Imaging Equipment and Maintenance PDF

IMAGING EQUIPMENT AND MAINTENANCE RAFAEL SANTOS, RRT FACULTY, COLLEGE OF RADIOLOGIC TECHNOLOGY LYCEUM-NORTHWESTERN UNIVERSITY BASIC CIRCUITRY  PRE- TEST 1. IT IS THE RATE OF WHICH CHARGE IS FLOWING A. CURRENT B. VO...

IMAGING EQUIPMENT AND MAINTENANCE RAFAEL SANTOS, RRT FACULTY, COLLEGE OF RADIOLOGIC TECHNOLOGY LYCEUM-NORTHWESTERN UNIVERSITY BASIC CIRCUITRY  PRE- TEST 1. IT IS THE RATE OF WHICH CHARGE IS FLOWING A. CURRENT B. VOLTAGE C. RESISTANCE D. POWER 2. DIFFERENCE IN CHARGE BETWEEN TWO POINTS A. CURRENT B. VOLTAGE C. RESISTANCE D. POWER 3. CONSIDERED TO BE THE SMALLEST MAGNET A. NEUTON B. PROTON C. NUCLEONS D. ELECTRON  PRE- TEST 4. THE SUBSTANCE WHICH HAVE A LARGE NUMBER OF FREE ELECTRONS AND IFFER A LOW RESISTANCE IS CALLED? A. INSULATOR B. INDUCTOR C. SEMICONDUCTOR D. CONDUCTOR 5. THE S.I UNIT PF POWER a. HENRY b. COULOMB c. WATT d. AMP 6. THE RESISTANCE OF A CONDUCTOR VARIES INVERSE WITH a. LENGTH b. AREA OF CROSS-SECTION c. TEMPERATURE d. RESISTIVITY  PRE- TEST 7. WITH RISE OF TEMPERATURE THE RESISTANCE a. DOESN’T CHANGE b. INCREASE c. DECREASE d. HALVED 8. LIKE CHARGES…. a. REPEL b. ATTRACT c. RETRACT d. UNITES 9. DOES NOT PERMITS THE FLOW OF ELECTRICITY a. INSULATROR b. CONDUCTOR c. SEMICONDUCTOR d. SUPER CONDUCTER  PRE- TEST 10. WHAT DEVICE MEASURES POTENTIAL DIFFERENCE? a. AMMETER b. VOLTMETER c. OHM METER d. THERMOMETER NGAYON KA PA BA SUSUSKO? KUNG KELAN 2ND YEAR KANA? DAPAT NUNG 1ST YEAR PA LANG ELECTRICITY  ELECTRICITY  form of energy created by the activity of electrons and other subatomic particles in motion  Dr. William Gilbert – coined the term “electrica”, a Latin word which describes the static charge that develops when certain materials are rubbed against amber  a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge  ELECTRICITY Electrostatics  study of stationary electric charges  Electrodynamics  science of electric charge in motion  deals with electric current  ELECTRICITY  Electrification  transfer of one electron from one object into another  Electric Potential  a system that possesses potential energy is a system with stored energy; such system has the ability to do work when this energy is released  sometimes called “voltage”  Electric Current  flow of electricity through a conductor  Unit: ampere (A)  ELECTROSTATIC LAW  Attraction/Repulsion  like charges repel, unlike charges attract  the electric line of force points outward from a positive charge and towards for a negative charge  Coulomb’s Law  force of attraction (or repulsion) between two charged objects is directly proportional to the product of charges magnitude and inversely proportional to the square of the distance between them  ELECTROSTATIC LAW  Electric Charge Concentration  electric charge of a conductor is concentrated along the sharpest curvature of the surface  ELECTROSTATIC LAW  Electric Charge Distribution  electric charge distribution is uniform throughout the surface  ELECTRIC CLASSIFICATION OF MATTER  Conductor  allows the flow of electrons  ex: copper, gold, aluminum  Semiconductor  can behave as insulator or conductor  ex: silicon, germanium  Insulator  inhibits flow of electrons  ex: plastics, rubber  Superconductor  allows flow of electrons freely even without voltage  must be very cold  ELECTRICITY  When beginning to explore the world of electricity and electronics, it is vital to start by understanding the basics of voltage, current and resistance. These are the three building blocks required to manipulate and utilize electricity.  At first, these concepts can be difficult to understand because we cannot “see” them.  Electricity is the movement of electrons. Electrons create charge, which we can harness to do work.  Voltage – difference in charge between two points  Current – rate of which charge is flowing  Resistance – material’s tendency to resist the flow of charge (current)  ELECTRICITY  When we talk about these values, we are describing the movement of charge, and thus, the behavior of electrons. A circuit is a closed loop that allows charge to move from one place to another. Components in the circuit allow us to control this charge and use it to do work.  Georg Ohm was a German scientist who studied electricity. Ohm starts by describing the unit of resistance that is defined by current and voltage.  WHAT IS CURRENT?  An electrical phenomenon is caused by the flow of free electrons from one atom to another. The characteristics of current electricity are opposite to those of static electricity.  Wires are made up of conductors such as copper or aluminum. Atoms of metal are made up of free electrons, which freely move from one atom to another. If an electron is added in wire, a free electron is attracted to a proton to be neutral. Forcing electrons out of their orbits can cause lack of electrons. Electrons, which continuously move in wire are called electric current.  WHAT IS CURRENT?  Current is flow electrons, but current flow and electron flow is in opposite directions. Current flow from positive to negative and electron flows from negative to positive.  Current is determined by the number of electrons passing through a cross-section of a conductor in a second.  Current is measured in amperes, which is abbreviated in “amps”. WHAT IS VOLTAGE?  Electric current is flow of electrons in a conductor. The force required to make current flow through a conductor is called voltage and potential is the other term of voltage.  