Radiology - Learning the Basics Dr. B. Justin William

X-Ray Production Acceleration of electrons with a high voltage and allowing them to collide with a metal target X-rays are produced when the electrons are suddenly decelerated upon collision with the metal target These x-rays are commonly called bremsstrahlung or "braking radiation"

If the bombarding electrons have sufficient energy, they can knock an electron out of an inner shell of the target metal atoms. Then electrons from higher states drop down to fill the vacancy, emitting x-ray photons with precise energies determined by the electron energy levels. These x-rays are called Characterisitc X-rays

X-Ray Properties X-ray production by energy conversion. Events 1, 2, and 3 depict incident electrons interacting in the vicinity of the target nucleus, resulting in bremsstrahlung production caused by the deceleration and change of momentum, with the emission of a continuous energy spectrum of x-ray photons. Event demonstrates characteristic radiation emission, where an incident electron with energy greater than the K-shell binding energy collides with and ejects the inner electron creating an unstable vacancy. An outer shell electron transitions to the inner shell and emits an x-ray with energy equal to the difference in binding energies of the outer electron shell and K shell that are "characteristic" of tungsten.

Opacity Opacity is a description of the radiographic appearance of an object. If refers to how many x-rays are allowed to pass through that object. Object that allow many x-rays to pass through are black on a radiograph. Objects that do not allow many x-rays to pass through are white. Whiter areas on a radiograph are more opaque than black ones. Whiter areas are called radiopaque. Blacker areas are called radiolucent.

1. Gas: organs such as lungs and a gas within the stomach have a gas opacity 2. Fat: falciform fat, perirenal fat 3. Fluid or Soft tissue: all soft tissues structures are of soft tissue opacity 4. Mineral: bone 5. Metal: fracture fixation devices, arrowheads, gun shot pellets, barium

More radiation is absorbed by more dense objects (bone). Therefore, fewer x-rays will expose the film. The film under these areas will be underexposed and the part will appear whiter on the radiograph. Bones are radiopaque. Conversely, less dense organs (lungs) will have less interaction. This will allow more x-rays to hit the film and the organ will appear black on the radiograph. Lungs are radiolucent.

kVP kVp: kilovoltage potential. –kVp describes the electrical potential across the x-ray tube when x-rays are produced. –kVp affects both the energy of the x-ray beam and the number of x-rays produced. The energy of the x-rays determines if they can penetrate an anatomic part. –Increasing kVp will increase the penetrability of the x-ray beam and therefore increase the exposure of the film since it increases the number of x-rays, which have sufficient energy to penetrate the subject. –Increasing kVp will also increase the exposure because more x- rays are produced. –kVp is also a major determinant of contrast

mAs mAs: milliamperage seconds mA stands for milliamperage. S stands for seconds. mAS is the product of these two( mA x S = mAs) mAs describes the amount of current applied to the cathode. mAs determines the number of electrons that are boiled off of the cathode filament. mAs represents the number of x-ray photons that are produced by the anode. mAs is important because it is one of the settings you must give the x-ray machine before you expose a radiograph

Contrast Subject Contrast Film contrast Development Time KvP –Increasing kVp decreases film contrast by a producing many shades of gray –Increasing kVp increases the amount of scatter radiation formed Scatter decreases image quality by decreasing contrast FFD closer the object is to the film the better focal film distance of less than thirty inches results in significant magnification. In general, the tube is places 40 inches from the film

Portable X-ray Units Widely used in Veterinary Practice Suitable for Radiography of limbs below stifle and elbow joint in Large Animals Output is mAs and kV

Mobile X-ray Large transformer mounted on wheels Output 90kV to 125 kv and mAs

Fixed X-ray Machine Output 100 to 1000 mA 120 to 200 kV

Accessory Equipment Lead Aprons and Gloves –0.5mm thickness gloves and 0.25mm thickness lead aprons Collimators –Prevent fogging of films due to unnecessary radiation Aluminium Filters –Prevent unwanted soft and non penetrating X-rays Grids –Lead foil strips separated by X-ray transparent spaces and are used to absorb scattered radiation and improves contrast Cassettes and Intensifying Screens

Use of Grid

Intensifying Screens Usually made of thin layer of phosphor crystals with a suitable binder and coated on a smooth layer of cardboard or plastic sheet with a cleanable surface layer Advantages –Decrease patient motion due to shorter exposure time –Decrease patient exposure level –Decrease scatter radiation level to personnel –Permit use of smaller focal spot size; hence better detail –Increase tube life because of lower mAs required –Permits greater selection in kVp settings

Film Processing Developer –Primary function is to reduce exposed silver halide crystals to metallic silver –The developer consists of Reducing Agents –Hydroquinone/ Metol (Developing agents convert exposed silver bromide crystals into black metallic silver ) Activator –Sodium carbonate Swells and softens emulsion so that reducing agents may work more effectively. Provides required alkalinity for reducing agents Restrainer –Potassium bromide (Restrains reducing agents from causing fog ) Preservative –Sodium sulfite Solvent –Water

Fixer Fixing Agent –Sodium thiosulfate (hypo) convert undeveloped silver bromide crystals left on the film into a soluble compound and dissolve them away Acidifier –Acetic acid or sulfuric acid Stops development by neutralizing developer Hardener –Ammonium chloride Preservative –Sodium sulfite Solvent –Water

Other Equipments Lead Markers Film holders and Hangers Viewing boxes Film Driers