Neuroinstrumentation in clinical neurology (EEG&NCS).pptx

Electroencephalography (EEG) and Nerve Conduction Studies (NCS). This presentation delves into the essential tools and technologies that power these critical diagnostic modalities. Learn about the hardware and software components of EEG systems, from electrodes and amplifiers to signal processing techniques. Discover the mechanisms behind NCS equipment, including stimulators and recording devices. Understand how these instruments are employed to diagnose and monitor neurological conditions, paving the way for effective treatments and improved patient outcomes. Join us to unlock the secrets of the brain and nervous system through advanced neuroinstrumentation.

1. Neuroinstrumentation in clinical Neurophysiology: principles, parts and settings parameters Nitish kumar M.Sc Neurotechnology JIPMER

2. Contents Introduction Amplifiers Filters Montages ADC Sweep & Sensitivity Caliberation Electrodes and salt bridge Sensory NCS Stimulators  Conclusion and summary

3. Introduction (EEG) What is EEG? Electroencephalography (EEG) is a non-invasive neurodiagnostic method used to record electrical activity of the brain.  EEG captures the spontaneous electrical activity generated by neuronal firing, primarily from the cerebral cortex, and represents it as waveforms on a graph.

4. Intro (NCS) Nerve Conduction Studies (NCS) are diagnostic tests used to evaluate the function and integrity of peripheral nerves. By stimulating nerves with small electrical impulses, NCS measures the speed and strength of electrical signals traveling through the nerves.

5. Amplifiers Amplifiers play a critical role in both EEG and NCS by boosting the small electrical signals generated by neuronal and nerve activities, making them measurable and interpretable. Here's a detailed overview of the types and functions of amplifiers used in these modalities.

6. Functions  of amplifiers

7. Types of amplifiers in EEG 1.Differential Amplifier: Differential amplifiers measure the voltage difference between two input electrodes (active and reference electrodes) and amplify this difference while rejecting any common signals (common-mode signals).         Application: They are essential for reducing noise and interference from external sources, which is crucial for obtaining clean EEG signals. 2.    Instrumental Amplifiers: These are high-precision amplifiers that offer high input impedance, low offset, low drift, and high common-mode rejection ratio (CMRR).   Application: Used in medical and research-grade EEG systems to ensure accurate signal acquisition. 3. AC Coupled Amplifiers: These amplifiers block direct current (DC) components and allow alternating current (AC) signals to pass through. They are used to eliminate baseline drift and low-frequency noise.   Application: Suitable for capturing the fluctuating EEG signals while removing slow drifts.

8. Types of amplifiers in NCS Differential Amplifiers: Similar to EEG, these amplifiers measure the voltage difference between two points and amplify it, rejecting common-mode signals. Application: Essential for reducing noise and improving the signal quality in NCS. 2. Operational Amplifiers: These amplifiers can be configured to perform a variety of signal processing tasks, such as amplification, filtering, and integration. Application: Used in NCS equipment to enhance and process nerve conduction signals. 3. Isolation Amplifiers: Provide electrical isolation between the patient and the recording equipment to ensure patient safety. Application: Important in clinical settings to protect patients from potential electrical hazards.

9. Filters

10. Filter types: High-Pass Filters: Allows frequencies higher than a certain cutoff frequency to pass through while attenuating lower frequencies. Used to remove low-frequency noise such as sweat artifacts, baseline drift, and slow electrical changes. Low-Pass Filters: Allows frequencies lower than a certain cutoff frequency to pass through while attenuating higher frequencies.  Used to remove high-frequency noise such as muscle artifacts (electromyogram, EMG) and electrical interference.

11. Band-Pass Filters: Allows frequencies within a certain range to pass through while attenuating frequencies outside this range. Used to isolate specific EEG frequency bands, such as delta (0.5-4 Hz), theta (4-8 Hz), alpha (8-13 Hz), and beta (13-30 Hz) waves. Notch Filters: Attenuates a narrow band of frequencies around a specific frequency. Commonly used to eliminate power line interference, typically at 50 Hz or 60 Hz, depending on the local power grid frequency.

