Basic Physics for Todays Radiographer

Wilhelm Conrad Roentgen Matter versus Energy: Matter - anything that occupies space and has form or shape Energy - the ability to do work Energy can exist in several forms: Potential Kinetic Chemical Electrical Thermal (heat) Nuclear Electromagnetic E = mc2 Radiation Ionizing Radiation Non-Ionizing Radiation Radioactivity Electromagnetic energy / Electromagnetic radiation Alpha Rays Beta Rays Gamma Rays Neutrons X-Rays   Legend: 1-Paper 2-Plastic 3-Lead 4-Concrete Ionizing Radiation Types Learn about the types of Ionizing Radiation Element HTMLParticulate Radiation Alpha particles Beta particles Electromagnetic Radiation X rays Gamma Rays When complete, select the X in the upper-right corner to close the window and continue. Sound File Audio ScriptIonizing Radiation can be classified into two categories: particulate radiation and electromagnetic radiation. We’ve just learned that alpha and beta particles travel a short range through matter that they can be shielded by a piece of paper. They are types of particulate radiation. X rays and gamma rays are considered electromagnetic radiation. These two types of radiation are often called photons. They have no mass and no charge and travel at the speed of light. In the Radiology field, only x-rays are of prime importance.   Roentgen (R) RAD (radiation absorbed dose) REM (rad equivalent man) Curie (Ci) Gray (Gy) Sievert (Sv) Atoms Elements Molecules Compounds 2H2 + O2 ⇒ 2H2O (water)   or     Sodium Bicarbonate   Helium Has an atomic number of 2 Elemental mass of 4.0026 The three primary constituents of an atom are: Electron (-) Proton (+) Neutron (0) The Atom: Nucleus (protons +) and (neutrons 0 ) Number of protons determines the chemical element, or behavior of the atom Nucleus contains all the mass of the atom The Electron: Negatively charged Orbits the nucleus in the orbiting shell In a neutral atom the number of electrons equals the number of protons Electromagnetic energy Photon Quantum Velocity and Amplitude Photons Travel at the speed of light (186,000 miles per second) Move in a sine wave fashion Alternating current Amplitude Crest Valley Amplitude Amplitude Amplitude Frequency and Wavelength Frequency Number of wavelengths Wavelength Distance between wavelengths Wave parameters Velocity Frequency Wavelength Three important regions Visible light Radiofrequency X-radiation Ionizing Radiation X-rays Gamma rays Wave-particle duality Visible light photons X-ray Photons Visible Light Transmission – Transparent Attenuation – Translucent Absorption – Opaque Relationship between radiation intensity and distance from source Distance from source is doubled, the intensity of radiation is reduced by one fourth X-rays are identified by their energy Measured in electron volts (eV) Planck’s quantum theory Planck’s constant Primary function of an x-ray machine Conversion of electrical energy Unit of electric potential volt (V) Electrical charge Positive  (+) Negative (-) Electrodynamics - the study of electrostatic charges in motion Conductors Insulators Electric currents measure in amperes (A) Direct current (DC) Alternating current (AC) Measured in watts (W) Electricity Magnetism Electromagnetic force (EMF) Right hand rule Wire Current Direction of Magnetic Field Lines Solenoid Electromagnet Self-induction Mutual Induction Primary Secondary Transformers Step-Up transformers Increases voltages and decreases amperage Step-Down transformers Decreases voltages and increases amperage Rectification Rectification is converting AC to DC Tube rectifiers Three basic parts include: X-ray tube Generator Control console X-ray Tube in Roentgens Lab (X-ray tube used to image arm in background)   Diagnostic x-ray machines Voltage (kVp) Tube currents (mA) X-ray Tube and Protective Housing Learn more about the X-ray tube and its protective housing. Element HTMLX-ray tubes consist of two primary parts: Cathode Anode Electrode - each cathode and anode Diode - any tube made up of two electrodes  CathodeAnodemAkV-+Diagram of the tube unit  Protective housing  Protective housing   Isotropically Window Useful Beam Leakage Radiation AnodeWindowCathode Electrical Insulator Thermal Cushion OilHousing portPlastic coverMirrorAluminum plateX-ray tube windowGlass Housing X-ray tube 8 to 12 inches long 6 inches in diameter Tube window is approximately 5cm square When complete, select the X in the upper-right corner to close the window and continue. Sound File Audio ScriptThe x-ray tube is made up of two primary parts: the cathode and the anode. Each of these is called an electrode, any tube made up of two electrodes is called a diode. The x-ray tube is a component of the x-ray machine that is rarely seen by the technologist. It is contained in a protective housing that the technologist does not have access to. The x-ray tube is mounted inside a metal lead-lined  protective housing. This protective housing protects the technologist from excessive radiation and electric shock. When x-rays are produced, they are emitted isotropically, meaning in all directions, we want to use only those emitted through the window. Those x-rays emitted through window are called the useful beam. The other x-rays that penetrate through the protective housing are leakage radiation; they are of no diagnostic information and result in unnecessary exposure to the patient and the technologist. The protective housing reduces the level of the leakage radiation to less than 100 mR/hr at 1 meter when operated at maximum conditions. The protective housing around some x-ray tubes contains oil that is sealed and acts as both an electrical insulator and a thermal cushion. The protective housing may also have a cooling fan to air-cool the tube or the oil which the tube is surrounded in. The x-ray tube is an electronic vacuum tube. The glass envelope is usually made of Pyrex glass, which withstands tremendous heat. The vacuum allows for more efficient x-ray production and longer tube life. The x-ray tube is 8 to 12 inches long and 6 inches in diameter. The useful beam of x-rays exit through the tube window. This window is approximately 5 cm square, and contains a thin section of glass where the x-rays are emitted.   