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MR imaging of intravoxel incoherent motions: application to diffusion and perfusion in neurologic disorders
Abstract:
Molecular diffusion and microcirculation in the capillary network result in a distribution of phases in a single voxel in the presence of magnetic field gradients. This distribution produces a spin-echo attenuation. The authors have developed a magnetic resonance (MR) method to image such intravoxel incoherent motions (IVIMs) by using appropriate gradient pulses. Images were generated at 0.5 T in a high-resolution, multisection mode. Diffusion coefficients measured on images of water and acetone phantoms were consistent with published values. Images obtained in the neurologic area from healthy subjects and patients were analyzed in terms of an apparent diffusion coefficient (ADC) incorporating the effect of all IVIMs. Differences were found between various normal and pathologic tissues. The ADC of in vivo water differed from the diffusion coefficient of pure water. Results were assessed in relation to water compartmentation in biologic tissues (restricted diffusion) and tissue perfusion. Nonuniform slow flow of cerebrospinal fluid appeared as a useful feature on IVIM images. Observation of these motions may significantly extend the diagnostic capabilities of MR imaging.
Insights
This study introduces a magnetic resonance imaging method to visualize intravoxel incoherent motions (IVIMs), revealing differences in apparent diffusion coefficients across various tissues. This technique enhances diagnostic capabilities by assessing tissue perfusion and water compartmentation.
Area of Science:
- Magnetic Resonance Imaging
- Biophysics
- Medical Imaging
Background:
- Magnetic field gradients in MRI cause phase dispersion within a voxel due to molecular diffusion and microcirculation.
- This phase dispersion leads to spin-echo attenuation, complicating accurate diffusion measurements.
- Intravoxel incoherent motions (IVIMs) represent the combined effects of diffusion and microcirculation within a single imaging voxel.
Purpose of the Study:
- To develop and validate a novel magnetic resonance (MR) imaging method for visualizing intravoxel incoherent motions (IVIMs).
- To assess the utility of IVIM imaging in differentiating between normal and pathological tissues in the neurologic area.
- To evaluate the relationship between IVIM-derived parameters and tissue water compartmentation and perfusion.
Main Methods:
- Development of a specialized MR pulse sequence to selectively image IVIMs.
- Acquisition of high-resolution, multisection MR images at 0.5 T.
- Phantom studies using water and acetone to validate diffusion coefficient measurements.
- Analysis of apparent diffusion coefficients (ADC) in healthy subjects and patients, incorporating IVIM effects.
Main Results:
- MR images accurately depicted IVIMs, with phantom data showing consistency with published diffusion coefficients.
- Significant differences in ADC were observed between various normal and pathological tissues.
- The ADC of in vivo water was found to differ from the diffusion coefficient of pure water, reflecting tissue complexity.
- Nonuniform slow flow of cerebrospinal fluid was visualized as a distinct feature on IVIM images.
Conclusions:
- The developed MR method effectively images IVIMs, providing insights into tissue microcirculation and diffusion.
- IVIM imaging demonstrates potential for enhanced diagnostic capabilities in neurology by distinguishing tissue types.
- The findings support the assessment of water compartmentation and tissue perfusion through IVIM analysis.