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Shear wave ultrasound elastography of the prostate: Initial results, "Beyond the Abstract," by Richard Memo, MD, FACS and Richard G. Barr, MD, PhD, FAC

BERKELEY, CA (UroToday.com) - There are several decision points when evaluating patients for carcinoma of the prostate. The first is whether the patient should have a PSA test.

When using PSA as a screening method, the patient must be willing to undergo prostate biopsy with its inherent risk of bleeding and possible infection, to the point of sepsis, if the PSA is abnormal. If a cancer is found, a second decision point is whether the carcinoma should be treated surgically or non-surgically. If the patient is not willing to undergo these options, then he should understand the possibilities of his course without PSA, be the prostate benign or malignant. Once the patient with an elevated PSA for his age and/or abnormal digital rectal exam (DRE) agrees to a biopsy, the patient is usually evaluated using transrectal ultrasound (TRUS). However, gray-scale imaging and color flow Doppler abnormalities are often detected, but these modalities are not very sensitive or specific for prostate cancer, and many cancers are not identified on TRUS. This has led to the sextant biopsy method where at least 12 biopsies are taken randomly in the prostate. However this technique triggers a significant number of unnecessary biopsies in patients with no or indolent cancer, that do not need immediate treatment. It also has a high false negative rate (17-21%) of biopsies due to the lack of biopsy guidance to suspicious areas.

"The addition of SWE has the potential to significantly improve the diagnostic role of prostate imaging."
The addition of shear wave elastography (SWE) is another potentially cost effective, non-radiation wave accessing the prostate when done in conjunction with TRUS at the same setting. SWE color mapping of the shear wave velocities onto a B mode image allows for quick categorization of patients’ high or low suspicion of malignancy. For exam, when one sees a blue area (low stiffness), our study suggests that the chance of malignancy is extremely low. On the other hand when one sees a red area corresponding to a high shear wave velocity (high stiffness), there is a high suspicion of malignancy. If there is an intermediate color of yellow or green, there is still a suspicion of a potential malignancy. SWE is limited in that the test works very well in the peripheral zone, where 70-80% of cancers occur, but has not yet been assessed in the central or transitional zones (20-30% of prostate cancers) secondary to these regions having high shear wave velocities and artifacts in the absence of cancer. Another limitation of the examination is that areas containing macro-calcifications often appear stiff and may mimic a malignancy, although macro-calcifications can be characterized from the B-mode image to allow for a differential diagnosis.

Further work and evaluation of elastography of the prostate is needed. Based on our preliminary results, the areas of low stiffness (low shear wave velocity) may not require biopsy, even in the face of elevated PSA. A stiff area (high shear wave velocity), leads one to increased suspicion and even the possibility of re-biopsy. Given the recent recommendations of the US Preventative Task Force of not recommending routine PSA secondary to a large number of negative biopsies and possible complications, the use of SWE prostate to evaluate patients with elevated PSA, and only biopsy those with an abnormal SWE, would significantly decrease the number of unnecessary biopsies required while guiding biopsies to more suspicious areas and therefore detecting most cancers. It is also possible, given our initial high sensitivity and specificity, that instead of a sextant biopsy procedure with at least 2 biopsies in each sextant, biopsies can be limited to the areas that are abnormal on elastography.

Unlike other organs, there has not been an imaging test with high sensitivity and specificity which would help guide diagnosis and treatment of prostate cancer. The addition of SWE has the potential to significantly improve the diagnostic role of prostate imaging. Recent work with MR imaging is also promising. The value of MR imaging is that it can detect cancers in areas of the prostate in which SWE is less sensitive. However, image guided biopsy on MRI is more difficult. The potential fusing of MRI data into an ultrasound machine, which could then perform elastography and guide biopsies, would be extremely helpful in limiting the number of biopsies performed.

 

Written by:
Richard Memo, MD, FACSa and Richard G. Barr, MD, PhD, FACRb as part of Beyond the Abstract on UroToday.com. This initiative offers a method of publishing for the professional urology community. Authors are given an opportunity to expand on the circumstances, limitations etc... of their research by referencing the published abstract.

a Associate Clinical Professor of Surgery, NEOMED
NEO Urology, Youngstown, Ohio

b Professor of Radiology, NEOMED
Radiology Consultants, Inc., Youngstown, Ohio  

 

Shear wave ultrasound elastography of the prostate: Initial results - Abstract

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