Ch 1 System Operation And Components Flashcards
Ct uses X-rays to image individuals at different
P 1
Cross sectional anatomy
Reconstructed image
Measurement of photons of xray beam in which each tissue has its own characteristic intensity
Overview of Ct system
Control panel Computer Scan controller Digital analog converter Gantry High voltage Generator Info converted into tiny electrical signals Pass through amplifier Analog signal sampled Then digitized by analog digital converter Data stored temporarily in raw data file Calculated image by array processor Image transferred to host computer
Scan controller
Responsible for timing and operation of patient table , gantry , and high voltage generator
Digital analog converter (dac)
Electronic signal converted into analog or continuous waveform
Gantry
Contains X-ray tube and detectors
High voltage generator
Generates high voltage potential between cathode and anode
1st commercial scanner
1973
First gen scanner
Type beam?
What does?
Scan time?
Pencil beam
Single detector moved 180 degrees
Tube detector moved across patient then rotated 1 degree
Scan time : 5mins
2nd gen Ct
Type beam?
What does?
Scan time?
Fan beam
Multiple detectors in straight line
Tube detector moved across patient then rotated 5 degrees
Total scan time : 20 sec per image
3rd gen Ct
Type beam? What does? Major difference? What does difference help with? Scan time?
Fan beam geometry
Detector array rotates with tube in tube/detector assembly within gantry
Detector array curved arc
Arc arrangement improves reproducibility across array and minimize artifacts
Scan time: less 1 sec per image
Scanners today mostly based off?
3rd gen scanner
Scan
Collection of anatomical information during time X-ray beam is on
4th gen scanner
Similar to 3rd gen
Tube generates X-rays in fan beam geometry , rotates about gantry same as 3rd
Difference: detectors don’t travel with tube in 4th. Circle around patient. Many more detectors
Same time: less 1 sec per image
Slip ring technology
Large rotating ring surrounds gantry aperture
Eliminates winding of high tension cables from high frequency generator
Electrical brushes
Conveys electrical power and data to components on rotating ring
Slip rings conveys scanning instructions from _______to gantry component in order preform scan
Conveys measure attenuation data from patient to computer and _______ in order facilitate and image
Host computer
Array processor
Sling ring transfers
Electrical signal
Scanning instructions
Detected signal between stationary components and rotating gantry components
Multi row detectors From? Scan time vs? Type beam? Aka?
Collect from multi slices
Faster scan without increase in slice thickness or varying pitch
Very thick X-ray beam and multiple detector arrays
Aka : mdct, msct, multi array scanners
Each parallel detector array composed hundreds scanners along arc
Single row detector
Detector array aligned in one row
Multi row detector scanner
Detectors/ why?
Equation
Multiple parallel detector arrays in order to vary the number of slices collected in single,rotation and to vary slice thickness
When thick X-ray beam is measured by multiple parallel detector array , thickness of beam \ total number detectors = desired slice thickness
Mdct beam is ____ shape?
Cone
___ detector scanners collect info from multiple anatomical slices in each rotation of the X-ray tube
Multirow detector scanner
Benefits of multi row detector scanner
Fast scans
Increased anatomical coverage
Scanner with thinner slices to improve resolution along slice direction
Electron beam Ct (ebct)
No X-ray tube
Very fast scan times: good for cardiac Ct and coronary artery imaging
Produce electron beam that streams from electron gun and which I electromechanical directed toward an army of tungsten anodes.
X-ray beam generated when electron beam strikes anode
Pet/Ct scanner
Nuclear imaging modality that involved injection of slightly radioactive pharmaceutical
Malignant tissue characterized by rapid growth and high metabolism , agent accumulation in abnormal tissue
Fusion imaging
Comparison of two imaging modality yielding coregistered images
Value in pet image resulting Ct
Associate change in metabolism with a specific structure
Attenuation correction
S
Cone beam oncology
Verifies patient positioning before radiation therapy
High quality 3D image while patient positioning in linear accelerator
Clinicians can compare images for patients treatment plan and positioning adjustment that puts tumor in direct in X-ray beam path
Operator console
Key point of interaction between technologist and imaging system
Consists of: keyboard, monitor, and mouse
Keyboard
Alphanumeric keys to type
System command for post processing
Image manipulation/ archiving
Mouse/ trackball
Graphic input device purpose of planing a scan, selecting image parameters, displaying images, selecting post processing parameters
Monitor
Provides feedback on data entry and displaying images
Host computer
Primary link between tech and other components of imaging system. Also controls storage devices
Host computer storage devices
Hard discs and removable media
Gantry contains
Ct tube
Detectors
Slip ring
High voltage generator
Patient table fed through _____ of the gantry
Aperture
Rotating frame assembly location
Located central aspect of gantry
Rotated assembly frame gantry contains
Tube, detector array, data acquisition system
Gantry tilts
+ or - 30
Gantry tilt
Tilting rotational angle of detector array and Ct tube as it moves around patient
- result: generating attenuated projection along slice plane that is encircled by the tube as it evolves around patient
Patient table movement
Controlled by software according to instructions entered by tech
Patient coordinate system
Z axis
Y axis
X axis
Z axis
Long axis of patients body( along table)
X axis
Extends patients left and right
Y axis
Extends posteriorly to anteriorly of patient
Ct tube located
In rotating frame assembly of the gantry
Electrons of X-ray charge?
Negative
Most X-ray reaction in Ct?
Bremsstahlung
Bremsstahlung radiation
Breaking radiation in which electrons Lose energy of X-ray photons
Characteristic radiation % or Ct X-rays?
