Q&As Flashcards
The velocity of sound is greatest through? A. Fat B. Bone C. Fluid D. Muscle E. A vacuum
B. Bone
Interfaces which produce echoes depend on? A. Shape of interface B. Attenuation of the tissue C. Propagation speed of tissue D. Change in acoustical impedance E. Magnitude of the acoustical impedance
D. Change in acoustical impedance
Which of the following equations does NOT accurately describe the relationship of wavelength, frequency, and velocity? A. F=v/wl B. Wl=v/f C. V=wl/f D. V=f x wl
C. V= wl/f
What is the wavelength in mm if velocity is 1540m/s and frequency is 2.5 MHz? A. 0.062 mm B. 0.62 mm C. 6.2 mm D. 62 mm E. 620 mm
B. 0.62 mm
A particle is moving vertically in a transverse wave, what direction is the wave moving?
Horizontally
One cycle consists of:
A compression (peak) and a rarefaction (trough)
Transducers most likely consist of?
Lead zirconate titanate
Piezoelectric effect can be best described as:
Mechanical deformation that results from a high voltage applied to crystal that in turn generates a pressure wave
Diffraction refers to:
Spreading out of the ultrasound beam
What is an effect of focusing?
Improved lateral resolution
Echoes are stored before final display by:
Computer memory
How many shades of gray can the human eye discern?
100, eye has dynamic range of 20 dB
Preprocessing of info that is fed to the scan converter determines?
The assignment of echoes to predetermined gray levels
In B-mode imaging, amplitude is represented on the ___ axis of image
Z
Absorption is the conversion of?
Sound energy to heat
If a 10 MHz sound travels through soft tissue, how much total attenuation has occurred at a depth of 5 cm?
25 dB
What causes acoustic speckle?
When the sound beam hits a number of scatterers and the scatter waves interact with each other and send the results back to transducer
What are Rayleigh scatterers?
Extremely small reflectors that scatter omnidirectionally
Example : red blood cells
What does Snells law describe?
The angle of transmission at an interface based on the angle of incidence and the propagation speeds of the two media
Sound travels through an interface at normal incidence and 40% of the sound is reflected back to the transducer. How much sound was transmitted at the interface?
ITC = 60%
The spatial peak is measured at?
The center of the beam
The spatial average is measured at?
Across the face of entire beam
Which intensity is used when describing thermal bio effects?
SPTA
What device is used to measure the output intensity of the transducer?
Hydrophone
What is the total amount of attenuation that occurs if a 6 MHz sound beam travels through 4 cm of soft tissue?
12dB
Inertia of the medium describes its:
Density
If the angle of incidence is 40 degrees, what is the angle of transmission at the interface if medium 1 has a prop speed of 1320 m/s and medium 2 has a prop speed of 1700 m/s? A) 0 degrees B) >40 degrees C) <40 degrees D) cannot tell
C) <40 degrees
What is it called when the transducer is unable to recognize where an echo originated from?
Range ambiguity
What does Huygens principle claim?
Waves are a result of the interference of many wavelets produces at the face of the transducer
When waves are 180 degrees opposite each other, they undergo destructive interference and are considered what?
Out of phase
What reduces the impedance mismatch between the crystal and the patients skin, allowing better transmission?
The matching layer.
What is the purpose of the backing material?
Reduce ringing of the crystal, causing less numbers of cycles in a pulse, shortening the pulse length
Increased bandwidth of the transducer mean?
A wider range of frequencies present in the beam
How do mechanical transducers steer the element?
With either a motor or a mirror
What type of transducer is typically used in vascular or small parts imaging?
Linear sequential array
What type of transducer would be best for imaging neonatal brains or cardiac anatomy?
Vector transducer
What are the three ways to create a 3D image?
Freehand
With a mechanical transducer
Electronically
What is an advantage of PW over CW?
Continuous wave has no range resolution so there won’t be an image, and you won’t be able to tell where exactly the echo is coming from
What are the four components of spatial resolution?
Axial res
Lateral res
Elevational res
Contrast res
The SPL of the transducer is 0.2 mm. What is the smallest distance two reflectors can be apart in order to appear as two echoes on the screen?
0.1 mm
What type of transducer has the ability to electronically focus in the z plane?
1.5D array
How can you improve your temporal resolution? A) widen the field of view B) increase the depth C) increase the PRF D) increase the number of focuses
C) increase PRF
Along with the aperture, the divergence in the far field is also determined by?
Frequency
Which resolution typically has the lowest number in clinical imaging?
Axial res
Which of the following electrical patterns reduce electronic focusing of the ultrasound beam? A) curved B) sloped C) spiral D) circular
A) curved
What is represented on the x axis and the y axis of the display when using A mode?
X axis - depth
Y axis - amplitude of reflector
What axis is the amplitude of a B mode image displayed on?
The z axis
What is apodization?
It decreases the strength of the voltage pulse sent to the outermost elements to decrease the risk of grating lobes
If a 2 MHz beam is sent out, what frequency of beam do we expect to receive with harmonics on?
4 MHz
What are the functions of the receiver, in order?
Amplification Compensation Compression Demodulation Rejection
How can one counteract the effect of attenuation when scanning?
Adjusting the TGCs
What are the two components of demodulation?
Rectification and smoothing
Which process removes signal amplitudes to reduce image noise?
Rejection
If there are 6 bits of memory, how many shades of gray are available?
64
What preprocessing function enlarges the image while maintaining the pixel density?
Write zoom
What are the assumptions that ultrasound machine makes?
- Sound beams travel in a straight line and go directly from the transducer and back
- The only propagation speed in the body is 1540 m/s
- Any reflection that comes back to the transducer must have been along the path of the beam
- The slice thickness plane is razor thin
What artifact occurs when the sound bounces back and forth between two closely spaced strong speculate reflectors?
Reverberation
Where are mirror artifacts commonly seen?
Near the diaphragm and pleura
What is an example of refraction artifacts?
Edge shadowing
Spatial compounding can result in a smoother image with improved contrast by?
Reducing speckle artifact and reverberation
What are some ways to reduce or eliminate grating lobes?
Tissue harmonics, apodization and subdicing
What potentially beneficial artifact occurs when sound travels through an area of higher attenuation?
Shadowing
Why does acoustic enhancement occur?
Because the beam has traveled through an area of weak attenuation.
What type of display uses a backlight with two polarized filters to produce an image? A) LCD B) plasma C) CRT D) OLED
A) LCD
What does RAID array do?
It’s a back up system used to protect the stored data on a PACS
A reflector is 20 mm away from the transducer. How long does it take for sound to travel to the reflector and back to the transducer?
26 us
What describes the relationship between gravity, density of blood, and the distance between the area and the heart?
Hydrostatic pressure
Where can plug flow be found?
In large blood vessels (ascending AO) and at entrance of vessels (CCA)
What does bernoullis principle state?
An increase in velocity must be accompanied by a decrease in pressure
What is considered to be a hemodynamically significant cross sectional loss?
75%
Poiseulles law is analogous to what principle in electronics?
Ohm’s law
The resolution capabilities of the system are mainly functions of the:
Transducer
The maximum heating of tissue is related to the sound beams:
SPTA
What type of harmonic signal is one half the fundamental frequency?
Subharmonics
Name two important mechanisms likely to induce bioeffects.
Thermal
Cavitation
