Numerical 3D modeling of heat transfer in human tissues for microwave radiometry monitoring of brown fat metabolism.
BACKGROUND
Brown adipose tissue (BAT) plays an important role in whole body metabolism and could potentially mediate weight gain and insulin sensitivity. Although some imaging techniques allow BAT detection, there are currently no viable methods for continuous acquisition of BAT energy expenditure. We present a non-invasive technique for long term monitoring of BAT metabolism using microwave radiometry.


METHODS
A multilayer 3D computational model was created in HFSS™ with 1.5 mm skin, 3-10 mm subcutaneous fat, 200 mm muscle and a BAT region (2-6 cm3) located between fat and muscle. Based on this model, a log-spiral antenna was designed and optimized to maximize reception of thermal emissions from the target (BAT). The power absorption patterns calculated in HFSS™ were combined with simulated thermal distributions computed in COMSOL® to predict radiometric signal measured from an ultra-low-noise microwave radiometer. The power received by the antenna was characterized as a function of different levels of BAT metabolism under cold and noradrenergic stimulation.


RESULTS
The optimized frequency band was 1.5-2.2 GHz, with averaged antenna efficiency of 19%. The simulated power received by the radiometric antenna increased 2-9 mdBm (noradrenergic stimulus) and 4-15 mdBm (cold stimulus) corresponding to increased 15-fold BAT metabolism.


CONCLUSIONS
Results demonstrated the ability to detect thermal radiation from small volumes (2-6 cm3) of BAT located up to 12 mm deep and to monitor small changes (0.5 °C) in BAT metabolism. As such, the developed miniature radiometric antenna sensor appears suitable for non-invasive long term monitoring of BAT metabolism.
Department of Radiation Oncology, Hyperthermia Division, PO BOX 3085 Duke University Medical Center, Durham, NC 27710, USA ; CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal.
Dario B
DB
Rodrigues
Paolo F
PF
Maccarini
Sara
S
Salahi
Erin
E
Colebeck
Erdem
E
Topsakal
Pedro J S
PJ
Pereira
Paulo
P
Limão-Vieira
Paul R
PR
Stauffer
3D multiphysics modeling; Brown fat metabolism; log spiral antenna; microwave radiometry; noninvasive monitoring