Modes of Data Acquisition

Question 1

Digital imaging

Answer 1

• X, y and z values are limited to certain discrete values

Question 2

Analog to digital converter

Answer 2

accepted photon signals are converted to digital data

Question 3

Matrix

Answer 3

• grid of squares where information can be placed to create a digital image
• dimensions x, y, and depth

Question 4

Byte mode

Answer 4

• 1 byte (8 bits) of memory are alotted per pixel
• Limits max number per pixel to 225

Question 5

Word Mode

Answer 5

• 2 bytes (16 bits) of computer memory is alotted per pixel
• allows 16 535 counts per pixel

Question 6

Pixel saturation

Answer 6

• Certain systems use different data overflow rules
• One must be aware of the possibility that data and image quality may be lost because of pixel overflow in byte mode
• word mode is sufficient for nuclear medicine studies and is recommended

Question 7

What happens when matrix size is doubled?

Answer 7

• smaller pixels by a factor of 2
• counts per pixel will be decreased by a around a factor of 4
• Count variation will be less (less contrast)
• noise may be introduced

Question 8

Matrix affect on noise and resolution

Answer 8

-Small matrix solves noise, but lowers spatial resolution
- small matrix decreases edge definition
- pixel size 1/3 or 1/2 of the system resolution is ideal

Question 9

Pixel size calculation

Answer 9

• Pixel size= FOV/matrix
• pixel size chosen should not limit the image resolution

Question 10

Zooming

Answer 10

• Improves spatial resolution
• Accomplished with hardware or software

Question 11

Hardware zoom

Answer 11

• through collimation
• converging or pinhole
• most commonly used in analog imaging

Question 12

Software Zoom

Answer 12

• Post acquisition: Magifies image making each pixel bigger by the zoom factor
• Pre acquisition: Applies the zoom factor before image acquisition

Question 13

What is frame mode?

Answer 13

• Image matrix or frame is created prior to acquisition
• each count is assigned a pixel in the frame
• held in a buffer during acquisition and sent to long term memory when complete
• Small but finite amount of time is required to save the buffer
• Buffer pixels are reset to zero once saved

Question 14

Image acquisitions that use frame mode

Answer 14

• static
• whole-body
• dynamic
• dual-isotope
• gated

Question 15

Image acquistions that use list mode

Answer 15

• dynamic
• gated

Question 16

List mode pros

Answer 16

• handles high count rates
• high temporal resoltuion
• fllexible post processing

Question 17

list mode cons

Answer 17

• memory requirements
• post-processing time requirement

Question 18

What is list mode

Answer 18

• Serial mode acquisition
• each pixel is stored separately as an x and y value
• timing markers stored in sequence
• physiologic markers (r-waves) may also be stored
• requires reformatting post-acquisition
• used for short durations with high transient count rates

Question 19

Dynamic frame mode

Answer 19

• series of images taken sequentially for a predetermined length of time
• good for visualization and quantification of flow kinetics of RP
• requires a pair of buffer frames
• one buffer is used for active acquisition, one buffer is used to send data to long term storage and resets to zero
• the zeroed buffer is then used for the next acquisition

Question 20

Dual isotope imaging

Answer 20

• Acquires simultaneous images using multiple energy windows
• system needs to have good energy resolution
• can be done planar or spect

Question 21

Spatial resolution

Answer 21

• ability of a camera to visualize small objects
• ability to reproduce details from a non uniform source of gamma rays

Question 22

Contrast resolution

Answer 22

• ability to distinguish between areas of an image
• visualization of difference in count densities of two different areas

Question 23

Temporal resolution

Answer 23

ability of the imaging system to detect rapid changes in tracer distribution

Question 24

Noise

Answer 24

• undesired fluctuations that appear superimposed on a signal
• electrical variations
• random nature of radioactive decay
• variability in detection efficiency
• variability associated with assigning counts to pixels in a matrix

Question 25

Background

Answer 25

• detected counts that do not come from the radiation source or organ being measured

Question 26

Signal-to-noise ratio

Answer 26

• relative amounts of desired signal and unwanted noise
• ratio needs to be greater than at least 3 to reliably distinguish signal above the noise