Calibration of the bone mineral density scale on X-ray microtomography

Coded excitation speeds up the detection of the fundamental flexural guided wave in coated tubes

The fundamental flexural guided wave (FFGW) permits ultrasonic assessment of the wall thickness of solid waveguides, such as tubes or, e.g., long cortical bones. Recently, an optical non-contact method was proposed for ultrasound excitation and detection with the aim of facilitating the FFGW reception by suppressing the interfering modes from the soft coating. This technique suffers from low SNR and requires iterative physical scanning across the source-receiver distance for 2D-FFT analysis. This means that SNR improvement achieved by temporal averaging becomes time-consuming (several minutes) which reduces the applicability of the technique, especially in time-critical applications such as…

Photo-acoustic excitation and optical detection of fundamental flexural guided wave in coated bone phantoms.

Abstract Photo-acoustic (PA) imaging was combined with skeletal quantitative ultrasound (QUS) for assessment of human long bones. This approach permitted low-frequency excitation and detection of ultrasound so as to efficiently receive the thickness-sensitive fundamental flexural guided wave (FFGW) through a coating of soft tissue. The method was tested on seven axisymmetric bone phantoms, whose 1- to 5-mm wall thickness and 16-mm diameter mimicked those of the human radius. Phantoms were made of a composite material and coated with a 2.5- to 7.5-mm layer of soft material that mimicked soft tissue. Ultrasound was excited with a pulsed Nd:YAG laser at 1064-nm wavelength and received on the s…

Morphological analysis of human cortical bone using high-resolution X-ray microtomography

Structural and elastic properties of bone are related to microstructural parameters such as porosity and anisotropy. Microtomography (μCT) enables assessment of bone microstructural geometry, typically down to a voxel size of 5 microns. The purpose of this thesis was to evaluate whether using a higher (sub-micrometer) voxel resolution in X-ray μCT enables detection of new, finer, details in human cortical bone. The second objective was to measure several morphological parameters that determine the microstructure, and to compare two different microtomographs. To this end, twenty four human cadaveric femur samples were imaged by Xradia XCT-400 at a voxel size of 0.56 - 0.59 μm and spatial res…

A free plate model can predict guided modes propagating in tubular bone-mimicking phantoms

The goal of this work was to show that a non-absorbing free plate model can predict with a reasonable accuracy guided modes measured in bone-mimicking phantoms that have circular cross-section. Experiments were carried out on uncoated and coated phantoms using a clinical axial transmission setup. Adjustment of the plate model to the experimental data yielded estimates for the waveguide characteristics (thickness, bulk wave velocities). Fair agreement was achieved over a frequency range of 0.4 to 1.6 MHz. A lower accuracy observed for the thinnest bone-mimicking phantoms was caused by limitations in the wave number measurements rather than by the model itself.