Digital image processing

use of computer enhanced x-ray imaging before they are viewed by radiologists.

pre-processing, post-procession

what are the two stages of digital image processing

raw data detector

two satge of digital imaging s work together to convert this into a clinically usable image.

pre-processing

happen immediately after exposur e and it purpose is to standardize and clean the raw image data so that the image accurately represents the anatomy being examined.

acquisition processing

other term for the pre-processsing

to clean and standardize raw image data

what is the purpose of the pre processing

exposure field recognition

Ability of a digital imaging system to identify the borders of a collimated x - ray exposure field

remove unnecessary background

why is EFR important

computed radiography

allow more than one image can be recorded on a single PSP plate

Digital radiography

allow only one exposure on each detector "plate,"

field uniformity recognition

make brightness or density even across the image

detector flaws, electronics., anode heel effect

what cause the uneven brightness

Field uniformity correction

compensates for these variations so that the background of the image appears even and consistent.

Correction dexel and mottle

the second step for digital preprocessing, the computer looks for "dead pixels,

detector element

what is dexel

dead dexel

a dexel that does not produce a signal

interpolation

works by analyzing the values of the surrounding pixels and calculating an average value to replace the missing signal.

kernel

defined as a sub-matrix that is passed over the larger image executing some mathematical function on the pixels.

mottle

a form of noise that manifests a s a grainy appearance to the image

quantum mottle and electronic mottle

two very common types of mottle

Periodic mottle

e is best corrected using during frequency processing,

quantum mottle

occurs due to the random nature of x-ray photon distribution.

electronic mottle

originates from fluctuations in electrical current within the detector and imaging electronics.

periodic mottle

results from repeating electronic patterns in the detector system.

histogram

the graph of pixel brightness vs the number of the pixel

SMIN and SMAX

which define the limits of useful data

volume of interest

Portion of an image histogram that contains data useful for digital processing and for calculating an accurate exposure indicator

histogram

a graphical representation showing how many pixels exist at each brightness level within the image.

automatic rescaling

adjust brightness automatically

quantum mottle

happens in low exposure

look-up table

tool to adjust brightness and contrast also sometimes used to reverse or invert image grayscale

Look up table

Automatic rescaling relies on a computational tool called

look-up table

essentially a pre-calculated table that converts input pixel values into output brightness levels

post-processing

image adjustment after acquisition and can be adjust automatically or manually

post-processing

the purpose is to improve image for diagnosis

gradient processing

purpose is to tailor the final image brightness and contrast according to the anatomy and predominant pathologies to be displayed,

anatomically LUT

stored by the computer for each specific type of radiographic procedure.

window level

controls the average or overall brightness of the image

Window width

controls the gray scale, (the inverse of contrast).

high contrast

what happens when WW is narrow

low contrast

what happens when WW is wide

frequent processing

allows an image to be sharpened, improving its appearance

fourier transformation

mathematical process use in frequent processsing to separate structures according to their size

low pass filtering

smoothing is also known as

smoothing

recommended to correct for moderate amounts of mottle appearing in the image.

softened

effect of smoothing on edges will appear

Edge Enhancer

when the radiologist needs to better visualize small details at the edges of bones, cartilage, or organs such as the kidneys.

High pass filtering

Edge enhancement is also known as

increase image noise

disadvantage of using edge enhancement

equalization

alters the pixel values across the image to present a more uniform image appearance

brighter

what happen to dark area when we use eqaulization

image reversal, image stitching, dual-energy subtraction, grid line suppresion

other pro-processing feature

black bone

image reversal is also known as

image reversal

invert black to white

image stiching

great invention that replaces the need for the heavy, oversized cassettes that used to be used for scoliosis series.

dual-energy subtraction

can separate the original image into a tissue only image and a bony image

grid line supression

"erase" the grid lines they cause with digital processing

automatic rescaling

Incorrect anatomic menu selection is accompanied by the .

30%

minimun plate exposure need

exposure field recognition errors

occur when the system cannot recognize the collimation borders, resulting in images that are either overexposed or underexposed.

collimation border recognition

errors may occur if the X-ray exposure field is not properly collimated, and positioned, which can be considered a histogram analysis error.

large overexpose error

caused by inappropriately high technical factors.