Theoretical Analysis of the Large Blood Vessel Influence on the Local Tissue Temperature Decay After Pulse Heating

1993 ◽  
Vol 115 (2) ◽  
pp. 175-179 ◽  
Author(s):  
L. X. Xu ◽  
M. M. Chen ◽  
K. R. Holmes ◽  
H. Arkin
Keyword(s):  
Temperature Field ◽  
Blood Vessel ◽  
Point Source ◽  
Blood Perfusion ◽  
Tissue Temperature ◽  
Surrounding Tissue ◽  
Heating Pulse ◽  
Local Tissue ◽  
Large Blood Vessel ◽  
Temperature Decay

The influence of a large blood vessel (larger than 500 μm in diameter) on the local tissue temperature decay following a point source heating pulse was determined numerically using a sink/source method. It was assumed that the vessel was large enough so that the temperature of blood flowing within it remained essentially constant and was unaffected by any local tissue temperature transients. After the insertion of a point source heating pulse, the vessel influence on the local tissue transient temperature field was estimated by representing the vessel as a set of negative fictitious instantaneous heat sources with strength just sufficient to maintain the vessel at a constant temperature. In the surrounding tissue, the Pennes’ tissue heat transfer equation was used to describe the temperature field. Computations have been performed for a range of vessel sizes, probe-vessel spacings and local blood perfusion rates. It was found that the influence of a large vessel on the local tissue temperature decay is more sensitive to its size and location rather than to the local blood perfusion rate. For a heating pulse of 3s duration and 5 mW of power, there is a critical probe-vessel center distance 7R (R, vessel radius) beyond which the larger vessel influence on tissue temperature at the probe can be neglected.

Theoretical and Experimental Studies of Local Tissue Temperature Oscillation Under Hyperthermic Conditions Using Preserved Pig Kidney

2000 ◽  
Author(s):  
Cuiye Chen ◽  
Lisa X. Xu
Keyword(s):  
Heat Transfer ◽  
Experimental Studies ◽  
Temperature Oscillation ◽  
Tissue Temperature ◽  
Surrounding Tissue ◽  
Transient Temperature ◽  
Thermal Bath ◽  
Target Tissue ◽  
Local Tissue ◽  
Pig Kidney

Abstract It has been long recognized that local tissue temperature may osculate due to vascular thermo-regulation under hyperthermic conditions. To effectively heat the target tissue while sparing its surroundings, it is necessary to understand and then to control the temperature oscillation. A model based on the pig kidney vasculature was developed to study the transient temperature variations in the kidney when subjected to heating in a thermal bath. In the medullary region, a vascular model previously developed in (Chen and Xu, 2000) was used to account for the conjugate heat transfer between the paired artery and vein, and their surrounding tissue. Considering that numerous small vessels exist in the cortex region, the Pennes bio-heat transfer equation was used for modeling in this region. A code was written to numerically compute the 3-D transient temperature distribution in the kidney subjected to heating. To examine the validity of the model, experiments were performed to measure the temperatures and perfusion rates using thermistor microprobes in the cortex of the preserved pig kidney. This model will be utilized for future studies to investigate the relationships among the local blood perfusion rate, the heating rate, and the tissue temperature oscillation.

Mathematical Modeling of Thermal Ablation in Tissue Surrounding a Large Vessel

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Xin Chen ◽  
Gerald M. Saidel
Keyword(s):  
Temperature Distribution ◽  
Blood Vessel ◽  
Thermal Ablation ◽  
Large Vessel ◽  
Tissue Temperature ◽  
Maximum Temperature ◽  
Capillary Perfusion ◽  
Distribution Dynamics ◽  
Large Blood Vessel ◽  
Power Inputs