For example, the first element has more positive charges, so it has higher potential. On the other hand, the second element has charges that are more negative so it has lower potential. The difference between two points is called potential difference.  WHAT IS VOLTAGE?  Electromotive force means the force which makes current continuously flows through a conductor. This force can be generated from power generator., battery, flashlight battery and fuel cell, etc.  Volt, abbreviated as “V”, is the unit for measurement used interchangeably for voltage, potential and electromotive force. One volt means a force which makes current of one amp move through a resistance of one ohm.  WHAT IS RESISTANCE?  Electrons move through a conductor when electric current flow. All materials impede flow of electric current to some extent. This characteristic is called resistance.  The unit of measurement for resistance is ohms(Ω). The resistance of one ohm means a conductor allows a current of one amp to flow with a voltage of one volt.  LAWS OF RESISTANCE  Law of Lengths  resistance of conductor is directly proportional to its length  Law of Diameter  resistance is inversely proportional to the square of its diameter or its cross-sectional area  Law of Nature of Material  resistance depends on the kind of material  Law of Temperature  resistance decreases as temperature decreases  ELECTRIC CIRCUIT  An unbroken loop of conductive material that allows electric charges to flow through continuously without beginning or end  If a circuit is “broken”, that means its conductive elements no longer form a complete path and continuous electron flow cannot occur in it.  ELECTRIC CIRCUIT  Series circuit is a circuit whose all circuit elements are connected in a line along the same conductor.  Parallel circuit is a circuit whose elements are connected at their ends rather than lie in a line along the conductor. ELECTRIC CIRCUIT  OHM’S LAW  A law that states that the total voltage across a circuit will always be equal to the product of the total current and total resistance across the same circuit.  Voltage (volts or V)  product of current and resistance in a circuit  Current (amp or A)  ratio of the voltage and resistance in a circuit  Resistance (ohms or Ω)  ratio of the voltage and current in a circuit OHM’S LAW  ELECTRIC CIRCUIT Series Circuit VT = V1 + V2 + V3... IT = I1 = I2 = I3... RT = R1 + R2 + R3... Parallel Circuit VT = V1 = V2 = V3... IT = I1 + I2 + I3... 1/RT = 1/R1 + 1/R2 + 1/R3...  ELECTRIC CIRCUIT Three resistors of 25 Ω, 50 Ω and 100 Ω are connected in a series circuit. Determine the unknown values described below, if the circuit draws 100 volts from an AC source. Total Resistance Total Current Voltage across R3  ELECTRIC CIRCUIT If the resistors from the previous problem were now connected in a parallel circuit, calculate the following. Total Resistance Total Current Current across R2  POWER  Electrical power (P) in a circuit is the rate at which energy is absorbed or produced within a circuit.  time rate at which work is done  SI Unit: watt (w) [ 1w = 1 J/sec]  named after James Watt  1 watt = current flow of 1 ampere with voltage of 1 volt.  1 watt = V x A  POWER An x-ray imaging system that draws a current of 100 A is supplied with 220 V. What is the power consumed?  POWER The overall resistance of a mobile x-ray imaging system is 10 Ω. When plugged into a 110 V receptacle, how much current does it draw and how much power is consumed? MAGNETISM MAGNETISM  No discussion of electric circuit would be complete without an introduction to magnetism, a phenomenon that underlies a variety of circuit devices such as inductors and transformers, as well as other devices you’ve probably encountered in daily life.  Magnets exert a force on each other and on certain metals (iron and certain types of steel for instance): this force is called the magnetic force. What you may not know, however, is  MAGNETISM  Fundamental property of matter  All matter are magnetic to some degree, even subatomic particle have magnetic properties.  Field effect is associated with certain types of materials.  Similar in many ways to electric field but its manifestations are different.  Ability of a material to attract iron.  MAGNETISM  Any charged particle in motion will create a magnetic field.  The magnetic field is always perpendicular to the motion of the charged particle.  The lines of a magnetic field are always in closed loops.  A magnet is said to be bipolar/dipolar. MAGNETISM MAGNETISM  TYPES OF MAGNETS  Naturally Occurring Magnets  ex: Earth  Artificially Induced Permanent Magnets  available in many sizes and shapes but principally as a bar or horseshoe-shaped magnets, usually made up of iron.  ex: compass  Electromagnets  consist of wire wrapped around an iron core  magnets that run through electricity  MAGNETIC STATES OF MATTER  Nonmagnetic/Diamagnetic  unaffected by a magnetic field  ex: zinc, bismuth, sodium chloride, gold  Paramagnetic  weakly attracted to both poles of a magnetic field  ex: wood, aluminum, platinum, oxygen  Ferromagnetic  can be strongly magnetized  ex: iron, steel, cobalt, nickel  MAGNETIC LAWS  Dipole  dividing a magnet into smaller pieces will only create smaller magnets with 2 poles  MAGNETIC LAWS  Attraction/Repulsion  like magnetic poles repel, unlike magnetic poles attract  MAGNETIC LAWS  Induction  some materials can be magnetic through induction  ELECTROMAGNETISM  Until the 19th Century, electricity and magnetism were viewed as separate effects.  