Normalized Microcirculatory Resistance Calculation
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Solution Overview
Problem
Current methods for computing microcirculatory resistance values and transit times for vessels are prone to errors due to imprecise definitions of distal positions, difficulties in accurately determining vessel lengths, and variations in vessel lengths between subjects.
Innovation Solution
A system that normalizes microcirculatory resistance values by dividing them by a transit length, providing a more reliable metric less sensitive to the location of the distal position. Additionally, a method to correct transit times by using reference fluid velocity data and cardiac cycle data to account for variations in blood velocity throughout the cardiac cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the distal position is chosen within the distal two-thirds of the target vessel according to guidelines, then the measurement can be performed with available guidance, but the microcirculatory resistance values are subject to error due to imprecise location definition
Solution Approach 1:
The patent changes the parameter used for calculating microcirculatory resistance from transit time to transit velocity. By dividing the vessel length by the transit time to obtain velocity, the measurement becomes independent of the exact distal position location within the distal two-thirds range, thereby resolving the contradiction between ease of operation and measurement precision
Solution Approach 2:
The patent introduces transit velocity as an intermediary parameter that mediates between the imprecise distal position selection and the final microcirculatory resistance calculation. This intermediary transforms the relationship between position and measurement outcome, allowing accurate results even with variable position selection
2Ease of operation
If the vessel length is measured from X-ray projection images, then the measurement can be obtained from available imaging data, but the length determination is subject to error
Solution Approach 1:
The patent changes from directly measuring vessel length in X-ray images to calculating effective transit length based on proximal and distal position coordinates. This parameter transformation allows derivation of the functional length needed for velocity calculation without requiring precise absolute length measurement from potentially distorted projection images
3Productivity
If the transit time is measured between proximal and distal positions, then the microcirculatory resistance can be calculated, but the value varies significantly between subjects due to vessel length variations
Solution Approach 1:
The patent transforms the calculation parameter from transit time to transit velocity by dividing transit time into the vessel transit length. This normalization allows comparison across subjects of different sizes and vessel lengths, as velocity accounts for the distance factor, thereby improving reliability and consistency of the microcirculatory resistance values
Solution Approach 2:
Instead of using transit time directly as the basis for resistance calculation, the patent inverts the approach by first calculating transit velocity (distance/time) and then using this velocity parameter. This inversion compensates for inter-subject variability in vessel dimensions
Data Source
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AI summary
A system (100) for providing a normalised microcirculatory resistance value for a vessel (110), is provided. The system includes one or more processors (120) configured to: compute(S110) a microcirculatory resistance value for the vessel (110) based on a transit time (TT) taken for an injected bolus to travel between a proximal position (Posa) in the vessel, and adistal position (Posd) in the vessel; and divide (S120) the computed microcirculatory resistance value by a transit length (dT) representing a length of the vessel between theproximal position (Posa) and the distal position (Posd), to provide the normalisedmicrocirculatory resistance value.