Display Format, Frame Rate, Temporal Resolution, Spatial Resolution

What is the fundamental limitation of temporal resolution? A. imaging depth B. speed of sound in the medium C. line density D. sector size

B. Speed of sound in the medium is the fundamental limitation of temporal resolution.

Of the following, which imaging modality has the poorest temporal resolution? A. two-dimensional, real-time B. A-mode C. color flow imaging D. M-mode

C. Of the choices, color flow imaging has the lowest temporal resolution. Many pulses are required to create a single color flow image. The large number of pulses required for each image results in a low frame rate and poor temporal resolution.

A sonographer reduced the sector size from 90 degrees to 30 degrees. Frame rate, however, did not change. What else happened? A. imaging depth decreased B. pulse duration increased C. multi-focus was turned on D. PRF was increased

C. The question states that sector size was decreased. By itself, this would increase frame rate. Thus, the correct answer to this question is something that would decrease frame rate. The only selection that decreases frame rate is the use of multiple focal points, choice C.

Which of the following will improve a system's temporal resolution? A. increased sector angle B. increased line density C. increased PRF D. increased frequency

C. To improve temporal resolution, increase the number of images produced each second. If the number of pulses emitted per second is increased (choice C) then the system can increase the frame rate. Increased PRF is obtained by decreasing the maximum imaging depth. A, B, and D all decrease frame rate and decrease temporal resolution.

All of the following reduce temporal resolution by increasing the number of pulses per image except: A. increasing the number of foci B. increasing line density C. increasing field of view D. increasing depth of view

D. Increasing the depth of view does not alter the number of pulses per image. Increasing depth of view decreases temporal resolution by changing the pulse repetition period while leaving the number of pulses in each image unchanged.

When the frame rate is 30 Hz, how long does it take to create a frame? A. 30 sec B. 3 sec C. 0.3 sec D. 1/30 sec E. 1/3 sec

D. Recall that frame rate and Tframe are reciprocals. Thus, if the frame rate is 30 per second, the time to create each frame is one-thirtieth of a second,

Which ultrasound imaging modality has the best temporal resolution? A. B-scanning B. duplex imaging C. color flow imaging D. M-mode

D. Temporal resolution is the ability to accurately record the position of moving reflectors. With M-mode, the ultrasound pulse tracks reflector position in only a single dimension (depth only) and delivers extremely fine temporal resolution. The remaining choices all operate in two dimensions and do so by compromising temporal resolution.

Two imaging systems produce acoustic pulses; one pulse is 0.4 usec long and the other is 0.2 usec long. Which is most likely to provide the best temporal resolution? A. 0.4 usec system B. 0.2 usec system C. they are the same D. cannot be determined

D. Temporal resolution is unrelated to pulse duration. Temporal resolution is determined by the number of frames, or images, that are produced each second. There is insufficient information to answer the question.

____ refers to how the image appears on the screen, as either a rectangular display or a sector display.

Display Format

Phased array transducers increase temporal resolution. True or False

False- because of their multi-focus capabilities: temp res is best with only ONE focus meaning only one pulse per scan line

True or False? An ultrasound system with a longer pulse duration will generally have better temporal resolution.

False. Temporal resolution of a system is unaffected by the pulse duration.

Low Pixel Density results in....

Few pixels per inch Larger pixels Less detailed image Lower spatial resolution

Narrow sector/FOV on pulses per frame, Tframe, frame rate, and temporal resolution

Fewer pulses per frame Shorter T frame Higher frame rate Better temporal resolution

The formula describing the relationship between frame rate and Tframe

Frame rate x T frame = 1 (reciprocals)

Frame rate is measured in..

Hertz (Hz) or "per second". Units are "images per second"

Spatial resolution menas

Image sharpness

What is a pixel?

It is the smallest building block of a digital picture

Deep Imaging will result in...

Long go-return time Longer T frame Lower frame rate Inferior temporal resolution (degraded)

Is temporal resolution better with high or low line density?

Low line density

High Pixel Density results in...

Many pixels per inch Smaller pixels More detailed image Better spatial resolution

Wide sector/FOV on pulses per frame, Tframe, frame rate, and temporal resolution

More pulses per frame Longer T frame Lower frame rate Poorer temporal resolution

What happens when the sonographer increases the sector size (FOV). Will there be more or less pulses needed?

More pulses when the fov is increased which means more time needed to create a frame

The us system slows down when there are more or less scan lines?

