What Are the Similarities and Differences Between an MRI Machine and a PET Scan?

Both MRIs and PET scans are used to produce images of organs and other tissues within the human body, reports Bay Moon Gynecological Cancer Resources. MRIs use magnets to produce images of structures in the body, while PET scans use positively charged particles to examine the metabolic activity of organs.

While both MRI and PET scans produce images of organs and tissues within the body, they are used for separate purposes, according to Bay Moon Gynecological Cancer Resources. An MRI is used to simply examine the structures within the body in detail, but it has limited ability to detect cancers. PET scans, however, reveal the metabolic activity of tissues, and thus can be used to identify cancer and scar tissue in the body. As cancer cells replicate rapidly, this activity is highlighted in a PET scan; scar tissue is metabolically inactive and easily identified.

The process of undergoing these imaging techniques differs greatly as well, reports Bay Moon Gynecological Cancer Resources. During an MRI, patients lie in a narrow cylinder and their atoms are excited by the machine's magnetic field, thus producing an image. Before a PET scan, patients must ingest or inhale a radioisotope. During the scan, patients pass through a scanning ring, which tracks the ingested or inhaled isotope's journey through the body.