Part II Flashcards by Queenie Francisco

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]

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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

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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]

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2nd Generation CT Scanner [adv]

-over 1st gen: faster scanning time
-multiple pencil beam = more pt throughput = more slices

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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]

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3rd Generation CT Scanner [adv/disadv]

-adv. fast
-disadv. cannot do cardiac CT scan bc of cardiac motion

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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

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4th Generation CT Scanner [adv]

Adv.
-multiple detectors - stationary and x-ray tube rotating
-more utilized
-can do cardiac but not optimal

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5th Generation CT Scanner

-high speed CT scanning
-based on special configurations intended to facilitate fast scanning
-does not rotate
-continuous principle

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Two types of 5th Generation CT Scanner

EBCT - External Beam CT
DSR - Dynamic Spatial Reconstructor

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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

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6th Generation CT Scanner

Dual Scanner Source CT (DSCT) Scanner
-multiple x-ray rubes and detectors
-intended for moving structures like heart

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6th Generation CT Scanner [adv]

-great recorded artifact with less motion artifact
-2 x-ray used for cardiac CT

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7th Generation CT Scanner

Flat-Panel CT Scanners

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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

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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.

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Spatial R. Is expressed in: [..]

Line pairs/mm (lp/mm)

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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

MTF value : image in blank, no info

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

Scan Parameters Affecting CR [She ReImagined X-ray Size DetectorS]

1. SLICE THICKNESS 2. RECONSTRUCTION ALGORITHM 3. IMAGE DISPLAY (WINDOW WIDTH) 4. X-RAY BEAM ENERGY 5. SIZE OF PT 6. 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

1. Multi detector - continuous absorb and erase 2. Tube/gantry rotation time - faster aquisition 3. Dual-Source CT - 6th generation

Most common cause of noise in CT

Quantum noise

Primarily affects CR

Noise

Scan Parameters that influence noise

1. Matrix size 2. Slice thickness 3. Reconstruction algorithms 4. Scattered radiation and patient size