The development of methods for producing a stable source of flow of electric charges stimulated investigations of both electricity and magnetism  Electromagnetism – fundamental interaction between magnetic field and motion of electric charge.  Electromagnetic – object that acts like a magnet, but its magnet force is created and controlled by electricity. ELECTROMAGNETISM  ELECTROMAGNETISM  Luigi Galvani (Italian Anatomist)  dissected frog leg twitched when touched by 2 different metals  Alessandro Volta (Italian Physicist)  questioned whether an electric current might be produced when 2 different metals are brought into contact  Voltaic Pile  stacks of zinc-copper plates  each zinc-copper sandwich is called “cell” of the battery  precursor of modern battery  considered as the 1st wet cell battery ELECTROMAGNETISM  ELECTROMAGNETISM  Hans Oersted (Danish Physicist)  discovered that electric currents create magnetic field  fashioned a long wire, supported near a free rotating magnetic compass pointed north as expected  when a current was passed through the wire, however, the compass needle swung to point straight to the wire  He therefore conclude that:  Any charged particle in motion induces a magnetic field  Any charged particle at rest induces no magnetic field. ELECTROMAGNETISM  ELECTROMAGNETISM  Michael Faraday  credited with the discovery of induction in 1831  first dynamo in 1837  an electric current is induced in a circuit if some parts of that circuit are in changing magnetic field (electromagnetic induction) ELECTROMAGNETISM  PRACTICE QUESTION 1. OHM’S LAW  ELECTRIC CIRCUIT Series Circuit VT = V1 + V2 + V3... IT = I1 = I2 = I3... RT = R1 + R2 + R3... Parallel Circuit VT = V1 = V2 = V3... IT = I1 + I2 + I3... 1/RT = 1/R1 + 1/R2 + 1/R3...  ELECTRIC CIRCUIT Three resistors of 25 Ω, 50 Ω and 100 Ω are connected in a series circuit. Determine the unknown values described below, if the circuit draws 100 volts from an AC source. Total Resistance Total Current Voltage across R3  ELECTRIC CIRCUIT If the resistors from the previous problem were now connected in a parallel circuit, calculate the following. Total Resistance Total Current Current across R2 TRANSFORMERS  TRANSFORMERS  a device that changes the intensity of alternating voltage and current by mutual induction  Converts low voltage to high voltage, vice- versa  Does not convert any form of energy into another  TRANSFORMERS  its main function is to change the magnitude of an alternating voltage  consists of two coils, electrically insulated from one another  primary coil  defined as the coil to which the supply (input) is connected  secondary coil  defined as the coil from which the output is taken TRANSFORMERS  TRANSFORMERS  2 Types of Transformers  Self Induction (autotransformer)  utilizes one coil, which act both as a primary and a secondary coil  Mutual Induction Transformers  a change in voltage/current in the secondary coil is cause by a change in voltage/current in the primary coil  step up/step down  TRANSFORMERS  2 Classifications of Transformers  Step-up Transformer  used to increase the incident voltage  number of turns in the secondary coil is larger than the number of turns in the primary coil  the output voltage is higher than the input voltage  Step-down Transformer  used to decrease the incident voltage  number of turns in the primary coil is larger than the number of turns in the secondary coil  the output voltage is lower than the input voltage  TRANSFORMERS STEP-UP TRANSFORMER STEP-DOWN TRANSFORMER TRANSFORMERS  TRANSFORMERS  Example 1:  Primary coil = 500 turns  Secondary Coil = 1000 turns  Primary volt = 200V  Secondary volt = ???  Turns ratio?  TRANSFORMERS  Example 2:  Primary coil = 1000 turns  Secondary Coil = 10 turns  Primary volt = ???  Secondary volt = 100V  Step up or step down transformer?  TRANSFORMERS  5 Construction of Transformer (Main Types)  Air-Core Transformer  consists simply of 2 insulated coils lying side by side  Open Core Transformer  an iron core is inserted into a coil of wire carrying an electric current  Closed-Core Transformer  type of iron core that provide continuous path for the magnetic flux, so that a small fraction of the magnetic energy is lost by leakage  built about a square of core of a TRANSFORMERS  TRANSFORMERS  5 Construction of Transformer (Main Types)  Shell-Type Transformer  most advance type of transformer used as a commercial or power transformer  more efficient than 3 transformers, most currently used transformer  Autotransformer  sometimes called auto-step down transformer  an electrical transformer with one winding TRANSFORMERS  X-RAY IMAGING SYSTEM THE X-RAY TUBE, THE OPERATING CONSOLE, AND THE HIGH- VOLTAGE GENERATOR.  