Week 12 - Post Processing Flashcards
-referred to as multiplanar reconstruction, image reformatting, image reformation
-computer program that can create coronal, sagittal and paraxial images from stack of continuous transverse axial scans
Multiplanar reformation
T/F
Most images are acquired in an axial format, head and extremities can be imaged in coronal
*transverse plane
True
T/F
The plane an image is acquired in depends on the patient positioning, not the way the gantry turns
True
Plane that passes through the body from anterior to posterior and divides the body into left and right
Sagittal
A plane that passes through the body from right to left, dividing the region into anterior and posterior sections
Coronal
T/F
An irregular(linear, curved), or oblique view can be reconstructed from a stack of contiguous transverse images
True
What are some advantages of reformatted images?
-enables visualization of specific structures in relation to surrounding structures
-determines extent of lesions or fracture
-helps localize lesions, bond fragments, foreign bodies
What is a disadvantage of reformatted images?
Loss of image detail
What are the 4 major steps of 3D imaging?
- Data acquisition
- Creation of 3D space
- Processing for 3D image display
- 3D image display
Tools such as windowing are computer programs that provide the observer-diagnostician with additional information to facilitate diagnosis
Visualization tools
*range from basic to advanced, have been implemented on graphic processing units (GPU)
What is the most used post processing technique?
Windowing
-allow the user to render various 3D images from the axial dataset
-3D rendering includes: SSD, VR, MIP, MinIP, cinematic rendering and global illumination
3D visualization tools
-provides detailed photorealistic visualization of high density objects, including contrast enhanced blood vessels, vascularized structures, tissues, organs and bones
Cinematic rendering
*movie
*common for stroke patients
-recent 3D/4D rendering technique that uses complex lighting and shading techniques to provide a more photorealistic image of patients anatomy
Global illumination
-technique based on volume data acquisition principles
-an application of 3D imaging and has become popular in the examination of circulatory system
Ex. 4D angio, vessel tracking, skull removal, multiple target volume
CT angiography (CTA)
-4th dimension of opacity instead of time and is based on VR technology
-changes in the opacity values of various tissues enables the observer to simultaneously visualize bone, soft tissue, vascular structures
-both foreground and background structures are visible
4D angio
Why is 4D angio preferred over conventional MIP techniques?
Visualization of aortic aneurysms, renal arteries, stents, carotid bifurcation
*MIP only allows the user to render only a selected volume data and does not require segmentation techniques
*4D angio - enhanced MIP
-allows the user to produce a set of MPR images, including curved MPR images for the entire vessel
-skull removing tool facilitates the subtraction of bones of the skull from the CTA image and allows the observer to visualize detailed images of vessels and soft tissue
Vessel tracking tool
-display all types of MPR images from the axial dataset in the axial, coronal, sagittal and oblique planes
MPR tools
Offer the following in any 3D rendering mode:
Window/level adjustment, volume of interest adjustment, scan info. Display, movie creation and playback, split screen presentation, zoom, measurements
Interactive visualization tools
-allows the user to view a large set of images very quickly
Cine visualization tools
-facilitate measurements such as distances, angles, areas, means, standard deviation, min/max voxel values, density value in HU, density histogram for particular ROI, volume of 3D objects
Advanced quantitative measurement tools
-allows user to combine images from different modalities
Multimodality image fusion tools
*advanced software needed
-include Voyager and 3D Navigator
-create 3D and 4D images of tubular structures and allow user to “fly though” the images of hollow organs - CT virtual endoscopy
Virtual reality visualization tools
To successfully reformat a CT image, all images must have:
-identical DFOV
-image center (x,y coordinates)
-gantry tilt
-contiguous (no nonimaged spaces between slices)
T/F
It is imperative for exact alignment to produce a diagnostic valuable end product
True
*no motion
T/F
Image reformation uses ONLY image data, NOT RAW DATA
True
T/F
Thinner slices are better for image reformation
True
Images created along center line of tubular organs
Ex. Vascular structure, ureters
Curved planar reformation
CPR
T/F
MDCT produces volumetric scans and high quality MPRs
-no data loos with isotropic voxels (x=y=slice thickness)
True
X, Y and slice thickness are all equal
Isotropic voxel
X, Y and slice thickness are not equal
Non-isotropic voxel
*50% overlap required
Ex. 3mm slice, reconstruct every 1.5mm
Need to input slice thickness, incrementation and number of images for MPR
Manual MPR
Operator can move a box to determine best plane imaged
Real time MPR
*not important
MPRs are pre determined before acquisition and done automatically
Advantage: straight sagittal and coronal created automatically; saves time
Disadvantage: oblique planes must be done after acquisition
Scanner created MPR
-can be done on PACS
-MPR done directly on monitor
-need thinnest slices to produce quality image
Workstation created MPR
T/F
Actual images sent to PACS are thicker than acquired raw slices
True
-represents the whole scan volume in one image
-complex process
-thinner slice = better final 3D image
3D reformation/reconstruction
-shaded surface display
-voxels located on edge of structures are used to show outline
-compares intensity of each voxel in data set to a predetermined threshold CT value
*software removes any value below or above threshold
Surface rendering/SSD
3D reformat
Tubular structures
-only the voxels with the highest values are displayed
Ex. Bone, contrast filled structures
Maximum Intensity Projection
MIP
*this is the visualization tool that is most used
-only the voxels with the smallest/minimum values are displayed
Ex. Bronchial tree, airways
Minimum intensity projection
MinIP
-3D semi transparent representation of imaged structures
-all voxels contribute to image
-pixels can be assigned: colour, brightness, opacity
Volume rendering
-visualization inside lumens
-aka virtual endoscopy
-can fly though lumen
-can adjust to see inside walls from all angles
Endoluminal imaging
-to better demonstrate areas of interest by removing obscuring structures
Manual segmentation: user identifies data to be removed
ROI editing
ROI editing
-software does the segmentation
-impractical due to image complexity, types, and clinical indications
Fully automated segmentation
ROI editing
-combines manual and automatic segmentation
-user selects a point on bone, software can reflect the structure and adjacent tissue to be removed
Semiautomatic segmentation
-when voxels are not isotropic
-when slice exceeds pixel dimensions
-appearance of flight of stairs on smooth objects
Stair step artifact
