Small Molecule Imaging
Ultrahigh field magnetic resonance spectroscopy (MRS) is one of those new techniques that is yielding higher resolution images, higher signal-to-noise ratios, and, sometimes, greater speed.
“Ultrahigh fields for magnetic resonance are being used to target molecules other than water,” explains Jullie Pan, M.D., Ph.D., associate professor of neurosurgery at Yale University. We can now image biochemically important molecules such as lactate, glutamate, and GABA with an imaging resolution that is informative and pertinent to living tissue. Ultrahigh field MRS gives researchers a new slant on what they are looking at, how aggressive a tumor is, whether it’s necrotic or proliferative, et cetera,” she elaborates.
Her lab has had success using ultrahigh field MRS to study brain tumors and epilepsy. “The latter condition works with patients who are mainly MRI-negative but who are clearly suffering from a focal brain disease,” she notes.
“The developments and implementation of ultrahigh field MRS imaging opens a distinctively functional and metabolic avenue to imaging the brain, with resolution comparable to that of a PET scan without the issue of radioactivity, which limits repeatability. There also is long-standing research interest in using MRS imaging to study muscle, liver, prostate, and other cancers.”
In the 1990s, Dr. Pan says, typical field strength for human imaging was 1.5 Tesla. In fact, “whether 1.5 Tesla was the optimum field strength was being debated.” Now, the preferred clinical imaging field strength for the human brain is 3 Tesla. However, at higher field strengths, “the size of the human body is closer to the wavelength of the radiofrequency signal at 7 Tesla,” so the detector technology to optimally generate and detect the signals has had to evolve.
“For even higher magnetic fields such as 9.4 and 11.7 Tesla (which exist for human application), this area of work will continue. It’s a long road.” Nonetheless, while technical difficulties of detectors, homogeneity, and relaxation are major challenges, effective approaches are being developed, opening the way to take advantage of the ultrahigh field’s higher signal-to-noise ratio for imaging of anatomy and biochemistry in human study.