Page 72 - Vibrational Spectroscopic Imaging for Biomedical Applications

48 Cha pte r T w o

–1
functional groups in Carbohydrates; at 1530 cm , corresponding to
–1
absorption by amide 2 in protein; and at 2920 cm , for CH stretches
found in many biological constituents are shown. This data cube was
collected in 1 minute. Several spectra from individual pixels are also
–1
–1
shown. Note that information between 1580 cm to 1650 cm has
been removed because these spectral regions are completely domi-
nated by 15-micron water layer absorption. The developments
described in this section are crucial for future time-resolved experi-
ments on living biological systems using IRENI.

2.4. Biomedical Application: Calcium-Containing
Crystals in Arthritic Cartilage
Calcium-containing crystals, including CPPD and BCP crystals, are
common components of osteoarthritic joints and contribute to the
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irreversible tissue destruction seen in this form of arthritis. Little is
known about how and why these crystals form, and consequently
few effective therapies for this type of arthritis are available.
FTIR-based imaging technologies have been used to image and
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analyze normally mineralizing tissues such as bone. Several groups
of investigators assessed both matrix and mineral properties of bone
using FTIR spectral analysis, 37–40 and described several key advan-
tages over more traditional methods of biochemical analysis. In bone,
FTIR-based technologies have facilitated mapping of matrix and min-
eral components in a small area, and provided information about the
polarity of cells, the quality of mineral, and the type and integrity of
fibrillar matrix components. The fact that this work can be performed
in intact tissue is also a major advantage over other technologies.
We became interested in this methodology because of difficulties
encountered in applying traditional methods of crystal analysis to
our biologic models of calcium-crystal formation in articular carti-
lage. The crystals formed in these models were small and sparse and
firmly embedded in a dense, well-hydrated extracellular matrix. The
use of a synchrotron beam with FTIR spectral imaging improves SNR
with smaller aperture sizes. We adapted synchrotron FTIR spectral
microscopic analysis to crystal identification. Our success with this
technology led to further studies analyzing the extracellular matrix
components in and near crystals.

2.4.1 Calcium-Containing Crystals and Arthritis
Two types of calcium crystals are associated with arthritis. These
include CPPD crystals and a trio of hydroxyapatite-like crystals
known as basic calcium phosphate (BCP) crystals. BCP crystals are
comprised of tricalcium phosphate, octacalcium phosphate and
carbonate-substituted hydroxyapatite. In a normal synovial joint, the
articular hyaline cartilage, which provides the smooth covering