Key Concepts in Medical Imaging and Radiation Safety

Ionization

It refers to the process where radiation removes electrons from atoms in tissues, allowing image creation but also posing tissue damage risk.

Father of Western medicine

Hippocrates.

Wilhelm Röntgen's discovery

He discovered X-rays on November 8, 1895.

Major certification agencies in medical imaging

ARRT, ARDMS, NMTCB.

Fight-or-flight response

A physiological reaction to perceived threats involving increased metabolism, hormone release, and heightened CNS activity.

PACS

Picture Archiving and Communication System; it stores, retrieves, and shares digital imaging data.

mAs in radiography

The quantity of X-ray production and image receptor exposure.

Collimator

To shape and limit the X-ray beam, reducing patient dose and scatter.

Photoelectric effect

A process where an X-ray photon is completely absorbed, ejecting an inner-shell electron—key to image formation but increases patient dose.

ALARA

As Low As Reasonably Achievable.

Most sensitive cells to radiation

Rapidly dividing cells, according to the Law of Bergonie and Tribondeau.

Stages of Acute Radiation Syndrome (ARS)

Prodromal, Latent, Manifest illness, Recovery or death.

Approach to pediatric patients during imaging

Speak softly, stay at eye level, reduce room stimuli, and explain shielding to family.

Key body mechanics for lifting patients

Use your legs, avoid twisting, keep the object close, and communicate throughout the move.

Latent image

The invisible image formed on an image receptor before processing.

Contrast resolution in radiography

The ability to distinguish between small differences in shades of gray on an image.

Spatial resolution

The ability to visualize small structures clearly on an image.

Mottle

Noise—grainy appearance on an underexposed image.

Difference between CR and DR

CR uses phosphor plates and requires scanning; DR uses flat-panel detectors and is immediate.

Calculating mAs

mAs = mA × exposure time (seconds).

kVp

Kilovoltage peak; controls the energy (penetrating ability) of X-ray photons.

Effect of increasing kVp on patient dose

It decreases dose per photon but increases penetration—overall dose may change depending on settings.

Remnant radiation

X-rays that exit the patient and reach the image receptor.

Purpose of the rotating anode

To spread heat during exposures and allow higher tube currents.

Beam filtration

Removing low-energy photons from the beam to reduce patient skin dose.

Backscatter radiation

Radiation that scatters back toward the source after interacting with the patient.

Compensating filter

To even out exposure when anatomical parts vary widely in thickness/density.

Automatic exposure control (AEC)

A system that automatically terminates exposure when enough radiation reaches the IR.

Gonadal shields

Protect reproductive organs during X-ray exams to reduce genetic risk.

Repeat imaging

Taking images again due to error; increases patient radiation dose—should be minimized.

Latent vs manifest illness in ARS

Latent is symptom-free period; manifest illness is when symptoms appear and intensify.

Inverse square law

Radiation intensity decreases proportionally to the square of the distance from the source.

Lead apron thickness

Thicker lead (e.g., 0.5 mm) offers greater attenuation of scatter and radiation.

Occupational dose limit for radiation workers

Generally 50 mSv/year (5 rem/year) in the U.S.

Film-screen imaging

Traditional analog method using X-ray film and intensifying screens.

Field size

Collimator settings control width and height of the X-ray beam.

Scatter radiation

Secondary radiation from interactions; reduce using collimation and grids.

Pediatric radiosensitivity

They have more rapidly dividing cells and longer lifespan for effects to manifest.

PBL collimator

Positive Beam Limitation—automatically adjusts beam to size of IR.

Cesium iodide dr flat panel

High quality DR imaging: improved resolution and lower dose.

Centering error

When the X-ray beam is not centered on anatomy or IR—leads to cutoff or artifacts.

DICOM

Digital Imaging and Communications in Medicine—standard for managing medical imaging data.

Windowing in digital imaging

Adjusting brightness (level) and contrast (width) on digital images.

Back-up timer on an AEC

Prevents overexposure if the AEC fails—terminates exposure at a set maximum time.

Patient size and exposure technique

Larger patients require higher mAs and/or kVp to penetrate.

Fluoroscopic dose regulation

Time, pulse rate, filtration, and distance factors to minimize exposure.

Patient motion problem

Causes blur, reduces sharpness—repeat images may be needed, increasing dose.

Bucky tray/grids

A tray with grid beneath IR to reduce scatter improving image quality.

Technologist responsibility in image critique

Ensure proper positioning, exposure, artifact absence, and adequacy for diagnosis.

Beam hardening

Increase in average beam energy as low-energy photons are filtered, common in CT.