OPERATING CONSOLE The part of the x-ray imaging system most familiar to radiologic technologists is the operating console. USE TO CONTROL TUBE CURRENT AND VOLATAGE RADIATION QUANTITY Refer to the number of xrays It is expressed wiy mgya/ mAs RADIATION QUALITY Refers to the penetrability of the xray beam Express in Kvp Most of xray imaging systems are designed to operate on 220v  Line compensating device Most of x-ray imaging systems are designed to operate on 220v m Because of the variation in power distribution in the hospital and in power consumption The voltage provided in x-ray unit may vary do 5 % Measure the voltage provided to the x-ray imaging system and adjust the voltage to precisely 220 volts line compensator measures the voltage provided to the x-ray imaging system and adjusts that voltage to precisely 220 V. Line compensating device  AUTOTRANFORMER The power supplied to the x-ray imaging system is delivered first in Autotransformer AUTOTRANSFORMER Has a single winding and is designed to supply a precise voltage to the filament circuit and to high voltage circuit of the x-ray imaging system. ADJUSTMENT OF KILOVOLT PEAK (KVP) Some older xray imaging system have adjustment control labeled Major kVp and Minor kVP MAJOR kVp- adjust of kvp by 10 MINOR KVp – adust the kVp by 1 - along called finetunes kVp meter – is placed across the output terminals of the autotransformer and therefore actually reads voltage not kVp. Prereading kVp meter – allows the voltage to be monitored before exposure ADJUSTMENT OF MILLIAMPERAGE (mA) The x-ray tube current, crossing from cathode to anode is measured in milliamperes. The number of electrons emitted by filament is determined by the temperature of the filament. FILAMENT TEMPERATURE= FILAMENT CURRENT= NUMBER OF ELECTRONS X-ray tube current is controlled through a separate circuit called FILAMENT CIRCUIT mA Meter- is placed in the tube circuit to measure x-ray tube current  FILAMENT TRANSFORMER Also known as FILAMENT HEATING ISOLATION STEP-DOWN TRANSFORMER This is a stepdown transformer The purpose of this transformer is to lower the voltage by having lesser winding in the secondary side thus increasing the current  HIGH-VOLTAGE GENERATOR Responsible for increasing the output voltage from the autotransformer to the kVp necessary fo X-ray production Has three primary parts: HIGH-VOLTAGE TRANSFORMER Step-up transformer FILAMENT TRANSFORMER RECTIFIERS Is an electronic device that allows current flow in only on direction Ensures the flow electrons from cathode to anode RECTIFICATION is the process of converting AC to DC Accomplished by using DIODES  SINGLE – PHASE POWER This is caused by the alternate swing in voltage from zero to maximum potential 120 times each second under full- wave rectification. The x-rays produced when the single-phase voltage waveform has a value near zero are of little diagnostic value because of their low energy  HIGHT FREQUENCY GENERATOR High-frequency circuits are finding increasing applica tion in generating high voltage for many x-ray imaging systems. High-frequency generators produce a nearly constant potential voltage waveform, improv ing image quality at lower patient radiation dose.  VOLTAGE RIPPLE Single-phase power has 100% voltage ripple: The voltage varies from zero to its maximum value. Three-phase, six-pulse power produces voltage with only approximately 14% ripple; consequently, the voltage supplied to the x-ray tube never falls to below 86% of the maximum value Three-phase, 12-pulse power results in only 4% ripple; therefore, the voltage supplied to the x-ray tube does not fall to below 96% of the maximum value. High-frequency generators have approximately 1% ripple and therefore greater x-ray quantity and quality.  POWER RATING Transformers and high-voltage generators usually are identified by their power rating in kilowatts (kW) Question: When a system with low-voltage ripple is energized at 100 kVp, 100 ms, the maximum possible tube current is 800 mA. What is the power rating?  HEAT UNITS SINGLE PHASE GENERATOR HU= mA x time x kVp THREE PHASE, SIX PULSE HU= mA x time x kVp x 1.35 THREE PHASE, TWELVE PULSE HU= mA x time x kVp x 1.41 X-RAY CIRCUIT  X-RAY CIRCUIT Simplified diagram of an x-ray circuit. Electric circuit going into the x-ray room is at far left (1) and circuit ends at x-ray tube far right (14).  LOW VOLTAGE CIRCUIT  It is the subcircuit between the alternating current (AC) power supply (1) and the primary (input) side of the high-voltage (step-up) transformer (7).  If you trace this circuit beginning at the AC power supply, you will note that current flows through several devices before reaching the primary  LOW VOLTAGE CIRCUIT  From the transformer, it returns to the power source, forming an enclosed loop. With the exception of the step-up transformer, all of the devices in this subcircuit are actually located within the control console. The control console is the unit where the operator sets all of the exposure techniques, such as kilovolts peak (kVp), milliamperes (mA), and exposure time. They include the main switch  LOW VOLTAGE CIRCUIT  The AC power supply (1) is wired into the building, providing electric power from the local power company. Most outpatient facilities have a 220-V power supply going into the x-ray room. Hospitals with more powerful equipment may have a larger supply. The main switch (2) controls the power to the control console. Many of the components in this circuit operate at the standard 120 volts.  Although the power supply may be rated at 220 V, the actual voltage can vary as much as ±5%, depending on the demand for power in the building or the neighborhood. Small variations in the incoming line voltage may cause large variations in the kVp to the x-ray tube. For this reason, the incoming voltage is monitored and  LOW VOLTAGE CIRCUIT  The autotransformer (3) is a single-coil transformer that serves three functions: it provides the means for kVp selection, it provides compensation for fluctuations in the incoming line voltage, and it supplies power to other parts of the x-ray circuit.  