Abstract: Chemical Exchange Saturation Transfer Imaging in Multiple Sclerosis (The 27th Annual Meeting of the CMSC and the 5th Cooperative Meeting of the CMSC-ACTRIMS)

Saturday, June 1, 2013

Craig Jones, PhD , F.M. Kirby Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD

Chase Figley, BSc , Department of Psychological and Brain Sciences, Johns Hopkins University, Baltimore, MD

Peter van Zijl, PhD , Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, MD

Peter A Calabresi, MD, FAAN , Neurology, Johns Hopkins School of Medicine, Baltimore, MD

Susan Courtney, PhD , Department of Psychological and Brain Sciences, Johns Hopkins University, Baltimore, MD

Background:

Chemical exchange saturation transfer (CEST) is a new MRI technique that uses saturation (signal destruction) to detect exchangeable protons (such as in OH, NH groups) in very low concentration solutes (mM) via the water signal in MRI. Previous work showed that CEST is related to mobile proteins. The technique is similar to a traditional magnetization transfer (MT) pulse sequence but uses longer duration and low power pulses with minimal effect on MT. In order to assess multiple exchangeable pools, saturation pulses are applied at a number of offset frequencies relative to water, and the free water signal is quantified.

Objectives:

To apply a new CEST MRI acquisition and data processing technique to MS patients that has minimal MT contribution, and to quantify the CEST-NOE (nuclear overhauser effect).

Methods:

Patients with multiple sclerosis were scanned on a 3T MRI scanner. The CEST acquisition consisted of a 3D segmented-EPI readout with a 7 shot EPI. Each excitation was preceded by a 25 ms, 1µT saturation pulse. The volume acquisition time was approximately 11s. Volumes were acquired with the saturation pulse frequency swept from -10 to 10 ppm in 65 steps. For each voxel, a subset of the z-spectrum was fit to a Lorentzian function and the Lorentzian difference (LD) was calculated. MPRAGE, T2-weighted, and FLAIR images were also acquired as part of the imaging protocol.

Results:

Two female, secondary progressive MS patients have been analyzed. The first was a 58 year old female who had a single large periventricular lesion that was hyperintense on both T2 and FLAIR. The corresponding CEST-NOE image showed a hypointensity of approximately the same size. The second was a 55 year old who had multiple lesions, both periventricularly and in the deep white matter. Several lesions showed the same pattern to the first patient in that the lesion was hyperintense on T2 and FLAIR and hypointense on CEST-NOE. Another lesion was hyperintense on T2 and FLAIR, but the hypointensity was less than half the size on the CEST-NOE image. Another frontal, periventricular lesion was hyperintense on T2, but was isointense on FLAIR and hypointense on CEST-NOE.

Conclusions:

These results suggest the CEST-NOE image has contrast different from T2 and FLAIR images. Due to the low power saturation pulse, it is not likely to be MT dependant, and therefore might show novel protein changes compared to standard MRI sequences.

P35 Chemical Exchange Saturation Transfer Imaging in Multiple Sclerosis