Maulik R. ShahB. E. (Inst & Control Engg.)M. S. (Biomed Engg., USA)PGDHA (Apollo Hospital)
Consultant Biomedical EngineerMedical Equipment PlannerHospital Project Consultant
Mobile : 9824019971Email : [email protected]
www.atozforhospital.com
Basic & Conceptual Information
aboutComputed Tomography.
Equipment Arrangement
Radiography v/s
Tomography
Tomo = image // to long axis of the body CT = image is transverse to the body
Basic C T Principles
• Computed Tomography has the x-ray tube move across the so the image is called a transverse image or one perpendicular to the long axis of the body.
Computed Tomography Development
• Computed tomography has gone through five major design advancements since 1970
• Each development improved both scan time and resolution or image quality.
• Scan time have been reduced from 5 minutes to 50 ms.
• First scanner used a very tightly collimated pencil beam.
Generations
• First Generation Scanners– Translation/Rotation– Tube produced a finely collimated beam or pencil
beam– 1 to 3 detectors were placed opposite the tube for
radiation detection– 4.5 minutes to gather enough information for one
slice– Tube was only able to rotate 180 degrees
First Generation
• 1971• Pencil Thin Beam of Radiation• Translate and Rotate
– X-ray source and detector fixed relative position
– One degree of rotation possible
• Scan Time (Single Image)– 5 min
• 128 x 128 images
Patient
X-ray tube
Detector
First Generation CT Scanner
• Pencil Beam• Translate-Rotate Design• 180 one degree images
or translations.• One or two detectors.• 5 minutes scan time
Second Generation
• Fan-shaped x-ray beam• 30 or more detectors• 20 seconds per slice or 10 minutes for a 40
slice exam• 180 degree rotation• Long data reconstruction time
Second Generation
• 1974• X-rays
– Multiple Pencil– Fan Shaped 3 - 26 degrees
• Still Translate and Rotate– X-ray source and detector still fixed
relative position– Rotation increased from one to three
degrees• Scan time (Single Image)
– 3.5 min– Eventually 5.3 sec
X-ray tube
Detectors
Second Generation CT Scanner
• Translate-Rotate• Fan beam collimation so
there is more scatter radiation.
• 5 to 30 detectors• 10 degrees /translation
18 per scan.• 30 second scan times• Faster scan time
Third Generation
• Fan-shaped x-ray beam• 960 detectors opposite the x-ray tube• Complete 360 degree rotation Rotate/Rotate
movement • One rotation = one slice• Second data acquisition could be made as the
tube and detectors move in the opposite direction.
• Time reduced to 1 sec per slice
3rd generation configuration
Third Generation
• 1977• X-ray
– Fan Shaped– 21 - 45 degrees
• Rotation Only– Array of Detectors
• Scan Time (Single Image)– 4.8 sec– Eventually reduced to 2.5
seconds
Detectors
X-ray tube
Third Generation CT Scanner
• Rotate-Rotate• Fan shaped beam of 30
to 60° for full patient coverage.
• Constant Source to detector distance due to curvilinear detector array.
Third Generation CT Scanner
• If one detector fails, a ring artifact appears.
• 1 second scan times• Superior reconstruction
and resolution.
Fourth Generation
• Developed in 1980’s • Fixed ring of as many as 4800 detectors,
completely surrounding the patient, Rotate only movement
• Rotating x-ray tube provides short bursts of radiation
• Detectors collect the remnant radiation to reconstruct into an image
• 1 minute for multiple slices
• 4th generation configuration
Fourth Generation
• 1980• X-ray
– Wide Fan– 48 - 120 degrees
• Rotation Only– Full Ring of Detectors
• Scan Time (Single Image)– 5 Sec– Eventually reduced to ~1 sec
X-ray tube
Ring of Detectors
Fourth Generation CT Scanner
• The tube rotates around a stationary ring of detectors.
• Fan beam• Variable slice thickness
with pre and post patient collimation.
Fourth Generation CT Scanner
• As many as 8000 detectors.
• 1 second scan time.• Auto-detector
calibration so no ring artifact.
• High radiation dose compared to earlier scanners.
Fifth Generation CT Scanner
• This is the latest generation of CT.
• Allows for continuous rotation of the tube for spiral CT.
• 5th Generation also includes two novel designs:
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