Huda US Flashcards
- The velocity of an ultrasound beam is always:
(A) Constant for all solids
(B) Proportional to frequency cubed
(C) Equal to the velocity of the molecules of the
medium
(D) Equal to frequency times wavelength
(E) 3 X 108 m/second
1-D. The velocity (v) of any wave is always the
product of the frequency ( f ) and wavelength (λ)
(i.e., v = f x λ).
2. Sound waves are: (A) Constant velocity (B) Low-frequency electromagnetic radiation (C) Ionizing radiation (D) Audible at 1 MHz (E) Longitudinal waves
2-E. In ultrasound, the displacement is along the
direction of travel (electromagnetic waves are
transverse, because the displacement is perpendicular
to the direction of the wave motion).
3. A 2 MHz transducer has an approximate wavelength of: (A) 0.01 mm (B) 0.1 mm (C) 1.0 mm (D) 10 mm (E) More than 10 mm
3-C. Because v = f x λ, and the velocity of
sound is 1540 m/second, the wavelength is given
by [(l,540)/(2 X 106)] m. or about 1 mm
4. The wavelength of a 3 MHz sound beam is shortest in: (A) Air (B) Castor oil (C) Fat (D) Muscle (E) Bone
4-A. The wavelength (X) is given by v/f, and because
the speed of sound in air (330 m/second) is
much less than in soft tissue (1,540 m/second). the
wavelength is correspondingly shorter.
5. Acoustic impedance (Z) is primarily dependent on tissue: (A) Density (B) Attenuation (C) Atomic number (D) Temperature (E) Oxygenation
5-A. Acoustic impedance is dependent on tissue
density and is obtained using the equation Z = ρ x
v, where ρ is the tissue density, and v is the velocity
of sound in the tissue.
6. Which of the following has the highest acoustic impedance? (A) Bone (B) Fat (C) Air (D) Water (E) Eye lens
6-A. Acoustic impedance is the product of the
density and velocity of sound, both of which are
the highest for bone.
7. The wavelength of a 1 MHz sound beam is not: (A) The same in all solid media (B) 0.3 mm in air (C) 1.5 mm in soft tissue (D) 4.1 mm in bone (E) Velocity divided by frequency
7-A. Wavelength generally changes with
medium because frequency will be the same, but
velocity depends on the medium.
8. If an ultrasound beam is attenuated by 99%, the attenuation is: (A) 1 dB (B) 3 dB (C) 10 dB (D) 20 dB (E) Greater than 20 dB
8-D. Decibels are 10 x log10 (I0/I), where I0 is
100 and I is 1: this corresponds to 20 decibels.
9. The key factor determining the fraction of ultrasound reflected at a large interface is the: (A) Depth of the interface (B) Transducer diameter (C) Transducer output intensity (D) Differences in acoustic impedance (E) Scan mode (A, B. or M)
9-D. The difference in acoustic impedance between
the two tissues (Z1,Z2) determines the fraction
of incident energy reflected.
- What fraction of ultrasound is reflected from
a liver (Z = 1.55) and soft tissue (Z = 1.65) interface?
(A) 1/2
(B) 1/10
(C) 1/100
(D) 1/500
(E) 1/1,000
10-E. The reflected fraction of an ultrasound
beam is given by [(Z1 — Z2)/(Z1 + Z2)]2, which
gives 1/1,000.
11. Ultrasound shadowing artifacts are unlikely behind: (A) Strong attenuators (B) Bone (C) Air (D) Fluid-filled cysts (E) Metallic clips
11-D. Shadowing artifacts occur because of a
large loss of transmitted signal intensity caused by
either attenuation or reflection; fluid-filled cysts
transmit ultrasound and result in enhancement of
echoes beyond the cyst.
12. Reflections occur from all of the following except: (A) Smooth surfaces (B) Kidney interior (C) Fat-kidney interfaces (D) Bladder wall (E) Bladder contents
12-E. There are no reflections from fluids in the
bladder.
- Snell’s law describes the relation between the:
(A) Angle of incidence and transmission
(B) Fraunhofer angle and wavelength
(C) Angle of incidence and angle of reflection
(D) Focus and transducer curvature
(E) Fresnel zone and wavelength
13-A. Snell’s law describes the angle of refraction
that occurs when an ultrasound beam passes
from one medium to another.
14. An ultrasound beam traveling through tissue cannot be: (A) Absorbed (B) Amplified (C) Scattered (D) Reflected (E) Refracted
14-B. There is no mechanism for amplifying ultrasound
beams in patients. Echoes from tissue interfaces.
however, can be amplified electronically.
15. Higher-frequency transducers have increased: (A) Thickness (B) Intensity (C) Attenuation (D) Velocity (E) Wavelength
15-C. The attenuation in tissue is about 1 dB/cm
at 1 MHz and increases approximately linearly
with frequency (there is no direct relationship between
intensity and frequency).
