PRINCIPLES OF XRAY.pptx principle of xra

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1. PRINCIPLES OF XRAY A SEMINAR PRESENTATION BY, Rad Zainab Adam & Rad Ojukwu Stephanie Department Of Radiodiagnosis , Lagos University Teaching Hospital.

2. LEARNING OBJECTIVES Introduction Equipment Physics Image generation Patient safety considerations

3. INTRODUCTION Electromagnetic radiation refers to waves of energy that travel through space, consisting of electric and magnetic fields that oscillate perpendicular to each other and to the direction of wave propagation. It covers a wide spectrum which includes visible light, radio waves, microwaves, infrared, ultraviolet light, x-rays and gamma rays X-rays are a form of electromagnetic radiation, discovered by Wilhelm Conrad Roentgen in 1895 with wavelengths shorter than visible light making them capable of penetrating various materials, including human tissues making them essential in medical imaging

4. EQUIPMENT The general radiographic room contains a few basic components to produce x-ray beams: The x-ray tube Collimator Detector/film Control console

5. The x-ray tube The major components of the modern x-ray tube are Cathode : It is the negative electrode in an X-ray tube and is made of a tungsten filament. It is the source of electrons through a process called thermionic emission. This electrons are focused into a beam and directed towards the anode. Anode: It is the positive electrode in an X-ray tube and has a tungsten target material. It is where x-rays are produced. The anode could be stationary or rotating stationary anodes were used in the past, but their small focal spot limited x-ray production without damaging the anode. Modern x-ray machines uses rotating anodes which helps spread heat over a larger area, allowing for higher tube currents and longer exposure times without overheating

6. iii. Rotor/stator : The rotor consists of a center iron cylinder with surrounding copper bars. The stator device is made of electromagnets that surround the rotor. When the X-ray tube is turned on, the stator generates a rotating magnetic field. This field causes the rotor to spin, which in turn rotates the anode. The rotation spreads the heat generated by the electron impact over a larger area on the anode, preventing overheating and allowing for more powerful and longer X-ray exposures. iv. Glass/ metal envelope : this contains the anode assembly and cathode assembly. It is a vacuum sealed tube usually made of glass or metal so that electrons can move freely without colliding with air molecules v . Tube housing : provides shielding and cooling of the X-ray tube insert. There is a layer of oil or air between the envelope and the housing that provides heat conduction and electrical insulation

7. The collimators : it controls the size and shape of the x-ray field. A light source is placed at a virtual focal spot location and is reflected by a mirror angled at 45 degrees. It consists of two pairs of parallel opposed lead shutters that block portions of the beam. Film/detector: In traditional X-ray systems, X-rays pass through the body and expose a photographic film, which must then be chemically developed to produce a visible image. This is similar to how photographic film works in older cameras.Digital Radiography (DR): Modern X-ray systems use digital detectors to capture X-rays directly and convert them into digital images Control Console: The operator uses this to adjust exposure settings like voltage ( kVp ), current (mA), and exposure time. Other equipments include the table, bulky system, high voltage generator,grid.

8. IMAGE PHYSICS A low-voltage current is supplied to the filament within the cathode to heat it up. When the filament gets hot, it undergoes thermionic emission, where electrons are "boiled off" and released from the surface of the filament. Simultaneously, a high-voltage potential (typically in the range of 30–150 kV) is applied between the cathode and the anode using the high-voltage generator. This creates a strong electric field within the tube, causing the electrons emitted from the cathode to be rapidly accelerated toward the anode. The energy the electrons gain while being accelerated toward the anode comes from the high-voltage difference applied across the tube. When the high-speed electrons collide with the tungsten target in the anode, their kinetic energy is converted into X-ray photons and heat.

9. X-rays are produced in the X-ray tube by two interactive processes between incoming electrons and the atoms of the target: 1. Bremsstrahlung : The term Bremsstrahlung is German for "braking radiation”. In an X-ray tube, electrons are accelerated toward the tungsten target by a high voltage. When these electrons approach the positively charged nucleus of a tungsten atom, they are slowed down due to the attractive force of the nucleus. As the electron loses speed (energy), this lost energy is emitted in the form of an X-ray photon. 2. Characteristic radiation : In an X-ray tube, an accelerated electron with enough energy strikes the tungsten atom, knocking an electron out of its inner shell (K-shell). An electron from a higher energy level (L-shell, M-shell, etc.) drops down to fill this vacancy. The energy difference between the shells (K and L, for example) is released as an X-ray photon.

10. COMPARISON Bremsstrahlung radiation Characteristic radiation Produced when high-speed electrons are decelerated near the nucleus of a target atom. Produced when an electron from an inner shell of the target atom is ejected, and an electron from an outer shell drops down to fill the vacancy. The energy of the X-rays varies, depending on how much the electron is slowed down. The energy of the X-rays is fixed, determined by the difference in energy between electron shells. Responsible for the majority of X-rays produced in an X-ray tube Contributes a smaller but significant portion of the total X-rays, especially at specific energy levels. Occurs at all energy levels within the tube. Requires the incoming electron to have enough energy to eject an inner-shell electron.

