What is a MRI?
When placed in the strong magnetic field of an MRI scanner, the protons of hydrogen atoms in the prostate tissue align with the magnetic field. Radio frequency pulses applied to that field produce images that the radiologist can review when the protons are displaced by this alignment.
The patient is placed in a magnetic field, radio waves are applied in pulses and the protons in the hydrogen cells are able to give off a signal that can be visually detected. By applying different “weighting” to the signal, more specific information can be elucidated from the images. The radiologist uses terms like T-2 weighting, dynamic contrast enhanced imaging and diffusion-weighted imaging. All of these methods of manipulating the pulse and images lead to greater in-depth information of the man’s prostate anatomy.
All the man has to do is be very still during the test and make sure the insurance company pays for the test!
Prostate cancer occurs most commonly in the peripheral area of the prostate. That is why the urologist always does a DRE. The rectal surface of the prostate is where most cancers reside. By using the MRI techniques, the urologist, with the assistance of the radiologist, can determine more than we can learn with ultrasound, CAT scan or PET scanning.
As you might imagine, the ability to get this information will be determined by the quality of the MRI equipment used, and the experience of the MRI radiologist interpreting the study and the coordination of detailed information provided by the urologist.
As in all radiology tests, there are conditions that can make the test less accurate. Prostatitis, benign prostatic hypertrophy, post radiation, post-surgery, post biopsy and hormone ablation must all be taken into consideration within interpreting the MRI.
To help understand how an MRI could give a tissue diagnosis, we must understand the basics of tumor biology. Cancers, particularly high-grade cancers, typically have higher cell density and more complex microstructure that restricts diffusion of water. In simple terms, cancer cells tend to be more disorganized and clump together and be more chaotic than normal tissue. This phenomenon is detected as a bright white image on one type of MRI signal. So by manipulating the characteristics of the MRI signal, the radiologist can get information about the types of cells that might be in the prostate.
MRI, CT and PET scans can all give information about local spread of prostate cancer and lymph node involvement of prostate cancer. But only MRI can come close to helping determine cancer from non-cancer and low grade cancer from high grade cancer.
This is a very simplistic overview of what MRI can do. The radiologist can inject many types of biologically active compounds into the blood stream that can be taken up by different types of cells and can give even more information.
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