Principles of Biomedical Instrumentation

Citation

Webb, A. G. (2018). Principles of Biomedical Instrumentation. Cambridge University Press.

Chapter Summary

The book has nine chapters and about 320 pages in the Cambridge Texts in Biomedical Engineering series; it ends with a glossary, and the chapters on wireless implants and on safety each carry an appendix of reference standards or policy documents. The author directs a high-field MRI centre at Leiden University Medical Center. The preface explains the approach: since only a handful of the thousands of devices on the market can be studied in detail, each one is approached through the same questions. What clinical measurement is needed, and what pathophysiology lies behind it? What are the magnitude, frequency and bandwidth of the signal, and which interfering signals must be suppressed? What specifications should the device meet, and how is it designed to meet them? How are its biocompatibility and electrical safety tested? A second theme is mobile health, in which devices work in the patient's home and send data wirelessly to the physician, together with the trade-off between signal-processing power, miniaturization and battery life.

Chapter 1: Biomedical Instrumentation and Devices

A short overview of how devices are classified, how a design moves from concept to clinical device, how devices are regulated, which ISO and IEC safety standards and biological tests apply, and how a new device is evaluated. Paul King's review in IEEE Pulse notes that the chapter gives device recall statistics and introduces failure modes and effects analysis.

Chapter 2: Sensors and Transducers

After an introduction to micro-electro-mechanical systems (MEMS) and their noise, the chapter treats five sensor types, each with a device example: biopotential electrodes (voltage), the pulse oximeter (optical), displacement and pressure sensors, including resistive, piezoelectric, capacitive and inductive transducers, with a disposable blood pressure monitor as the example, the glucose monitor (chemical), and the hearing-aid microphone (acoustic). Each example opens with the clinical need before the design.

Chapter 3: Signal Filtering and Amplification

Bode plots, passive filters of first and higher order, resonant circuits, operational amplifiers and the instrumentation amplifier, active filters (Butterworth, Chebyshev and Sallen–Key) and circuit noise. The chapter ends by designing the signal conditioning for the pulse oximeter and the glucose sensor introduced in Chapter 2.

Chapter 4: Data Acquisition and Signal Processing

Sampling and aliasing, dynamic range and quantization noise, the circuit building blocks of analogue-to-digital converters, and the main converter architectures (flash, successive approximation, pipelined and oversampling, with delta-sigma conversion). Commercial converter specifications are chosen for the pulse oximeter and glucose meter. A final section classifies biomedical signals and introduces the Fourier transform, cross-correlation and methods for low signal-to-noise data, with examples from cardiac output measurement and EEG.

Chapter 5: Electrocardiography

The electrical activity of the heart, electrode placement and the twelve-lead configuration, then ECG system design: common-mode signals and how to reduce them, lead-off detection, filtering and sampling. The chapter continues with automatic diagnosis (the Glasgow algorithm), abnormal recordings and their clinical interpretation, exercise ECG for detecting ischaemia, and high-frequency ECG analysis.

Chapter 6: Electroencephalography

How the brain's postsynaptic potentials produce scalp signals, EEG electrodes and amplifiers, and the normal rhythms. Clinical applications include epilepsy and monitoring anaesthesia with the bispectral index. The chapter ends with brain–computer interfaces for communication and neuroprostheses, and with source localization.

Chapter 7: Digital Hearing Aids

The most detailed device chapter: the auditory system and causes of hearing loss, hearing-aid styles and components, microphones and directional processing, and a long section on digital signal processing (feedback and noise reduction, compression, frequency lowering). It also covers the receiver, batteries, wireless and binaural connections, and testing with the KEMAR manikin.

Chapter 8: Mobile Health, Wearable Health Technology and Wireless Implanted Devices

Smartphone apps and wearable monitors, then the design of wireless implants, including data transmission through the body. Examples are cardiovascular implantable electronic devices, continuous glucose monitors and implanted pressure sensors for glaucoma, followed by packaging. An appendix lists standards for wireless implant technology.

Chapter 9: Safety of Biomedical Instruments and Devices

The physiological effects of current, the hospital electrical supply, macroshock, microshock and leakage currents and protection against them, equipment classes and types, and safety testing. The chapter then addresses implanted devices (biocompatibility tests such as cytotoxicity and haemocompatibility, electromagnetic safety, clinical studies) and ends with designing devices that can be used in an MRI scanner.

