Photo-plethysmography Blood Flow Assessment in Cardiac Bypass
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Solution Overview
Problem
Conventional imaging modalities during cardiac bypass surgery, such as X-ray angiography and ultrasound, are limited in validating blood flow in smaller vessels and may not be available to surgeons, potentially leading to unsuccessful perfusion of heart muscle despite successful revascularization.
Innovation Solution
A system utilizing photo-plethysmography (PPG) to evaluate patency by positioning a light sensor relative to blood vessels, converting light into image signals, and generating PPG maps for analysis, which can be overlaid on endoscope or X-ray images to compare blood flow before and after bypass procedures, with a robot-assisted setup for precise positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional imaging modalities (X-ray angiography, ultrasound) are used to validate blood flow, then graft flow can be confirmed, but flow in smaller vessels and myocardial tissue cannot be adequately assessed
Solution Approach 1:
The patent transitions from conventional 2D planar imaging (X-ray angiography, ultrasound) to 3D volumetric imaging using light transmission through the chest wall. This dimensional change enables simultaneous visualization of graft vessels and underlying myocardial tissue perfusion, resolving the contradiction between assessing large vessel flow and small vessel/tissue perfusion.
Solution Approach 2:
The system uses a multi-wavelength light source (red and infrared LEDs) that can assess multiple parameters simultaneously: graft patency, myocardial perfusion, and tissue oxygenation. This universal approach replaces multiple specialized imaging modalities, enabling comprehensive blood flow assessment across different tissue levels with a single system.
2Measurement precision
If advanced imaging modalities (CT, MRI) are used postoperatively to assess perfusion, then comprehensive tissue visualization is achieved, but these modalities are often not available intraoperatively and require additional hardware
Solution Approach 1:
The system utilizes the patient's own chest wall and tissue as the imaging medium, eliminating the need for complex contrast agents, specialized sensors, or additional imaging hardware. The existing surgical field and patient anatomy serve the dual purpose of surgical access and imaging target, enabling intraoperative perfusion assessment without external equipment.
Solution Approach 2:
The patent replaces complex mechanical imaging systems (CT scanners, MRI machines, ultrasound probes) with a simple optical system using LEDs and photodetectors. This substitution of mechanical/electromagnetic imaging mechanisms with optical absorption measurement enables perfusion assessment using basic components already present in the operating room.
3Measurement precision
If a robot is used for precise light sensor positioning, then repeatable measurements at the same location are achieved, but system complexity increases
Solution Approach 1:
The patent introduces a robotic manipulator as an intermediary device that precisely positions the light sensor array over the surgical site. The robot acts as a mediator between the surgeon's intent and the measurement system, enabling repeatable positioning at identical locations before and after bypass procedures while maintaining measurement consistency.
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 non-invasive, real-time monitoring of blood flow through bypass grafts and myocardial tissue, providing a comprehensive validation of revascularization success without the need for additional imaging hardware, allowing for effective evaluation of graft patency and blood flow changes.
Implementation Method 1
a light sensor positionable relative to a vessel to receive light from the vessel and convert the light into an image signal
Implementation Method 2
A photo-plethysmography (PPG) interpretation module is configured to receive the image signal and output pixel values in an image representing PPG information
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A system for evaluating patency includes a light sensor (128) positionable relative to a blood vessel to receive light from the blood vessel and convert the light into an image signal. Aphoto-plethysmography (PPG) interpretation module (115) is configured to receive the image signal and output pixel values in an image representing PPG information. An image generation module(148) is coupled to the PPG interpretation module to receive the pixel values and generate a PPG map to be output to a display for analysis.