Radiology Test 2


2 types of X-ray Machines

  • Intra-oral

  • extra-oral

Dental X-ray Holders

  • hold and align intra-oral receptors

  • Prevent patient from holding the receptor.

  • Required for paralleling technique

Beam Alignment Devices

  • Combine receptor holders with collimators.

  • Restrict beam size to match receptor size → reduces patient exposure.

Xray production

  • Cathode (–) → produces electrons.

  • Anode (+) → target where electrons strike to produce x‑rays.

  • X‑ray machines use electricity as the energy source.

Voltage

  • Voltage is the measurement of electrical force pushing electrons from cathode → anode.

  • Higher voltage = faster electrons = more penetrating x‑ray beam (shorter wavelength).

  • Voltage is measured in volts or kilovolts

  • 1000 volts (V) = 1 kilovolt (kV)

  • Dental x-ray equipment requires: 60 – 100 kilovolts (kV

  • Kilovoltage Peak (kVp) = the maximum or peak voltage

  • Kilovoltage peak controls= the speed of e- as they cross to other side of tube and the quality or the wavelength/penetrating ability of the x-ray beam

  • 2 qualities of the dental radiograph which are affected by kilovoltage are = Density and Contrast

Density

  • its the overall darkness or blackness of a dental radiograph

  • Higher kVp → more penetration → increased density (darker).

  • Lower kVp → less penetration → decreased density (lighter).

Contrast

  • how sharply dark and light areas are differentiated on a film

High Contrast

  • Many blacks/whites, few grays.

  • Low kVp (65–70).

  • Best for caries detection.

Low Contrast

  • Many shades of gray.

  • High kVp (≥90).

  • Best for periodontal/periapical disease.

Milliamperage (mA)

  • current flowing through the cathode filament

  • Dental units use 7–15 mA.

  • More mA → darker image.

  • Less mA → lighter image.

Exposure time

  • time during which x-rays are produced

  • Measured in impulses

  • 1 impulse = 1/60 second.

  • X‑rays are produced in pulses

mA and Exposure time

  • Inversely related.

  • If mA increases → exposure time must decrease to maintain same density

Milliampere-Seconds

  • mAs= milliamperes and exposure time into one common factor

Intensity

  • effected by

    • kVp

    • mA

    • Exposure time

    • Distance

Distance & Intensity – Inverse Square Law

  • Intensity is inversely proportional to the square of the distance.

  • If distance doubles → intensity becomes ¼.

  • If distance decreases → intensity increases.

Filtration

Purpose

  • Removes long‑wavelength, low‑energy, nonpenetrating x‑rays.

  • Makes beam safer and more penetrating.

Types

  1. Inherent Filtration

    • Occurs naturally as x‑ray passes through oil, glass window.

    • Equivalent to 0.5–1 mm aluminum.

  2. Added Filtration

    • Aluminum disks (0.5 mm each).

    • Removes weak rays.

  3. Total Filtration

    • Inherent + added.

    • Federal Standards:

      • ≥70 kVp → 2.5 mm aluminum

      • <70 kVp → 1.5 mm aluminum

Half‑Value Layer

  • Thickness of aluminum needed to reduce beam intensity by half.

  • Higher HVL = more penetrating beam.

Collimation

  • Made of lead.

  • Restricts size and shape of beam.

  • Beam cannot exceed 2.75 inches at patient’s face.

  • Rectangular reduces exposure by 60%.

Useful Beam

  • Beam after filtration + collimation.

  • Contains only strong, properly shaped rays.

Collimator Cutoff (Cone Cutting)

  • Occurs when beam is not centered on receptor.

  • Results in a clear, unexposed area on the image.