Biomedical Engineering Reference
In-Depth Information
Administration of Fluorescence Agents
Fluorescence can be enhanced using exogenously administered photosensitis-
ers such as those used in photodynamic therapy. The benefit here is that the
operator is looking for a relatively sharp positive fluorescence signal, rather
than a reduction in a broad fluorescence signal. Photodiagnosis predomi-
nantly uses 5-aminolevulinic acid (5-ALA) which can be administered either
locally to the oesophagus or systemically [50]. Others report that 5-ALA can
achieve high sensitivity in detecting dysplasia, but lacks the appropriate se-
lectivity, again due to the presence of inflammatory cells which induce a high
fluorescence [52].
Multimodal Optical Diagnosis
Several groups have applied a multimodal approach to optical diagnosis. In-
trinsic fluorescence, diffuse reflectance and light scattering spectroscopic (LSS)
techniques have been assessed alone and in combination for the detection of
cervical squamous intraepithelial lesions [53]. In the upper gastrointestinal
tract, near infrared (NIR) autofluorescence and LSS were combined to iden-
tify dysplastic oesophageal lesions on biopsy samples from 20 patients [54].
In this study, a classification model was developed to discriminate between
low risk (Barrett's mucosa without dysplasia and other benign samples) and
high risk (dysplasia, squamous cell carcinoma and adenocarcinoma) with a
sensitivity and specificity of 86 and 96%, respectively. The most effective di-
agnostic algorithms are seen to be those developed using a combination of
Raman and autofluorescence spectroscopy [55, 56].
13.1.2 Potential Raman techniques
In Vivo Endoscopy
Many technical problems must be solved to enable routine use of Raman spec-
troscopy as an in vivo clinical tool. The employment of Raman spectroscopy
in situ for the study of most tissues necessitates the use of fibre optics to
deliver and return the signal from the tissue site. There have been a num-
ber of fibre probe designs considered and this is an active area of research
[57-60, 10]. Clinical applications to date include GI tract [61], urology [62],
lung [63], stomach [64] and cervix [65].
The major problem associated with Raman probes is that Raman sig-
nals are generated by the fibres themselves. The signal is proportional to the
length of the fibre and to the excitation light intensity. It can have magni-
tudes equal to and often greater than that of the sample under study [66]. The
development of fibre optic Raman probes for biomedical and pharmaceutical
applications is discussed further in Chap. 2.
Search WWH ::
Custom Search