10-12%
Characteristic radiation
Electron Collides with inner electron shell of target atom ejected, outer shell electron shifts positions , then X-ray photon produced . X-rays produced when fast moving electrons collide with target material and lose energy
X-ray tube two electrodes
Anode and cathode
Electron beam flow?
Cathode to anode
Cathode contains
Filament heating wires
Filament is in cup shaped _____
Cathode
Cup shaped region part cathode
Focuses electron beam to anode target material
Filament temp controlled by?
Ma selected by tech
Ma
Tube current that determines number of X-ray photons produced
Kv
Tube voltage that controls photo energy level selected by tech
Ma=_____ ampere
1/1000
Ct voltage range
90-140
Space charger compensator
Applied to tube filament which cools filament slightly as tube voltage increases in order to prevent an unwanted elevation in tube current in response to higher kv levels
X-ray photons produced at?
Anode
Target material
Tungsten
Whyntungsten target material?
High atomic number #74
Withstand heat
Melting point 3400degree c
Target located
Rotating anode
Why anode rotates
Avoid excess heat and extends life tube
Cathode of Ct tube
Contains more than one filament
Small filament - smaller area covered- determines focal spot
Focal spot
Area of target from which useful X-rays emitted
Small focal spot
Thin slices, higher resolution
Interscan delay
Minimum amount of time frame that must transpire between one scan and initiation of next
Shorter the better
Window of tube
X-ray beam exits
Filter restricts low level X-ray photons
Beam hardening
Filter out low energy rays to lessen patient dose and improve image quality
Collimation
Restricts X-rays only to selected cross section region thereby minimizing patient dose and reducing scatter
Scatter radiation
X-rays that are deflected at many angles
- degrades image
Two types collimation
-
Pre patient
Post patient
Pre patient collimating
Restricts X-ray beam to thickness of the slice in single row detector
- made of thick metal plates attached to bottom tube housing
Multi row detector pre patient collimating
Select thickness of X-ray beam which spreads over multiple detectors
- reduces dose
Slice thickness in mdct
Determined by image reconstruction
Post patient collimating
Further refines the path of X-ray photons after they pass through the patient and before they enter detectors
Two main purposes of post collimtion
Conjunction with pre patient collimator assembly to provide better definition of slice thickness ( single slice Ct)
Reduce scatter radiation to detectors
Detectors
First component of data acquisition system (das)
Measures in coming X-rays
In order X-ray photon to generate a signal
X-ray must be able to enter the chamber of the detector and be captured
X-ray collides with atom in detector material
Collision of X-ray photon and detector material must produce a measurable event( electricity or light)
Two categories :
Gas and solid state
Gas detector
Large detector array with hundreds of chambers with the array ( gas detectors)
Gas used in gas detector
Xenon
Pressure to compress gas?
Decrease vacant space and increase probability X-ray photons collide with xenon atom
Collision of X-rays gas detector
Xenon atom splits into xenon ion and an electron which migrates to detector electrode plates which detects event
Gas detector located
In stationary ring around the gantry in 4th gen
Gas chambers and collimating
Provides own post collimation
Must prevalent type detector
Solid state detector
Solid state detectors
Scitilation detectors
Solid state detector material
Solid crystalline
Solid state detector photon collision
Photon and detector atom occurs closer to surface then gas detector
Solid state detector arrangement
Multiple detector arrays , uses flash of light which is sensed by photodiode
Photodiode
Photon strikes the solid state material emits flash of light which converted into electrical pulse by
- attached to bottom of solid state material on detector
Single row detector arrays
Have single row array of detectors arranged along curved arc- opposite X-ray tube
On single row detector scanner _____ of X-ray determines final slice thickness
Collimation
Multiple parallel rows detector elements arranged along
Curved arc opposite X-ray tube
Mdct X-ray beam collimated
Thickly
Acquired slice thickness formula
Thickness of beam
_______________________
Total number of slices acquired in single rotation
How many adjacent multi row detectors in mdct
64
Thinner slices
Attenuation info for one slice can be measured by detectors in single detector array
Thicker slices
Measured by detectors in several adjacent detector arrays
Types detector arrays
Symmetric and asymmetric
Symmetric detector array
Size each detector is identical
Assymetric detector array
Detector size varies
Mdct several channels of measured attenuation info can be added together to generate
Slice thickness
Array processor
Primary location for all complex mathematical calculations involved in generation of Ct
Reconstruction of projected attenuation raw data into Ct images
Site to generate retrospective reconstruction and sometimes post process image data
Picture archiving and communication system( PACS)
Connects operator console to storage system and distribution images
- also patient list for console
Dicom- digital imaging and communications in medicine
Goal is to achieve compatibility and workflow efficiency between imaging systems in healthcare environments worldwide
Specified protocol for dicom
Tcp/ip
Network
A number of interconnected digital devices that need to share information
Devices operators consoles of digital imaging modalities , image workstations , image viewing stations, image storage devices, printers and personal computers
A network comprised of:
Server and client
Server
Archive device that stores image
Client
Image workstation which needs to access the images that are stored on a server
Hub
Receives incoming packets of data , amplifies electrical signal and then it broadcasts these packets out to all devices on the network
Includes one that originally sent packet
Network switch
Connects multiple clients to a server but individual traffic elements and selectively forwarding data to the one device that actually needs it
Bandwidth
Rate of transfer which in bits per second
File sizes denoted
MB( megabytes)
Bandwidth denoted in
Mb ( megabits)
Virtual private networks (vpn)
Allows remote authorized individuals to connect in secure fashion to server located in a location , using the routing infrastructure provided by public network
Electronic health network (ehr)
Contains and shares information from all providers involved in patient care
Electronic medical record ( emr)
Contains standard medical data gathered from a patient in a single provider office
- electronic medical records
