Chapter 30

Physicists use the designation "Q ____ values" to indicated finalized "for presentation" pixel values after gradation processing and all other postprocessing operations are complete

"p"

List two aspects of image acquisition in which flaws can occur:

1) field uniformity; 2) electronic gain and response offsets; 3) variable scintillator thickness; 4) light guide variations; 5) pixel drop-out

A reference histogram that never changes is called an ___________ histogram

A priori

In CR phosphor plates and indirect-capture DR detector, different portions of the phosphor layers have slightly greater ___________ efficiency and produce more light than other areas

Absorption

Because they use electronic receptors, DR systems undergo more pre-display processes than those required in ___________

CR

Although the computer can align the average, high and low brightness values of the histogram, it cannot alter the pixel ___________ in each bin

Count

All data outside of the two graph points Smin and Smax must be _____________ from the calculations used to produce the final image

Eliminated (removed)

Histogram analysis failure is less common with DR systems because they include only the ___________ pixels or dexels in the image data base, whereas CR systems scan the entire plate

Exposed

This roughly rescales the ___________ __________ of the image

Gray scale

The full range of acquired image data is used, ranging from S _______ to S ____________

Min; max

Partitioned ____________ recognition software is used to scan across the receptor plate and determine the number and orientation of views, a process also called _____________

Pattern

After corrections have been made for data acquisition, additional operations targeted at refinement of the image, whether made by the computer or by a radiographer, are properly classified as ____________-processing

Post-

All corrections that are made to the "raw" digital image data due to flaws in image acquisition fall under the term __________-processing

Pre

At the console, selecting _______ algorithm assigns the type of histogram analysis to be used.

Procedure

The range of S values from incoming histogram must match the number of ________ values in the permanent LUT

Q

Rescaling is simply a process of algebraically "_____________" incoming data

Re-labeling

The "bins" of data from the acquired image to be used for rescaling are designated as _______ values

S

For both "solid column" barium procedures and mammograms, a histogram analysis algorithm must be used that seeks for both __________ and ____________ points

SMIN; SMAX

A kernel may be defined as a ___________ that is passed over the original image matrix, executing a mathematical function on it

Submatrix

To accentuate particular anatomy, a particular target range of densities from the image can be selected to operate on. This range is defined as the __________ of interest, (VOI)

Values of interest

Most histograms are presented on a simple scale of brightness from ________________ to ____________, as read from left to right

White; black (light; dark)

The S-average point is the average density or pixel value within the ____________ and is used to calculate the exposure indicator

anatomy

To correct for pixel drop-out, kernels can be use to sum and ________________ the values from pixels surrounding each dead pixel and fill this "dead" space by interpolation

average

When the final displayed image is reconstructed, final values from each "bin" (or ______ in the modified histogram) are then assigned to all pixels from the matrix that held those original values

bar

All rescaling and other processing operations are performed on ____________ (computer files) holding a simple pixel count for each density value in the image

bins

Flat-field uniformity corrections even out the __________ across the area of the image field

brightness

Compiling the histogram is a matter of counting the number of pixels holding each:

brightness level

The acquired image histogram can attain a bizarre, unexpected shape from the image data when multiple errors _________, or when very ___________ exposure conditions exist

combine; extreme

All acquired histograms for that view are ____________ with an "ideal" reference histogram for each projection

compared

Dark noise includes background exposure to a CR plate and _________ ____________ in a DR detector system

dark current

In DR systems, _________ dexels can result from TFT failure or switching transistor malfunction

dead

The computer must also distinguish darker anatomical structures from the "background density" in the image field. This process is called exposure ___________ recognition

field

All digital images have some non-uniformity due to electronic and optical _________ in the receptor system and processor

flaws

An averaged ___________ __________ curve is usually included in the displayed histogram for the acquired image

gray scale

Consistency in CR also suffers from variations in the light _____________ that steer the light from the phosphor plate to the photomultiplier tube

guides

When the "body" portion of the gray-scale curve is steep, __________ image contrast is indicated

high

Thus, the __________ and ________ points of the S and Q ranges can be made to match

high; low

The "Q values" in a permanent look-up table represent the "ideal" ___________ for each particular anatomical procedure.

histogram

To analyze the histogram for landmarks, the computer scans ____________ from both the right and left ends of the histogram

inward

Type 3 histogram analysis allows for large boluses of positive contrast agents, shielding, or appliances to be included in the projection. It anticipates a third lobe, a "spike" to the ______________ in the acquired histogram

left

Before any processing occurs, the computer ___________ the locations of every pixel value by its matrix designation

logs

The histogram for a typical extremity consists of two lobes, the "tail" spike, and the __________ lobe

main

In this way, a ______ is maintained of where each pixel value belongs throughout histogram processing

map

A reference histogram that evolves by averaging it with the previous 50 procedures is called a _________ histogram

neutral

The type of histogram analysis used must match the shape and the ______________ of lobes in the actual acquired histogram

number

Flat field uniformity is simple to test by making a low exposure to the image receptor without any ____________ in the field

object

Re-mapping means that regardless of the specific input values (S values), the _________ values (Q values) are always the same

output

Two types of noise that must be eliminated from the data set of the acquired image before it is analyzed include densities ____________ collimated fields, and pitch black ____________ densities

outside; background

For these reasons, rescaling can align image brightness perfectly, but can only align image gray scale _____________

partially

The term rescaling of the image refers to the ____________ of the brightness and gray scale of the image so that it appears like a "normal" or conventional radiograph

re-mapping

Depending on the degree to which incoming pixel values are ____________ up or down by digitization, they can be made to fit a pre-set range of S values

rounded

Entire __________ or columns of pixels can also drop out

rows

Individual detector elements (dexels) are manufactured with slightly less or slightly greater ____________ to the x-rays or light. These differences and differences in electronic amplification must also be corrected

sensitivity

Histogram analysis errors can occur from several causes. One is when the acquired histogram attains a bizarre, unexpected ____________

shape

Type 2 histogram analysis is essential for projections of large body parts, such as the abdomen, which may leave no "background density" to work with. It operates on the assumption that there will be no _______________ in the histogram shape

tail spike

A ____________ algorithm is a histogram analysis algorithm that begins storing pixel values only when a certain minimum number of pixels holding these values is reached

threshold

If the wrong ___________ of histogram analysis is applied, analysis errors will occur

type

Digital processing errors can be ___________ to the original radiographic technique used

unrelated

Rescaling operations affect each pixel throughout the image which holds a particular initial value, regardless of _________ it is within the image matrix

where

The range of the Q scale is far beyond the discernment of the human eye, so this allows for ____________ the image up and down

windowing