Projectional Radiography (X-Ray)

Medical Imaging
Written By John Twomey

Video

What

Projectional radiography is the practice of imaging the body's internal structures using X-rays or other forms of high-energy electromagnetic radiation.

X-Ray of Total Hip Replacement

X-Ray of Total Hip Replacement

Why

Projectional radiography is often used for the following purposes:

  • To look at bones in order to see bone fractures, find bone pathology, and to measure bones for growth studies.

  • To look at implanted devices such as an artificial knee or hip.

  • To look for objects in the body that aren't supposed to be there.

  • To look at soft tissues such as the lungs, heart, bowel, neck, orbits of the skull, and soft tissue trauma resulting from bone fractures.

  • To look at the teeth and gums.

  • To look at the breasts to screen for breast cancer and to identify suspicious tissues before a biopsy or a lumpectomy. This specific type of projectional radiography is called mammography.

How

A typical projectional radiography system consists of the following components:

  • X-Ray Tube: This is what produces the X-rays. An X-ray tube is a vacuum tube which applies a high voltage to accelerate electrons released from a hot cathode to an extremely high velocity. These high-energy electrons collide with a metal anode, producing X-rays. The voltage of the X-ray tube and the material of the anode determine the energy of the resulting X-rays. An anode made of tungsten or a more crack-resistant alloy of rhenium and tungsten is typically used to produce high-energy X-rays up to 150 keV for imaging hard tissues. An anode made of molybdenum is typically used to produce low-energy X-rays down to 5 keV for imaging soft tissues in mammography.

  • Collimator: This focusses the X-ray beam by allowing only X-rays traveling in a certain direction to pass through.

  • Patient: The X-rays go through the patient and some of the radiation is absorbed. Denser structures such as bone absorb more X-rays than softer structures.

  • Table and/or Wall Stand: This is what the patient lays on or stands in front of.

  • Bucky-Potter Grid: This may be placed between the patient and the image detector to reduce the quantity of scattered X-rays reaching the detector. This improves the contrast resolution of the image but also increases the radiation exposure for the patient.

  • Image Detector: This is what collects the X-rays that went through the patient to form the image. There are three main types of image detectors. The first type uses X-ray film in combination with an X-ray sensitive screen. The second type uses an image intensifier, which is a vacuum tube coated with caesium iodide that converts the acquired X-ray image into one visible on a video screen. The third type uses digital array detectors, which consist of thin-film transistors that either indirectly detect light emitted from a scintillator material like caesium iodide or directly capture the electrons produced when X-rays hit the detector. Digital detection is becoming the standard image detection method today.

  • User Interface: This is how the user operates the radiography system.

  • Processor or Image Reader: This is what the user uses to view and analyze the X-ray images.

  • Radiocontrast Agent: Projectional radiography is often performed using a radiocontrast agent to improve visibility of the target structures. Common radiocontrast agents include iodine, barium, air, and carbon dioxide.

Components of a Typical Projectional Radiography System

Components of a Typical Projectional Radiography System

X-Ray Tubes

X-Ray Tubes

Image Detectors

Image Detectors

John Twomey https://www.twomeyconsulting.com
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