Components of CT Scan

Ever seen this giant machine before?

CT Scan Components  and Functions

CT imaging system is made up of two main components located within the simulator which are :

1) CT Scanner
2) Laser System

Scanner Gantry

• The gantry includes the x-ray tube, the detector array, the high-voltage generator, the patient support couch, and the mechanical support for each.
•  The scanner acquire the image data that will be constructed by the virtual  simulation application into  3D virtual model of the patient.

A)    X-ray Tube

•  The x-ray tube use in multislice helical CT imaging have special requirements. The x-ray tube  can be energized up to 60s continuously.
•  Some x-ray tube operate at relatively low tube current, however  for  many, the instantaneous power capacity must be high.

B)     Scanner Bore

•  The traditional 70 cm scanner aperture with 50 cm  maximum field of view is too limiting for many radiotherapy technique. Therefore, the manufacturer  now produce ‘large bore’ versions providing apertures up to 85 cm which enable most therapy patient to be scanned in an optional position without gantry restriction.
• However, the use of wide-bore scanner will results in low contrast resolution and will increase image noise compared standard scanner.

C)     High-speed Rotor

• High-speed rotors are used in most for the best heat dissipation. Experience has shown that x-ray tube failure is a principal cause of CT imaging system malfunction and is the principal limitation on sequential imaging frequency.

D)    Focal Spot Size

•  CT imaging systems designed for high spatial resolution imaging incorporate x-ray tubes with a small focal spot.

E)     Detector Array

•  Multislice helical CT imaging systems have multiple detectors in an array up to tens of thousands. Previously, gas-filled detectors were used, but now, all are scintillation, solid state detectors.
• Scintillation detectors have high detection efficiency. Approximately 90% of the x-rays incident on the detectors are absorbed.

F)      Scanner Couch

•  A flat, stable couch is essential for radiotherapy  planning.
• Usually made up of carbon fibre which can be be adapted to fit any scanner cradle.
•  The couch must be level and orthogonal in its movement through the scanner aperture with maximum deflection of 2mm along its range.

Figure of basic components of CT Scanner

Laser System

 There are 3 types of lasers used in the CT Scan which are :

•  Internal  laser
• Wall-mounted laser
• Overhead saggital laser 

When lasers are position at zero setting, their intersection point is coincident with the center of the scan plane.

 A) Internal laser

• All scanners contain an internal laser to identify the scan plane.
• This internal laser is mounted at the scanner bore of the CT scan machine.
• This type of  laser use to mark the patient during the simulation process as well as treatment process.
• Other than that, it is also used during the QA test to determine the alignment of the laser with the center of the water phantom.

B) Wall-mounted Laser

• These types of laser usually situated at right and left of the room .
• These laser is used to mark a reference within the image data from which beam isocenter coordinate are defined.
• Other than that, it is also used to aligned the patient during  simulation and treatment process as well as aligned the couch.
• If non-moving laser is provided, these are mounted at a set height in relation to the scan aperture, requiring vertical movement to be affected  through adjustment of couch height.

C) Overhead Saggital Laser

• These laser also have the same function as wall-mounted laser which is used to mark (on the patient) coordinates defined during simulation and that may represent isocenter, field corners or markers.
• It is projecting at the same fixed distance  as lateral laser bot orthogonal to the scan plane.
• These lasers are always capable  of lateral movement because the scanner couch may not.

Treatment Couch for CT Scanner in Diagnostic Imaging

Treatment Couch for CT Scanner in Radiotherapy

Flash CT (open) rotating at full speed! 0.28sec!