Output Measurements for Medical Ultrasound

by Roy C. Preston (Editor)

Overview

Medical applications of ultrasound range from therapy, foetal monitoring, diagnostic imaging and blood flow measurement, to surgery and lithotripsy. Ever since the earliest developments of medical ultrasound there has been an interest in the measurement and characterisation of the ultrasonic fields generated in these applications, either for assessment of performance of equipment or for safety. Until recently, procedures for acoustic output measurements were ill-defined, but standards are now being developed internationally by the International Electrotechnical Commission (1EC) and reliable commercial measuring equipment is becoming more widely available. The aim of this book is to introduce acoustic output measurement techniques and to provide an insight into the measurement methods. The material presented is based on a course originally run during November 1989 at the National Physical Laboratory. In addition to the lectures, the course consisted of a series of practicals to allow participants to gain experience of making measurements. Teddington, UK Roy C. Preston February 1991 Contents List of Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii List of Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 Safety of Diagnostic Ultrasonic Equipment: The Relevance of Acoustic Output Information to the Clinical User R. C. Preston 1. 1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1. 2 The Relevance of Acoustic Output Information. . . . . . . . . . . . . 6 1. 2. 1 What Is Acoustic Output Information? . . . . . . . . . . . . . . . . . . . 6 1. 2. 2 What Is Acoustic Output Information Used For? . . . . . . . 6 1. 2. 3 Why Should You Know the Acoustic Output Levels of Your Equipment? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1. 2. 4 Are Acoustic Output Levels Really that Important? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Product Details

ISBN-13:	9781447118855
Publisher:	Springer London
Publication date:	11/23/2011
Edition description:	Softcover reprint of the original 1st ed. 1991
Pages:	180
Product dimensions:	6.69(w) x 9.53(h) x 0.02(d)

