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MRI, CT, and other imaging tests in diagnosis of prostate cancer

Posted Sep 17 2008 1:52am

Although bone scans are the primary and most important imaging test used in the diagnosis of prostate cancer, several other imaging tests also have significant — if slightly less central — roles. If you are one of the people who needs one of these tests, it will help you to have some idea what is going on.

When Is an MRI Appropriate? 

Magnetic resonance imaging or MRI uses strong magnetic fields instead of x-rays to produce images of parts of the body. MRI scans can be very helpful in looking at prostate cancer. By producing a very clear picture of the prostate gland, an MRI can show whether the cancer has spread outside the gland into the seminal vesicles or bladder. Unfortunately the cost of carrying out MRI examinations on every patient who might have prostate cancer extending beyond the prostate capsule would be enormous. Thus, from a diagnostic point of view, the important question is, “When is an MRI really appropriate?”

It is hard to give a precise answer to this question, but some form of MRI may be most apppropriate in a patient at clear risk for T3NxM0 or T4NxM0 disease. Such patients are unlikely to be able to receive surgery alone with curative intent. So, in order to determine whether treatment with curative intent is even possible, one needs to have the clearest possible understanding of the extent of the cancer before deciding how to proceed.

MRI can be carried out either using traditional “whole body” MRI scanning or through the use of “endorectal coil” MRI. However, the optimal MRI technique for the staging of prostate cancer has not been established. At the present time, endorectal MRI appears more accurate than body-coil MRI in the local staging of the primary tumor. However, this is an area of rapid evolution, and currently experimental imaging techniques may become standard within the next few years, making highly accurate visualization of cancer in and around the prostate possible for clinical staging purposes (and for the planning of surgery, radiotherapy, and other treatment techniques).

The Role of CT Scans

CT or computerized tomography is a computer-controlled x-ray procedure that produces detailed cross-sectional images of the body using hundreds of x-ray-like images. This test can help to tell whether prostate cancer has spread beyond the prostate to other organs. However, CT scans are much better at identifying skeletal structures than soft tissue structures.

The role of CT or CAT scanning in the diagnosis of prostate cancer is really very limited today because almost anything one can do with a CT scan can be done just as well or better with an MRI scan. The one place where CT scans appear to have a small advantage is in the early identification of soft tissue metastases (as opposed to bone metastases). However, the need for this type of information outside clinical trials is relatively limited.

Color Döppler Ultrasound

A select group of subspecialists have been strong advocates for the use of color Döppler ultrasound imaging in the diagnosis of prostate cancer. They have claimed that the use of this technique permits much greater accuracy in the identification of prostate cancer, and also in carrying out appropriate prostate biopsies.

It is hard to know whether such claims are really accurate because of the limited use of this equipment and the lack of controlled trials. However, a study published in 2007 in the Journal of Urology, and involving 690 men, appears to support the value of color Döppler ultrasound compared to standard ultrasound-guided biopsy as a highly accurate method which is helpful in the pretreatment staging and grading of prostate cancer.

The ProstaScint Imaging Technique

The ProstaScint imaging technique first became available in the mid 1990s as a highly promising technique that appeared to be able to identify prostate cancer that had escaped from the prostate and into the pelvic lymph nodes and other surrounding tissues. As such, this test gave hope that it would be possible to better identify those patients in whom surgery alone as a treatment carried out with curative intent would not be feasible.

Unfortunately, the ProstaScint test has never been able to achieve its initial promise, despite every effort by the manufacturer to improve technical aspects of the means to image the indium-111-labeled monoclonal antibody on which the test is based.

When  this test works well, using the current “fusion imaging” process, it can produce remarkable results, but the repeatability of these results and the effort needed to gain the necessary image quality appear to be problematic for the majority of centers.

Having said that, a patient who is at high risk for micrometastatic disease may wish to seek out a center with the technical ability to use the ProstaScint fusion imaging process well — if his insurer will cover the use of the process. There seems to be little doubt that for some patients this technique has provided great assistance in identifying the precise location of potentially troublesome tumors.

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