1. Introduction, History, Clinical Equipment Overview
Course introduction. Historical overview covering early
attempts to use ultrasound in diagnosis. Early equipment configurations and
general principles of ultrasound equipment operation.
2. Plane Wave Ultrasound
Derivation of the one dimensional equation in a lossless
medium. Harmonic solutions of the wave equation. Factors determining the speed
of sound. Relationship between wave variables, such as particle displacement,
acoustic pressure, and particle velocity. Intensity and energy density
calculations.
3. Reflection and Transmission at Interfaces
Boundary conditions at planar interfaces. Amplitude
reflection and transmission coefficients. Sound power reflection and
transmission coefficients.
4. Propagation Through Tissue
Outline of methods for measuring speed of sound. Attenuation
and absorption of sound waves in biological tissue. Experimental data on
propagation speed in tissues. Dependence of sound speed on frequency,
temperature, and tissue composition. Experimental data on attenuation and
absorption of sound waves in tissues. Hypothesized mechanisms for absorption and
attenuation. In vivo measurement methods and data in normal and abnormal tissue.
Nonlinear propagation. Finite amplitude ultrasound. Equation of state. Waveform
distortion. Definition of B/A. Values of B/A for tissues. Harmonic imaging on
clinical scanners.
5. Single Element Transducers
Design and construction of single element transducers.
Piezoelectric effect. Half wave resonance. Matching and backing layers. Effect
on pulse duration and axial resolution. Spherical waves. Radiation from planar
piston transducers, including axial solution, near field and far field
characteristics and far-field directivity function. Methods for focusing single
element transducers. Focused transducer beam patterns.
6. Transducer Arrays
Transducer array types, construction, advantages and
disadvantages of arrays. Beam forming with array transducers. Rectangular
aperture directivity functions. Focusing, apodization, expanding aperture.
7. Ultrasound Scattering
Mechanisms for ultrasonic scattering. Scattering
cross-sections as they relate to acoustic measurements. Scattering versus
frequency and angle. The backscatter coefficient. Methods for measuring
backscatter coefficients for selected tissues and the relationship to tissue
structure. Statistical properties of echo signals including origin of Rayleigh
statistics.
8. Clinical B-mode Equipment
Overall operation. Pulse-receivers, TGC, dynamic range, and
signal processing. Beam formers. A-mode, B-mode, and M-mode. Scanning methods
including sequential arrays, phased arrays, mechanical scanners, and water bath
scanners. Image storage and recording. Scan conversion. Interpolation
algorithms.
9. Doppler Ultrasound and Color Flow Imaging
The Doppler effect. Continuous wave Doppler equipment.
Quadrature detection for directional Doppler. Pulsed Doppler. Aliasing and
maximum detectable velocity versus depth. Spectral analysis. Examples of
applications including deriving physiological parameters, estimating qualitative
flow characteristics, and quantifying flow. Methods for deriving color flow
images including Doppler processing and time-domain correlation. Quantifying
flow with color flow imaging. Contrast agents in ultrasound.
10. Resolution, Performance Testing, Image Artifacts
Image artifacts including reverberations, refraction,
shadowing, enhancement. Image texture. Rayleigh distribution and other
statistical properties of texture. Geometric accuracy. Axial, lateral
resolution, slice thickness. Rayleigh criteria. Lesion resolution. Source of
image contrast on B-mode images. Detectability of masses versus
object-backscatter contrast, size, and depth.
11. Examples of use in the clinic including echocardiography,
obstetrical ultrasound, and abdominal ultrasound.
12. Specification of Acoustic Output Levels
Definitions of acoustic output quantities including acoustic
power, peak compressional and rarefactional pressure amplitude. Time average,
pulse average and temporal peak intensities. Spatial average and spatial peak
intensities. Measurement methods including radiation force balances,
hydrophones, and scanning apparatus. Typical output levels as a function of
operating mode.
13. Biological Effects and ALARA
Mechanisms by which ultrasound waves induce biological
effects including cavitation, thermal, and "direct" effects. In vitro
effects, In vivo animal experiments. Risk versus benefit considerations. Thermal
and mechanical indices.
