Digital Radiographic Image Processing and Manipulation Chapter 7

We’ve learned how images are captured….now What happens in the reader (CR) pre processing? How is the image constructed digitally? LET’S FIND OUT!!!

PRE-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

HISTOGRAM Graphical 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, Carter pg 110 and Page 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 ANATOMY SPECIFIC

histogram my-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 EXPLANATION AND RESOURCE

NYQUIST THEOREM When sampling(converting from analog to digital) a signal, the sampling frequency must be greater than the bandwidth of the input signal = /nyquist.gif&imgrefurl= c.uk/Dave/Multimedia/node149.html&h=4 20&w=529&sz=6&hl=en&start=10&um=1 &tbnid=zyDOLJNUH6mM8M:&tbnh=105&t bnw=132&prev=/images%3Fq%3Dnyquis t% = /nyquist.gif&imgrefurl= c.uk/Dave/Multimedia/node149.html&h=4 20&w=529&sz=6&hl=en&start=10&um=1 &tbnid=zyDOLJNUH6mM8M:&tbnh=105&t bnw=132&prev=/images%3Fq%3Dnyquis t%

Sample? Try this eRate-c.html eRate-c.html

WHAT DO YOU THINK THIS IS? PAGE 113 CARTER Automatic rescaling

LUT Automatic rescaling to achieve appropriate contrast on an image htm#13

LUT –HISTOGRAM OF BRIGHTNESSS LEVELS VALUES FROM IMAGE ACQUISITION PG 114 IN CARTER NOTE HOW VALUES LESS THAN 50 ARE BLACK AND THOSE HIGHER THAN 150 ARE WHITE

Lut histogram

Exposure latitude CCD’s FPIR PSP/CR systems DR (direct or indirect) High dynamic range of receptors which is the ability of the receptor to respond to exposure Example of Receptors??

MTF The 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 manipulation Changing brightness, contrast post processing. “No amount of adjustment can take the place of proper technical factor selection”

Edge 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”

Smoothing Reduction of noise and contrast. Good for visualizing fine bone tissues

Let’s discuss image manipulation Window Level Window Width Stitching

REVIEW THOSE PESKY ACRONYMS! 1. PSP 2. CRT 3. ADC 4. IP 5. CR 6. DR 7. DQE 8. 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