Miniature microwave applicator for murine bladder hyperthermia studies

Figures & data

Table I.  Properties of murine tissues at 2.45 GHz [18].

	Dielectric constant, ε	Electrical conductivity, σ (S/m)	Specific heat, Cp (J/kg°C)	Thermal conductivity, k (W/m°C)	Density, ρ (kg/m^3)
Body (muscle)	52.729	1.7388	3546	0.53	1041
Bladder (urine)	71.238	7.4257	4200^†	0.561	1000
Uterus	57.814	2.2465	3580	0.50	1052
Colon	53.879	2.0383	3653	0.56	1044

^†Urine and water have similar thermal conductivity and density values, so we assume that the specific heat of urine is also similar to water.

Figure 1. (A) Parameters varied to optimise SAR and S₁₁, (B) front view picture of 2.45 GHz applicator, (C) bottom view picture of 2.45 GHz applicator, (D) HFSS^™ model of the applicator on the mouse, (E) snapshot of experimental set-up for murine bladder hyperthermia study with applicator positioned on the skin overlying the pelvis.

Figure 2. S₁₁: HFSS^™ simulation compared to measurements using an Agilent E5071C network analyser.

Figure 3. SAR: HFSS™ simulation compared to measurements with all values normalised to the maximum value at 3 mm depth: (A) profile across x-axis, (B) profile across y-axis, (C) depth profile, (D) 3D SAR measurements in muscle phantom.

Figure 4. HFSS^™ SAR simulation in mouse model (A) x-axis profile and (B) y-axis profile.

Figure 5. 2D slice temperature profiles in mouse body, bladder, vagina and rectum with bolus temperature (A) unregulated, (B) constant 41°C, (C) constant 38°C and (D) constant 35°C and RF power set at (A) 5 W and (B), (C), (D) 12 W.

Figure 6. COMSOL simulation of average temperatures as a function of bolus temperature.

Figure 7. Temperature data taken from five independent murine bladder hyperthermia studies. Temperature increases occur when RF power is turned on (around the 2–5 min mark) and decreases occur when RF power is turned off (around the 18–20 min mark). The dotted line signifies 42°C.

Gabriel C, Compilation of the dielectric properties of body tissues at RF and microwave frequencies. Brooks Air Force Base, TX: Occupational and Environmental Health Directorate Radiofrequency Radiation Division, 1996

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