What is X-ray

X-ray is an important diagnostic tool for veterinary practitioners. Since its discovery, X-ray technology has relatively remained the same. However, the process of radiograph production has evolved dramatically, particularly the introduction of digital radiography. Digital radiography has revolutionized the efficiency of radiograph production and dissemination.
The aim of this article is to highlight the fundamental aspects of X-ray production and shed light on the various type of X-ray systems currently available for veterinary practice. With a focus on the benefits of digital radiology.

In 1895, X-rays were discovered by Wilhelm Conrad Roentgen. Roentgen (1895) discovered that the application of a high voltage to a cathode‐ray tube resulted in the fluorescence of phosphorescent material in the room and determined that this resulted from exposure to a previously unknown form of electromagnetic radiation which he called ‘X’‐rays.
According to Roentgen (1895), X-ray photons are created as a result of electrons hitting metal when traveling at high speed. This is done by applying an electric current to a cathode (negative electrode) using a high voltage power source which then enables electrons to be released from the cathode into the X-ray tube. once these electrodes are negatively charged, they are attracted to the positive electrode (anode). When the electrons hit the anode, it creates heat and X-rays.

Radiographic exposure factors
The quality X-ray images are influenced by a number of exposure factors. These exposure factors are integral to the quality of the Image and need to be manipulated accordingly to achieve a quality X-ray image.
• Milliamperage (mA) – This is the current that is applied to the cathode of the X-ray tube to produce X-rays. A greater amount of X-ray is produced when the mA is higher.
• Time (seconds) – This is the length of time that X-rays are being produced during each exposure. A longer exposure time produce more X-rays.
• mAs – The milliamperage and the time are often combined on the generator settings as the mAs. Therefore, to achieve a given number of X- rays per exposure, as mA is increased, exposure time is shortened.
• Kilovoltage (KV) – This is the voltage that is applied across the X-ray generator at the time of X-ray production. An increase in KV increases the energy of the X- rays. This then increases the ability of the X-ray beam to penetrate the patient’s tissue.

It is a combination of the above factors which determines the overall exposure of a radiographic image. If an X-ray image is deemed to be underexposed, increasing either the mAs or the KV will result in greater radiographic exposure. It is also advised to not only asses the radiograph for adequate exposure, but to also asses the quality of the image. This will then enable individual exposure factors to be altered to optimize image contrast, brightness, and clarity.

Type of X-ray systems
Analog X-ray (film screen) system – Analog radiography is the traditional method of producing X-ray images. an exposed film undergoes wet- processing. The primary components of the Analog X-ray are as follows:
• X-ray cassette – the X-ray cassette is a flat, light-tight box with clips
• Intensifying Screens – intensifying screens are used to convert X-ray into visible light.
• Radiographic film – the film is a polyester base, coated with an emulsion of gelatin containing fine silver halide crystals. These crystals are sensitive to X-rays, ultraviolet and visible light, as well as physical pressure, chemicals, and gasses.

Digital X-ray systems – Digital X-ray uses the same generator as conventional X-ray systems to produce X-rays. However, the image is produced using a capture device (plate) to capture X-rays. This is then converted to digital signals and displayed on a computer.

There are currently two types of digital X-rays available in today’s market- Computed Radiography (CR) and Direct Digital radiography (DR).
Computed Radiography – computed radiography uses a portable image plate that contains an interior screen, which records the raw image of the patient. The exposed plate is then manually placed in a digital reader, the interior screen is then scanned by a laser and a digital X-ray image is then produced. The image can then be manipulated and viewed using computer software.
Direct Digital Radiography– Direct digital X-ray systems are similar to the computed X-ray system; however, the user does not have to place the image plate in a digital reader. The image is sent directly from an X-ray detector plate directly to the computer.
The differences between conventional X-ray and digital X-ray system
Digital X-ray systems have multiple advantages over conventional X-ray system:
• Faster image acquisition
• Wider latitude
• Post-exposure image manipulation (brightness and contrast)
• Able to zoom, crop, measure and add annotations
• No need to wet-process image