The autotransformer’s primary purpose is to vary the voltage to the primary side of the step-up transformer. This is accomplished by the kVp selector (4), which is on the secondary (output) side of the autotransformer. The autotransformer varies the kVp to the tube by controlling the input to the step-up transformer.  LOW VOLTAGE CIRCUIT  The exposure switch (5) closes the circuit, allowing electric current to flow through the primary side of the step-up transformer. When this occurs, current is induced to flow through the secondary side of the transformer, creating voltage across the x-ray tube. As discussed earlier, this voltage causes the electron stream to flow across the tube, producing x-rays. The exposure timer (6) is a device that terminates the exposure and is set by the operator on the control console.  FILAMENT CIRCUIT  The filament circuit is divided into two parts by the step- down transformer (11 and 12). The primary purpose of the filament circuit is to supply a low current to heat the x-ray tube filament for thermionic emission of electrons. The filament circuit is activated any time the operator adjusts the mA on the generator.  FILAMENT CIRCUIT  The primary side of this circuit begins and ends with the contacts on the autotransformer (9). Current in this circuit flows from the autotransformer, through the mA selector (10) and the primary side of the step- down transformer (11), and back to the autotransformer. The secondary side begins and ends with the secondary side of the step-down transformer (12) conducting current through the x-ray tube  FILAMENT CIRCUIT  The mA selector (10) controls amperage in the filament circuit. Since the current through this circuit controls filament heat, this setting determines the number of available electrons at the x-ray tube HIGH-VOLTAGE CIRCUIT  The high-voltage circuit begins and ends with the secondary side of the step- up transformer (8). It includes the x-ray tube (14) and the rectifier unit (15). Current flows in this circuit only during an exposure. This is a dangerous circuit due to the very high voltage. The high-  HIGH-VOLTAGE CIRCUIT High-voltage cables going into the x-ray tube. Note their large size due to the high-voltage electricity moving in the copper wire.  HIGH-VOLTAGE CIRCUIT  The step-up transformer is also referred to as the high-voltage or high- tension transformer. It increases the incoming voltage by the value of the transformer ratio. This transformer has a very high ratio of at least 500:1. For example, if the primary side of the step-up transformer receives 180 V from the autotransformer, and the ratio is 500 : 1, the voltage induced on the secondary side will be 90,000 V, or 90 kVp.  The primary purpose of the high-voltage circuit is to supply the x-ray tube with  HIGH-VOLTAGE CIRCUIT  The step-up transformer is also referred to as the high-voltage or high- tension transformer. It increases the incoming voltage by the value of the transformer ratio. This transformer has a very high ratio of at least 500:1. For example, if the primary side of the step-up transformer receives 180 V from the autotransformer, and the ratio is 500 : 1, the voltage induced on the secondary side will be 90,000 V, or 90 kVp.  The primary purpose of the high-voltage circuit is to supply the x-ray tube with  X-RAY CONTROL PANEL  The console or control panel is the part of the machine that the operator controls the operation of the x-ray machine.  All machine console are a little different but there are always similarities. The console is where we control x-ray tube current and voltage.  Console will have controls for:  mA and time or mAs  kVp  focal spot  line voltage compensation  LINE COMPENSATION  At the bottom left is the control for line voltage compensation.  Most machine are designed to operate at 220 volts while some will work with 110 volts or 440 volts.  The power company often  LINE COMPENSATION  More modern units automatically adjusts for the incoming power so a meter is not provided.  Often over looked by the operator.  Results in improper exposure. AUTOTRANSFORMER  The autotransformer is designed to supply voltage of varying magnitude to several different circuits of the x-ray machine including both the filament circuit and high voltage circuits.  The autotransformer has only one winding and one core.  The single winding has a number of connection or electric  kVp ADJUSTMENT  Most consoles will have one or two knobs that change the taps on the autotransformer for major and minor kVp.  Modern units have a LED readout of kVp.  kVp ADJUSTMENT  Setting the desired kVp will determine the voltage applied to the step-up transformer in the high voltage section of the machine.  If a meter is provided, it is placed across the output terminals of the autotransformer and therefore it reads voltage and  mA CONTROL  The tube current, the number of electrons crossing from the cathode to anode per second is measured in milliamperes (mA).  The quantity of electrons is determined by filament temperature.  mA CONTROL  The filament normally operates at currents between 3 and 6 A.  The tube current is controlled through a separate circuit called the filament circuit.  