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DigitalStethoscope

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Title Digital wireless stethoscope with ambient noise cancelation
Advisor João M. O. S. Rodrigues
Level MSc
Target MIEET / MIECT
Area Electronics, signal processing, web/mobile programming
See also

For more info: mailto:jmr@ua.pt?subject=DigitalStethoscope

Contents

Introduction

Stethoscopes are used in clinical practice to listen to various body sounds, particularly heart sounds and lung sounds, as a means to aid diagnosis of several pathologies. Traditional stethoscopes are fully acoustic instruments that must be used by a trained practitioner to form a judgement in real-time. There are also electronic stethoscopes that use a microphone to convert the sounds into electrical signals, which allow amplification, processing, and recording of the sounds, so that the auscultation signal could be made part of a permanent medical patient record, much like X-rays, ECGs and other diagnostic aid means. However, these newer systems are not as inexpensive and simple to use as traditional stethoscopes, and so they're not widely adopted.

For research purposes, a stethoscope may be used simultaneously with other sensors, such as other stethoscopes on different locations, spirometers, heart rate monitors, and others. Such applications generally require synchronization of the multiple devices.

Today, digital microphones, accelerometers and other highly integrated sensors may be connected to low-power microcontrollers and wireless interfaces to produce small, inexpensive devices that can be combined in multiple ways to acquire data and transmit it to a portable computer, tablet or phone.

Objective

Design and implement a digital wireless stethoscope.

  • It should be light, small, and inexpensive.
  • It should be applied to the skin and held in place by adhesive tape, suction cups or other hands-free means.
  • It shall use fully digital, integrated microphones to minimize the number of components and improve immunity to electromagnetic interference.
  • The device shall have one microphone (A) to acquire the body sounds, and an identical microphone (B) to acquire ambient sound.
  • The two microphones should be in close proximity but acoustically insulated from each other as much as possible.
  • Mic A shall be air-coupled to the skin through a custom-made coupler, possibly of conical shape.
  • Synchronous signals from both mics shall be transmitted using a standard wireless interface, possibly bluetooth.
  • Use of multiple sensors (of the same or other types) synchronously should be possible.
  • Simple software on a receiving device (PC or mobile platform) shall be developed and demonstrated.
  • Explore possibility/interest of some signal processing, such as pre-filtering and noise cancellation, directly on the device.
  • Synchronously acquire accelerometer data that could be used to extract chest movement information for respiratory phase annotation.
  • Alternatively: use accelerometers attached to skin to pick up acoustic vibrations instead of microphones.

Problems to solve

  • Are the digital mic specs (sensitivity, SNR, etc) good enough?
  • What's the best design for the coupler?
  • Make coupler with 3D printer?
  • What material and design to use for the acoustic insulator?
  • Design circuit with minimum components.
  • Which microcontroller?
  • How to synchronize data from several devices (of the same or different types)?
  • How to measure performance? See Kraman2006 for a measuring system.

More info

Google search: digital wireless stethoscope

Digital microphones:

MICROPHONE SPECIFICATIONS EXPLAINED http://www.invensense.com/mems/microphone/documents/AN-1112.pdf

InvenSense (bought AnalogDevices MEMs mics) ICS-43432: Low-Noise Microphone with I2S Digital Output http://www.invensense.com/mems/microphone/ics43432.html

Knowles MEMS microphones: http://www.knowles.com/eng/Products/Microphones/Surface-mount-MEMS

SiSonic™ MEMS Microphones http://www.digikey.com/product-highlights/en/sisonic-mems-microphones/51052

ST MEMS microphones: http://www.st.com/web/catalog/sense_power/FM125/SC1564

Akustica (Bosch): http://www.akustica.com/Files/Admin/PDFs/Datasheets/DS25-2.1%20AKU230%20Datasheet.pdf

DigiKey microphone catalog: http://www.digikey.pt/product-search/en/audio-products/microphones/720968

Wireless kits

TI SensorTag 2.0 ($29) Includes Bluetooth + ZigBee + others, battery + sensors (including digital microphone, accelerometers, termistor...): https://store.ti.com/cc2650stk.aspx

Papers:

Design and development of wireless stethoscope with data logging function: http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=6719946&url=http%3A%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.jsp%3Farnumber%3D6719946

WIRELESS DIGITAL STETHOSCOPE USING BLUETOOTH TECHNOLGY: http://connection.ebscohost.com/c/articles/87753353/wireless-digital-stethoscope-using-bluetooth-technolgy

Comparison of lung sound transducers using a bioacoustic transducer testing system (Kraman2006): http://jap.physiology.org/content/101/2/469

Analog and Digital MEMS Microphone Design Considerations: http://www.invensense.com/mems/gyro/documents/whitepapers/INVN%20Analog%20vs%20Digital.pdf http://www.analog.com/media/en/technical-documentation/technical-articles/Analog-and-Digital-MEMS-Microphone-Design-Considerations-MS-2472.pdf

Effects of sound inlet variations on microphone response: http://www.knowles.com/eng/content/download/2782/32737/version/6/file/TB-03.pdf

Tables of acoustical properties: http://www.ondacorp.com/tecref_acoustictable.shtml

Bluetooth time synchronization

Bluetooth Health Device Progfile (HDP) Implementation Guidance Whitepaper: https://www.bluetooth.org/docman/handlers/downloaddoc.ashx?doc_id=225927 Citation: "HDP also defines an optional Clock Synchronization Protocol (CSP) that allows for precise timing synchronization (theoretically in the microsecond range) between health devices. This feature is for health devices, such as high-speed sensors, that require close synchronization."

Maróti-2010, Flooding time synchronization protocol: http://www.math.u-szeged.hu/tagok/mmaroti/okt/2010t/ftsp.pdf

Ringwald-2007, Practical time synchronization for Bluetooth Scatternets: http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=4550453

Casas-2005, Synchronization in Wireless Sensor Networks Using Bluetooth: http://www.ti5.tuhh.de/events/wises05/Proc/03_session2_4_casas_synchronization.pdf

Synchronizing microcontrolers: http://electronics.stackexchange.com/questions/77629/how-to-synchronize-two-microcontrollers-to-micro-second-accuracy

Other resources

SUNMEDITEC WISE (wireless digital stethoscope): http://www.telehealthtechnology.org/toolkits/electronic-stethoscopes/assessment-process/product-cut-sheets/wise-life-w10 http://www.sunmeditec.cn/eng/sub02/sub021.html

Wireless Wonder—a Bluetooth electronic stethoscope: http://blogs.msdn.com/b/healthblog/archive/2010/11/15/wireless-wonder-a-bluetooth-electronic-stethoscope.aspx