Chemical Shift magnetization transfer magnetic resonance imaging

Abstract

Purpose To develop a chemical shift magnetization transfer (CSMT) MRI method to provide accurate MTR measurements in the presence of fat. Methods Numerical simulations were performed to compare MTR measurements at different echo-times (TEs) for voxels with varying fat/water content. The CSMT approach was developed using water fraction estimates to correct for the impact of fat signal upon observed MTR measurements. CSMT method was validated with oil/agarose phantom and animal studies. Results Simulations demonstrated that the observed MTRs vary with water fraction as well as with the TE dependent phase difference between fat and water signals; simulations also showed that a linear relationship exists between MTR and water fraction when fat and water signals are in-phase. For phantom studies, observed MTR decreased with increasing oil fraction: 42.41 ± 0.54, 38.12 ± 0.33, 32.93 ± 0.56 and 26.08 ± 0.87 for 5 % to 40 % oil fractions respectively, compared to 42.63 ± 1.04 for phantom containing 4% agarose only. These offsets were readily corrected with the additional acquisition of a water fraction map. Conclusion Fat fraction and TE can significantly impact observed MTR measurements. The new CSMT approach offers the potential to eliminate the effects of fat upon MTR measurements.

Preoperative Evaluation of Pancreatic Fibrosis and Lipomatosis

“…20,49,50 However, fat-suppression and water-or fat-selective pulses may cause additional MT effects and/or alter the steady state of MT sequences. 48 Because the measured PDFF values in this study correlate well with histopathologic grading of the pancreatic lipomatosis, it can be assumed that the applied chemical shift-based multiecho gradient imaging sequence for fat quantification actually measures the fat deposition in the pancreas. Also the MTR measurements in the subcutaneous fat show good agreement with published data with MTR close to zero.…”

“…Fat deposition in soft tissue environment has a confounding effect on MTR values. 17,18,20,48 The MT effect grows with the number of hydrogen nuclei that switch from a high-mobility environment, such as in a free water molecule, to a low-mobility environment, such as, for example, in a hydroxyl group bound to a macromolecule. 17 The free water proton pool is diminished in a fatty environment and therefore the measured MTR are reduced.…”

Combining inhomogeneous magnetization transfer and multipoint Dixon acquisition: Potential utility and evaluation

“…The contribution of fat to the ihMT signal has not previously been investigated. Previous studies of MT, 11,24 CEST, 25 and quantitative MT 26 imaging showed evidence of variation on MTR, MTR asym , and quantitative MT values, depending on the fat fraction in the corresponding voxel. While similar to ihMT, these sequences rely on different chemical or physical principles and use different postprocessing, thus demonstrating salient differences with respect to the influence of fat.…”

“…The IhMT applications outside of the central nervous system would involve imaging in close proximity to adipose tissue (which is found near nerves and muscles) and may be further complicated by infiltration into the surrounding fat by different pathologies 10 . The presence of fat is known to create chemical shift artifacts and compromise tissue characterization 11‐13 . Moreover, neuroradiological studies of the head and neck routinely use fat‐suppression methods that improve visualization of pathology 14‐16 .…”

Prediction of small for size syndrome after extended hepatectomy: Tissue characterization by relaxometry, diffusion weighted magnetic resonance imaging and magnetization transfer

“…This increased cellular lipid content may additionally be accountable for a further reduction of magnetization transfer. [ 32 ]. Thus, either a potentially elevated cellular hypertrophy or a higher number of proliferating, hence swollen hepatocytes, or both, together with a possibly enhanced lipid content might eventually account for the rather pronounced decline in MTR after ePH as compared to cPH.…”