Magnetic Resonance Imaging Technology Development

National Institute Of Neurological Disorders And Stroke

Investigators

Linked publications, trials & patents

Abstract

A rebuilt high field (11.7T) MRI system has arrived at NIH and will be energized in late 2019 as soon as liquid helium becomes available. One of the major areas needing technical development is that of RF transmission, and we have continued working in this area in two ways: single channel volume transmission with birdcage-type transmitters, and 8 channel array transmission. For the former, we have completed the electronic parts, as well as the mechanical part attaching to the patient bed to physically support this technology. A prototype 8-channel transmitter has been completed and tested for 7T. It was found that with the current design, at least 16 channels will be needed to get sufficient transmit power for typical imaging experiments. Based on the 7T design, we are designing the amplifiers for the 11.7T version of this approach. A second technical project dealt with a novel MRI acquisition method to detect myelin loss in the brain that has particular advantages at high field. The method is based on the notion that myelin alters the MRI signal based on the phenomenon of magnetization transfer (MT). It uses a novel way to generate MT contrast that eliminates the often overwhelming background signal from water not participating in the MT process and interfering with the MT detection. Evaluation of the method showed that it is particularly effective in the presence of motion, where it avoids excessive contamination from background water signals. A scientific paper reporting this method and its evaluation is currently in press in Magnetic Resonance in Medicine. In a third project, we continued improving robustness of our high resolution, high field (7T and above) MRI techniques to study brain anatomy. A unique approach was developed that improves the suppression of the effects of subject head motion on MRI quality. There are many motion correction methods currently available, however they often do not work satisfactorily at high field, in particular for techniques that exploit contrast based on the magnetic properties (magnetic susceptibility) of tissue. The approach simultaneously corrects for spatial encoding errors associated with head motion as well as accompanying magnetic field changes. The latter effects so far have been ignored in high resolution MRI techniques, but nevertheless they can affect image quality in a major way. Results show substantial improvements in image quality, even in cases of minor head motion. In particular, fine anatomical details are better resolved with this motion correction approach. In part, this is attributed to the fact magnetic field changes cause by the respiratory motion of the chest are also corrected with this approach. It is anticipated that the approach will also be valuable at lower strength MRI systems, which are in much more widespread use compared to high field. A manuscript reporting the finding was accepted for publication in Magnetic Resonance in Medicine. In collaboration with the group of Daniel Reich, we are currently evaluating the effectiveness of the approach for the study of MS patients. Our preliminary experience on 5 patients indicate a substantial improvement in lesion visualization, even in cases of minimal ( 1mm) head motion.