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A couple early warning signs of possible prostate cancer are a high level of prostate-specific antigen (PSA) in the bloodstream and an abnormal digital rectal exam (DRE). When either occurs, a prostate biopsy is usually done to see if that warning sign is being caused by prostate cancer. New research indicates that images from an MRI scan can help improve biopsy results.
The correct descriptive term for this type of imaging is “MRI Ultrasound Fusion Guided Biopsy.” However, other terms are frequently used and refer to the same process. These terms include Fusion-Guided Biopsy, Fusion Biopsy, MRI/US Biopsy,MRI-Ultrasound Fusion Biopsy, and simply MR Fusion Biopsy. Because these terms can be confusing, we prefer the technically correct name for this procedure.
How does it work?
A urologist must be specially trained to read prostate MRI and identify the area of interest (suspected tumor). The urologist must also “segment” or input the prostate outline into the computer to facilitate matching MRI and TRUS shapes. Special software is necessary that can recognize both types of images, assign “coordinates” to each type, and match (register) the images, coordinate by coordinate. This is called image registration or co-registration, and it overlays the live TRUS image onto the static MRI image. The result a synthetic 3D image of the patient’s gland that is quite accurate, but not perfect, due to small variables such as patient movement or inaccurate segmentation. The final 3D image can be manipulated on the computer screen so the urologist can view it from every angle, and the suspicious area is highlighted within the image.
To get the idea, imagine you insert several photos of your face from various angles into a computer that can scan and read them. Now imagine a friend taking a video all around your face, and the video image inputted into the same computer, which matches the live video with the still photos. The computer now blends all the images and creates a 3D view of you that looks like a Pixar image of yourself. Your friend can use the computer mouse to rotate the Pixar image of you from different angles. The resemblance may be quite remarkable, but there may be some slight differences or distortions.
Prostate MRI Ultrasound Fusion imaging is done in the urologist’s office to help identify the target area for the biopsy and guide needles into it.
Is It Accurate?
Some experts agree that targeted MRI Ultrasound Fusion Guided Biopsies are generally more accurate than traditional TRUS biopsies (ultrasound only) in detecting and diagnosing prostate cancer. Depending on the software or fusion device, the computer may help plan the sampling based on the target area(s) within the gland as depicted in the fused images. The urologist using fusion technology can follow the plan or override it. This includes the number of needles and angle of approach. The real-time TRUS verifies the placement of the needles, which show up on the monitor.
Comparison of MRI-guided biopsy vs. fusion-guided biopsy
|MRI-guided biopsy||MRI Ultrasound Fusion Guided Biopsy|
Conventional detection methods
Prostate ultrasound is done using a wand inserted into the rectum. Thus, it is called Transrectal Ultrasound, or TRUS. The wand transmits sound waves through the rectal wall toward the prostate gland. The waves bounce off of different kinds of tissue, and register as black-and-white images on a computer monitor. Although abnormal prostate tissue may show up differently than normal tissue, the information about the true nature of the abnormality may be limited.