胸部计算DWI(computed DWI,cDWI)用于提高肺结节或肿块鉴别能力的最佳b值选择
Which is the Appropriate b Value Selection at Chest Computed Diffusion-Weighted Imaging for Improving Pulmonary Nodule/Mass Differentiation?
高b值DWI可显著降低T2透射效应，图像对比度更高。但临床扫描的b值不能太高，一方面受MRI梯度场硬件的限制，另一方面高b值下涡流、磁敏感伪影和T2*衰减效应显著，图像SNR较低、明显畸变。因此临床常采用较低分辨率和较低b值采集DWI数据。计算DWI(computed DWI,cDWI)方法在一定程度上可克服以上问题，并满足临床需求。
cDWI的基本原理是：首先通过DWI数据获得ADC图，其次假设ADC和b0图已知量，自定义b值，通过公式(1)计算出任意b值的DWI图像。既往研究表明，cDWI图像可更好地显示病变，已经用于宫颈癌、前列腺癌、卵巢癌、肝脏转移瘤等的诊断和鉴别诊断。
Computed diffusion-weighted imaging (cDWI) is the newly proposed method to generate DWI with arbitrary b values from acquired DWIs (aDWIs) with different b values.
In addition, cDWI reportedly allows higher b value images to be obtained with a good signal intensity ratio (SNR), because it can suppress background noise while maintaining the original lesion signal.
Blackledge MD, et al. Radiology 2011;261:573–581
Therefore, the choice of b value is clinically important, and may have an influence to diagnostic performance of cDWI.
However, there was no major reports regarding appropriate b value selection for pulmonary nodule/mass differentiation at chest cDWI.
To determine an appropriate b value selection for improving pulmonary nodule/mass differentiation at chest cDWI.
By our propriety software, cDWIs with six different b values, i.e., 600 (cDWI600), 800 (cDWI800), 1000 (cDWI1000), 1200 (cDWI1200), 1400 (cDWI1400), and 1600 (cDWI1600) s/mm2, were computationally generated from actually acquired DWIs (aDWI) with b values at 0 and 500 s/mm2.
Conclusion
On diagnosis of pulmonary nodules/masses, cDWIwould be better to be generated from aDWI with 500 s/mm2 as b value at 800 - 1200 s/mm2, and considered at least as valuable as aDWI with 1000 s/mm2.
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