Maas Marnix C, Fütterer Jurgen J, Scheenen Tom W J
From the Department of Radiology, Radboud University Nijmegen Medical Centre, Nijmegen, the Netherlands.
Invest Radiol. 2013 Nov;48(11):779-86. doi: 10.1097/RLI.0b013e31829705bb.
Computed diffusion-weighted magnetic resonance imaging (cDWI) refers to the synthesizing of arbitrary b value diffusion-weighted images (DWI) from a set of measured b value images by voxelwise fitting. The objectives of this study were to quantitatively analyze the noise and the contrast-to-noise ratio (CNR) in cDWI as a function of b value by numerical simulations and by measurements in patients with prostate cancer and to compare cDWI to directly measured DWI at a b value of 1400 s/mm2.
Numerical simulations were performed to assess image noise and CNR in both cDWI and regular DWI. Forty-two patients with prostate cancer (age, 51-73 years; prostate specific antigen level, 0.5-30 ng/mL; and biopsy Gleason score, 6-9) received 2 DWI examinations at 3.0 T (one with b values of 100, 500, and 1400 s/mm2 and another with b values of 0, 100, 400, and 800 s/mm2) to create cDWI images at arbitrary b values, both with and without incorporating a b value of 0 s/mm2 in their calculation. Regions of interest were drawn to compare the scan time adjusted CNR (CNR eff) between cDWI and directly measured DWI at b = 1400 s/mm2 on tumor-suspicious lesions and normal-appearing regions.
In the numerical simulations, noise depended strongly on the b value, the diffusion coefficient, and the signal intensity at a b value of 0 s/mm2 in cDWI but not in regular DWI. The CNR between simulated tumor and normal regions showed a continuous increase with increasing b value. Both these findings were also observed in tumor-suspicious and normal-appearing regions in in vivo data. In vivo prostate DWI at a b value of 1400 s/mm2 showed a similar CNR eff between the tumor-suspicious regions and the normal-appearing tissue in cDWI as in the directly measured DWI (P = 0.395).
The CNR eff between tumor-suspicious and normal-appearing prostate tissue in DWI images at a b value of 1400 s/mm2 is comparable in cDWI and directly measured DWI. Computed DWI at even higher b values, calculated from measured images with b values between 0 and 800 s/mm2, yields higher CNR eff than measured DWI, which may be of clinical aid in the management of prostate cancer.
计算机扩散加权磁共振成像（cDWI）是指通过体素拟合从一组测量的b值图像中合成任意b值的扩散加权图像（DWI）。本研究的目的是通过数值模拟以及对前列腺癌患者的测量，定量分析cDWI中噪声和对比噪声比（CNR）随b值的变化情况，并将cDWI与在b值为1400 s/mm²时直接测量的DWI进行比较。
进行数值模拟以评估cDWI和常规DWI中的图像噪声和CNR。42例前列腺癌患者（年龄51 - 73岁；前列腺特异性抗原水平0.5 - 30 ng/mL；活检Gleason评分6 - 9）在3.0 T下接受2次DWI检查（一次b值为100、500和1400 s/mm²，另一次b值为0、100、400和800 s/mm²），以创建任意b值的cDWI图像，计算时分别纳入和不纳入b值为0 s/mm²的图像。绘制感兴趣区域以比较在b = 1400 s/mm²时，cDWI与直接测量的DWI在可疑肿瘤病变和正常区域的扫描时间校正CNR（CNR eff）。
在数值模拟中，cDWI的噪声强烈依赖于b值、扩散系数以及b值为0 s/mm²时的信号强度，而常规DWI则不然。模拟肿瘤与正常区域之间的CNR随b值增加持续升高。在体内数据的可疑肿瘤和正常区域也观察到了这两个结果。在b值为1400 s/mm²时，体内前列腺DWI显示，cDWI中可疑肿瘤区域与正常组织之间的CNR eff与直接测量的DWI相似（P = 0.395）。
在b值为1400 s/mm²的DWI图像中，cDWI与直接测量的DWI在可疑肿瘤与正常前列腺组织之间的CNR eff相当。从b值在0至800 s/mm²之间的测量图像计算得到的更高b值的cDWI，其CNR eff高于测量的DWI，这可能有助于前列腺癌的临床管理。
