Separation of diffusion and perfusion in intravoxel incoherent motion MR imaging.

Abstract

Intravoxel incoherent motion (IVIM) imaging is a method the authors developed to visualize microscopic motions of water. In biologic tissues, these motions include molecular diffusion and microcirculation of blood in the capillary network. IVIM images are quantified by an apparent diffusion coefficient (ADC), which integrates the effects of both diffusion and perfusion. The aim of this work was to demonstrate how much perfusion contributes to the ADC and to present a method for obtaining separate images of diffusion and perfusion. Images were obtained at 0.5 T with high-resolution multisection sequences and without the use of contrast material. Results in a phantom made of resin microspheres demonstrated the ability of the method to separately evaluate diffusion and perfusion. The method was then applied in patients with brain and bone tumors and brain ischemia. Clinical results showed significant promise of the method for tissue characterization by perfusion patterns and for functional studies in the evaluation of the microcirculation in physiologic and pathologic conditions, as, for instance, in brain ischemia.

Diffusion‐weighted MRI and intravoxel incoherent motion model for diagnosis of pediatric solid abdominal tumors

“…The analysis algorithm for IVIM was developed in Python (v. 2.7). The relationship between the diffusion signal intensities and the b ‐values can be described by a biexponential relationship introduced by Le Bihan12: $S_b/S_0=f\cdot \text{exp}\left(-bD*\right)+\left(1-f\right)\cdot \text{exp}\left(-bD\right)$where S 0 and S b are the signal intensities at b  = 0 and b  = 50, 100, 150, 600, or 1000 s/mm 2 , respectively. Using this relationship, a nonlinear least‐squares fit was applied to the data on a voxel‐by‐voxel basis.…”

Magnetic resonance imaging‐estimated placental perfusion in fetal growth assessment

“…Calculation of the perfusion fraction is performed with the intravoxel incoherent motion technique, which is based on the fact that a diffusion‐weighted sequence is affected not only by molecular diffusion, but also by tissue perfusion. If the sequence is repeated with different degrees of motion sensitization (different b ‐values), the perfusion fraction can be calculated15. In each slice of the diffusion‐weighted sequence, regions of interest were selected, including as much of the placenta as possible, but excluding areas with artifactual signal loss.…”

“…However, MRI can also provide physiological information such as the perfusion fraction, an in‐vivo estimate of the volume fraction of perfused tissue13, 14, 15, the examination for which can be performed within minutes. Previous studies have investigated the placental perfusion fraction in vivo 16, 17, 18, 19.…”

Intravoxel incoherent motion modeling in the kidneys: Comparison of mono-, bi-, and triexponential fit

“…In addition to the microscopic motion of water in tissue, diffusion MRI is also sensitive to processes such as vascular perfusion and tubular flow 15. Because the signal attenuation due to perfusion is much greater than attenuation caused by diffusion, both signals can be separated by using a two‐component intravoxel incoherent motion (IVIM) model.…”

“…Because the signal attenuation due to perfusion is much greater than attenuation caused by diffusion, both signals can be separated by using a two‐component intravoxel incoherent motion (IVIM) model. This is done by fitting of the diffusion signal decay over a range of b‐values to a biexponential function, in which the fast signal decay at lower b‐values (b < 200) is attributed to fast water movement processes, "pseudodiffusion," and the decay at higher b‐values to hindered diffusion 15. The two‐component model was shown to be a better fit to the diffusion signal in the kidney than the one‐compartment models 16.…”