Week 3: Session 5 – Radiographic Equipment and Controls

Text Explanation for Session 5

1. Components of an X-ray Machine

• X-ray Tube:
  The X-ray tube is the heart of the radiographic machine. It consists of a cathode (negatively charged) and an anode (positively charged). When the machine is activated, the cathode emits electrons, which are accelerated toward the anode. When the electrons collide with the anode’s target material (usually tungsten), X-rays are produced. This process is essential for generating the radiation required to capture an image.

• Collimator:
  The collimator is a box-like device attached to the X-ray tube that helps limit the size and shape of the X-ray beam. Collimators reduce patient exposure by restricting the beam to the area of interest, ensuring that nearby tissues are not unnecessarily exposed to radiation. It is essential to use proper collimation techniques to protect the patient and improve image quality.

• Control Panel:
  The control panel allows the operator to adjust key exposure factors, such as kilovoltage peak (kVp) and milliampere-seconds (mAs).

  • kVp: This controls the energy and penetrating ability of the X-rays. Higher kVp results in X-rays with more energy, enabling them to penetrate denser tissues.

  • mAs: This controls the quantity of X-rays produced, which directly affects the density (blackness) of the radiographic image. Higher mAs means more X-rays are produced, leading to a denser image.

• Grid:
  The grid is a device placed between the patient and the image receptor (detector) to reduce scatter radiation, which can degrade image quality. It consists of thin lead strips that allow primary X-rays to pass through while absorbing scattered radiation. Grids are typically used for body parts larger than 10 cm to improve contrast on the image.

• Image Receptor:
  This is the component that captures the X-rays after they pass through the patient and form the radiographic image. In modern systems, the image receptor can be a Computed Radiography (CR) or Digital Radiography (DR) detector. The type of detector used influences image processing, storage, and quality.

2. Technical Factors and Image Quality

• kVp and Image Quality:
  The kilovoltage peak (kVp) controls the energy and penetration ability of the X-ray beam. Higher kVp results in more penetration, leading to lower contrast images where the differences between tissues are less distinct. Lower kVp results in higher contrast images where differences between tissues are more distinct but can also lead to inadequate penetration in denser body parts.

• mAs and Image Quality:
  Milliampere-seconds (mAs) control the number of X-rays produced during an exposure. Increasing the mAs results in a denser (darker) image, while decreasing the mAs leads to a lighter image. Proper mAs settings ensure adequate exposure and help avoid image repeat due to underexposure or overexposure.

• Collimation and Image Quality:
  Proper collimation improves image quality by reducing scatter radiation, which can fog the image and reduce contrast. Tight collimation around the area of interest also minimizes patient exposure.

3. Exposure Technique Charts

• Purpose of Technique Charts:
  These charts provide recommended exposure settings (kVp, mAs) based on patient size, body part being imaged, and the type of X-ray procedure. They serve as a guide to ensure consistent, high-quality images while minimizing radiation exposure.

• Using Technique Charts:
  The operator selects exposure settings based on the patient’s body part and size. For example, a chest X-ray for a small adult may require a lower kVp and mAs compared to a large adult. By following the technique chart, the LXMO ensures that the image is diagnostic and that unnecessary exposure is avoided.