Radiology Informatics & X-Ray Physics – Key Vocabulary

Vocabulary flashcards covering imaging informatics (PACS, DICOM, HL7, security), digital image processing, display requirements, x-ray production physics (mAs, kVp, filtration, interactions), anode mechanics, CR/DR technology, and image quality metrics.

PACS (Picture Archiving and Communication System)

System that manages, stores, retrieves, and displays medical images.

PACS Challenges

Cost, maintenance, system compatibility, security, and data-integrity issues that affect PACS performance.

DICOM (Digital Imaging and Communications in Medicine)

Standard protocol for formatting and transmitting medical images and related information.

DICOM Header

Embedded file data containing patient, acquisition, and facility information.

DICOM GSDF (Grayscale Standard Display Function)

Calibration curve used to verify grayscale performance of medical display monitors.

HL7 (Health Level Seven)

Standard for exchanging clinical and administrative data across healthcare systems.

HIPAA

U.S. law that sets privacy and security standards for protecting patient health information (PHI).

PHI Security Protocols

Access control, encryption, auditing, and user authentication measures that safeguard patient data.

Radiology Informatics

Field that manages imaging data within and outside healthcare enterprises.

Diagnostic Workstation

High-resolution, DICOM-compliant computer used for primary interpretation of medical images.

Luminance

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

Primary Diagnostic Monitor Requirement

≈5-megapixel resolution for radiologist image interpretation.

mAs (milliampere-seconds)

Product of tube current (mA) and exposure time (s); controls x-ray quantity.

mAs Reciprocity

IR exposure remains constant if mA and time are adjusted inversely to keep mAs unchanged.

Quantum Noise

Speckled image appearance caused by insufficient x-ray photons reaching the detector.

Exposure Indicator

Numeric value on digital images reflecting radiation amount received by the image receptor.

Film Density

Overall darkness of a film-screen radiograph; directly controlled by mAs.

30 Percent Rule

Minimum mAs change (≈30%) needed to produce a visible film-screen density difference.

Filtration (X-Ray Beam)

Removal of low-energy photons to harden the beam and reduce patient dose.

Total Filtration

Sum of inherent and added filtration; minimum 2.5 mm Al equivalent in general-purpose tubes.

Beam Quality

Average energy (penetrability) of the x-ray beam; increased by filtration and higher kVp.

X-Ray Tube Leakage Limit

≤100 mR/hr measured 1 m from housing.

Heat Units (HU)

kVp × mA × time × factor (1.4 for 3-phase/high-frequency) that estimates tube heat load.

Differential Absorption

Selective absorption/transmission that creates image contrast in the patient.

Image Receptor (IR)

Device that captures x-ray photons exiting the patient (film, CR plate, DR panel).

Attenuation

Reduction in x-ray beam intensity through absorption and scatter in tissue.

Transmission

Photons that pass through tissue without interaction and reach the IR.

Photoelectric Effect

Inner-shell electron ejection with complete photon absorption; major source of patient dose.

Compton Scatter

Interaction with an outer-shell electron producing deflected, lower-energy photons that degrade image.

Coherent Scatter

Low-energy photon interaction that changes direction without ionization or energy loss.

Secondary Radiation

Characteristic photons produced after a photoelectric event within tissue.

Atomic Number Effect

Higher atomic number tissues show more photoelectric absorption, increasing image contrast.

Tissue Density

Compactness of atomic particles; denser tissue increases attenuation.

Tissue Thickness

Greater part thickness increases number of photon interactions, raising attenuation.

kVp Influence on Interactions

Low kVp increases photoelectric events; high kVp favors transmission.

Rotating Anode

Spinning tungsten disk (≈3,000–10,000 rpm) that spreads heat during x-ray production.

Stator

Electromagnetic motor outside the x-ray tube envelope that turns the rotor.

Rotor

Inside-tube component connected to the anode target; rotates the anode.

Focal Spot

Specific anode area struck by electrons to generate x-rays.

Line Focus Principle

Angling the anode creates a small effective focal spot while maintaining a large heat capacity.

Anode Heel Effect

Beam intensity higher on cathode side; place thicker anatomy under cathode to compensate.

Bremsstrahlung Radiation

X-ray photons produced when electrons slow or change direction near the nucleus.

Characteristic Radiation

X-rays emitted when an inner-shell electron is ejected and an outer electron fills the vacancy (≥69.5 keV in tungsten).

kVp-keV Relationship

Maximum photon energy in keV equals the kVp setting (e.g., 100 kVp → 0–100 keV photons).

Voltage Ripple

Variation in tube voltage during exposure; lower ripple improves beam consistency.

Histogram (Digital Imaging)

Graph of pixel value distribution used for exposure analysis and processing.

Values of Interest (VOI)

Pixel value range selected for proper image display during processing.

