8 Radiation and Medical Imaging Free Online FlashCards

What makes radiation ionizing?

Ionizing radiation has enough energy to remove electrons from atoms, creating charged particles called ions.

Which two imaging methods use non-ionizing energy?

Ultrasound and MRI use non-ionizing energy and do not use X-rays.

How do bone and air-filled regions differ on a typical radiograph?

Bone attenuates more X-rays than soft tissue, while air-filled regions attenuate less. These differences create image contrast.

How do iodine- or barium-based contrast agents improve visibility?

Iodine- or barium-based agents attenuate X-rays strongly, making selected structures easier to see.

What is the attenuation model for a narrow X-ray beam?

For a narrow, monoenergetic beam through a uniform material, transmitted intensity is modeled as $I=I_0e^{-\mu x}$, where $I_0$ is initial intensity, $\mu$ is the linear attenuation coefficient, and $x$ is thickness.

How does CT produce cross-sectional images?

CT measures X-ray transmission from many angles as the source and detectors rotate around the patient; a computer reconstructs cross-sectional images from these projections.

What is fluoroscopy used for during procedures?

Fluoroscopy displays X-ray images continuously or in rapid succession to guide procedures.

What radiation do SPECT and PET detect?

Nuclear medicine detects radiation emitted from a radiopharmaceutical inside the body. SPECT detects gamma rays; PET detects paired photons produced after tracer positrons annihilate with electrons.

What happens during photoelectric absorption?

The photon transfers its energy to an electron and disappears. This interaction contributes to image contrast and is more likely in higher-atomic-number materials, such as bone or iodine contrast.

How can Compton scattering affect an X-ray image?

A photon transfers some energy to an electron and changes direction. Scattered photons can reach the detector from the wrong direction, reducing contrast, and deposit energy in tissue.

What defines coherent scattering?

The photon changes direction without appreciable energy transfer. Coherent scattering has a smaller role in most diagnostic imaging.

How do absorbed dose and effective dose differ?

Absorbed dose, measured in gray, is energy deposited per kilogram. Effective dose, measured in sievert, compares approximate population-level risk across exposure types; it does not precisely predict an individual’s risk.