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MicrowaveRadiometryforInternalBodyTemperatureMonitoring

CONFERENCEPAPER·AUGUST2014

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ParisaMomenroodaki

UniversityofColoradoBoulder

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Microwave Radiometry for Internal Body Temperature Monitoring

Summary

References

Preliminary Setup- Based on off-the-shelf components -

Antenna temperature (TA) and top water layerthermocouple measurement (Tt1) along with radiometricestimate of the subsurface water layer (Tv3) andthermocouple measurement (Tt3) as the system reachesequilibrium after subsurface water layer heated to 44°C.

Main Results Temperature Retrieval

Tv3 =TA −TfWf − TuWu −Tv1Wv1 −Tv2Wv2

Wv3

Radiometric estimate of the temperature above a waterhalf-space (Tv) using 1.4 GHz radiometer is compared tothe measured thermocouple temperature (Tt). The wateris heated to 44°C and the measured data shows thecooling when placed at room temperature.

• Comparison of raw radiometer estimate andthermocouple measurement shows an error of 0.4°Cto 1.1°C. The discrepancy over time is probably dueto an incorrect assumption of the feed temperature(Tf), and/or changes in the weighting function overtime due to the changing dielectric properties.

Measurement setup on three-layer phantom:(1) 10.3mm water (2) Glass pyrex dish(3) 7cm water

𝐓𝐀 = TuWu + TfWf+Tv1Wv1 + Tv2Wv2+Tv3Wv3

The motivation for internal body temperaturemeasurements, and a possible non-invasive approachwith an external device is presented.

A 1.4GHz folded-dipole probe and radiometer isdesigned with off-the-shelf components, and used fora proof-of-principle demonstration with one-layerand three-layer (water-glass-water) phantoms.

The estimated temperature shows an accuracy of0.4°C compared to thermocouple measurements.

Current research and challenges:• Improve temperature estimation accuracy• Reduce RF interference by miniaturization,

integration and new probe design• Perform measurements with better phantoms and

improve calibration

𝐓𝐀

Probe at feed temperature (Tf) and

weighting function (Wf)

Upper half space attemperature (T𝑢) andweighting function (Wu)

Introduction to the ProblemBlack body radiation: all materials at non-zerotemperature emit electromagnetic radiation over allfrequencies (Plank’s law, Rayleigh-Jeans law). At microwave frequencies (1-30GHz), sensitive

radiometers are used to detect the radiated power. Temperature of an object can be deduced from the

very low measured power. At microwave frequencies, EM waves penetrate body

tissues as much as 3-7 cm and can be used forinternal temperature sensing.

Microwave Thermometry• Knowledge of internal (core) body temperature

important for health diagnostics and therapy: Athletes and soldiers under heavy training;

e.g. long duration of exercise in heat Cancer cells have increased temperature

compared to surrounding tissues Inflamed tissues, e.g. in arthritis patients, have

elevated temperatures Sleeping disorders are accompanied by

changes in the circadian cycle, which in turn isaccompanied by changes in phase andamplitude of periodic difference between thecore body and peripheral temperatures

Infants suffering from hypoxia-ischemia havean elevated brain temperature, and if detectedcan be treated by hypothermic neural rescue

During tissue ablation (laser, ultrasonic ormicrowave), it is important to monitortemperature of surrounding tissues

Power received by a radiometer: 𝑃 = 𝑘𝑇𝐴𝐵- TA is the temperature in Kelvin- B is the radiometer bandwidth- k =1.3810-23 J/K (Boltzmann constant)

• A near-field probe antenna is placed on the skin• The probe is connected to a Dicke radiometer• Radiometer receives black-body power from all

layers• Electromagnetic modeling needed to estimate

temperatures of the different layers

Radiometry

[1] K. Carr, “Microwave radiometry: its importance to the detection ofcancer,” IEEE Trans. Microwave Theory Techn., pp. 1862–1869, Dec.1989.[2] S. Jacobsen et al., “Multi-frequency radiometric determination oftemperature profiles in a lossy homogeneous phantom using a dual-mode antenna with integral bolus,” IEEE Trans. Microwave TheoryTechn., pp. 1737–46, Jul. 2002.[3] J. W. Hand, et al.,“Monitoring of deep brain temperature in infantsusing multi-frequency microwave radiometry and thermal modelling,”Physics in Medicine and Biology, vol. 46, pp. 1885–1903, Jul. 2001.[4] T. Sugiura et al., “Five band microwave radiometer system for non-invasive measurement of brain temperature in new-born infants:system calibration and its feasibility,” vol. 3. IEEE, 2004, pp. 2292–2295.[5] R. Scheeler et al., “Sensing depth of microwave radiation forinternal body temperature measurements,” IEEE Trans. MicrowaveTheory Techn., pp. 1293- 1303, March 2014.

Reflection coefficient

1.4GHz folded dipole probe

Data logger

1.4GHz radiometer

1.4GHz probe

Agilent hot noise source

Material Relative permittivity(𝜺𝒓)

Water 78

Glass 5.5

Skin 40

Fat 5.4

Muscle 54

• Antenna temperature (TA) is a weighted average ofthe temperature of the surrounding objects, andtherefore weighting functions (W) will be used todefine the antenna temperature.

Tv1,Wv1

Tv2,Wv2

Tv3,Wv3(1)(2)(3)

Antenna temperature

Lower half space attemperature (T𝑣) andweighting function (Wv)

Rad

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Rad

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Robert Scheeler, Parisa MomenRoodaki, Zoya PopovicUniversity of Colorado, Boulder, CO 80309, U.S.A.