Multiscale Multispectral Optoacoustic Tomography by a Stationary Wavelet Transform Prior to Unmixing

Abstract

Multispectral optoacoustic tomography (MSOT) utilizes broadband ultrasound detection for imaging biologically-relevant optical absorption features at a range of scales. Due to the multiscale and multispectral features of the technology, MSOT comes with distinct requirements in implementation and data analysis. In this work, we investigate the interplay between scale, which depends on ultrasonic detection frequency, and optical multispectral spectral analysis, two dimensions that are unique to MSOT and represent a previously unexplored challenge. We show that ultrasound frequency-dependent artifacts suppress multispectral features and complicate spectral analysis. In response, we employ a wavelet decomposition to perform spectral unmixing on a per-scale basis (or per ultrasound frequency band) and showcase imaging of fine-scale features otherwise hidden by low frequency components. We explain the proposed algorithm by means of simple simulations and demonstrate improved performance in imaging data of blood vessels in human subjects.

Optoacoustic Imaging of Human Vasculature: Feasibility by Using a Handheld Probe

“…Two peripheral arteries and two microvascular landmarks were imaged, that is, the dorsalis pedis and tibialis posterior arteries and medial and distal hallux, respectively. The handheld MSOT probe was positioned on the landmark, and clear US gel (Aquasonic unmixing was applied by using nonnegative least squares to produce images of oxy-and deoxyhemoglobin (26). To compute hemoglobin oxygen saturation (SO 2 ), the oxyhemoglobin (HbO 2 ) and deoxyhemoglobin (Hb) images were placed into the following formula on a per-pixel basis: SO 2 = HbO 2 /(HbO 2 + Hb).…”

Targeting Acidity in Pancreatic Adenocarcinoma: Multispectral Optoacoustic Tomography Detects pH-Low Insertion Peptide Probes In Vivo

“…Although it was not the focus of this study, optimization of the acquired wavelengths and averaging, in combination with the use of a laser with a 50Hz repetition rate, can produce faster multispectral results up to 2Hz for handheld imaging in human subjects, enabling imaging on a faster time scale than observer or patient motion. (61) While these preliminary studies using a hand-held MSOT indicate potential clinical use, we believe that the addition of targeted contrast agents, such as V7–750, could allow for identification of pancreatic tumors in the clinical setting with similarities to diagnostic sonography, endoscopy and laparoscopy.…”

Optical innovations in surgery

“…Haemoglobin contrast can be used to assess tumour vasculature ( Fig. c ), as well as tissue or organ perfusion. Melanin contrast can be used to detect melanoma metastasis in lymph nodes and to measure primary melanoma depth.…”