Radt 228 mod 5 ppt dig process & manipula

Elsevier items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc. 1

ChapterChapter 7 7

Digital Radiographic Image Processing Digital Radiographic Image Processing and Manipulationand Manipulation


ObjectivesObjectives

Describe formation of an image histogram.Describe formation of an image histogram. Discuss automatic rescaling.Discuss automatic rescaling. Compare image latitude in digital imaging with Compare image latitude in digital imaging with

film/screen radiography.film/screen radiography. List the functions of contrast enhancement List the functions of contrast enhancement

parameters.parameters. State the Nyquist theorem.State the Nyquist theorem.


ObjectivesObjectives

Describe the effects of improper algorithm Describe the effects of improper algorithm application.application.

Explain modulation transfer function.Explain modulation transfer function. Discuss the purpose and function of image Discuss the purpose and function of image

manipulation factors.manipulation factors. Describe the major factors in image management.Describe the major factors in image management.


Key TermsKey Terms

Archive queryArchive query Automatic rescalingAutomatic rescaling Contrast manipulationContrast manipulation Edge enhancementEdge enhancement High-pass filteringHigh-pass filtering HistogramHistogram

Image annotationImage annotation Image orientationImage orientation Image samplingImage sampling Image stitchingImage stitching LatitudeLatitude


Key TermsKey Terms

Look-up tableLook-up table Low-pass filteringLow-pass filtering MagnificationMagnification Manual sendManual send Modulation transfer Modulation transfer

functionfunction Nyquist theoremNyquist theorem

Patient demographicsPatient demographics ShutterShutter SmoothingSmoothing Spatial frequency Spatial frequency

resolutionresolution Window width and Window width and

window levelwindow level


Digital Radiographic Image Processing and Digital Radiographic Image Processing and ManipulationManipulation

In cassette-based and cassetteless systems, once In cassette-based and cassetteless systems, once the x-ray photons have been converted into electrical the x-ray photons have been converted into electrical signals, these signals are available for processing signals, these signals are available for processing and manipulation. and manipulation.

The reader is used only for cassette-based systems, The reader is used only for cassette-based systems, but the processing parameters and image but the processing parameters and image manipulation controls are similar for both systems.manipulation controls are similar for both systems.


PreprocessingPreprocessing

Preprocessing takes place in the computer where the Preprocessing takes place in the computer where the algorithms determine the image algorithms determine the image histogramhistogram. .

Postprocessing is done by the technologist through Postprocessing is done by the technologist through various user functions. various user functions.

Digital preprocessing methods are vendor-specific.Digital preprocessing methods are vendor-specific.


CR Reader FunctionsCR Reader Functions

The computed radiography (CR) imaging plate The computed radiography (CR) imaging plate records a wide range of x-ray exposures.records a wide range of x-ray exposures.

If the entire range of exposure were digitized, values If the entire range of exposure were digitized, values at extremely high and low ends of range would also at extremely high and low ends of range would also be digitized.be digitized.

This would result in low-density resolution.This would result in low-density resolution. To avoid this, exposure data recognition processes To avoid this, exposure data recognition processes

only the optimal density exposure range.only the optimal density exposure range.



Data recognition program searches for anatomy Data recognition program searches for anatomy recorded on the imaging plate as follows: recorded on the imaging plate as follows: • Finding collimation edgesFinding collimation edges• Eliminating scatter outside the collimationEliminating scatter outside the collimation

Failure of the system to find the collimation edges Failure of the system to find the collimation edges can result in incorrect data collection.can result in incorrect data collection.

Images may be too bright or too dark. Images may be too bright or too dark.



Data within collimation result in generation of a Data within collimation result in generation of a graphic representation called a histogram.graphic representation called a histogram.

Because information within the collimated area is Because information within the collimated area is signal used for image data, the information is the signal used for image data, the information is the source for a vendor-specific exposure data indicator. source for a vendor-specific exposure data indicator.


CR Image SamplingCR Image Sampling

Plate is scanned.Plate is scanned. Image location and orientation is determined.Image location and orientation is determined. Size of the signal is determined.Size of the signal is determined. Value is placed on each pixel.Value is placed on each pixel.



Histogram is generated that allows system to find useful Histogram is generated that allows system to find useful signal by locating the minimum (S1) and maximum (S2) signal by locating the minimum (S1) and maximum (S2) signal within the anatomic regions of interest in the signal within the anatomic regions of interest in the image. image.

Histogram identifies all densities on the imaging plate in Histogram identifies all densities on the imaging plate in the form of a graph:the form of a graph:• X-axis is related to amount of exposure.X-axis is related to amount of exposure.• Y-axis displays the number of pixels for the exposure. Y-axis displays the number of pixels for the exposure. • Graphic representation appears as a series of peaks and valleys Graphic representation appears as a series of peaks and valleys

and has a pattern that varies for each body part.and has a pattern that varies for each body part.

