Preface

Photoacoustic imaging (PAI) is an emerging non-invasive imaging modality that integrates the advantages of deep ultrasound penetration and high optical contrast. The fundament of PAI is photoacoustic effect, which takes place when a lightabsorbing material sample is irradiated by a laser pulse, causing temporal changes of the temperature at loci where light energy is absorbed. Due to this temperature change, the region where light energy is absorbed exhibits transient thermoplastic expansion, generating a pressure pulse. This pressure pulse propagates within the sample body to the surrounding areas and is detected by a set of ultrasonic sensors. The amplitude, time of arrival at the sensor, and duration of each detected pulse are proportional to the absorption coefficient, the location, and the size of the vibrating region, respectively. The set of detected ultrasonic signals are used by different image reconstruction algorithms to produce an image that maps the spatial distribution of the light absorption coefficient within the material sample. Because it is nonionizing, nondestructive, and high-resolution, PAI is opening new frontiers in medical imaging. It provides diagnostic imaging for the anatomy and physiology of small animals, anatomical tissue/organ structure, oxygenation status, blood flow, abnormal morphology, functional vasculature characteristics, skin burns, hypermetabolism, and vulnerable plaques in the coronary arteries.

This book, *Photoacoustic Imaging: Principles, Advances and Applications*, provides interested readers with the principle knowledges, advanced methodologies, and new applications associated with PAI technology. The first section, which contains four chapters, covers the generation and detection of photoacoustic signals, sound source localization, and image reconstruction and formation. This section cites different research papers on emerging deep learning-based image reconstruction. In the second section, which contains two chapters, presents relatively new diagnostic PAI applications. The first chapter discusses PAI application in gastroenterology. It explores the clinical use of PAI-based endoscopy in the diagnosis of esophageal cancer, inflammatory bowel diseases, and pancreatic cancer. The final chapter reports that many eye diseases, including macular degeneration and diabetic retinopathy, involve abnormalities in the vasculature. Therefore, PAI for visualizing and investigating the vasculature can be incredibly helpful as a diagnostic tool for eye diseases. These include iris vasculature, corneal neovascularization, retinal vasculature, choroidal vasculature, and retinal neovascularization. PAI is also used to visualize retinal metabolism and melanin of the eye.

We believe that the applications of PAI in gastroenterology and eye diseases are relatively new and deserve attention. In the future, there is sure to be more literature on using PAI in other areas. We hope this book serves as a channel for exchanging perspectives, experiences, and research results within the scientific community.

Finally, the editor acknowledges and appreciates the effort and kind cooperation of all the chapter authors and their willingness to exchange their experiences and research outcomes with other colleagues. The editor also acknowledges and appreciates the important editing and reviewing services, strong support, and kind cooperation from the staff at IntechOpen: Ms. Klara Mestrovic, Commissioning Editor; Ms. Nina Kalinic Babic, Author Service Manager; and Mr. Ivan Butkovic, Author Service Manager.

> **Reda R. Gharieb** Assiut University, Egypt

> > Section 1

Photoacoustic Imaging:

Principles and Advances

**1**

Section 1
