Knobology Flashcards
Velocity of sound in soft tissue
1540 m/s
M-mode
Brightness mode vs time
2D grayscale imaging
Multiple M-mode scan lines spliced together to form a sector
Multiple pulses from multiple crystals
Phased array allows electronic focusing and beam steering
3D Imaging
Pyramid of M-mode scan lines
Wave properties — time
Period — amount of time to complete a single cycle
Frequency — number of cycles / second
• u/s > 20 KHz
•increased frequency —> better axial resolution (decreased SPL)
•increased frequency —> more attenuation
Pulse duration — time to complete an entire pulse
•PD = period x # cycles
Pulse repetition period — time from beginning of one pulse to beginning of another pulse
•includes pulse duration and listening time
•depends on depth of object
Pulse repetition frequency — # pulses / second
•inverse of PRP
•important for temporal resolution
•determines the Nyquist limit (1/2 PRF)
Wave properties — length (distance)
Wavelength — length of a single cycle
Spatial pulse length — length of an entire pulse
•determines axial resolution —> 1/2 SPL
•”LARD” - longitudinal, axial, radial, range, depth
Wave properties — strength
Amplitude — difference between the average and max acoustic variable
Power — amount of work the u/s beam can do
Intensity — amount of power per unit area
•determines the bio effects of u/s
Spatial resolution
Ability to discern the correct space/place of a structure
•axial (pulse length) > lateral (beam width) > elevational (beam height)
Temporal resolution
Ability to accurately determine the position of a structure at a particular instant in time
Determined by: •how much something moves •frame rate = # frames / second # pulses / scan line Line density Image depth (listening time) Sector width PRF proportional to frame rate — as PRF increases the temporal resolution improves Nyquist limit = 1/2 PRF
Gain
Amplifies returning signals
•post processing function
Power
Transducer output
•increases amount of energy transmitted to the body
Time/depth gain compensation
Compensation for attenuation with depth
Lateral gain compensation
Compensation for attenuation laterally
Compression
Compresses the range of signals and decreases the dynamic range
•dynamic range is the inverse of compression and can be thought of as the # shades of gray
Focus
When beam is narrowest there is the best lateral resolution