Ultrasound scans use sound waves, which are converted by a computer to produce pictures of internal organs.

For transrectal ultrasound scans (TRUS) a narrow tube, or probe, is inserted into the back passage (the rectum) and placed against the prostate gland. High frequency sound waves then produce the picture. The test only lasts a few minutes and although the insertion of the lubricated probe may be a bit uncomfortable the actual scan itself is painless.

TRUS is used in two different ways in prostate cancer: 

•  the scan can be used to guide a fine needle, attached to the probe, to take tissue samples from the prostate.These samples will be examined under the microscope, to confirm the diagnosis (this is called an ultrasound guided biopsy). This helps to ensure that tissue is taken from exactly the right part(s) of the gland. Often a local anaesthetic is given but even so there can be a momentary pricking sensation as each of the biopsies is taken. There is also a small risk of infection with this procedure so you are normally given antibiotics at the time of the test to prevent this from happening. Taking the biopsies often causes a little bleeding so you may see some blood in your urine and/or bowel motions and in the semen, or ejaculate, for a week or so afterwards. The procedure is usually done as an out-patient and only takes a few minutes.
•  TRUS can also be used as part of the process to work out the extent of a prostate cancer (staging). Here the pictures of the prostate can give useful information about how much of the gland is affected and whether or not the tumour has spread beyond the capsule surrounding the gland, into the nearby tissues. The TRUS will usually be combined with a CT scan, which will give information about whether or not nearby lymph glands in the pelvis are affected. Sometimes an MRI scan is used as an alternative to TRUS and the CT scan. Once again the TRUS will be done on an out-patient basis and only takes a few minutes.