The document describes the major components and systems of a computed tomography (CT) scanner. It discusses three main systems: the imaging system, computer system, and image display/recording/storage system. The imaging system includes components like the x-ray tube, generator, collimator, filter, and detector that work together to produce x-rays and detect the attenuated radiation passing through the patient. The computer system receives the digital data and performs image reconstruction. The display system shows the reconstructed images and allows storage and recording. Key components discussed in more detail include the gantry assembly, detectors, and computer processing architecture.

1. ComputedTomography
Components

2. Three Major Systems
 Imaging System
 Computer System
 Image Display/Recording/Storage
System
 Each system in a separate
room

3. Major Components
 Scanner room
– Imaging system
1. gantry assembly
2. patient table
 Computer/Electronics Room
– Power
– Computer
– Generator
 Operator’s Area
– Display / recording / storage
– Computer

4. Imaging System
Propose:
1. To Produce x-ray
2. Shapes & filters (hardens) beam
3.Detect (measure) radiation passing
through patient
4. Convert transmitted photons
– Provides digital intensity data to computer

5. Imaging System
Components:
X-ray Beam
slice thickness, restricts beam
Protect Patient, Uniform beam-Detector
• X-ray tube
• Generator
• Collimator
• Filter
• Detector capture photon, convert to elect.signal
• Detector electronics (DAS) convert to digital

6. Gantry Assembly
 All previous components in
Gantry Assembly
 Moving Frame, Tilt, Gantry aperture
 Rotational components including slip
ring , positioning laser lights,

7. Gantry: Components
• X-ray tube
– high heat capacity
– modern tubes very large & heavy
– external cooling (oil heat exchanger)
– high speed rotation of the anode
– Heat units: heat capacity of 3.5 to 5 million
heat units (MHU)
– focal spot size of an x-ray tube is determined
by the size of the filament and cathode which
is determined by the manufacturer

8. Gantry: Components
• Generator, inside gantry
– supplies power to x-ray tube
• filament
• high voltage
– Different power 30-60Kilowatts
– Allowing range of exposure techniques:
80,100,120,130,and 140kV and
30,50,65,100,125,150,175, and 200,mA

9. Gantry: Components
• Collimators
– Tube/Source collimators: restricts beam to
slice of interest
– Pre-patient collimators: maintain the width of
the beam as it travels toward the patient
– Post-patient/Pre-detector collimators: below
patient and above detector proper beam
width at detector and reduce no. of
scattered photons at detector

10. Gantry: Components
• Filter
– protects patient from low-energy photons
– provides a beam closer to mono-energetic
– provides a more uniform beam (hardening)
• Mathematical filtration: bone/tissue algorithms
(recons. Process)
• Inherent tube filtration
• Filters made of aluminum or Teflon; to shape
beam-low energy photons and scatter

11. Gantry Components
• Detector = image receptor
• beam travels through patient and
attenuates by the anatomical structures it
passes through
• Job: collect attenuated photon energy
and convert it to electrical signal, which
will then be converted to a digital signal
for computer reconstruction

12. Detectors
• Crystal or ionizing gas
• When struck by x-ray photon , produces light or electrical
energy
• Two types : scintillation or solid state and xenon gas
detectors
• Scintillation detectors- uses a crystal that fluoresces
when struck by x-ray photon which produces light energy
– A photodiode, attached to scintillation portion, transforms light
energy into electrical or analog energy
– Strength of the detector signal is proportional to number of
attenuated photons that are successfully converted to light
energy and then to an electrical signal

13. A Note on Detectors
• Detector: single element of detector array,
produces electrical/light signal as a response to
x-rays
• Detector array: total number of detectors that a
CT system utilizes for collecting attenuated
information
• A Ray: path that an x-ray beam travels from
tube to a single detector
• Detector reads each ray and measures resultant
beam attenuation

14. Cont.
• Ray Sum: attenuation measurement of
each ray
• Projection (view): a complete set of ray
sums
– It takes many projections to createa
computed tomography image

15. Gantry Components
• Detector electronics, data
acquisition system (DAS)
– Receives weak signal form detector
– includes A-D converter
– Amplification
• provides digital information to
reconstruction computer

16. Gantry Requirements
• Patient size
• size of room
• Patient aperture
from 50-85cm
• Tilt range +/-30°

17. Patient Couch
Strong, safe, and hygienic, made of
radiolucent material
1.Couch top: carbon fiber composite, low
absorption
2.Pedestal: mechanical and electrical
components

18. Patient Couch
• Vertical travel
– minimum height for stretcher transfer
• Horizontal travel
– reduces need for re-positioning patient
– accuracy

19. Patient Couch Requirements
• Radiolucent
• Easy to clean
• Weight limits: 450lb
• Total travel: 180cm
• Accuracy: +/- 0.25mm
• Speed: 25mm/sec

20. Computer System
• Receives digital data from DAS
• Reconstructs cross-sectional image
• Image display, manipulation, & processing
– windowing
– enhancement
– zoom
– quantitative measurements
– multi-planar & 3D reconstruction

21. Computer System Components
• Input / output
devices
– Detectors
– Printer
• Central processing
units (CPU’s)
• Array Processor
– Reconstruction
Hardware
 Interfaces to other
computers
• Remote service
• RIS
• Archive
• Web browser
 Communications hardware
 Software
• enables above hardware
operation
• image manipulation
• scanning control

22. Computer System
• Processing architecture
• Hardware
• Software

23. Processing
Architecture
Capable of Multi-processing
– Scanning, reconstructing, archiving
Three Types:
1. Pipeline processing architecture
– various reconstruction steps may be
performed by separate processors
– Very fast image reconstruction, after
scanning image can be viewed
– Overlapping moving data into pipe

