Emerging Dental Applications of Raman Spectroscopy - Emerging Raman Applications and Techniques in Biomedical and Pharmaceutical Fields - page 273

Fig. 11.8. A binormal receiver operating characteristic (ROC) curve ( solid line )
plotting the sensitivity versus 1-specificity using the 850 nm OCT attenuation coef-
ficient to distinguish between early caries and healthy enamel. The dashed line rep-
resents the ROC curve for a nondiscriminatory test. The markers on the curve rep-
resent setting an OCT attenuation coecient threshold between caries and healthy
enamel at 0 . 9mm − 1 ( diamond ) and at 1 . 08 mm − 1 ( star )

specificity, 96.9% (see diamond in Fig. 11.8). A second threshold, marked
on Fig. 11.8 with a star, corresponding to an attenuation of 1 . 08 mm − 1 pro-
vides high sensitivity, 91%, but rather low specificity, 80%. In the setting
of screening for early caries lesions, the threshold should be set to provide
maximum sensitivity while controlling for false positives. The strategy of rais-
ing the threshold in order not to miss potential lesions (sensitivity) can only
be carried to the point where the false positives stay within an acceptable
rate.
While the application of OCT for caries characterization is not new, its
combination with PRS is novel. In a sequential OCT-PRS approach, a high
false-positive rate would necessitate a large number of confirmatory Raman
measurements which in turn would slow the total time required to exam-
ine the oral cavity. Using an OCT 850 nm attenuation coecient between
0.95 and 1 . 1mm − 1 as the threshold provides a suitable compromise between
sensitivity ( > 85%) and specificity ( > 85%). OCT measurements lying above
the selected attenuation threshold would be flagged as normal or healthy
enamel not requiring further examination, while sites with an attenuation be-
low the threshold would be subject to a confirmatory Raman measurement
of the depolarization ratio of the

ν 1 PO 4 − 3 stretching vibration. Preliminary
studies have shown that regions of high backscattering due to genetic de-
fects in enamel formation such as hypocalcification can be misinterpreted as
regions of OCT lesions. Setting the threshold for the OCT attenuation coef-
ficient at 1 . 0mm − 1

to flag possible regions of caries and following up those