Exposure Midterm Flaschards

Vocabulary flashcards covering discovery of X-rays, tube components, radiation interactions, digital imaging concepts, informatics standards, and exposure principles from the lecture notes.

Wilhelm Roentgen

German physicist who discovered X-rays on November 8, 1895 and received the first Nobel Prize in Physics (1901).

Crookes tube

Early vacuum tube Roentgen used to generate the first X-rays.

X-rays

High-energy electromagnetic radiation with wavelengths of 0.1–1 Å and frequencies of 3×10¹⁸–3×10¹⁹ Hz.

Roentgen rays / Roentgenology

Original names for X-rays and the study of X-ray science, honoring Roentgen.

Electromagnetic radiation

Energy that travels as waves at the speed of light; includes X-rays, visible light, etc.

Angstrom (Å)

Unit of length equal to 10⁻¹⁰ m, commonly used for X-ray wavelengths.

c = λv

Equation linking speed of light (c), wavelength (λ), and frequency (v) for electromagnetic waves.

Wave-particle duality

Concept that X-rays behave as both waves and particles (photons).

Fluorescence

Immediate light emission when certain materials are struck by X-rays.

Barium platinocyanide

Fluorescent screen compound that glowed during Roentgen’s discovery of X-rays.

Ionization

Process of removing electrons from atoms; primary biological hazard of X-radiation.

ALARA

Radiation-protection principle: keep doses As Low As Reasonably Achievable by time, distance, shielding.

Cathode

Negative side of the X-ray tube containing the filament and focusing cup.

Filament

Tungsten coil in the cathode that emits electrons via thermionic emission.

Tungsten

Filament/target material chosen for high melting point and high atomic number.

Thermionic emission

Electron release from a heated filament prior to X-ray production.

Space charge effect

Negative electron cloud that limits further thermionic emission around the filament.

Focusing cup

Nickel structure with negative charge that directs electrons toward the anode.

Tube current (mA)

Flow of electrons from cathode to anode; controls X-ray quantity.

Filament current

Current that heats the filament to produce thermionic emission, separate from tube current.

Anode

Positive side of the tube where electrons decelerate to produce X-rays.

Rotating anode

Spinning tungsten target (3,000–10,000 RPM) that spreads heat over a larger area.

Target / Focal track

Tungsten ring on a rotating anode struck by electrons to create X-rays.

Rotor

Internal component that turns the anode in concert with the external stator.

Stator

Electromagnetic motor outside the glass envelope that spins the rotor/anode.

Focal spot

Precise area on the anode where electrons strike.

Line focus principle

Design that uses a large actual focal spot but projects a smaller effective focal spot for better resolution.

Anode heel effect

Variation in beam intensity—stronger on cathode side, weaker on anode side—up to about 45% difference.

Bremsstrahlung interaction

X-ray production when an electron slows near a tungsten nucleus and releases energy as a photon.

Characteristic interaction

X-ray production when an electron ejects a K-shell electron; requires ≥69.5 keV for tungsten.

kVp (kilovoltage peak)

Peak tube voltage; determines photon energy (quality) and affects beam penetrability.

keV

Unit of photon energy; maximum photon energy equals the selected kVp value.

Voltage ripple

Percent variation in generator voltage during exposure; lower ripple yields more consistent beam output.

Filtration

Aluminum or inherent barriers that remove low-energy photons, hardening the beam.

Beam hardening

Increase in average photon energy after filtration removes low-energy photons.

Total filtration

Sum of inherent and added filtration; legal minimum for general tubes is 2.5 mm Al equivalent.

Heat units (HU)

Quantify tube heat: HU = kVp × mA × time × 1.4 (for 3-phase/high-frequency units).

Differential absorption

Selective absorption of X-rays in tissue that creates radiographic image contrast.

Attenuation

Loss of X-ray beam energy through absorption and scatter as it passes through tissue.

Transmission

X-ray photons that exit the patient without interaction and reach the image receptor.

