2 minutes reading time (490 words)

How to improve your diagnostic DPOAE interpretation

Titan-DPOAE-Hischam-2Artboard-13

This tip discusses why you need to be careful when analyzing otoacoustic emissions (OAEs) using the traditional signal to noise ratio method and which criterion to use instead to improve confidence in analysis.

DPOAEs are traditionally interpreted as being present when the difference between the OAE and the noise level is significant, i.e., when you obtain a signal-to-noise ratio (SNR) of 6 dB. Caution is needed for two reasons:

Reason 1: Noise level is an average level

Firstly, the noise level is an average level. While the OAE level is relatively stable, noise fluctuates.

If fluctuations around the measured frequency are large, a signal to noise ratio of 6 dB does not imply that the OAE appears significantly outside the noise spectrum. The OAE can actually be an accidental peak of the noise. 

Figure 1 shows a good example of a 6.5dB SNR where there is still a high possibility that the detected response is part of the noise spectrum. A reliability of 79% equates to a 1 in 5 chance that the displayed OAE is noise and not a true biological response from the cochlea.

Reason 2: A 6 dB SNR may not be the best criterion

Secondly, the often-used criterion of a 6 dB SNR finds its origin in newborn hearing screening.

Test protocols in this area require high sensitivity values of around 99.9%. As more than one frequency, usually 3 out of 4, is required for a pass, a 6 dB SNR at 3 of the 4 frequencies provides certainty that the pass result reflects the measurement of real OAEs.

As the number of frequencies required for a pass is reduced to - let's say 2 out of 4 - a greater SNR for the remaining frequencies is required in order to maintain an overall test sensitivity of 99.9%.

When evaluating each frequency individually, as required in diagnostic evaluations, a simple 6 dB SNR cutoff may not be sufficient or reliable enough to be certain that the DP point reflects a true OAE response from the cochlea.

Use the reliability criterion instead

This is where use of a reliability setting alongside the SNR can provide more certainty that the detected OAE is not just part of the noise. For example, a reliability setting of 98% for an individual frequency equates to a chance that a single response is actually just noise, 1 out of every 20 times, whereas using a 99.99% reliability setting reduces the chance to only 1 out of 1000.

Figure 2 shows OAEs well outside the noise spectrum with high reliability percentages.

Using the reliability instead of (or in addition to) the SNR criterion will give you more confidence in the OAE result. The time you spend on the measurement will typically not increase.

In those few cases, where longer measurement times are needed, it allows you to make a diagnostic conclusion that can be trusted.  

Read more about otoacoustic emissions and pressurized OAE in this article in Hearing Review.  

Career

Working at Interacoustics means being part of the world leaders in our field and a rewarding work environment.

News

Read our latest news for more details and tips about our company and what we do.

Events

Do you want to gain new insights? Join one of our seminars or meet us at congresses and exhibitions around the world.

About us

With more than 50 years’ experience, we are dedicated to supplying healthcare professionals.

Anniversary

Hearing and balance since 1967 - Celebrating the past, embracing the future.

Contact us

Click here to find a local sales or service office near you.

We are social

Follow us to get the latest updates, news and information about our company and solutions.
Find ways to buy our products: Visit an Interacoustics sales office, call 45-6371-3555, or find a distributor.
Features and/or functions may not be available for all countries or all areas and product specifications are subject to change without prior notification.