Image Analysis CH 2 Pt 1

Question 1

What does understanding the acquisition and processing steps of your digital system?

Answer 1

helps prevent errors that cause poor processing of the image and understand the results seen on the image and exposure indicators when it is less than optimal

Question 2

know what the mAs is chosen for on an image

Answer 2

number of photons needed to produce an image without quantum noise

Question 3

know what the kVp is chosen for

Answer 3

the desired subject contrast

Question 4

know why it is important to select the correct examination/body part on your workstation

Answer 4

ensures the correct lookup table is applied when the image is reached

Question 5

know how the reader unit works

Answer 5

an infrared laser beam is scanned back and forth across the plate, releasing the stored energy in the form of visible light

Question 6

know where the kVp is best set for the most efficient detection and capture of radiation

Answer 6

best set at the phosphors k-edge

Question 7

know what happens once the light is then collected from the reader

Answer 7

converted to an electrical signal by the photomultiplier (PMT) and then sent to the analog to digital converter (ADC) to be digitized

Question 8

know what happens during digitization

Answer 8

the analog image is divided into a matrix and each pixel (cell) in the matrix is assigned a digital number (brightness value) that represents the amount of light that was emitted from the surface of the IR

Question 9

be able to describe the difference in pixels in reference to their brightness

Answer 9

pixels that received greater radiation exposure are assigned values that represent less brightness, whereas the pixels receiving less exposure are assigned values that represent more brightness

Question 10

define raw image data

Answer 10

all the brightness values together

Question 11

know when in the process a histogram is generated

Answer 11

after the image data from the exposure field had been recognized

Question 12

know what is represented on both the x and y axis of a histogram

Answer 12

pixel values on the x-axis and the number of pixels with that brightness values on the y-axis

Question 13

know what the histogram represents

Answer 13

the subject contrast in the remnant radiation

Question 14

know what the histogram is determined by

Answer 14

total exposure used to make the image

Question 15

know what the peaks and valleys of a histogram represent

Answer 15

subject contrast of the structure images

-the VOI is identified, SI representing the minimum useful signal and S2 representing the maximum useful value

Question 16

know why each structure (chest, abdomen, hand) histogram should be fairly consistent across the board

Answer 16

because the subject contrast of a particular anatomic structure is fairly consistent from exposure to exposure the shape if each structures should be fairly consistent

Question 17

know where items fall on a histogram (metallic obj, bone, fat, etc)

Answer 17

Metallic or contrats in the left
followed by bone
soft tissue(near the center)
fat
gaseous or air densities on the right

Question 18

know what the tail or high spiked far right on a histogram represents

Answer 18

the background brightness value that is in the exposure field

Question 19

know why the background value will be the darkest image data value on the histogram

Answer 19

this area is exposed to primary radiation that does not go through any parts of the patient

Question 20

know when you would not see this background value spike

Answer 20

on images in which the entire cassette is covered with anatomy or on images where collimation is within the skin line

Question 21

know the reasons for poor histogram formation and subsequent histogram analysis errors

Answer 21

poor positioning, collimation, or alignment of part on the IR, with unusual pathologic conditions, with artifacts, by including anatomy that is not typically present or removing anatomy that is typically present, with excessive scatter fogging

Question 22

know what a lookup table (LUT) is

Answer 22

ideal histogram for every part imaged

Question 23

know how the LUTs were developed

Answer 23

using exposure techniques, positioning, collimation that produced optimal histogram for that projection and provides a means for the computer to automatically rescale the image before its displayed

Question 24

know how the computer aligns the image histogram with the LUT

Answer 24

the computer compares the image histogram with the selected LUT and applies algorithms to the actual data as needed to align the image histogram with the LUT

Question 25

know what the most common rescaling process is

Answer 25

adjust the brightness and contrast of the image

Question 26

know what the approximate percentages are for over and under exposures that automatic rescaling can fix

Answer 26

overexposure= 120%
underexposure= 60%

Question 27

know and describe what happens if the image histogram and selected LUT do not have a similar shape

Answer 27

the computer software will be unable to align them resulting in a histogram analysis error that produces a poor quality image and provides an error exposure indicator value

Question 28

know what exposure indicators ARE ?

Answer 28

are readings that express the amount of light given off by the IP and that demote the amount of exposure to the patient and IP

Question 29

know what exposure indicators are NOT?

Answer 29

not a measure of dose to the patient, but an indication of what the patient has received

Question 30

know what to do with your collimation so that you do not cause a histogram analysis error

Answer 30

collimating to within 0.5 inches of the skin line–prevents too much background data from being include within the exposure field

Question 31

know how to control the amount of scatter on an image so you do not cause a histogram analysis error

Answer 31

tight collimation, appropriate grid usage, and by placing a lead sheet against the edge of exposure field