12. Filter Applications

13. Montages Montages in EEG refer to the specific configurations of electrode placements and the method used to display and interpret the electrical activity recorded from these electrodes. Different montages can be used to highlight various aspects of brain activity, making it easier to diagnose neurological conditions. Here’s an overview of the types and uses of EEG montages.

14. Bipolar Montage

15. Referential montage

16. Common average montage

17. Laplacian Montage

18. Significance of EEG montages

19. Criteria for choosing the right montage Clinical Objective: The choice of montage depends on the clinical question. For example, bipolar montages are preferred for seizure localization, while referential montages are better for detecting diffuse abnormalities. Electrode Placement: Accurate electrode placement according to the International 10-20 system or its variations is crucial for reliable results, regardless of the montage used. Patient Condition: Consider the patient's condition and the specific area of the brain that needs to be monitored. For instance, if there is a known lesion in a specific region, a montage that best highlights that area should be chosen.

20. Analog to Digital converter (ADC)

21. 1.Signal Conversion: The primary function of an ADC is to convert the continuous-time and continuous-amplitude analog signals into discrete-time and discrete-amplitude digital signals. Importance: Digital signals are essential for computerized data processing, analysis, and storage. 2. Sampling: The ADC samples the analog signal at regular intervals, known as the sampling rate. Each sample represents the signal's amplitude at a specific point in time. Importance: The sampling rate must be sufficiently high to accurately capture the signal without losing important information. According to the Nyquist theorem, the sampling rate should be at least twice the highest frequency present in the analog signal. 3. Quantization: Quantization involves mapping the continuous amplitude values of the sampled signal to discrete levels. Importance: The number of discrete levels is determined by the bit depth (resolution) of the ADC. Higher resolution results in more accurate representation of the signal.

22. ADC specifications

23. Considerations with ADC 1. Aliasing: Issue: If the sampling rate is too low, aliasing can occur, where higher frequency components of the signal are incorrectly represented as lower frequencies. Solution: Use anti-aliasing filters and ensure the sampling rate adheres to the Nyquist criterion. 2. Dynamic Range: Issue: The ADC must handle the full range of signal amplitudes without distortion. Solution: Choose an ADC with an appropriate dynamic range and use gain control to optimize signal levels. 3. Latency: Issue: Conversion and processing delays can affect real-time applications. Solution: Use high-speed ADCs and optimize system design to minimize latency.

24. Sweep and sensitivity The sweep (or time base) in EEG and NCS refers to the horizontal scale on the display that represents the time axis.  It determines how much time is represented across the screen or recording. Sensitivity , also known as gain, refers to the vertical scale on the display that represents the amplitude axis.  It determines how much the signal is amplified and how the amplitude of the signal is represented.

25. Sweep Common Sweep Settings: EEG: Typically, sweep settings range from 1 second/division to 10 seconds/division. NCS: Common settings range from 1 millisecond/division to 10 milliseconds/division. Impact on Recording: Shorter Sweep Time: Displays a smaller time window, providing more detail of fast events but less overall context. Longer Sweep Time: Shows a longer period, useful for observing slower or longer-lasting events but with less detail.

26. Sensitivity 

27. Electrodes Electrodes are essential components in both EEG (Electroencephalography) and NCS (Nerve Conduction Studies) as they are the interface between the biological tissue and the recording system.  They capture the electrical activity generated by the brain and nerves, respectively. They can be made of various metals including copper, silver & gold.

28. Underlying principles Signal Capture: Electrodes detect the electrical potentials generated by neuronal and nerve activity. Importance: Accurate detection is crucial for reliable recordings and interpretations. Biocompatibility: Electrodes must be biocompatible to avoid causing irritation or harm to the skin or underlying tissues. Importance: Ensures patient comfort and safety during long recording sessions. Low Impedance: Electrodes should have low impedance to ensure efficient signal transfer and reduce noise. Importance: Low impedance improves the signal-to-noise ratio, leading to clearer recordings. Stable Contact: Electrodes must maintain stable contact with the skin or scalp to ensure consistent signal quality. Importance: Stability is essential for accurate and reliable recordings, especially during movement.

