Detection of Vesicoureteral Reflux Using Microwave Radiometry—System Characterization With Tissue Phantoms

Abstract

Microwave (MW) radiometry is proposed for passive monitoring of kidney temperature to detect vesicoureteral reflux (VUR) of urine that is externally heated by a MW hyperthermia device and thereafter reflows from the bladder to kidneys during reflux. Here we characterize in tissuemimicking phantoms the performance of a 1.375 GHz radiometry system connected to an electromagnetically (EM) shielded microstrip log spiral antenna optimized for VUR detection. Phantom EM properties are characterized using a coaxial dielectric probe and network analyzer (NA). Power reflection and receive patterns of the antenna are measured in layered tissue phantom. Receiver spectral measurements are used to assess EM shielding provided by a metal cup surrounding the antenna. Radiometer and fiberoptic temperature data are recorded for varying volumes (10-30 mL) and temperatures (40-46°C) of the urine phantom at 35 mm depth surrounded by 36.5°C muscle phantom. Directional receive pattern with about 5% power spectral density at 35 mm target depth and better than −10dB return loss from tissue load are measured for the antenna. Antenna measurements demonstrate no deterioration in power reception and effective EM shielding in the presence of the metal cup. Radiometry power measurements are in excellent agreement with the temperature of the kidney phantom. Laboratory testing of the radiometry system in temperature controlled phantoms supports the feasibility of passive kidney thermometry for VUR detection.

Radiometric temperature reading of a hot ellipsoidal object inside the oral cavity by a shielded microwave antenna put flush to the cheek

“…According to Snow et al (2011), CT images of children (age 2-5 years) show a distance of about 10 mm from the skin interface to the anterior bladder surface and correspondingly 30 mm to the center of the bladder. A representative CT image depicted in figure 2 displays these distances to be 11.7 mm and 34.3 mm, respectively.…”

“…As the target patient group consists of small children, these potential side effects need to be addressed in future work. Nevertheless, in a recent paper by Snow et al (2011), pathological evaluation of three pigs (where the urine was heated to [40][41][42][43][44] o C) showed that heating could be done without tissue damage, mainly due to the low power levels (10-20 W) needed to maintain elevated bladder temperatures.…”

“…The method is based on heating of the pediatric bladder above normal body temperature and using microwave radiometry to monitor induced temperature rise in the kidney if a urine reflux occurs. Preliminary results using animal experiments are promising (Snow et al 2011), and data is also encouraging for initial human trials (B. Snow, University of Utah, Salt Lake City, UT USA, private communication).…”

Utility of microwave radiometry for diagnostic and therapeutic applications of non-invasive temperature monitoring

“…Optimization parameters included the number and winding of spiral turns, and thickness and dielectric properties of the substrate and matching layer. A 7cm tapered log spiral was determined most appropriate for recording temperature rise in kidney located 3-5cm below the skin [13,14], and a 2.6cm diameter tapered log spiral was found to maximize coupling through the human skull into brain. [15] Fig .…”

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

“…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. Each of these surrogate core temperature measurements has inherent problems with probe placement, time delays in reading changing body temperature, and/or are objectionably invasive [9,10].…”