Knobology

Question 1

Velocity of sound in soft tissue

Answer 1

1540 m/s

Question 2

M-mode

Answer 2

Brightness mode vs time

Question 3

2D grayscale imaging

Answer 3

Multiple M-mode scan lines spliced together to form a sector

Multiple pulses from multiple crystals

Phased array allows electronic focusing and beam steering

Question 4

3D Imaging

Answer 4

Pyramid of M-mode scan lines

Question 5

Wave properties — time

Answer 5

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)

Question 6

Wave properties — length (distance)

Answer 6

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

Question 7

Wave properties — strength

Answer 7

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

Question 8

Spatial resolution

Answer 8

Ability to discern the correct space/place of a structure

•axial (pulse length) > lateral (beam width) > elevational (beam height)

Question 9

Temporal resolution

Answer 9

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

Question 10

Gain

Answer 10

Amplifies returning signals

•post processing function

Question 11

Power

Answer 11

Transducer output

•increases amount of energy transmitted to the body

Question 12

Time/depth gain compensation

Answer 12

Compensation for attenuation with depth

Question 13

Lateral gain compensation

Answer 13

Compensation for attenuation laterally

Question 14

Compression

Answer 14

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

Question 15

Focus

Answer 15

When beam is narrowest there is the best lateral resolution