Faculty Bibliography

The primary role of sectional imaging of the oromaxillofacial region in patients who have AIDS is to assess the extent of disease already identified by the clinician. In patients in whom the clinical presentation is complex or confusing, radiographic detection of otherwise occult manifestations of HIV infection plays a key role in the management of the patient with AIDS. The varied manifestations of HIV infection in the oromaxillofacial region and the indications for imaging have been reviewed

By paying careful attention to the details of surgical technique, many of the complications which have occurred to date may be avoided. Some, such as late electrode and receiver/stimulator migration, device failures, and late flap necrosis due to excessive magnetic forces cannot be avoided by the surgeon, but may be prevented by further advances in implant designs. Although the incidence of life-threatening complications is minimal, and that of major complications is acceptable, every effort should be made by the surgeon, audiologist and manufacturer to further diminish these problems

Parametric variations in the ratio of primary-tone frequencies were explored to optimize the amplitude of the 2f1-f2 distortion product otoacoustic emission for clinical purposes. Ten ears from 5 normally hearing human subjects were examined with primary tones geometrically centred around the standard audiometric frequencies of 0.5, 1, 1.5, 2, 3, 4, 6 and 8 kHz. The distortion product at the frequency 2f1-f2 (f1 < f2) was measured at six probe tone frequency ratios (f2:f1) varying between 1.15 and 1.40 using equal level primaries of 75 dB SPL. The results showed that a single f2:f1 ratio between 1.20 and 1.25 provides a reasonable value for clinical use in that it optimizes the magnitude of the distortion product at 2f1-f2, provides for sufficient resolution in the test frequency range, and is applicable to the standard clinical test frequencies.

Four noise reduction methods for use in sensory aids for hearing impairment were evaluated. These include a two-microphone adaptive noise canceller, short-term Wiener filtering, a transformed spectrum subtraction technique, and sinusoidal modelling. The largest improvements in speech recognition were obtained with the two-microphone adaptive noise canceller in a moderately reverberant room. Significant improvements were also obtained for short-term Wiener filtering for some hearing-impaired subjects. The transformed spectrum-subtraction technique failed to improve performance as the front-end of a hearing aid, but yielded improvements in performance as a preprocessor for the Nucleus Cochlear Implant. Sinusoidal modelling resulted in significant improvements in signal-to-noise ratio, but without a corresponding improvement in speech intelligibility