X axis is related to amount of exposureX axis is related to amount of exposureY axis displays the number of pixels Y axis displays the number of pixels




Low energy (kilovoltage peak) gives a wider Low energy (kilovoltage peak) gives a wider histogram. histogram.

High energy (kilovoltage peak) gives a narrow High energy (kilovoltage peak) gives a narrow histogram. histogram.

Histogram shows the distribution of pixel values for Histogram shows the distribution of pixel values for any given exposure.any given exposure.



For example:For example:• Pixels have a value of 1, 2, 3, and 4 for a specific exposure.Pixels have a value of 1, 2, 3, and 4 for a specific exposure.• Histogram shows the frequency of each of those values and Histogram shows the frequency of each of those values and

actual number of values. actual number of values. • Histogram sets the minimum (S1) and maximum (S2) Histogram sets the minimum (S1) and maximum (S2)

“useful” pixel values.“useful” pixel values.


Histogram Analysis Histogram Analysis

Analysis is complex.Analysis is complex. Shape of the histogram stays fairly constant for each Shape of the histogram stays fairly constant for each

part exposed (anatomy specific). part exposed (anatomy specific). For example:For example:

• Shape of histogram for a chest radiograph on a large adult Shape of histogram for a chest radiograph on a large adult patient looks different from a knee histogram generated from patient looks different from a knee histogram generated from a pediatric knee exam. a pediatric knee exam.


Histogram AnalysisHistogram Analysis

It is important to choose the correct anatomic region It is important to choose the correct anatomic region on the menu before exposing the patient. on the menu before exposing the patient.

Raw data used to form the histogram are compared Raw data used to form the histogram are compared with a “normal” histogram of the same body part by with a “normal” histogram of the same body part by the computer.the computer.


The Nyquist TheoremThe Nyquist Theorem

Theorem states that when sampling Theorem states that when sampling a signal, the a signal, the sampling frequency must be greater than twice the sampling frequency must be greater than twice the bandwidth of the input signal so that the bandwidth of the input signal so that the reconstruction of the original image will be nearly reconstruction of the original image will be nearly perfect. perfect.

At least twice the number of pixels needed to form At least twice the number of pixels needed to form the image must be sampled. the image must be sampled.

If too few pixels are sampled, the result is a lack of If too few pixels are sampled, the result is a lack of resolution.resolution.



The number of conversions in CR—electron to light, The number of conversions in CR—electron to light, light to digital information, digital to analog signal—light to digital information, digital to analog signal—results in loss of detail.results in loss of detail.

Some light is lost during the light-to-digital conversion Some light is lost during the light-to-digital conversion because of the spreading out of light photons.because of the spreading out of light photons.

Because there is a small distance between the Because there is a small distance between the phosphor plate surface and the photosensitive diode phosphor plate surface and the photosensitive diode of the photomultiplier, some light spreads out there of the photomultiplier, some light spreads out there as well, resulting in loss of information. as well, resulting in loss of information.



The longer the electrons are stored, the more energy The longer the electrons are stored, the more energy they lose. they lose.

When laser stimulates electrons, some lower-energy When laser stimulates electrons, some lower-energy electrons escape the active layer.electrons escape the active layer.

If enough energy was lost, some lower-energy If enough energy was lost, some lower-energy electrons are not stimulated enough to escape and electrons are not stimulated enough to escape and information is lost. information is lost.

All manufacturers suggest that imaging plates be All manufacturers suggest that imaging plates be read as soon as possible to avoid this loss.read as soon as possible to avoid this loss.



Indirect and direct radiography lose less signal to Indirect and direct radiography lose less signal to light spread than conventional radiography.light spread than conventional radiography.

The The Nyquist theoremNyquist theorem is still applied to ensure that is still applied to ensure that sufficient signal is sampled.sufficient signal is sampled.

Because sample is preprocessed by the computer Because sample is preprocessed by the computer immediately, signal loss is minimized but still occurs. immediately, signal loss is minimized but still occurs.


AliasingAliasing

Spatial frequency is greater than the Nyquist Spatial frequency is greater than the Nyquist frequency.frequency.

Sampling occurs less than twice per cycle.Sampling occurs less than twice per cycle. Information is lost.Information is lost. Fluctuating signal is produced. Fluctuating signal is produced.