More, this will degrade temporal resolution

Multi focus affect on pulses per scan line, Tframe, frame rate, temporal res, and lateral res

Multiple pulses per scan line (#of focal zones) Longer T frame Lower frame rate Poorer temporal resolution Better lateral resolution

Is temporal resolution better with a narrow or wide FOV?

Narrower FOV/sector

Single focus affect on pulses per scan line, Tframe, frame rate, temporal res, and lateral res

One pulse per scan line Shorter T frame Higher frame rate Better temporal resolution Poorer lateral resolution

If imaging depth halves, PRP ___ and FR ___

PRP also halves (DR) FR doubles (IR)

What is the formula for determining the scan line density for a sector display?

Scan line density (lines/angle) = scan lines per frame / sector angle

What is the formula for determining Scan-Line Density for a rectangular display?

Scan line density (lines/cm) = scan lines per frame / display width (cm)

Which sector imaging system will provide the best image detail (spatial resolution) if all other parameters are identical? A. 80 degree sector with 110 pulses/image B. 70 degree sector with 86 pulses/image

Scan line density (lines/cm) = scan lines per frame / display width (cm) System A provides 1.4 pulses per 1 degree (110/80) System B provides 1.2 pulses in degree cm (86/70) Answer: system A will provide the best image detail since there are more pulse density. However, it will degrade temporal resolution more than system A

Which linear imaging system will provide the best image detail (spatial resolution) if all other parameters are identical? A. 6 cm width with 100 pulses/image B. 4 cm width with 86 pulses/image

Scan line density (lines/cm) = scan lines per frame / display width (cm) System A provides 16.7 pulses in 1 cm (100/6) System B provides 21.5 pulses in 1 cm (86/4) Answer: system B will provide the best image detail since there are more pulse density. However, it will degrade temporal resolution more than system A

Is temporal resolution better with deep or shallow imaging?

Shallow

Shallow Imaging will result in...

Short go-return time Shorter T frame Higher frame rate Superior temporal resolution

Is temporal resolution better with a single focus or multi focus?

Single focus

Equation: If the sonographer changed the depth from 10 cm to 5 cm, the pulse's time of flight or PRP or go-return time is going to be half the first scenario which is half the 1/1000 seconds which is equal to 0.0005 seconds. What is the frame rate?

Step 1: Calculate the Tframe: T frame = # pulses X PRP T frame = 100 x 0.0005 seconds = 0.05 seconds = 5/100 or 1/20 second Because T frame and frame rate are reciprocal, the frame rate is 20 Hz and temporal resolution is improved when the sonographer reduced the depth

Solve: If an US system creates each image with 100 distinct sound pulses. The sonographer sets the depth at 10 cm. If it takes each pulse 1/1000 second for the go-return time (PRP). What is the frame rate?

Step 1: calculate the time needed to make a single frame: T frame = # pulses X PRP T frame = 100 X 1/1000 = 0.1 second = 1/10 second Step 2: Because T frame and frame rate are reciprocals, the frame rate is 10 Hz

Time for a single frame rate is represented in ___

T frame

Formula for Tframe

T frame = # pulses X PRP

____ describes the ability of the US system to precisely position moving structures from instant to instant

Temporal Resolution

High Line Density results in...

Tightly packed lines More pulses per frame Longer T frame Lower frame rate Poorer temporal resolution Excellent spatial resolution

Tframe means...

Time for a single frame rate

Better Spatial Resolution means More/Better Line Density. True or False?

True

Frame rate of a TV is how often the TV changes the image on screen. True or False?

True

Multi-focus generally improves lateral resolution but reduces frame rate and temporal resolution. True or False?

True

When the sonographer adds focal zones, it means more pulses are transmitted down each scan line, therefore, the number of pulses required to create an image also increases. True or False?

True

temporal resolution is not as important as when scanning stationary tissue. E.g. liver, spleen, kidneys. True or False?

True

Linear and convex switched (or sequential arrays) do not steer sound beams. True or false?

True - Rather, a small group of the elements produce a pulse that travels straight ahead.

In clinical settings, depending on what study the sonographer is doing, he/she can decide whether getting an excellent image quality is a priority or getting a superior movie is a priority.Treu or False?

True In other words, compromising the temporal resolution to get a nice picture or maximizing the temporal resolution to get a quick update (or refresh) is the priority

True or False, If 100 scan lines make up an image and the frame rate is 30 per second, then the system's pulse repetition frequency is 3,000 Hz.

True. Pulse repetition frequency is the number of pulses created per second In this example, it is lines per image multiplied by frame rate.

