MRSI or MRIS - Magnetic Resonance Imaging With Spectroscopy

MRSI or MRIS -
Magnetic Resonance Imaging With Spectroscopy

What is MRSI?

Magnetic Resonance Imaging with Spectroscopy (MRIS) is also known as Magnetic Resonance Spectrocopic Imaging (MRSI). This is a technique for non-invasive, high resolution imaging of the pelvic region with standard magnetic resonance imaging (MRI) technology.

In addition, the spectroscopic part refers to an analysis of the metabolism of cells in and around the prostate. The technology can differentiate between

normal cells
cancerous cells
cell with BPH (a benign condition)
dead cells (say, after seed implants or radiation therapy)

MRSI was invented at UCSF (the University of California at San Francisco) and is only done there and at Memorial Sloan Kettering, in New York City. It is a very useful technique for determining where cancer may be and in helping plan whatever medical treatments are being considered, or to track the results of a previous treatment. It is both sensitive and selective, meaning that it has a low false positive and a low false negative rate. (That is, it is unlikely to say there is cancer where there is none, or to miss cancer that is present.)

How Is It Done?

The procedure takes about an hour. A technician gently inserts a probe (lubricated and covered by two condoms) into the patient's rectum, then carefully positions him on his back. A flat pickup coil is placed over his abdomen and he is inserted into an MRI tube. The individual images take from 2 to 7 minutes or so each. During the imaging one must lie still. The machine makes a variety of noises -- clicks, bangs, whirrs, clangs, and so on -- which are the nature of the apparatus. One has headphones on and can choose the music that is played. There is a microphone that allows instant two-way communication with the operator.

A report from the radiologist is usually available to your urologist within about a week.

Resolution and Some Details

The MRI part of the images consists of 0.5mm by 0.5 mm pixels; each slice is about 3 mm apart. The grey scale allows differences in tissue density to be determined as well as an distortions due to tumor growth, etc. The gland volume can be calculated as well as the PSA density.

The spectroscopic part is of lower resolution. The voxels (or volume elements) are cubes 6mm on a side and are color coded in the images. In each volume element, the relative and absolute signal levels of three metabolic pathways is measured and compared to determine the nature of the cells within that volume. These spectroscopic signatures can be overlaid on the MRI images to indicate where cancer (and the other conditions) can be found.