AliasingAliasingOften occurs during a high frequency electrical signal (which is indicative of the dose values being collected Often occurs during a high frequency electrical signal (which is indicative of the dose values being collected from the cassette based or cassetteless system) is being sampled in the ADC (analog to digital converter). If from the cassette based or cassetteless system) is being sampled in the ADC (analog to digital converter). If not enough sampling frequency is conducted on the high frequency system then the high frequency signal (and not enough sampling frequency is conducted on the high frequency system then the high frequency signal (and image) can end up looking like a low frequency signal (image). Remember a “cycle” is from where I have the image) can end up looking like a low frequency signal (image). Remember a “cycle” is from where I have the pointer to where the pointer ends up. In the low frequency signal things are OK because there are greater than pointer to where the pointer ends up. In the low frequency signal things are OK because there are greater than two samples per cycle. But in the high frequency signal there is not enough sampling going on and this two samples per cycle. But in the high frequency signal there is not enough sampling going on and this changes the appearance of what the ADC (analog to digital converter) is going to turn that signal into. Not changes the appearance of what the ADC (analog to digital converter) is going to turn that signal into. Not enough samples per cycle.enough samples per cycle.



AliasingAliasing Wraparound image is produced.Wraparound image is produced. Image appears as two Image appears as two

superimposed images slightly superimposed images slightly out of alignment.out of alignment.

Aliasing results in a moiré effect.Aliasing results in a moiré effect. Aliasing can be problematic Aliasing can be problematic

because of the same effect because of the same effect occurring with grid errors. occurring with grid errors.

It is important that the It is important that the technologist remembers to look technologist remembers to look at both.at both.


Automatic RescalingAutomatic Rescaling

Exposure is greater than or less than what is needed Exposure is greater than or less than what is needed to produce an image.to produce an image.

Automatic rescalingAutomatic rescaling occurs to display the pixels for occurs to display the pixels for the area of interest.the area of interest.

Images are produced that have uniform density and Images are produced that have uniform density and contrast regardless of the amount of exposure.contrast regardless of the amount of exposure.


Automatic RescalingAutomatic Rescaling

Problems occur with rescaling: Problems occur with rescaling: • When too little exposure is used, resulting in quantum mottleWhen too little exposure is used, resulting in quantum mottle• When too much exposure is used, resulting in loss of When too much exposure is used, resulting in loss of

contrast and loss of distinct edges because of increased contrast and loss of distinct edges because of increased scatter productionscatter production

Rescaling is no substitute for appropriate technical Rescaling is no substitute for appropriate technical factors.factors.

Danger exists of using higher than necessary Danger exists of using higher than necessary milliampere-second values to avoid quantum mottle.milliampere-second values to avoid quantum mottle.


Look-Up TableLook-Up Table

The The look-up tablelook-up table (LUT) is a reference histogram. (LUT) is a reference histogram. LUT is used as a cross-reference to transform the LUT is used as a cross-reference to transform the

raw information.raw information. LUT is used to correct values.LUT is used to correct values. LUT has a mapping function:LUT has a mapping function:

• All pixels are changed to a new gray value.All pixels are changed to a new gray value. Image will have appropriate appearance in brightness Image will have appropriate appearance in brightness

and contrast. and contrast. LUT is provided for every anatomic part.LUT is provided for every anatomic part.


Look-Up TableLook-Up Table LUT can be graphed as follows:LUT can be graphed as follows:

• Plotting the original values ranging from 0 to 255 on the Plotting the original values ranging from 0 to 255 on the horizontal axis horizontal axis

• Plotting new values, also ranging from 0 to 255 on the Plotting new values, also ranging from 0 to 255 on the vertical axisvertical axis

Contrast can be increased or decreased by changing Contrast can be increased or decreased by changing the slope of this graph.the slope of this graph.

Brightness (density) can be increased or decreased Brightness (density) can be increased or decreased by moving the line up or down the y-axis. by moving the line up or down the y-axis.

LUTLUT

Look Up Table (LUT)Look Up Table (LUT) Each anatomic area has a LUTEach anatomic area has a LUT Used to adjust contrast and densityUsed to adjust contrast and density Other terms that may be used for this from Other terms that may be used for this from

various vendors (don’t need to memorize various vendors (don’t need to memorize them, just tellin’ you)them, just tellin’ you) Contrast rescalingContrast rescaling Contrast processingContrast processing Gradation processingGradation processing Tone scalingTone scaling

LOOK UP TABLE (LUT)LOOK UP TABLE (LUT)

Linear LUT

Black Shirt

Facial Tones

Black Saturation

White Saturation

* No Detail in Black Areas* High Contrast* Only Detail in White Areas can be seen

* No Detail in White Areas* Low Contrast* Only Detail in Black Areas can be seen


LatitudeLatitude

LatitudeLatitude is the amount of error that still results in a is the amount of error that still results in a quality imagequality image. .

Histograms show a wide range of exposure because Histograms show a wide range of exposure because of automatic rescaling of the pixels.of automatic rescaling of the pixels.

Actual exposure latitude is slightly greater than that of Actual exposure latitude is slightly greater than that of screen/film exposuresscreen/film exposures..

