Measuring Ocular Microtremor

The Brainstem

• Has 3 components

• 4 cranial nerves on each section

Assessing Brainstem Activity• “High Tech”

BIS Technology Expensive (sensors & trained technicians) Can’t use if swelling from head injuries

Glasgow Coma Scale

• “Low Tech”

Cranial Nerves

Unconscious Patients

Very uncomfortable procedures to assess intactness of cranial nerves

Flush 60 oz. of ice cold water in ear

Ocular Microtremors (OMT)OMT have been shown in clinical studies

to accurately reflect brainstem activity

Ocular motor nerves originate in the brainstem where sensory signals are pre-processed and sent to the cerebrum

Oculo-motor nerves originate in the brainstem

These signals are necessary for consciousness

Packaging & Architecture

• Incorporate a disposable element into the sensor mounting apparatus.  • Redesign and re-package the electronics for miniaturization and packaging for in-line dongle-type element on the cable.

Objective 1

Objective 2

SignalProcessing

- Signal processing for signal amplification and/or noise reduction

 

Objective 3Integration Into

Patient Overhead Monitor

• Research and understand the standard(s) used to integrate into this technology • Implement in software with potential hardware modifications for the physical interface.

Current Trend Analysis Software

Component OverviewWaveform Generator

OMT Simulator

Sensor (Provided)

Power Supply

Analog Input/

Preprocessing Circuitry

- Amp

Test MUX

XRAM

Microprocessor with Integrated A/D, UART, and

DSP

Bedside Monitor (Philips MP-

60/70 or Agilent V24/26)

Philips VueLink Module – M1032A

For MCU, currently looking at Atmel AVR32 with 12-bit A/D and integrated DSP functions,50 MHz clock.

OMT Sensor

Composed of a piezoelectric transducer, and a surface mount IC amplifier

The sensor generates voltage when it undergoes stress, in this case eye movement

The piezoelectric transducer was designed to be really sensitive to slight amounts of stress

Power ManagementThe current “Blackbox” is powered by a

medical grade power supply which provides ±12V for the sensor, and 5V for the processing unit

The Atmel AVR32 processor has a maximum voltage rating of 3.6V

The interface module to the bedside monitor will be powered by the monitor itself

Originally the bedside monitor was going to be used to power both the processor and sensor

Power optionsDual PS/2 – output voltage 5V ±10%Dual MIB/RS232 – output voltage 5V ±5%USB 2.0 – low power mode, output voltage 4.4V

It is more convenient to construct our own custom power supply that is capable of powering both the sensor and processor

Power Management continued

Power Flow

Sensor

Power supply

Signal processing unit

Monitor interface

Bedside monitor

Sample Signal until XRAM Buffer Full

Perform DSP Algorithm on Buffer

Contents

Extract Necessary Data From DSP Output

Send Wave Samples, Freq,

and Amp. to UART(Monitor)

Broad Overview of Software

Sampling Sampling will be interrupt driven, and will continue until a buffer a buffer is filled. Buffer must be large enough for an adequate analysis of signal.

When the first buffer is full, the DSP algorithm will be started on the signal and sampling will continue to a secondary buffer of equal size. Sampling and DSP will alternate between buffers so no data is lost.

The buffer size and sampling rate will be configurable over the UART.

A/D

DSP

Buffer 1

Buffer 2

XRAM

DSP Output

Bus

FFT – Generate

Output Array in XRAM

Search Valid Range of Array for

Max Energy

Zero Out Locations

Outside of OMT Range (Filter)

Inverse FFT to Obtain Filtered

Waveform in Time Domain

FFT Method

Amplitude/

Frequency

Output

Filtered Waveform Output

-An FFT is performed on the contents of the sample buffer, with spectrum data saved to an array.

-The array locations corresponding to the valid OMT range are searched for the maximum energy, giving the Frequency and Amplitude of the OMT signal.-An inverse FFT on only the valid OMT frequency range is required to reconstitute a time-domain waveform that can be sent to the bedside monitor.

Digital HPF/LPF/Not

ch Filter Routines

Modify Buffer

Filtered Wavefor

m Output

Peak-Count and

Amplitude-Averaging Algorithm

Amplitude/

Frequency

Output

Peak-Detection Method

-Digital filter routines modify the contents of the buffer, giving a filtered signal that could be sent to the bedside monitor.

-Positive-to-negative changes in slope are counted, giving the frequency. The amplitudes at which this occurs are averaged.

Wavelets – Short Oscillations of a given frequency. Can be compared to our signal to determine if energy at that frequency is present.

Bedside Monitor InterfacePhilips VueLink Module

1032ARS-232 Input – Open

Interface ProtocolAllows 1 Waveform (OMT

Signal), 2 Numerics (Amplitude and Frequency), Diagnostic Messages (ex. OMT out of valid range), and Alarms (ex. OMT below certain value)

http://www.sentec.ch/fileadmin/documents/manuals/EN-HB-005928-b-SDM_VueLink_Installation_Manual.pdf

Testing and Data MiningImportant in order to determine the pattern

and/or trend of OMT signalsDetermining a pattern is vital to the signal

processing componentThe process involves a subject (one of us) to

lie down and have the sensor mounted on a closed eyelidusing surgical sensitive tape

Due to a lack of FDA approval and other required certification, we will not be able to gather data on a large scale basis

Vivian’s OMT

Mark’s OMT

Division of LaborMark Tom Vivian Salman Steve

PowerPower Supply x xPowering Sensor x xMCUSignal Sampling - A/D x xDSP of Signal x xInterfaceAnalog Sensor x xOutput Interface (monitor) x xManufacturingPCB x x xDongle x x xAdministrativeMediary to EyeTect x xMediary to medical experts xDocumenatationTechnical Manual xUser's Manual xUROP/EEF xExtra (if time)Data Mining/Trend Evaluation x xBedside Monitor x x

Schedule

First Milestone Second Milestone Pre-Expo

Grants Throughout Semester

BudgetExpenses

Product Unit Cost Amount Total Cost ProviderProcessing/Manufacturing

Atmel AVR32 Development Kit 179.00 1 179.00 http://mouser.com/2-layer PCB 33.00 3 99.00 http://www.4pcb.comPackaging 20.00 1 20.00

InterfaceVuelink M1032A 300.00 1 300.00 http://www.hp.com

Philips M3 Bedside Monitor 2,650.00 1 2,650.00 http://www.dotmed.comMedical Grade Power Supply

Capacitors 10 30.00Diodes 10 30.00

Power MOSFET Transistor 4.25 10 42.50Cooling Fan/Heat Sink 42.00 1 42.00

Power MCU 74.00 1 74.00Packaging 20.00 1 20.00

Administrative CostsPrinting Manuals 40.00 1 40.00

Poster 75.00 1 75.00Shipping/Handling Fees 200.00 1 200.00

Margin7% 266.11

Total 4,067.61

FundingOutside Funds

EyeTect 3,000.00UROP ?

Interference Concerns

Accidental patient movementElectrical noise from other equipment in

the ICU roomNoises in excess of 95 dBHeartbeat

ContingenciesSoftware implementation of display if

bedside monitor is not able to be acquired

Scaling number of processors to ensure proper operation

Purchasing additional components to ensure minimal downtime especially before expo

RisksDuring application of sensor patients’

eye may be agitated

Additional cord is hanging off of patient

Possibility of dongle removing sensor from patients’ eye if too heavy

Components may be destroyed if wired incorrectly

Extension possibilities

Add through connections in order to minimize hanging cables

Adding accelerometer to measure patient movement to find bad samples

Questions?