Physics of Radiography and Radiation Safety

Physics of Radiography and Radiation Safety

• Radiography uses X-rays to create images of internal structures.
• The generation of X-rays involves converting electrical current to electrons, then photons.
• X-ray photons interact differently with different tissues, creating varying shades of grey (contrast) on the image.
• Radiation is a biological hazard and precautions are necessary to minimize occupational exposure.

Learning Objectives

• Students will understand the process of X-ray generation from standard equipment.
• Students will learn the requirements for safe operation of radiographic equipment.
• Students will understand the legal requirements for personnel protection during radiographic exposure.
• Students will be familiar with the preparation steps for animals undergoing radiographic procedures.

X-ray Generation

• X-ray machines consist of a generator, tube, and an imaging device (e.g., film, screen or digital detector)
• Photons emitted from the generator are targeted at the patient.
• The patient's anatomy creates different levels/intensity of contrast on the imaging device.
• The output image of the patient is captured on film, screen, or a digital detector.

X-ray Tube

• Tungsten target acts as the anode. This target emits the x-ray photons.
• A cathode produces the electrons necessary to generate the X-rays.
• The x-ray beam is collimated (shaped) to better target the patient.

Exposure Settings

• kVp (Peak Kilovoltage): Controls the energy of electrons, affecting the penetration power of the X-ray beam. Increasing kVp leads to more photons and increased penetration.
• mA (Milliamperage): Controls the number of electrons produced, increasing the intensity/quantity of the X-ray beam.
• Time (Seconds): Determines the duration the X-ray beam is on, also influencing the intensity/quantity.
• FFD (Film Focal Distance): The distance between the X-ray tube and the imaging device. It influences the spreading of the beam and affects density and contrast.

mA and Time

• mA × time (mAs): Reflects the intensity of the X-ray beam.
• Increasing mAs leads to more X-ray photons and greater intensity.

Film Focal Distance (FFD)

• FFD = the distance between the focal spot of the X-ray tube and the image receptor.
• The radiation intensity is inversely proportional to the square of the FFD (1/FFD²).

Interaction of X-rays with Matter

• Absorption: Energy is transferred to the patient, contrast between tissues is created. Absorption increases with increasing atomic number of the material.
• Scatter: Energy is deflected away from the patient, reducing image quality and potentially harming the radiographer. Scatter is worse with higher kVp.

Interaction of X-rays with Film/Screen Detectors

• Image recorded on film or intensifying screens is a result of how X-ray photons interact and are absorbed along with differing amounts of film blackening, resulting in differing degrees of contrast.
• Overexposure: excessive film blackening.
• Underexposure: insufficient film blackening.

Interaction of X-rays with Various Tissues

• Gas: appears very dark or black on a radiograph.
• Fat: appears grey.
• Soft tissue/fluid: appears intermediate grey.
• Bone: appears white.
• Metal: appears very white or bright white.

Recording and Displaying the Image

• X-ray film uses silver bromide crystals. The photon interacts with the crystals, causing them to become latent images that can be developed.
• Chemical processing converts the latent image to a viewable image.
• More modern systems use intensifying screens and cassettes which reduce occupational exposure, improve image quality, and reduce exposure times.

Digital Radiography

• Digital radiography uses image plates that are sensitive to X-rays. This sensitive plate is scanned, converting energy into a digital format, immediately accessible on a monitor.

Radiation Safety

• Work practices should be followed for proper radiation safety precautions.
• ALARA technique: radiation is kept as low as reasonably achievable for personnel and the patient.
• Shielding, and distance control reduce exposure to personnel.

Principles of Radiation Protection

• Radiography should only be used when necessary.
• Exposure of personnel should be kept to a minimum.
• No legal dose limits should be exceeded.

Limiting Occupational Exposure

• Time: Limit exposure time with staff rotation.
• Distance: Position personnel at a safe distance, and to maximize the distance from the machine to the operator and patient.
• Shielding: Use appropriate personal protective equipment (PPE) and structural shielding.

Patient Preparation

• Elective procedures vs. emergencies: preparation varies between electivity vs. emergency, including food, positioning and restraint, and coat cleaning.
• Imaging type, view(s), and patient positioning should be planned before the procedure.

Monitoring Personal Exposure

• Personal dosimeters are used to monitor radiation exposure levels for staff. Badges are worn, stored outside areas, and changed regularly.

Summary

• X-ray images are created from electrical impulses converting into photons and interacting with tissue.
• Tissue density affects how photons interact causing varying shades of grey, and ultimately the visible image.
• Radiation safety is crucial to prevent occupational exposure dangers.

This quiz covers the fundamental principles of radiography, specifically focusing on X-ray generation and radiation safety protocols. Students will learn about the processes involved in X-ray imaging and the necessary precautions for minimizing exposure. Essential legal and operational requirements for safe radiographic practices will also be examined.