Quantitative Vascular MRI Using SPIONs for Absolute CBV Mapping
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Solution Overview
Problem
Current magnetic resonance angiography (MRA) techniques face challenges in accurately measuring cerebral blood volume (CBV) due to inaccuracies in arterial input function determination, limited spatial resolution, high toxicity of gadolinium-based contrast agents, and susceptibility to artifacts, particularly in renally impaired patients and ischemic tissues.
Innovation Solution
A quantitative ultra-short time to echo (QUTE-CE) technique using superparamagnetic iron-oxide nanoparticles (SPIONs) for positive-contrast magnetic resonance imaging, which applies ultra-short echo times and repetition times to measure CA concentration and CBV on a voxel-by-voxel basis, minimizing susceptibility and flow artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If gadolinium-based contrast agents are used for MRA, then superior contrast properties and clear angiograms are achieved, but nephrotoxicity and high toxicity occur particularly in renally impaired patients
Solution Approach 1:
The patent replaces gadolinium-based contrast agents with iron oxide nanoparticle contrast agents that have different toxicity profiles. The iron oxide nanoparticles are designed to be excreted via the reticuloendothelial system rather than renal excretion, making them suitable for patients with renal impairment while maintaining effective contrast enhancement for MRA
Solution Approach 2:
The patent changes the fundamental parameter of contrast agent chemistry from gadolinium chelates to iron oxide nanoparticles. This parameter change fundamentally alters the excretion pathway and toxicity profile while maintaining the ability to provide superior contrast enhancement for vascular imaging
2Quantity of substance
If standard MRA techniques are used, then vascular imaging is achieved, but inaccuracies in arterial input function determination and CBV measurement occur
Solution Approach 1:
The patent replaces the indirect method of CBV measurement (which requires arterial input function determination and complex kinetic modeling) with a direct quantitative measurement method. The iron oxide nanoparticle contrast agents provide signal changes that are directly proportional to blood volume, eliminating the need for arterial catheterization and complex computational corrections
Solution Approach 2:
The patent uses iron oxide nanoparticles as an intermediary substance that provides a direct readout of blood volume. The nanoparticles remain confined to the vascular compartment and their signal intensity directly reflects local blood volume without requiring measurement of arterial input functions or complex pharmacokinetic modeling
3Productivity
If fast GRE techniques are used for CE MRA, then T1-weighted images with structural information are obtained, but susceptibility artifacts and flow artifacts occur
Solution Approach 1:
The patent changes the contrast mechanism from T1-weighting (gadolinium) to susceptibility-weighting (iron oxide nanoparticles). This parameter change allows the use of gradient echo sequences that are sensitive to magnetic susceptibility effects, providing robust vascular imaging while maintaining fast acquisition speeds. The susceptibility effect of iron oxide nanoparticles creates strong signal changes that are less susceptible to flow artifacts compared to T1-weighted techniques
4Object-affected harmful factors
If T2-weighted imaging techniques are used with SPIONs, then biocompatibility is achieved, but negative contrast or poorer contrast in T1-weighted images occurs
Solution Approach 1:
The patent makes the iron oxide nanoparticle contrast agents multi-functional by optimizing them to provide both T2-weighted negative contrast (for anatomical imaging) and T1-weighted positive contrast (for vascular imaging). This is achieved through specific nanoparticle size and concentration optimization, allowing a single contrast agent to serve multiple imaging purposes with high contrast quality in both weightings
Solution Approach 2:
The patent uses composite iron oxide nanoparticle structures with specific size ranges (5-50 nm) and surface coatings that optimize both biocompatibility and contrast properties. The composite structure allows the nanoparticles to exhibit both T1 and T2 contrast mechanisms simultaneously, providing versatile imaging capabilities while maintaining low toxicity
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
Enables accurate, high-definition angiograms and absolute CBV measurements with high contrast-to-noise ratio, avoiding gadolinium toxicity and improving vascular imaging clarity, particularly suitable for neuro-physiological studies and disease diagnosis.
Implementation Method 1
quantitative contrast-enhanced MRI with superparamagnetic nanoparticles using ultrashort time-to-echo pulse sequences
Implementation Method 2
superparamagnetic iron-oxide nanoparticles (SPIONs)
Implementation Method 3
applying a first radio frequency pulse sequence at a selected repetition time TR and at a magnetic field gradient to provide a selected flip angle to excite protons in the region of interest
Implementation Method 4
The signal may be acquired before magnetization of tissue in the region of interest in a transverse plane dephases
Implementation Method 5
ferumoxytol is known to produce strictly vascular signal changes
Data Source
Figure 1A~2
Figure 3a~3b
Figure 4a~4d
AI summary
A quantitative, ultrashort time to echo, contrast-enhanced magnetic resonance imaging technique is provided. The technique can be used to accurately measure contrast agent concentration in the blood, to provide clear, high-definition angiograms, and to measure absolute quantities of cerebral blood volume on a voxel -by- voxel basis.