Medical imaging
Because CT and MRI are sensitive to different tissue properties, the appearances of the images obtained with the two techniques differ markedly. In CT, X-rays must be blocked by some form of dense tissue to create an image, so the image quality when looking at soft tissues will be poor. In MRI, while any nucleus with a net nuclear spin can be used, the proton of the hydrogen atom remains the most widely used, especially in the clinical setting, because it is so ubiquitous and returns a large signal. This nucleus, present in water molecules, allows the excellent soft-tissue contrast achievable with MRI.
Interventional magnetic resonance imaging
The non-magnetic environment required by the scanner and the strong magnetic radiofrequency and quasi-static fields generated by the scanner hardware require the use of specialized instruments. For example, use of non-magnetic (e.g. Titanium) surgical instruments and MR compatible patient surveillance accessories in addition to the MRI scanner itself increase the cost of IMRI. Often required is the use of an "open bore" magnet, which permits the operating staff better access to patients during the operation. Such open bore magnets are often lower field magnets, typically in the 0.2 tesla range, which decreases their sensitivity and temporal efficiency but also decreases the radio frequency power potentially absorbed by the patient during a protracted operation. Higher field magnet systems are beginning to be deployed in intraoperative imaging suites, which can combine high-field MRI with a surgical suite and even CT in a series of interconnected rooms. Specialty high-field interventional MR devices, such as the IMRIS system, can actually bring a high-field magnet to the patient within the operating theatre, permitting the use of standard surgical tools while the magnet is in an adjoining space.