Temperature simulations in tissue with a realistic computer generated vessel network

Leeuwen, van; Kotte, Antj Alexis; Raaymakers, B.W.; Lagendijk, J.J.W.

doi:10.1088/0031-9155/45/4/317

Cited by 34 publications

(18 citation statements)

References 19 publications

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“…An explicit finite-difference approximation of Equation 2 was implemented with a temporal resolution of 1 s and a spatial resolution of 1 Â 1 Â 1 mm 3 . This magnitude of resolution was found to be adequate in previous studies that involved various sizes of discrete blood vessels with sharp, localised temperature gradients [17][18][19][20]. In addition, this optimisation algorithm was designed to be used in a MRgHIFU system, where temperature measurement resolution is larger than the present study.…”

Section: Simulation Geometrymentioning

confidence: 81%

Minimisation of HIFU pulse heating and interpulse cooling times

Payne

Vyas

Blankespoor

et al. 2010

International Journal of Hyperthermia

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This study presents results from a new optimisation technique that reduces HIFU treatment times by minimising individual heating and interpulse cooling times while adhering to normal tissue constraint limits at each sonication position. The potential clinical usefulness of this technique is demonstrated through its implementation in three dimentsional (3D) simulations of HIFU treatments for a range of tumour geometries, normal tissue constraint values, tissue perfusion levels and focal zone scanning path trajectories, all studied as a function of the applied power magnitude. When compared to typical open loop values the optimised treatment times were lower for all conditions studied, including when treatment-limiting normal tissue thermal build-up was present. While use of this technique guarantees minimum pulse heating and interpulse cooling times for each pulse, the total treatment time gains realised depend on the individual clinical treatment configuration. In combination with a judiciously selected scan path, use of the pulse time optimisation procedure reduced treatment times in a small, superficial tumour by 85%. In addition, in all cases studied the use of an increased applied power always decreased the treatment time, including cases when significant normal tissue thermal build-up was present. Importantly, the power maximisation and pulse time minimisation procedures can be applied independently of the optimisation of the focal zone's scan path, size and shape. Given the basic nature, universal applicability and ready clinical adaptability for use in real time model predictive control, the pulse time minimisation and power maximisation approaches have significant clinical promise for reducing HIFU treatment times.

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Section: Simulation Geometrymentioning

confidence: 81%

Minimisation of HIFU pulse heating and interpulse cooling times

Payne

Vyas

Blankespoor

et al. 2010

International Journal of Hyperthermia

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“…Thus, such vessels must be modeled using separate equations. The effect of such vessels have been studied by Chato [12] and Huang et al [13,14] who developed analytical models for single vessels, and by other investigators [15-23] who have done numerical and experimental hyperthermia studies of single vessels and/or counter current vessel pairs imbedded in either a purely conductive media (with either a normal thermal conductivity, or an enhanced, effective thermal conductivity) or in media modeled by the Pennes BHTE. One of those studies, by Rawnsley et al [22], compares the predictions from such a combined model (approximate field equation plus a separate blood vessel model) with experimental hyperthermia results.…”

Section: Introductionmentioning

confidence: 99%

“…It clearly showed the increased accuracy of such combined models. Leeuwen et al [23] also stressed that efforts to obtain information on the positions of the large vessels in an individual hyperthermia patient will be rewarded with a more accurate prediction of the temperature distribution. Finally, a few studies have modeled the effect of collections of a large number of parallel vessels or of networks of vessels [23-26].…”

Section: Introductionmentioning

confidence: 99%

Predicting effects of blood flow rate and size of vessels in a vasculature on hyperthermia treatments using computer simulation

