BASIC X-RAY TECHNICAL TRAINING

Prepared by: Armando Darino Ngojo

Senior Engr, Biomedical & Facility

OBJECTIVES

• To enhance the troubleshooting skills of in-house technical staffs

• To demonstrate understanding, knowledge and skills in applying maintenance activities

• To minimize the cost of repairs and spare parts• To maintain high-uptime rate of the machine

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Goals - After the training, the trainees should be able to:

1. Explain what X-rays are.

2. Identify the parts of the X-ray Machine

3. Perform basic check, maintenance & PPM

4. Explain the hazards of X-ray devices

5. Explain the requirements and responsibilities for the safe use of X-ray devices.

6. Recognize and respond to unsafe conditions.

7. Respond to simple faults

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CHAPTER 1: INTRODUCTION

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X-rays were discovered in 1895 when Wilhelm Conrad Roentgen observed that a screen coated with a barium salt fluoresced when placed near a cathode ray tube. Roentgen concluded that a form of penetrating radiation was being emitted by the cathode ray tube and called the unknown rays, X-rays.

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First X-ray Image

What are X-rays?• X rays are the ionizing electromagnetic radiation emitted from a highly evacuated high-voltage tube. Inner orbital electrons in the target anode are stimulated to emit x-radiation via bombardment by a stream of electrons from a heated cathode.

• X-rays, like gamma rays, are penetrating and carry enough energy to ionize atoms in their path. Nearly identical to gamma rays, x-rays require shielding to reduce their intensity and minimize the danger of tissue damage to personnel. Mishaps with x-rays can cause severe radiation burns and deep tissue damage and can lead to various cancers.

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•Radiation is energy in the form of waves or particles.

•Radiation which is high enough in energy to cause ionization is

called ionizing radiation. It includes particles and rays given off by

radioactive material and high-voltage equipment. Ionizing

radiation includes x-rays, gamma-rays, beta particles, alpha

particles, and neutrons.

•Without the use of monitoring equipment, humans are not able to

"find" ionizing radiation. In contrast to heat, light, odors and noise,

humans are not able to see, feel, taste, smell, or hear ionizing

radiation.

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What is Radiation?

Sources of Radiation• Cosmic: altitude and latitude

• Terrestrial: geographically

• Food (pCi): brazil nuts; cereals; teas; liver and kidney; flours; peanut

butter; chocolates; biscuits; cheese; vegetables

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Units of Radiation Exposure and Dose

• Exposure (Roentgens)

• Dose Equivalence (Sievert)Relative biological effectiveness of different types of ionising radiation

• The Effective Dose Rate (Sievert)

• Absorbed dose (Gray)

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DoseInternational Commission on Radiological Protection (ICRP) Prescribed Limits per annum

• Members of public

• Radiation workers20 mSv per annum above background150 mSv to eye500 mSv to hands

1 mSv per annum above background5 mSv to eye20 mSv to hands

•Pregnant women must receive no more than 2mSv per annum

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PERSONNEL MONITORING

• X-ray devices users must wear personnel radiation monitoring devices (dosimeters / film badges). Dosimeters measure and document accrued dose to operators.

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CHAPTER 2:

An x ray machine is a complex device used in variety of applications around the world. With the ability to penetrate hard objects, they are used for purposes such as to look for broken bones or problems within the body in the medical community, air port security check points, in the industrial QC applications and for research purposes.

X-RAY MACHINE

PRINCIPLES OF OPERATIONS

• An x-ray machine is essentially a camera. Instead of visible light, however, it uses X-rays to expose the film. X-rays are like light in that they are electromagnetic waves, but they are more energetic so they can penetrate many materials to varying degrees. When the X-rays hit the film, they expose it just as light would.

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Since bone, fat, muscle, tumors and other masses all absorb X-rays at different levels, the image on the film lets you see different (distinct) structures inside the body because of the different levels of exposure on the film.

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…CONT

Production of X-ray

An x-ray tube requires a source of electrons, a means to accelerate the electrons, and a target to stop the high-speed electrons.

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•The filament is heated to boil off electrons which are then accelerated to the anode•The filament is contained within the cathode which is cup shaped to focus the electrons onto the focus spot on the anode•Tube currents of 50-800 milliamperes are used whereas filament currents are in the range of 2-5 amperes•The anode is bevelled at an angle of 12 to 17 degrees in order to maximise the contact area while focussing the resultant beam •The anode is usually composed of tungsten or molybdenum as it must withstand very high temperatures (>3000 degrees C)•Correct warm up and stand by procedures are essential to maximise tube and filament life

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When the electrons from the cathode are accelerated at high voltage to the anode:

• 99% of the energy is dissipated as heat (anode materials are selected to withstand the high temperatures they are able to withstand)

1% is given off as x-rays.

