Transcript You Already Know Some Electronics!

CT
Seeram:
Components of a
CT Scanner
Major Components
 Scanner room
 Imaging system
 Generator (?)
 Electronics Room
 Power
 Computer (?)
 Generator (?)
 Operator’s Area
 Display / recording /
storage
 Computer (?)
Gantry Provides Structural
Framework for
 x-ray tube
 modern tubes very large & heavy
 external cooling (oil heat exchanger)
 generator / transformer (slip ring
technology)
 Extreme mechanical stability requirements
 Very tight tolerances for
 vibration
 Give / sag
Gantry Provides Structural
Framework for
 collimators
 filters
 Detectors / electronics
Gantry Size Must Accommodate
The gantry is
pre-assembled at
the factory
 patients
 size of room
 Truck transport to
hospital
Gantry Size Must Accommodate
 Transport within hospital
 hallways
 doors
 elevators

Typical weight: 3500 lb.
Special Clinical Gantry Concerns
Patient aperture
Tilt range
Cooling of
 electrical components
 x-ray tube
Patient Couch
 Vertical travel
 minimum height for stretcher transfer
 Horizontal travel
 reduces need for re-positioning patient
 accuracy
Patient Couch
 Weight capacity
 Strength

cantilevered
 Rigidity
Patient Couch Requirements
 Safe for patients
 Easy to clean
 Radiolucency
 Speed
 Pretty?
 Siemens offers
colors
Imaging System
 Produces x-rays
 Shapes & filters (hardens) beam
 collimates
 attenuates for uniformity
 May detect (measure) pre-patient beam
intensity
 Provides digital intensity data to computer
Imaging System Components
 X-ray tube
 Generator
 supplies power to x-ray tube


filament
high voltage
 Collimators
 restricts beam to slice of interest
Imaging System Components
 Filter
 protects patient from low-energy photons
 provides a beam closer to mono-energetic
 provides a more uniform beam
 Detector & electronics
 also called data acquisition system (DAS)
 includes A-D converter

provides digital information to reconstruction
computer
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
Reconstruction Computer
 Receives digital data from DAS
 Reconstructs cross-sectional image
 Image display, manipulation, & processing
 windowing
 enhancement
 zoom
 quantitative measurements
 multi-planar & 3D reconstruction
Image Display, Record, Storage
 Display output image
 Facilitate storage / retrieval of digital data
 Provide permanent hard-copy for
 referring physician (?)
Computer & Image Processing
 Hardware
 Special processing
architecture
 Software
Processing Architecture
 Multi-processing capability
 scanning
 reconstructing
 archiving
 Distributed processing
architecture
 many independent
processors
 each controls specific
function
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
CT Software Functions
 Control of imaging
 selection of pre-stored image protocols
 Selection of reconstruction algorithm
 Operating System
 often UNIX


multiuser
multitasking
 controls hardware
Image Display, Storage, &
Recording
 Display
 CRT or flat panel


images in gray shade
non-image data in color or B/W
 often hi-resolution
 Can display 4-on-1 or zoomed image at full resolution
 Display processor provides
 display functions
 image manipulation
Image Storage
 Typical CT image
 512 X 512 pixels
 8-12 bits deep

often stored as 2 bytes / pixel (16 bits / pixel)
 Multiply image size by # images
Image Size
 512 X 512 image = 262,144 pixels
 262,144 pixels X 2 bytes / pixel =
524,288 bytes per image ~ 512 KB ~
0.5 MB
Image Storage (cont.)
 Assume 0.5 Mbytes per image
 If 100 images / patient
 50 Mbytes / patient
 25 patients / day X 50 MBytes / patient =
1.25 GBytes per day
High Capacity Image Storage
Types
 Magnetic disk
 Magnetic tape
 Digital videotape
 Optical disks
 Optical Tape
Considerations
 Capacity
 Access Speed
 Rewritable?
 Size / space
 Longevity
 On line?
 $$$
CT Hard Copy on Laser Printer
 Stringent quality
requirements broad grayscale contrast resolution
 high spatial resolution
 No film processor
required
CT Hard Copy on Laser Printer
 Requires special film
 Film’s spectral sensitivity must match laser
 Laser types
 solid state
 gas (He-Ne)
Laser Printing
 Film exposed by scanning line by line with laser
Laser Printer Features
 Contains image buffer (computer
memory)
 Buffer stores images in memory until
printed
 Camera prints multiple images on
one film
 Camera can receive & buffer multiple
image sources images
simultaneously
CT Console
 Keyboard
 Mouse
 Display
 CRT
 Flat panel
 Touch panel
CT Console Allows Operator to
Control
 Gantry tilt
 scanning parameters
 Slice thickness
 Spacing
 Technique
 image manipulation
 multiplanar reformatting
 3D
 zoom / pan
CT Available Automatic
Control Functions
 Archiving
 Voice instruction to patient
 Visual instructions to patient
 Auto-film protocols (?)
 Window / level
 Format (12 on 1 for example)
Optional Purchases
CT Hardware
 Archival systems
 Independent workstations
 Physicians
 3D
 Printing
 Laser
 Multi-format
CT Options
 Bone mineral analysis
 Dynamic scan
 rapid sequential scans of single
slice
 Multiplanar reformatting
 3D image reconstruction
 Regional cerebral blood flow
analysis
 CT Angiography
 Dental CT (surgery planning,
implants)
 Networking
CT Room Layout
 Gantry
 Couch
 Room for
 Resuscitation team
 Emergency equipment
 Stretchers
 Medical Gasses
 Shielding
CT Room Layout
 Equipment room
 not always necessary as scanners become smaller
 Control room
 Film recording
 may be combined with control room
Purchasing CT;
Specifications
 List of Items
 Major components
 Optional equipment
 Major technical features
 should be measurable
CT Specifications
Who’s Involved?
 Radiologist
 Technologist
 Physicist
 Administrators
Technical Specifications
 X-ray generator parameters
 operational parameters


maximum kVp
kW rating
 X-ray
tube
• heat capacity
• cooling rates
 Detector
efficiency
 Reconstruction
time
 Throughput
CT Specifications
 Gantry
 aperture size
 tilt range
 laser positioning aids
 controls
 Couch
 strength / weight limits
 movement characteristics


Speed
Limits
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
CT Specifications
 Physician’s console & other workstations
 functions available
 speed
 Simultaneity
 Computer
 storage requirements
 CPU
 networking
CT Specifications
 Interfaces
 PACS hooks & DICOM
compatibility
 Worklist management

Pulling patient demographics
from RIS
 Image storage

Transfer of images to archive /
PACS
Computer Software
CT Specifications
 image reconstruction options
 FOV
 filters
 display options
 annotation
 analysis options
 regions of interest
CT Specifications
 Hardcopy devices & interface
 laser printer
 Quality control equipment
 phantoms
 software
 Remote Diagnostics
CT Specifications
 Acceptance Testing
 Who performs
 What tests done
 Technology Changes
 “Latest model available at time
of delivery”
 Service
 Warranty
 Binding service contract prices
Purchasing CT
 Room planning
 in consultation with equipment
vendor
 Property ownership. Who owns?
And when does ownership
transfer?
 service manuals
 diagnostic software
 operating system
 Property ownership dictates
hidden software costs & service
options
CT Specifications: Training
 For whom?
 Technologists
 How many?
 Where?
 Vendor site
 On-site
 Local
 What’s included
 Registration
 Books
 Travel expenses