Ultrasound and Imaging of the Prostate

Transrectal Ultrasound of the Prostate

Ultrasound is a technique in which sound waves are used to make images of the organs and structures in the pelvic area. In men, this includes the prostate gland, bladder, and seminal vesicles. A transrectal ultrasound is the most common test used to examine the male pelvic organs. An instrument called a transducer is shaped to fit into the rectum, where it sends reflected sound waves to a computer. In some cases, a biopsy of the prostate is done during a transrectal ultrasound.

The images obtained during the transrectal ultrasound give your doctor an idea of the size of your prostate as well as any potential abnormalities.

Magnetic Resonance Imaging (MRI)

An MRI is a noninvasive imaging technique that uses a magnetic field, radio waves, and a computer to produce very clear pictures of internal structures without the use of x-rays. Images from an MRI can provide physicians with information that may not be visualized adequately using x-rays, ultrasound, or computed tomography (CT).

The main reason clinicians get an MRI of the prostate is to evaluate a patient for prostate cancer after a prostate biopsy has confirmed cancer. The MRI can allow clinicians to evaluate the prostate and nearby lymph nodes to distinguish between benign and malignant areas. An MRI of the prostate is also sometimes used to evaluate prostatitis or BPH. Researchers have also found that MRI may be helpful in predicting the chances prostate cancer will return and spread following radiation therapy. (McKenna)

An MRI is a painless procedure and typically takes about 45 to 60 minutes, not including preparation time. Most MRI machines require patients to lie down and be slid into a tube that can cause anxiety and panic in people who are claustrophobic. Men who know they are claustrophobic can request a sedative before the procedure. Some facilities have open MRI machines that are much less confining.

Men need to tell their doctor about any implanted devices they may have, such as a pacemaker or cochlear implant, as certain items should not be subjected to MRI scans. An MRI also is not recommended for individuals who weight more than 300 pounds, who cannot lie on their back for 30 to 60 minutes, or who have severe acid reflux.

PET/CT Scan

A positron emission tomography (PET) is a type of nuclear imaging technique that uses small amounts of radioactive materials to diagnose or treat diseases. Clinicians turn to a PET scan for prostate cancer to help them determine if the cancer has spread and if it has, where it is located. A PET scan is noninvasive and painless except for the intravenous injections of the radioactive materials.

The injected substance is a radioactively tagged glucose (sugar), which cancer cells are attracted to because they use glucose to reproduce. After injection of the radioactive substance, the PET scanner is passed over the body to determine the location of cancer cells.

Combining computed tomography (CT) with PET increases the specificity and sensitivity of the examination and helps clinicians more precisely identify where cancer has spread. Unlike a PET scan, a CT scan utilizes x-rays, which are focused from various points around the patient to get the images.

A study published in the September 2009 issue of The Journal of Nuclear Medicine reported that the PET/CT scan using the radioactive marker choline is capable of detecting recurring prostate cancer sooner than conventional imaging techniques in some men who have had a prostatectomy. Choline has been shown to be more accurate than conventional CT and MRI in detecting recurrent prostate cancer.

References

Castellucci P et al. Influence of trigger PSA and PSA kenetics on 11C-choline PET/CT detection rate in patients with biochemical relapse after radical prostatectomy. J Nuc Med 2009 Sept; 50(9): 1394-400

McKenna DA et al. Prostate cancer: role of pretreatment MR in predicting outcome after external-beam radiation therapy—initial experience. Radiology 2008 Apr; 247(1): 141-46