A configurable tool for the analysis of human auditory evoked potentials

Author(s):
L. Benetazzo - UNIVERSITY OF PADOVA, DEPARTMENT OF INFORMATION ENGINEERING
M. Bertocco - UNIVERSITY OF PADOVA, DEPARTMENT OF INFORMATION ENGINEERING
P. Zanchetta - UNIVERSITY OF PADOVA, DEPARTMENT OF INFORMATION ENGINEERING
F. Saccomandi - UNIVERSITY OF PADOVA, DEPARTMENT OF MEDICAL-SURGICAL SPECIALTIES

Industry:
Research

Products:
Report Generation Toolkit, PCI-GPIB, LabVIEW, Multifunction DAQ, Database Connectivity Toolkit

The Challenge:
Development of a hardware/software system for the analysis of human auditory evoked potentials to be employed both in clinical screening and for medical research purposes. The system must be flexible in order to be employed for different types of clinical tests unlike commercial systems dedicated to a particular one.

The Solution:
Use of different traditional and ad-hoc designed devices, employed for the signal generation and acquisition, offering a great configurability and remote control capability. Development of a software for exams configuration and administration and for patients’ data storing and management.

Short summary
The analysis of auditory evoked potentials is very useful for human disease screening and medical research. Commercial systems are usual dedicated to few particular tests and can be adopted only in clinical screening. On the contrary, the proposed system is very flexible and fully re-configurable for different typologies of tests. Moreover the developed tool allows to remotely control the employed devices, to manage the test administration and to store and process acquired data.

Article
Introduction
ERA (Evoked Response Audiometry) tests refer to evoked potentials generated by a particular electrical stimulus transduced into a sound. The evoked waveform response, measured by surface electrodes, is characterized by an amplitude of about few microvolts. Before being acquired the evoked signal has to be conditioned in order to isolate it from other biological activities signals (i.e. EEG).

The Hardware
A simplified scheme of the system hardware is reported in Figure 1.
The core of the system is a Personal Computer (CPU: INTEL Pentium IV 3.00 GHz; OS: Microsoft Windows XP) including the NI PCI Boards and with the developed software installed. It controls all the connected instrumentation, which can be divided into two groups, depending on the carried signal type. The first one performs the stimulus generation and conditioning, the second one is dedicated to the conditioning and acquisition of the biological signal evoked from the patient.
In order to allow many different screening types, it is important to generate a large variety of stimuli. To this purpose an arbitrary waveform generator (HP 33120A or Agilent 33220A, VISA standard programmed using GPIB or USB connection) creates the stimulus which can be attenuated according to the setting of an ad-hoc designed analog attenuator (attenuation range 0-99 dB, step 1 dB; bandwidth 0 Hz-100 KHz; SNR 106 dB). The attenuator is previously calibrated by a phonometer and can be remotely controlled in BCD code by a 16 digital input lines provided by the NI PCI DIO 96. Subsequently the signal is converted to a sound by an acoustic transducer.
The electrical activity evoked by the sound is picked up by three electrodes applied on the patient head. The signale is amplified by a differential preamplifier, ad-hoc designed to perform high accuracy, featuring high impedance differential input (> 10 MΩ) and optoisolation.
The acoustic transducer, the patient and the preamplifier are located inside an acoustically and electrically shielded room in order to avoid that external sounds and electrical noises (i.e. from power lines, mobile phones, etc) interfere with the useful signal.
The pre-amplified signal is the input of a second ad-hoc designed amplifier, characterized by low distortion. This device can also condition the signal by analog low and high-pass filters with settable cut-off frequencies and it is remotely controllable by 16 digital input lines provided by the NI PCI DIO 96. The amplifiers allow to achieve a maximum gain of 100 dB with a bandwidth of 20 kHz.
The final accurate measurement of the evoked potential is performed by means of the NI PCI 6052E, which also provides the synchronization to the stimulation and acquisition process.

ERA Tools Software
Era Tools software is a complete set of tools, implemented in NI LabVIEW environment, to manage different types of test. The developed software consists of different modules each corresponding to a peculiar function. A simplified scheme of the software modular structure is reported in Figure 2.
The LOGIN module controls the access to the MAIN module of Era Tools. In particular a first function allows to password-protect the software login and to choose among different classes of users with different permissions. A second function permits to select different file locations in order to share patients’ data within the medical staff.
The MAIN module is the core of the application that allows to entirely control the screening activity and analysis. A first function performed by this module is the management of patients personal and screening data that are stored in a specific database, connected to the software by means of the Connectivity Database Toolkit. A second function offered by the module is the post-processing of acquired data during ERA screenings. Specific routines allow to compare the acquired traces and to process them by applying digital filtering functions. Once the acquired waveforms are analyzed and the diagnostic values are evaluated, the program gives the possibility to create a final report of the test. This report, created using the Report Generation Toolkit, complies with the most common office automation programs in order to be easily integrated with other clinical documentation.
ACQUISITION (i.e. ABR, ECOCHG, etc.) modules are dedicated to the stimulus administration and to the acquisition of auditory evoked potentials. The core module has been designed to simplify the realization of new modules for different ERA tests. Particular care has been taken in order to achieve good measurement accuracy with specific routines to auto-scale the acquisition devices. Another important aspect of the acquisition module is the control of measurement timing in order to ensure the correct synchronization among instruments and stimulus generator and respect the time constraints of the specific test. A second important feature is the possibility to generate any arbitrary waveform by building it directly in the application environment. Once the potential waveform is acquired, it is possible to store it in the patient database or delete it.
Finally, the SETUP module allows to perform the software configuration and remotely change the hardware settings.

Example of a Specific Test (ABR)
Figure 3 reports a screeenshot of the acquisition front panel referred to a particular test named ABR (Auditory Brainstem Response). The main waveform diagram (in the centre) charts the evoked potential during the acquisition process (green) which can be compared with others (like the red one) previously acquired. There is the possibility to visualize a particular time window and to use cursors for run-time clinical measurements. The small chart at the top left displays the whole trace being acquired at the moment, like an oscilloscope. Nearly on the right a tab control allows to compute the FFT of the current acquisition and also other diagrams related to clinical useful parameters.

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