In CR, if exposure is more than 50% below ideal In CR, if exposure is more than 50% below ideal exposure, quantum mottle results.exposure, quantum mottle results.


LatitudeLatitude

If exposure is more than 200% above ideal exposure, If exposure is more than 200% above ideal exposure, contrast loss results.contrast loss results.

Biggest difference between digital and film/screen Biggest difference between digital and film/screen radiography lies in the ability to manipulate the radiography lies in the ability to manipulate the digitized pixel values, which results in what seems digitized pixel values, which results in what seems like greater exposure latitude.like greater exposure latitude.

Proper kilovolt and milliampere-second values Proper kilovolt and milliampere-second values prevent mottle and contrast loss.prevent mottle and contrast loss.


Enhanced Visualization Image ProcessingEnhanced Visualization Image Processing

KodakKodak Takes image diagnostic quality to a new levelTakes image diagnostic quality to a new level Increases latitude while preserving contrastIncreases latitude while preserving contrast Process decreases windowing and levelingProcess decreases windowing and leveling Virtually eliminates detail loss in dense tissuesVirtually eliminates detail loss in dense tissues


Modulation Transfer FunctionModulation Transfer Function

Modulation transfer functionModulation transfer function (MTF) is the ability of (MTF) is the ability of a system to record available spatial frequencies.a system to record available spatial frequencies.

Sum of the components in a recording system cannot Sum of the components in a recording system cannot be greater than the system as a whole.be greater than the system as a whole.

When the function of any component is compromised When the function of any component is compromised because of interference, the overall quality of the because of interference, the overall quality of the system is affected. system is affected.



MTF is a way to quantify the contribution of each MTF is a way to quantify the contribution of each system component to the overall efficiency of the system component to the overall efficiency of the entire system—e.g., ratio of the image to the object.entire system—e.g., ratio of the image to the object.

A perfect system would have an MTF of 1 or 100%.A perfect system would have an MTF of 1 or 100%.



Digital detectorsDigital detectors• X-ray photon energy excites a phosphor.X-ray photon energy excites a phosphor.• Phosphor produces light.Phosphor produces light.• Spreading out of the light will always occur.Spreading out of the light will always occur.• Light spread reduces system efficiency.Light spread reduces system efficiency.• The more light spread, the lower the MTF. The more light spread, the lower the MTF.


Quality Control Workstation FunctionsQuality Control Workstation Functions

Image processing parametersImage processing parameters Contrast manipulationContrast manipulation Spatial frequency resolutionSpatial frequency resolution Spatial frequency filteringSpatial frequency filtering


Image Processing ParametersImage Processing Parameters

Digital systems have greater dynamic range than Digital systems have greater dynamic range than film/screen imaging.film/screen imaging.

Initial digital image appears linear when graphed Initial digital image appears linear when graphed because all shades of gray are visible.because all shades of gray are visible.

Digitalization gives the image a wide latitude.Digitalization gives the image a wide latitude. If all shades were left in the image, contrast would be If all shades were left in the image, contrast would be

too low.too low.


Image Processing ParametersImage Processing Parameters

To avoid this, digital systems make use of various To avoid this, digital systems make use of various contrast-enhancement parameters.contrast-enhancement parameters.

Names differ by vendor; Agfa uses MUSICA, Fuji Names differ by vendor; Agfa uses MUSICA, Fuji uses Gradation, and Kodak uses Tonescaling.uses Gradation, and Kodak uses Tonescaling.

Purpose and effects are basically the same.Purpose and effects are basically the same.


Contrast ManipulationContrast Manipulation

Contrast-enhancement parameters convert the digital input data to an image with Contrast-enhancement parameters convert the digital input data to an image with appropriate density and contrast. appropriate density and contrast.

Image contrast is controlled by using a parameter that changes the steepness of the Image contrast is controlled by using a parameter that changes the steepness of the exposure gradient. exposure gradient.

Graph on right demontrates a gradient line that is steeper and therefore higher in contrast. Graph on right demontrates a gradient line that is steeper and therefore higher in contrast. Jumps from black to white more quickly.Jumps from black to white more quickly.

exposure


Contrast ManipulationContrast Manipulation

Density can be varied at the toe and shoulder of the Density can be varied at the toe and shoulder of the gradient (to is gradient tip area near the bottom of the gradient (to is gradient tip area near the bottom of the gradient line), removing the extremely low and gradient line), removing the extremely low and extremely high density values using a different extremely high density values using a different parameter (shoulder is region at top of the gradient parameter (shoulder is region at top of the gradient line)line)

Another parameter allows density to remain Another parameter allows density to remain unchanged while contrast is varied. These unchanged while contrast is varied. These parameters should be used to enhance the image parameters should be used to enhance the image only; no amount of adjustment takes the place of only; no amount of adjustment takes the place of proper technical factor selection.proper technical factor selection.


