System Components Flashcards
-ring /donut shaped
Aperture (internal opening / center) : 70-90cm
Can be tilted forward & backward
Has a laser light for positioning
Control panel on sides (can also be in control console)
Contains : embedded microphone and speaker
Gantry
Control panel of gantry controls:
Alignment of lights
Tilt of gantry
Table movement of gantry
Gantry houses imaging components:
Slip ring s
Xrt
High voltage generator
Collimators
Detectors
Other than ct what are other machines that also have their generators inside
Portable xray
Muo: carbon fiber
Patient table or couch
Why carbon fiber
Lightweight (to not absorb or attenuate much of the xrays)
Strong and rigid
Best material
Provide comfort
2 division of xray system
Generator
CT scan xray tube
Uses 3 phase power for the efficient production of xrays
Located inside the gantry
The voltage ripple from a high frequency generator is 1%
Generator
Generator of ct before
High voltage generator
- generator was outside before
Generator of ct now and its benefits
High frequency generator
-small
-comoact
-more efficient
Problem w ct generator before
Can’t rotate normally due to wiring of cables and generator outside
Fluctuations of current after being rectified
Voltage ripple
Current in xray system
Direct current
(always in one direction)
Never in Ac cuz it can cause tube failure and no efficiency of xray production
Ac to dc
Rectified
Momentarily stores energy
Capacitor
Permits gantry to rotate continuously eliminating the need to straighten turned system cable
Use a brush-like apparatus = to provide continuous electric power
Slip ring
Component of tube enclosure of ct scan xrt
Metal instead of glass
Cuz of electrical arcing
Component fo glass enclosures
Borosilicate
Explain electrical arcing
When there’s too much heat - that damages or melts the target material - which will vaporate - as tube also rotates it will splatter around the xr and can attach to the enclosure = as cathode continues to produce electrons - electricity flow or induced current would be distracted will it go to the filament or the follow material of the target was melted ===tube arcing / tube failure
Consists of tungsten filaments positioned in a focusing cup
Cathode assembly
Muo: barium
Coil of wire
Fx: absorbs gas in a vacuum cud the presence of gas decreases efficiency of tube / xray production cuz it interfered flow of electrons
Internal getter
Appearance of Barium
Not pressured or is contaminated = WHITE
Vaccuum maintained =silver
Anode assembly consists
Disk
Rotor stud
Hub
Rotor
Bearing assembly
Small target angle around 12 deg
Anode assembly
Small focal spot = higher spatial resolution
Cuz it limits the size of the usable xray field
Anode heel effect - angulated therefore less surface exposed
Relevance of fast xray tube / high rotational anode
= heat dissipation is not concentrated on 1 area / for cooling
CT XRT uses?
Ceramic insulator
- so it would not involve the current on the cathode side
So that if you touch the xrt you won’t be electrocuted
Uses thicker (5cm) larger diameter anode disk (200mm)
Ct xrt
So that if projectile electrons Hit the focal spot the heat will be shared on the external structure (heat transfer by conduction)
Energy transfers
Conduction
Induction
Convection
3 basic designs of anode disk
All metal disk design
Braced graphite anode disk
Chemical vapor deposition
Base bodies of all metal like design
Titanium
Zirxonium
Molybdenum
Focal track layer
10% rhenium
90% tungsten
Advantage and disadvantage of all metal disk design
Adv: quick heat transfer
Disad: heavy weight (can’t rotate efficiently)
BASE BODY of Braced graphite anode disk
Majority graphite (10x higher heat capacity(ability to absorb heat) than tungsten)
FOCAL TRACK LATER of Braced graphite anode disk
Tungsten rhenium
Advantage of Braced graphite anode dism
High heat storage capacity
Faster anode cooling
BASE BODY of chemical vapor deposition graphite disk
Graphite
FOCAL TRACK of chemical vapor deposition graphite disk
TUNGSTEN - RHENIUM
can accommodate large, lightweight disks w/ large heat storage capacity
Helps reduce the radiation dose to the patient and
Improves image quality
Filtration
Purpose of filtration
Removed long wavelength (lowenergy) xrays
Shares the energy distribution across the radiation beam by using shaped filter
Controls slice thickness
Restricts xr beam to specific area
Collimator
2 types of Collimators
Prepatient Collimators
Postpatient Collimators
Determine rad dose profile and pt rad dose
Prepatient /Postpatient source Collimator
Determine sensitivity profile and improves image contrast
Higher tendency of scatter after passing thru the patient
Predetector Collimator
Lighter than peripheral cuz head is thicker
Peripheral or sides is dark cuz not the same thickness
Homogenous beam
Eliminate scatter
Bow tie filter
Capture the rad Beam from pt and convert it into electrical signals, which are subsequently converted into binary coded information
Ct detector
2 types of Detectors accdg, to material
Xenon gas detector
Solid-state crystal detector
Adv: ability to remain stable under pressure, cheaper, easier to calibrate
Disadv: xenon gas must be kept under pressure in an aluminum casing
Xenon has detector
Adv: higher absorption coefficient (100%)(xenon - 60-87%)
Disadv: sensitive to fluctuatkonin temperature & moisture
Solid-state crystal detector (scintillating detectors
Composition of solistate detector
-cadmium tungstate
Bismuth germinate
Cesium iodide
Gadolinium or yttrium