29. Types of electrodes in EEG

30. Types of electrodes in NCS Surface Electrodes: Material: Silver/silver chloride, gold, or conductive adhesive. Application: Placed on the skin overlying nerves and muscles to record electrical activity. Types: Disc electrodes, ring electrodes, and bar electrodes. Needle Electrodes: Material: Stainless steel or platinum. Application: Inserted into the skin to record from deeper nerves or muscles. Use Case: Used in electromyography (EMG) and some NCS to obtain more precise recordings.

31. Ring Electrodes: Material: Silver/silver chloride. Application: Placed around fingers or toes to stimulate or record nerve activity. Use Case: Often used in sensory nerve conduction studies. Bar Electrodes: Material: Silver/silver chloride. Application: Placed on the skin overlying a nerve to stimulate or record nerve activity. Use Case: Commonly used in motor nerve conduction studies.

32. Settings for sensory NCS Sensitivity (Gain): Range: Typically set between 1 µV/division and 20 µV/division. Purpose: Adjust to ensure that the amplitude of the sensory nerve action potential (SNAP) is clearly visible without saturation. Sweep Speed (Time Base): Range: Typically set between 1 ms /division and 2 ms /division. Purpose: Allows for the clear visualization of the waveform and measurement of latency.

33. Filter Settings: Low-Frequency Filter (High-Pass): Usually set between 20 Hz and 30 Hz to remove baseline drift and slow artifacts. High-Frequency Filter (Low-Pass): Usually set between 2 kHz and 5 kHz to remove high-frequency noise. Stimulus Duration: Range: Typically set between 0.1 ms and 0.2 ms. Purpose: Short enough to stimulate the nerve without causing discomfort or artifact.

34. Calliberation

35. Why Calibration is Important?

36. Electrical Caliberation

37. Biocaliberation

38. Stimulators

39. Constant current  stimulator

40. b. Constant voltage stimulator

41. Parameters for stimulation Stimulus Intensity: Range: Typically between 0-100 mA for constant current stimulators and 0-400 V for constant voltage stimulators. Adjustment: Start with a low intensity and gradually increase until a clear and reproducible response is obtained. Stimulus Duration: Range: Typically between 0.05 ms to 1 ms. Adjustment: Short durations (0.1-0.2 ms ) are usually sufficient for stimulating sensory and motor nerves.

42. Repetition Rate: Range: Typically between 1 Hz to 10 Hz. Adjustment: Set a rate that allows for clear separation of individual responses. Polarity: Function: Determines the direction of the current flow. Adjustment: Positive or negative polarity can be selected based on the nerve being studied and the specific protocol.

43. Summary  Electrodes for EEG and NCS: Detect electrical signals from the brain (EEG) or nerves/muscles (NCS). Made of materials like silver/silver chloride, gold, or stainless steel. Electrode Cap or Headset (EEG): Holds electrodes in place according to the International 10-20 system. Ensures consistent and accurate electrode placement. Stimulator (NCS): Delivers controlled electrical pulses to nerves. Types include constant current and constant voltage stimulators. Recording Electrodes: Capture electrical responses from the nerve or muscle (NCS) or brain (EEG). Includes active and reference electrodes. Ground Electrode: Reduces electrical noise and stabilizes the baseline. Placed between stimulating and recording electrodes. Amplifiers: Amplify low voltage signals from the brain (EEG) or nerves/muscles (NCS). Characterized by high gain and low noise.

44. References   Technical aspects of EEG: William O Tatum IV DO FACNS ,  Anteneh M Feyissa MD MSc ,  Valerie Davis R.EEG.T CLTM . Kalitha & Mishra: Clinical Neurophysiology 1&2 The Ultimate Guide of EEG Tech Features:  Bitbrain Electrodiagnosis In  clinical neurology, Shapiro