SIU 2018: Multiparametric Ultrasound in Diagnosis of Prostate Cancer

Seoul, South-Korea ( Dr. Rukstalis gave a great talk about the role of “multiparametric” ultrasound in the diagnosis (and eventually treatment?) of prostate cancer – his terminology of multiparametic is slightly tongue-in-cheek, to take over the terminology from the MRI world. The basis for this talk is the concept that the future is merging diagnostics with therapeutics. Eventually, it will be hard to separate these two into distinct steps – and so, those who the diagnostics will do the therapeutics. If urologists are not careful, this can transition completely to radiology – in order to counteract this, we need to be on the forefront of the imaging diagnostics as well!

His talk focused on the improvements and new parameters / modes of ultrasound that can help improve ultrasound imaging, hopefully to a quality that can compete with mpMRI. More importantly, if it gets to that point, its ease of use and combination with biopsy can make this a more effective tool for prostate cancer diagnosis – no need for 2 appointments, 2 different rectal preparations, fusion of imaging modalities, etc. 

Prostate ultrasound, as with all ultrasound, is based on imaging obtained from pulses sound waves being sent at the tissue at a certain frequency, hitting the tissue and bouncing back – this information is processed into an image. However, the technology is rapidly improving – with much of the work being done in Europe and Asia. 

There are 3 modes to his multiparametric ultrasound (mpUS) of the prostate.
1. B-mode (brightness mode) or Grey-scale – the “standard” imaging we think about when we do ultrasounds. Provides a 2D representation of the tissue. 
  • Traditionally, probes have used frequencies between 4-9 MHz – but this limits resolution in the tissue to 0.39 mm, which is not detailed enough to find and diagnose prostate cancer! Hence, the reason we moved to mpMRI.
  • However, there are newer probes with frequency of 29 MHz – with resolution of tissue down to 70 micrometers. As context – capillaries are 50 micrometers and single prostate glands are ~70 micrometers. Diameter of clinically significant PCa is ~ 5 mm.
  • Interestingly, due to increased resolution, PCa actually appears hyperechoic on this!
2. Doppler US of the prostate – employs M-mode (motion mode) to measure the doppler shift (effect on sound of the speed of flow). May use contrast agents (only 1 approved in the FDA and not specifically for prostate ultrasound).
  • Prostate cancer tends to be hypervascular – increased blood flow
  • Prior studies from European and Asian cohorts have demonstrated increased sensitivity for PCa by targeting hypervascular areas
3. Elastography – ultrasound probes generate pressure waves that hit tissue and return to the probe. This can be used to measure the “stiffness” of the tissue, similar to way we look for “nodules” on DRE.
  • Malignant tissue is more stiff than surrounding benign tissue
  • Elastography has been demonstrated in smaller trials to have good sensitivity and specificity for PCa diagnosis
Therefore, the new mpUS is a combination of these three modes. Regions with hyperechoic, hypervascular regions that are poorly elastic are highly concerning for cancer – similar to PIRADS 5 lesions on mpMRI!
  • There is a likert scale for ultrasound reporting
There is still work that needs to be done to improve the technology, but at some point in the future, we will need to compare to mpMRI. There is still a role for mpMRI, but it will be better to get a better ultrasound guided initial prostate biopsy in patients – and reduce the need for future biopsies and mpMRI! 

Presented By: Dan Rukstalis, Professor of Urology at Wake Forest University School of Medicine, Winston Salem, North Carolina

Written By: Thenappan Chandrasekar, MD, Clinical Instructor, Thomas Jefferson University Twitter: @tchandra_uromd, @TjuUrology at the 38th Congress of the Society of International Urology - October 4- 7, 2018 - Seoul, South Korea

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