Diagnostic ultrasound ( PDFDrive )

PART ONE: Physics
CHAPTER
1
Physics of Ultrasound
Christopher R.B. Merritt
SUMMARY OF KEY POINTS
• Quality imaging requires an understanding of basic
acoustic principles.
• Image interpretation requires recognition and
understanding of common artifacts.
• Special modes of operation, including harmonic imaging,
compounding, elastography, and Doppler, expand the
capabilities of conventional gray-scale
imaging.
• Knowledge of mechanical and thermal bioeffects of
ultrasound is necessary for prudent use.
• High-intensity focused ultrasound has potential therapeutic
applications.
CHAPTER OUTLINE
BASIC ACOUSTICS
Wavelength and Frequency
Propagation of Sound
Distance Measurement
Acoustic Impedance
Relection
Refraction
Attenuation
INSTRUMENTATION
Transmitter
Transducer
Receiver
Image Display
Mechanical Sector Scanners
Arrays
Linear Arrays
Curved Arrays
Phased Arrays
Two-Dimensional Arrays
Transducer Selection
IMAGE DISPLAY AND STORAGE
SPECIAL IMAGING MODES
Tissue Harmonic Imaging
Spatial Compounding
Three-Dimensional Ultrasound
Ultrasound Elastography
Strain Elastography
Shear Wave Elastography
IMAGE QUALITY
Spatial Resolution
IMAGING PITFALLS
Shadowing and Enhancement
DOPPLER SONOGRAPHY
Doppler Signal Processing and Display
Doppler Instrumentation
Power Doppler
Interpretation of the Doppler Spectrum
Interpretation of Color Doppler
Other Technical Considerations
Doppler Frequency
Wall Filters
Spectral Broadening
Aliasing
Doppler Angle
Sample Volume Size
Doppler Gain
OPERATING MODES: CLINICAL
IMPLICATIONS
Bioeffects and User Concerns
THERAPEUTIC APPLICATIONS:
HIGH-INTENSITY FOCUSED
ULTRASOUND
All diagnostic ultrasound applications are based on the detection
and display of acoustic energy relected from interfaces
within the body. hese interactions provide the information
needed to generate high-resolution, gray-scale images of the
body, as well as display information related to blood low. Its
unique imaging attributes have made ultrasound an important
and versatile medical imaging tool. However, expensive stateof-the-art
instrumentation does not guarantee the production
of high-quality studies of diagnostic value. Gaining maximum
beneit from this complex technology requires a combination
of skills, including knowledge of the physical principles that
empower ultrasound with its unique diagnostic capabilities. he
user must understand the fundamentals of the interactions of
acoustic energy with tissue and the methods and instruments
used to produce and optimize the ultrasound display. With this
knowledge the user can collect the maximum information from
each examination, avoiding pitfalls and errors in diagnosis that
may result from the omission of information or the misinterpretation
of artifacts. 1
Ultrasound imaging and Doppler ultrasound are based on
the scattering of sound energy by interfaces of materials with
diferent properties through interactions governed by acoustic
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