Workstation Screen Showing Contrast Workstation Screen Showing Contrast Manipulation ChoicesManipulation Choices


Spatial Frequency ResolutionSpatial Frequency Resolution

Sharpness control is referred to as Sharpness control is referred to as spatial frequency spatial frequency processing.processing.

Sharpness is controlled in film/screen by various Sharpness is controlled in film/screen by various factors such as focal spot size, screen and/or film factors such as focal spot size, screen and/or film speed, and object image distance. speed, and object image distance.

Digitized images can be further controlled for Digitized images can be further controlled for sharpness.sharpness.


Spatial Frequency ResolutionSpatial Frequency Resolution

Controls are available for the following:Controls are available for the following:• Structure to be enhancedStructure to be enhanced• Degree of enhancement for each density to reduce image Degree of enhancement for each density to reduce image

graininessgraininess• How much How much edge enhancementedge enhancement is applied is applied

If improper algorithms are applied, image formation is If improper algorithms are applied, image formation is affected. affected.

It is possible to degrade image information if It is possible to degrade image information if algorithms are improperly applied.algorithms are improperly applied.


Spatial Frequency FilteringSpatial Frequency Filtering

Edge enhancementEdge enhancement SmoothingSmoothing


Edge EnhancementEdge Enhancement

When the signal is obtained, averaging of the signal When the signal is obtained, averaging of the signal occurs to shorten processing time and storage.occurs to shorten processing time and storage.

The more pixels involved in the averaging, the The more pixels involved in the averaging, the smoother the image appears.smoother the image appears.

Signal strength of one pixel is averaged with the Signal strength of one pixel is averaged with the strength of adjacent pixels or neighborhood pixels.strength of adjacent pixels or neighborhood pixels.



Edge enhancement occurs when fewer pixels in the Edge enhancement occurs when fewer pixels in the neighborhood are included in the signal average.neighborhood are included in the signal average.

The smaller the neighborhood, the greater the The smaller the neighborhood, the greater the enhancement.enhancement.

When frequencies of areas of interest are known, When frequencies of areas of interest are known, they can be amplified and other frequencies can be they can be amplified and other frequencies can be suppressed.suppressed.



• Amplification, also known as Amplification, also known as high-pass filteringhigh-pass filtering, results in , results in an increase of contrast and edge enhancement.an increase of contrast and edge enhancement.

• Suppression of frequencies, also known as masking, can Suppression of frequencies, also known as masking, can result in loss of small details.result in loss of small details.

• This technique is useful for enhancing large structures such This technique is useful for enhancing large structures such as organs and soft tissues but can be noisy. as organs and soft tissues but can be noisy.

standard image edge enhancement


SmoothingSmoothing

Smoothing is another type of spatial frequency Smoothing is another type of spatial frequency filtering.filtering.

Smoothing is also known as Smoothing is also known as low-pass filteringlow-pass filtering.. Smoothing results from averaging of the frequency of Smoothing results from averaging of the frequency of

each pixel with surrounding pixel values to remove each pixel with surrounding pixel values to remove high-frequency noise.high-frequency noise.

Result is a reduction of noise and contrast.Result is a reduction of noise and contrast. Low-pass filtering is useful for viewing small Low-pass filtering is useful for viewing small

structures such as fine bone tissues.structures such as fine bone tissues.


Basic Functions of theBasic Functions of theProcessing SystemProcessing System

Image manipulationImage manipulation Image managementImage management


Image ManipulationImage Manipulation

Window and levelWindow and level Background removal or Background removal or shuttershutter Image orientationImage orientation Image stitchingImage stitching Image annotationImage annotation MagnificationMagnification


Window and LevelWindow and Level

Window and level are the most common controls for brightness Window and level are the most common controls for brightness and contrast. One sets window level (range of white to black we and contrast. One sets window level (range of white to black we want to look at) for the type of anatomy one is imaging. Then want to look at) for the type of anatomy one is imaging. Then from there either squish down the grays in that range (narrow from there either squish down the grays in that range (narrow window width) or open up more grays that we are not yet seeing window width) or open up more grays that we are not yet seeing in the range (wide window width).in the range (wide window width).

Window level controls how light or dark the image isWindow level controls how light or dark the image is Window width controls the ratio of black to white, or contrast.Window width controls the ratio of black to white, or contrast. User is able to manipulate quickly through use of the mouse.User is able to manipulate quickly through use of the mouse.

Here is a slide from a website that shows Here is a slide from a website that shows you window width and window level.you window width and window level.


http://www.slideshare.net/narikr/ct-windowsetting


Window and LevelWindow and Level

One direction, vertical or horizontal, controls One direction, vertical or horizontal, controls brightness, and the other direction, contrast. brightness, and the other direction, contrast.

