MRI Perfusion Quantification Without Radiation
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Solution Overview
Problem
Current MRI-based perfusion imaging methods provide only relative measurements of cerebral blood flow and volume, lacking the ability to produce quantitative values on a subject-by-subject basis, and require radiation or radio-labeled tracers, limiting their clinical application.
Innovation Solution
An MRI system employs a pulse sequence for acquiring perfusion-weighted image data before and after contrast agent injection, using self-calibration techniques to measure T1 relaxation times and apply correction factors for water diffusion, enabling the production of quantitative cerebral blood flow and volume maps without radiation or tracers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If CT or PET imaging is used to obtain quantitative perfusion measurements, then measurement precision is improved, but harmful factors (radiation exposure and radio-labeled tracers) increase
Solution Approach 1:
The patent replaces CT/PET imaging systems with MRI system to perform quantitative perfusion measurements. Specifically, it uses arterial spin labeling (ASL) technique with magnetization-prepared rapid gradient echo (MP-RAGE) pulse sequence to obtain quantitative cerebral blood flow and cerebral blood volume maps without requiring ionizing radiation or exogenous contrast agents, thereby eliminating the harmful effects associated with CT and PET while maintaining quantitative measurement capability
Solution Approach 2:
The patent introduces magnetically labeled blood water protons as an endogenous tracer for perfusion measurement. The ASL technique labels arterial blood water with magnetic inversion, which then serves as a flow-sensitive marker that can be detected by MRI without requiring external radio-labeled tracers or contrast agents, thus providing a safe intermediary for quantitative perfusion assessment
2Device complexity
If population averaged values are assumed for white matter to produce quantitative perfusion maps, then device complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The patent implements a self-calibration approach where the MRI system automatically determines subject-specific baseline CBF and CBV values through the MP-RAGE pulse sequence and automated analysis algorithms. The system performs internal reference measurements and computational processing to establish individualized perfusion baselines without requiring manual intervention or population-averaged assumptions, thereby achieving both operational simplicity and measurement accuracy
Solution Approach 2:
The patent employs automated analysis algorithms that process the MP-RAGE imaging data to generate subject-specific perfusion parameters. The system uses feedback loops to iteratively refine the quantitative CBF and CBV calculations based on the acquired signal data, ensuring accurate subject-by-subject quantification while maintaining automated operation and reducing manual complexity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method allows for accurate, quantitative perfusion measurements in a broader clinical population, avoiding the limitations of radiation exposure and tracer administration, thereby enhancing diagnostic capabilities in conditions like stroke and Alzheimer's disease.
Implementation Method 1
When a substance such as human tissue is subjected to a uniform magnetic field (polarizing field B0), the individual magnetic moments of the spins in the tissue attempt to align with this polarizing field, but precess about it in random order at their characteristic Larmor frequency. If the substance, or tissue, is subjected to a magnetic field (excitation field B1) which is in the x-y plane and which is near the Larmor frequency, the net aligned moment, Mz, may be rotated, or 'tipped', into the x-y plane to produce a net transverse magnetic moment Mt. A signal is emitted by the excited spins after the excitation signal B1 is terminated
Implementation Method 2
When utilizing these signals to produce images, magnetic field gradients (Gx, Gy and Gz) are employed. Typically, the region to be imaged is scanned by a sequence of measurement cycles in which these gradients vary according to the particular localization method being used
Implementation Method 3
an imaging pulse sequence is performed to acquire perfusion weighted image data between the rapid acquisition of T1-weighted images acquired before and after the injection of a T1-shortening contrast agent
Implementation Method 4
using self-calibration techniques to measure T1 relaxation times and apply correction factors for water diffusion
Data Source
AI summary
A method for calculating quantitative perfusion measurements using an MRI system includes a pulse sequence that acquires perfusion weighted images and additionally measures T1 values before and after the administration of a contrast agent. T1 values are measured by rapidly sampling a longitudinal relaxation curve and employed to determine the blood volume in tissue. A correction factor for the effect of water diffusion between blood vessels and the extravascular space is determined.