title: Evaluation and comparison of diffusion MR methods for measuring apparent transcytolemmal water exchange rate constant.
abstract: Two diffusion-based approaches, CG (constant gradient) and FEXI (filtered exchange imaging) methods, have been previously proposed for measuring transcytolemmal water exchange rate constant kin, but their accuracy and feasibility have not been comprehensively evaluated and compared. In this work, both computer simulations and cell experiments in vitro were performed to evaluate these two methods. Simulations were done with different cell diameters (5, 10, 20μm), a broad range of kinvalues (0.02-30s-1) and different SNR's, and simulated kin's were directly compared with the ground truth values. Human leukemia K562 cells were cultured and treated with saponin to selectively change cell transmembrane permeability. The agreement between measured kin's of both methods was also evaluated. The results suggest that, without noise, the CG method provides reasonably accurate estimation of kinespecially when it is smaller than 10s-1, which is in the typical physiological range of many biological tissues. However, although the FEXI method overestimates kineven with corrections for the effects of extracellular water fraction, it provides reasonable estimates with practical SNR's and more importantly, the fitted apparent exchange rate AXR showed approximately linear dependence on the ground truth kin. In conclusion, either CG or FEXI method provides a sensitive means to characterize the variations in transcytolemmal water exchange rate constant kin, although the accuracy and specificity is usually compromised. The non-imaging CG method provides more accurate estimation of kin, but limited to large volume-of-interest. Although the accuracy of FEXI is compromised with extracellular volume fraction, it is capable of spatially mapping kinin practice.
authors.affiliation: Institute of Imaging Science, Vanderbilt University, Nashville, TN 37232, USA; Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN 37232, USA; Department of Radiology, The Second Hospital of Hebei Medical University, Shijiazhuang, Hebei, PR China.
authors.forename: Xin
authors.initials: X
authors.lastname: Tian
authors.affiliation: Institute of Imaging Science, Vanderbilt University, Nashville, TN 37232, USA; Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN 37232, USA.
authors.forename: Hua
authors.initials: H
authors.lastname: Li
authors.affiliation: Institute of Imaging Science, Vanderbilt University, Nashville, TN 37232, USA; Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN 37232, USA.
authors.forename: Xiaoyu
authors.initials: X
authors.lastname: Jiang
authors.affiliation: Institute of Imaging Science, Vanderbilt University, Nashville, TN 37232, USA; Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN 37232, USA.
authors.forename: Jingping
authors.initials: J
authors.lastname: Xie
authors.affiliation: Institute of Imaging Science, Vanderbilt University, Nashville, TN 37232, USA; Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN 37232, USA; Department of Biomedical Engineering, Vanderbilt University, Nashville, TN 37232, USA; Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37232, USA; Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37232, USA; Vanderbilt-Ingram Cancer Center, Vanderbilt University, Nashville, TN 37232, USA.
authors.forename: John C
authors.initials: JC
authors.lastname: Gore
authors.affiliation: Institute of Imaging Science, Vanderbilt University, Nashville, TN 37232, USA; Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN 37232, USA; Department of Biomedical Engineering, Vanderbilt University, Nashville, TN 37232, USA; Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37232, USA; Vanderbilt-Ingram Cancer Center, Vanderbilt University, Nashville, TN 37232, USA. Electronic address: junzhong.xu@vanderbilt.edu.
authors.forename: Junzhong
authors.initials: J
authors.lastname: Xu
mesh_terms: D000465:Algorithms; D003585:Cell Biology; D002463:Cell Membrane Permeability; D048429:Cell Size; D002477:Cells / Q000378:metabolism / Q000648:ultrastructure; D003198:Computer Simulation; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D004574:Electromagnetic Fields; D006801:Humans; D020014:K562 Cells; D007700:Kinetics; D012503:Saponins / Q000494:pharmacology; D059629:Signal-To-Noise Ratio; D014867:Water / Q000737:chemistry*
chemical_list: D012503:Saponins; D014867:Water
keywords: CG; Constant gradient; Diffusion; FEXI; Filter exchange imaging; MRI; Membrane permeability; Saponin; Transcytolemmal water exchange