11. X-RAY INTERACTION WITH MATTER Here are the primary types of interactions between X-rays and matter: Photoelectric Effect : an X-ray photon is completely absorbed by an atom, resulting in the ejection of an inner-shell electron from that atom . The energy of the incoming photon must be greater than the binding energy of the electron it interacts with. When this occurs, the photon transfers all its energy to the electron, causing it to be emitted from the atom . This interaction creates a vacancy in the inner electron shell. An outer-shell electron then fills this vacancy, releasing energy in the form of a secondary X-ray photon . It contributes significantly to image contrast in radiographic imaging, as dense materials absorb more X-rays.

12. COMPTON SCATTERING It occurs when an X-ray photon collides with a loosely bound outer-shell electron, resulting in partial energy transfer and scattering. The incoming photon loses some of its energy to the electron, which is then ejected from the atom. The photon is scattered at a different angle with reduced energy (longer wavelength ). The ejected electron (called a Compton electron) has kinetic energy equal to the difference between the energy of the incoming photon and the energy of the scattered photon . Compton scattering is the most common interaction in soft tissues and contributes to the dose delivered to patients

13. IMAGE GENERATION

14. Film-based X-ray imaging This is often referred to as traditional radiography, relies on photographic film to capture X-ray images. T he X-ray tube emits X-rays that pass through the patient. Behind the patient, a radiographic film is placed in a light-tight cassette. The film consists of a photographic emulsion coated on a flexible base, typically made of polyester . The x-ray photons they interact with the film, exposing it After exposure, the film must be developed to produce a visible image through chemical processes : Development: The exposed film is immersed in a developer solution that reduces the exposed silver halide crystals in the emulsion to metallic silver, creating a visible image. The developer also acts on areas of the film that were exposed to X-rays, causing them to darken.

15. Stop Bath : After development, the film is rinsed in a stop bath to halt the development process, preventing overdevelopment. Fixing : The film is then placed in a fixer solution that removes unexposed silver halide crystals, making the image stable and light-resistant. Washing: Finally, the film is washed to remove any remaining chemicals, ensuring that it can be stored without degrading. Drying and Viewing : After development, the film is dried and can be viewed. The resulting radiograph is a permanent record that can be interpreted by radiologists.

16. Computed Radiography (CR) This is a bridge between traditional film-based X-ray and full digital radiography. The X-ray tube emits X-rays that pass through the patient and instead of using film, the X-rays are captured on a photostimulable phosphor plate (PSP). The PSP is coated with materials such as barium fluorohalide , which temporarily store the energy from the X-rays in the form of trapped electrons. After the X-ray exposure, the imaging plate is placed in a CR reader. Inside the reader, the plate is scanned by a laser beam, which releases the stored energy in the form of visible light. The emitted light is detected by photomultiplier tubes (PMTs) in the CR reader, which convert the light into an electrical signal. This electrical signal is then digitized to form a digital X-ray image. The digital image is processed by a computer. Adjustments such as contrast enhancement and noise reduction can be made to improve image quality. The image is displayed on a monitor and can be stored digitally.

17. Direct Digital Radiography (DR) This is the more advanced of the two digital systems. It uses flat-panel detectors to convert X-ray photons directly into electrical signals without any intermediate processing steps The X-ray tube emits X-rays, which pass through the patient's body and reaches the flat-panel detector, which contains either amorphous selenium (for direct conversion) or amorphous silicon (for indirect conversion with a scintillator ). The X-rays are directly absorbed by the amorphous selenium detector, which produces a charge. the flat-panel detector uses a scintillator layer (typically made of cesium iodide) to convert X-rays into visible light photons. These light photons are then detected by photodiodes, which convert them into an electrical charge.

18. The electrical signals from the detector are collected by thin-film transistors (TFTs), which process the signals and form a digital representation of the X-ray image. The digital image data is then sent to a computer workstation for processing. Software can enhance the image by adjusting brightness, contrast, and sharpazazness for optimal viewing . The final image is displayed on a monitor and can be adjusted in real-time for diagnosis. The digital format allows for easy storage in a PACS

19. PATIENT SAFETY CONSIDERATIONS Radiation Exposure : X-rays involve ionizing radiation, which can damage tissues and DNA. To minimize exposure, the ALARA principle (As Low As Reasonably Achievable) is used. Shielding: Lead aprons and shields are often used to protect sensitive body parts, especially reproductive organs. Dose Limitation : Proper equipment settings, including low-dose techniques, can reduce unnecessary radiation exposure. Frequent monitoring and calibration of equipment are essential. Pregnancy Considerations : Extra precautions are necessary for pregnant women to avoid exposure to the fetus. Positioning and Communication : Proper patient positioning reduces the need for repeat exposures, and clear communication ensures that the patient remains still during the procedure, further reducing risk.

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