Design and Evaluation of a Medical Microwave Radiometer for Observing Temperature Gradients Subcutaneously in the Human Body

The topic covered in this thesis is medical temperature measurement of subcutaneous parts of human tissue with use of microwave radiometry. Radiometry is a completely non-invasive, non-toxic and relatively inexpensive sensing modality. The radiometric technique is based on the measurement of electromagnetic noise power emitted by lossy materials. The method has explicit low investment costs and low technological complexity, but relatively low spatial resolution. Still the method can be useful for some dedicated medical applications. Fundamental radiometric theory and dielectrical properties of biological tissues are derived. The process to realize a miniaturized radiometer is going from active antenna configuration to a complete miniaturized radiometer and finally to a modular radiometer, that is used \textsl{in-vivo} on humans. Different radiometers were designed, simulated, built and tested on realistic human phantoms. \textit{In vivo} experiments were also conducted to verify the prototype radiometer and to test the ability to be used in tailored medical diagnostics. The primary application covered is temperature gradient measurement during microwave hyperthermia and in pediatric vesicouretaral reflux (VUR) detection. Hyperthermia is a therapeutic technique in which cancerous tissue is heated to 40-45$^\circ$C, inducing vascular and cellular changes that improve the therapeutic effectiveness when used in conjunction with chemotherapy or radiation therapy. VUR is abnormal flow of urine from the bladder back to the upper urinary tract. Another application where this radiometer can be of great interest is in breast cancer diagnostic. Breast cancer is a type of cancer that forms in tissues of the breast; usually in the ducts and lobules and can occur in both men and woman. We present results from radiometric measurement on human phantoms during a hyperthermia heating sequence. Experimental evidence shows that radiometry can be used for temperature quality assurance of the heated volume in depth. In VUR detection, the first step is to heat the bladder prior to detection of the reflux. We present results from measurements \textsl{in-vivo} with a water filled balloon in the human mouth, that mimics pediatric bladder heating. Results show that the radiometer can be used as the first step in the novel VUR detection. Radiometry antennas are one of the most critical components in a radiometer system. An elliptical printed circuit board antenna is designed and matched to the human body. Further, an antenna with suction, with use of negative pressure to mount the antenna onto the human body for improved radiometric performance, was also proposed and built. The simple and elegant solution for the coupling of the antenna with use of negative pressure, documents improved performance in estimating the true temperature as well as exhibiting smaller fluctuation in the radiometric signal

Mikrobølgeradiometri anvendt til deteksjon av temperaturgradienter i brystvevsfantom

En passiv, ikke-invasiv og ufarlig metode for detektering av brystkreft er motivasjonen for denne oppgaven. Basisen for mikrobølgeteori og radiometrisk teori er presentert. Videre presenteres grunnlaget for å kunne foreta passive målinger på brystvevsmodeller, målemetoder og forbedringsmuligheter innen mikrobølge radiometri. Vi studerer ulike forbedringsmuligheter ved å se på systemet ved Institutt for fysikk og teknologi. Forbedringer er realisert ved å lage et interferensfritt system som i tillegg er automatisert. En forbedring av systemets signal-til-støyforhold er oppnådd ved å benytte prinsippet om å plassere en forforsterker på utsiden av Dicke-venderen i en Dickemottaker. Dette prinsippet er pretestet før det implemeteres i radiometeret. Det er utviklet metoder for deteksjon av varme legemer og det er foretatt radiometriske målinger for ulike oppsett. Det nye prinsippet med en lavstøyforsterker før Dicke-venderen er testet ut på radiometriske gradientmålinger, og vi presenterer resultatene av en slik studie. Metodene som er utprøvd gir en gevinst i signal-til-støyforhold på 34%

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

A new scheme for detection of vesicoureteral reflux (VUR) in children has recently been proposed in the literature. The idea is to warm bladder urine via microwave exposure to at least fever temperatures and observe potential urine reflux from the bladder back to the kidney(s) by medical radiometry. As a preliminary step toward realization of this detection device, we present non-invasive temperature monitoring by use of microwave radiometry in adults to observe temperature dynamics in vivo of a water-filled balloon placed within the oral cavity. The relevance of the approach with respect to detection of VUR in children is motivated by comparing the oral cavity and cheek tissue with axial CT images of young children in the bladder region. Both anatomical locations reveal a triple-layered tissue structure consisting of skin–fat–muscle with a total thickness of about 8–10 mm. In order to mimic variations in urine temperature, the target balloon was flushed with water coupled to a heat exchanger, that was moved between water baths of different temperatures, to induce measurable temperature gradients. The applied radiometer has a center frequency of 3.5 GHz and provides a sensitivity (accuracy) of 0.03 °C for a data acquisition time of 2 s. Three different scenarios were tested and included observation through the cheek tissue with and without an intervening water bolus compartment present. In all cases, radiometric readings observed over a time span of 900 s were shown to be highly correlated (R ~ 0.93) with in situ temperatures obtained by fiberoptic probes