W8 IMAGE PROCESSING.pdf

Image processing W8 ILO’s: On completion of this section, the student should be able to know the following: 1. GRAY SCALE 2. MANIPULATIO...

Image processing W8 ILO’s: On completion of this section, the student should be able to know the following: 1. GRAY SCALE 2. MANIPULATION TECHNIQUES (WINDOWING) S. Jastaniah, J. Al-Ghamdi, A. Aref (KAU), A. Musa (KKU), K. Hassan (BMC) 4/22/2024 1  IMAGE MANIPULATION & REFORMATTING IMAGE MANIPULATION, THOSE TECHNIQUES OR PROCESSES WHICH MODIFY AN IMAGE TO ENHANCE THE VISIBILITY OF USEFUL INFORMATION WHILE SUPPRESSING NOISE. MODERN CT ALLOW MANY OPPORTUNITIES TO MANIPULATE IMAGE DATA AFTER SCANNING (POST-PROCESSING). THE TERM “RECONSTRUCTION” IS USED WHEN RAW DATA ARE MANIPULATED TO CREATE PIXELS THAT ARE THEN USED TO CREATE AN IMAGE. THE TERM “REFORMATION” IS USED WHEN IMAGE DATA ARE ASSEMBLED TO PRODUCE IMAGES IN DIFFERENT PLANES, OR TO PRODUCE 3D IMAGES.  GRAY SCALE THE IMAGE WOULD BE DISPLAYED WITH A DIFFERENT SHADE OF GRAY FOR EACH CT NUMBER. HOWEVER, ALTHOUGH THERE ARE MORE THAN 2,000 DIFFERENT HOUNSFIELD VALUES, THE MONITOR CAN DISPLAY ONLY 256 SHADES OF GRAY. EVEN MORE LIMITING, THE HUMAN EYE CAN DIFFERENTIATE ONLY A FRACTION OF THOSE SHADES-TYPICALLY FEWER THAN 40. AS A GENERAL RULE, THE HUMAN EYE CANNOT APPRECIATE CONTRAST DIFFERENCES OF LESS THAN ABOUT 10%, WHEREAS CT SCANNERS CAN EASILY DEMONSTRATE DIFFERENCES OF LESS THAN 1%.  Contrast Enhancement (Windowing): IS THE MOST COMMON PROCESSING TECHNIQUE IN CT. IT IS THE MANIPULATION OF CT IMAGE GRAY SCALE USING CT NUMBERS OF THAT IMAGES. THIS TECHNIQUE ALLOWS THE TECHNOLOGIST TO ALTER THE CONTRAST OF THE DISPLAYED IMAGE BY ADJUSTING THE WINDOW WIDTH AND WINDOW LEVEL, SO PRODUCE OPTIMUM DISPLAY OF THE DIFFERENT STRUCTURES, E.G., THE CHEST, THE ABDOMEN, BONE, ETC. 4  The Window Width (W W) and The Window level (W L): THE WINDOW WIDTH ( WW) IS THE RANGE OF THE GRAYSCALE THAT CAN BE DISPLAYED. THE CENTER OF GRAYSCALE RANGE IS REFERRED TO AS THE WINDOW LEVEL( WL). 5  EFFECTS OF WINDOWING EFFECT OF WL ON CT IMAGE: ① IT CHANGES THE OVERALL IMAGE BRIGHTNESS. EFFECT OF WW ON CT IMAGE: ① IT DEFINES IMAGE CONTRAST. ② WIDER WW DECREASES IMAGE CONTRAST AND VISE VERSA. TISSUE TYPES WITH SIMILAR DENSITIES BEST DISPLAYED IN NARROW WW,  REGION OF INTEREST ROI A DISPLAY FUNCTION AVAILABLE ON ALL SCANNERS IS THAT OF DEFINING AN AREA ON THE IMAGE. THIS AREA IS REFERRED TO AS THE REGION OF INTEREST (ROI). ROI IS MOST OFTEN CIRCULAR, BUT MAY BE ELLIPTIC, SQUARE, OR RECTANGULAR, OR MAY BE CUSTOM DRAWN BY THE OPERATOR. DEFINING THE SIZE, SHAPE, AND LOCATION OF THE ROI IS THE FIRST STEP IN MANY DISPLAY AND MEASUREMENT FUNCTION.  IMAGE MAGNIFICATION IMAGE MAGNIFICATION ONLY USES IMAGE DATA, BY SIMPLY ENLARGING THE EXISTING IMAGE WITHOUT IMPROVING RESOLUTION.  MULTIPLE IMAGE DISPLAY THIS FEATURE FUNCTION ALLOWS MORE THAN ONE IMAGE TO BE DISPLAYED IN ONE FRAME AT A TIME. Image courtesy of http://www.belizehealthcare.com/  HISTOGRAM A HISTOGRAM IS A GRAPHICAL REPRESENTATION OF FREQUENT CHANGES OF A RANGE OF CT NUMBERS WITHIN AN ROI. Romans L, Computed Tomography for Technologists: a comprehensive text, 2011, pg 39.