24. Processing Architecture
(cont.)
2. Parallel processing architecture
– 3 multi-task computers coupled
– More than one CPU to execute program
– Coordination, dividing program instructions
– separate scan, display, & file processors
3. Distributed processing architecture
– many independent processors
– each controls specific function
– each runs a different activity

25. CT Software Functions
• Operator console
– Allows operator to
communicate with
computer &
scanner
– keyboard
– touch screen
– mouse / trackball
• Control of scanner
– Gantry tilt
– scout / axial
– field of view
– x-ray technique
– slices
• how many
• thickness
• overlap

26. CT Software Functions
• Control of imaging
– selection of pre-stored image protocols
– Selection of reconstruction algorithm
• Operating System
– Control hardware of computer
– often UNIX
• multiuser
• multitasking

27. Image Display, Record, Storage
Summary:
• Display output image
• Provide permanent hard-copy for
– radiologist interpretation
– referring physician
– archival
• Facilitate storage / retrieval of digital data

28. Image Display
• Display
– CRT or flat panel
• images in gray shade
• non-image data in color or
• often hi-resolution
• Can display 4-on-1 or zoomed image at
full resolution
• Display processor provides
– display functions
– image manipulation

29. Image Storage
• Storage:
• 512x512x2 bytes (16bits) deep
• Requires 0.5MB storage
• 1 Examination= 50 images, 25MB
• 50/day = 1.25GB

30. Image Size
• 512 X 512 image = 262144
pixels
• 262144 pixels X 2 bytes / pixel =
524288 bytes per image ~ 512
KB ~ 0.5 MB

31. High Capacity Image Storage
• Magnetic disk
• Magnetic tape
• Digital videotape
• Optical disks
• Optical Tape
• Capacity
• Access Speed
• Rewritable?
• Size / space
• $$
Types Considerations

32. CT Hard Copy on Laser Printer
• Requirements for hard copy
–broad gray-scale contrast
resolution
–high spatial resolution
• Two types :
• Solid state and gas lasers

33. Laser Printing
• Unexposed film will move to exposure
region, film exposed by scanning line by
line with laser
• Producing a latent image

34. CT Console
• Keyboard
– Alphanumeric,
special function
keys, trackball,
windowing controls
• Display
– CRT
– Flat panel
– Touch panel

35. CT Console Allows Operator to
Control
• Gantry tilt
• scanning parameters
– Slice thickness
– Spacing
– Technique
• image manipulation
– multiplanar reformatting
– 3D
– zoom / pan

36. Control
Functions
• Archiving
• Voice instruction to patient
• Visual instructions to patient
• Filming protocols
– Window / level (for contrast)
– Format (12 on 1 for example)

37. Options and Accessories
Hardware:
• Archival systems
• Independent workstations
– Physicians
– 3D
• Printing
– Laser
– Multi-format

38. CT Options
• Software:
• Bone mineral analysis
• Dynamic scan
– rapid sequential scans of singleslice
• Multiplanar reformatting
• 3D image reconstruction
• Regional cerebral blood flow analysis
• CT Angiography
• Dental CT (surgery planning, implants)
• Networking

39. Accessories
• Support – immobilization
• Pads, wedges, head rests, straps,
mattress, knee support pad

40. CT Room Layout
Scanning Room:
• Gantry, Patient Couch
• Room for
– Resuscitation team
– Emergency equipment
– Stretchers
• Medical Gasses
• Shielding

41. CT Room Layout
Equipment room/Computer
– Host computer and computing equipment
• Control room
– Control console, film recording equipment

42. Purchasing
Specifications
• List of Items
– Major components
– Optional equipment
• Major technical features
– should be measurable

43. CT Specifications Who’s
Involved?
• Radiologist
• Technologist
• Physicist
• Biomedical Engineer
• IT
• Engineering Management (new)

44. Technical Specifications
• X-ray
generator
parameters
– operational parameters
• maximum kVp
• kW rating
• X-ray tube
– heat capacity
– cooling rates
• Detector
efficiency
• Reconstruction
time

45. CT Specifications
• Gantry
– aperture size
– tilt range
– laser positioning aids
– controls
• Couch
– strength / weight limits
– movement characteristics
• Speed
• Limits

46. CT Specifications Operator’s
Console
• Display, keyboard,
mouse, touch panel
characteristics
• Software design
– Choice box of available
options vs. manual typing
• Film recording &
archival considerations

47. CT Specifications
• Physician’s console & other
workstations
– functions available
– speed
– Simultaneity
• Computer
– storage requirements
– CPU
– networking

48. CT Specifications
• Interfaces
• PACS hooks & DICOM (digital imaging and
communication in medicine ) compatibility
– Worklist management
• Pulling patient demographics from RIS (
radiology information system )
– Image storage
• Transfer of images to archive / PACS

49. Computer Software CT
Specifications
• image reconstruction options
– FOV
– filters
• display options
– Annotation ( syntactic metadata)
• analysis options
– regions of interest

50. CT Specifications
• Hardcopy devices &
interface
– laser printer
• Quality control
equipment
– phantoms
– software
• Remote Diagnostics

51. CT Specifications
• Acceptance Testing
– Who performs
– What tests done
• Technology Changes
– “Latest model available at
time of delivery”
• Service
– Warranty
– Binding service contract
prices

52. Room Requirements
• Scanner Room
• Console Area
• Computer Room
• Design

53. CT Specifications Training
• For whom?
– Technologists
– How many?
• Where?
– Vendor site
– On-site
– Local
• What’s included
– Registration
– Books
– Travel expenses