MRI-Guided Biopsy Benefits

Who invented the microscope? Credit for putting multiple lenses in a tube in order to gain a magnified view goes to two Dutch lens makers in the 1590s, Zacharias Jansen and his father, Hans. One of the first uses of microscopy in medicine occurred around 1650 when a Jesuit priest named Athanasius Kirchner saw little “worms” in blood samples, and he thought they might be connected to the plague. Medicine would not be where it is today without the ability to examine the sources of disease at great magnification.

Diagnosing prostate cancer currently requires a needle biopsy to remove very tiny threads of prostate tissue for evaluation under a microscope. (You can see a pathologist using a microscope to examine tissue, and how the magnified tissue looks, at http://www.hopkinsmedicine.org/hmn/F02/feature2.html) Until very recently, the standard biopsy has been guided by transrectal ultrasound (TRUS guided biopsy) and usually involves 10-14 systematic but random needles. Thanks to multiparametric MRI (mpMRI), the biopsy need not be random because the scan shows any locations that are suspicious for tumor.

However, a targeted biopsy done under real-time MRI (MRI guided targeted biopsy) is not yet feasible for everyone. Many urologists, who lack access and training for the use of MRI, rely on some form of co-registration or “fusion” of previously captured MR images with real-time ultrasound (MRI/US fusion guided biopsy). There are two kinds of fusion: a) cognitive fusion means the doctor looks at the MR images and mentally calculates where to direct the TRUS guided biopsy needles, and b) computer software that merges the two types of imaging and creates a 3D “cartoon” showing the suspicious area and suggesting needle trajectories into it.

A new study offers a comparative biopsy yield among three different image-guided biopsy methods:

  • Systematic TRUS guided biopsies
  • Cognitive fusion guided biopsies
  • In-bore real-time MRI guided biopsies.[i]

Acar et al. (2015) identified 100 patients who were suspected of having prostate cancer based on screening but had no previous biopsy. All patients underwent mpMRI using T2-weighted imaging, diffusion weighted imaging, and dynamic contrast enhanced MRI. They were then assigned to one of three arms for diagnosis, and the men with prostate cancer were treated with radical prostatectomy. Finally, the specimens from surgery were compared with the biopsy findings, and the results are summed up in this table:

Type of biopsy Number of patients Positive diagnosis Detection of significant cancer identified from RP specimens
TRUS guided, systematic 37 51.3% 69.1%
Cognitive fusion 49 55.1% 70.3%
Real time in-bore MRI 14 71.4% 90%

In terms of the most accurate biopsy results, mpMRI targeted biopsies offer patients the greatest benefit for the fewest needles. There is a benefit to the pathologist, thanks to the “direct hit” of the needles, because targeted biopsy needles have the best probability of containing any significant cancer that lurks at the tumor’s core. Finally, there is benefit to the patient’s doctor who can discuss the nature of the patient’s disease and the most appropriate treatment choices. Though the study is small, it shows how mpMRI is the most advantageous guidance for prostate biopsy.

 


 

[i] Acar Ö, Esen T,  Çolako?lu B et al. Multiparametric MRI guidance in first-time prostate biopsies: what is the real benefit? Diagn Interv Radiol. 2015 May 29. doi: 10.5152/dir.2015.46014. [Epub ahead of print]

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