Automatic Rescaling

Software adjustment that normalizes brightness and contrast to reference standards.

Lookup Table (LUT)

Preset data that maps input pixel values to desired output contrast levels.

Window Width

Control that adjusts gray-scale range (contrast) displayed on a monitor.

Window Level

Control that sets the mid-point brightness of displayed image data.

Edge Enhancement

Post-processing technique that exaggerates high-contrast borders for better detail visibility.

Smoothing

Noise-reduction algorithm that averages adjacent pixels to create a cleaner image.

Electronic Health Record (EHR)

Digital record that shares comprehensive patient information across facilities.

Radiology Information System (RIS)

Database that stores imaging orders, scheduling, and reports—without full patient care data.

Vendor Neutral Archive (VNA)

Image storage platform independent of specific PACS vendors; doesn’t need duplicate copies for disaster recovery.

Teleradiology

Transmission of images for remote interpretation; improves access but may create communication gaps.

Reversible (Lossless) Compression

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

Primary Display Monitor Specs

≥1 cd/m² minimum, ≤350 cd/m² maximum luminance, and contrast ratio >250.

Physical Collimation

Mechanical restriction of the beam before exposure; cannot be replaced by electronic masking.

Pixel Density

Number of pixels per unit area; higher density means smaller pixels and better spatial resolution.

Pixel Pitch

Distance from center of one pixel to the next; decreased pitch improves resolution.

Spatial Frequency

Number of line pairs per millimeter in an image; higher frequency equals better detail.

Bit Depth

Number of bits used to represent each pixel’s gray level; determines available gray shades.

Contrast Resolution

Ability of an imaging system to differentiate small differences in signal intensity.

Matrix Size

Number of pixel rows and columns in a digital image; larger matrix yields finer detail.

Pixel Size

Physical dimension of a pixel; smaller size improves spatial resolution.

Modulation Transfer Function (MTF)

Quantitative measure of how faithfully an imaging system reproduces contrast at different spatial resolutions.

Computed Radiography (CR)

Imaging method using photostimulable phosphor plates to capture x-ray energy.

Photostimulable Phosphor (PSP)

Barium fluoro-bromide layer in CR plates that traps electron energy to form latent images.

Latent Image (CR)

Invisible stored energy pattern in PSP created by x-ray exposure.

Helium-Neon Laser

Common laser type used to scan CR plates and release stored energy as light.

Photostimulable Luminescence

Light emitted by PSP phosphors when stimulated by a laser during readout.

Photomultiplier Tube (PMT)

Device that amplifies the light from PSP and converts it into an electronic signal.

Sampling Frequency

Rate at which analog signal is measured during digitization; higher frequency improves resolution.

Sampling Pitch

Distance between measurement points; larger pitch lowers sampling frequency and resolution.

Plate Erasure (CR)

Exposure of PSP to intense white light to remove residual image and allow reuse.

Digital Radiography (DR)

Detector technology that directly converts x-ray energy into digital signals without a cassette.

Flat-Panel Detector

Thin, large-area DR detector integrated into tables or wall stands.

Image Processing

Computer manipulation of digital data to optimize image quality.

Electronic Masking

Cropping or shuttering after exposure; cannot substitute for proper collimation.

Alternate Processing Algorithm

Different software applied to image data; may not always enhance quality.

Quantum Mottle

Synonym for quantum noise; mottled appearance due to insufficient exposure.

Beam Hardening

Increase in average photon energy after filtration removes low-energy x-rays.

Inherent Filtration

Beam filtration provided by the tube envelope, oil, and window.

Added Filtration

Aluminum or equivalent material placed in beam path to meet total filtration requirements.

High-Frequency Generator

X-ray generator type with <1% voltage ripple and higher output efficiency.

Voltage Ripple Values

100% (single phase), 13–25% (three-phase), <1% (high frequency).

Actual Focal Spot

Physical area on the anode struck by electrons.

Effective Focal Spot

Apparent focal spot size projected toward the patient/detector.

80/20 Brems-Characteristic Rule

At 90 kVp, ~85% of beam photons are Bremsstrahlung and 15% characteristic.

Beam Penetrability

Ability of x-ray photons to pass through tissue; primarily controlled by kVp.

HU Correction Factor

1.4 multiplier used when calculating heat units for 3-phase or high-frequency generators.

Spatial Resolution

Ability of an imaging system to distinguish small, closely spaced objects.

Contrast

Visible difference in brightness between image areas.

Brightness (Digital)

Overall light level of a displayed image; adjusted by window level rather than mAs.

Dose Creep

Unintentional increase in patient dose when technologists rely on post-processing to correct overexposures.

Display Contrast Ratio

Ratio of maximum to minimum luminance produced by a monitor.

System Compatibility

Ability of different hardware/software to communicate and function together within PACS.

Encryption

Process of coding data to prevent unauthorized access during transfer or storage.