True or False? The length of a pulse does not directly influence the temporal resolution.

True. Temporal resolution is not affected by the length of the pulses produced by the system. The factors that influence the temporal resolution are maximum imaging depth, sector angle, line density, and the number of foci per scan line.

Low Line Density results in....

Widely spaced lines Fewer pulses per frame Shorter T frame Higher frame rate Better temporal resolution Poor spatial resolution

If the sonographer is doing an OB study and he/she wants to accurately display the motion of a rapidly moving structure, such as fetal heart which requires excellent temporal resolution, the sonographer would use

a single focus, a narrow field of view (narrow sector size), and low line density, so the images would be adequate, but the movie would be great

Temporal resolution pertains to...

accuracy in time

The greater the number of lines, the ____ the spatial resolution

better

Higher pixel density results in _____ spatial resolution, whereas lower pixel density results in _____ spatial resolution

better, poorer

The width of a rectangular display is given in

centimeters

When the sonographer expands the sector size, aka, the field of view, then more pulses are needed to create the image, so frame rate is ____ and temporal resolution is ____

decreased frame rate, degraded temporal resolution

High line density means number of pulses per image is increased and the frame rate is ____ and temporal resolution is ____

decreased, degraded

More pulses per scan line (due to the addition of more focal zones) has what affect on frame rate and temporal resolution?

decreases the frame rate and degrades temporal resolution

Scanning ____ depth, more time is needed to make each frame, the frame rate is slower and the temporal resolution is degraded

deeper (increase the depth by turning the depth knob on the other direction)

When the system slows down, temporal resolution will...

degrade. The more scan lines the slower the system which degrades temporal resolution (but lateral resolution will improve)

Low line density means _____ spatial resolution

degraded

imaging depth and T frame are ____ related

directly

To determine the line density for a rectangular display, the lines per frame are ___ by the display width in ___

divided, centimeters

When a system produces many frames per second, temporal resolution is ____

excellent

Refresh rate aka

frame rate

Temporal resolution is determined by

frame rate

Real-time imaging relies on the ability of the US system to create numerous frames each second, this is called

frame rate (refresh rate)

If a US system creates a 90-degree sector image with a line every 2 degrees (the image is formed by 45 distinct sound pulses). If the sonographer increases the line density to 1 line per degree, the pulses that form the image now are 90 distinct sound pulses meaning more time is needed to make the image. What happens to the frame rate and temporal resolution?

frame rate decreases and temporal resolution is degraded

If imaging at a lower/shallower depth, what happens to frame rate?

frame rate is higher (Tframe would be lower since its directly related to imaging depth and inversely related to frame rate)

imaging depth of view is doubled (for example from 6cm to 12cm), the frame rate will be

halved. (Deep imaging- longer prp, longer Tframe, lower frame rate, poorer temporal res)

Frame rate is measured in ___. What does it reflect?

hertz (Hz) as it reflects # of images per second

Lines that are closely packed, means the line density is ___

high

Low line density means few pulses are needed to create each image, the frame rate is ____ and the temporal resolution is ____

high, improved

If the display was a monitor, spatial resolution is affected by the number of _____ scan lines per frame.

horizontal

High line density means ____ spatial resolution

improved

When a picture is divided into a grid (similar to a checkerboard), each individual box is a pixel Pixel density is the number of picture elements per

inch

When the sonographer minimizes the sector size, aka, the field of view, fewer pulses are needed to create the image, so frame rate is ____ and temporal resolution is ____

increased, improved

The relationship between frame rate and T frame is...

inversed but it's also reciprocal meaning when they are multiplied, the result is 1

Field of view and frame rate are ____ related

inversely

Line density and frame rate are _____ related

inversely

Pulses per frame and frame rate are ____ related

inversely

What is a pixel derived from?

is derived from the term picture element

If a tv is "60Hz," this means

it can draw 60 images per second

When scanning a fetus or the pulsating aorta, adding more focal zones will slow down updating the image and will have what affect on temporal resolution?

it will degrade the temporal resolution

Adding more focal zones, each scan line has better ____ resolution because it is narrow over a greater range of depths as the focus is the area of the beam where the beam is narrowest (waist of the beam)

lateral

Decreasing the FOV requires ____ pulses to create an image

less

The scan lines in a sector display image form an angle so that the line density is expressed as

lines per degree

Deep imaging means ____ go-return time (PRP) and ___ T frame

long, longer

Lines may be spaced far apart, meaning the line density is ___

low

Increasing the FOV will require ___ pulses to create an image

more

If the sonographer adjusted the system and expanded the sector, so the system can create a 90-degree sector image, the complete image will now require 90 distinct sound pulses which means...

