Q&As Flashcards by Alexis Drew

The velocity of sound is greatest through?
A. Fat
B. Bone
C. Fluid
D. Muscle
E. A vacuum

B. Bone

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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

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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

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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

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A particle is moving vertically in a transverse wave, what direction is the wave moving?

Horizontally

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One cycle consists of:

A compression (peak) and a rarefaction (trough)

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Transducers most likely consist of?

Lead zirconate titanate

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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

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Diffraction refers to:

Spreading out of the ultrasound beam

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What is an effect of focusing?

Improved lateral resolution

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Echoes are stored before final display by:

Computer memory

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How many shades of gray can the human eye discern?

100, eye has dynamic range of 20 dB

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Preprocessing of info that is fed to the scan converter determines?

The assignment of echoes to predetermined gray levels

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In B-mode imaging, amplitude is represented on the ___ axis of image

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Absorption is the conversion of?

Sound energy to heat

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If a 10 MHz sound travels through soft tissue, how much total attenuation has occurred at a depth of 5 cm?

25 dB

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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

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What are Rayleigh scatterers?

Extremely small reflectors that scatter omnidirectionally

Example : red blood cells

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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

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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%

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The spatial peak is measured at?

The center of the beam

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The spatial average is measured at?

Across the face of entire beam

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Which intensity is used when describing thermal bio effects?

SPTA

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What device is used to measure the output intensity of the transducer?

Hydrophone

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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?

What preprocessing function enlarges the image while maintaining the pixel density?

Write zoom

What are the assumptions that ultrasound machine makes?

1. Sound beams travel in a straight line and go directly from the transducer and back 2. The only propagation speed in the body is 1540 m/s 3. Any reflection that comes back to the transducer must have been along the path of the beam 4. 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

Q&As Flashcards

(75 cards)