Voltage is provided by taps of the autotransformer. This voltage is reduced with precise resisters  mA CONTROL  The voltage is then delivered to the filament transformer. The filament transformer lowers the voltage so it is called a step down transformer. RADIOGRAPHIC EQUIPMENT  RADIOGRAPHIC EQUIPMENT X-RAY TUBE COLLIMATOR  RADIOGRAPHIC EQUIPMENT X-RAY TABLE CONTROL PANEL RADIOGRAPHIC EQUIPMENT X-RAY TUBE STAND  RADIOGRAPHIC EQUIPMENT  These units are used for radiographic imaging of patients who cannot be moved to the radiology department and who are in areas—such as intensive and critical care units or operating and emergency rooms—that lack standard, fixed radiographic equipment. Medical applications can include general radiography and orthopedic, pediatric, skeletal, and abdominal imaging. MOBILE X-RAY UNIT  RADIOGRAPHIC EQUIPMENT  Mobile radiographic units consist of a wheeled cart that transports an x-ray generator (line- or battery- powered transformer), an x-ray tube and moveable tubestand, collimators, and a filmcassette or flat- panel detector storage drawer. Battery-powered units also contain a battery and charging system, and selfpropelled units contain a motor MOBILE X-RAY UNIT drive.  RADIOGRAPHIC EQUIPMENT  X-rays are produced by the x-ray tube (an evacuated tube with an anode and a cathode) when a stream of electrons, accelerated to high velocities by a high- voltage, collides with the tube’s target anode. A set of collimators confines the primary beam to the approximate size and shape that will cover only the area of diagnostic interest. Mobile CR units capture images using a photostimulable- phosphor plate. Mobile DR units are equipped with built-in or tethered flat panel detectors, which use a scintillator material to convert x-rays to visible light. An array of photodiodes on the a-Si layer absorbs the light and translates it into a signal for digital display. On some units, the x-ray exposure is powered directly from the line voltage. While on others, the input line voltage charges the battery that powers the x-ray exposure. MOBILE X-RAY UNIT  RADIOGRAPHIC EQUIPMENT  Operating steps:  The patient is prepped and provided some form of radiation shielding.  The unit is positioned around the patient, who is asked to remain motionless while the image is being taken.  The operator takes the image by activating the x- ray beam using an exposure switch.  The operator repositions the patient or unit if needed. Multiple images may be taken. MOBILE X-RAY UNIT  AUTOMATIC EXPOSURE CONTROL  The radiographer is tasked with selecting exposure factor techniques to produce quality radiographs for a wide variety of equipment and patients. When combined with patients of various sizes and with various pathologic conditions, the selection of proper exposure factors becomes a formidable task. An automatic exposure control (AEC) system is a tool available on most modern radiographic units to assist the radiographer.  Automatic exposure control (AEC) systems are designed to adjust the kilovoltage, milliamperage, or exposure time in order to obtain an image of diagnostic quality, be it for radiography or fluoroscopy. These systems sense the amount of radiation immediately in front of the image receptor and adjust the dose or dose rate to the patient in order to assure sufficient photons are reaching the image receptor. However, these systems can also result in high patient doses, especially with digital image receptors. AUTOMATIC EXPOSURE CONTROL  Automatic Exposure Control (AEC) is an x- ray exposure termination device. A medical radiography x-ray exposure is always initiated by a human operator but an AEC detector system may be used to terminate the exposure when a predetermined amount of radiation has been received. The intention of AEC is to provide consistent x-ray image exposure, whether to film, a digital detector or a CT scanner. AEC systems may also automatically set exposure factors such as the x-ray tube current and voltage. AUTOMATIC EXPOSURE CONTROL  AEC systems work on different principles, primarily based on the design goals of the manufacturer. Some systems may preferentially adjust the exposure time or tube current, while others may preferentially adjust the kilovoltage. Some systems insert extra filtration (typically a copper filter) into the beam to filter out additional soft radiation thereby reducing patient dose. AUTOMATIC EXPOSURE CONTROL  AEC systems may not produce the same image quality, e.g., film density, over the typical range of thicknesses encountered in the clinical setting. Consequently, a part of a good quality control program will be to test image quality and patient dose over a typical range of patient thicknesses.  AEC systems may also be known by other names including automatic dose control (ADC), automatic dose rate control (ADRC) and automatic brightness control (ABC). AUTOMATIC EXPOSURE CONTROL  Principle of Automatic Exposure Control Operation  Once a predetermined amount of radiation is transmitted through a patient, the x-ray exposure is terminated. This determines the exposure time and therefore the total amount of radiation exposure to the image receptor. AUTOMATIC EXPOSURE CONTROL  Phototimers  uses a fluorescent screen and device that converts light into electricity (PM tube)  considered exit-type devices (radiation must exit first the image receptor before being measured by the detector)  light paddles (coated with fluorescent material), serve as detectors, and the radiation interacts with paddles, producing visible light and is transmitted to remote PM tube  the timer is tripped and radiographic exposure is terminated AUTOMATIC EXPOSURE