Page 53 - Vibrational Spectroscopic Imaging for Biomedical Applications

30 Cha pte r T w o

detector. Signal to noise, point spread functions and IR images of
micrometer-sized polystyrene beads and metal grid are presented.
The flow chamber incorporates several important features that
make diffraction limited, spatially resolved imaging of living cells
feasible as demonstrated by studies on microalgae. Biomedical
experiments focusing on development of calcium-containing crys-
tals in cartilage model systems demonstrate the role of ATP and
BGP in calcium crystal growth. By combining all of these advances
in instrumentation and recent experimental findings, future research
will be focused on kinetics of pathological mineralization of in vivo
systems monitoring the chemistry in the neighborhood of calcium
crystal growth during the crystal formation, rather than examining
only snapshots in time.

2.1 Introduction
Diffraction-limited imaging of samples of biological and medical
interest is an area of increasing interest, including measuring biologi-
cal samples and tissue cultures in vivo. Many different groups focus-
ing on a wide range of topics 1–18 have recently reported mid-IR studies
of tissues and other living cells. Also, diffraction-limited mid-IR
results have been reported in several of these papers, 1–6,8,9,14–21
although to date, the combination of both in vivo and diffraction-
limited results have been difficult to achieve since they require very
strict experimental conditions that can be challenging to maintain
and can interfere with IR measurements. 1,8,18
Many of the examples above have utilized a broadband synchro-
tron source, where light is emitted from relativistically accelerated
electrons that is bright and stable. Most of the synchrotron studies to
date have utilized raster-scanning methods based on a serial collec-
tion scheme to collect the spatially dependent hyperspectral data
cubes, where the spatial resolution of the images is dependent on
both the effective geometric aperture size at the sample plane and the
wavelength of the incident radiation. Recent efforts at synchrotron
facilities, and the basis of the first part of this chapter, have focused
on coupling an IR beamline 22,23 that collects a large swath of radiation
with an FPA detector to obtain diffraction-limited IR maps, where
pixels are collected in parallel at all wavelengths in the mid-IR range,
20
with high signal-to-noise ratios. The impact of this is twofold.
First, images with high-spatial resolution will be collected quickly,
so living biological systems that are changing, growing, or adapting
to varying environs can be monitored on a relevant timescale. Second,
samples with large sample areas and features of the order of the
mid-IR wavelengths that require a large dataset to utilize statistical
analysis methods can be studied since large quantities of high-quality
data can be gathered quickly.