Ultrasound

Question 1

What is are advantages of Power Doppler over Conventional Doppler Imaging?

Answer 1

1) More sensitive to low flow
2) Less dependent on Doppler angle

Question 2

What is a disadvantage of Power Doppler?

Answer 2

No flow direction information

Question 3

The display on clinical ultrasound units shows values of both thermal index (TI) and mechanical index (MI). What is the lowest value of TI at which adjustments to the examination should be considered when that value is exceeded?

Answer 3

** Check answer Raphex 2020

Question 4

The speed of sound in ultrasound imaging is affected by the tissue property of ______.

Answer 4

Impedance

Question 5

Improved axial resolution in ultrasound image can be best accomplished with _______.

Answer 5

Shorter pulse length

Question 6

What are common ultrasound frequencies for imaging thick body parts and thin body parts?

Answer 6

Thin: 7-15 MHz
Thick: 2-5 MHz

Higher frequencies attenuate faster, meaning less capable of imaging greater depths

Question 7

As a rule of thumb, what is the approximate decibal attenuation of an ultrasound beam?

Answer 7

0.5 dB MHz^-1 cm^-1

Question 8

What causes shadowing artifacts in ultrasound?

Answer 8

Ultrasound assumes a uniform attenuation through material. When the sound wave passes through a highly attenuating object, the reduced signal intensity on the echo shows as a shadow.

Question 9

How do you calculate the length of the near field?

Answer 9

= d^2 / (4*lambda)

lambda = frequency
d = transducer length

Question 10

What causes enhancement artifacts in ultrasound?

Answer 10

Ultrasound assumes a uniform attenuation through material. When the sound wave passes through a weakly attenuating object, the high signal intensity at greater depths on the echo shows as an enhancement.

Question 11

How do you calculate the divergence angle of the far field of an ultrasound beam>

Answer 11

sin(theta) = 1.22 * (lambda / d)

lambda = wavelength
d = transducer length

Question 12

How to determine the axial spatial resolution?

Answer 12

= 1/ (2* SPL)

Question 13

How do you calculate the doppler frequency?

Answer 13

f_d = 2 * f_0 * (v/c) * cos(theta)

f_d = doppler frequency
f_0 = incident frequency
v = speed of sound
c = speed of light
theta = doppler angler

Question 14

What is the Q factor of an ultrasound beam and how to calculate it?

Answer 14

Q-factor describes the ratio of the center frequency to the bandwidth of the beam

Q = f_0 / bandwidth

Question 15

What is an application for high Q ultrasound beams?

Answer 15

The long spatial pulse length and narrow frequency bandwidth is good for Doppler imaging which is sensitive to frequency changes

Question 16

What is an application for low Q ultrasound beams?

Answer 16

The heavy damping to generate the low Q makes for short pulse lengths, allowing for high axial spatial resolution

Question 17

What is the matching layer? What is the thickness of the matching layer?

Answer 17

The matching layer is used to minimize reflections between the transducer and skin, and is constructed of a material with intermediate impedance between them.

The thickness is 1/4 of the center operating frequency of the transducer.

Question 18

How is the resonant frequency of a piezoelectric material determined?

Answer 18

The thickness of the crystal is equal to 1/2 the resonant wavelength

Question 19

What is the thermal index (TI)?

Answer 19

The ratio of the acoustical power prodcued by the transducer required to raise the tissue temperature in the beam area by 1 degree C.

Question 20

What is the mechanical index (MI)?

Answer 20

A value that estimates the likelihood of cavitation. It increases linearly with output power and decreases by the frequency squared (prop. to f^-2)

Question 20

What is the threshold intensity for ultrasound biological effects?

Answer 20

100 mW/cm^2