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CS TC 22 CT principle Scanner design 2 CT principle Scanner design CS TC 22 Scanner Design Variazioni nel design dello scanner Generazioni Gantry geometry.

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Presentation on theme: "CS TC 22 CT principle Scanner design 2 CT principle Scanner design CS TC 22 Scanner Design Variazioni nel design dello scanner Generazioni Gantry geometry."— Presentation transcript:

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2 CS TC 22 CT principle Scanner design

3 2 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

4 3 CT principle Scanner design CS TC 22 Scanner – 3° generazione

5 4 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?

6 5 CT principle Scanner design CS TC 22 Scatter radiation

7 6 CT principle Scanner design CS TC 22 Gantry: geometria ottimizzata Componenti

8 7 CT principle Scanner design CS TC cm = 327 mAs 63 CM = 350 mAs 65 CM = 377 mAs Componenti 57 CM = 290 mAs [ (SID 1 )² / (SID 2 )² = 57² / 63² = 0.8]

9 8 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

10 9 CT principle Scanner design CS TC 22 Tipi di Detector Xenon detector Solid state detector

11 10 CT principle Scanner design CS TC 22 Xenon detector

12 11 CT principle Scanner design CS TC 22 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.

13 12 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.

14 13 CT principle Scanner design CS TC 22 Solid state detector

15 14 CT principle Scanner design CS TC 22 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

16 15 CT principle Scanner design CS TC 22 Xenon vs Solid State

17 16 CT principle Scanner design CS TC 22 Xenon vs Solid State

18 17 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

19 18 CT principle Scanner design CS TC 22 Numero dei detectors e proiezioni

20 19 CT principle Scanner design CS TC 22 Tipico per Scanner di 3 generazione: w Lower range scanners: detectors. w Top range scanners: detectors (per row). Numero dei detectors e proiezioni

21 20 CT principle Scanner design CS TC 22 Numero dei detectors e rows

22 21 CT principle Scanner design CS TC 22 Numero dei detectors e rows

23 22 CT principle Scanner design CS TC 22 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

24 23 CT principle Scanner design CS TC 22 Multi-row detector systems for spiral CT Number of detectors and rows

25 24 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.

26 25 CT principle Scanner design CS TC 22 Lower range scanners: per image. Top range scanners: per image. Number of projections

27 26 CT principle Scanner design CS TC 22 Number of projections

28 27 CT principle Scanner design CS TC 22 Increased In-Plane Resolution Focal Spot Detector Flying Focal Spot: Double the Number of Samples Scan- FOV

29 28 CT principle Scanner design CS TC 22 Increased In-Plane Resolution Focal Spot Detector Quarter Detector Offset: Double the Number of Samples Scan- FOV

30 29 CT principle Scanner design CS TC 22 Increased In-Plane Resolution Focal Spot Detector Quarter Detector Offset: Double the Number of Samples Scan- FOV

31 30 CT principle Scanner design CS TC 22 Increased In-Plane Resolution Focal Spot Detector Quarter Detector Offset: Double the Number of Samples Scan- FOV

32 31 CT principle Scanner design CS TC 22 Increased In-Plane Resolution Il Somatom Volume Zoom Combina Flying Focal Spot e Quarter Detector Offset Incremento del numero di misure con fattore Canali di misura Effettivi Rilevatore Ogni rilevatore ha due canali di misura

33 32 CT principle Scanner design CS TC 22 Number of projections

34 33 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

35 34 CT principle Scanner design CS TC 22 Slip Ring Scanning

36 35 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

37 36 CT principle Scanner design CS TC 22 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)

38 37 CT principle Scanner design CS TC 22 Velocità di Rotazione

39 38 CT principle Scanner design CS TC 22 Velocitàdi Rotazione

40 39 CT principle Scanner design CS TC 22 Rotazione con cinghia

41 40 CT principle Scanner design CS TC 22 Rotazione no belt

42 41 CT principle Scanner design CS TC 22 Trasmissione Dati con carbon brush

43 42 CT principle Scanner design CS TC 22 Trasmissione Dati più veloce e rumorosa

44 43 CT principle Scanner design CS TC 22 Trasmissione Dati con Radiofrequenza

45 44 CT principle Scanner design CS TC 22 Advantage of slip ring scanners wCine scanning (no table feed) continuous series of images at one position. w“CT fluoroscopy” new image reconstructed several times during one rotation. wSpiral scanning (continuous table feed)

46 45 CT principle Scanner design CS TC 22 Advantage of slip ring scanners

47 46 CT principle Scanner design CS TC 22


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