16. The Q factor of a transducer refers to: (A) Coupling efficiency (B) Minimum intensity (C) Maximum intensity (D) Purity of the frequency (E) Transducer dead time
16-D. Q is defined as the operating frequency
(MHz) divided by the bandwidth, so that high Q
values correspond to a pure frequency and vice
versa.
17. The damping material behind the crystal transducer reduces: (A) Pulse frequency (B) Ring-down time (C) Echo amplitude (D) Lateral resolution (E) PRF
17-B. The ring-down time is reduced and very
short pulses of only two or three wavelengths are
generated.
18. The Fresnel zone length of an ultrasound beam increases with increasing: (A) Transducer diameter (B) Transducer thickness (C) Wavelength (D) Intensity (E) TGC
18-A. The Fresnel zone is given by r2/λ. where r
is the transducer radius and λ is the wavelength
- TGC corrects for which of the following?
(A) Signal losses at skin interface
(B) Velocity of moving objects
(C) Intensity decrease with tissue penetration
(D) Transducer damping material
(E) Image fading on cathode ray tube
19-C. TGC corrects for normal attenuation in tissue,
and is generally assumed to be 1 dB/cm per 1
MHz.
20. An echo received 65 microseconds after the signal is sent is from what depth? (A) 2 cm (B) 5 cm (C) 7 cm (D) 10 cm (E) 15 cm
20-B. The equation to use is d = c x t, where d is
the total travel distance, c is the speed (1,540
m/second), and t is the time (65 microseconds); we
obtain a round trip distance of 10 cm, which corresponds
to depth of 5 cm.
21. In B-mode ultrasound, the PRF does not affect: (A) Pulses per second (B) Frame rate (C) Number of lines per frame (D) Maximum penetration depth (E) Ultrasound frequency
21-E. Ultrasound frequency has no relationship
to the PRF but is determined by the transducer
crystal thickness.
- Choice of frequency in ultrasound is most
likely a trade off between patient penetration and:
(A) Contrast
(B) PRF
(C) Noise
(D) Lateral resolution
(E) Axial resolution
22-E. As frequency increases, the wavelength is
reduced, which improves resolution but reduces
patient penetration.
23. Ultrasound signals are converted from digital data to a video monitor display using a: (A) Log amplifier (B) Photomultiplier tube (C) Photocathode (D) Scan converter (E) Array processor
23-D. Scan converters convert ultrasound data
into an image that is displayed on a video monitor
24. The best axial resolution is obtained using: (A) 5.0 MHz phased array (B) 5.0 MHz linear array (C) 5.0 MHz continuous-wave Doppler (D) 10 MHz sector scanner (E) 10 MHz continuous-wave Doppler
24-D. Highest frequency normally gives the best
axial resolution. However, continuous-wave
Doppler provides little spatial information and has
the “worst” axial resolution.
25. Lateral resolution in ultrasound imaging would most likely be improved by: (A) Increasing transducer focusing (B) Imaging in the Fraunhofer zone (C) Using fewer scan lines (D) Increasing the frequency (E) Reducing the pulse length
25-A The lateral resolution improves with focussing
26. Below a structure, a very faint image of the structure is probably owing to: (A) Reverberation artifact (B) Side lobes (C) Specular reflection (D) Nonspecular reflection (E) Incorrect TCG
26-A. Reverberation artifact is produced by the
beam bouncing off the posterior interface, then
off the anterior interface, then back off the posterior
interface, and finally being recorded as a
faint image further away from the actual structure.
27. All of the following may cause significant ultrasound artifacts except: (A) Reverberation (B) Side lobes (C) Nonspecular reflections (D) Refraction (E) Speed displacement
27-C. Nonspecular reflection will result in the
beam being scattered in all directions and is unlikely
to be the direct cause of image artifacts.
28. Clinical ultrasound beams normally have an intensity of: (A) 0.5 mW/cm2 (B) 5 mW/cm2 (C) 50 mW/cm2 (D) 0.5 W/cm2 (E) 5 W/cm2
28-B. Diagnostic ultrasound uses 1 to 10
mW/cm2.
29. The Doppler shift from a moving object depends on all of the following except: (A) Speed of ultrasound beam (B) Frequency (C) Angle between beam and object (D) Object depth (E) Object speed
29-D. The depth of the moving object is immaterial.
30. Continuous-wave Doppler uses: (A) One transducer (B) High frequency transducers (C) A low Q factor (D) A scan converter (E) Little spatial information
30-E. Continuous-wave Doppler provides little
spatial information because the beam is continuously
on, which permits detection of the frequency
differences between emitted and reflected
signals.
