Andreas Julian Riexinger1, Jan Martin1, Susanne Rauh1, Andreas Wetscherek2, Mona Pistel1, Tristan Anselm Kuder3, Armin Michael Nagel1, Michael Uder1, Bernhard Hensel4, Lars Müller3,5, Frederik Bernd Laun1. 1. Institute of Radiology, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany. 2. Joint Department of Physics, Institute of Cancer Research and Royal Marsden NHS Foundation Trust, London, UK. 3. Department of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany. 4. Center for Medical Physics and Engineering, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany. 5. CUBRIC, School of Psychology, Cardiff University, Cardiff, UK.
Abstract
BACKGROUND: Studies on intravoxel incoherent motion (IVIM) imaging are carried out with different acquisition protocols. PURPOSE: To investigate the dependence of IVIM parameters on the B0 field strength when using a bi- or triexponential model. STUDY TYPE: Prospective. STUDY POPULATION: 20 healthy volunteers (age: 19-28 years). FIELD STRENGTH/SEQUENCE: Volunteers were examined at two field strengths (1.5 and 3T). Diffusion-weighted images of the abdomen were acquired at 24 b-values ranging from 0.2 to 500 s/mm2 . ASSESSMENT: ROIs were manually drawn in the liver. Data were fitted with a bi- and a triexponential IVIM model. The resulting parameters were compared between both field strengths. STATISTICAL TESTS: One-way analysis of variance (ANOVA) and Kruskal-Wallis test were used to test the obtained IVIM parameters for a significant field strength dependency. RESULTS: At b-values below 6 s/mm2 , the triexponential model provided better agreement with the data than the biexponential model. The average tissue diffusivity was D = 1.22/1.00 μm2 /msec at 1.5/3T. The average pseudodiffusion coefficients for the biexponential model were D* = 308/260 μm2 /msec at 1.5/3T; and for the triexponential model D 1 * = 81.3/65.9 μm2 /msec, D 2 * = 2453/2333 μm2 /msec at 1.5/3T. The average perfusion fractions for the biexponential model were f = 0.286/0.303 at 1.5/3T; and for the triexponential model f1 = 0.161/0.174 and f2 = 0.152/0.159 at 1.5/3T. A significant B0 dependence was only found for the biexponential pseudodiffusion coefficient (ANOVA/KW P = 0.037/0.0453) and tissue diffusivity (ANOVA/KW: P < 0.001). DATA CONCLUSION: Our experimental results suggest that triexponential pseudodiffusion coefficients and perfusion fractions obtained at different field strengths could be compared across different studies using different B0 . However, it is recommended to take the field strength into account when comparing tissue diffusivities or using the biexponential IVIM model. Considering published values for oxygenation-dependent transversal relaxation times of blood, it is unlikely that the two blood compartments of the triexponential model represent venous and arterial blood. LEVEL OF EVIDENCE: 1 Technical Efficacy Stage: 2 J. Magn. Reson. Imaging 2019;50:1883-1892.
BACKGROUND: Studies on intravoxel incoherent motion (IVIM) imaging are carried out with different acquisition protocols. PURPOSE: To investigate the dependence of IVIM parameters on the B0 field strength when using a bi- or triexponential model. STUDY TYPE: Prospective. STUDY POPULATION: 20 healthy volunteers (age: 19-28 years). FIELD STRENGTH/SEQUENCE: Volunteers were examined at two field strengths (1.5 and 3T). Diffusion-weighted images of the abdomen were acquired at 24 b-values ranging from 0.2 to 500 s/mm2 . ASSESSMENT: ROIs were manually drawn in the liver. Data were fitted with a bi- and a triexponential IVIM model. The resulting parameters were compared between both field strengths. STATISTICAL TESTS: One-way analysis of variance (ANOVA) and Kruskal-Wallis test were used to test the obtained IVIM parameters for a significant field strength dependency. RESULTS: At b-values below 6 s/mm2 , the triexponential model provided better agreement with the data than the biexponential model. The average tissue diffusivity was D = 1.22/1.00 μm2 /msec at 1.5/3T. The average pseudodiffusion coefficients for the biexponential model were D* = 308/260 μm2 /msec at 1.5/3T; and for the triexponential model D 1 * = 81.3/65.9 μm2 /msec, D 2 * = 2453/2333 μm2 /msec at 1.5/3T. The average perfusion fractions for the biexponential model were f = 0.286/0.303 at 1.5/3T; and for the triexponential model f1 = 0.161/0.174 and f2 = 0.152/0.159 at 1.5/3T. A significant B0 dependence was only found for the biexponential pseudodiffusion coefficient (ANOVA/KW P = 0.037/0.0453) and tissue diffusivity (ANOVA/KW: P < 0.001). DATA CONCLUSION: Our experimental results suggest that triexponential pseudodiffusion coefficients and perfusion fractions obtained at different field strengths could be compared across different studies using different B0 . However, it is recommended to take the field strength into account when comparing tissue diffusivities or using the biexponential IVIM model. Considering published values for oxygenation-dependent transversal relaxation times of blood, it is unlikely that the two blood compartments of the triexponential model represent venous and arterial blood. LEVEL OF EVIDENCE: 1 Technical Efficacy Stage: 2 J. Magn. Reson. Imaging 2019;50:1883-1892.
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