Department of Radiology, Mayo Clinic, Rochester, Minnesota 55905, USA.
Magn Reson Med. 2009 Dec;62(6):1457-65. doi: 10.1002/mrm.22091.
A novel imaging technique is described in which the mode conversion of longitudinal waves is used for the qualitative detection of stiff lesions within soft tissue using magnetic resonance elastography (MRE) methods. Due to the viscoelastic nature of tissue, high-frequency shear waves attenuate rapidly in soft tissues but much less in stiff tissues. By introducing minimally-attenuating longitudinal waves at a significantly high frequency into tissue, shear waves produced at interfaces by mode conversion will be detectable in stiff regions, but will be significantly attenuated and thus not detectable in the surrounding soft tissue. This contrast can be used to detect the presence of stiff tissue. The proposed technique is shown to readily depict hard regions (mimicking tumors) present in tissue-simulating phantoms and ex vivo breast tissue. In vivo feasibility is demonstrated on a patient with liver metastases in whom the tumors are readily distinguished. Preliminary evidence also suggests that quantitative stiffness measurements of stiff regions obtained with this technique are more accurate than those from conventional MRE because of the short shear wavelengths. This rapid, qualitative technique may lend itself to applications in which the localization of stiff, suspicious neoplasms is coupled with more sensitive techniques for thorough characterization.
本文介绍了一种新的成像技术，该技术利用磁共振弹性成像（MRE）方法，通过纵波的模式转换，对软组织内的硬性病变进行定性检测。由于组织的粘弹性，高频剪切波在软组织中迅速衰减，但在硬性组织中衰减较少。通过向组织中引入显著高频的低衰减纵波，在界面处由模式转换产生的剪切波在硬性区域是可检测到的，但在周围的软组织中会显著衰减，因此无法检测到。这种对比可用于检测硬性组织的存在。该技术可用于检测组织模拟体模和离体乳房组织中存在的硬性区域（模拟肿瘤）。在一名患有肝转移的患者中进行了体内可行性验证，结果表明，该技术可以很容易地分辨出肿瘤。初步证据还表明，由于剪切波的短波长，该技术获得的硬性区域的定量硬度测量比传统 MRE 更准确。这种快速的定性技术可能适用于将硬性可疑肿瘤的定位与更敏感的全面特征描述技术相结合的应用。
