Fourier-Domain Ultrasonic Imaging of Cortical Bone Based on Velocity Distribution Inversion

Morphobiometry of the scleral ossicle rings in Chelonia mydas sea turtles

OBJECTIVE

Scleral ossicle rings of reptiles have endoskeletal functions that are not completely understood. Moreover, descriptive reports on the anatomy of those rings are scarce. We tried to make an anatomical description that could contribute to a better understanding of their functions.

ANIMAL STUDIED AND PROCEDURES

We quantified, histologically characterized and evaluated the morphobiometry of the scleral ossicles, and measured the aditus orbitae of 25 sea turtle (Chelonia mydas) heads.

RESULTS

The aditus orbitae represented about one-third of the total head length and the mean area of the internal opening of each ring was up to 8.37% of the aditus orbitae area. The mean internal diameter of the rings (6.32 mm) was characteristic of scotopic species and the most frequent number of ossicles per ring varied between 11 and 12. Two new classifications were proposed for the ossicle types: plus-Verzahnung (+V) and minus-Verzahnung (-V). The bone tissue revealed a lamellar arrangement typical of compact and resistant bones.

CONCLUSION

The obtained data may be used to support and expand the understanding of functions, animal activity patterns, distinctions between taxa and taphonomic interpretations.

Femoral neck phantom imaging using time-domain topological energy method

Ultrasonic bone imaging is a complex task, primarily because of the low energy contained in the signals reflected from the internal bone structures. In this study, the reconstruction of a bone-mimicking phantom echographic image using time-domain topological energy (TDTE) is proposed. A TDTE image results from a combination of forward and adjoint fields. The first is a solution of a numerical model that reproduces the setup of the experimental data acquisition to the best extent possible. The second has similar characteristics, but the source term is the time-reversed residue between the forward field and signals obtained from the experiment. The acquisition-reconstruction system used a linear phased-array transducer with a 5 MHz center frequency to acquire the signals and was coupled with a k-wave toolbox to implement the numerical models and perform the image reconstruction. The results showed good agreement between the geometry of the real phantom and the ultrasonic images. However, thickness evaluation errors were observed, which may be due to incorrect assumptions about the velocity models throughout the medium, a priori assumed to be known. Thus, this method has shown promising results and should be applied to the real femoral neck as a long-term objective.

Index-Rotated Fast Ultrasound Imaging of Cortical Bone Based on Predicted Velocity Model

Due to the significant acoustic impedance contrast at cortical boundaries, highly inside attenuation, and the unknown sound velocity distribution, accurate ultrasound cortical bone imaging remains a challenge, especially for the traditional pulse-echo modalities using unique sound velocity. Moreover, the large amounts of data recorded by multielement probe results in a relatively time-consuming reconstruction process. To overcome these limitations, this article proposed an index-rotated fast ultrasound imaging method based on predicted velocity model (IR-FUI-VP) for cortical cross section ultrasound tomography (UST) imaging, utilizing ray-tracing synthetic aperture (RTSA). In virtue of ring probe, the sound velocity model was predicted in advance using bent-ray inversion (BRI). With the predicted velocity model, index-rotated fast ultrasound imaging (IR-FUI) was further applied to image the cortical cross sections in the sectors corresponding to the dynamic apertures (DAs) and ring center. The final result was merged by all sector images. One cortical bone phantom and two ex vivo bovine femurs were utilized to demonstrate the performance of the proposed method. Compared to the conventional synthetic aperture (SA) imaging, the method can not only accurately image the outer cortical boundary but also precisely reconstruct the inner cortical surface. The mean relative errors of the predicted sound velocity in the region of interest (ROI) were all smaller than 7%, and the mean errors of cortical thickness are all less than 0.31 mm. The reconstructed images of bovine femurs were in good agreement with the reference images scanned by micro-computed tomography ( μ CT) with respect to the morphology and thickness. The speed of IR-FUI is about 3.73 times faster than the traditional SA. It is proved that the proposed IR-FUI-VP-based UST is an effective way for fast and accurate cortical bone imaging.