To control density and contrast further, contrast To control density and contrast further, contrast enhancement parameters are used.enhancement parameters are used.


Background Removal or ShutterBackground Removal or Shutter

Unexposed borders around the collimation edges Unexposed borders around the collimation edges allow excess light to enter the eye.allow excess light to enter the eye.

Effect is known as veil glare.Effect is known as veil glare. Glare causes oversensitization of a chemical within Glare causes oversensitization of a chemical within

the eye called rhodopsin.the eye called rhodopsin. This results in temporary white light blindness.This results in temporary white light blindness.



Eye recovers quickly enough so that viewer Eye recovers quickly enough so that viewer recognizes only that the light is very bright.recognizes only that the light is very bright.

Glare is a great distraction that interferes with image Glare is a great distraction that interferes with image reception by the eye.reception by the eye.

In film/screen radiography, black cardboard glare In film/screen radiography, black cardboard glare masks or special automatic collimation view boxes masks or special automatic collimation view boxes were used to lessen the effects of veil glare, but no were used to lessen the effects of veil glare, but no techniques were entirely successful or convenient.techniques were entirely successful or convenient.



In CR, automatic shuttering is used to blacken out the In CR, automatic shuttering is used to blacken out the white collimation borders.white collimation borders.

This eliminates veil glare.This eliminates veil glare. Shuttering is a viewing technique only.Shuttering is a viewing technique only. Shuttering should never be used to mask poor Shuttering should never be used to mask poor

collimation practices.collimation practices.



Removal of the white unexposed borders results in Removal of the white unexposed borders results in an overall smaller number of pixels.an overall smaller number of pixels.

This reduces the amount of information to be stored.This reduces the amount of information to be stored.


Image OrientationImage Orientation

Image reader scans and reads the image from the Image reader scans and reads the image from the leading edge of the imaging plate to the opposite leading edge of the imaging plate to the opposite end.end.

Image is displayed exactly as it was read. Image is displayed exactly as it was read. Different vendors mark the cassettes in different Different vendors mark the cassettes in different

ways. ways. Cassette must be oriented so that the image is Cassette must be oriented so that the image is

processed to display as expected.processed to display as expected.


Image OrientationImage Orientation

Fuji uses a tape-type orientation marker.Fuji uses a tape-type orientation marker. Kodak uses a sticker.Kodak uses a sticker. Some exams require unusual orientation of the Some exams require unusual orientation of the

cassette.cassette. Reader must be informed of the orientation of the Reader must be informed of the orientation of the

anatomy with respect to the reader.anatomy with respect to the reader. In digital radiography, the position of the part should In digital radiography, the position of the part should

correspond with the marked top and sides of the correspond with the marked top and sides of the imaging plate.imaging plate.


Image StitchingImage Stitching

Stitching is used for anatomy or areas of interest too Stitching is used for anatomy or areas of interest too large to fit on one cassette.large to fit on one cassette.

Multiple images can be “stitched” together.Multiple images can be “stitched” together. Sometimes, special cassette holders are used and Sometimes, special cassette holders are used and

positioned vertically, corresponding to foot to hip or positioned vertically, corresponding to foot to hip or entire spine radiography.entire spine radiography.


Image StitchingImage Stitching

Images are processed in computer programs that Images are processed in computer programs that nearly seamlessly join the anatomy.nearly seamlessly join the anatomy.

Computer displays one single image.Computer displays one single image. Process eliminates the need for large (36-inch) Process eliminates the need for large (36-inch)

cassettes previously used in film/screen radiography.cassettes previously used in film/screen radiography.


Image AnnotationImage Annotation

Information other than standard identification must be Information other than standard identification must be added to the image.added to the image.

In screen/film radiography, additional information is In screen/film radiography, additional information is marked by the following:marked by the following:• Time and date stickersTime and date stickers• Grease pencilsGrease pencils• Permanent markers Permanent markers


Image AnnotationImage Annotation Annotation function allows Annotation function allows

selection of preset terms and/or selection of preset terms and/or manual text input.manual text input.

Annotation can be useful when Annotation can be useful when such additional information is such additional information is necessary.necessary.

Annotations overlay the image as Annotations overlay the image as bitmap images.bitmap images.

Annotations may not transfer to Annotations may not transfer to picture archival and picture archival and communication systemcommunication system (PACS). (PACS).

Input of annotation for Input of annotation for identification of the patient’s left identification of the patient’s left or right side should never be or right side should never be used as a substitute for used as a substitute for technologist’s anatomy markers.technologist’s anatomy markers.


