X-rays

What are X-rays?

- Invisible electromagnetic radiation that is similar to visible light, but a shorter wavelength.

- Capable of penetrating opaque or solid substances, gases, and tissues.

- They affect photographic plates (X-ray film)

- They interact with matter - ionizing (removing electrons) and can damage tissues and DNA - this effect is worse in rapidly dividing tissues - reproductive, fetal tissue, epithelial tissue.

X-ray Settings

A radiograph (X-ray) is a photographic image generated when the electromagnetic radiation interacts with the X-ray film after passing through an object.
The density of a material will affect how much radiation gets to the film.

Most dense: metal (radiopaque), bone, tissue, liquid, air (radiolucent).

Radiopaque = impermeable to x-rays; gives a white image on film

Radiolucent = permeable to x-rays resulting in black image with no details

Air is radiolucent (black) on film, bone is radiopaque (white) on film...
The thickness of an object will also affect this.

Kvp

"Quality of X-rays" Penetrating power. Is the kilovoltage peak. A higher kvp means that more radiation will get to the X-ray film, so a thicker body part generally needs a higher kvp. Higher kvp also shows more "shades of gray" - contrast, and is used for soft tissue x-rays (chest and abdomen) and a lower kvp for bones.
This is the most common adjustment of the X-ray machine.

mA

Controls the quantity of X-rays. Is the milliamperage. Is a measure of the quantity of electrons projected by the X-ray machine. More means that more will reach the film. So a denser part will be done at a higher setting (actually mAs). Not adjusted as much - bigger difference between the different settings than with kvp.

S

Exposure time. Longer time = more x-rays reaching the film. Measured as seconds. But a long time makes movement a bigger problem, so times are usually very short 1/20 of a second to 1/120 of a second (possibly longer on some machines).

mAS

mA x S

ie., the number of x-rays for a period of time.

Distance

(Set at the table area) - relates to bucky setting on console, and may have a setting on console to match up with what the table is at. Generally 40 inches from X-ray tube to X-ray film. So when using bucky, the tube should be about 2 inches lower (from top of table) for the best focus. Not all machines move this way. X-rays are adequate without this adjustment.

What This All Means?

We figure out what settings to use by using a technique chart (pre-determined settings to get the ideal picture for that thickness and body part) - relates to that x-ray machine, and film type. A different type of film, cassette, or X-ray machine needs a new technique chart. If the X-ray is not good (too light or too dark) adjustments are made. Too dark means that too many X-rays have gotten to the film and it is difficult to see contrast - the settings are too high and need to be lowered. Too light means that not enough X-rays have reached the film - the settings need to be raised.

The X-ray Machine

Composed of two parts - one to generate the X-rays, and other is the control panel area where various settings are entered.

X-ray Tube

- May be completely stationery.

- Ideally will move - up and down, possibly side to side (or table moves), and tilt or rotate.

- Will have light shutters to adjust the focus and area that will be X-rayed (primary beam) and a cross-hair pattern which shows the central focus area (focus directly over part to be X-rayed).

Adjusting the area to be x-rayed to the smallest possible size is called collimating. Good for safety. Want to make sure that area to be x-rayed is not larger than the film size, too.

Control Panel

- On/off switch (may be two)

- kvp selector (kilovoltage peak) - controls the penetration ability of the X-rays

- mA selection (milliamperage) - controls the number of X-rays

- Time selection - control the length of time the X-rays are directed at the plate
mAs = mA x time (seconds)

- Bucky vs. Non Bucky selection

X-ray Table

Where the animal is put. There is a tray under the table to put a cassette in (Bucky) or can be done with cassette directly on the table (table top technique)
May be stationery or mobile.

Scatter

Radiation that bounces off the animal, plate, table, etc. This is where most of the exposure to x-rays comes from, not the primary beam.

Collimation

Method of focusing the x-ray beam.

Cassette/Plate

A rigid lightproof container for holding radiographic film in x-ray photography. (cassette also called the "plate" Or the film is called the "plate").

Lead blocker

Sheet of lead used to protect portion of x-ray film so two images can be imprinted on same plate.

