Digital Radiographic Digital Radiographic Image Processing and Image Processing and

ManipulationManipulationChapter 7

We’ve learned how images are We’ve learned how images are captured….nowcaptured….now

What happens in the reader (CR) pre processing?

How is the image constructed digitally?

LET’S FIND OUT!!!

PRE-PROCESSINGPRE-PROCESSING

THE READER IS TO BE INFORMED AS TO WHAT EXAM WILL BE PROCESSED.

So when you “flash” the cassette, or scan with a bar code reader or in DR, choose the patient and the examination and the views that are to be done

HISTOGRAMHISTOGRAMGraphical representation of optimal densities collected by exposure data recognition .

Exposure data recognition finds the collimated edges , disregards the scatter outside of these edges

Searches for anatomy

This area is the source of exposure data indicator

CR sampling, CR sampling, Carter pg 110 and Carter pg 110 and Page 492 BushongPage 492 Bushong

Notice the collimated area of the lungs in A and find the associated area in B on histogram and C on the response cure. Do the same for the black areas around the chest.

THE SHAPE OF THE HISTOGRAM IS THE SHAPE OF THE HISTOGRAM IS ANATOMY SPECIFICANATOMY SPECIFIC

histogramhistogramhttp://bloggingradiography.blogspot.com/2007/08/

anatomy-of-histogram.html

High energy=less frequency of the same density = narrower histogram

Low energy=more frequencies of the same density= wider histogram

The Nyquist Theorem How are signals converted from analog to digital?

THIS IS STILL THE BEST THIS IS STILL THE BEST EXPLANATION AND RESOURCEEXPLANATION AND RESOURCE

NYQUIST THEOREMNYQUIST THEOREM

When sampling(converting from analog to digital) a signal, the sampling frequency must be greater than the bandwidth of the input signal

http://images.google.com/imgres?imgurl=http://www.cs.cf.ac.uk/Dave/Multimedia/nyquist.gif&imgrefurl=http://www.cs.cf.ac.uk/Dave/Multimedia/node149.html&h=420&w=529&sz=6&hl=en&start=10&um=1&tbnid=zyDOLJNUH6mM8M:&tbnh=105&tbnw=132&prev=/images%3Fq%3Dnyquist%

Sample? Try thisSample? Try this

http://www.pcguide.com/art/soundSampleRate-c.html

WHAT DO YOU THINK THIS IS? PAGE 113 CARTER

Automatic rescaling

LUTLUTAutomatic rescaling to achieve appropriate contrast on an

image

http://www.sprawls.org/resources/DIGPROCESS/module.htm#13

LUT –HISTOGRAM OF LUT –HISTOGRAM OF BRIGHTNESSS LEVELS BRIGHTNESSS LEVELS VALUES FROM IMAGE VALUES FROM IMAGE

ACQUISITIONACQUISITIONPG 114 IN CARTER

NOTE HOW VALUES LESS THAN 50 ARE BLACK AND THOSE HIGHER THAN 150 ARE WHITE

Lut histogramLut histogram

Exposure latitudeExposure latitude

CCD’sFPIRPSP/CR systemsDR (direct or

indirect)

High dynamic range of receptors which is the ability of the receptor to respond to exposure

Example of Receptors??

MTFMTFThe ability to faithfully reproduce the image from the

object…More light in the process of capturing image, the lower the MTF. High MTF is preferred

Contrast manipulationContrast manipulationChanging brightness, contrast post processing. “No amount of adjustment can take the place of proper

technical factor selection”

Edge EnhancementEdge Enhancement

Improving visibility of small high contrast areas (ex: finger fractures)

Usually signals are averaged to shorten processing time and storage

In Edge Enhancement, less pixels are included in the average=more true in signal “size”

SmoothingSmoothingReduction of noise and contrast. Good for visualizing fine

bone tissues

Let’s discuss image manipulation

Window Level

Window Width

Stitching

REVIEW THOSE PESKY REVIEW THOSE PESKY ACRONYMS!ACRONYMS!

1. PSP2. CRT3. ADC

4. IP5. CR6. DR

7. DQE8. PMT

9. PACS

Bit-binary digit, 0 or 1.Grouped in bunches of 8 = byte

Pixel pitch

Structured needle phosphor vs Turbid phosphor

Available gray scale Bit depth=shades of gray

Measure of distance from middle of one pixel to another

Active layer structure/organized vs. random –Mosby pg 68