Department of Radiology and Biomedical Imaging, Yale School of Medicine, New Heaven, Connecticut, USA.
Siemens Healthcare, Erlangen, Germany.
Med Phys. 2021 Oct;48(10):5804-5818. doi: 10.1002/mp.15100. Epub 2021 Sep 24.
Prostate cancer remains the second leading cancer killer of men, yet it is also a disease with a high rate of overtreatment. Diffusion-weighted imaging (DWI) has shown promise as a reliable, grade-sensitive imaging method, but it is limited by low image quality. Currently, DWI quality image is directly related to low gradient amplitudes, since weak gradients must be compensated with long echo times.
We propose a new type of MRI accessory, an "inside-out" and nonlinear gradient, whose sole purpose is to deliver diffusion encoding to a region of interest. Performance was simulated in OPERA and the resulting fields were used to simulate DWI with two-compartment and kurtosis models. Experiments with a nonlinear head gradient prove the accuracy of DWI and apparent diffusion coefficient (ADC) maps encoded with nonlinear gradients.
Simulations validated thermal and mechanical safety while showing a 5- to 10-fold increase in gradient strength over prostate. With these strengths, lesion contrast to noise ratio in ADC maps approximately doubled for a range of anatomical positions. Proof-of-principle experiments show that spatially varying b-values can be corrected for accurate DWI and ADC.
Dedicated nonlinear diffusion encoding hardware could improve prostate DWI.
前列腺癌仍然是男性第二大癌症杀手，但它也是一种过度治疗率很高的疾病。扩散加权成像（DWI）已显示出作为一种可靠的、分级敏感的成像方法的潜力，但它受到图像质量低的限制。目前，DWI 质量图像直接与低梯度幅度相关，因为必须使用长回波时间来补偿弱梯度。
我们提出了一种新型的 MRI 附件，即“内-外”和非线性梯度，其唯一目的是将扩散编码到感兴趣的区域。在 OPERA 中对性能进行了模拟，并使用两室和峰度模型模拟了 DWI。非线性头部梯度的实验证明了使用非线性梯度编码的 DWI 和表观扩散系数（ADC）图的准确性。
模拟验证了热和机械安全性，同时显示出梯度强度比前列腺提高了 5-10 倍。在这些强度下，对于一系列解剖位置，ADC 图中病变与噪声比大约增加了一倍。原理验证实验表明，可以对空间变化的 b 值进行校正，以实现准确的 DWI 和 ADC。
专用的非线性扩散编码硬件可以提高前列腺 DWI 的性能。