more time> frame rate decreases and temporal resolution is degraded

The significance of higher frame rate in TVs or cameras is to avoid...

motion blur problem or flickering

If imaging a stationary organ, such as the liver, to produce excellent-quality images, the sonographer would use....

multiple focus, wide field of view, and high line density (very tightly packed scan lines and small gaps) ****All these settings will produce an excellent image, but a poor movie as the frame rate is slower and the temporal resolution is degraded

With single focus imaging, ____ sound pulse is transmitted down each scan line

only one

A sector display image yields a

pie-shaped image

When the image information is in digital form, spatial resolution is related to ____density

pixel

When a system produces a small amount of frames per second, temporal resolution is ____

poor

The number of lines per frame and the frame rate determine the

pulse repetition frequency.

A rectangular display image appears in the form of a

rectangle

Frame rate is in Hz so Tframe has to be in....

seconds

Scanning _____ depth, less time is needed to make each frame, the frame rate is higher and the temporal resolution is better

shallower(decrease the depth by turning the depth knob)

Shallow imaging means ____ go-return time (PRP) and ____T frame

short, shorter

Higher pixel density means many pixels per inch and it is achieved with _____ pixels

smaller (so more pixels are required to create the image)

Refreshing the image at 50 or 60 Hz, to the human eye this looks...

smooth and is unnoticeable

US systems can alter the ___ between sound beams

spacing (line density). **Some machines enable the sonographer to adjust that

The higher the scan line density the better the ___ resolution

spatial

___ resolution is accuracy in regards to a position of a reflector in space

spatial

Which resolution is related to the overall detail in an image?

spatial resolution

the line density of a rectangular display is expressed as

the number of lines per centimeter

The critical factor in determining frame rate, line density, and imaging depth is

time.

When the sonographer adds focal zones, it means more pulses are...

transmitted down each scan line

To determine which imaging system provides the best spatial resolution, what do you have to know?

you have to know the pulse density in 1 cm if it is a rectangular image format or in 1 degree if it is a sector format

Lower frame rate or degraded temporal resolution is done by

1- increasing the depth 2- adding more focal zones 3- widening the sector or the field of view 4- increasing the line density which on the other hand improves spatial resolution or how clear the image is

Spatial Resolution is determined by multiple factors, including

1- line density (how closely sound pulses are packed) the higher the line density, the clearer the image The lower the line density, the blurrier the image 2- axial resolution 3- lateral resolution 4- Also, the system's display affects spatial resolution

Determine the scan line density of a sector image that has a 90 degree angle and 180 scan lines.

**Scan line density (lines/angle) = scan lines per frame / sector angle Scan line density (lines/angle)= 180 (lines) / 90 degrees= 2 lines/angle

If the width of a rectangular display (linear sequential) is 5cm and there are 20 scan lines. What is the scan line density?

**Scan line density (lines/cm) = scan lines per frame / display width (cm) Scan line density (lines/cm)= 20 (lines)/5 (cm) = 4 lines/cm

Factors that affect the number of pulses per frame are...

1- number of focal zones (caret is an arrow used to indicate the focal zone on a 2 D image) 2-display format size: sector size for sector image display format and the rectangular width in rectangular image display format 3-line density: the number of lines per angle of sector for sector image display format and the number of lines per centimeter for rectangular image display format

Higher frame rate or improved temporal resolution is achieved with

1- shallower imaging 2- single focus 3- narrow sector or field of view 4- low line density

Frame rate is determined by...

1- speed of sound in soft tissues 2- imaging depth (adjustable by sonographer) 3- The number of pulses per frame (adjustable by sonographer)

Some modern TVs can refresh at much higher rates, most commonly 120 Hz which means...

120 frames per second

Example: If the sonographer adjusts the system to operate with 4 focal zones (instead of 1) and the image to be created requires 90 scan lines (penetration lines), so four pulses are needed to create one scan line, how many pulses are needed to create an image?

4 x 90 = 360 pulses are needed to create on image

If the US system creates a 40-degree sector image with 1 transmit line for each degree of the sector, the complete image will require how many sound pulses?

40 distinct sound pulses

When a system creates an image in 1/50 of a second, the frame rate is....

50 frames/second or 50 Hz

If lateral resolution needs to be improved, what can the sonographer do?

Add more focal zones, however, temporal resolution will degrade (this is fine if the area of interest is a stationary structure)