Abstract
PurposeFlow‐compensated (FC) diffusion‐weighted MRI (DWI) for intravoxel‐incoherent motion (IVIM) modeling allows for a more detailed description of tissue microvasculature than conventional IVIM. The long acquisition time of current FC‐IVIM protocols, however, has prohibited clinical application. Therefore, we developed an optimized abdominal FC‐IVIM acquisition with a clinically feasible scan time.MethodsPrecision and accuracy of the FC‐IVIM parameters were assessed by fitting the FC‐IVIM model to signal decay curves, simulated for different acquisition schemes. Diffusion‐weighted acquisitions were added subsequently to the protocol, where we chose the combination of b‐value, diffusion time and gradient profile (FC or bipolar) that resulted in the largest improvement to its accuracy and precision. The resulting two optimized FC‐IVIM protocols with 25 and 50 acquisitions (FC‐IVIMopt25 and FC‐IVIMopt50), together with a complementary acquisition consisting of 50 diffusion‐weighting (FC‐IVIMcomp), were acquired in repeated abdominal free‐breathing FC‐IVIM imaging of seven healthy volunteers. Intersession and intrasession within‐subject coefficient of variation of the FC‐IVIM parameters were compared for the liver, spleen, and kidneys.ResultsSimulations showed that the performance of FC‐IVIM improved in tissue with larger perfusion fraction and signal‐to‐noise ratio. The scan time of the FC‐IVIMopt25 and FC‐IVIMopt50 protocols were 8 and 16 min. The best in vivo performance was seen in FC‐IVIMopt50. The intersession within‐subject coefficients of variation of FC‐IVIMopt50 were 11.6%, 16.3%, 65.5%, and 36.0% for FC‐IVIM model parameters diffusivity, perfusion fraction, characteristic time and blood flow velocity, respectively.ConclusionsWe have optimized the FC‐IVIM protocol, allowing for clinically feasible scan times (8‐16 min).
Highlights
MRI offers several approaches to assessing perfusion, of which the intravoxel incoherent motion (IVIM) model fit to diffusion‐weighted MRI (DWI) data is a promising example without contrast injection
IVIM is described by a bi‐exponential signal decay, with a diffusion coefficient (D), pseudo‐diffusion coefficient (D*), and perfusion fraction (f)
Our results demonstrate the feasibility of implementing FC‐IVIM in clinical studies and provide data on precision to inform power calculations
Summary
Capillary perfusion plays a large role in many major diseases, including cancer, and is prognostic for many indications.[1,2] MRI offers several approaches to assessing perfusion, of which the intravoxel incoherent motion (IVIM) model fit to diffusion‐weighted MRI (DWI) data is a promising example without contrast injection. Almost all IVIM studies assume the pseudo‐diffusion limit of the IVIM model, which requires the diffusion time (T) to be several times larger than the characteristic time scale (τ) of the capillary perfusion.[3] In this limit, IVIM is described by a bi‐exponential signal decay, with a diffusion coefficient (D), pseudo‐diffusion coefficient (D*), and perfusion fraction (f) This bi‐exponential IVIM model was used to characterize lesions and monitor treatment response in several studies.[5,6,7] accurate and precise characterization of IVIM remains challenging, because the estimated values of the IVIM parameters depend on acquisition settings[8] and show large day‐to‐day variations.[9,10]
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