Radiographic Basics

Rui Domingues, MDLincoln Mental and Medical Center

September 2008

What causes the blacks, whites and grays of an x-ray image?

X-ray beams contains x-ray photons of differing energies

As these photons pass through a patient…

Some are absorbed completely Some penetrated directly to the plain film Some are absorbed partially, and While others are deflected (Scatter)

Tissue Density A product of the type of tissue and

the thickness of that tissue

Results in differential absorption

Differential Absorption Penetration of the x-ray beam is

dependent on tissue density

Denser object = less penetration

Less beam striking the film (more absorption) = WHITER

More beam striking the film = BLACKER

Glass Test Tube

Air

Fat

Water

Bone + Water

Metal

Differential AbsorptionBlack Air (Lungs / Trachea / Outside the body)

Fat (Perirenal fat / Fascial plane)

Water (Muscle / Organs)

Bone (Bone / Atherosclerotic plaquing)

White Metal (Fillings / Markers / Ortho devices)

Radiographic Image Adjacent structures of similar

densities are not visualized

Kidney (water density) against liver (water density)

Radiographic Image Adjacent structures of different

densities are visualized

Liver (water density) next to Bowel (air density)

References Felson’s Principles of Chest Roentgenology: A

Programmed Test, 2nd Edition. Goodman, Lawrence R.; W.B. Saunders Co., 1999.

Pocket Atlas of Radiographic Anatomy. Moller, TB et al.; Thieme Medical Publishers, 1993

Clinical Imaging with Skeletal, Chest and Abdomen Pattern Differentials, Dennis Marchiori, ed. (WN 180 M317c)