1. Computed Tomography Image Manipulation

2. Image Manipulation Defined
“Techniques (operations) or processes which modify an image to enhance visibility of useful information while suppressing ‘noise’ or non-useful information”
No additional or new information produced
Content of interest emphasized
Overall information content reduced

3. Windowing
Manipulation of image gray scale using image’s CT numbers

4. Window Width & Level
Contrast visible only for pixel values within selected window.
All CT #’s below/above window will be all white or all black & display no contrast. WW WL

5. Window Width & Level WL WW Window width Window level
range of CT #’s displayed
Window level
center or midpoint of CT # range
CT #’s WW WL

6. Advantage of Windowing
Possible to display & enhance contrast in selected segments of total CT # range

7. CT Image Manipulation Magnification Distance angle measurement
Region of interest (ROI) analysis
Rectangular
Circular
Values
Average CT #
Standard deviation
Area

8. Histogram Analysis # pixels with particular range of values
graph of CT # frequency
can apply to
ROI
entire image

9. Specialized CT Image Manipulation Programs
Multiplanar reconstruction
3D reconstruction
Quantitative CT
Osteo CT / bone densitometry
Xenon CT
Radiation therapy treatment planning using CT data

10. Multiplanar Reconstruction
Creates non-axial images from stack of contiguous transverse axial scans
stack contains 3 dimensional CT data
pixels identified & selected from each axial slice

11. Cuts
coronal
sagittal
paraxial
oblique

12. Coronal Reconstruction Example
Stack of
Axial Slices
Reconstructed
Slice

13. Coronal Reconstruction Example
Stack of
Axial Slices
Reconstructed
Slice

14. Sagittal Reconstruction Example
Stack of
Axial Slices
Reconstructed
Slice

15. Oblique Reconstruction Example
Stack of
Axial Slices
Reconstructed
Slice

16. CT Applications Angiography Multimodality Image Fusion PET/CT
Overlaying of images of various modalities
One anatomical (CT), one functional (Nuc med)