Digital Imaging Exam 4

smallest element in the digital image

pixel

each pixel represents the anatomical areas:____ and ___

physical location and gray level

the less space a pixel has to represent the ___accurate the information is

more

is an image more or less blurry with large pixels

more blurry

if pixel size decreases what happens to image detail

increases

what type of relationship is pixel size and image detail

inversely proportional

an arrangement of numbers in columns and rows

matrix

in a matrix what do the numbers represent

brightness level

in a matrix what do the columns and rows represent

spatial location

The size of the matrix determines the size of the___

pixels

if matrix size is increased what happens to the pixel size and sharpness of the image

pixel size is decreased and sharpness increases

if pixel size increase what happens to the available grays

fewer gray shades (more black and white increased contrast)

what is the limiting factor of the minimum object size that can be imaged

pixel size

what is the equation for minimum object size

½ (1/SF)

what is the equation for spatial frequency (lp/mm)

1/ 2(PS)

for a pixel side of .3mm what is the associated resolution in line pairs per millimeter

1.7 lp/mm

portion of the imaging plate that contains relevant anatomic information and is displayed at the monitor screen

Field of View (FOV)

Greater FOV = ___

more patient anatomy being imaged

what is the equation for pixel size

PS= FOV/Matrix size

A change in either the matrix size or FOV will do what to pixels

will change the size

Would just changing the FOV effect the matrix size

no

would changing the matrix size effect the FOV

no

what type of relationship does FOV and pixel size have

directly proportional

if we decrease FOV we do what to pixel size

decrease

the size of the image matrix , by pixel could is (inversely/directly) proportional to pixel size

inversely

the size of the matrix is (inversely/directly) proportion to spatial resolution

directly

if the images are both the small and large anatomy are displayed at the monitor using the same image matrix, the smaller the field of view would consist of ____pixels in the display

smaller

three steps in digitizing a image

matrix assignment (scanning)

image sampling

quantization

field of the image is divided into an array(matrix) of small cells by a process called ___

scanning (matrix assignment)

what does the software ‘sweep’ for during the scanning process

matrix size and pixel allocation

the intensity of light (radiation) from each pixel area is measured by the detector

image sampling

the size of the signal is determined by what

image sampling

assigning a numeric value to a corresponding gray level

quantization

computer language of 1s and 0s

binary code

circuit closed (current)

1

circuit open (no current)

0

single unit of data

bit

Made up of 8 bits

byte

when a system is on what number does that correlate with

1

when a system is off what number does that correlate

0

sum of the values of the marked digits

value

the number of bits within a pixel (max number of values the computer can store)

bit depth

the range of grays made available to construct the image

dynamic range

the greater the dynamic range the ___grayscale

longer

the greater the dynamic range the ___ detail

more

What is the advantage of digital imaging’s ability to manipulate the grayscale levels of pixels?

we can change the appearance of the image without re-exposing the patient because our contrast is determined through numeric values that the computer can manipulate

customized protocols that come programmed into the operating system for each type

Look-up table

what are the two things that the LUT is responsibe for

ideal contrast and brightness

adjusting the brightness and contrast of the image as its being viewed (raw data)

windowing

adjusts the center of the window (brightness)

window level

adjusts the length of grayscale in the image (contrast)

window width

when you increase the window width what happens

more grays, longer scale, lower contrast

increasing the window level makes the overall image darker but the number of steps in the gray scale ____ ____

remain equal

corrections that are made to the ‘raw’ digital image data die to physical flaws

preprocessing

manipulation and adjustments of the digital image, made after corrections have been made for data acquistition (refinement)

Postprocessing

purpose of field uniformity

evens out the overall signal (brightness) across the entire area of the field

low exposure is made to the IR without any objects in the x-ray beam

process

individual hardware cells in a DR image receptor, capable of producing a single electronic readout from the photon energy

(captures info from the exposure to be sent to the computer for readout)

DEL (detector element)

what is the purpose of field uniformity

correct inherent flaws within the IR from the electronic’s unavoidable variations that effect the uniformity of the detected field

longer wires create___ electrical resistance compared to those with shorter wires

more

something that creates light

scintillator

thicker/narrow portions of phosphor layers have greater absorption efficiency and will produce slightly more light output

thicker

what are the four types of corrections in the field uniformity

1. flat-field uniformity correction

2. electronic response and gain

3. variable scintillator thickness

4. light guide variations in CR

The job of the photodiode

absorb the electrons and generate electrical charges

what is the job of the thin-field transistor (TFT)

1) isolate each pixel

2) reacts like a switch, sends electrical charges to image processor

when a circuit is closed what is the data doing

is being transmitted

when a circuit is open what is the data doing

is being stored

submatrix that is passed over the larger matrix of the image that executes some mathematical function

kernel

what fills in the dead space of a matrix

interpolation

flaws in the IR that results in missing information in the data sent into the computer for processing

DEL drop out

how does image analysis work

segmentation

exposure field recognization

histogram formation

histogram analysis

used to count the number of exposures on a single PSP plate, each exposed area can be treated separately

segmentation

if enough scatter reaches beyond collimated borders ____ occurs

segmentation errors

identify the pitch black background densities form raw x-ray beam exposure

exposure field recognition

a graphical representation of the collected exposure values extracted from the receptor

histogram

how does a histogram work

collects raw data from the collimated area by marking the minimum and maximum signals

what color is the Smin

white

what color is the Smax

black

what is the x axis (horizontal)

receptor exposure

what is the Y axis

number of pixels in each shade of gray

computer counting how many times a gray shows up

sampling frequency

low kVps/low energy

wider histogram

high kVp/high energy

narrow histogram

most common

When the body doesn’t cover the entire area

requires the bone or raw radiation

(right side)

must identify Smax

foot

type 1

simplest form

entire anatomy covers the collimated area

no spike of raw radiation or tail

example is anatomy

type 2

used with a prosthetic or barium

excludes outlier area form the minimal signal (left side)

bone becomes the highest attenuator

type 3

what system uses the most recent 50 histograms

neural histogram

occurs when the type of histogram analysis used is mismatched to the shape of the actual histogram, or when an unexpected shape is acquired

histogram analysis processing errors

what are the results of a histogram analysis processing errors

image that is too light, too dark, with excessive contrast or excessive gray scale (mathematical errors)

portion of the image that contains data useful for digital processing and for calculating an accurate EI

volume of interest (VOI)

plotting the output “densities” (inverse of brightness) in the final processed image against the input exposure that they were generated from

__is manipulated by changing the steepness of the characteristic curve

contrast

the steeper the curve the ___ the contrast

higher (exposure increases, darkness of the pixel goes up)

software that allows images to have uniformity density and contrast, regardless of the amount of exposure

automatic rescaling

what are the steps of automatic rescaling

1. brightness values are assigned algebraic labels

2. pre-set LUT defines range of grays

3. match the Q range to the S range(re-mapping)

what are the limits on what the computer can do with a data set from an image

can assign new numbers to pixel counts

cannot change the pixel counts within the bings

what is important to know about automatic rescaling

has the power to align image brightness, but can only align contrast partially (aligns the low, high, and average values)

what is on the main menu options for the study data screen

patient ID, demographic, info on the exam, and submit button to PACS

what is on the image review screen

displays acquired image

image refinement options

what is the only means for determining whether a correct technique was used for the original exposure

exposure indicators