Vesicoureteral Reflux in Children: A Phantom Study of Microwave Heating and Radiometric Thermometry of Pediatric Bladder

Abstract

We have investigated the use of microwave heating and radiometry to safely heat urine inside a pediatric bladder. The medical application for this research is to create a safe and reliable method to detect vesicoureteral reflux, a pediatric disorder, where urine flow is reversed and flows from the bladder back up into the kidney. Using fat and muscle tissue models, we have performed both experimental and numerical simulations of a pediatric bladder model using planar dual concentric conductor microstrip antennas at 915 MHz for microwave heating. A planar elliptical antenna connected to a 500 MHz bandwidth microwave radiometer centered at 3.5 GHz was used for non-invasive temperature measurement inside tissue. Temperatures were measured in the phantom models at points during the experiment with implanted fiberoptic sensors, and 2D distributions in cut planes at depth in the phantom with an infrared camera at the end of the experiment. Cycling between 20 second with 20 Watts power for heating, and 10 seconds without power to allow for undisturbed microwave radiometry measurements, the experimental results show that the target tissue temperature inside the phantom increases fast and that the radiometer provides useful measurements of spatially averaged temperature of the illuminated volume. The presented numerical and experimental results show excellent concordance, which confirms that the proposed system for microwave heating and radiometry is applicable for safe and reliable heating of pediatric bladder.

Using a conformal water bolus to adjust heating patterns of microwave waveguide applicators

“…In 2011, the single input-single output (SISO) bolus configuration was introduced, which included Tygon tubes perforated with holes approximately 1 cm apart along the two sides of the bolus. 20 However, this configuration works well only for small boluses since temperature varies significantly (>2°C) in larger boluses as required for the MA-120 applicator. 20 Dual input-dual output (DIDO) water boluses have been described previously which provide highly uniform distribution of water flow through much larger conformal water boluses but suffer from the added weight and impracticality of having two Tygon supply tubes to each side of bolus.…”

“…20 However, this configuration works well only for small boluses since temperature varies significantly (>2°C) in larger boluses as required for the MA-120 applicator. 20 Dual input-dual output (DIDO) water boluses have been described previously which provide highly uniform distribution of water flow through much larger conformal water boluses but suffer from the added weight and impracticality of having two Tygon supply tubes to each side of bolus. 21 In this effort, we developed a modified SISO bolus with a center feed design that distributes water flow uniformly across a moderately large bolus sufficient for the MA-120 waveguide applicator.…”

A novel compact microwave radiometric sensor to noninvasively track deep tissue thermal profiles

“…For rapid recovery to good health, reestablishing normothermic temperature of the internal organs is essential. Although brain is the most critical temperature sensitive tissue [8], core temperature, currently considered the temperature of internal body organs, can differs significantly from brain. In fact, current thermometry devices typically measure only intracavitary surrogates of body temperature that do not accurately reflect core temperature of the deep lying organs, especially brain.…”

“…There have been many reports of medical applications of MW radiometry, including the detection of breast cancer [13], monitoring and control of superficial and deep hyperthermia applicators [14][15][16][17], measurement of brain temperature in infants [10] or adults [18], vesicoureteral reflux detection in young children [19,20] and more recently monitoring of brown fat metabolism [21]. In the particular case of monitoring adult brain temperature, there are no reports to our knowledge of an antenna small enough to conform to the human head during prolonged surgery; present a stable reading over several hours; and offer an accuracy of 0.5°C, which is the smallest difference that has been associated with hypothermia-induced complications [8].…”

“…The amount of microwave energy received by a surface antenna increases with increasing tissue temperature and may be used to quantify deep tissue temperature. We choose to monitor temperature inside the brain [17] rather than alternative sites due to the critical nature of this organ and its central role in thermoregulation [8,16]. The purpose of this study is to characterize the sensitivity and accuracy of a new radiometric thermometer for long-term monitoring of core temperature in brain.…”