Testing of a Noninvasive Probe for Measurement of Blood Perfusion

2008 ◽  
Vol 2 (1) ◽  
Author(s):  
Paul S. Robinson ◽  
Elaine P. Scott ◽  
Thomas E. Diller
Keyword(s):  
Heat Flux ◽  
Parameter Estimation ◽  
Thermal Contact ◽  
Calculated Data ◽  
Blood Perfusion ◽  
Heat Flux Sensor ◽  
Time Resolved ◽  
Estimation Techniques ◽  
Controlled Flow ◽  
Parameter Estimation Techniques

Parameter estimation techniques have been utilized in the development of a methodology to noninvasively measure blood perfusion using a new thermal surface probe. The core of this probe is comprised of a small, lightweight heat flux sensor that is placed in contact with tissue and provides time-resolved signals of heat flux and surface temperature while the probe is cooled by air jets. Parameter estimation techniques were developed that incorporate heat flux and temperature data with calculated data from a biothermal model of the tissue and probe. The technique simultaneously estimates blood perfusion and thermal contact resistance between the probe and tissue. Validation of this concept was carried out by experimentation with controlled flow through nonbiological porous media. Warm water was circulated through a fine pore sponge to provide a phantom model for blood perfusion through biological tissue. The parameter estimation technique was applied to measurements taken over a range of flow rates. Heat flux and temperature measurements and the resulting perfusion estimates correlated well with the experimentally imposed perfusion rate. This research helps establish the validity of using this method to develop a practical, noninvasive probe to clinically measure blood perfusion.

Modeling and Estimating Simulated Burn Depth Using the Perfusion and Thermal Resistance Probe

2013 ◽  
Vol 7 (3) ◽  
Author(s):  
Abdusalam Al-Khwaji ◽  
Brian Vick ◽  
Tom Diller
Keyword(s):  
Mathematical Model ◽  
Heat Flux ◽  
Parameter Estimation ◽  
Thermal Resistance ◽  
Contact Resistance ◽  
Core Temperature ◽  
Thermal Contact Resistance ◽  
Thermal Contact ◽  
Blood Perfusion ◽  
Thermal Event

A new thermal perfusion probe operates by imposing a thermal event on the tissue surface and directly measuring the temperature and heat flux response of the tissue with a small sensor. The thermal event is created by convectively cooling the surface with a small group of impinging jets using room temperature air. The hypothesis of this research is that this sensor can be used to provide practical burn characterization of depth and severity by determining the thickness of nonperfused tissue. To demonstrate this capability the measurement system was tested with a phantom tissue that simulates the blood perfusion of tissue. Different thicknesses of plastic were used at the surface to mimic layers of dead tissue. A mathematical model developed by Alkhwaji et al. (2012, “New Mathematical Model to Estimate Tissue Blood Perfusion, Thermal Contact Resistance and Core Temperature,” ASME J. Biomech. Eng., 134, p. 081004) is used to determine the effective values of blood perfusion, core temperature, and thermal resistance from the thermal measurements. The analytical solutions of the Pennes bioheat equation using the Green's function method is coupled with an efficient parameter estimation procedure to minimize the error between measured and analytical heat flux. Seven different thicknesses of plastic were used along with three different flow rates of perfusate to simulate burned skin of the phantom perfusion system. The resulting values of thermal resistance are a combination of the plastic resistance and thermal contact resistance between the sensor and plastic surface. Even with the uncertainty of sensor placement on the surface, the complete set of thermal resistance measurements correlate well with the layer thickness. The values are also nearly independent of the flow rate of the perfusate, which shows that the parameter estimation can successfully separate these two parameters. These results with simulated burns show the value of this minimally invasive technique to measure the thickness of nonperfused layers. This will encourage further work with this method on actual tissue burns.

New Mathematical Model to Estimate Tissue Blood Perfusion, Thermal Contact Resistance and Core Temperature

2012 ◽  
Vol 134 (8) ◽  
Author(s):  
Abdusalam Alkhwaji ◽  
Brian Vick ◽  
Tom Diller
Keyword(s):  
Heat Flux ◽  
Parameter Estimation ◽  
Contact Resistance ◽  
Core Temperature ◽  
Thermal Contact Resistance ◽  
Thermal Contact ◽  
Simulated Data ◽  
Thermal Conditions ◽  
Blood Perfusion ◽  
Simple Parameter

Analytical solutions were developed based on the Green’s function method to describe heat transfer in tissue including the effects of blood perfusion. These one-dimensional transient solutions were used with a simple parameter estimation technique and experimental measurements of temperature and heat flux at the surface of simulated tissue. It was demonstrated how such surface measurements can be used during step changes in the surface thermal conditions to estimate the value of three important parameters: blood perfusion (wb), thermal contact resistance (R″), and core temperature of the tissue (Tcore). The new models were tested against finite-difference solutions of thermal events on the surface to show the validity of the analytical solution. Simulated data was used to demonstrate the response of the model in predicting optimal parameters from noisy temperature and heat flux measurements. Finally, the analytical model and simple parameter estimation routine were used with actual experimental data from perfusion in phantom tissue. The model was shown to provide a very good match with the data curves. This demonstrated the first time that all three of these important parameters (wb, R″, and Tcore) have simultaneously been estimated from a single set of thermal measurements at the surface of tissue.

Time-Resolved Heat Transfer Measurements on the Tip Wall of a Ribbed Channel Using a Novel Heat Flux Sensor: Part II — Heat Transfer Results

2006 ◽  
Author(s):  
Sean Jenkins ◽  
Jens von Wolfersdorf ◽  
Bernhard Weigand ◽  
Tim Roediger ◽  
Helmut Knauss ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Flux Sensor ◽  
Internal Cooling ◽  
Time Resolved ◽  
Mean Values ◽  
Cooling Channels ◽  
Ribbed Channel ◽  
Detailed Surface ◽  
Flux Sensor

Measurements using a novel heat flux sensor were performed in an internal ribbed channel representing the internal cooling passages of a gas turbine blade. These measurements allowed for the characterization of heat transfer turbulence levels and unsteadiness not previously available for internal cooling channels. In the study of heat transfer, often the fluctuations can be equally as important as the mean values for understanding the heat loads in a system. In this study comparisons are made between the time-averaged values obtained using this sensor and detailed surface measurements using the transient thermal liquid crystal technique. The time-averaged heat flux sensor and transient TLC results showed very good agreement, validating both methods. Time-resolved measurements were also corroborated with hot film measurements at the wall at the location of the sensor to better clarify the influence of unsteadiness in the velocity field at the wall on fluctuations in the heat flux. These measurements resulted in turbulence intensities of the velocity and heat flux of about 20%. The velocity and heat flux integral length scales were about 60% and 35% of the channel width respectively, resulting in a turbulent Prandtl number of about 1.7 at the wall.

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