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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

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CT

Seeram:

Components of a CT Scanner


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Major Components

  • Scanner room

    • Imaging system

    • Generator (?)

  • Electronics Room

    • Power

    • Computer (?)

    • Generator (?)

  • Operator’s Area

    • Display / recording / storage

    • Computer (?)


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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


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Gantry Provides Structural Framework for

  • collimators

  • filters

  • Detectors / electronics


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Gantry Size Must Accommodate

  • patients

  • size of room

  • Truck transport to hospital

The gantry is pre-assembled at the factory


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Gantry Size Must Accommodate

  • Transport within hospital

    • hallways

    • doors

    • elevators

      • Typical weight: 3500 lb.


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Special Clinical Gantry Concerns

  • Patient aperture

  • Tilt range

  • Cooling of

    • electrical components

    • x-ray tube


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Patient Couch

  • Vertical travel

    • minimum height for stretcher transfer

  • Horizontal travel

    • reduces need for re-positioning patient

    • accuracy


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Patient Couch

  • Weight capacity

    • Strength

      • cantilevered

    • Rigidity


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Patient Couch Requirements

  • Safe for patients

  • Easy to clean

  • Radiolucency

  • Speed

  • Pretty?

    • Siemens offerscolors


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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


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Imaging System Components

  • X-ray tube

  • Generator

    • supplies power to x-ray tube

      • filament

      • high voltage

  • Collimators

    • restricts beam to slice of interest


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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


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Computer System Components

  • Interfaces to other computers

    • Remote service

    • RIS

    • Archive

    • Web browser

  • Communications hardware

  • Software

    • enables above hardware operation

    • image manipulation

    • scanning control

  • Input / output devices

    • Detectors

    • Printer

  • Central processing units (CPU’s)

  • Array Processor

    • Reconstruction Hardware


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Computer System

  • Receives digital data from DAS

  • Reconstructs cross-sectional image

  • Image display, manipulation, & processing

    • windowing

    • enhancement

    • zoom

    • quantitative measurements

    • multi-planar & 3D reconstruction


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Image Display, Record, Storage

  • Display output image

  • Provide permanent hard-copy for

    • radiologist interpretation

    • referring physician

    • archival

  • Facilitate storage / retrieval of digital data


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Computer & Image Processing

  • Hardware

    • Special processing architecture

  • Software


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Processing Architecture

  • Multi-processing capability

    • scanning

    • reconstructing

    • archiving

  • Pipeline processing architecture

    • various reconstruction steps may be performed by separate processors

  • Parallel processing architecture

    • separate scan, display, & file processors


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Processing Architecture (cont.)

  • Distributed processing architecture

    • many independent processors

    • each controls specific function


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CT Software Functions

  • Control of scanner

    • Gantry tilt

    • scout / axial

    • field of view

    • x-ray technique

    • slices

      • how many

      • thickness

      • overlap

  • Operator console

    • Allows operator to communicate with computer & scanner

    • keyboard

    • touch screen

    • mouse / trackball


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CT Software Functions

  • Control of imaging

    • selection of pre-stored image protocols

    • Selection of reconstruction algorithm

  • Operating System

    • often UNIX

      • multiuser

      • multitasking

    • controls hardware


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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


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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


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Image Size

  • 512 X 512 image = 262144 pixels

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


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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


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High Capacity Image Storage

Types

Considerations

  • Magnetic disk

  • Magnetic tape

  • Digital videotape

  • Optical disks

  • Optical Tape

  • Capacity

  • Access Speed

  • Rewritable?

  • Size / space

  • Longevity

  • On line?

  • $$$


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CT Hard Copy on Laser Printer

  • Stringent quality requirements (images often used for interpretation)

    • broad gray-scale contrast resolution

    • high spatial resolution

  • No film processor required


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CT Hard Copy on Laser Printer

  • Requires special film

    • Film’s spectral sensitivity must match laser

  • Laser types

    • solid state

    • gas (He-Ne)


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Laser Printing

  • Film exposed by scanning line by line with laser


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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


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CT Console

  • Keyboard

  • Mouse

  • Display

    • CRT

    • Flat panel

    • Touch panel


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CT Console Allows Operator to Control

  • Gantry tilt

  • scanning parameters

    • Slice thickness

    • Spacing

    • Technique

  • image manipulation

    • multiplanar reformatting

    • 3D

    • zoom / pan


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CT Available Automatic Control Functions

  • Archiving

  • Voice instruction to patient

  • Visual instructions to patient

  • Filming protocols

    • Window / level

    • Format (12 on 1 for example)


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Optional PurchasesCT Hardware

  • Archival systems

  • Independent workstations

    • Physicians

    • 3D

  • Printing

    • Laser

    • Multi-format


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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


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CT Room Layout

  • Gantry

  • Couch

  • Room for

    • Resuscitation team

    • Emergency equipment

    • Stretchers

  • Medical Gasses

  • Shielding


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CT Room Layout

  • Equipment room

    • not always necessary as scanners become smaller

  • Control room

  • Film recording

    • may be combined with control room


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Purchasing CT;Specifications

  • List of Items

    • Major components

    • Optional equipment

  • Major technical features

    • should be measurable


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CT SpecificationsWho’s Involved?

  • Radiologist

  • Technologist

  • Physicist

  • Administrators


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Technical Specifications

  • X-ray generator parameters

    • operational parameters

      • maximum kVp

      • kW rating

  • Detector efficiency

  • Reconstruction time

  • Throughput

  • X-ray tube

    • heat capacity

    • cooling rates


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CT Specifications

  • Gantry

    • aperture size

    • tilt range

    • laser positioning aids

    • controls

  • Couch

    • strength / weight limits

    • movement characteristics

      • Speed

      • Limits


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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


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CT Specifications

  • Physician’s console & other workstations

    • functions available

    • speed

    • Simultaneity

  • Computer

    • storage requirements

    • CPU

    • networking


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CT Specifications

  • Interfaces

  • PACS hooks & DICOM compatibility

    • Worklist management

      • Pulling patient demographics from RIS

    • Image storage

      • Transfer of images to archive / PACS


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Computer SoftwareCT Specifications

  • image reconstruction options

    • FOV

    • filters

  • display options

    • annotation

  • analysis options

    • regions of interest


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CT Specifications

  • Hardcopy devices & interface

    • laser printer

  • Quality control equipment

    • phantoms

    • software

  • Remote Diagnostics


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CT Specifications

  • Acceptance Testing

    • Who performs

    • What tests done

  • Technology Changes

    • “Latest model available at time of delivery”

  • Service

    • Warranty

    • Binding service contract prices


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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


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CT Specifications:Training

  • For whom?

    • Technologists

    • How many?

  • Where?

    • Vendor site

    • On-site

    • Local

  • What’s included

    • Registration

    • Books

    • Travel expenses


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