Clinical Engineering

A Handbook for Clinical and Biomedical Engineers

Azzam Taktak, Paul Ganney, David Long, Richard Axell, Azzam Taktak, Paul Ganney, David Long, Richard Axell

• Publisher: Academic Press
• Year: 2019
• ISBN:
  9780081026953
• Edition: 2
• Topic: Computer Science
• Subtopic: Bioinformatics
• Index: Computer Science

Clinical Engineering: A Handbook for Clinical and Biomedical Engineers, Second Edition, helps professionals and students in clinical engineering successfully deploy medical technologies. The book provides a broad reference to the core elements of the subject, drawing from a range of experienced authors. In addition to engineering skills, clinical engineers must be able to work with both patients and a range of professional staff, including technicians, clinicians and equipment manufacturers. This book will not only help users keep up-to-date on the fast-moving scientific and medical research in the field, but also help them develop laboratory, design, workshop and management skills.

The updated edition features the latest fundamentals of medical technology integration, patient safety, risk assessment and assistive technology.

• Provides engineers in core medical disciplines and related fields with the skills and knowledge to successfully collaborate on the development of medical devices, via approved procedures and standards
• Covers US and EU standards (FDA and MDD, respectively, plus related ISO requirements)
• Includes information that is backed up with real-life clinical examples, case studies, and separate tutorials for training and class use
• Completely updated to include new standards and regulations, as well as new case studies and illustrations

Section III

Clinical instrumentation & measurement

Outline

Chapter 11. An introduction to clinical measurement

Chapter 12. Medical electronics and instrumentation

Chapter 13. Electrical safety of medical equipment and systems

Chapter 14. Basic anatomy and physiology

Chapter 15. Respiratory measurement

Chapter 16. Cardiovascular measurement

Chapter 17. Urodynamic measurement

Chapter 18. Neurological measurement

Chapter 19. Visual electrophysiology measurement

Chapter 11

An introduction to clinical measurement

Richard G. Axell ^{a , b a} University College London Hospitals NHS Foundation Trust, London, United Kingdom ^b University College London, London, United Kingdom

Abstract

Clinical measurement is fundamental to patient diagnostics, and good measurement forms the basis of good science. This chapter outlines the factors pertinent to good clinical measurement within a healthcare environment. The concept that a medical device can be precise but not accurate is explained, and that calibration against a traceable standard before use is crucial for the accurate interpretation of patient data. The idea that measurement error is a combination of human, systematic, and random errors summated is introduced. Measurement uncertainty, and the process of using Type I and Type II errors in hypothesis testing is described.

Keywords

Clinical measurement; Accuracy and precision; Measurement errors; Calibration; Traceability; National or international standard; Uncertainty; Sensitivity and specificity and type I and type II errors

1. Introduction
   1. Accuracy and precision
   2. Measurement device errors
   3. Measurement errors
   4. Calibration
   5. Traceability
   6. Uncertainty
   7. Sensitivity and specificity of measurement technique
   8. Type I and type II errors
2. Abbreviations
3. Further reading

Introduction

Measurement underpins science and good measurement forms the basis of good science. A measurement tells us a property of the quantity to be measured and by assigning that property a number and expressing it in the correct SI unit within a healthcare environment allows us to interpret the patient's condition to provide a diagnosis or appropriate intervention. Clinical measurements are obtained using invasive and noninvasive methods, with blood pressure being an ideal example of both. The gold standard technique for the accurate measurement of blood pressure is to use an invasive catheter and advancing the catheter tip to the exact point in the aorta to be measured. However, the most common technique used to measure blood pressure within a clinical environment is to perform the measurement noninvasively. Noninvasive blood pressure measurement is performed by placing a cuff around the patient's arm and listening for Korotkoff sounds due to the turbulence of the blood underneath the cuff. Although the most accurate method of measuring blood pressure is to perform an invasive measurement, this is at an increased risk to the patient when compared to noninvasive measurement techniques. It is the responsibility of the clinician to decide on the condition of the patient and whether the patient will benefit most from the most accurate, potentially harmful invasive measurement of blood pressure, or if the slightly less accurate noninvasive measurement is sufficient. This chapter provides an introduction into the theory and concepts of accuracy and precision of measurement and measurement errors, as well as identifying the importance of calibration, sensitivity, and specificity of measurements that are common across many different clinical measurement modalities.

Accuracy and precision

Firstly, to understand the concept and scientific requirement of the equipment calibration needed to perform a clinical measurement, we must consider the accuracy and precision of the measurement. Resolution is the smallest incremental value that can be measured. The digital measurement display on an ultrasound scanner with a larger number of digits (0.001 mm) has a higher measurement resolution than one with fewer digits (0.01 mm). Similarly, an analogue measurement display on a sphygmomanometer with a tick mark every 1 mmHg has a higher measurement resolution than one with a tick mark every 5 mmHg. However, a higher resolution does not imply higher measurement accuracy; it provides a high measurement precision. Measurement precision is the repeatability of obtaining the ou...