Transcript Mobile Radiographic Equipment

Mobile Radiographic
Equipment
Introduction
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In-patients who could not leave their beds
 Surgeons who required x-ray control guidance
during the course of their work in the operation
theatre
The basic design for a mobile unit
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A wheeled base
 Built in X-ray generator
 Control panel
 Supported X-ray tube
Some of the general rules
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The exposure hand-switch cable must be at
least 2 m long to allow radiographer to stand
distant from irradiated patient
 Lead protection must be used for personnel not
involved with the examination
 Protect other staff not involve with the
examination
Electrical energy source
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Directly from the mains voltage supply in this
case static generator is installed permanently
A Capacitor can be charged from the mains
voltage to the required potential difference and
discharged through the x-ray tube
Battery design, which can provide the energy
required by an x-ray generator
Main-dependant mobile
equipment
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The mains voltage supply
must have robust
connection cable
That cable encloses three
low resistance conductors
Two of the conductors
carry the current which
the generator draws
when an exposure is
made
The third provide a safe,
reliable connection to
earth
Main-dependant mobile
equipment
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The cable must be long enough for
the equipment to be used in most
locations
Should provide a convenient mains
outlet socket
The cable must be wound onto a
wheel-type storage drum built into
the equipment, when not in use to
protecting it from physical damage
Using extension cable is not
recommended
Extra length of cable will cause:
1- Drop of voltage which may occur during an
exposure
2- Earth connection will be weak, that will reduce
the safety of the equipment
Conventional generators
X-ray generator is commonly about 30 A and may
be higher
Capacitor discharge equipment
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The main advantage is producing X-rays from
the energy stored in and discharged from a
capacitor
 Main voltage and resistance variations only have
their effects upon the act of charging the
capacitor
 When exposure is required the radiographer
select the values of kVp and mAs.
 The switch is then operated to charge the
capacitor to the required kilovoltage via the high
tension generator
Capacitor discharge equipment
Capacitor discharge equipment
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The X-ray exposure involves first disconnecting
the capacitor from the high-tension supply and
then connecting it cross the X-ray tube
 A special X-ray tube is required which
incorporates a third electrode (grid) interposed
between cathode and anode which is at a high
negative potential (bias)
 The effect of negative bias is to prevent filament
electrons from crossing to the anode
Capacitor discharge equipment
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When the exposure begins the negative bias is
removed and it end when the bias is re-imposed
 At the end of the time exposure when required
mAs has crossed the tube, the negative grid
(bias) is re-imposed to prevent further
conduction
 mAs = mC
 The capacitance of the capacitor its ability to
store electric charge and that measured as a
ratio between the charge stored on the plates
and the potential difference between them
Capacitor discharge equipment
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The unit is farad = 1 coulomb per volt
In a mobile unit the capacitor employed usually
has capacitance of 1 microfarad that can create
1 kV cross it
When discharge the potential difference falls of 1
kV for every mC i.e. every mAs
e.g. 90 kV and 20 mAs results in a final potential
difference across the tube of 70 kV
If a large mAs is selected the kVp used should
be low
Battery-powered generators
Provide correct, regular charging
procedures
 The direct voltage output has to converted
into an alternating voltage, so that it can
be transformed into a kV
 Then followed by rectification
 Batteries maybe nickel-cadmium or more
conventional lead-acid type
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Battery-powered generators
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All batteries are sealed for safety
 Charging is achieved by connecting the
generator to a mains voltage supply at times
when it is not required for radiography
 Security is essential
X-ray tubes
- The anode is rotating and sometimes is in a high
speed
- Some x-ray tube require a low voltage
- The capacitor discharge equipment units have xray tubes which incorporate a grid to switch
exposures
- X-ray tubes are invariably fitted with LBD (Light
Beam Diaphragm)
- Scales and angle indicators are fitted to guide
radiographers
- The x-ray tube is delicate and expensive
component of a mobile equipment unit. It is
essential to protected against physical damage
Physical feature
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The wheels are fitted with
tyres made from antistatic
rubber for safety
Motor is installed in some
mobile equipment unit
Brakes and locks to slow
down and immobilization
The tube support
- Security
Special technical factor selection
consideration
- Kilovoltage it produce different from the
stationary equipment
- mAs the low power unit not capable of the high
mAs and use high kVp instead to obtain sufficient
density
- The distance, should be estimated within 15% to
avoid producing a visible density difference
- The grid problem is proper alignment, low grids
ratio 5:1 or 6:1 are often preferred and parallel
instead of focused grid