Photoelectric effect

Complete photon absorption with ejection of an inner-shell electron; increases patient dose & contrast.

Compton effect

Photon interaction with an outer-shell electron resulting in scatter and partial energy loss.

Coherent (classical) scatter

Low-energy interaction causing direction change without energy loss or ionization.

Radiographic contrast

Visible difference between densities on an image produced by differential absorption.

Subject contrast

Contrast resulting from patient anatomy and beam energy; higher at low kVp.

Signal-to-noise ratio (SNR)

Ratio of useful image signal to background noise; higher SNR = better image quality.

Quantum noise (quantum mottle)

Graininess from too few photons reaching the detector; linked to low mAs.

Spatial resolution

Ability to visualize small, closely spaced details; measured in line pairs per millimeter (lp/mm).

Contrast resolution

Ability to distinguish minimal differences in grayscale in an image.

Shape distortion

Elongation or foreshortening from misalignment of tube, part, or receptor.

Size distortion (magnification)

Enlargement when object-to-receptor distance increases relative to source distance.

Pixel size

Physical dimensions of one digital image element; smaller pixels improve resolution.

Field of view (FOV)

Displayed anatomy size; larger FOV for fixed matrix increases pixel size.

Matrix size

Total number of rows and columns of pixels; larger matrix with fixed FOV reduces pixel size.

Pixel density

Number of pixels per unit area; higher density improves detail.

Pixel pitch

Center-to-center distance between adjacent pixels; smaller pitch = better resolution.

Spatial frequency

Number of line pairs per millimeter representing detail; higher frequency = higher resolution.

Bit depth

Number of bits used to store each pixel’s gray level; greater depth yields more grayscale shades and contrast resolution.

Modulation Transfer Function (MTF)

Measure of an imaging system’s ability to reproduce contrast at different spatial resolutions; max value is 1.0.

Photostimulable phosphor (PSP)

Barium fluorohalide layer in CR plates that stores x-ray energy as trapped electrons.

Photostimulable luminescence

Light emitted when trapped PSP electrons are released by laser scanning in CR.

Photomultiplier tube (PMT)

Device that amplifies light emitted by PSP and converts it into an electrical signal for digitization.

Sampling frequency

How often detector data are measured during digitization; higher frequency = better resolution.

Histogram

Graph of pixel value distribution used in digital processing to identify values of interest (VOI).

Lookup table (LUT)

Preset curve applied to pixel values to determine final image contrast in digital systems.

Window width

Display control that sets the range of grayscale values shown; affects image contrast.

Window level

Display control that sets the midpoint of displayed grayscale; affects image brightness.

Edge enhancement

Post-processing that increases contrast at boundaries to emphasize detail.

PACS

Picture Archiving and Communication System for storing, retrieving, and displaying medical images.

DICOM

Digital Imaging and Communications in Medicine; standard file format and protocol for medical images.

HL7

Health Level 7; standard for exchanging clinical and administrative data across healthcare systems.

Electronic Health Record (EHR)

Integrated digital record of patient health information shared across facilities.

Radiology Information System (RIS)

Database managing imaging orders, reports, and scheduling, not full patient care data.

Vendor Neutral Archive (VNA)

Image storage system designed for long-term retention independent of specific PACS vendors.

Teleradiology

Electronic transmission of images for remote interpretation by radiologists.

Reversible (lossless) compression

Image compression that allows exact restoration of original data at the end user.

DICOM GSDF

Grayscale Standard Display Function; guideline for consistent monitor luminance response.

HIPAA

U.S. law establishing standards for privacy and security of patient health information.

Luminance

Amount of light emitted or reflected from a monitor surface, measured in cd/m².

mAs

Product of tube current (mA) and exposure time (s); governs X-ray quantity reaching the detector.

Exposure indicator

Numeric value on digital images indicating amount of radiation the detector received.

30% rule (mAs)

Minimum mAs change needed to produce a visible density difference on film-screen radiographs.