Cathode Learn more about the Cathode. Element HTMLCathode (negative) Filament Made of thoriated tungsten 3380º C melting point Does not vaporize easily 1% to 2% of thorium added to the tungsten filament increases efficiency and tube life Focusing cup (negatively charged) Filament imbedded in the focusing cup Condenses the electron beam Filament Current (amperes) Tube Current (mill amperes) Tube Voltage (kVp) AnodeWindowCathode  Space Charge  FilamentFocal Spots Small Large Guide grooveL/IIS/IC/0L/IIC/0S/IGS,I  = Small focal spot L,II = Larger focal spot C,0 = Neutral conductor G    = GridWhen complete, select the X in the upper-right corner to close the window and continue. Sound File Audio ScriptThe cathode is the negative side of the x-ray tube and is made up of the filament and the focusing cup. The filament is a very small coil of wire that is about 2mm in diameter and 1 to 2 cm long. When the current that is going through the filament is intense enough, it emits electrons. The outer-shell electrons of the filament atoms get so hot that they are ejected from the filament. This term is called thermionic emission. Therm stands for heat, ionic for the ionized atoms of the filament, and emission for the electrons that are emitted from the filament. The filament is usually made of thoriated tungsten, which has a melting point of 3380º C (Celsius) and is unlikely to burnout. It does not vaporize easily and by the addition of 1% to 2% of thorium added to the tungsten filament it increase efficiency of thermionic emission and prolongs tube life. The filament is imbedded in the focusing cup, which is negatively charged. It condenses the electron beam to a small area of the anode. The x-ray tube current is controlled by changing the filament current. A small change in filament current results in a large change in tube current. When talking about the space charge we are speaking of the cloud of electrons that form around the filament. These are the electrons that have been emitted by the filament and remain around the filament before being accelerated to the anode. The dual filament cathode means that the x-ray tube has two focal spots. One small focal spot, which with the Siemens tube is .6mm, and a large focal spot, which with the Siemens tube is 1.0mm. Remember the filaments are embedded in the focusing cup, the smaller filament is the small focal spot, while the larger filament is the large focal spot. When you pick either the small or large focal spot you have just directed where the electric current flows. The focal spot is the area where the x rays are emitted and the source of radiation. The smaller the focal spot the sharper the image.   Anode Learn more about the Anode. Element HTMLPositive side of the x-ray tube Stationary anode Rotating anode BearingsHigh voltage circuitStatorStatorEvacuated envelopeRotorFocal spotAnode diskStemFunctions of anode Receives electrons Conducts them to the connecting cables Then to the high-voltage section of the x-ray machine CathodeAnodemAkV+- Electrical conductor Mechanical support Thermal conductor 95% of energy converted to heat Target Tungsten High atomic number Good thermal conductor High melting point 3380º C CathodeElectronAnodeInduction Motor Electromagnetic Stator Rotor To anode cableGlass envelopeRotorStatorThree-phase stator312PIN "1"PIN "2"PIN "4"SupportsWhen complete, select the X in the upper-right corner to close the window and continue. Sound File Audio ScriptThe anode is the positive side of the x-ray tube. There are two types of anodes, the stationary anode, which is used in dental x-ray machines, portable machines, and other equipment where high tube current and power are not required. Most general purpose x-ray tubes are rotating anodes due to they must be able to produce high-intensity x-ray beams in a short time. The three functions of the anode are to: receive electrons, conduct them to the connecting cable and then to the high-voltage section of the x-ray machine. The anode is an electrical conductor. It provides mechanical support for the target, and must be a good thermal conductor. When the electrons hit the anode more than 95% of their kinetic energy is converted into heat. The heat must be conducted away quickly so it does not melt the anode. When we speak of the target we are talking about the area of the anode that is struck by electrons from the cathode. In the stationary anode tubes the target consists of a tungsten-alloy metal that is embedded in the copper anode. In the rotating anode tube the entire rotating disc is the target. The target is made of tungsten, which