Mobile Radiographic Equipment

Introduction In-patients who could not leave their beds 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 Surgeons who required x-ray control guidance during the course of their work in the operation theatre

The basic design for a mobile unit A wheeled base A wheeled base Built in X-ray generator Built in X-ray generator Control panel Control panel Supported X-ray tube Supported X-ray tube

Some of the general rules The exposure hand-switch cable must be at least 2 m long to allow radiographer to stand distant from irradiated patient 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 Lead protection must be used for personnel not involved with the examination Protect other staff not involve with the examination Protect other staff not involve with the examination

Electrical energy source 1) Directly from the mains voltage supply in this case static generator is installed permanently 2) A Capacitor can be charged from the mains voltage to the required potential difference and discharged through the x-ray tube 3) Battery design, which can provide the energy required by an x-ray generator

Main-dependant mobile equipment The mains voltage supply must have robust connection cable The mains voltage supply must have robust connection cable That cable encloses three low resistance conductors That cable encloses three low resistance conductors Two of the conductors carry the current which the generator draws when an exposure is made 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 The third provide a safe, reliable connection to earth

Main-dependant mobile equipment The cable must be long enough for the equipment to be used in most locations The cable must be long enough for the equipment to be used in most locations Should provide a convenient mains outlet socket 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 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 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 The main advantage is producing X-rays from the energy stored in and discharged from a capacitor 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 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. 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 The switch is then operated to charge the capacitor to the required kilovoltage via the high tension generator

Capacitor discharge equipment

The X-ray exposure involves first disconnecting the capacitor from the high-tension supply and then connecting it cross the X-ray tube 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) 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 The effect of negative bias is to prevent filament electrons from crossing to the anode

Capacitor discharge equipment When the exposure begins the negative bias is removed and it end when the bias is re-imposed 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 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 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 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 The unit is farad = 1 coulomb per volt 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 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 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 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 If a large mAs is selected the kVp used should be low

Battery-powered generators Provide correct, regular charging procedures 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 The direct voltage output has to converted into an alternating voltage, so that it can be transformed into a kV Then followed by rectification Then followed by rectification Batteries maybe nickel-cadmium or more conventional lead-acid type Batteries maybe nickel-cadmium or more conventional lead-acid type

Battery-powered generators All batteries are sealed for safety 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 Charging is achieved by connecting the generator to a mains voltage supply at times when it is not required for radiography Security is essential 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 x- ray 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 The wheels are fitted with tyres made from antistatic rubber for safety The wheels are fitted with tyres made from antistatic rubber for safety Motor is installed in some mobile equipment unit Motor is installed in some mobile equipment unit Brakes and locks to slow down and immobilization Brakes and locks to slow down and immobilization The tube support - Security 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