4.LATERAL RESOLUTION Flashcards
What is lateral resolution?
Answer: Lateral resolution is the ability to resolve structures lying side by side or perpendicular to the main axis of the ultrasound beam. It is the minimum distance that two structures are separated by side to side or perpendicular to the sound beam that produces two distinct echoes. Lateral resolution is determined by the ultrasound beam width.
The unit of lateral resolution is same as units of distance such as millimeters.
Lateral resolution is also known as, Angular, Transverse, and Azimuthal (LATA).
What factors can improve the lateral resolution?
Answer:
The decreased beam diameter improves the lateral resolution.
using smaller diameter ultrasound beams will improve lateral resolution.
The ultrasound beams created by a small diameter crystal will produce
smaller diameter sound beams and will have better lateral resolution
The factors that affect
* ultrasound beam width are diameter of the piezoelectric element
* frequency of the ultrasound beam,
* focusing of the ultrasound beam.
The high frequency ultrasound beams are narrower than low frequency ultrasound beams. The use of high frequency transducers improves lateral resolution.
The ultrasound beam is narrowest at its focal point. Focusing of ultrasound beam narrows its diameter within the focal zone area and improves the lateral resolution.
What factors can affect the lateral resolution?
Answer: Any factors that can affect the beam width such as frequency, aperture, focus, parallel processing, and multiple transmit foci can affect the lateral resolution.
Side lobes, grating lobes and refraction artifacts all reduce lateral resolution?
Answer: True
Side lobes, grating lobes and refraction artifacts all reduce lateral resolution.
What is axial resolution?
Answer: Axial Resolution is the ability of the ultrasound system to distinguish two structures which are very close to each other and are parallel to the axis of sound beam.
What factors can give the best axial resolution?
Answer: Short spatial pulse length, short pulse duration, shorter wavelength, fewer cycles in a pulse, use of higher frequencies for imaging, and lower numerical values can give the best axial resolution.
What will improve both axial and lateral resolution?
Answer: Higher transducer frequency will improve both axial and lateral resolution.
The transducers with higher frequency have the longer near zone length.
With longer near zone length there is less divergence of sound beam in the far field which improves both axial and lateral resolution.
What is the effect of wavelength on axial resolution?
Answer: The shorter wavelength decreases the spatial pulse length which improves the axial resolution.
Axial Resolution is related to the spatial pulse length. The shorter the spatial pulse length, the better the axial resolution. The pulse length can be decreased by decreasing the wavelength. The wavelength can be decreased by increasing the frequency. Higher frequency transducers have shorter wavelength which shortens the spatial pulse length and provides the better axial resolution.
If the spatial pulse length is 10 mm, what is the axial resolution?
Answer: 5 mm
axial resolution = spatial pulse length / 2
axial resolution = 10 mm/2
axial resolution = 5 mm
An ultrasound pulse has a PRP of 2 m/sec, a SPL of 4.0 mm, and a wavelength of 0.8 mm. What is the axial resolution of the system?
Answer: 2 mm
axial resolution = spatial pulse length / 2
axial resolution = 4 mm / 2
axial resolution = 2 mm
You don’t need all other information to calculate axial resolution because axial resolution is one half the spatial pulse length.
Which of the following transducers has the best axial resolution?
a) 3 MHz and 4 cycles/pulse
b) 2.5 MHz and 3 cycles/pulse
c) 1.7 MHz and 5 cycles/pulse
d) 5 MHz and 2 cycles/pulse
d. 5 MHz and 2 cycles/pulse
Axial resolution is best in transducers with the highest frequency and the fewest numbers of cycles per pulse.
Which of the following transducers has the worst axial resolution?
a) 3 MHz and 4 cycles/pulse
b) 2.5 MHz and 3 cycles/pulse
c) 1.7 MHz and 5 cycles/pulse
d) 5 MHz and 2 cycles/pulse
Answer: c. 1.7 MHz and 5 cycles/pulse
Axial Resolution is worst in transducers with the lowest frequency and the largest number of cycles per pulse.
What factors can affect the lóngitudinal resolution?
Answer: Any factor that can affect spatial pulse length such as frequency, wavelength, cycles in a pulse, pulse duration, backing or damping material, can affect the longitudinal resolution.
The other terms used for Axial resolution are Longitudinal, Range, Radial, and Depth resolution (LARRD).
What is the effect of backing material on the axial resolution?
Answer: The backing material reduces the ringing of the PZT crystal which shortens the spatial pulse length and improves the axial resolution.
Backing material or damping material is used in imaging transducers.
What is the effect of frequency on axial resolution?
Answer: Frequency affects axial resolution.
With higher frequencies, the wavelength decreases, and the axial resolution improves and thus higher image quality.
With lower frequencies, the wavelength increases, and the axial resolution degrade and thus lower image quality.
If the frequency is decreased, the numerical value of the radial resolution will increase.
For soft tissue:
0.77 x # cycles in pulse
Axial Resolution = 0.77 x # cycles in pulse / Frequency (MHz)
Two imaging systems produce sound pulses; one pulse is 0.6 usec long and the other pulse is 0.3 usec long. Which pulse is likely to produce the best radial resolution?
Answer: The 0.3 sec pulse will produce the best radial resolution.
Radial resolution is determined by the pulse duration, or the SPL. The shorter the pulse duration, better the radial resolution. The 0.3 sec pulse duration is shorter than 0.6 usec.
The axial resolution of an ultrasound system is 0.7 mm at the focal point of the ultrasound beam. What will be the radial resolution of the ultrasound system at a location that is 5 cm deeper than the focus?
Answer: The radial resolution will be .7 mm. The radial resolution is same at all imaging depths
Radial resolution is determined by the spatial pulse length or the pulse duration. The radial resolution or axial resolution remains constant regardless of the imaging depth. The radial resolution does not change with changing the imaging depth.
What is temporal resolution?
Answer: Temporal resolution is the ability of the ultrasound system to accurately identify the position of a moving reflector at any particular instant in real time.
The temporal resolution is determined by the number of frames or images produced in one second. A system with a higher frame vate has superior temporal resolution.
What factors affect the temporal resolution?
Answer: The factors which affect the temporal resolution are frame rate, imaging depth, use of single or multiple focus, sector size and line density.
What factors will decrease temporal resolution?
Answer A low frame rate) deeper imaging, use of multiple focus, a wider sector size and high line density will decrease temporal resolution. The temporal resolution depends on the frame rate. Lower frame rate decreases temporal resolution. Any factor that decreases the frame rate
will decrease temporal resolution.
What factors will improve temporal resolution?
Answer: A high frame rate, shallow imaging, use of single focus, a narrow sector size and low line density will improve temporal resolution. The temporal resolution depends on the frame rate, Higher frame rate improves temporal resolution. Any factor that increases the frame rate will improve temporal resolution.
A sonographer increases the line density from 5 lines per degree of sector to 10 lines per degree of sector. What will be the effect on temporal resolution?
Answer: The temporal resolution will decrease.
The temporal resolution depends on the frame rate. Increasing line density will take more time to construct a frame and will decrease the frame rate. Lower frame rate decreases temporal resolution.
What is the slice thickness or elevational resolution?
Answer: The third dimension of the ultrasound beam is called the slice thickness plane or elevational plane. Slice thickness resolution or elevational resolution is the resolution in the third dimension of the sound beam.
The focus is achieved in the slice thickness plane with lens. Therefore, the focus is fixed and does not change by changing the depth
