Reduction in Beam Positioning Error During HIFU Ablation Studies in Tissue Phantoms

2010 ◽  
Author(s):  
Subhashish Dasgupta ◽  
Prasanna Hariharan ◽  
Matthew R. Myers ◽  
Rupak K. Banerjee
Keyword(s):  
Blood Flow ◽  
Iterative Method ◽  
Temperature Rise ◽  
Focused Ultrasound ◽  
High Intensity Focused Ultrasound ◽  
Measured Temperature ◽  
Positioning Error ◽  
Tissue Phantoms ◽  
Order Of Magnitude ◽  
Source Of Error

Measurements of high intensity focused ultrasound (HIFU) induced temperature rise using thermocouples in tissue phantoms are subject to several types of error which must be accounted for in order to accurately assess the thermal field and predict the outcome of clinical procedures. Thermocouple artifacts due to viscous heating is one source of error. A second source of error involves displacement of the beam relative to the targeted thermocouple junction, due to the difficulty in precisely positioning the very narrow beam. This paper presents an iterative method for removing inaccuracies due to positioning error from the measured temperature data. The refined data is used to quantify the effect of blood flow through large vessels on the efficacy of HIFU procedures. It was determined that blood flow cooling effect causes an order of magnitude decrease in thermal dose at the target within 2 mm of the blood vessel, potentially resulting in incomplete ablation of the tumor. The technique also reveals that thermocouple artifacts exist in significant proportions from about 0.5 to 2.2 times the computed temperature rise in the initial few seconds. The iterative method can aid in clinical procedure planning, especially in predicting the proper HIFU intensity and duration for complete destruction of tumors.

Delineation of Noise Signals From MRI Measured Temperature Rise During HIFU Ablation Procedure

2011 ◽  
Author(s):  
Subhashish Dasgupta ◽  
Seyed Ahmed Dibaji ◽  
Janaka Wansapura ◽  
Matthew R. Myers ◽  
Rupak K. Banerjee
Keyword(s):  
Temperature Rise ◽  
Focused Ultrasound ◽  
High Intensity Focused Ultrasound ◽  
Heat Equations ◽  
Intensity Level ◽  
Measured Temperature ◽  
Mr Thermometry ◽  
Porcine Liver ◽  
Heating Phase ◽  
Set Up

A relatively recent and non invasive method for characterizing thermal fields generated by high intensity focused ultrasound (HIFU) transducers is Magnetic Resonance (MR) Thermometry method. However, noise signals generated by external RF sources infiltrate the scanner orifice and limit its ability to measure temperature rise during the heating or ablation phase. In this study, MRI monitored HIFU ablations are performed on freshly excised porcine liver samples, at varying sonication times, 20, 30 and 40 s at a constant acoustic intensity level of 1244 W/cm2. Temperature rise during the procedure is measured using Proton Resonant Frequency MR thermometry. Preliminary experiments without an adequate noise filter, failed to record temperature rise during the heating phase. A low pass R-C filter circuit is subsequently incorporated into the experimental set up to prevent infiltration of noise signals in the MRI orifice. This modified RC filter enables measurement of temperature rise during the heating phase followed by temperature decay during cooling. The measured data is within 12% agreement with the temperature rise computed by solving the acoustic and heat equations.

Effect of Rate of Blood Flow Through Large Blood Vessels on HIFU Temperature Rise

2008 ◽  
Author(s):  
Subhashish Dasgupta ◽  
Prasanna Hariharan ◽  
Matthew R. Myers ◽  
Rupak K. Banerjee
Keyword(s):  
Blood Flow ◽  
Temperature Rise ◽  
Focused Ultrasound ◽  
Small Region ◽  
High Intensity Focused Ultrasound ◽  
Acoustic Energy ◽  
Tissue Temperature ◽  
Invasive Technique ◽  
Cell Necrosis ◽  
Flow Through

High Intensity Focused Ultrasound (HIFU) shows considerable promise as a minimally-invasive technique for tumor ablation. A typical HIFU procedure involves focusing of acoustic energy in a small region, with the absorbed acoustic energy causing localized rise in tissue temperature. Temperature rise of the order of 40–60°C is achieved within seconds, causing immediate cell necrosis in the targeted region.

Effekt of blood flow shutdown on the vein damage when exposed to HIFU

2017 ◽  
pp. 46-50
Author(s):  
Н.Н. Петрищев ◽  
Д.Ю. Семенов ◽  
А.Ю. Цибин ◽  
Г.Ю. Юкина ◽  
А.Е. Беркович ◽  
...  
Keyword(s):  
Blood Flow ◽  
Structural Changes ◽  
Focused Ultrasound ◽  
Vena Cava ◽  
Posterior Wall ◽  
High Intensity Focused Ultrasound ◽  
Vein Wall ◽  
Ultrasound Exposure ◽  
Isolated Segment ◽  
The Impact

The purpose. In the study we investigated the impact of the partial blood flow shutdown on structural changes in the rabbit vena cava posterior wall after exposure to high-intensity focused ultrasound (HIFU). Methods. Ultrasound Exposure: frequency of 1.65 MHz, the ultrasound intensity in the focus of 13.6 kW/cm, the area of the focal spot 1 mm, continuous ultrasound, exposure for 3 seconds. Results. Immediately after HIFU exposure all layers of the vein wall showed characteristic signs of thermal damage. A week after exposure structural changes in the intima, media and adventitia was minimal in the part of vessel with preserved blood flow, and after 4 weeks the changes were not revealed. A week after HIFU exposure partial endothelium destruction, destruction of myocytes, disorganization and consolidation of collagen fibers of the adventitia were observed in an isolated segment of the vessel, and in 4 weeks endothelium restored and signs of damage in media and adventitia persisted, but were less obvious than in a week after exposure. Conclusion. The shutdown of blood flow after exposure to HIFU promotes persistent changes in the vein wall. Vein compression appears to be necessary for the obliteration of the vessel, when using HIFU-technology.

Sign in / Sign up

Export Citation Format

Share Document