Spectral Imaging: Methods, Design, and Applications - Biomedical Optical Imaging Technologies: Design and Applications - page 111

of cancer cells and all the way to atomic and nucleus structure analysis. It is a
method that truly span all across the sciences. It certainly plays a major role in
the biomedical field.
Interestingly, the word spectrum originates from Latin where it literally means
appearance or image. Imaging on the other hand is a relatively new science. It
is intuitive since most of the information we learn is gathered through our vision
system, and imaging is just another innovative and sophisticated tool that allows
us to gather better images and store them at the same time. Thanks to the digital
cameras which are now common everywhere, imaging is disseminated not only to
scientists but also to millions of users of phone and internet.
Spectral imaging simply combines these two widespread methodologies
together, providing a lot of the benefits that each can provide onto a single technique.
In biological and clinical studies, spectral imaging extends the existing capabilities
by allowing the simultaneous study of multiple features such as organelles and
proteins qualitatively and quantitatively.
In order to acquire a spectral image, it is required to measure a spectrum at each
point of an image. For this to happen, it requires combining dispersive optics with
imaging equipment, and as usually happens, it also introduces constrains.
In that light, the following chapter will discuss the principles of spectral imaging,
various optical designs, and spectral imaging analysis, while a few of the algorithms
will be discussed with emphasis on the usage for different experimental modes
(fluorescence and bright field). Finally, spectral imaging, like any method, should
be evaluated in terms of its advantages to specific applications, a selection of which
will also be described.

4.2 Imaging and Spectroscopy

Spectral imaging combines spectroscopy and imaging. In principle, spectral imag-
ing requires creating a three-dimensional data set that contains many images of the
same object, where each one of them is measured at a different wavelength. It is
clear that creating such a large data set costs a longer acquisition time, which stands
in contrast to the requirements of many biomedical applications. Therefore, for
some applications, compromises must be made for achieving high quality images
in a limited amount of time. In order to understand the characteristics of spectral
imaging, it is worth to introduce its two building blocks - imaging and spectroscopy.

4.2.1 Imaging Fundamentals

An image is usually referred to as a two-dimensional representation of an object.
For many years, it was materialized through paintings and drawings, but for the last
decades, different types of cameras evolved allowing image acquisition in a realistic
way. Most common and practical today are the digital cameras, based on either