Ultrasound imaging systems provide, a medical doctor with a real time imaging system, which also has spectral analysis, and flow speed metering capabilities.
Abstract
Ultrasound imaging systems provide, a medical doctor with a real time imaging system, which also has spectral analysis, and flow speed metering capabilities. These attributes coupled with a good cost efficiency ratio makes medical ultrasound imaging systems highly popular.
The goals of this project where to build an experiment system, gather data, design and code an application which calculates the PI and RI blood flow indices.
Pulse Cycle Diagram Parameters
The pulse cycle diagram which is also related to as the spectra envelop shows the maximum frequency with respect to time.
Figure 1 The Pulse Cycle Diagram
The main pulse cycle diagram parameters are:
S: The peak systolic value.
D: The minimal diastolic value.
M: The mean over the pulse cycle
The Pulsatility index and Resistance Index
The Pulsatility Index or PI (1) is a measure for the oscillatory energy in the flow-velocity waveform. The purpose of this index is to summarize the degree of pulse-wave damping at different arterial sites; the smaller the PI the greater the degree of damping. A stenosis in a vessel will lead to a reduced PI at points distal from the stenosis.
The Resistance Index or RI (2) is used as an indicator of the circulatory resistance beyond the measurement point. A stenosis will lead to a reduced blood flow and therefore increase the resistance to blood flow in the vessel. A high resistance index can also be a sign of decreased flow in the capillary system as can be found e.g. in diabetic patients
The System Structure
Figure 2 The System Structure
The experiment system simulates pulsating arterial blood flow. An artery is simulated by a latex made tube which is strung inside a water filled tank. Pulsating flow is generated by a programmable controller, which switches the flow from two water tanks. The two water tanks are placed at different heights. Systolic pressure is provided by the higher tank, diastolic pressure is provided by the lower tank.
In order to enhance echoes generation, corn starch is added to the water. The corn starch granules act as isotropic ultrasound reflectors, much like red blood cells do in blood. Continuous system action is achieved by using an electric pump, to pump up water back to the tanks.
The synergy ultrasound imaging system provides real time imaging, data sampling, and data processing. The synergy probe is mounted on a 3D controllable fixture.
The Software
The goal of the software is to calculate the PI and RI indices. During the software development great emphasize was takes in order to fulfill the following points:
- Providing a modular and, readable code
- Efficient Matlab © programming, which makes use of Matlab © built in functions ,and its vector and matrix operations
- Providing an easy to use graphical user interface ( GUI ), following the What You See is What You Get ( WYSWYG ) concept
Figure 3 The Software Modules
The Software Output
Conclusion
The PI and RI indices calculation, and data preprocessing applications provide, a precise, efficient, and easy to use tool. Due to their modular design and coding, these application can be modified, extended, and used in future applications.