It's all about components of computed tomography....

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