3T MR improves multiple sclerosis assessment

Armed with 3T MRI, neuroradiologists are making progress in assessing multiple sclerosis through application of newer techniques such as diffusion tensor and triple-dose gadolinium imaging.

MR has proven extremely useful as a diagnostic and monitoring tool in MS, which traditionally has been considered mainly a disease of white matter. Compared with 1.5T systems, 3T MR offers higher signal-to-noise ratio, faster scanning times, and better visualization of lesions.

In recent years, 3T has become more accessible, said Dr. Fernanda Tovar-Moll, a postdoctoral fellow at the neuroimmunology branch at the National Institute of Neurological Disorders and Stroke at the National Institutes of Health.

"There is a great push for the use of 3T in clinical practice, especially in neuroradiology. The costs of these scanners have dropped substantially in the past few years, and technical problems related to very high field imaging have been solved for the most part," Tovar-Moll said.

Advantages of 3T imaging are particularly important for relatively new MR techniques, such as DTI, which are still mainly confined to the research environment, Tovar-Moll said.

Though MR has proven valuable in MS, it has always shown a clinical-radiological paradox, or a mismatch between clinical signs of disability and MR findings. It's possible that not all of the MS pathology shows up on conventional images, and alternative techniques such as DTI may help provide a more accurate assessment.

What appears to be normal white matter on conventional images may actually be diseased, Tovar-Moll said. DTI studies indicate that MS may also involve gray matter disease, and this may be why conventional images have not proven adequate in entirely explaining patients' clinical disability.

Since the thalamus has been shown to be one of the areas most highly correlated with disability in MS, National Institute researchers performed a study examining the value of 3T DTI in assessing occult thalamic injury. As part of the study, they correlated DTI measurements (mean diffusivity and fractional anisotropy) with clinical disability. Findings from 24 healthy volunteers were compared with 24 MS patients, and results were presented at the 2006 RSNA meeting.

The researchers found that DTI at 3T was effective for finding disease in areas that appeared normal and that DTI measures were higher in patients with MS in comparison to healthy patients. The mean diffusivity scores on DTI were correlated with motor and cognitive disability in the MS patient group (see graph).

Better correlation with disability may allow more effective monitoring of treatment effects in patients, according to Tovar-Moll.

"We found that disease in the normal-appearing thalamus of patients with multiple sclerosis correlated well with patients' functional disability scores. This finding suggests that probing of this region might turn out to be important in assessing MS patients in routine clinical neuroradiological practice," she said. "Naturally, future studies will need to validate these measures, but the potential is certainly exciting."

Meanwhile, researchers at the New Jersey Medical School have found promising results in MS patients with a robust triple-dose gadolinium technique. Patients were recruited from the MS center at the medical school and the Gimbel Multiple Sclerosis Comprehensive Care Center at Holy Name Hospital in Teaneck, NJ. All MR imaging was conducted on a 3T unit at the Center for Advanced Imaging at the medical school.

The triple-dose technique has been around for about a decade now, but it has not been widely practiced, probably due to higher costs, said Dr. Leo Wolansky, a professor of radiology and MRI section chief at New Jersey Medical School.

Research has shown that peak enhancement in MS occurs, on average, 28 minutes after injection. In clinical practice, however, scans are typically done only five to 10 minutes postinjection, most likely due to higher costs associated with prolonged scan times.

Past trials have also shown the superiority of 3T over 1.5T MRI in detecting MS lesions. Higher signal-to-noise ratios in 3T imaging are particularly beneficial for detecting thin sections and small lesions, Wolansky said.

While performing research on the BECOME drug trial, the first head-to-head MR study of MS medications, Dr. Wolansky employed all of these techniques-triple-dose contrast, postinjection delays of 20 minutes and 40 minutes, and 3T-to enhance MS imaging. Results are due to be presented this month at the European Congress of Radiology in Vienna.

Wolansky's team found that this extremely robust MR approach increases sensitivity to the point where almost all new lesions demonstrate enhancement on T2-weighted scans. In comparison, when monthly contrast-enhanced scans are obtained with the standard contrast dose, no postinjection delay, and standard field strength, up to 20% to 40% of new MS lesions on T2-weighted scans do not enhance.

Accurate assessment of actively enhancing lesions in MS patients will help guide the most appropriate treatment.

"I believe that eventually triple-dose imaging will become standard in certain circumstances. Treatment could change dramatically, resulting in decreased morbidity and, ultimately, decreased costs," Wolansky said.