Mobiles and mammography Flashcards
3 reasons why a patient may need a mobile x-ray
1) too ill to come down to the department
2) May be in an isolation unit- cannot travel
3) May have equipment attached to them that cannot be transported
examples of where a mobile x-ray is necessary
- ITU/ICU/HDU
- SCBU
- Theatre
- Resus
- Cardiac care unit
name the 9 components of a mobile x-ray machine
1) Pedestal
2) Control panel; Kvp;ma;time
3) wheels
4) Adjustable arm
5) x-ray tube housing
6) Power cable
7) applicator
8) handle
9) base
what is the target-rotating anode made of?
tungsten-rhenium
what design is the tube head
‘tank head’ design
what are the two reasons for it being mounted on a pivot joint?
makes it;
flexible and manoeuvrable
What is the purpose of the telescopic arm? (3 things)
1) holds tube housing
2) carries power cable
3) allows for extendable ‘reach’
what two things does the pedestal for attachment to telescopic arm do
1) gives stability
2) allows varying height of tube
what does the control panel allow you to change
exposure factors; KvP and mAs
Why is the base weighted
to stabilise to the centre of gravity
what other 4 things does the machine have to aid movement?
1) wheels to allow movement/motor assisted
2) handle with automated locking device/wheel break when released
3) Collision sensors
4) Power indicator on console
what are the function of the base (6 things)
1) stability
2) houses a large battery
3) Contains step-up/down HV transformers
4) provides a rectifier system
5) contains an oil coolant
6) Made of grounded steel with fibreglass cover to provide durability
How does the battery work (4 points)
1) stores electrical energy taken from the mains supply when the unit is plugged in-provides a constant potential
2) Power indicator shows 100%/FULL when fully charged
3) can be used under 100%
4) discharges some of its energy during an exposure- independent of the mains
What is the purpose of the step-up/down transformers? (4 points)
1) as in a static x ray tube, voltage from the battery needs adjustments before it reaches the tube
2) Step-up transformer increases the voltage to cathode/anode creating high potential across the tube to allow photon production
3) Step-down transformer decreases voltage to the filament to allow thermionic emission without damage to the filament
4) modern mobile units usually have a choice of two focal spot sizes
why is a rectifier needed?
as electrical supply from the mains is an alternating current. If left like then photon production is inefficient
what is half wave rectification
when a direct current is needed to maintain constant flow of photons in beam
what is single phase full wave rectification
when a double electrical current is needed
what is 3 phase full wave rectification
this is the ideal current ‘smooth’
how does a theatre C-arm work? (5 points)
1) still a mobile x-ray unit with additional functionality
2) isocentric arm-i.e. rotates around a point in air
3) Image capture using an intensifying screen
4) CANNOT be used independently of mains power supply
5) Allows DYNAMIC SCREENING i.e. live images
name 5 additional features of a theatre C-arm
1) PULSED screening available to reduce patient dose
2) Stationary or rotating anode depending on manufacturer
3) Digital functionality
4) Instant image display
5) Instant hard copy available- mini laser printer
what is the aim of a mammography unit
to image soft tissue only- design of the equipment must allow for this functionality
what is needed due to the low mass attenuation of soft tissue
photons with very low energy
why is a high speed rotating anode made of a high atomic number (tungsten-rhenium) no good for a mammography unit?
as it produces relatively high energy photons
what kvP range does mammography units use
20-45 kV
what is the problem with a low kV range being used for mammography units?
1)thermionic electrons do not have enough energy to cross to the anode which produces a beam of low quality- low intensity
what is the problem with using a longer exposure time for mammography
this increases movement unsharpness
what is the problem with breast tissue
has very little subject contrast
What 4 things resolve these problems with a mammography units?
1) shorter distance between anode and cathode
2) short SID of 45-60cm
3) use a fine focal spot size of 0.4 to 0.6mm (or less)
4) use a rotating anode of molybdenum
what SID is used for mammography units
45-60cm
why is a focal spot size of 0.4 to 0.6mm (or less) used in mammography units
reduces geometric unsharpness
what is the rotating anode made of in a mammography unit
molybdenum
what does a molybdenum rotating anode produce
a MONOENERGETIC beam when filtered
