Regarding real-time B-mode imaging: a. A typical number of scan lines

1.	Regarding real-time B-mode imaging: a. A typical number of scan lines in B-mode imaging of the abdomen is 256 b. To avoid flicker, the frame rate should be at least 20–25 frames per second (fps) c. The maximum scan line density at a frame rate of 25 fps and a pulse repetition frequency (PRF) of 2 kHz is 50 d. The maximum depth of view at a frame rate of 30 fps and a scan line density of 100 is approximately 33 cm e. The maximum achievable frame rate with a line density of 100 and a depth of view of 15 cm is approximately 50 fps
Answer» a. False. Such a high number of lines is unnecessary, as the lateral resolution is limited anyway. A typical line density is about 100 or slightly more as a compromise between achievable frame rate and scanning depth. b. True. The limit of temporal resolution of a human eye is about 40 ms, so ideally the frame rate should be above 25 fps. Below 20 fps, flicker (seeing images as separate in time) becomes obvious. c. False. With a PRF of 2 kHz, an ultrasound pulse is sent 2000 times per second. If 25 frames are to be obtained per second, each of them can have 2000/25 = 80 lines. d. False. In 1 s, ultrasound needs to travel double the distance d (from the probe to the depth of view and then back) as many times as the number of scan lines multiplied by frame rate. Therefore, it travels a total distance of 2 x d x frame rate x number of scan lines with an average velocity of 1540 m s^-1 . Therefore, the depth of field can be calculated as d = 1540/(2 x frame rate x number of scan lines) = 1540/(2 x 30 x 100) = 1540/6000 x 0.25 (m). e. True. As per the above equation, the frame rate can be calculated as 1540/(2 x depth of view x number of scan lines) = 1540/30 x 50 (fps).

Regarding real-time B-mode imaging: a. A typical number of scan lines in B-mode imaging of the abdomen is 256 b. To avoid flicker, the frame rate should be at least 20–25 frames per second (fps) c. The maximum scan line density at a frame rate of 25 fps and a pulse repetition frequency (PRF) of 2 kHz is 50 d. The maximum depth of view at a frame rate of 30 fps and a scan line density of 100 is approximately 33 cm e. The maximum achievable frame rate with a line density of 100 and a depth of view of 15 cm is approximately 50 fps

Answer»

a. False. Such a high number of lines is unnecessary, as the lateral resolution is limited anyway. A typical line density is about 100 or slightly more as a compromise between achievable frame rate and scanning depth.

b. True. The limit of temporal resolution of a human eye is about 40 ms, so ideally the frame rate should be above 25 fps. Below 20 fps, flicker (seeing images as separate in time) becomes obvious.

c. False. With a PRF of 2 kHz, an ultrasound pulse is sent 2000 times per second. If 25 frames are to be obtained per second, each of them can have 2000/25 = 80 lines.

d. False. In 1 s, ultrasound needs to travel double the distance d (from the probe to the depth of view and then back) as many times as the number of scan lines multiplied by frame rate. Therefore, it travels a total distance of 2 x d x frame rate x number of scan lines with an average velocity of 1540 m s^-1 . Therefore, the depth of field can be calculated as d = 1540/(2 x frame rate x number of scan lines) = 1540/(2 x 30 x 100) = 1540/6000 x 0.25 (m).

e. True. As per the above equation, the frame rate can be calculated as 1540/(2 x depth of view x number of scan lines) = 1540/30 x 50 (fps).

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