Image Analysis CH 2 Pt 1 Flashcards Preview

Radiography Spring 2016 > Image Analysis CH 2 Pt 1 > Flashcards

Flashcards in Image Analysis CH 2 Pt 1 Deck (31):

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

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


know what the mAs is chosen for on an image

number of photons needed to produce an image without quantum noise


know what the kVp is chosen for

the desired subject contrast


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

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


know how the reader unit works

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


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

best set at the phosphors k-edge


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

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


know what happens during digitization

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


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

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


define raw image data

all the brightness values together


know when in the process a histogram is generated

after the image data from the exposure field had been recognized


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

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


know what the histogram represents

the subject contrast in the remnant radiation


know what the histogram is determined by

total exposure used to make the image


know what the peaks and valleys of a histogram represent

subject contrast of the structure images
-the VOI is identified, SI representing the minimum useful signal and S2 representing the maximum useful value


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

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


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

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


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

the background brightness value that is in the exposure field


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

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


know when you would not see this background value spike

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


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

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


know what a lookup table (LUT) is

ideal histogram for every part imaged


know how the LUTs were developed

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


know how the computer aligns the image histogram with the LUT

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


know what the most common rescaling process is

adjust the brightness and contrast of the image


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

overexposure= 120%
underexposure= 60%


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

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


know what exposure indicators ARE ?

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


know what exposure indicators are NOT?

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


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

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


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

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