Screen

Fluorescent or sometimes metallic sheet used to intensify the effect of radiation on x-ray film.

Bucky

If scattered x rays or photons reach the x-ray film, they fog the film, which decreases the quality of the image and provides no useful information in the picture. A grid is a device containing lead strips that is placed between the patient and the x-ray film to absorb scattered x-rays before they reach the x-ray film. A Bucky is a device that moves the grid while the x ray is being taken. The motion keeps the lead strips from being seen on the x-ray film.

Calipers

Any of various measuring instruments having two usually adjustable arms, legs, or jaws used to measure thickness, diameter, and distance between surfaces.

Collimator

A device that restricts the beam to a set area in order to minimize exposure.

Dosimetry Badge

An indicator badge worn by those taking radiographs that measures the RADs a person receives. Should be checked/updated quarterly. Also called a dosimeter badge.

FFD (Focal Film Distance)

The distance between the x-ray tube and the film. Increasing or decreasing this distance will have an effect on radiographic density.

Grid

A series of thin lead strips designed to absorb scatter radiation, typically mounted above where the cassette lies in the bucky. Not visible externally.

Intensifying Screens

Thin layers of crystals inside the lining of the film cassette that glow when struck by radiation, therefore reducing the amount of radiation required to produce the image.

Scatter Radiation

Radiation that has interacted with the patient's tissues and is scattered multi-directionally.

Cassettes

Cassettes are metal boxes designed to protect and hold radiographic film and intensifying screens. They are made of materials such as to protect the film from light.
Cassettes are used to reduce the required amount of x-ray radiation because of the intensifying screens within the cassette.
From top to bottom, a cassette is layer as follows:
• Cassette front
• Front padding
• Intensifying screen
• Double coated film - the x-ray film
• Intensifying screen
• Back padding
• Cassette back

Cassettes are loaded in the x-ray darkroom since the film must not be exposed to room light. Once loaded the castes are stored usually in the same room as the radiographic machine but in a lead compartment to prevent accidental exposure when other x-rays are being taken.
Cassettes come in standard sizes to accommodate the various standard sized radiographic films.

Intensifying Screen

A sheet of crystals of inorganic salts (called phosphors) which emit fluorescent light when excited by X-ray radiation. The sheets are used to intensify the effect of X-rays during exposure of X-ray film.

Labelling X-rays

Ideally the labelling will be incorporated into the x-ray (legal record), but if one of the following methods doesn't work remember to still label with a felt tip pen, or a piece of tape on to the x-ray (better to have any ID, rather than none).

ID with: name, date, clinic, and possibly an ID #, the anatomical part, and time if relevant.

Also with R/L, and VD or DV if applicable.

Common Methods:
for R/L, V/D, something will be placed onto the table or cassette during film exposure. (Make sure it will be in the area of the beam but not obstructing anything. Leaded Right or Left markers are placed on the cassette at the time of exposure to identify the extremity x-rayed or the side on which the animal is positioned for the radiograph.

For the animal's info on the film - two main types:

1. Lead impregnated tape - you write with a ball point pen onto a small piece of soft lead which is placed on top of the cassette while the x-ray is taken.

2. After x-ray labeller: you write a label on paper, and using a little machine, the label is transferred onto the film before developing (in the lead blocker area). Usually requires fairly thick writing to be visible - felt tip pen.

X-ray Log

Record of x-rays taken: animal, part, settings, date, etc. Important source of quick info - nice way to find information without pulling files or x-rays. Good when need to repeat a shot on an animal - make sure the settings that worked are the recorded ones.

Positioning

Positioning of the patient and the markers placed on the radiograph are described by the direction of the primary beam from entrance to exit.

Right - R = right side of patient down (on table top)

Left - L = left side down
Dorsal/Ventral - DV = lying with chest on table and back upper most.

Ventral/Dorsal - VD = lying on back with chest upper most.

The first position letter indicates the first part of the body to receive the x-ray beam.

DV or dorsoventral: The beam enters the dorsal surface and exits the ventral surface. This is the standard position for small animal thoracic cavity images with the patient in the sternal recumbency (back upwards, abdomen on table).