Book contents
- Frontmatter
- Contents
- List of Contributors
- Preface to the second edition
- Preface to the first edition
- 1 Introduction to B-mode imaging
- 2 Physics
- 3 Transducers and beam-forming
- 4 B-mode instrumentation
- 5 Properties, limitations and artefacts of B-mode images
- 6 B-mode measurements
- 7 Principles of Doppler ultrasound
- 8 Blood flow
- 9 Spectral Doppler ultrasound
- 10 Colour flow and tissue imaging
- 11 Quality assurance
- 12 Safety of diagnostic ultrasound
- 13 3D ultrasound
- 14 Contrast agents
- 15 Elastography
- Appendices
- A The decibel (dB)
- B The binary system
- C The British Medical Ultrasound Society. Guidelines for the safe use of diagnostic ultrasound equipment
- D Useful contacts
- E Acoustic output parameters and their measurement
- Glossary of terms
- Index
E - Acoustic output parameters and their measurement
Published online by Cambridge University Press: 06 July 2010
- Frontmatter
- Contents
- List of Contributors
- Preface to the second edition
- Preface to the first edition
- 1 Introduction to B-mode imaging
- 2 Physics
- 3 Transducers and beam-forming
- 4 B-mode instrumentation
- 5 Properties, limitations and artefacts of B-mode images
- 6 B-mode measurements
- 7 Principles of Doppler ultrasound
- 8 Blood flow
- 9 Spectral Doppler ultrasound
- 10 Colour flow and tissue imaging
- 11 Quality assurance
- 12 Safety of diagnostic ultrasound
- 13 3D ultrasound
- 14 Contrast agents
- 15 Elastography
- Appendices
- A The decibel (dB)
- B The binary system
- C The British Medical Ultrasound Society. Guidelines for the safe use of diagnostic ultrasound equipment
- D Useful contacts
- E Acoustic output parameters and their measurement
- Glossary of terms
- Index
Summary
Acoustic output parameters
Many different parameters have been defined in order to try and characterize medical ultrasound fields. Due to the complexity of these fields, it is not possible to describe the parameters fully and unambiguously here. Definitions of some terms are given; the more interested reader can find further formal definitions and description in IEC 62127–1 (2007a) and AIUM/NEMA (2004). There are five which seem to be most important to safety: peak negative pressure, pulse average intensity, temporal average intensity, total power and acoustic frequency.
Peak negative acoustic pressure
The peak negative acoustic pressure (also called the peak rarefactional pressure and given the symbol pr) is simply the most negative pressure that occurs during the pulse: in Figure 12.1, this is about 3.5 MPa. This is an important parameter because it relates to the occurrence of cavitation. Negative acoustic pressure means that the acoustic wave is trying to pull the water molecules apart; the water molecules resist this separation but if the pressure is sufficiently negative and lasts for long enough, it is possible to produce a small void, a cavitation bubble. If there are pre-existing gas bubbles or dust particles in the water, cavitation occurs more easily. A similar effect can occur in tissue.
- Type
- Chapter
- Information
- Diagnostic UltrasoundPhysics and Equipment, pp. 227 - 229Publisher: Cambridge University PressPrint publication year: 2010