Computer Architecture and Networks Lab. 컴퓨터 구조 및 네트워크 연구실 CHAPTER 16 Auditory Brainstem Response : Differential Diagnosis 윤 정 희

Computer Architecture and Networks Lab. Amplitude Measures Peak amplitudes of components in an ABR depend on two Equally important aspects of neural activity. 1. The number of neural elements activated by the sound stimulus. 2. The degree of synchronization of the activity of those neural elements. CAN Lab. INHA University.

Computer Architecture and Networks Lab. Amplitude Measures Wave V Amplitude Similar to the simple wave V latency measure is the simple wave V amplitude measure. The amplitude is typically determined by the difference in magnitude between the peak of wave V and the succeeding trough (Fig. 16.2) Limitation : The overall conclusion in wave V amplitude measure, it has poorer sensitivity to tumors than do latency measures. 1. ABR electrical fields are weak. 2. ABRs have poor signal-to-noise ratios(SNRs). 3. Both the peak and trough must be identified. 4. Phase cancellation of neural elements can be significant. 5. Cochlear hearing loss complicates the interpretation of amplitude measures. CAN Lab. INHA University.

Computer Architecture and Networks Lab. Amplitude Measures Interaural Wave V Amplitude Comparison This interaural measure compares the wave V amplitude in the suspected ear to the wave V amplitude in the nonsuspected ear and is analogous to the IT5 latency comparison. Limitation : Variable SNRs and correcting or accounting for the effects of cochlear losses are still significant problems for this interaural amplitude measure. This measure is particularly limited when the nonsuspected ear has a significant cochlear loss. As with the IT5 latency measure, this interaural amplitude should not be used in cases where binaural tumors are suspected. CAN Lab. INHA University.

Computer Architecture and Networks Lab. Amplitude Measures Intra-aural Wave V to I Amplitude Ratio This measure is the ratio of the amplitude of wave V to the amplitude of wave I, that is, the amplitude of wave V divided by the amplitude of wave I. In nontumor patients, wave V is typically much greater than wave I. Limitations : This measure has poor sensitivity but good specificity. Other problems with this amplitude ratio are (a) it depends on the presence of wave I, which is often absent in eighth nerve tumor patients (b) it may be more sensitive to variable results in an even more highly variable measure. CAN Lab. INHA University.

Computer Architecture and Networks Lab. Amplitude Measures Interaural Wave V to I Amplitude ratio This is similar to the third amplitude measure noted above, except the reference for the wave V to wave I amplitude ratio is the patient’s nonsuspected ear instead of the distribution of values from a population of nontumor individuals. Limitations : (a) dependence on recording a measurable wave I (b) the effect of the configuration of any cochlear sensory loss because of the differential dependence of wave I and V on different parts of the cochlear, and (c) the increased variability due to the use of a ratio of highly variable measures. One additional problem is determining how to correct for differences in sensory losses between ears. CAN Lab. INHA University.

Computer Architecture and Networks Lab. CRITICAL EVALUATION OF STANDARD ABR LATENCY AND AMPLITUDE MEASURES Current Status of Standard ABR Measures Early studies reported sensitivity of standard ABR measures in the 95 to 98% range, but these tumors were typically fairly large. Impact of tumor size on sensitivity and concluded that tumors smaller than 1.0cm often go undetected by standard clinical ABR methodology. For tumors smaller than 1.0cm, the sensitivity of standard latency measures varied across studies from 63 to 93%, with corresponding false-negative rates ranging from 7 up to 37%. CAN Lab. INHA University.

Computer Architecture and Networks Lab. Why Standard ABR measures cannot Detect Small Tumors Two requirements for any ABR measure used for tumor detection are that (a) the tumor exerts sufficient pressure to desynchronize, block, or alter the conduction properties of eighth nerve elements. (b) The tumor affects a sufficient number of those neural elements. Two major contributors to this amplitude variability discusses above are (a) the residual noise in the average and (b) phase cancellation of activity related to progressive activation and response time variations across the cochlea. CAN Lab. INHA University.

Computer Architecture and Networks Lab. Why Standard ABR measures cannot Detect Small Tumors An ABR method capable of detecting small tumors with good specificity would be invaluable because it could (a) reduce health care costs, (b) reduce the number of patients having to endure the anxiety and discomfort of an MRI test, (c) provide a screening tool to rural communities and countries with limited access to MRIs, (d) provide an alternate test when an MRI is contraindicated, and (e) provide justification for expensive MRI testing. CAN Lab. INHA University.

Computer Architecture and Networks Lab. Anatomic Considerations CAN Lab. INHA University.

Computer Architecture and Networks Lab. Description of the Stacked ABR CAN Lab. INHA University.

Computer Architecture and Networks Lab. CAN Lab. INHA University.

Computer Architecture and Networks Lab. CAN Lab. INHA University.