Thermal ablation of a solid tumor in a tissue with radio-frequency (rf) energy can be accomplished by using a probe inserted into the tissue under the guidance of magnetic resonance imaging. The extent of the ablation can be significantly reduced by heat loss from capillary perfusion and by blood flow in a large vessel in the tissue. A mathematical model is presented of the thermal processes that occur during rf ablation of a tissue near a large blood vessel, which should not be damaged. Temperature distribution dynamics are described by the combination of a 3D bioheat transport in tissue together with a 1D model of convective-dispersive heat transport in the blood vessel. The objective was to determine how much of the tissue can be ablated without damaging the blood vessel. This was achieved by simulating the tissue temperature distribution dynamics and by determining the optimal power inputs so that a maximum temperature increase in the tissue was achieved without inducing tissue damage at the edge of the large vessel. The main contribution of this study is to provide a model analysis for pretreatment and, eventually, for intra-operative application to thermal ablation of a tumor located near a large blood vessel.

Evaluation of the Effectiveness of Transurethral Radio Frequency Hyperthermia in the Canine Prostate: Temperature Distribution Analysis

1999 ◽  
Vol 121 (6) ◽  
pp. 584-590 ◽  
Author(s):  
Liang Zhu ◽  
Lisa X. Xu
Keyword(s):  
Temperature Field ◽  
Steady State ◽  
Radio Frequency ◽  
Blood Perfusion ◽  
Bioheat Transfer ◽  
Prostatic Tissue ◽  
Tissue Temperature ◽  
Distribution Analysis ◽  
Rf Power ◽  
Steady State Temperature

The heating pattern of a transurethral radio frequency (RF) applicator and its induced steady-state temperature field in the prostate during transurethral hyperthermia treatment were investigated in this study. The specific absorption rate (SAR) of the electromagnetic energy was first quantified in a tissue-equivalent gel phantom. It was used in conjunction with the Pennes bioheat transfer equation to model the steady-state temperature field in prostate during the treatment. Theoretical predictions were compared to in vivo temperature measurements in the canine prostate and good agreement was found to validate the model. The prostatic tissue temperature rise and its relation to the effect of blood perfusion were analyzed. Blood perfusion is found to be an important factor for removal of heat especially at the higher RF heating level. To achieve a temperature above 44°C within 10 percent of the prostatic tissue volume, the minimum RF power required ranges from 5.5 W to 36.4 W depending on the local blood perfusion rate (ω = 0.2−1.5 ml/gm/min). The corresponding histological results from the treatment suggest that to obtain better treatment results, either higher RF power level or longer treatment time (>180 minutes) is necessary. This is consistent with the predictions from the theoretical model developed in this study.

scholarly journals Muscle Heating With Megapulse II Shortwave Diathermy and ReBound Diathermy

2013 ◽  
Vol 48 (4) ◽  
pp. 477-482 ◽  
Author(s):  
David O. Draper ◽  
Amanda R. Hawkes ◽  
A. Wayne Johnson ◽  
Mike T. Diede ◽  
Justin H. Rigby
Keyword(s):  
Heat Dissipation ◽  
Subcutaneous Fat ◽  
Muscle Group ◽  
Triceps Surae ◽  
Tissue Temperature ◽  
Measured Temperature ◽  
Temperature Decay ◽  
Triceps Surae Muscle ◽  
Subcutaneous Fat Thickness ◽  
Shortwave Diathermy

Context: A new continuous diathermy called ReBound recently has been introduced. Its effectiveness as a heating modality is unknown. Objective: To compare the effects of the ReBound diathermy with an established deep-heating diathermy, the Megapulse II pulsed shortwave diathermy, on tissue temperature in the human triceps surae muscle. Design:  Crossover study. Setting: University research laboratory. Patients or Other Participants: Participants included 12 healthy, college-aged volunteers (4 men, 8 women; age = 22.2 ± 2.25 years, calf subcutaneous fat thickness = 7.2 ± 1.9 mm). Intervention(s):  Each modality treatment was applied to the triceps surae muscle group of each participant for 30 minutes. After 30 minutes, we removed the modality and recorded temperature decay for 20 minutes. Main Outcome Measure(s): We horizontally inserted an implantable thermocouple into the medial triceps surae muscle to measure intramuscular tissue temperature at 3 cm deep. We measured temperature every 5 minutes during the 30-minute treatment and each minute during the 20-minute temperature decay. Results: Tissue temperature at a depth of 3 cm increased more with Megapulse II than with ReBound diathermy over the course of the treatment (F6,66 = 10.78, P < .001). ReBound diathermy did not produce as much intramuscular heating, leading to a slower heat dissipation rate than the Megapulse II (F20,220 = 28.84, P < .001). Conclusions:  During a 30-minute treatment, the Megapulse II was more effective than ReBound diathermy at increasing deep, intramuscular tissue temperature of the triceps surae muscle group.

