Biomedical Optics

Chapter 12 - Photoacoustic Tomography

12.1.   INTRODUCTION

The term photoacoustic tomography (PAT) refers to imaging that is based on
the photoacoustic effect. Although the photoacoustic effect was first reported on
by Alexander Graham Bell in 1880, PAT was invented only after the advent
of ultrasonic transducers, computers, and lasers. In PAT, the object is usually
irradiated by a short-pulsed laser beam. Some of the light is absorbed by the
object and partially converted into heat. The heat is then further converted to a
pressure rise via thermoelastic expansion. The pressure rise is propagated as an
ultrasonic wave, which is referred to as a photoacoustic wave. The photoacoustic
wave is detected by ultrasonic transducers and is used by a computer to form an
image.

12.2.   MOTIVATION FOR PHOTOACOUSTIC TOMOGRAPHY

The motivation for PAT is to combine the contrast of optical absorption with the
spatial resolution of ultrasound for deep imaging in the optical quasidiffusive or
diffusive regime. Optical absorption is desirable because of its high sensitivity to
molecules such as oxygenated and deoxygenated hemoglobin. In Table 12.1, PAT
is compared with optical coherence tomography (OCT; see Chapters 9 and 10),
diffuse optical tomography (DOT; see Chapter 11), and ultrasonography (US).
Because of the strong optical scattering, pure optical imaging in biological tissue
has either shallow imaging depth or low spatial resolution. Pure ultrasonic
imaging can provide better resolution than pure optical imaging in the optical
quasidiffusive or diffusive regime because ultrasonic scattering is two to three
orders of magnitude weaker than optical scattering. Ultrasonic imaging, however,
detects only mechanical properties and has weak contrast in early-stage tumors.

UNLIMITED FREE
ACCESS
TO THE WORLD'S BEST IDEAS

SUBMIT
Already a GlobalSpec user? Log in.

This is embarrasing...

An error occurred while processing the form. Please try again in a few minutes.

Customize Your GlobalSpec Experience

Category: Raman Spectrometers
Finish!
Privacy Policy

This is embarrasing...

An error occurred while processing the form. Please try again in a few minutes.