Part II Flashcards
1st Generation CT Scanner
Method: Rectilinear Pencil Beam Scanning
Acquisition Geometry: Parallel Pencil Beam Geometry
Principle: Translate-Rotate Principle
Rotation degree: 1 degree to next angular posi
Time: 4.5 - 5.5 min data acquisition
[EMI MARK I - made by Hounsfield]
1st Generation CT Scanner [disadv]
-CT techs manually move to rotate - tedious
-too long
-limited to head scanning
-not allowed for chest,abdomen
-motion artifact
2nd Generation CT Scanner
Method: Rectilinear Multiple Pencil Beam Scanning
Acquisition Geometry: Fan Beam Geometry
Principle: Translate-Rotate Principle
Rotation: 6 degrees increment
Time: 20 seconds
[utilized multiple beams]
2nd Generation CT Scanner [adv]
-over 1st gen: faster scanning time
-multiple pencil beam = more pt throughput = more slices
3rd Generation CT Scanner
Method: Continuously Rotating Fan Beam Scanning
Acquisition Geometry: Fan Beam Geometry
Principle: Continuous Principle
Rotation: Complete Rotation of Tube & Detectors
Time: 2 seconds per rotation; scan time 5 seconds or less
[utilize slip ring] [arc centric detector cells]
3rd Generation CT Scanner [adv/disadv]
-adv. fast
-disadv. cannot do cardiac CT scan bc of cardiac motion
4th Generation CT Scanner
Acquisition Geometry: a rotating fan beam within a stationary ring of detectors and a complete rotation of the x-ray tube
Principle: complete rotation - no translation
Rotation: multiple detectors - stationary and X-ray tube rotating
4th Generation CT Scanner [adv]
Adv.
-multiple detectors - stationary and x-ray tube rotating
-more utilized
-can do cardiac but not optimal
5th Generation CT Scanner
-high speed CT scanning
-based on special configurations intended to facilitate fast scanning
-does not rotate
-continuous principle
Two types of 5th Generation CT Scanner
- EBCT - External Beam CT
- DSR - Dynamic Spatial Reconstructor
EXPLAIN electron gun
ELECTRON GUN (like filament → DEFLECT electron to TARGET TUNGSTEN RING (when hit produce x-ray) → electron PROJECTED UP to patient → ABSORBED BY DETECTOR
6th Generation CT Scanner
Dual Scanner Source CT (DSCT) Scanner
-multiple x-ray rubes and detectors
-intended for moving structures like heart
6th Generation CT Scanner [adv]
-great recorded artifact with less motion artifact
-2 x-ray used for cardiac CT
7th Generation CT Scanner
Flat-Panel CT Scanners
DIFFERENTIATE the IMAGE QUALITY of CONVENTIONAL R and CT IMAGES
CONVENTIONAL R.
1. Spatial R
2. Contrast R
3. Noise
CT IMAGES
1. Spatial R.
2. Contrast R.
3. Noise
4. Linearity
5. Uniformity
Ability to image small objects that have a subject contrast
Degree of blur or ability to see difference b/w two objects that are close together
Spatial R.
Spatial R. Is expressed in: [..]
Line pairs/mm (lp/mm)
A high-contrast line that is separated by an interspace of equal width
Line pair
SR for a CT image is limited to the [..]
Pixel size
[..] and [..] powerful way to affect SR
Image reconstruction and post-processing
Scan Parameters affecting SR [Sexy Dudes Measure Right Ds]
- Section/Slice Thickness
- Display FOV
- Matrix
- Reconstruction Slice Thickness
- Detector Aperture Width
-mathematical expression for measuring resolution
-the ratio of the image to the object as a function of SF
-used to describe CT spatial res.
Modulation Transfer Function (MTF)
-determine fidelity of images
Modulation Transfer Function (MTF)
MTF value : faithfully represents the object
1
MTF value : image in blank, no info
0
MTF value : intermediate levels of fidelity
Intermediate
Fidelity with which the anatomy is represented on the radiograph
Image quality
Accuracy of actual object presented on a radiograph
Fidelity
Accuracy of actual image presented in image (there will always be magnification but should be close)
Fidelity
Collection of pixels (picture element)
Always square in CT
Matrix
3d element
Voxel
Pixel size formula
DFOV/matrix
CT PROCESS
IMAGE AQUI → IMAGE RECONSTRUCTION →DISPLAY → ARCHIVING
Ability to differentiate b/w small structures in different density within the image
Tissues with density differences of less than 0.5 % can be distinguished
CR
Scan Parameters Affecting CR [She ReImagined X-ray Size DetectorS]
- SLICE THICKNESS
- RECONSTRUCTION ALGORITHM
- IMAGE DISPLAY (WINDOW WIDTH)
- X-RAY BEAM ENERGY
- SIZE OF PT
- DETECTOR SENSITIVITY
[..] determine the slice thickness
Collimator
Better CR needs [..] collimator; Wider can cause [..]
Smaller/narrow
Scatter radiation
Removal of low energy by filter
Beam hardening [x-ray beam energy]
-importance for cardiac imaging
-the ability of CT system to freeze any motion of a scanned object
-shortest amount of time needed to acquire a complete data set
Temporal R
Factors that improve TR
- Multi detector - continuous absorb and erase
- Tube/gantry rotation time - faster aquisition
- Dual-Source CT - 6th generation
Most common cause of noise in CT
Quantum noise
Primarily affects CR
Noise
Scan Parameters that influence noise
- Matrix size
- Slice thickness
- Reconstruction algorithms
- Scattered radiation and patient size