Key Concepts

Chapters 1–4: Building blocks

• Device classification and regulation: the schemes regulators and manufacturers use and the steps from concept to clinical device.
• Transducer: a sensor that converts a physiological quantity into an electrical signal, from electrodes to MEMS pressure sensors.
• Instrumentation amplifier and active filters: the circuits that amplify small biosignals and reject interference.
• ADC architecture: the trade-offs among converter designs in resolution and sampling rate.

Chapters 5–7: Device chapters

• Common-mode rejection: removing interference common to both ECG electrodes, central to ECG system design.
• Bispectral index: an EEG-derived measure used to monitor depth of anaesthesia.
• Hearing-aid signal processing: feedback cancellation, directionality, noise reduction and compression on a low-power chip.

Chapters 8–9: Wireless devices and safety

• Wireless implanted devices: implants that send data through the body to external receivers.
• Macroshock and microshock: dangerous currents through the body or directly to the heart, and the design measures that prevent them.
• Biocompatibility testing: biological tests that implanted materials must pass.

Critical Analysis

Strengths

• One method applied to every device. The preface's sequence of questions, from clinical need to signal characteristics, specification, design and safety, is a transferable way of studying any instrument.
• Running examples that connect chapters. The pulse oximeter is followed through sensor (2.3), conditioning (3.6.1) and conversion (4.5.1), and the glucose sensor likewise. King singles out this feature as particularly useful, since the sensors met in Chapter 2 return in later chapters.
• Modern devices. Chapters on digital hearing aids, mobile health and wireless implants, and the closing section on MRI-compatible design, follow the shift towards home monitoring and implants that the preface describes. King calls the book concise and well illustrated, with a reference list and problems at the end of every chapter and a solutions manual for instructors.
• Problems that reach beyond the text. The preface explains that the problems for Chapters 2–4 test circuit analysis, some requiring short computer programs, while those for Chapters 5–9 ask students to research devices the book does not cover and to study device failures.

Limitations

• Selective coverage. Only ECG, EEG, hearing aids and a few implants are treated in depth. King notes that areas such as radiology, clinical chemistry analysers and other instruments are absent; blood pressure, flow and respiratory measurements appear only as sensor examples.
• No laboratory component. King suggests that hands-on laboratory exercises in data acquisition would be a valuable addition.
• Circuits assumed. The book assumes second-year circuits and signal processing, and King recommends prior coursework for Chapter 3. Students without that background will find Chapters 3–4 fast.
• Concise. King judges the book suitable for a course of about two credit hours; a longer course needs another text.

Where It Fits in the Course

Christe's Introduction to Biomedical Instrumentation is an accessible survey of hospital equipment from the point of view of the people who maintain it, at block-diagram level; it suits students without a circuits background or as a clinical companion to Webb. Webb is the circuit-level and design-level introduction. Webster and Nimunkar's Medical Instrumentation: Application and Design, which Webb's preface calls the classic textbook in the field, covers the same building blocks and many more measurement types (blood pressure and flow, respiration, blood chemistry, therapeutic devices). It is the natural next book, or the main text for a longer course with Webb as a concise first reading.

For depth in particular stages: Northrop's Analysis and Application of Analog Electronic Circuits to Biomedical Instrumentation is a graduate-level treatment of the analog electronics in Chapter 3, with emphasis on noise; Togawa, Tamura and Öberg's Biomedical Sensors and Instruments is a reference organized by measured quantity that extends Chapter 2; and Cobbold's Transducers for Biomedical Measurements is a much older (1974) treatment of transducer principles.

How to Use This Book

The book is for undergraduates in their second or third year of biomedical or electrical engineering. The preface assumes a second-year level of circuits and signal processing and no clinical knowledge, though a basic anatomy course helps. A first circuits course is essential before Chapter 3.

A practical plan:

• Core: Chapters 1–4 in order, working the circuit problems. Follow the pulse oximeter and glucose examples across the chapters, and sketch the complete signal chain for each.
• Device chapters: Chapter 5 (ECG) is the natural first application, since it uses all the building blocks. Then choose among Chapters 6–8 according to the course; Chapter 7 is the place to study digital signal processing in a real product.
• Safety: Chapter 9 should not be skipped; pair it with the regulatory and safety material in Chapter 1.

Use the open-ended problems in Chapters 5–9 as small research assignments, and use Webster and Nimunkar for instruments the book leaves out. If the course has a laboratory, build and test the amplifier and filter circuits of Chapter 3 with a real sensor.