Radiation Safety Measures

• Measures ensure radiographic equipment operates safely for patients and personnel.
• Every diagnostic imaging system must have a protective tube housing and a correctly functioning control panel.
• Radiographic examination tables and accessories must be designed to reduce patient radiation dose.

Diagnostic-Type Protective Tube Housing

• Requirements include lead-lined & metal construction.
• Designed to protect patients and imaging personnel from off-focus or leakage radiation.
• Restricts x-ray emission to the useful or primary beam area.
• Radiation leakage through the housing must not exceed 0.88 mGya/hr, measured 1 meter from the x-ray source.
• Leakage is measured when the tube operates at its highest voltage and current for continuous operation.

Control Panel or Console

• Must be located behind a suitable protective barrier with a radiation-absorbent window.
• Must provide positive indication when the x-ray tube is energized.
• Should have visible milliampere (mA) and kilovoltage peak (kVp) digital readouts.
• Readouts permit operator assessment of exposure conditions.
• A tone is emitted when exposure begins, stopping when exposure terminates.
• Audible sound indicates when the x-ray tube is energized and emitting radiation.

Radiographic Examination Table

• Must be strong enough to adequately support patient weights exceeding 300 pounds.
• Often features a floating tabletop for easy patient maneuvering.
• Must be of uniform thickness.
• Needs to be constructed with a radiolucent material to minimize radiation absorption for patient safety.
• Frequently made of carbon fiber material.

Source-to-Image Receptor Distance (SID) Indicator

• Provides a way to measure the distance from the anode focal spot to the IR.
• Ensures that the correct SID is maintained.
• Often is a simple device, like a tape measure, attached to the collimator or tube housing.
• Lasers can measure SID.
• Distance must be accurate to within 2% of the SID.
• Centering indicators must be accurate to within 1% of the SID.

X-Ray Beam Limitation Devices

• The primary x-ray beam should be adequately collimated.
• Size should be no larger than the size of the image receptor (IR) being used for the examination.
• Light-localizing variable-aperture rectangular collimator adjusts x-ray beam size and shape automatically or manually.
• Collimators are the most common x-ray beam limitation device.
• Other types include cones and cylinders.
• Restricting x-ray field size reduces patient dose and improves image quality.

Positive Beam Limitation (PBL)

• Collimates the radiographic beam to the IR size.
• Supports the law that collimation cannot be larger than the IR.

Cones

• Often used with dental x-ray machines.
• Sometimes used for examinations of specific areas, such as the head.
• Features flared metal tubes and straight cylinders.

Filtration

• Purpose is to reduce absorbed dose to the patient by removing low-energy photons.
• Types of filtration: inherent + added = total filtration.
• Minimum total filtration required for machines at 70kVp or higher: 2.5 mm Al/Eq.
• Aluminum is widely selected for its effectiveness in removing low-energy x-rays from a polyenergetic x-ray beam.
• It removes them without severely decreasing x-ray beam intensity.
• A diagnostic x-ray beam must always be adequately filtered.

Half-Value Layer (HVL)

• The thickness of a designated absorber, such as aluminum, reduces primary beam intensity by 50% of its initial value.
• Needs to be measured to verify adequate filtration of the x-ray beam.
• Measurement should be taken by a radiologic physicist at least once a year.
• Measurement is also taken after an x-ray tube is replaced or after repairs.
• Expressed in millimeters of aluminum.
• It measures beam quality or effective energy of the x-ray beam.
• A minimal HVL is required at a given kVp.

Compensating Filters

• Filters are made of aluminum, lead-acrylic, or other suitable materials.
• Used to accomplish uniform imaging of body parts with varying thickness or tissue composition.
• Partially attenuates x-rays directed toward the thinner areas of the filter.
• Permits more x-radiation to pass through the thicker areas.
• Examples: wedge filter and trough (bilateral wedge) filter.

Exposure Reproducibility

• Is the consistency in output in radiation intensity, for identical generator settings.
• Requires one individual exposure to subsequent exposures
• May be verified by making a series of repeated exposures using the same technical factors.
• Monitor radiation intensity variation with a calibrated ion chamber.
• Variance of 5% or less is acceptable.

Exposure Linearity

• Is the consistency in output radiation intensity at selected kVp settings.
• Linearity changes generator settings from one mA and time combination to another.
• Variance of 10% or less is acceptable.

Mobile Radiography

• Only for patients who cannot be transported to a fixed radiographic installation.
• The SID generally used for mobile radiography is 100 cm (40 inches) or 120 cm (48 inches).
• The minimum SSD is at least 30 cm (12 inches).
• Remember for stationary machines minimum SSD is at least 38cm (15 inches).
• Increased SSD such as 100 or 120 cm yields a more uniform distribution of exposure.
• Examples: portable machines and C-arm machines.