• The energy of the x-rays (keV) is determined by the voltage applied (kVp) while,

• The amount of x-rays is determined by the current (mA).

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Block Diagram of the X-ray Machine

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Parts & definitions:

• X-Ray Generator: High voltage generator: modifies incoming voltage and current to provide an x-ray tube with the power needed to produce an x-ray beam of the desired peak-kilo-voltage (k V p) and current (mA) and duration (Time).

• Control panel: Permits the selection of technique factors and initiation of radiographic exposures mA, kV, Time

• Transformer: Transformers modify the voltage of incoming alternating-current (AC) electrical signals to increase or decrease the voltage in a circuit.

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…CONT• Step-up transformer: Supplies the high voltage to the x-ray

tube (voltage increases and current decreases)• Step-down transformer: Supplies power to heat the

filament of the x-ray tube (voltage decreases and current increases)

• Autotransformer: Supplies the voltage for the two circuits and provide a location for the K v p meter (indicates the voltage applied across the x-ray tube)

• Rectifiers: Convert AC into the direct current (DC) required by the x-ray tube. A rectifier restricts current flow in an x-ray tube to one direction (from cathode to anode), thereby preventing damage to the x-ray tube filament. Two types: Half wave and Full wave.

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…CONT

• X-RAY TUBE: It is an expensive wearing element in medical radiological equipment. It consists of

Expansion bellows (provide space for oil to expand),Anode,Cathode (and heating-coil),Tube envelope (evacuated) , Tube housing, Cooling dielectric oil, Rotor,

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…CONT• High Tension Cable: Special highly

insulated cables Considered are the cable capacitance (130-230 pF/m) because it affects the average value of the voltage and current across the x-ray tube (increases the power delivered to the tube.

• Collimators and Grids: They are used to increase the image contrast and to reduce the dose to the patient by mean limiting the x-ray beam to the area of interest.

• Collimator: It is placed between the x-ray tube and the patient and Usually provided with an optical device, by which the x-ray filed can be exactly simulated by a light filed.

• Grid: It is inserted between the patient and the film cassette in order to reduce the loss of contrast due to scattered radiation.

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…CONT

• X-ray film: X-ray film is a sensitive material (sheet) for the x-ray. A film that has been exposed to x-rays shows an image of the x-ray intensity.

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External Compponents: Mobile X-ray• 11) cassette holder 12) Cable 13) Imaging hand switch 14) Control panel 15)

Generator 16) Display screen 17) Stretcher 18) X-ray tube 19) Collimator 20) Cassette 21) Interface cable 22) trolley 46) Hand grip 66)tube

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ExAMPLE of X-ray Machine Technical Specs:

X-RAY MACHINE 300mA. 125 KVP Full Wave Rectified X-ray Generator for Radiography suitable for single Tube.

TIMER The exposure timer should be digital & from 0.02to 5 sec.

CONTROL Consisting of On & Off Switches, with Voltmeter, Voltage Compensator, Tube overload indicator provided, Space charge compensator. etc

Static balancer 30 KVA capable of converting 3 phase in range 365-400 VAC with ‑0.2 ohms resistance at 50-60Hz to single phase 230VAC/50Hz

HV TRANSFORMER Compact Heavy Duty Transformer comprising HV Silicon Rectifiers, Filament Transformer, bushings all immersed in oil.

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…contACCESSORIES Hand Switch with Flexible long cord enables

the operator to keep away from the Radiation area during exposure.- Aluminum Filter.

POWER SUPPLY REQUIREMENT 440V + 10% V AC, 50 Hz, Three Phase

TUBE UNIT One No. 20/40 Rotating Anode Tube (BEL / TOSHIBA or equivalent) with Dual Focus (Large & Small).

HV CABLE One Pair of 10 meter High Voltage Cables Sleeping’s - Straight.

STAND Floor to Ceiling Stand & with Counter Balanced Tube Head (Rotatable+180 Degree), 360 Degree Rotatable;

TABLE 5 Position Table Hand tilt; 15 Degree trendelenburg to vertical

VERTICAL BUCKY Vertical Bucky Stand with moving Grid of Ratio 8:1, 103 lines/inch.

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CHAPTER 3: Maintenance Activities

MAINTENANCE ACTIVITIES INCLUDE:• Repairs

• Repair activities are reactive.• Breakdowns and malfunctions typically occur when

equipment is in use.• Standby machines and parts can speed repairs.

