Clinical Testing of New MR Pulse Sequences

Magnetic resonance (MR) scanners use computer software, called pulse sequences, to extract different types of information from the human body. Though MR has largely matured to become a routine clinical imaging modality, substantial development is still underway in order to fully exploit the technology. BWH Radiology has been a leader in pulse sequence development and the protocol under review has played a large part in this development over the last several years.

The importance of further development in MR cannot be understated. In particular, biochemical information, detailed properties of water diffusion and perfusion in tissue, cardiac imaging, and high-resolution brain imaging, all hold great potential for improving medical diagnosis and monitoring.

MR pulse sequence software is typically developed in small incremental steps. For example, an investigator may receive a new state of the art sequence from the manufacturer of the scanner equipment. (S)he may then decide to add flow-sensitizing gradients. This process is not straightforward, but requires extensive testing, first in phantoms and then in-vivo, to determine if the pulse sequence is capable of performing the new task and, moreover, to see if the new feature does not introduce undesired artifacts.

Some modifications, like the introduction diffusion-sensitizing gradients, must be tested in patients, since changes of tissue diffusion can only be observed in stroke victims. Once the researcher attained the first goal, (s)he may proceed with other modifications, e.g., modifications which will improve the temporal resolution. The completion of a new sequence, which ultimately may be used in a large normal subject or patient study, may involve a large number of design steps, where each step must be tested in one or a few subjects before development proceeds. Another scenario is the application of an existing patient protocol to different, existing, and FDA approved equipment. For example the need may arise to use a different radiofrequency coil (surface coil instead of head coil) or a scanner system with different magnetic field strength (3.0 Tesla instead of 1.5 Tesla). Several parameters, such as signal-to-noise ratio, or T1 and T2 weighting may change under such circumstances. In most cases only a study in a subject will reveal if protocol parameter settings are adequate. Therefore, this protocol is different from a conventional study, where exactly the same protocol will be applied to each of a large number of subjects. However, the protocol and the general procedures of data handling used during the different scans is similar enough, so it can be summarized into a general development protocol.

The purpose of this protocol is to test and validate newly developed MR pulse sequences.