Open-Ended Transmission Coaxial Probes for Sarcopenia Assessment.

Paul Meaney,Shireen D Geimer,Robin Augustine,Roberta M Diflorio-Alexander,Timothy Raynolds

doi:10.3390/s22030748

Abstract

We developed a handheld, side-by-side transmission-based probe for interrogating tissue to diagnose sarcopenia—a condition largely characterized by muscle loss and replacement by fat. While commercial microwave reflection-based probes exist, they can only be used in a lab for a variety of applications. The penetration depth of these probes is only in the order of 0.3 mm, which does not even traverse the skin layer, and minor motion of the coaxial feedlines can completely dismantle the calibration. Our device builds primarily on the transmission-based concept that allows for substantially greater signal penetration depth operating over a very broad bandwidth. Additional features were integrated to further improve the penetration, optimize the geometry for a more focused planar excitation, and juxtapose the coaxial apertures for more controlled interrogation. The larger coaxial apertures further increased the penetration depth while retaining the broadband performance. Three-dimensional printing technology made it possible for the apertures to be compressed into ellipses for interrogation in a near-planar geometry. Finally, fixed side-by-side positioning provided repeatable and reliable performance. The probes were also not susceptible to multipath signal corruption due to the close proximity of the transmitting and receiving apertures. The new concept worked from 100 MHz to over 8 GHz and could sense property changes as deep as 2–3 cm. While the signal changes due to deeper feature aberrations were more subtle than for signals emanating from the skin and subcutaneous fat layers, the large property contrast between muscle and fat is a sarcopenic indication that helps to distinguish even the deepest objects. This device has the potential to provide needed specificity information about the relevant underlying tissue.

Highlights

Sarcopenia is a muscle disorder distinguished by the loss of muscle mass [1]
Patients scoring low on these tests are recommended for further interrogation via imaging and sensing to evaluate muscle mass and/or muscle quality to definitively diagnose sarcopenia
Muscle quality consists of the degree of intramuscular fat or fibrosis, which is a secondary manifestation in muscle atrophy

Summary

Introduction

Sarcopenia is a muscle disorder distinguished by the loss of muscle mass [1] It has a direct impact on the strength and function of the combined muscle and skeletal system. In its early stages there is a decrease in muscle quality, while the later stages involve a more pronounced replacement of fibers with fat and different forms of fibrosis [2,5] These impact overall operation, including reduced metabolism and impaired mechanical functionality [2,5]. Sarcopenia is most often identified individually or by a combination of several metrics, including muscle strength, muscle function, muscle mass, and muscle quality [1] The former two are essentially measured using mechanical or observational tests, while the latter involve conventional imaging and sensing. Muscle function tests characterize sarcopenia severity, typically by examining gait speed and other aspects of muscle coordination [11]

Methods

Results

Discussion

Conclusion