Jami Shepherd

University of Auckland · Department of Physics

We present a technique called photoacoustic vector-flow (PAVF) to quantify the speed and direction of flowing optical absorbers at each pixel from acoustic-resolution PA images. By varying the receiving angle at each pixel in post-processing, we obtain multiple estimates of the phase difference between consecutive frames. These are used to solve th...

We present a Depth-resolved vibrometry system using a Fourier-domain mode-locked laser based optical coherence tomography system. We further present the first measurements of mechanical responses of snapping shrimp superficial hair to acoustic particle motion stimuli.

By changing the ultrasonic receiving angle in post-processing, we can obtain flow vectors from a photoacoustic experiment on a blood vessel phantom by solving the photoacoustic Doppler using a least-squares optimisation approach.

Intraosseous blood circulation is thought to have a critical role in bone growth and remodeling, fracture healing, and bone disorders. However, it is rarely considered in clinical practice due to the absence of a suitable non‐invasive in vivo measurement technique. In this work, we assessed blood perfusion in tibial cortical bone simultaneously wit...

Intraosseous blood circulation is thought to have a critical role in bone growth and remodeling, fracture healing, and bone disorders. However, it is rarely considered in clinical practice due to the absence of a suitable non-invasive in vivo measurement technique. In this work, we assessed blood perfusion in tibial cortical bone simultaneously wit...

Photoacoustic (PA) imaging is an emerging modality, which combines the high optical absorption contrast of biological chromophores with centimeter imaging depths and sub-millimeter resolution of ultrasonic (US) waves. However, PA imaging through cortical bone remains an unmet challenge. Cortical bone is an anisotropic medium, which is not accuratel...

Photoacoustic (PA) imaging may be advantageous as a safe, non-invasive imaging modality to image the carotid artery. However, calcification that accompanies atherosclerotic plaque is difficult to detect with PA due to the non-distinct optical absorption spectrum of hydroxyapatite. We propose reflection-mode all-optical laser-ultrasound (LUS) imagin...

From acoustics to medical imaging and seismology, one strives to make inferences about the structure of complex media from acoustic wave observations. This study proposes a solution that is derived from the multidimensional Marchenko equation, to learn about the acoustic source distribution inside a volume, given a set of observations outside the v...

Arterial tissue imaging and characterization is important for disease diagnosis, treatment planning and monitoring, and research into disease processes. The high optical contrast of photoacoustic imaging can distinguish molecules with unique optical spectra from surrounding arterial tissue, while ultrasound is sensitive to variations in acoustic pr...

Biomedical imaging systems incorporating both photoacoustic (PA) and ultrasound capabilities are of interest for obtaining optical and acoustic properties deep in tissue. While most dual-modality systems utilize piezoelectric transducers, all-optical systems can obtain broadband high-resolution data with hands-free operation. Previously described r...

Elastic waves are used across a broad spectrum in medicine to non-invasively probe and image tissues up to centimeters deep. Ultrasonic (US) imaging is the most well-known modality used to image acoustic density and velocity contrasts. US is useful for imaging overall structure in tissue, however, acoustic contrasts are relatively low in biological...

Biomedical image reconstruction using photoacoustic (PA) and -- more recently -- laser-ultrasound (LU) data is an active area of investigation. Previously, we demonstrated that a framework for LU image reconstruction can be developed based on reverse-time migration (RTM), an approach originally developed for seismic imaging. When combined with a mu...

Conventional contacting transducers are highly sensitive and readily available for ultrasonic and photoacoustic imaging. On the other hand, optical detection can be advantageous when a small sensor footprint, large bandwidth and no contact are essential. However, most optical methods utilizing interferometry or Doppler vibrometry rely on the reflec...

Conventional contacting transducers for ultrasonic wave detection are highly sensitive and tuned for real-time imaging with fixed array geometries. However, optical detection provides an alternative to contacting transducers when a small sensor footprint, a large frequency bandwidth, or non-contacting detection is required. Typical optical detectio...

We propose a new reconstruction algorithm for photoacoustic and laser-ultrasound imaging based on reverse time migration (RTM), a time reversal imaging algorithm originally developed for exploration seismology. RTM inherently handles strong velocity heterogeneity and complex propagation paths. A successful RTM analysis with appropriate handling of...

In modern laboratories, software can drive the full experimental process from data acquisition to storage, processing, and analysis. The automation of laboratory data acquisition is an important consideration for every laboratory. When implementing a laboratory automation scheme, important parameters include its reliability, time to implement, adap...

Multi-channel photo-acoustic and laser ultrasonic waves are used to sense the characteristics of proxies for healthy and diseased vessels. The acquisition system is non-contacting and non-invasive with a pulsed laser source and a laser vibrometer detector. As the wave signatures of our targets are typically low in amplitude, we exploit multi-channe...