What Is a Transrectal Ultrasound (TRUS)?

The digital rectal examination (DRE) and the prostate-specific antigen (PSA) blood test are two important ways to detect changes in the prostate gland.

However, they cannot determine if the changes are due to prostate cancer or to a non-cancerous condition. In the event of a significantly elevated PSA test and/or abnormal DRE, a prostate needle biopsy — the surgical removal of tissue for examination under a microscope — must be performed in order to make a definitive diagnosis of prostate cancer. The biopsy is taken with the guidance of transrectal ultrasound.

Transrectal ultrasound (TRUS) is a 5- to 15-minute outpatient procedure that uses sound waves to create a video image of the prostate gland. A small, lubricated probe placed into the rectum releases sound waves, which create echoes as they enter the prostate.

Prostate tumors sometimes create echoes that are different from normal prostate tissue. The echoes that bounce back are sent to a computer that translates the pattern of echoes into a picture of the prostate. While the probe may be temporarily uncomfortable, TRUS is essentially a painless procedure.

Although TRUS alone cannot detect every tumor, it has been shown to detect some tumors that cannot be felt by a DRE. In addition, TRUS is used to estimate the size of the prostate gland, helping doctors get a better idea of PSA density, which helps distinguish benign prostatic hyperplasia (BPH) from prostate cancer. Finally, it plays a vital role in a prostate needle biopsy, guiding the needle to just the right part of the prostate gland.

How Do I Prepare for TRUS?

Prior to TRUS, the patient may be instructed to have an enema to remove feces and gas from the rectum, which might impede the progress of the rectal probe.

How Is TRUS Performed?

The patient traditionally lies on his left side, which is considered a more relaxing position as well as allowing for easier insertion of the rectal probe. After the probe is inserted into the rectum, the tester adjusts the console on the ultrasound machine to a baseline for the echoes of normal prostate tissue, which will serve as the standard by which other tissue will be classified. Imaging usually starts at the base of the bladder, as the probe is rotated to provide a full picture of the prostate.

What Kind of Images Does TRUS Take?

The rectal probe sends sound waves to the prostate gland; normal and abnormal tissue bounce back different kinds of echoes that are relayed to the computer, which translates their pattern into a video picture of the prostate.

  • Isoechoic areas — represent normal tissue and bounce back, or echo, the same amount sound waves as they received.
  • Hypoechoic areas — send back significantly fewer echoes than they received and often indicate the presence of cancer.
  • Hyperechoic areas — send back significantly more echoes than they received and often indicate the presence of prostatic calcifications, or tiny stones, in the prostate. The stones are usually harmless unless they become infected.

Prostate-Specific Antigen Density (PSAD)

Most men in the age group for prostate cancer usually have some BPH as well, which can elevate PSA levels and make prostate cancer diagnosis more difficult. PSA density — the blood PSA level divided by the size of the prostate, as determined by TRUS — can help distinguish between BPH and prostate cancer.

With BPH, the PSA level should not be more than 15 percent of the size of the prostate. PSA levels exceeding 15 percent of the size of the prostate are more likely to indicate the presence of prostate cancer, and the need for a biopsy.


The Prostate Cancer pages of this website are part of the Comprehensive Prostate Cancer Awareness Program (CPCAP), a major regional effort to reduce the rates of death and illness caused by prostate cancer in southwestern Pennsylvania. Funding for CPCAP is provided by a grant from the Commonwealth of Pennsylvania.

Transrectal Ultrasound for Prostate Cancer