Optical Detection of Ultrasound in Photoacoustic Imaging

Abstract

Objective Photoacoustic (PA) imaging emerges as a unique tool to study biological samples based on optical absorption contrast. In PA imaging, piezoelectric transducers are commonly used to detect laser-induced ultrasonic waves. However, they typically lack adequate broadband sensitivity at ultrasonic frequency higher than 100 MHz while their bulky size and optically opaque nature cause technical difficulties in integrating PA imaging with conventional optical imaging modalities. To overcome these limitations, optical methods of ultrasound detection were developed and shown their unique applications in photoacoustic imaging. Methods We provide an overview of recent technological advances in optical methods of ultrasound detection and their applications in PA imaging. A general theoretical framework describing sensitivity, bandwidth, and angular responses of optical ultrasound detection is also introduced. Results Optical methods of ultrasound detection can provide improved detection angle and sensitivity over significantly extended bandwidth. In addition, its versatile variants also offer additional advantages, such as device miniaturization, optical transparency, mechanical flexibility, minimal electrical/mechanical crosstalk, and potential noncontact PA imaging. Conclusion The optical ultrasound detection methods discussed in this review and their future evolution may play an important role in photoacoustic imaging for biomedical study and clinical diagnosis.

A frequency‐domain non‐contact photoacoustic microscope based on an adaptive interferometer

“…These phase modulations are read out as intensity modulations obtained by interfering the signal beam with a reference beam. The amplitude of the modulations can be used to quantitatively determine the ultrasound amplitude [27,28].…”

“…Optical detection of acoustic waves requires careful consideration because the reflected or backscattered optical (signal) beam may be modulated in several waves. Three mechanisms are generally discussed in literature in relation to PA detection: (1) photoacoustically induced surface vibrations can modulate the phase of the reflected optical beam, (2) subsurface changes in optical refractive index due to local changes in pressure can directly modulate the intensity of the backscattered probe beam [28,37] and (3) subsurface changes in optical refractive index due to local changes in temperature (from light absorption) also can directly modulate the intensity of the backscattered probe beam [38,39]. In addition to this, any low frequency thermal expansion or contraction of the absorber due to temperature change as a result of light absorption may also modulate the phase of the reflected beam from the interface.…”

Breakthroughs in modern cancer therapy and elusive cardiotoxicity: Critical research‐practice gaps, challenges, and insights

“…Medical diagnosis and therapeutic options benefit greatly from imaging technologies that combine molecular and microscopic parameters with clinical observations; such a combination is provided by photoacoustic imaging (also known as optoacoustic imaging) . Photoacoustic imaging is a label‐free, non‐ionizing, noninvasive, high‐resolution optical imaging modality that uses optical absorption contrast and ultrasonic resolution . This technology has a high scalability and allows imaging of biological structures, ranging from molecules, organelles, cells, and tissues to entire organs and even entire small animal bodies .…”

“…[272][273][274][275][276] Photoacoustic imaging is a label-free, non-ionizing, noninvasive, high-resolution optical imaging modality that uses optical absorption contrast and ultrasonic resolution. [277][278][279][280][281][282] This technology has a high scalability and allows imaging of biological structures, ranging from molecules, organelles, cells, and tissues to entire organs and even entire small animal bodies. 273,275,280,[283][284][285][286] The anatomical, functional, metabolic, and histologic properties of tissues or organs can be solely revealed by endogenous contrast (e.g., hemoglobin, lipids, melanin, and collagen), while exogenous contrast agents are only used to further increase the imaging contrast and specificity.…”

Error dependence on operating point for phase modulation in dynamic displacement measurement using interference signal envelope

“…4,6,[10][11][12][13] However, a higher time resolution of even less than 10 ns is also required for some biometric applications that capture two-dimensional images of vibration distribution by scanning the position of the probe. [14][15][16][17] As a method to achieve high time resolution and high precision of displacement measurement with a simple setup, we have proposed an interferometer-based dynamic displacement measurement method that applies phase modulation to a reference light 18) for measuring the instantaneous displacement from the changes in durations of interference signal components. [19][20][21][22] Thus far, we have successfully demonstrated the displacement measurement of transient state vibration with an instantaneous frequency of up to 100 MHz and a maximum peak-to-peak amplitude of around 100 nm.…”