Biomedical Engineering Reference
In-Depth Information
in water-filled tissues. To enable sampling of tissues they must be sectioned
and dried, which has time and resource implications. FTIR of touch imprint
cytology has provided detailed spectra which can be used to differentiate
various tissue pathologies, circumventing sample processing problems [34].
FTIR spectroscopic imaging with multivariate clustering techniques has been
investigated as a tool to detect the changes in cellular composition that may
reflect the onset of a disease [35].
Infrared spectroscopy has been shown to spectrally discriminate normal
and malignant tissues in conjunction with statistical analysis methods, many
of these mathematical methods are applicable to Raman spectral analysis.
Elastic Scattering (Reflectance) Spectroscopy
Elastic scatter is light scattered with the same wavelength as the incident light.
Elastic scattering spectroscopy (ESS) includes light scattering spectroscopy
(LSS) and diffuse reflectance spectroscopy (DRS) which utilise single and
multiple scattering, respectively, to indirectly obtain morphological informa-
tion about a tissue sample. Only 2-5% of the total reflectance signal can be
attributed to singly scattered photons. Despite this, the LSS signal can still
be extracted using mathematical models or polarisation since the multiple
scattered light becomes depolarised [36].
Elastic scattering probe systems suitable for endoscopic use are simple and
cheap to manufacture. They utilise a white light source and the backscattered
signal is strong and easy to detect. The technique has been shown to be ca-
pable of detecting precancerous degeneration including changes in the nuclear
size and degree of pleomorphism (cellular atypia) [37]. Dysplastic changes
characterised by nuclear crowding and an increase in nuclear size have been
detected using single point acquisitions of less than 1 s [38]. Furthermore,
LSS is reported to reliably distinguish between low and high grade dyspla-
sia in patients with Barrett's oesophagus, although this was a limited study
with only 4-5 patients in each category [39]. A recent more substantial and
important clinical study has used ESS measurements at endoscopy to differ-
entiate non-dysplastic and low grade dysplasia from high grade dysplasia and
cancer. Overall 81 patients (181 biopsies) were examined. Elastic scattering
spectroscopy detected high grade dysplasia/cancer with 92% sensitivity and
60% specificity and separated these pathologies from inflammation with a
sensitivity and specificity of 79% [40]. One major disadvantage is that ESS
only probes the morphology of the tissue and not the biochemical changes.
Importantly, the technology is simple and inexpensive, making it a possible
tool for in vivo diagnosis or multimodal techniques.
Optical Coherence Tomography (OCT)
OCT is an imaging technology based on low-coherence interferometry [41].
OCT is often compared with ultrasound by its virtue of probing for the
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