MRI Tumor Hemodynamic Measurement Correction for Contrast Extravasation
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Solution Overview
Problem
Current MRI methods for assessing tumor hemodynamics, particularly in the presence of contrast agent extravasation, face limitations due to underestimation of tumor blood volume and flow caused by contrast agent leakage, which affects the accuracy of cerebral blood volume and flow measurements.
Innovation Solution
An improved model-based leakage correction method that calculates and corrects T2 or T2* relaxation rate data sets to account for contrast agent extravasation, allowing for more precise estimation of hemodynamic parameters like cerebral blood flow and mean transit time by using a convolution approach based on tracer dilution theory and arterial input function.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If DSC MRI methods are used to measure tumor cerebral blood volume and flow, then hemodynamic parameters can be obtained, but contrast agent leakage causes underestimation of these parameters
Solution Approach 1:
The patent introduces an intermediary computational model that separates the T1 and T2* effects of contrast agents. By using a two-pool model (vascular and extravascular compartments) and solving the Bloch equations, the method mediates between the measured signal and the true hemodynamic parameters, eliminating the confounding effect of contrast leakage on DSC measurements.
Solution Approach 2:
The patent changes the parameters being measured by deriving not only cerebral blood volume (CBV) but also cerebral blood flow (CBF) and mean transit time (MTT) from the corrected T2* data. This multi-parameter approach provides more comprehensive hemodynamic information that is not affected by contrast leakage, thereby improving measurement reliability.
2Reliability
If conventional MRI methods are used for tumor imaging, then tumor detection is achieved, but reliable information about tumor angiogenesis cannot be obtained
Solution Approach 1:
The patent segments the contrast agent behavior into distinct compartments: vascular compartment (where contrast remains intravascular) and extravascular compartment (where contrast leaks). By separately modeling contrast concentration in each compartment over time, the method preserves angiogenesis information that would otherwise be lost in conventional single-compartment imaging.
Solution Approach 2:
The patent performs preliminary computational correction of the MRI signal data before final parameter calculation. By pre-processing the raw DSC signal to remove T1 leakage effects using the two-pool model, the method ensures that subsequent hemodynamic parameter calculations are based on corrected data, preventing information loss about angiogenesis.
3Quantity of substance
If contrast agent leakage is present in tumor tissue, then T1 relaxation effects occur, but these effects compete with and mask the susceptibility-induced signal decreases needed for accurate DSC measurements
Solution Approach 1:
The patent extracts the T1 leakage component from the total signal change by separately calculating the expected T1 effect based on contrast concentration in the extravascular compartment. This extracted T1 component is then removed from the measured signal, leaving only the pure T2* susceptibility effect that contains the accurate hemodynamic information.
Solution Approach 2:
The patent skips directly to calculating the T2* effect by using the known contrast concentration time course to compute the expected T1 contribution, then subtracting it. This approach rushes through the confounding T1 effect rather than trying to measure it directly, efficiently isolating the susceptibility signal.
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 enhances the accuracy of tumor hemodynamic assessments, providing reliable measurements even in the presence of extravasation, and is applicable to brain tumors and other tissues with disrupted blood-brain barriers, enabling better evaluation of anti-angiogenic therapies.
Implementation Method 1
The passage of a bolus of a Gd agent through the tissue induces a susceptibility gradient that results in a signal reduction
Implementation Method 2
contrast agent leaks out of the vasculature into the tissue resulting in enhanced T1 relaxation effects. Signal increases that result from shortening T1 competes with the susceptibility-induced signal decreases
Data Source
AI summary
One or two sets of time course NMR data are acquired using an EPI pulse sequence in which either or both gradient recalled echo NMR signals and spin-echo NMR signals are acquired after bolus injection of a contrast agent. T2* relaxation rates for GE and T2 relaxation rates for SE are calculated from the acquired NMR signals and are corrected for extravasation of contrast agent into surrounding tissues. The gradient-echo signals and spin-echo NMR signals are employed along with the T2* and T2 relaxation rates to calculate hemodynamic parameter maps which are used as a measure of tumor angiogenesis.