Biophotonics_Concepts_to_Applications

technologies described in the previous two chapters, photonics-based methodologies
such as optical coherence tomography, miniaturized endoscopic processes, laser
speckle imaging, optical coherence elastography, photoacoustic tomography, and
hyperspectral imaging have emerged in biophotonics applications. These tech-
nologies are the topics of this chapter.

10.1 Optical Coherence Tomography.

Optical coherence tomography(OCT) is an optical imaging modality that can
capture real-time, 3D images of biological tissues and materials in vivo and non-
invasively with a 1–15-μm resolution depending on the specific OCT method that is
used. OCT functions by measuring the intensity and time-of-flight information
collected from backscattered light coming from different points within a tissue
sample, and then uses that information to reconstruct 3D depth-resolved images up
to 2–3 mm deep in soft tissue and at least 24 mm deep for the more transparent eye
tissue. This imaging technique has been used in a wide range of preclinical and
clinical applications infields such as ophthalmology (its initial application), car-
diology, dentistry, dermatology, gastroenterology, oncology, and otolaryngology
[ 4 – 11 ].
When reading the literature for creating 3D images with OCT and other imaging
techniques, one often sees the terms A-scan, B-scan, and C-scan. These are illus-
trated in Fig.10.2. The termA-scanorA-line scanrefers to the use of a camera that
captures one line of depth information (e.g., backscattered reflectance as a function
of depth) for each readout cycle. This scan is done along an illumination axis and is
known as anaxial-line scanor anA-line image. In the following discussions, the
illumination axis will be designated by the z-axis. Making a series of A-line scans
by means of a lateral scan (for example, along a y-direction) forms a

100 μm

1 mm

1 cm

10 cm

Whole

body

Penetration depth

Ultrasound

Confocal microscopyUltra-high resolution OCT

Conventional OCT

HRCT MRI

Tissue surface

1 μm

1 μm 10 μm

150 μm

300 μm 1 mm

Photoacoustictomography

μm to

mm

Fig. 10.1 Tissue penetration depth and resolution of some common medical imaging techniques

292 10 Optical Imaging Procedures