CONTROL AUTOMATIC EXPOSURE CONTROL  Ionization (Ion) Chamber  a hollow cell that contains air and is connected to a timer circuit via an electrical wire  considered entrance-type devices (detectors are positioned in front of the image receptor)  when the chamber is exposed to radiation , air inside becomes ionized, creating an electrical charge. This charge travels to the timer circuit and exposure stops when sufficient charge is received. AUTOMATIC EXPOSURE CONTROL  IMAGE INTENSIFIED FLUOROSCOPY AND OTHER EQUIPMENT  IMAGE INTENSIFIED FLUOROSCOPY  Shortly after Dr. Roentgen’s discovery of x-rays and subsequent announcement, many other scientists began experimenting with this new phenomenon. Among them was the famed American inventor Thomas Edison who has notable inventions in this area was the first commercially available fluoroscope in 1896, although it was not in a form we would recognize today.  His fluoroscope was a calcium tungstate screen that interacted with the remnant beam, producing a very faint image that one viewed while standing in the path of the x-ray beam as it exited the patient and screen. The  IMAGE INTENSIFIED FLUOROSCOPY  Additionally, because the image was very dim, the fluoroscopist had to “dark-adapt” by sitting in a darkened room for a period or by wearing adaptation goggles with red lenses before performing the fluoroscopic examination. However, fluoroscopy’s great advantage, which ensured its continued development, was that it allowed for dynamic radiographic  IMAGE INTENSIFIED FLUOROSCOPY  In the 1950s the image intensifier was introduced into the fluoroscopic system. The image intensifier improved the process in two ways. First, it brightened the image significantly, eliminating the need to dark-adapt and improving the details that could be seen. Second, it allowed for a means of indirectly viewing the fluoroscopic image, first by mirror optics and later by television monitors, greatly reducing the radiation dose to the fluoroscopist. IMAGE INTENSIFIED FLUOROSCOPY IMAGE INTENSIFIED FLUOROSCOPY  Schematic Diagram of a fluoroscopic system using an X-ray image intensifier (XRII) and video camera  IMAGE INTENSIFIED FLUOROSCOPY  Conventionally the fluoroscopic chain consists of an x-ray tube, an image intensifier, a recording system, and a viewing system. The integration of digital technology is changing parts of this system, as is discussed at the end of this chapter. Here the focus is on the design and function of the image intensifier, recording, and viewing systems.  IMAGE INTENSIFIED FLUOROSCOPY  The image intensifier is an electronic vacuum tube that converts the remnant beam to light, then to electrons, then back to light, increasing the light intensity in the process. It consists of five basic parts: the input phosphor, photocathode, electrostatic focusing lenses, accelerating anode, and output phosphor.  The input phosphor is made of cesium iodide and is bonded to the curved surface of the tube itself. Cesium iodide absorbs the remnant x-ray photon energy and emits light in response.  The photocathode is made of cesium and antimony compounds. These metals emit electrons in response to light stimulus in a process called photoemission. The photocathode is bonded directly to the input phosphor using a very thin adhesive layer. These layers are curved so that all of the electrons emitted from the photocathode travel the same distance to the output IMAGE INTENSIFIED FLUOROSCOPY  IMAGE INTENSIFIED FLUOROSCOPY  The electrostatic focusing lenses are not really lenses at all, but are negatively charged plates along the length of the image intensifier tube. These negatively charged plates repel the electron stream, focusing it on the small output phosphor.  To set the electron stream in motion at a constant velocity, an accelerating anode is located at the neck of the image intensifier near the output phosphor. This accelerating anode maintains a constant potential of approximately 25 kV.  The output phosphor is made of silver-activated zinc cadmium sulfide and is much smaller than the input phosphor. It is located at the opposite end of the image intensifier tube, just beyond the accelerating anode. This layer absorbs electrons and emits light in response.  INTENSIFICATION PRINCIPLES  The radiographer must be familiar with several principles and concepts associated with image intensification. Brightness gain is one such principle. Brightness gain is an expression of the ability of an image intensifier tube to convert x-ray energy into light energy and increase the brightness of the image in the process. Traditionally, brightness gain was found by multiplying the flux gain by the minification gain.  INTENSIFICATION PRINCIPLES  Flux gain has to do with the very concept of using an image intensifier to create a brighter image by taking a few x-ray photons and converting that energy into many light photons. Flux gain is expressed as the ratio of the number of light photons at the output phosphor to the number of light photons emitted in the input phosphor and represents the tube’s conversion efficiency.  Minification gain is an expression of the degree to which the image is minified (made smaller) from input phosphor to output phosphor. This characteristic makes the image appear brighter because the same number of electrons is being concentrated on a smaller surface area. It is found by dividing the square of the diameter of the input phosphor by the square of the diameter of the output phosphor. (Generally, the input phosphors are 15 to 30 cm and the output phosphor is usually 2.5  CINERADIOGRAPHY  A diagnostic technique in which a camer a is used to record images of internal bod y structures produced through radiography or fluoroscopy.  