MagnificationMagnification

Two basic types of magnification techniques are Two basic types of magnification techniques are standard with digital systems:standard with digital systems:• One type functions as a magnifying glass:One type functions as a magnifying glass:

• A box is placed over a small segment of anatomy on the main A box is placed over a small segment of anatomy on the main image.image.

• Box shows a magnified version of the underlying anatomy.Box shows a magnified version of the underlying anatomy.

• The size of the magnified area and the amount of magnification The size of the magnified area and the amount of magnification can be made larger or smaller.can be made larger or smaller.


MagnificationMagnification

• Other technique is “zoom.” Other technique is “zoom.” • Zoom allows magnification of the entire image.Zoom allows magnification of the entire image.• Image can be enlarged enough that only parts of it are Image can be enlarged enough that only parts of it are

visible on the screen.visible on the screen.• Those parts can be seen through mouse navigation.Those parts can be seen through mouse navigation.


Image ManagementImage Management

Patient demographicsPatient demographics input input Manual sendManual send Archive queryArchive query


Patient Demographics InputPatient Demographics Input

Proper identification of the patient is even more Proper identification of the patient is even more critical.critical.

Retrieval can be nearly impossible if image is not Retrieval can be nearly impossible if image is not properly and accurately identified.properly and accurately identified.



Demographic information about the patient includes Demographic information about the patient includes the following:the following:• NameName• Health care facility Health care facility • Patient identification numberPatient identification number• Date of birthDate of birth• Exam dateExam date• Other pertinent informationOther pertinent information• Input or linked via barcode label scans, before the start of Input or linked via barcode label scans, before the start of

the exam and before the processing phasethe exam and before the processing phase



Occasionally, errors are made and demographic Occasionally, errors are made and demographic information must be altered.information must be altered.

If technologist performing the exam is absolutely positive If technologist performing the exam is absolutely positive that image is of the correct patient, then demographic that image is of the correct patient, then demographic information can be altered at the processing stage.information can be altered at the processing stage.

This function should be tracked and changes should be This function should be tracked and changes should be linked to the technologist altering the information to linked to the technologist altering the information to ensure accuracy and accountability.ensure accuracy and accountability.



Problems occur if the patient name is entered Problems occur if the patient name is entered differently from visit to visit or exam to exam.differently from visit to visit or exam to exam.

For example:For example:• Patient’s name is Jane A. Doe and is entered that way.Patient’s name is Jane A. Doe and is entered that way.• Name must be entered that way for every other exam.Name must be entered that way for every other exam.• If name is entered as Jane Doe, then system will save it as a If name is entered as Jane Doe, then system will save it as a

different patient.different patient.• Merging of files can be difficult.Merging of files can be difficult.



Problems:Problems:• Several versions of the name are given.Several versions of the name are given.• Suppose the patient gives a middle name on one visit but Suppose the patient gives a middle name on one visit but

has multiple exams under his or her first name.has multiple exams under his or her first name.• Retrieval of previous files will be difficult.Retrieval of previous files will be difficult.• The right images must be placed in the correct data files.The right images must be placed in the correct data files.


Manual SendManual Send

Because the quality control workstation is networked Because the quality control workstation is networked to the PACS, it also has the capability to send images to the PACS, it also has the capability to send images to local network workstations.to local network workstations.

The manual send function allows the quality control The manual send function allows the quality control technologist to select one or more local computers to technologist to select one or more local computers to receive images.receive images.


Archive QueryArchive Query

PACS archive can be queried for historical images.PACS archive can be queried for historical images. Function allows retrieval of images from the PAC Function allows retrieval of images from the PAC

system based on the following:system based on the following:• Date of examDate of exam• Patient name or numberPatient name or number• Exam numberExam number• Pathologic conditionPathologic condition• Anatomic areaAnatomic area


Archive QueryArchive Query

Example:Example:• Technologist could query PACS to retrieve all chest Technologist could query PACS to retrieve all chest

radiographs for a particular date or range of dates.radiographs for a particular date or range of dates.• Technologist could query retrieval of all of a patient’s Technologist could query retrieval of all of a patient’s

images.images.• Multiple combinations of query fields are possible:Multiple combinations of query fields are possible:

• Can generate general retrievalCan generate general retrieval

• Specific recovery of imagesSpecific recovery of images


SummarySummary

Recognition of exposure data involves processing Recognition of exposure data involves processing only the optimal density exposure range and only the optimal density exposure range and generates a graphic representation or histogram of generates a graphic representation or histogram of the optimal densities.the optimal densities.

The plate is scanned, and the image location and The plate is scanned, and the image location and orientation are determined. A value is place on each orientation are determined. A value is place on each pixel, and the histogram is generated displaying the pixel, and the histogram is generated displaying the minimum and maximum diagnostic signal.minimum and maximum diagnostic signal.


