（EPI） experiments with orthogonal RF excitation are also performed. The results show that the signal-to-noise ratios of the images acquired by the proposed method can be higher than those obtained with the r FOV EPI. Moreover, the proposed method shows better performance in the cardiac imaging and perfusion imaging of rat kidney, and it can scan one or more regions of interest（ROIs） with high spatial resolution in a single shot. It might be a favorable solution to ultrafast imaging applications in cases with severe susceptibility heterogeneities, such as cardiac imaging and perfusion imaging. Furthermore, it might be promising in applications with separate ROIs, such as mammary and limb imaging.

常规视野与小视野IVIM扩散加权成像在正常胰腺的对比研究

目的比较正常胰腺组织小视野高分辨率多b值扩散加权成像(reduced field of view,r-FOV DWI)与常规视野多b值扩散加权成像(conventional field of view,c-FOV DWI)体素内非相干运动(IVIM)模型中各参数值及图像质量的差异。方法对59位经超声及临床资料未发现胰腺异常的志愿者行胰腺常规平扫、r-FOVDWI及c-FOVDWI相同多b值(b=0,25,50,75,100,150,200,300,400,600,800 s/mm2)序列扫描,将扫描图像传送到GE ADW4.6工作站,在胰头部测量相应的ADC_(tot),D,D*和f值;采取盲法由两名腹部影像诊断医师利用4分法分别对r-FOV DWI及c-FOV DWI图像质量进行评分。利用SPSS 19.0软件对数据进行统计学分析。结果胰头小视野及常规视野多b值双指数模型的ADCtot(10-3mm2/s),D(10-3mm2/s),D*(10-3mm2/s)和f值分别为1.58±0.22,1.24±0.22,99.61±56.25,0.24±0.06;1.64±0.24,1.17±0.26,54.34±49.67,0.24±0.07;两组间ADC_(tot),D及f值无统计学差异(P>0.05),而小视野中的D*值明显高于常规视野,差异具有统计学意义(P=0.000);r-FOV DWI图像质量4分法评分明显高于c-FOV DWI,差异具有统计学意义(P=0.000);2名影像诊断医师分别对图像质量评分一致性良好(Kappa=0.668)。结论与c-FOV DWI相比,r-FOV DWI在保证各参数值相对稳定的同时,可以提高胰腺DWI图像分辨率及图像质量。

不同高b值小视野扩散加权成像对非肌层与肌层浸润性膀胱癌的鉴别价值

目的分析非肌层浸润性膀胱癌(NMIBC)和肌层浸润性膀胱癌(MIBC)的征象差异,探究磁共振(MRI)采用不同高b值小视野(r FOV)扩散加权成像(DWI)对两者的鉴别价值。方法收集宜宾市第一人民医院2014年10月至2017年7月经手术病理证实的65例膀胱癌患者(109个癌灶,其中NMIBC 72个,MIBC 37个)的临床和MRI资料,并分为NMIBC组和MIBC组,分析其术前常规MRI中b值为800 s/mm^2、1 500 s/mm^2,2 000 s/mm^2时rFOV DWI图像的不同征象,以及b值为1 500 s/mm^2时两组的表观扩散系数(ADC值)比较,另选50例正常志愿者膀胱壁与两者做ADC值比较。结果两组间"马蹄征"、肿瘤下方低信号、肿瘤体积缩小、肿瘤信号减低、肿瘤下方膀胱壁高信号5项DWI征象比较差异均有统计学意义(P<0.05);NMIBC征象为"马蹄征"、肿瘤下方低信号、肿瘤体积缩小、肿瘤信号减低,其阳性率分别为88.89%、83.33%、59.72%%、61.11%;MIBC征象为肿瘤下方膀胱壁高信号,阳性率为86.49%;NMIBC、MIBC和正常膀胱壁的ADC平均值间比较差异均有统计学意义(P<0.05)。结论 NMIBC和MIBC在rFOV不同高b值DWI成像时的征象存在明显差异,b值为1 500 s/mm^2时的ADC值有助于两者鉴别。不同高b值rFOV DWI图像对比观察在两者鉴别中具有重要价值。