Chapter 14: Ultrasound Flashcards
A modality that uses Ultrasound Energy and the Acoustic properties of the body to produce an image from stationary and moving tissues.
Medical Diagnostic Ultrasound
The type of energy delivered to the tissues of the body when performing Ultrasound.
Short Pulse of Mechanical Energy
Discuss the propagation of Sound in Ultrasound.
Sound is a mechanical energy that propagates through a CONTINUOUS, elastic medium by COMPRESSION and RAREFRACTION of particles comprising it.
Note:
Rarefraction occurs following Compression event.
Type of wave where energy propagation occurs as a wave front in the direction energy travel:
LONGITUDINAL WAVE
This is the distance between compressions or rarefractions, or between any two points that repeat on the sinusoidal wave of pressure amplitude.
WAVELENGTH of Ultrasound Energy
This refers to the number of times the wave oscillates through one cycle each second.
FREQUENCY
Frequency Sound waves of INFRASOUND
Less than 15 cycles per second (Hz)
Range of sound waves comprising the AUDIBLE ACOUSTIC SPECTRUM
15Hz to 20 kHz
The frequency range of sound waves for Ultrasound
Above 20kHz
This refers to the time duration of one wave cycle.
PERIOD
This refers to the distance traveled by the wave per unit time.
=wavelength/period
SPEED OF SOUND
Average speed of sound of soft tissues:
1540 m/s
154,000cm/s or 1.5mm/us
Average speed of sound of fatty tissues:
1450 m/s
Average speed of sound of air:
330 m/s
What is the speed of sound utilized in the medical ultrasound machine in determining the localization of reflectors and creating the acoustic image?
1540 m/s
Ultrasound frequencies needed for body parts requiring greater travel distance of sound waves (ABDOMEN):
Lower Frequency Ultrasound of 3.5 to 5.0 MHz
Ultrasound frequencies needed for small body parts or organ closed to skin surface (THYROID and BREAST):
Higher Frequency Ultrasound of 7.5 to 10 MHz
What is the ultrasound frequency range of most Medical Imaging Applications?
2 to 10 MHz
This is defined as the peak maximum or peak minimum value from the average pressure on the medium in the absence of a sound wave.
PRESSURE AMPLITUDE
What is the SI unit of Pressure?
Pascal (Pa) = Newton/m2
This refers to the Amount of power per unit area (energy per unit).
This is proportional to the square of the pressure amplitude.
INTENSITY (I)
What is the unit of Intensity?
The amount of energy per unit time per unit area.
Milliwatts/cm2
The relative intensity and pressure levels are described as a logarithmic ratio:
DECIBEL (dB)
Discuss the relation of Intensity ratio with the decibels.
Intensity ratio > 1.0 = dB values are positive
Intensity ratio < 1.0 = dB values are negative
This occurs between 2 tissue boundaries where there is a difference in the acoustic impedance of adjacent materials.
REFLECTION
A conduit of tissue that allows ultrasound transmission through structures such as the lung.
ACOUSTIC WINDOW
This gives rise to the differences in transmission and reflection of ultrasound energy.
which is the means of producing image using pulse echo techniques.
ACOUSTIC IMPEDANCE
What is the SI unit of Acoustic Impedance?
rayl
1 rayl = kg/(m2s)
This described the change in the direction of the transmitted ultrasound energy with nonperpendicular incidence or the beam is not perpendicular to the boundary.
REFRACTION
This occurs by reflection or refraction, causes the beam to diffuse in many directions, and gives rise to the characteristic texture and grayscale in the acoustic image.
SCATTERING
A smooth boundary between 2 media, where the dimensions of the boundary are much larger than the wavelength of the incident ultrasound energy.
SPECULAR REFLECTOR
Discuss echogenicity in relation ro scatter amplitude.
HYPERECHOIC - higher scatter amplitude
HYPOECHOIC - lower scatter amplitude
This refers to the loss of acoustic energy with distance traveled or loss of intensity of the ultrasound beam caused by tissue absorption and scattering in the beam or medium.
ATTENUATION
The process whereby the acoustic energy is converted to heat energy.
ABSORPTION
This refers to the relative intensity loss per centimeter of travel for a given medium.
ATTENUATION COEFFICIENT
What is the unit of Attenuation Coefficient?
dB/cm
What is the Half Value Layer or Thickness of the Ultrasound?
3dB reduction in intensity
This material comprised of one or more ceramic elements with electrochemical properties and peripheral components used to produce and detect Ultrasound.
TRANSDUCER
What are the major components of Ultrasound Transducer? (STAMP-BIT)
Sensor Electrodes Tuning Coil Acoustic Absorber Matching Layer Piezoelectric Material
Backing Block
Insulating Cover
Transducer Housing
This is the functional component of the transducer that converts the electrical energy into mechanical energy.
PIEZOELECTRIC MATERIALS
A synthetic piezoelectric ceramic with a compound structure of molecular dipole most often used in Ultrasound Transducer for Medical Imaging Application.
Lead-Zirconate-Titanate (PZT)
This structure is layered on the back of the piezoelectric element, absorbs the backward directed ultrasound energy, and attenuates stray ultrasound signals from the housing.
DAMPING BLOCK
This provides the interface between the raw transducer element and the tissue.
This minimizes the acoustic impedance differences between the transducer and the patient.
MATCHING LAYER
Typically, 128-512 individual rectangular elements comprised of transducer assembly.
TRANSDUCER ARRAYS
This is the largest transducer assembly which typically contains 256-512 elements.
LINEAR ARRAY TRANSDUCER
This transducer assembly comprised of 64-128 individual elements in a smaller package.
PHASED ARRAY TRANSDUCER
This is another method of producing high frequency ultrasound which is made of silicon based electrostatic transducers. The basic element is a capacitor cell with a fixed electrode (backplate) and a free electrode (membrane).
CAPACITIVE MICROMACHINED ULTRASONIC TRANSDUCER (CMUT)
What is the principle of operation in CMUT?
ELECTROSTATIC TRANSDUCTION
- alternating voltage is applied between membrane and backplate, and the modulation of electrostatic force results in membrane vibration with generation of ultrasound.
What are the 2 distinct beam patterns of Ultrasound?
- Near Field
2. Far Field
A beam pattern which is adjacent to the transducer and has a slightly converging beam profile out to a distance determined by the geometry and frequency of transducers.
NEAR FIELD
Another term for Near Field.
FRESNEL ZONE
This describes a large transducer surface as an infinite number of point sources of sound energy where each point is characterized as a Radial Emitter.
HUYGENS’ PRINCIPLE
This type of beam pattern has a diverging beam beyond that point.
It is where the beam diverges.
FAR FIELD
Another term for Far Field?
FRAUNHOFER ZONE
The function of the transducer diameter, the center of operating frequency.
FOCAL DISTANCE
A method to rephrase the signals by dynamically introducing electronic delays as function of depth.
DYNAMIC RECEIVE FOCUSING
Increases the number of active receiving elements in the array with reflector depth, so that the lateral resolution does not degrade with the depth of propagation.
DYNAMIC APERTURE
Unwanted emissions of ultrasound energy directed away from the main pulse, caused by radial expansion and contraction of the transducer element.
SIDE LOBES
Results when ultrasound energy is emitted far off axis by multielement arrays.
GRATING LOBES