"If PSA is elevated, can ultrasound or MRI rule out cancer ?"

...was asked by an anonymous reader.

Neither Ultrasound nor MRI  can role out cancer completely. 

Ultrasound: is very useful to visualize the prostate during biopsy and other interventions. 

However, the prostate borders are not clearly seen.  Cancer, if big enough  and in locations closer to the rectum, can be seen, but not always.  New developments in ultrasound, especially contrast enhancement (a contrast agent is injected into the arm vein  - like in CT or MRI), and other new techniques, (currently investigated in research studies)  seem to make ultrasound better. 

MRI: is by far the best imaging modality for prostate at the moment. When performed right, the prostate gland, the capsule of the gland, the structures  around the prostate (like the neurovascular bundles and seminal vesicles) can be seen clearly; and cancer is much better seen on MRI than on Ultrasound or CT. If state-of-the-art MR imaging protocols are used, which include dynamic contrast enhanced MRI, or MR Spectroscopy, the results are even better, and most of the clinical relevant cancer are seen. With clinical relevant cancers are seen is meant, that tumors, which need clinical treatment, are picked up with MRI in most of the cases (up to 90-95% in experienced prostate MRI centers). MRI is not perfect (nothing is): very small tumors and in some cases even larger tumors are still not seen with MRI. 

Therefore, cancer can never be excluded completely. 

However,  if the PSA-level is elevated, yet, the experienced Urologist does not "feel" the cancer during his digital rectal exam (DRE; the urologist examines the prostate with his finger through the rectum); the Ultrasound is negative (does not show any suspicious area); and the MRI does not show any tumor, the chance that there is a cancer present, which needs immediate therapy is drastically reduced.  The urologist has to decide then, if he wants to perform a biopsy or not:  based on the patients history, PSA, DRE, findings on ultrasound and  - if performed  - findings of MRI. 

The advantages of prostate MRI are described and explained on several websites (see links on the right side). Currently,  MRI is generally performed only after cancer has been diagnosed with biopsy (for staging; is the cancer gland confined or not?); or after repeat negative biopsies and rising PSA (for detection); or after therapy and PSA relapse (for local recurrence).