Flashcards in Ch.2 Ct Image Formation Deck (83):
Digital images are?
Numerical representations of an object that can be recognized and processed by a computer
First step generating digital image of an object?
Divide the object into a grid of small regions
Picture element that's each small region of a grid
Rows and columns allows us to ?
Associate the location of specific structure within the object being imaged with specific pixel or group of pixels
Grid of pixels
2nd step generating image
Sample the object in order to differentiate structures within the object and assign various shades of gray to the pixels representing the structure
X-ray photons that pass thru the body are measure by ______and converted into ______?
Posit e or negative whole numbe
Value of integer determined by?
Assigns specific gray level to region of Ct image from which attenuation information was detected
View of anatomical cross section from particular vantage point
Ct scanning methods
Obtained with stationary X-ray tube and patient table in motion
Why localizer scan ?
Aligns cross sectional slices with specific anatomical structures
Views used with localizer?
Length of anatomical coverage with localizer depends on?
Speed of table
Amount time X-ray is on
Ct localizer scan the anatomical structure appears? P 10
Ap localizer image used? P 10
Planning to specify perfectly transverse slices
Lateral localizer is used? P 10
Intend to angle gantry to specific oblique slices
Which ct yields the best quality image free of helical artifacts?
Conventional ct used today?
Neurological studies involving temporal bones
Cardiac calcium scoring
Conventional ct the tube rotates around the patient while the table?
Data measured at each projection placed in computer file
Single row detector
When performing a conventional scan , raw data from ____ cross sectional slice location is collected during a single rotation of the gantry?
Multi row detectors
When performing a conventional scan of multi row detector scanner , the raw data is from ______ cross sectional slice locations collected during a single rotation of the gantry
Raw data sample formula
Rows of detectors x # of detectors X projections required
X-rays beam spiral or corkscrew paths around patients body as the table advances through the gantry
Most commonly used ct today?
Several advantages of helical ct
More coverage in breath hold
No missed anatomy
Less contrast agent needed
Arbitrary slice positioning
Ideal data for post processing
Disadvantage of helicL scan?
Helical path single row detector scanner in which thickness of X-ray beam _______ the thickness of the final slice
The helical path on multi row detector scanner in which thickness of X-ray beam is ________ over four rows of detectors
Mathematical problem in helical ct that changes helical data into raw data reconstructing it into final images
Most ct aytms today use reconstruction method called ?
Filter back projection
Two steps of filtered back projection?
Applying filter to raw data and back projection
Back projection p21
Calculation used for reconstructing final images from raw data by adding together the attenuation information collected from all projections
Through back,projection _______profiles are added together p 22
Convolution p 23
Reconstruction filter is Applied to raw data during image reconstruction
Kernel p 23
Two reconstruction filters? P 23
Sharp filter p 23
Improves definition of the edges of structures but doesn't minimize grainy or speckled appearance of image
Smooth filter p 23
Minimizes grainy appearance of noise in image so that the contrast between tissues can be better distinguished but does not improve edge definition
Sharp reconstruction filter are often us for ? P 24
Musculoskeletal detail ( high contrast area)
Smooth reconstruction filters are often used for ? P 24
Low contrast areas such as abdomen and brain
If back projection was applied to raw data without convolution , what happens to tissues? P 24
Image would have blurry edges and they be more difficult to differentiate
Iterative reconstruction p 25
Cycle of correction calculations which maybe applied during image reconstruction to reduce image noise and which allows greatly reduced dose to be used without compromising image quality
Grainy appearance on image
Important clinical significance of iterative reconstruction ? P 26
Significant less radiation dose while maintaining optimal image quality
Cone beam artifact p 27
spreading of photons long patient table results in spoke or star like appearance
Cone beam reconstruction p 28
Reconstruction algorithm designed for multi row scanner to collect more than four slices in a single rotation
Back projection is used on ______row detectors and on multi row detectors that collect no more than _____slices in one rotation . Cone beam reconstruction applied to all other mdct scanners.
When ct image is reconstructed it viewed on? P 29
Raw data is obtained on raw data device on?
Retrospective reconstruction p 29
Requires raw data, which is lost once that portion of raw data storage device is overwritten
On mdct scanner, a retrospective reconstruction is common,y used to modify reconstructed ? P 30
Most Ct images are acquired in which orientation? P 31
Multiplanar reconstruction p 31
Allows Reconstruction of images in planes that would be difficult or impossible to acquire
Multiplanar reconstruction requires ____ data ? P 31
Steps of multiplanar reconstruction? P 31
1. Region interest scanned to obtain transverse slices using helical imaging
2. Raw data reconstructed using filtered back projection or cone beam reconstruction and transverse imaging viewed on operators console
3. Multiplanar reconstruction initiated
4. Stacks transverse images on top each other generate volume anatomical imaging
5. Line places across stack transverse imaging indicating location of new image
Why curved cut line allowed on multiplanar reconstruction? P 32
Enables tracing curved structure such as vessel so that structure is displayed in cross section
Contiguous p 33
Slices with no gaps
Why must images be contiguous in multiplanar reconstruction p33
No gaps in images
Which type images best used for post processing techniques? P 33
3D shaded surface display p 34
Reconstructs images of the surfaces of the anatomical structure
3d SSD program process ? P 34
Stacks transverse slices to form a volume of anatomical data which must be contiguous
Dependent of determining difference of tissues being scanned through a threshold
In 3d SSD , types of tissues are separated by ______ settings?
What is threshold value set to during 3d SSD? P 34
Equal to ct number of tissue on which we want to surface rendering
Volume rendering p 35
Incorporates information from entire image data set , rather from the surface into processed image enabling visualization of structures above and below the surface
Voxels in volume rendering p 35
Each voxel assigned opacity value as function of its density
Each pixel in volume rendering p 35
Represents the sum of the contributions of each voxel along a ray passed through image data set
Maximum intensity projection p37
Generated from transverse slices of a cta study by projecting the brightest pixels onto a plane
Angiography p 37
Used to evaluate the vessels and is acquired with helical scan and timed iodinated contrast
Most accurate mip results are obtained when ? P 38
Small volume of interest is selected
Volume of interest p 38
In mip, affect way vessels appear
Volume of interest increased? P 38
Additional anatomical structures and noise are included in the data upon which the mip algorithmn is applied - apparent vessel diameter of the mip image may decrease
Ct images are filmed or transferred to ____ or ____? P 40
Viewing station or pacs
Ct uses _____ film? P 40
Window adjustments allow,us? P 40
High resolution detail or soft tissue contrast by varying brightness and contrast settings
Most ct systems today use a _______ camera ? P 40
Laser camera expose the image displayed on monitor directly onto _____ with a laser p 40