Correlative Imaging - Radiography

Discuss the historical development of Radiography.

November 8, 1895 - Wilhelm Conrad Roentgen observed a photographic screen emitting light (fluorescing) & called it x-rays

Hand-held fluoroscopes - helped made by Thomas Edison

1896 - realization that x-rays can be harmful

How x-rays are made

X-rays are produced by fast-moving electrons in an x-ray tube

X-ray tube contains an anode and cathode

Cathode electrons are released - thermionic emission

Properties of x-rays

Electromagnetic waves of very short wavelength and high frequency

Can penetrate matter

Affect a photographic emulsion in the same way that light does

Cause fluorescence (emotion of light) in certain materials

Cause ionization (gaining or losing an electron)

Unaffected by electric and magnetic fields

Cannot easily be reflected or refracted

May be diffracted by passage through crystals

Primary Radiation

Exists in x-ray tube

Absorbed or attenuated in patient

Remnant Radiation

Radiation that passes through and exits the patient

Used to produce radiographic images

Appearance of different tissues on radiographs

Metal: full attenuation of x-ray beam; resultant image is white.

Bone: nearly full attenuation of x-ray beam; resultant image is white to shades of gray.

Water and soft tissues: partial attenuation of x-ray beam; resultant image is gray.

Fat: almost no attenuation of x-ray beam; resultant image is very dark gray to black.

Air: no attenuation of x-ray beam; resultant image is black.

Density

The density of the structure (the amount of blackness on the image) may be affected by the superimposition of bones, muscles, or other soft tissue organs

The "denser" a structure is, the more it attenuates the x-ray beam

Contrast

Refers to the density difference between two adjacent structures

Recorded Detail

Refers to the spatial resolution of the image

Distortion

Refers to the accuracy of the shape of the structure represented in the image

Contrast Agents

Contrast media are solutions or gases introduced into the body to provide contrast on a radiograph between an organ and its surrounding tissue

Positive agents and negative agents decrease opacity (radiolucent). Positive and negative contrast media may be used at the same time for double contrast studies such as the barium enema. The barium coats the large intestine and provides density while the air acts to inflate and separate the haustral folds.

Positive Contrast Agents

Increase opacity (radiopaque) of a structure

Negative Contrast Agents

Decrease opacity (radiolucent) of a structure

Equipment used in interventional radiography

Fluoroscopy

Supine

Prone

Lateral

Oblique

Radiograph

Angiograph

CT

MRI