The influence of cortical end plate upon ultrasound transit time spectroscopy estimated bone assessment

Abstract

Quantitative ultrasound (QUS) is considered a reliable tool for routine assessment of bone. However, none of the QUS parameters has a direct measure of bone quantity or quality. The concept of ultrasound transit time spectroscopy (UTTS) has recently offered the possibility of effective estimates of bone volume fraction (BVF) as an indicator of bone density. This study aimed to investigate the influence of cortical end plate thickness around the cancellous bone on the measurement accuracy of UTTS solid volume fraction (UTTS-SVF). Two categories of cortical discs were designed and three-dimensional printed; category (I) is planer discs of constant different thickness and category (II) is variable-thickness step-wedge discs. In this experimental and simulated study, the discs were placed coaxially with the 3D-printed cylindrical iliac crest cancellous bone sample. A through-transmission 1 MHz ultrasound pulses were recorded, from which the deconvoluted TTS were derived. Then UTTS-SVF was determined and compared with the measured SVF via microcomputed tomography (μCT-SVF) showing a high agreement with an average of 94% ± 3.7% and 95% ± 4% for the planar cortical discs and 95.3% ± 5.5% and 96.5% ± 3.7% for variable-thickness step-wedge cortical discs for experiment and simulation respectively. The variations between the derived UTTS_SVF and the standard μCT-SVF are assumed to be due to the existence of phase interference within the cortical discs. Hence, the cortical end plate creates a negative influence on the derived UTTS-SVF.