Quantitative susceptibility mapping could detail pathophysiologic features of MS lesions

Quantitative susceptibility mapping (QSM) can quantify the magnetic susceptibility of multiple sclerosis (MS) lesions in vivo, according to a study published in the April issue of Radiology.

While MRI is useful in diagnosing and monitoring MS in patients, it fails to accurately exhibit underlying pathophysiologic information that’s necessary to monitor the progression of the disease. It's been previously observed that MS lesions consist of an abnormally high level of iron deposition, which impedes MRI's ability to accurately depict a white matter lesion load. However, explained lead author Weiwei Chen, MD, PhD, of Huazhong University of Science and Technology in Wuhan, China, and colleagues, "Paramagnetic iron causes an increase in tissue susceptibility, which can be detected by using MR imaging. Although phase MR imaging has been used to characterize the susceptibility change in MS, its nonlocal property and dependence on imaging parameters prevent it from being a direct measure for local tissue susceptibility." QSM therefore addresses this issue, as it allows for direct measurement of tissue susceptibility.

Chen and colleagues conducted a retrospective longitudinal study to examine MS lesions at a variety of ages through the use of QSM and conventional MRI.

The researchers retrospectively chose 32 MS patients who underwent two MRI exams with 3D gradient-echo sequence. After analysis, Chen and colleagues found 598 MS lesions in the patient cohort, ten of which were enhanced and 588 which were unenhanced. Of these lesions, 162 in 23 patients were age measurable and six were visible only at QSM.

Moreover, the susceptibilities relative to normal-appearing white matter were 0.53 ppb for acute enhanced lesions, 38.43 ppb for early to intermediately aged nonenhanced lesions and 4.67 ppb for chronic nonenhanced lesions. The temporal rates for susceptibility changes in relative to cerebrospinal fluid were 12.49 ppb per month for acute enhanced lesions, 1.27 ppb per month for early to intermediately aged nonenhanced lesions, and -0.004 ppb per month for chronic nonenhanced lesions.

“For practical radiologic implications, the timing of susceptibility that accumulates rapidly only during the lesion formation, which was observed in this QSM MR imaging study and corroborated by a previous histochemical study, suggested that lesion susceptibility measured by QSM is a useful biomarker for monitoring MS disease activities,” wrote Chen and colleagues.

Though future studies are needed to support their findings, the authors believe that “….with further validation it may help to improve understanding of the underlying MS pathophysiologic information and monitor disease activity in MS patients,” they concluded.