A comparison of phase imaging and quantitative susceptibility mapping in the imaging of multiple sclerosis lesions at ultrahigh field

Abstract

Objective The aim of this study was to compare the use of high-resolution phase and QSM images acquired at ultra-high field in the investigation of multiple sclerosis (MS) lesions with peripheral rings, and to discuss their usefulness for drawing inferences about underlying tissue composition.Materials and methodsThirty-nine Subjects were scanned at 7 T, using 3D T2*-weighted and T1-weighted sequences. Phase images were then unwrapped and filtered, and quantitative susceptibility maps were generated using a thresholded k-space division method. Lesions were compared visually and using a 1D profiling algorithm.ResultsLesions displaying peripheral rings in the phase images were identified in 10 of the 39 subjects. Dipolar projections were apparent in the phase images outside of the extent of several of these lesions; however, QSM images showed peripheral rings without such projections. These projections appeared ring-like in a small number of phase images where no ring was observed in QSM. 1D profiles of six well-isolated example lesions showed that QSM contrast corresponds more closely to the magnitude images than phase contrast.ConclusionsPhase images contain dipolar projections, which confounds their use in the investigation of tissue composition in MS lesions. Quantitative susceptibility maps correct these projections, providing insight into the composition of MS lesions showing peripheral rings.

Combining Quantitative Susceptibility Mapping with Automatic Zero Reference (QSM0) and Myelin Water Fraction Imaging to Quantify Iron-Related Myelin Damage in Chronic Active MS Lesions

“…38 In vivo imaging studies of phase or QSM have revealed conflicting results regarding the prevelance rim+ lesions among MS patients. 39 One previous study demonstrated a vast difference among QSM and phase results, wherein the authors concluded QSM was superior to depiction of spatial susceptibility patterns in MS lesions. 15 Similarly, we found wide-ranging differences in lesion classification based upon QSM versus phase images (data not shown).…”

Nuclei‐specific deposits of iron and calcium in the rat thalamus after status epilepticus revealed with quantitative susceptibility mapping (QSM)

“…Measured phase reflects a nonlocal convolution of the underlying magnetic susceptibility distribution, and is thus subject to contributions from perturbers outside the imaging voxel. Moreover, GRE signal phase is dependent on acquisition parameters (particularly TE), lesion shape and orientation with respect to the main magnetic field, and contrast in phase maps can also be affected by the spatial filtering method applied . Therefore, lesion contrast in phase maps needs to be interpreted with caution, and can lead to misclassification of paramagnetic and diamagnetic areas.…”

Insights from Ultrahigh Field Imaging in Multiple Sclerosis

“…Additionally, recent studies utilizing quantitative susceptibility mapping (QSM) may assist in detecting changes at the periphery of MS lesions, as QSM removes part of the non-local contributions (such as the dipolar patterns), which can complicate interpretation of phase images [46], sometimes at the expense of image quality. This highlights the inherent problems associated with reliance on a single sequence or quantitative post-processing technique.…”