Purpose Current imaging for vesicoureteral reflux requires a catheter and ionizing radiation. Both are best avoided in children. We present our progress toward development of a non-invasive device to detect vesicoureteral reflux. Conceptually, reflux will be detected by warming the bladder to a fever temperature and measuring kidney temperatures before and after. Reflux will be discovered if kidney temperature rises after bladder warming.
A 915 MHz microwave antenna array with an integrated antenna/radiometer was used for bladder heating (5-7.5 watts/minute) and temperature measurements.
Kidney temperatures were monitored with a specially designed receiving antenna and microwave radiometer characterized by 500 MHz frequency band and 1.35 GHz center frequency.
Phantom heating experiments: A 120 cc balloon representing the bladder was placed 1-1.5 cm within a complex fat/muscle phantom and was heated. Temperatures probes in each layer made measurements.
Phantom temperature measuring experiments: Temperatures were measured in a 30 cc balloon 3.5 cm from the surface using a radiometric system while the balloon was continuously perfused and intermittently injected with warm fluid.
Animal heating experiments: 16 Kg female pigs under anesthesia had their bladders warmed with a 915 MHz microwave antenna array composed by 2 dual concentric conductor (DCC) antennas while the skin was cooled with circulating room temperature water. Temperature probes monitored bladder and surrounding temperatures.
Animal temperature measuring experiments: A 30cc balloon was placed 3.5 cm from the skin in the renal fossa and was continuously perfused or intermittently injected and the balloon temperature was measured with the 1.35 GHz radiometer.
Phantom heating experiments: The phantom bladder was heated to 40-44ºC in 3-5 minutes and maintained for 20 minutes without the intervening layers increasing the temperature to 38.5 ºC.
Phantom temperature measuring experiments: Measurements using 1.35 GHz radiometer with a 500 MHz frequency bandwidth in a shielded room were accurate and matched temperature probe measurements.
Animal heating experiments: Bladder heating to 40-44 ºC occurred within 3-5 minutes and was maintained for 20 minutes and repeated a total of 3 times without pathological change in any intervening or surrounding tissues.
Animal temperature measuring experiments: 1.35 GHz radiometer clearly detected temperature changes of 7 ºC transiently and 3 ºC steady state within the 30 cc balloon 3.5 cm deep in the renal fossa.
- Microwave bladder warming to 40+ ºC can be accomplished safely.
- Temperatures in the kidney region can be measured accurately and may allow reflux detection in the future.
- The data is encouraging for human trials.