Lumped Parameter Thermal Model for the Study of Vascular Reactivity in the Fingertip

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
O. Ley ◽  
C. Deshpande ◽  
B. Prapamcham ◽  
M. Naghavi
Keyword(s):  
Heat Flux ◽  
Blood Flow ◽  
Thermal Model ◽  
Vascular Reactivity ◽  
Arterial Occlusion ◽  
Blood Perfusion ◽  
Cost Effective ◽  
Venous Occlusion ◽  
Cardiovascular Complications ◽  
Tissue Temperature

Vascular reactivity (VR) denotes changes in volumetric blood flow in response to arterial occlusion. Current techniques to study VR rely on monitoring blood flow parameters and serve to predict the risk of future cardiovascular complications. Because tissue temperature is directly impacted by blood flow, a simplified thermal model was developed to study the alterations in fingertip temperature during arterial occlusion and subsequent reperfusion (hyperemia). This work shows that fingertip temperature variation during VR test can be used as a cost-effective alternative to blood perfusion monitoring. The model developed introduces a function to approximate the temporal alterations in blood volume during VR tests. Parametric studies are performed to analyze the effects of blood perfusion alterations, as well as any environmental contribution to fingertip temperature. Experiments were performed on eight healthy volunteers to study the thermal effect of 3min of arterial occlusion and subsequent reperfusion (hyperemia). Fingertip temperature and heat flux were measured at the occluded and control fingers, and the finger blood perfusion was determined using venous occlusion plethysmography (VOP). The model was able to phenomenologically reproduce the experimental measurements. Significant variability was observed in the starting fingertip temperature and heat flux measurements among subjects. Difficulty in achieving thermal equilibration was observed, which indicates the important effect of initial temperature and thermal trend (i.e., vasoconstriction, vasodilatation, and oscillations).

Temperature Difference Between the Body Core and the Arterial Blood Supplied to the Brain During Hyperthermia or Hypothermia

2001 ◽  
Author(s):  
Liang Zhu ◽  
Maithreyi Bommadevara
Keyword(s):  
Blood Vessel ◽  
Temperature Difference ◽  
Carotid Arteries ◽  
Brain Temperature ◽  
Indirect Evidence ◽  
Blood Perfusion ◽  
The Body ◽  
Arterial Blood ◽  
Body Core ◽  
The Brain

Abstract In this study a theoretical model was developed to evaluate the temperature difference between the body core and the arterial blood supplied to the brain. Several factors including the local blood perfusion rate, blood vessel bifurcation in the neck, and blood vessel pairs on both sides of the neck were considered in the model. The theoretical approach was used to estimate the potential for cooling of blood in the carotid artery on its way to the brain by heat exchange with its countercurrent jugular vein and by the radial heat conduction loss to the cool neck surface. It shows that blood temperature along the common and internal carotid arteries typically decreases up to 0.86°C during hyperthermia. Selectively cooling the neck surface during hypothermia increases the heat loss from the carotid arteries and results in approximately 1.2°C in the carotid arterial temperature. This research could provide indirect evidence of the existence of selective brain cooling (SBC) in humans during hyperthermia. The simulated results can also be used to evaluate the feasibility of lowering brain temperature effectively by selectively cooling the head and neck surface during hypothermia treatment for brain injury or multiple sclerosis.

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