2010

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BackgroundPennes Bio Heat Transfer Equation (PBHTE) has been widely used to approximate the overall temperature distribution in tissue using a perfusion parameter term in the equation during hyperthermia treatment. In the similar modeling, effective thermal conductivity (Keff) model uses thermal conductivity as a parameter to predict temperatures. However the equations do not describe the thermal contribution of blood vessels. A countercurrent vascular network model which represents a more fundamental approach to modeling temperatures in tissue than do the generally used approximate equations such as the Pennes BHTE or effective thermal conductivity equations was presented in 1996. This type of model is capable of calculating the blood temperature in vessels and describing a vasculature in the tissue regions.MethodsIn this paper, a countercurrent blood vessel network (CBVN) model for calculating tissue temperatures has been developed for studying hyperthermia cancer treatment. We use a systematic approach to reveal the impact of a vasculature of blood vessels against a single vessel which most studies have presented. A vasculature illustrates branching vessels at the periphery of the tumor volume. The general trends present in this vascular model are similar to those shown for physiological systems in Green and Whitmore. The 3-D temperature distributions are obtained by solving the conduction equation in the tissue and the convective energy equation with specified Nusselt number in the vessels.ResultsThis paper investigates effects of size of blood vessels in the CBVN model on total absorbed power in the treated region and blood flow rates (or perfusion rate) in the CBVN on temperature distributions during hyperthermia cancer treatment. Also, the same optimized power distribution during hyperthermia treatment is used to illustrate the differences between PBHTE and CBVN models. Keff (effective thermal conductivity model) delivers the same difference as compared to the CBVN model. The optimization used here is adjusting power based on the local temperature in the treated region in an attempt to reach the ideal therapeutic temperature of 43°C. The scheme can be used (or adapted) in a non-invasive power supply application such as high-intensity focused ultrasound (HIFU). Results show that, for low perfusion rates in CBVN model vessels, impacts on tissue temperature becomes insignificant. Uniform temperature in the treated region is obtained.ConclusionTherefore, any method that could decrease or prevent blood flow rates into the tumorous region is recommended as a pre-process to hyperthermia cancer treatment. Second, the size of vessels in vasculatures does not significantly affect on total power consumption during hyperthermia therapy when the total blood flow rate is constant. It is about 0.8% decreasing in total optimized absorbed power in the heated region as γ (the ratio of diameters of successive vessel generations) increases from 0.6 to 0.7, or from 0.7 to 0.8, or from 0.8 to 0.9. Last, in hyperthermia treatmen...

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“…RF radiation at high SAR mainly results in heating of the cells. Heat is known to cause many biological changes and the heating effect of RF radiation is well established [Van Leeuwen et al, 2000]. However, there have been claims that RF radiation could exert non-thermal effects on biological systems.…”

Section: Introductionmentioning

confidence: 99%

Effects of continuous and intermittent exposure to RF fields with a wide range of SARs on cell growth, survival, and cell cycle distribution

Takashima

Hirose

Koyama

et al. 2006

Bioelectromagnetics

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To examine the biological effects of radio frequency (RF) electromagnetic fields in vitro, we have examined the fundamental cellular responses, such as cell growth, survival, and cell cycle distribution, following exposure to a wide range of specific absorption rates (SAR). Furthermore, we compared the effects of continuous and intermittent exposure at high SARs. An RF electromagnetic field exposure unit operating at a frequency of 2.45 GHz was used to expose cells to SARs from 0.05 to 1500 W/kg. When cells were exposed to a continuous RF field at SARs from 0.05 to 100 W/kg for 2 h, cellular growth rate, survival, and cell cycle distribution were not affected. At 200 W/kg, the cell growth rate was suppressed and cell survival decreased. When the cells were exposed to an intermittent RF field at 300 W/kg(pk), 900 W/kg(pk) and 1500 W/kg(pk) (100 W/kg(mean)), no significant differences were observed between these conditions and intermittent wave exposure at 100 W/kg. When cells were exposed to a SAR of 50 W/kg for 2 h, the temperature of the medium around cells rose to 39.1 degrees C, 100 W/kg exposure increased the temperature to 41.0 degrees C, and 200 W/kg exposure increased the temperature to 44.1 degrees C. Exposure to RF radiation results in heating of the medium, and the thermal effect depends on the mean SAR. Hence, these results suggest that the proliferation disorder is caused by the thermal effect.

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Temperature simulations in tissue with a realistic computer generated vessel network

Cited by 34 publications

References 19 publications

Minimisation of HIFU pulse heating and interpulse cooling times

Minimisation of HIFU pulse heating and interpulse cooling times

Predicting effects of blood flow rate and size of vessels in a vasculature on hyperthermia treatments using computer simulation

Effects of continuous and intermittent exposure to RF fields with a wide range of SARs on cell growth, survival, and cell cycle distribution

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