Equipment design for radiation protection, Lab Reports of Radiology

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Equipment Design for

Radiation Protection

by;: Allen G. Espanola

RADIATION SAFETY FEATURES OF RADIOGRAPHIC

EQUIPMENT, DEVICES, AND ACCESSORIES

• (^) Protective Tube Housing- A lead-lined metal protective tube housing required to protect the patient and imaging personnel from off-focus, or leakage radiation by restricting the emission of x-rays to the area of the useful, or primary, beam
• (^) must be constructed so that the leakage radiation measured at a distance of 1 m from the x-ray source does not exceed 1 mGya/hr (100 mR/hr) when the tube is operated at its highest voltage at the highest current that allows continuous operation

Control Panel, or Console

• (^) where technical exposure factors such as milliamperes (mA) and peak kilovoltage (kVp) are selected and visually displayed
• (^) must be located behind a suitable protective barrier that has a radiation-absorbent window that permits observation of the patient during any procedure
• (^) must indicate the conditions of exposure and provide a positive indication when the x-ray tube is energized.
• (^) The visible mA and kVp digital readouts permit the operator to assess exposure conditions

Radiographic Examination Table

• (^) must be strong and must adequately support the patient
• (^) Frequently, this piece of equipment has a floating tabletop that makes it easier to maneuver the patient during an imaging procedure
• (^) The thickness of the tabletop must be uniform, and for undertable x- ray tubes as used in fluoroscopy, the patient support surface also should be as radiolucent as possible so that it will absorb only a minimal amount of radiation, thereby reducing the patient's radiation dose
• (^) A carbon fiber material is commonly used in the tabletop to meet this requirement

X-Ray Beam Limitation Devices

• (^) Collimators
• (^) Aperture diaphragms- simplest , used in trauma radiographic units
• (^) Cones- replaced by collimators, used in coned view of the paranasal sinuses and sella turcica
• (^) Cylinders – same as cones but different in shape, flared down or cylindrical
• (^) these devices confine the useful, or primary, beam before it enters the area of clinical interest and thereby limit the quantity of body tissue irradiated.
• (^) This also reduces the amount of scattered radiation in the tissue and prevents unnecessary exposure to tissues not under examination
• (^) the patient's dose is significantly reduced because a smaller field size produces less scatter radiation. This improves the overall quality of the radiographic image

• (^) the collimator is the most versatile device for defining the size and shape of the radiographic beam
• (^) The light-localizing variable-aperture rectangular collimator is the type of collimator most often used with multipurpose x-ray units
• (^) Two sets of adjustable lead shutters mounted within the device at different levels
• (^) A light source to illuminate the x-ray field and permit it to be centered over the area of clinical interest
• (^) A mirror to deflect the light beam toward the patient to be radiographed

Beam Alignment

• (^) It is imperative that the x-ray beam and the image receptor be correctly aligned with each other
• (^) Every radiographic tube must have a device in place to ensure accurate beam alignment

Types of Filtration

• (^) Inherent filtration- Glass envelope encasing the x-ray tube ,Insulating oil surrounding the tube ,Glass window in the tube housing
• (^) Added filtration- Sheets of aluminum (or the equivalent) of appropriate thickness
• (^) Total filtration of 2.5 mm aluminum equivalent for fixed x-ray units operating above 70 kVp is the regulatory standard
• (^) radiographic equipment requires total filtration of 1.5 mm aluminum equivalent for x-ray units operating at 50 to 70 kVp, whereas fixed units operating at below 50 kVp require only 0.5 mm aluminum equivalent
• (^) Mobile diagnostic units and fluoroscopic equipment require a minimum of 2.5 mm aluminum equivalent.

Filtration for Mammographic Equipment