Isotropic generalized diffusion tensor MRI
Inventors
Basser, Peter J. • Avram, Alexandru V.
Assignees
US Department of Health and Human Services
Publication Number
US-11835611-B2
Publication Date
2023-12-05
Expiration Date
2038-04-06
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Abstract
Isotropic generalized diffusion tensor imaging methods and apparatus are configured to obtain signal attenuations using selected sets of applied magnetic field gradient directions whose averages produce mean apparent diffusion constants (mADCs) over a wide range of b-values, associated with higher order diffusion tensors (HOT). These sets are selected based on analytical descriptions of isotropic HOTs and the associated averaged signal attenuations are combined to produce mADCs, or probability density functions of intravoxel mADC distributions. Estimates of biologically-specific rotation-invariant parameters for quantifying tissue water mobilities or other tissue characteristics can be obtained such as Traces of HOTs associated with diffusion and mean t-kurtosis.
Core Innovation
The invention disclosed herein relates to isotropic generalized diffusion tensor imaging (IGDTI) methods and apparatus designed to measure orientationally-averaged diffusion weighted images and mean apparent diffusion constants (mADCs) over a wide range of b-values. These methods select sets of applied magnetic field gradient directions based on analytical descriptions of isotropic higher order diffusion tensors (HOT), and combine the averaged signal attenuations to produce rotation-invariant estimates. The approach permits estimation of biologically-specific parameters such as traces of HOTs and mean t-kurtosis, which quantify tissue water mobilities and intrinsic tissue characteristics.
The background identifies challenges with conventional diffusion tensor imaging (DTI) which is limited to low diffusion sensitizations and assumes Gaussian diffusion, thus becoming less accurate at higher b-values where diffusion anisotropy is more prominent. Obtaining mADC-weighted signals at high b-values conventionally requires a large number of diffusion weighted images with dense orientational sampling, leading to impractically long scan durations. There is a need for efficient diffusion-encoding schemes capable of measuring rotation-invariant diffusion tissue properties at high b-values within clinically feasible times.
The disclosed IGDTI approach efficiently obtains isotropic diffusion signals by acquiring signal attenuations using selected gradient directions in nested sets (3, 4, and 6 directions) tailored to different b-value ranges. By combining averages of signals acquired with these sets at multiple b-values, IGDTI accurately estimates rotation-invariant parameters such as the traces of 2nd, 4th, and 6th order diffusion tensors and mean t-kurtosis. This enables quantification of microstructural properties and intravoxel distributions of diffusivities in tissue with substantially fewer measurements than traditional methods, facilitating clinical application.
Claims Coverage
The patent includes six independent claims focusing on apparatus and methods for isotropic generalized diffusion tensor imaging using specific gradient directions and diffusion sensitizations to generate rotation-invariant diffusion metrics and images.
Magnetic resonance imaging apparatus with selected gradient directions and signal averaging
An MRI apparatus including gradient coils configured to produce magnetic field gradients in three mutually orthogonal directions and four directions evenly distributed over a sphere; a signal coil acquiring signal attenuations at multiple b-values corresponding to these directions; a data acquisition system producing averages of signal attenuations for these directions at each b-value; and a display to show images based on these averages.
Method for obtaining isotropic gradient diffusion tensor images (IGDTIs) and mADC distributions
A method comprising obtaining IGDTIs associated with 2nd, 4th, or 6th order diffusion tensors at multiple gradient magnitudes using at least two sets of gradient directions; combining and averaging signal attenuations from these sets to determine distributions of mADCs; and displaying images based on these distributions.
Method applying diffusion gradients at multiple magnitudes and directions for mADC estimation
A method applying diffusion gradient fields at ascending magnitudes along three orthogonal directions to obtain first mADC-weighted signals; applying gradients at an intermediate magnitude along four evenly distributed directions for second signals; applying gradients at a high magnitude along four and six specific directions for third signals; combining these signals to estimate 2nd, 4th, or 6th order mADCs; and generating images based on these estimates.
Method using three-dimensional, refocusing balanced gradient pulse sequences and MDD estimation
A method applying three-dimensional, refocusing balanced magnetic field gradient pulse sequences at multiple b-values; obtaining signal decays from voxels in response; estimating mean diffusivity distributions (MDDs) per voxel based on signal decays; and generating images from these MDDs.
MRI apparatus for applying balanced gradient pulse sequences and MDD estimation
An apparatus including gradient coils to apply three-dimensional, refocusing balanced gradient pulse sequences at multiple b-values; a receiver detecting signal decays from voxels corresponding to these gradients; and a processor estimating MDDs for voxels from detected signals and generating images displayed locally or remotely.
The claims cover an MRI apparatus and methods for obtaining rotation-invariant diffusion imaging metrics using selected sets of diffusion gradient directions at multiple b-values, enabling efficient estimation of mADCs and mean diffusivity distributions with reduced data acquisition and enhanced clinical feasibility.
Stated Advantages
Allows measurements of rotation-invariant diffusion parameters over a wide range of b-values within clinically feasible scan durations using efficient gradient sampling schemes.
Eliminates effects of diffusion anisotropy on MR signals, enabling accurate isotropic diffusion measurements with fewer diffusion-weighted images than conventional approaches.
Provides biologically-specific rotation-invariant parameters such as higher order tensor traces and mean t-kurtosis, enhancing tissue characterization.
Reduces quantitation errors and imaging artifacts caused by subject and physiological motion through shorter scan durations.
Enables estimation and visualization of intravoxel distributions of mean apparent diffusion coefficients, potentially differentiating tissue types and pathological states.
Documented Applications
Clinical imaging biomarkers for detecting and characterizing hypoxic ischemic brain injury, stroke, cancer, and neuropathologies including cerebral gliomas and prostate and breast tumors.
Preclinical and clinical brain imaging studies assessing tissue microstructure, water mobilities, and microstructural water pool distributions.
Whole-body MRI applications for organs including heart, placenta, liver, kidneys, spleen, colon, prostate, skeletal muscles, and peripheral nerves.
Studies of developmental trajectories, inflammatory processes (e.g., multiple sclerosis, traumatic brain injury), wound healing, and cellular or tissue time-dependent processes.
Quantification and visualization of tissue-specific signal fractions and orientationally-averaged diffusivity spectra in brain tissues for diagnostic and research purposes.
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