Table of Contents

1 Safety of Diagnostic Ultrasonic Equipment: The Relevance of Acoustic Output Information to the Clinical User.- 1.1 Introduction.- 1.2 The Relevance of Acoustic Output Information.- 1.2.1 What Is Acoustic Output Information?.- 1.2.2 What Is Acoustic Output Information Used For?.- 1.2.3 Why Should You Know the Acoustic Output Levels of Your Equipment?.- 1.2.4 Are Acoustic Output Levels Really that Important?.- 1.3 Acoustic Output Information.- 1.3.1 What Type of Acoustic Output Information Is Important?.- 1.3.2 What Type of Information Is Given?.- 1.3.3 Why Are Different Parameters Important?.- 1.3.4 How Can You Obtain Acoustic Output Information?.- 1.3.5 Are There Sources of Published Data on Acoustic Output?.- 1.4 Acoustic Fields and Output of Medical Ultrasonic Equipment.- 1.4.1 What Types of Ultrasonic Fields Are Generated?.- 1.4.2 What Type of Field Is Generated by Diagnostic Imaging Equipment?.- 1.4.3 What Type of Field Is Generated by Doppler Equipment?.- 1.4.4 What Type of Field Is Generated by Physiotherapy Equipment?.- 1.4.5 What Type of Field Is Generated by a Lithotripter?.- 1.4.6 What Are the Acoustic Output Levels of Different Equipment?.- 1.5 Standards and Regulations.- 1.5.1 What Is Being Done Internationally About Acoustic Output and Safety?.- 1.5.2 What Is Being Done Nationally About Acoustic Output and Safety?.- 1.6 The Impact on the Clinician.- 1.6.1 What Should You Be Doing?.- 1.6.2 What Are the Consequences of High Power/Intensities?.- 1.6.3 What Modes Produce the Highest Power/Intensities?.- 1.6.4 What Intensity Levels Are Acceptable?.- 1.6.5 What Can You Do to Minimise Exposure of Patients to High Power/Intensities?.- 1.6.6 What Are the Consequences of High Acoustic Pressures?.- 1.6.7 What Modes Produce the Highest Pressures?.- 1.6.8 What Pressure Levels Are Acceptable?.- 1.6.9 What Can You Do to Minimise Exposure to High Acoustic Pressures?.- 1.6.10 What Should You Do to Keep Up to Date?.- 1.6.11 What Should You Do if You Have the Opportunity of Buying New Equipment?.- 1.7 Conclusions.- 1.8 Recommended Additional Reading Material.- 1.9 References.- 2 Fundamentals of Ultrasonic Propagation.- 2.1 Introduction.- 2.2 Ultrasonic Wave Propagation.- 2.2.1 Types of Wave.- 2.2.2 Wave Parameters.- 2.2.3 Linear Wave Propagation.- 2.2.4 Mechanics of Echo Production.- 2.2.5 Attenuation.- 2.3 Transduction.- 2.3.1 Piezoelectric Materials.- 2.3.2 Transducer Construction.- 2.4 Ideal Fields.- 2.4.1 Sinusoidal Time Excitation.- 2.4.2 Axial Distribution Near Field.- 2.4.3 Far Field.- 2.4.4 Rectangular Sources.- 2.4.5 General Time Excitation.- 2.4.6 Focusing.- 2.5 Nonlinear Propagation.- 2.6 Recommended Additional Reading Material.- 3 Overview of Measurement Techniques.- 3.1 Introduction.- 3.2 Key Acoustical and Other Field Parameters.- 3.3 Acoustic Pressure.- 3.3.1 Pulse-echo Technique Using a Small Target.- 3.3.2 Piezoelectric Hydrophones.- 3.3.3 Optical Techniques.- 3.4 Acoustic Displacement.- 3.4.1 Optical Interferometry.- 3.4.2 The Capacitance Probe.- 3.5 Radiation Force.- 3.5.1 Large Target — The Radiation Force Balance.- 3.5.2 Small Target — The Suspended Sphere Radiometer.- 3.5.3 Surface Levitation.- 3.6 Temperature Rise.- 3.6.1 Calorimetry.- 3.6.2 Thermal Probes.- 3.7 Summary of Quantitative Measurement Techniques.- 3.8 Assessment of Measurement Uncertainty.- 3.9 Measurement Traceability.- 3.10 Qualitative Techniques.- 3.11 References.- 4 Hydrophones.- 4.1 Introduction.- 4.2 Types of Hydrophone.- 4.2.1 Ceramic Hydrophones.- 4.2.2 Pvdf Needle-Probe Hydrophones.- 4.2.3 Pvdf Membrane Hydrophones.- 4.2.4 Multielement Hydrophones - NPL Ultrasound Beam Calibrator.- 4.3 Using a Hydrophone.- 4.3.1 Water.- 4.3.2 Mounting and Alignment.- 4.3.3 Shielding.- 4.3.4 Reflections.- 4.3.5 Active Element Size.- 4.3.6 Temperature.- 4.3.7 Bandwidth Limitations.- 4.3.8 Calibration.- 4.3.9 Hydrophone and Amplifier Impedance.- 4.3.10 Which Hydrophone to Choose?.- 4.4 References.- 5 Ultrasonic Power Balances.- 5.1 Introduction.- 5.2 The Radiation Force Balance.- 5.3 Choosing a Configuration and Target.- 5.3.1 Reflecting Targets.- 5.3.2 Absorbing Targets.- 5.4 Examples of Radiation Force Balances.- 5.4.1 General.- 5.4.2 The NPL Radiation Force Balance.- 5.4.3 A Commercial Portable Power Balance.- 5.4.4 The Tethered Float Radiometer.- 5.5 Measurement Considerations.- 5.5.1 Propagating Medium and Attenuation.- 5.5.2 Streaming and Convection Currents.- 5.5.3 Cavitation.- 5.5.4 Thermal Drifts.- 5.5.5 Coping With Scanning Systems.- 5.6 Summary of Important Points to Note During Measurements.- 5.7 References.- 6 Hydrophone-Based Measurements on a Specific Acoustic Pulse Part 1: Field Characterisation.- 6.1 Introduction.- 6.2 The Acoustic Pulse Waveform.- 6.3 Pressure Parameters.- 6.4 Derivation of Intensity from Pressure Measurements.- 6.5 Intensity Parameters.- 6.6 Spatial-peak Parameters.- 6.7 Beam-Shape Information.- 6.8 Spatial-Average Parameters.- 6.9 Power Parameters.- 6.10 Output Beam Intensity.- 6.11 Locating Maxima in Fields.- 6.12 Concept of in-situ or Derated Levels.- 6.13 References.- 7 Measurements on a Specific Acoustic Pulse Part 2: Measurements.- 7.1 Introduction.- 7.2 The Measurement System.- 7.2.1 System Bandwidth.- 7.2.2 Spatial Resolution.- 7.2.3 Digital Acquisition Systems.- 7.2.4 Analogue Acquisition Systems.- 7.3 Spatial-Peak Measurements.- 7.3.1 Finding the Acoustic Axis.- 7.3.2 Finding the Measurement Plane.- 7.3.3 Calculation of Acoustic Parameters.- 7.4 Spatial-Average Measurements.- 7.4.1 Deciding on the Scan Parameters.- 7.4.2 Practical Details.- 7.5 Continuous-Wave Systems.- 7.5.1 CW Doppler Systems.- 7.5.2 Physiotherapy Equipment.- 7.6 Accuracy Assessment.- 7.7 Recommended Additional Reading Material.- 7.8 References.- 8 Real-Time Scanning Systems Part 1: Modes of Operation.- 8.1 Introduction.- 8.2 Principles of Operation.- 8.2.1 Imaging.- 8.2.2 Doppler.- 8.3 Pulse Characteristics.- 8.3.1 Imaging.- 8.3.2 Pulsed Doppler.- 8.3.3 Duplex.- 8.3.4 CW Doppler.- 8.4 Pulse Patterns.- 8.4.1 Discrete Modes.- 8.4.2 Combined Modes.- 8.4.3 Multiple Focal Zones.- 8.4.4 Repeated Lines.- 8.5 Scanner Settings.- 8.5.1 Imaging.- 8.5.2 Pulsed Doppler.- 8.5.3 Duplex.- 8.5.4 CW Doppler.- 8.6 Discussion.- 8.7 Recommended Further Reading Material.- 9 Real-Time Scanning Systems Part 2: Measurements.- 9.1 Introduction.- 9.2 Measurement Systems.- 9.2.1 Test-tank Arrangements.- 9.2.2 Mechanical Clamping of the Transducer.- 9.2.3 Bubbles.- 9.2.4 Measurement Methods Without an Electrical Trigger.- 9.2.5 Electrical Trigger.- 9.3 Making Measurements.- 9.3.1 Locking on to Repetitive Scan Lines.- 9.3.2 Modes of Operation - Special Problems.- 9.3.3 Scan Format.- 9.3.4 Variation Between Scan Lines.- 9.3.5 Multiple Focal Zones and Multiple Firing.- 9.3.6 Overlap Factor in Determining /spta.- 9.3.7 Asymmetrical Beam Shapes.- 9.3.8 Total Power.- 9.3.9 Corrections.- 9.4 Measurement Uncertainties.- 9.5 References.- Glossary: Definitions Relevant to Ultrasonic Field Measurements.