the making of a motion picture record of s uccessive imagesappearing on a fluorosc opic screen. DIGITAL FLUOROSCOPY  A digital fluoroscopy system is commonly designed as a conventional one in which the analog video signal is converted to and stored as digital data by an analog to digital converter (ADC) (DAC to print image). DIGITAL FLUOROSCOPY DIGITAL SUBTRACTION ANGIOGRAPHY  Digital subtraction angiography requires more complex equipment than digital radiography, specifically because it has to manipulate a number of pulsed images and at the same time create a subtracted image using the first pre contrast image as a mask. DIGITAL SUBTRACTION ANGIOGRAPHY DENTAL X-RAY UNIT  Dental X-rays (radiographs) are images of your teeth that your dentist uses to evaluate your oral health. These X-rays are used with low levels of radiation to capture images of the interior of your teeth and gums. This can help your dentist to identify problems, like  BONE DENSITOMETER  Bone densitometry is a test like an X-ray that quickly and accurately measures the density of bone. It is used primarily to detect osteopenia or osteoporosis, diseases in which the bone's mineral and density are low and the risk of fractures is increased. MAMMOGRAPHY UNIT  RADIOGRAPH PROCESSING (PROCESSING SYSTEM TANKS) for automatic processor developer fixer water for manual processor master tank insert tank  RADIOGRAPH PROCESSING (PROCESSING SYSTEM TANKS)  RADIOGRAPH PROCESSING (PROCESSING SYSTEM TANKS) AUTOMATIC PROCESSOR roller transport system PROCESSING CYCLE / DRY-TO-DROP TIME amount of time it takes to process a single film 45 seconds to 3.5 minutes PROCESSOR CAPACITY refers to the number of films that can be processed per hour  AUTOMATIC PROCESSOR TRANSPORT SYSTEM transports film and controls processing by controlling the time of film to be immersed in each of wet containers an automatic processor uses a vertical transport system FEED TRAY flat metal surface where film is introduced permits film to enter processor easily and correctly aligned ROLLERS / ENTRANCE ROLLERS consists of roller covered with corrugated rubber that straightens the path of the film so that it moves through the processor efficiently AUTOMATIC PROCESSOR TRANSPORT / PLANETARY ROLLERS moves film through the chemical tanks and dryer assembly TURNAROUND / SOLAR / MASTER ROLLER bottom of roller assembly that turns the film from moving down the transport assembly to moving up the assembly all rollers have a diameter of 1 inch except for the master roller which has a diameter of 3 inches CROSSVER ROLLER final type of roller used to move the film from one tank to another and in dryer assembly AUTOMATIC PROCESSOR SQUEEGEE ROLLER used to decrease or squeeze excess water in the film GUIDE PLATES / GUIDE SHOES slightly curved metal plates that property guide the leading edge of the moving film through the roller assembly MOTOR DRIVE electric motor provides power to the roller system on / off switch stand by control shuts off the power to the roller assembles when the processor is not being used AUTOMATIC PROCESSOR  REPLENISHMENT SYSTEM  refers to the replacement of fresh chemicals after the loss of chemicals during processing, specifically developer solution and fixer solution  physical and chemical means of maintaining the level of processing solutions  Microswitch  a device located at the entrance of the automatic processor which controls the replenishment rate of the processing chemicals. Replenishing rates are normally established on the basis of how much chemistry is required per 14 inches of film travel AUTOMATIC PROCESSOR  REPLENISHMENT SYSTEM  Volume Replenishment System  25-50 films used per day  Flood Replenishment System/Standby/Timed  60– 70 cc of developer (4-5 mL/inch)  100 – 110 cc of fixer (6-8 mL/inch) AUTOMATIC PROCESSOR  RECIRCULATION SYSTEM  keeps chemical mixed, which helps maintain solution activity and provides agitation of the chemicals about the film to facilitate fast processing  helps in maintaining proper temperature of the developer AUTOMATIC PROCESSOR  TEMPERATURE CONTROL SYSTEM  an increased or decreased in developer temperature can affect image quality  water temperature is maintained 5°F (2.8°C) below the developer temperature (93-95°F)  Gross Control Temperature/Warm Water Processor  affected by a water mixing valve, a device that interconnects the incoming hot and cold water  Fine Control of Temperature  occurs within the developer tank itself through a thermostatically controlled heating element or by means of a heat exchanger AUTOMATIC PROCESSOR  DRYING SYSTEM  controls the amount of moisture to be removed in order to maintain the archival quality of radiographic film  consists of blower, ventilation ducts, drying tubes and an exhaust system.  completely extracts all residual moisture from the processed radiograph so that it drops into the receiving bin dry.  The dryer blows hot air across the surface of the film.  Temperature of air = 110 to 120 °F to remove surface moisture  The air is continually dried by a humidifier.  The dryer must be vented to release built-up air as new air is pulled into the system.