Post on 01-Apr-2015
CS TC 22
CT principle
Scanner design
Scanner design
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CT principle
Scanner design
CS TC 22
Scanner Design
Variazioni nel design dello scanner
Generazioni
Gantry geometry
Detector
Numero dei detectors e proiezioni
Slip ring scanning
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CT principle
Scanner design
CS TC 22
Scanner – 3° generazione
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CT principle
Scanner design
CS TC 22
Cosa comporta ridurre la distanza tubo - detector ?
Cosa comporta la mancanza di questa collimazione?
A cosa serve il collimatore dalla parte del tubo ?
A cosa serve il collimatore dalla parte dei detector ?
Cosa comporta la mancanza di questa collimazione?
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CT principle
Scanner design
CS TC 22
Scatter radiation
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CT principle
Scanner design
CS TC 22
61 cm = 327 mAs61 cm = 327 mAs
63 CM = 350 mAs63 CM = 350 mAs
65 CM = 377 mAs65 CM = 377 mAs
ComponentiComponenti
57 CM = 290 mAs57 CM = 290 mAs
[ (SID1)² / (SID2)² = 57² / 63² = 0.8]
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CT principle
Scanner design
CS TC 22
Scanner Design
Variazioni nel design dello scanner
Generazioni
Gantry geometry
Detector
Numero dei detectors e proiezioni
Slip ring scanning
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CT principle
Scanner design
CS TC 22
Tipi di Detector
Xenon detector
Solid state detector
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CT principle
Scanner design
CS TC 22
Xenon detector
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CT principle
Scanner design
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Xenon detector
Si tratta di detector a gas, generalmente riempiti di un gas nobile come lo Xenon.
Consiste in un numero elevato di piccole camere a gas (500 – 700), separate da
placche di metallo che costituiscono l‘anodo e il catodo dell‘elemento.
Gli elettrodi ad alta tensione (catodi) sono collegati ad una tensione DC di 250 V.
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CT principle
Scanner design
CS TC 22
Xenon detector
Gli elettrodi di segnale (anodi) sono collegati al sistema di misura dei dati Data
Measurment System DMS o Data Acquisition System DAS e portano la corrente
misurata ai circuiti integrati.
La pressione dei detector è di circa 20 – 25 bar.
Principo dei gas detector:
X-rays ionnizza il gas Xenon e la quantità di ionizzazione determina la corrente
d‘uscita.
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CT principle
Scanner design
CS TC 22
Solid state detector
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CT principle
Scanner design
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Un detector allo stato solido consiste in scintillation crystal come il cesium iodide or
cadmium tungstate e materiale ceramico gadolinium oxysulfide.
Questo materiale converte i Raggi X in luce,e successivamente mediante un foto-
diodo in corrente.
Solid state detector
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CT principle
Scanner design
CS TC 22
Xenon vs Solid State
Xenon Single detector chambersub-divided by electrodes
Solid state Detector array made up ofindividual elements
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CT principle
Scanner design
CS TC 22
Xenon vs Solid State
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CT principle
Scanner design
CS TC 22
Scanner Design
Variazioni nel design dello scanner
Generazioni
Gantry geometry
Detector
Numero dei detectors e proiezioni
Slip ring scanning
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CT principle
Scanner design
CS TC 22
Numero dei detectors e proiezioni
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CT principle
Scanner design
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Tipico per Scanner di 3 generazione:
wLower range scanners:
400-600 detectors.
wTop range scanners:
650-900 detectors (per row).
Numero dei detectors e proiezioni
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CT principle
Scanner design
CS TC 22
Numero dei detectors e rows
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CT principle
Scanner design
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Numero dei detectors e rows
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CT principle
Scanner design
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Data Acquisition: UFC Adaptive Array Detector
Sensation 16: 24 detector rows
16 * 0.75 mm slices
16 * 1.5 mm slices
Sensation 4: 8 detector rows
z-overage: 24 mm at isocenter
Additionally: 2 * 0.6 mm for Ultra High Resolution
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CT principle
Scanner design
CS TC 22Multi-row detector systems for spiral CT
Number of detectors and rows
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CT principle
Scanner design
CS TC 22
Number of detectors and rows
Newest CT systems are equipped with a multi row detector of up to 24 rows,
which benefits the speed of the scanner.
The multi row detector allows a measurement of multiple images / revolution
and this in turn reduces the required scan time for patients. Additionally the
high speed of the measurement reduces motion artefacts and enables very
good cardio images.
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CT principle
Scanner design
CS TC 22
•Lower range scanners:
600-1000 per image.
•Top range scanners:
1100-1800 per image.
Number of projections
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CT principle
Scanner design
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Number of projections
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CT principle
Scanner design
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Increased In-Plane Resolution
Focal Spot
Detector
Flying Focal Spot: Double the Number of Samples
Scan-FOV
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CT principle
Scanner design
CS TC 22
Increased In-Plane Resolution
Focal Spot
Detector
Quarter Detector Offset: Double the Number of Samples
Scan-FOV
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CT principle
Scanner design
CS TC 22
Increased In-Plane Resolution
Focal Spot
Detector
Quarter Detector Offset: Double the Number of Samples
Scan-FOV
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CT principle
Scanner design
CS TC 22
Increased In-Plane Resolution
Focal Spot
Detector
Quarter Detector Offset: Double the Number of Samples
Scan-FOV
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CT principle
Scanner design
CS TC 22
Increased In-Plane Resolution
Il Somatom Volume Zoom CombinaFlying Focal Spot e Quarter Detector Offset
Incremento del numero di misure con fattore 4
2688 Canali di misura Effettivi
RilevatoreOgni rilevatore
ha due canali di misura
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CT principle
Scanner design
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Number of projections
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CT principle
Scanner design
CS TC 22
Scanner Design
Variazioni nel design dello scanner
Generazioni
Gantry geometry
Detector
Numero dei detectors e proiezioni
Slip ring scanning
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CT principle
Scanner design
CS TC 22
Slip Ring Scanning
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CT principle
Scanner design
CS TC 22
Slip Ring Scanning
Since 1990 the CT systems are operated with continues rotation.
This requires sliprings, to switch:
- Power to the tube (high voltage, when the generator is stationary, or low
voltage, when the generator is on the rotating gantry)
-- power to all rotating components
-- control signals between rotating and stationary gantry
--- the data to the image processor
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CT principle
Scanner design
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Advantage of slip ring scanners
•Faster conventional axial scanning (stepwise table feed)
–interscan delay governed only by time taken from
table to move to new position(~1 sec)
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CT principle
Scanner design
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Velocità di Rotazione
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CT principle
Scanner design
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Velocitàdi Rotazione
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CT principle
Scanner design
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Rotazione con cinghia
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CT principle
Scanner design
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Rotazione no belt
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CT principle
Scanner design
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Trasmissione Dati con carbon brush
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CT principle
Scanner design
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Trasmissione Dati più veloce e rumorosa
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CT principle
Scanner design
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Trasmissione Dati con Radiofrequenza
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CT principle
Scanner design
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Advantage of slip ring scanners
wCine scanning
(no table feed)
continuous series of images at one position.
“CT fluoroscopy”
new image reconstructed several times during one
rotation.
wSpiral scanning
(continuous table feed)
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CT principle
Scanner design
CS TC 22
Advantage of slip ring scanners
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CT principle
Scanner design
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