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1. CT INSTRUMENTATIONS S.MOHAMED ASIF

2. CT scanners are complex, with many different components involved in the process of creating an image. It consist of a scanning Gantry, x-ray generator, computer system, operator’s console, physician’s viewing console. Data are acquired when x-rays pass through a patient to strike a detector and recorded.

3. COMPONENTS OF CT

4. GANTRY Ring shaped. The range of aperture size is typically 70 to 90 cm. The degree of tilt ±15° to ±30°. It also includes a laser light. Control panels located on either side of the gantry. A microphone is embedded in the gantry.

5. CT GANTRY

6. GANTRY X-ray Tube Collimation Filtration Detector High frequency Generator Cooling System

7. X-RAY TUBE Rotating anode tube Tungsten (Z=74) - anode target material. Longer exposure > 90s Many CT tubes are designed with anode heat capacities > 1MHU. Cooling mechanism are included to reduce the heat effect. In modern CT units, the x-ray beam is collimated into a fan-shaped beam.

8. METAL CERAMIC X-RAY TUBE Glass envelope has been replaced by metal casing. it’s construction includes alloy of chromium and iron cylinder brazed to alumina ceramic (Al oxide) insulators at each end. These insulators carry the anode and cathode assemblies . Metal envelope grounded offers no chance of arcing of x-ray tube and hence increase tube life.

9. COMPARISION OF CT TUBE WITH CONVENTIONAL X-RAY TUBE CHARACTERISTIS DIAGNOSTIC X-RAY TUBE CT X-RAY TUBE TUBE Glass envelope Metal ceramic tube TYPE OF ANDODE Stationary or Rotating Rotating TARGET ANGLE 6˚ - 20˚ 12˚ FOCAL SPOT SIZE 0.3,0.6,1.2 mm 0.6 mm EXPOSURE TIME Shorter Longer HEAT UNIT CAPACITY 0.3 – 0.6 MHU 1-8 MHU

10. COLLIMATION Prepatient collimator limits the area of the patient, determines patient dose. Predetector collimator (i) restricts the X-ray beam seen by the detector array, (ii) reduces scatter and improves contrast, (iii) defines the slice thickness.

11. FILTRATION Al(2.5mm)+Cu(0.4mm)& 6mm Al X-ray passes lesser tissue at the periphery than at the centre of the body. Hence, the noise levels may vary, and it is highest at the center and lowest at the periphery. Dose is higher at the periphery than at the center.

12. SLIP RINGS Use electromechanical devices called slip rings. Slip rings use a brush like apparatus. Provides electrical power & electronic communication It allows the gantry frame to rotate continuously.

13. DETECTORS Scintillation Detectors Crystal – sodium iodide. Light->electron-> ampified by dynodes->increase no.of electron->electrical signal The scintillation crystals and PMT-early generations (phosphorescent afterglow properties of the scintillation crystals) Replaced by bismuth germanate and cesium iodide.

14. GAS-FILLED DETECTORS Zenon gas Thin tungsten plate 1.5mm. Photons->ionizes->accelerated& amplified The electric field pulls the – ve ions to the positive electrode and the + ve ions to the negative electrode. This flow of electrons is an electric current The detected energy makes up the digital signal. Disadvantage: Under pressure in aluminum casing Loss of x-ray photons in casing window

15. SOLID-STATE DETECTORS It combine a calcium tungstate, bismuth germanate and cesium iodide yttrium, or gadolinium ceramic scintillator with a photodiode. Photons->light->electrical signal

16. GENERATOR High- frequency generators are currently used. CT generators produce high kV (generally 120–140 kV) to increase the intensity of the beam, which will increase the penetrating ability of the x-ray beam and thereby reduce patient dose. In addition, a higher kV setting will help to reduce the heat load by allowing a lower mA setting. Reducing the heat load - x-ray tube will extend the life.

17. COOLING SYSTEMS Cooling mechanisms are included in the gantry. such as blowers, devices that perform oil-to-air heat exchange Cooling mechanisms are important because many components can be affected by temperature fluctuations.

18. PATIENT TABLE Patient lies on the couch and moved through the gantry aperture during the examination. Made of carbon fibres to prevent it from interfering with x-rays.

19. CONTROL CONSOLE There are 3 consoles in CT. Usually, 2 monitors are provided. The physician control console is used to manipulate the image, optimize the diagnostic information, contrast and brightness adjustments, magnification techniques, region of interest (ROI) viewing, use of on line software packages and picture archiving and communication systems (PACS) network.

20. PHILIPS INGENUITY 128 CT SCANNER

21. SPECIFICATIONS CT INGENUITY 128 NAME OF PRODUCT Multislice CT Scan 128 SLICE BRAND/ MANUFACTURER Philips

22. X-RAY TUBE & GENERATOR Anode Heat Storage Capacity 8 MHU Anode cooling rate 1,608KHU/min Large focal spot size 1.0mm x 1.0mm Small focus spot size 0.5mm x 1.0mm Tube cooling system Air cooled Generator power 80 kW KV selections 80, 100, 120 & 140kV mA Range 20 - 665 mA

23. TECHNOLOGY LOW DOSE WITH HIGHER IMAGE QUALITY Improvement in spatial resolution and or reduction at low dose (iterative reconstruction) Yes , iDose4 Generation of Reconstruction Generation 4 METAL ARTIFACT REDUCTION FOR LARGE ORTHOPEDIC IMPLANT (OMAR) Improves image quality through artifact prevention and increased spatial resolution at low dose, and reduces artifacts caused by large orthopedic implants Yes, OMAR

24. GANTRY Gantry Aperture 70 cm 360° Rotation Speeds 0.4 sec for full 360o scan Gantry controls on right and left of gantry Yes Gantry controls on front and back of gantry Yes Tilt ± 30° in 0.5° increment Gantry Cooling Method Air Cooling Laser positioning lights Yes DETECTORS Solid State CT Detector Yes, Gadolinium Oxisulfide (GOS) Number of detector rows 64

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