SummarySummary

The histogram is anatomic region specific and The histogram is anatomic region specific and remains fairly constant from patient to patient.remains fairly constant from patient to patient.

Automatic rescaling allows pixel display for the area Automatic rescaling allows pixel display for the area of interest, regardless of the amount of exposure of interest, regardless of the amount of exposure unless the exposure is too low or too high. In those unless the exposure is too low or too high. In those cases, quantum mottle or contrast loss occurs.cases, quantum mottle or contrast loss occurs.


SummarySummary

There is no substitute for proper kilovoltage peak and There is no substitute for proper kilovoltage peak and milliampere-second settings. Images cannot be milliampere-second settings. Images cannot be created from nothing; that is, insufficient photons, created from nothing; that is, insufficient photons, insufficient penetration, or overpenetration will result insufficient penetration, or overpenetration will result in loss of diagnostic information that cannot be in loss of diagnostic information that cannot be manufactured by manipulation of the image manufactured by manipulation of the image parameters.parameters.


SummarySummary

Exposure latitude is slightly greater with digital Exposure latitude is slightly greater with digital imaging than that of film/screen imaging because of imaging than that of film/screen imaging because of the wide range of exposures recorded with digital the wide range of exposures recorded with digital systems.systems.

Contrast-enhancement parameters allow Contrast-enhancement parameters allow enhancement of the image by controlling the enhancement of the image by controlling the steepness of the exposure gradient, density variance, steepness of the exposure gradient, density variance, and contrast amount.and contrast amount.


SummarySummary

Spatial frequency resolution is controlled by focal Spatial frequency resolution is controlled by focal spot, object image distance, and computer spot, object image distance, and computer algorithms.algorithms.

The Nyquist theorem is applied to digital images to The Nyquist theorem is applied to digital images to ensure that sufficient signal sampling occurs so that ensure that sufficient signal sampling occurs so that maximum resolution is achieved.maximum resolution is achieved.

MTF refers to the contribution of all system MTF refers to the contribution of all system components to total resolution. The closer the MTF components to total resolution. The closer the MTF value is to 1, the better the resolution.value is to 1, the better the resolution.


SummarySummary

Edge enhancement is accomplished by limiting the Edge enhancement is accomplished by limiting the number of pixels in a neighborhood of the matrix. number of pixels in a neighborhood of the matrix. Known area of interest frequencies can be amplified Known area of interest frequencies can be amplified or high-pass filtered to increase contrast and edge or high-pass filtered to increase contrast and edge enhancement. enhancement.

Suppression of frequencies of lesser importance, Suppression of frequencies of lesser importance, known as masking, can cause small detail loss.known as masking, can cause small detail loss.


SummarySummary

Low-pass filtering or smoothing is the result of pixel Low-pass filtering or smoothing is the result of pixel averaging to remove high-frequency noise. Contrast averaging to remove high-frequency noise. Contrast and noise are decreased, allowing small structures to and noise are decreased, allowing small structures to be seen.be seen.

Window and level parameters control pixel brightness Window and level parameters control pixel brightness and contrast.and contrast.


SummarySummary

Shuttering is a process that removes or replaces the Shuttering is a process that removes or replaces the background in order to block distracting light background in order to block distracting light surrounding a digital image. This does not take the surrounding a digital image. This does not take the place of proper collimation and can be removed to place of proper collimation and can be removed to show proper collimation.show proper collimation.

Digital imaging cassettes are marked for orientation Digital imaging cassettes are marked for orientation to the top and right sides. This ensures that images to the top and right sides. This ensures that images are displayed correctly.are displayed correctly.


SummarySummary

Image stitching is a computer program process that Image stitching is a computer program process that allows multiple images to be joined when the allows multiple images to be joined when the anatomy is too large for one exposure. The result is a anatomy is too large for one exposure. The result is a nearly seamless, single image.nearly seamless, single image.

Magnification techniques are available with digital Magnification techniques are available with digital systems that allow small area enlargement or whole systems that allow small area enlargement or whole image enlargement.image enlargement.


SummarySummary

Proper patient demographic input is the responsibility Proper patient demographic input is the responsibility of the technologist performing the exam. Any of the technologist performing the exam. Any alterations of patient demographics should be alterations of patient demographics should be avoided unless absolute identification is possible.avoided unless absolute identification is possible.

The manual send function allows images to be sent The manual send function allows images to be sent to one or more networked computers.to one or more networked computers.


SummarySummary

Historical study of patient exams can be Historical study of patient exams can be accomplished through the archive query function. accomplished through the archive query function. Retrieval of radiographic studies can be specific as to Retrieval of radiographic studies can be specific as to patient name, date, and exam or broad such as date patient name, date, and exam or broad such as date ranges and combinations of anatomic areas.ranges and combinations of anatomic areas.

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