Evaluation of intravoxel incoherent motion fitting methods in low‐perfused tissue

<jats:sec><jats:title>Purpose</jats:title><jats:p>To investigate the robustness of constrained and simultaneous intravoxel incoherent motion (IVIM) fitting methods and the estimated IVIM parameters (<jats:italic>D, D*</jats:italic> and <jats:italic>f</jats:italic>) for applications in brain and low‐perfused tissues.</jats:p></jats:sec><jats:sec><jats:title>Materials and Methods</jats:title><jats:p>Model data simulations relevant to brain and low‐perfused tumor tissues were computed to assess the accuracy, relative bias, and reproducibility (CV%) of the fitting methods in estimating the IVIM parameters. The simulations were performed at a series of signal‐to‐noise ratio (SNR) levels to assess the influence of noise on the fitting.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>The estimated IVIM parameters from model simulations were found significantly different (<jats:italic>P</jats:italic> < 0.05) using simultaneous and constrained fitting methods at low SNR. Higher accuracy and reproducibility were achieved with the constrained fitting method. Using this method, the mean error (%) for the estimated IVIM parameters at a clinically relevant SNR = 40 were <jats:italic>D</jats:italic> 0.35, <jats:italic>D</jats:italic>* 41.0 and <jats:italic>f</jats:italic> 4.55 for the tumor model and <jats:italic>D</jats:italic> 1.87, <jats:italic>D</jats:italic>* 2.48, and <jats:italic>f</jats:italic> 7.49 for the gray matter model. The most robust parameters were the IVIM‐<jats:italic>D</jats:italic> and IVIM‐<jats:italic>f</jats:italic>. The IVIM‐<jats:italic>D</jats:italic>* was increasingly overestimated at low perfusion.</jats:p></jats:sec><jats:sec><jats:title>Conclusion</jats:title><jats:p>A constrained IVIM fitting method provides more accurate and reproducible IVIM parameters in low‐perfused tissue compared with simultaneous fitting.</jats:p><jats:p><jats:bold>Level of Evidence</jats:bold>: 3</jats:p><jats:p>J. MAGN. RESON. IMAGING 2017;45:1325–1334</jats:p></jats:sec>