ABSTRACT

The increased stiffness of cancers relative to normal tissues and benign tumors has long been important in physical diagnosis. Recently, it has become possible to image this characteristic using strain imaging in ultrasound (US) or shear wave imaging in both US and magnetic resonance scanning. US stiffness imaging has been applied to a number of tumors including breast cancer, prostate cancer, thyroid cancer, and lymph node metastasis. By far, most research has been done on breast cancer diagnosis with reported ROC curve areas (AUC) of 0.89 to 0.95 for distinguishing benign from cancerous lesions for strain elastography when used with standard B-mode US. Widespread clinical adoption has been slow, however, due to difculties in training both operators and readers to properly acquire and interpret the elastograms. Shear wave elastography has shown promise, but the potential for falsely low shear wave speed estimates in cancers has recently been demonstrated. Lymph node strain elastography has given good results with AUC values of 0.87 to 0.91. Shear wave evaluation of lymph nodes, thyroid and prostate is still at an early stage with prostate results showing the most promise. Thyroid nodule evaluation using strain elastography has been challenging with lower sensitivity and specicity values than in breast or lymph nodes. Better results have been reported when strain ratios are calculated instead of using a visual scoring system.