Adaptive ECG Filtering Group 2: Edward Jezisek, Brandon Autrey, Edward Nowlin Renato Ortega Sponsored By:

Motivation To improve the quality of ECG signals acquired from patients in an MRI environment ECG quality in MRI machines is lacking Current filter selection is confusing Current filters are imperfect New MRI scans create problems

Objectives To filter out 80% of magnetic interference on an ECG signal caused by an MRI machine To convert an analog ECG signal into a digital signal that can be processed on a computer To convert a digital signal back into an analog signal that can be processed by legacy analog devices

Goals To further the use of adaptive algorithms in medical practice Improve the quality of ECG Signals Save a life

Specifications Receive and filter signals up to 250 KHz Perform real time ECG filtering Provide patient and device protection Function in an MRI environment

Requirements Analog Front End – Patient protection and differential Amplifier Data Acquisition – Analog to Digital Converter Data Processing – Filter out the noise sources Raw ECG Out – Provide clean ECG output

Project Implementation Receive ECG signals from 3 leads on the patient Receive magnetic field gradient signals from 3 leads Convert these 6 signals from analog to digital Use the microprocessor to subtract the gradients from the ECG signal Apply adaptive LMS algorithm to smooth out the signal and filter other noises Convert from digital to analog

Overall System Diagram

Noise Contributions Electrical interference from power lines add 50 or 60 Hz power-line frequency. Muscle contraction and muscle activity can generate high frequency electromyography (EMG) noise. Motion artifacts such as movement of the electrode over the skin surface.

Hardware

PCB Design considerations Routing of traces for high speed communications Electrical isolation Battery powered vs power outlet Cost Use of available components

Analog Front End Consists of 3 ECG inputs Consists 3 inputs from magnetic gradient Provides patient protection Provides front end filtering

Analog Front End Removed because of NDA

Analog Front End Sallen Key Filter Used for anti aliasing Low Pass Filter Sampling Frequency is 500 KHz Nyquist Frequency is 250 KHz Cut Off Frequency is 50 KHz Removed because of NDA

Analog to Digital Converter (TI- ADS8556EVM) It contains six low-power, 16-, 14-, or 12-bit, successive approximation register (SAR) based analog-to-digital converters Excellent Signal-to-Noise Performance of 91.5 dB Supports both serial and parallel At speeds up to 720 kSps Supports 6 channels

Alternative Converters LTC2376IMS analog to digital converter by Linear Technology 250 KSps Throughput Rate 16 bit Guaranteed 16-bit No Missing Codes SPI-Compatible Serial I/O with Daisy-Chain Mode

Digital to Analog Converter (AD5660) 16 Bit Single channel 3 wire serial interface Clock rate up to 30 MHz

Microprocessor Design Requirements I/O speed of the CPU is determined by the output of the A/D Minimum of 0.5 MHz with a device limited maximum of 20 MHz Must support enough memory to hold the program code plus at least 10 past data points of each signal Clock speed must be high enough to perform the algorithm at the I/O speed in real time

ARM Cortex M4F Works with Matlab Embedded Coder 80 to 160 MHz clock speed RISC based microprocessor

Xilinx Spartan 3E I/O speed of 33MHz Processor speed is 50MHz 376 Digital I/O pins FPGA based Very customizable especially with high speed special purpose applications Philips is able to advise us with this architecture

Software

Adaptive Filter Experimentation Verifies which adaptive filtering algorithm will work best Matlab and Simulink is faster to prototype Model Based Design Prototyping various algorithms on microcontroller would be very time consuming

Noise Cancellation

Least Mean Square Filter (LMS) Common filter for Signal Processing Adaptively removes noise Very good at removing noise as shown in the results. Matlab provides this filter The signal in Matlab before and after filtering, when using the Least Mean Squares Filter.

Butterworth Filter Linear filter to remove unwanted frequencies Easier to provide a first approach Low memory usage Can be Digital and Analog

Matlab Benefits Quick to create various adaptive filters due to a lot of them already being built in Removes a lot of debugging time Downfalls The Embedded Coder is expensive and doesn’t work on all embedded devices

Matlab vs. Embedded Coding Using Matlab to compare various filters and will possibly use the networking system through USB to offload tasks from the processor to the computer itself Benefits of MatlabBenefits of Embedded Coder Decreases risk in the projectLess hardware Lowers the amount of required workUses less energy Cheaper

Comparison Methods The perfect result will be stored. Noise will be added to the perfect result The filters results will be measured by subtracting the absolute value of the output from the result and squaring it The results will be divided by the number of input points to get a running average

Software Development Process Allows us to develop code while the PCB board is being designed and produced Development board enables us to test code on hardware to additional debugging tools Matlab enables fast testing of complex algorithms

Data Processing Networking System Graphical User Interface File Write System Filter Comparison System

Networking System Used to transfer data from the microcontroller to the program that modifies the data and back to the microcontroller. Asynchronous I/O utilizing Publish/Subscribe.

Publish/Subscribe System The software will be built with a list of publishers and subscribers The publishers will post data to a topic The event manager will send all subscribers the data that the publisher posted Publishers do not need to know subscribers

Topic Manager Manages the publish subscribe system Sends data received to a list of subscribers Manages the memory of the publishers and subscribers Can send data to a subscriber without knowing whether the receipt was successful

Subscriber Receives data from the topic manager Does not know about the Publisher Will be used for a lot of the input/output processing Will filter the signals Some subscribers will also be publishers

Publisher Publishes data to the Topic Manager in the form of a Topic Does not know about the subscribers Will send data to other applications to retrieve a result Many publishers will also be subscribers

Topic The topic is the data being sent by the Publisher to the Subscriber The topic will contain various types of data and an known amount of data The data will be sent as bytes and will be reconstructed based on the topic type

Graphical Display Displays the ECG signal Should be simple and easy to use Should work on a tablet computer requires touch screen for the interface

Compare Various Filters Uses a filter interface Needs to be easy to compare Requires some functions to be created on each filter to show the results.

File I/O Store filtered signals for each filter Will be used to compare various files/results Will allow us to test easily

Testing Methods Perform functional test in an MRI environment Perform test in a simulated environment. A simulated environment will consist of a rapidly rotating magnet placed over ECG cables while collecting a signal.

Budget PartsPriceQuantityTotal Tiva C Series Dev. Board$ $ Analog to Digital Converter (ADS8556EVM) $ Circuit Board$ $ Total Costs$ Total Budget$10, Extra Budget$

Milestones ItemsDates PCB design completionFebruary 3 rd Successful interface between processor and A/D February 5 th PCB board arrivalFebruary 15 th PCB board populatedMarch 1 st Successful interface between all components March 1 st Operational filterMarch 10 th Final TestingMarch 20 th

Progress

Work Distribution TasksGroup Member Front End DesignEdward Nowlin PCB Design and LayoutEdward Nowlin and Renato Ortega Integration of Experimental BoardBrandon Autrey and Edward Jezisek Filter Comparison ProgrammingEdward Jezisek Least Mean Squares FilterEdward Jezisek Matlab DisplayEdward Jezisek and Brandon Autrey ADCBrandon Autrey DAC and SPIEdward Jezisek and Brandon Autrey

Issues Takes time to manufacture PCB Learning to code to the microprocessor Time constraint

Questions?