Photoacoustic F-Mode imaging for scale specific contrast in biological systems

Abstract

In photoacoustic (PA) imaging, time domain reconstruction techniques are the current gold standard for image formation. While these techniques provide high-resolution spatial maps of optical absorption, they neglect the structural information encoded in the frequency domain of the broadband PA signals. In this work, we introduce a frequency domain technique for PA image formation, termed F-Mode. By leveraging information contained in the frequency content of PA signals, F-Mode can be used to generate images with scale-specific contrast. To demonstrate the robustness of our technique, we apply F-Mode to datasets acquired using both PA tomography and PA microscopy systems, utilizing linear array and singleelement transducers with central frequencies ranging from 40-400 MHz. Here we show that the technique can be used to: differentiate between vessels and microspheres of different size in phantoms, enhance visualization of organelles in cultured cells, and selectively display single blood vessels in vivo in zebrafish larvae.

Determination of cell nucleus-to-cytoplasmic ratio using imaging flow cytometry and a combined ultrasound and photoacoustic technique: a comparison study

“…25 Alternatively, signal analysis techniques can be applied to individually acquired PA radio-frequency (RF) lines to ascertain information pertaining to the morphology of the source object. 26 When applied to PA signals containing ultrahigh frequencies (UHFs), such techniques enable the extraction of 3-D morphological information of optically absorbing cells such as RBCs and melanocytes. [27][28][29] Combining PA spectral analysis techniques with an equivalent US-based technique, capable of determining the size of liquid droplets from features in the power spectrum of backscattered US waves, 30,31 we have previously been able to assess the N:C ratio in cultured cancer cells.…”

Photoacoustic simulations of microvascular bleeding: spectral analysis and its application for monitoring vascular-targeted treatments

“…Such features are characteristic of increasing absorber sizes. 14 As the bleeding progresses, the slope of the power spectra decreases, and the y-intercept increases for this vessel geometry and ultrasound detection geometry/bandwidth.…”

“…Changes in the frequency content of the PA signals are associated with the size, concentration, and spatial distribution of dominant optical absorbing chromophores. [13][14][15] This is analogous to quantitative ultrasound analysis, which is associated with the dominant ultrasound scattering source. 16,17 PA spectral analysis provides system-independent parameters that are correlated to the structure of optically absorbing chromophores.…”

Acoustic Frequency-Based Approach for Identification of Photoacoustic Surgical Biomarkers

“…In contrast to spectral unmixing methods, two distinct approaches (i.e., F-mode imaging (Moore et al, 2019) and a method proposed by Cao et al (Cao et al, 2017)) utilize the complete acoustic spectra for differentiation of photoacoustic targets. F-mode imaging (Moore et al, 2019) consists of dividing the spectra with filter banks and displaying a series of images of a specific frequency content, which are later combined with a labelfree photoacoustic microscopy (PAM) map to selectively enhance the visualization of organelles. The method proposed by Cao et al (2017) uses the acoustic spectra filtered with the frequency response of the ultrasound transducer to perform k-means clustering of photoacoustic signals originating from two different photoacoustic-sensitive materials.…”