Bone dielectric property variation as a function of mineralization at microwave frequencies.

Paul M Meaney,Douglas Goodwin,Elia A Attardo,Keith D Paulsen,Tian Zhou,Amir Golnabi

doi:10.1155/2012/649612

Abstract

A critical need exists for new imaging tools to more accurately characterize bone quality beyond the conventional modalities of dual energy X-ray absorptiometry (DXA), ultrasound speed of sound, and broadband attenuation measurements. In this paper we investigate the microwave dielectric properties of ex vivo trabecular bone with respect to bulk density measures. We exploit a variation in our tomographic imaging system in conjunction with a new soft prior regularization scheme that allows us to accurately recover the dielectric properties of small, regularly shaped and previously spatially defined volumes. We studied six excised porcine bone samples from which we extracted cylindrically shaped trabecular specimens from the femoral heads and carefully demarrowed each preparation. The samples were subsequently treated in an acid bath to incrementally remove volumes of hydroxyapatite, and we tested them with both the microwave measurement system and a micro-CT scanner. The measurements were performed at five density levels for each sample. The results show a strong correlation between both the permittivity and conductivity and bone volume fraction and suggest that microwave imaging may be a good candidate for evaluating overall bone health.

Highlights

Osteoporosis is a major health problem for roughly 55% of the US population of 50 years of age or older
In this paper we describe the process used in these experiments including the tissue preparation, X-ray CT, and microwave imaging approaches
The bath was the same for all sessions as illustrated by the backgrounds of each image being identical to the others

Summary

Introduction

Osteoporosis is a major health problem for roughly 55% of the US population of 50 years of age or older. The most typical fractures occur in the hip, spine, wrist, and ribs, of which the hip and vertebral fractures can require long-term care and even cause death in as many as 24% of hip fracture cases [1] This dynamic aspect of bone physiology may facilitate the use of dielectric interrogation as a means of imaging bone health. The dielectric properties, themselves, may provide clinically useful information with respect to assessing overall bone health as in the case of osteoporosis and monitoring osteogenic response to treatment. These properties have been studied extensively up to 5 MHz [16,17,18,19]; tests beyond this frequency have not proved useful to date [20]. Measurements have been made using conventional open-ended coaxial dielectric probes at frequencies as high

Methods

Results

Conclusion