• Preventive Maintenance (PM)• Regularly scheduled inspections are performed.• PM activities are performed before equipment fails.• PM is usually performed during idle periods.

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3.2 FAILURE AND DIAGNOSIS

• Fault 1: no display after booting console • Diagnosis: Switch off the power and check the power source.

Check the power cabinet & confirm fuses are good. If power source is good, possible problem with the connecting cables, faulty control boards or corrupted software, check as necessary.

• Fault 2: no exposure • Diagnosis: Check the exposure hand switch and the console

exposure switch are both OK. If both exposure switches are OK, check the rotor control board in the power cabinet. If necessary, Call vendor for advise.

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…CONT

• Fault 3: soft image or over-exposed image • Diagnosis: Check the factors (KVp, mAs & time) set by the user.

Adjust if necessary. Also confirm if the film processor is properly calibrated to the film or digital cassettes in use by the department. If the problem is not corrected, the unit needs calibration

• Fault 4: X-ray tube is noisy• Diagnosis: Check the bearing noise if too loud and noisy. If

confirmed, the problem is an aged X-ray tube and needs replacement.

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3.3 PREVENTIVE MAINTENANCE• Preventive maintenance includes:

X-ray room inspection and minor repairs (adjustment)Calibration checkHigh voltage cables and electrical wiring inspection Electrical and mechanical locks adjustmentTube stand and table anchors inspectionBearing and tracks lubricationHandles and knobs inspectionVerify processor temperature (chemical-type film processor)Cassette identificationId printer operationCheck ID card qualityCertificate of completion.

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3.4 SCHEDULED MAINTENANCE

• Scheduled maintenance reduce incidence of failure through inspection designs to detect potential problems before they become reality.

• It is performed on an annual or semiannual basis, according to device uses or history. Equipment required for scheduled maintenance: Cleaning supplies, Vacuum cleaners, Lubrication, Tools etc.

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3.5 PLANNED MAINTENANCE

• Planned maintenance is maintenance organized and carried out with for thought, control, and records, to a predetermined plan. In doing this, the following factors have to be kept in mind: The extent of utilization (is the machine working), Severity of utilization (is the machine work under normal load condition), Operating condition, Are there any other specific factors that may affect the instrument among others.

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3.6 SPARE PARTS

Some of the spare parts provided for x-ray machine are:

• Cable• Cassette• Film• X-ray tube• Lead shield• Fuses, etc…

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CHAPTER 4: Safety with X-ray Apparatus

Principles of Radiation Safety:

1. Minimise Exposure Time

2. Maximise Distance from Source

3. Use Correct Shielding

4. Follow Manufacturers Instructions

5. Follow the ALARA principle - keep dose As Low As Reasonably Achievable

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1. Time

•Ensure all personnel minimise time spent close to machine

2. Distance

•Exposure falls at the square of distance from source. The longer the distance, the lower the dose.

•Therefore use distance to your advantage

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3. Shielding

•It is important to periodically verify that shielding is functioning properly

•Most analytical X-ray machines have adequate shielding provided

•Never tamper with or alter shielding

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4. Follow Manufacturers Instructions

•Never over-ride safety interlocks

•Only authorised operators of X-ray apparatus who are familiar with safe operation of machine use the apparatus.

•Document all repairs

•Ensure there are procedures to prevent unauthorised use of or access to X-ray equipment (ie only authorised key-holders can use apparatus)

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X-Ray Effects

• The effects of x-ray exposure depends upon:

1.Duration/Exposure time - How fast the dose is delivered.

2.Energy - How much energy was in the x-rayLow Energy (<50 KeV) - damage only to skin or

outer part of body

High Energy - damage to internal organs

1.Total Dose - The magnitude of the dose

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Condition of patient's back six to eight weeks following multiple coronary angiography and angioplasty procedures.

Appearance of skin injury approximately 18 to 21 months following procedures, evidencing tissue necrosis.

Close-up view of lesion shown in the middle photo

Radiation-induced Skin Injuries from FluoroscopyTaken from US FDA website.

Unsafe conditions• Examples of unsafe conditions which could produce an

unwanted radiation dose are,Access door interlocks not working shielding that has been removed/damagedX-ray “ON” light not lit when unit energized.

• IF AN UNSAFE CONDITION ARISES WITH YOUR X-RAY DEVICE:

Stop work!Immediately Turn OFF the X-ray powerNotify BEMS Office at loc. 789Post “Out of Service” tag on the machine until problem fixed.

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Thank you for participation !!

!

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