Real-time Tissue Elasticity Imaging (Elastography) for Prostate Cancer Detection

Stiffness of tissue is important information for cancer diagnosis, and it is also very commonly used for prostate cancer diagnosis. Digital rectal examination (DRE) is the easiest method to detect prostate cancer, but it has limited reproducibility, and lacks objectiveness. The positive predictive value of DRE alone has been shown to be as low as 30%. The second easiest imaging technique used for tumor location is transrectal ultrasonography (TRUS). One of the drawbacks of this technique is that location of tumors is often misjudged. In TRUS, cancer lesions are initially detected as low echoic lesions, but it is now recognized that cancer lesions may appear as hypo-, hyper-, or iso-echoic areas. For this reason, most urologists recognize that TRUS tends to provide guidance for biopsy, but is not used as a screening tool. Combination with DRE does not improve the detection of prostate cancer. Magnetic resonance imaging (MRI) is currently a promising tool to detect prostate cancer, and was reported to significantly increase the accuracy of prostate cancer diagnosis. Various studies have shown that MRI has sensitivity ranging from 51~95%, and specificity from 67~100%. However, the disadvantage of MRI is its lack of real-time feedback for prostate biopsy. The ultrasound real-time elasticity imaging system (Elastography) is a new technology that visualizes differences in tissue strain by free-hand compression. This technology is popular for use in examining breast lesions. Because breast cancer is harder than the adjacent normal breast tissue, palpation and also Elastography are used in the clinical assessment of breast abnormalities. Similar to breast lesions, prostate cancers generally are hard, and therefore Elastography is applicable for prostate cancer detection. Additionally, Elastography is substantially more useful than MRI because simultaneous TRUS biopsy can be performed viewing both B-mode and Elastography images. However, Elastography for the prostate has many disadvantages compared with that for breast lesions. One is that, whereas the compression site on a breast is visible, making the procedure easy, prostate examination requires the use of a transrectal probe and so the compression site is not visible and range of motion is small, making the procedure difficult (Fig. 1). Another disadvantage is that compared to a breast, the dynamic range of hardness between normal and cancerous tissue in the prostate is narrow (Fig. 2). Because of these handicaps, there have only been a few reports of Elastography regarding prostate disease so far including our own. Konig et al. reported the use of real-