withstands the stress of high rotation. Tungsten has a high atomic number, which means a higher efficiency x-ray production and higher energy x-rays. Tungsten's thermal conductivity makes it an efficient metal for dissipating the heat that is produced. Tungsten also has a high melting point of 3380º C (Celsius) and can handle the high tube current. If you’ve been wondering “how does the anode rotate”? It’s because it is driven by the electromagnetic induction motor, which consist of the stator and the rotor which are separated by the glass envelope. The stator is outside the glass envelope, and consists of a series of electromagnets. Inside the glass envelope is the rotor, which consists of a shaft made of bars of copper and soft iron fabricated into one mass. The current that flows in the stator produces a magnetic field that transverses the rotor.   High frequency generators Direct current (DC) Alternating current (AC) kVp MA mAs Focal spot AEC Electron-Target Interaction X-ray machine Kinetic energy – energy of motion Acceleration – kVp Projectile electrons Anode heat   Cathode Anode Electron Characteristic radiation K x-rays 70 keV Incident Electron Electron Ejected Leaving A "Hole" Characteristic X-ray Photons O-Shell N-Shell M-Shell L-Shell K-Shell Bremsstrahlung radiation Slowing down or braking Involves nucleus Shift in direction kVp mA Time Filtration X-ray Energy Fig. 8-7 General from emission spectrum Number of X-ray Per Unit Energy Discrete x-ray spectrum Characteristic x-rays – fixed energies Continuous x-ray spectrum Bremsstrahlung x-rays – from 0 to maximum value Quality – kVp Quantity – mA and mAs   Adding filtration Absorbs more low energy x rays More effective energy 2.5mm aluminum Compton effect Scattered x-rays Photoelectric effect Absorbed x-rays Differential absorption Bone Soft tissue Barium Atomic number of 56 Iodine Atomic number of 53 Control scatter radiation Effect the contrast of the image Grid Ratio Dimensions on a grid Thickness of grid material (radiopaque part) Thickness of interspace material (radiolucent part) Height of the grid Grid ratio  = Height of grid stripes                               Thickness of interspace   Grid frequency Pb15/80 15:1 grid with 80 lines/cm Pb17/70  17:1 grid with 70 lines/cm Ysio® Control Display Indirect conversion process is where the X-ray radiation is converted into light, which in turn is absorbed, creating electric charge. Incident X-ray Photoelectric absorption in the scintillator Ionization and generation of light quanta Conversion of light into electric charge in the photodiode Amorphous silicon active readout matrix circuitry Fig. 2 Schematics of the indirect conversion process X-ray   Indirect Converting Flat Detector Learn more about Indirect Converting Flat Detectors. Element HTMLSchematic view of an indirect converting flat detector based on CsI and an amorphous silicon active readout matrix  X-ray radiationCesium iodide (CsI)Driver electronicsTFTPhoto diodePixelReadout electronicsWhen complete, select the X in the upper-right corner to close the window and continue. Sound File Audio ScriptSchematic view of an indirect converting flat detector based on Cesium iodide and an amorphous silicon active readout matrix. The indirect converting flat detector is made of an absorption layer called the scintillator, in this diagram it is Cesium iodide. This layer acts as a light –guide and ensures that the light reaches the photodiode with minimal scatter.  Cesium iodide has a very high X-ray absorption property. This makes it the scintillator of choice for general radiography, angiography and fluoroscopy which require a wide range of kVp from 45kVp to 120kVp.   DQE has evolved as the fundamental physical parameter describing the performance characteristics of an X-ray detector. It describes a detector’s ability to convert efficiently the available X-ray radiation at it’s input into a useful image signal at its output. A high DQE is a precondition for dose saving without compromising image quality The TriXell Pixium 4600 detector acquires images in a 14 bit depth Has a matrix size of 43x43cm² Pixel pitch 143µm (3.5 Lp/mm) Exhibits very low electronic noise Shows a linear response as a function of dose Allows for a large dose range In Radiography, image processing takes on an important role, since it can provide additional diagnostic information. With analog screen/film systems image processing is not available in the digital format. With digital imaging you are able to change the image processing factors. This depends on the quality of the original image, algorithms are able to change the stored digital pixel values of the raw data, 14 bit image, into an image with improved results. 1895 Roentgen discovers x rays 1896 First medical applications of x rays in diagnosis and therapy 1900 First radiology organization formed 1901 Roentgen receives the first Nobel Prize in physics 1905 Einstein introduces his theory of relativity E = mc² 1920 The ASRT is founded 1929 Introduction of the rotating anode tube 1942 Morgan exhibits an electronic photo timing device 1948 Coltman develops the first fluoroscopic image intensifier 1951 Multidirectional tomography introduced 1953 The rad is officially adopted as the unit of absorbed dose 1956 Automatic film processing is developed Wave parameters describe a photon of electromagnetic radiation: Velocity Frequency Wavelength