Glossary

Active Lesson Terms

Bremsstrahlung

Physics/brem-shtrah-lung/

German for 'braking radiation'. X-rays produced when high-speed electrons decelerate and change direction due to the electromagnetic interaction with an atomic nucleus.

Attenuation

Physics

The reduction in intensity of an X-ray beam as it passes through matter, caused by absorption (Photoelectric effect) and scattering (Compton effect).

Photoelectric Effect

Interaction

An interaction where an X-ray photon is completely absorbed by an inner-shell electron, ejecting it. This is responsible for the white areas (bones) on a radiograph.

Compton Scatter

Interaction

An interaction where an X-ray photon collides with an outer-shell electron, ejecting it and scattering the photon in a new direction with less energy. Creates 'fog' on the image.

Health Sciences Hub

Radiology // Diagnostic Imaging

X-RAY
PHYSICS

To look inside the human body without surgery, we exploit the electromagnetic spectrum. By accelerating electrons into a metal target at half the speed of light, we generate photons energetic enough to pass directly through human tissue.

Tube Dynamics

An X-Ray tube is essentially a massive vacuum tube. A wire filament (the Cathode) is heated until electrons boil off. A massive electrical voltage (kVp) is then applied, violently ripping those electrons across the vacuum and smashing them into a Tungsten target (the Anode).

Over 99% of this kinetic energy is converted instantly into heat. Less than 1% is converted into X-Ray photons via Bremsstrahlung interactions.

Attenuation (Image Creation)

An X-Ray image is just a map of shadows. As the beam passes through the patient, photons interact with tissues based on their density and atomic number. The intensity of the beam as it exits the patient is calculated by the Beer-Lambert law:

I = I_0 e^{-\mu x}

Bone has a high density and atomic number, causing a high attenuation coefficient ( $\mu$ ). It absorbs photons (Photoelectric Effect), casting a white shadow on the detector. Air in the lungs absorbs nothing, turning the image black.

Tube Potential

kVp (Beam Quality)

50 kVp70 kVp120 kVp

High ContrastLow Contrast

Tube Current

mAs (Beam Quantity)

1 mAs10 mAs100 mAs

Underexposed (Noisy)Overexposed (Dark)

ALARA Principle: As Low As Reasonably Achievable. Higher mAs increases patient radiation dose linearly.

Vacuum Tube Dynamics

Cathode (-)

Anode (+)

Detector Output

EXP Index: 100

Optimal

Advanced Imaging Modalities

Standard radiography is just a 2D shadow. Explore advanced medical imaging.