Gradient Echo Plural Contrast Imaging — Signal model and derived contrasts: T2*, T1, Phase, SWI, T1f, FST2*and T2*-SWI

Abstract

Gradient Echo Plural Contrast Imaging (GEPCI) is a post processing technique that, based on a widely available multiple gradient echo sequence, allows simultaneous generation of naturally co-registered images with various contrasts: T1 weighted, R2* = 1/T2* maps and frequency (f) maps. Herein, we present results demonstrating the capability of GEPCI technique to generate image sets with additional contrast characteristics obtained by combing the information from these three basic contrast maps. Specifically, we report its ability to generate GEPCI-susceptibility weighted images (GEPCI-SWI) with improved SWI contrast that is free of T1 weighting and RF inhomogeneities; GEPCI-SWI-like images with the contrast similar to original SWI; T1f images that offer superior GM/WM matter contrast obtained by combining the GEPCI T1 and frequency map data; Fluid Suppressed T2* (FST2*) images that utilize GEPCI T1 data to suppress CSF signal in T2* maps and provide contrast similar to FLAIR T2 weighted images; and T2*-SWI images that combine SWI contrast with quantitative T2* map and offer advantages of visualizing venous structure with hyperintense T2* lesions (e.g. MS lesions). To analyze GEPCI images we use an improved algorithm for combining data from multi-channel RF coils and a method for unwrapping phase/frequency maps that takes advantage of the information on phase evolution as a function of gradient echo time in GEPCI echo train.

Quantitative susceptibility mapping for investigating subtle susceptibility variations in the human brain

“…Such a contrast can, e.g., be a GRE magnitude image or, in the case of multi-echo GRE data, derived quantitative maps of the effective transverse relaxation rate R 2 * or T 1 -weighted images (Luo et al, 2012) may be used. This information can, again, be converted into an additional mask according to…”

Biophysical mechanisms of MRI signal frequency contrast in multiple sclerosis

“…TDS around zero corresponds to normal tissue, and TDS = 1 corresponds to severely injured tissue (black holes). Both TDS and MRI signal frequency/phase are obtained herein using the GE plural contrast imaging (GEPCI) technique (22), which is described in Materials and Methods.…”

“…A convenient way to study phase contrast in multiple sclerosis is by means of a GEPCI (21,22,32)-an MRI imaging technique that, based on multi-GE sequence, generates high-quality, high-resolution images with multiple contrasts from a single in vivo scan in <10 min. In a GE experiment, MR signal evolution from a voxel at a GE time TE is described by the equation (Eq.…”

“…4 with F(TE) = 1 to the GEPCI signal was sufficient to generate GEPCI T2* and T1W images. GEPCI-FST2Star images that are R2* maps with suppressed signal from CSF and GEPCI T1f images (a combination of GEPCI T1W and frequency maps) with enhanced GM/WM contrast (22) were also created.…”

Efficient imaging of midbrain nuclei using inverse double‐echo steady‐state acquisition a)

“…9,[11][12][13] In SWI, filtered phase images are used to mask magnitude images, which increases sensitivity to tissue susceptibility changes such as from hemorrhage or from iron deposition. 1,[6][7][8][9][14][15][16] This study aims at imaging of midbrain nuclei with higher imaging efficiency compared to the T2*-weighted SPGR technique which is often regarded as the current clinical standard. To achieve this goal, an inverse double-echo steadystate (iDESS) sequence is proposed and compared with SPGR technique.…”