Radiographic Units

Mobile x-ray units can be smaller light-duty units or full-power units that are transported on wheels (Figure 15-1). These mobile units may be transported with or without the use of motors. Mobile units can be categorized in several ways depending on the design of the generator: direct power, battery power, capacitor-discharge, or high-frequency. Mobile units operated by plugging into a wall outlet for direct power may experience fluctuations in voltage, which affects the radiation output. Battery-operated units provide more consistent radiation output, similar to a three-phase generator, but need to be recharged. Capacitor discharge units must be plugged into a wall outlet during operation, but produce consistent radiation output, similar to a single-phase generator. High-frequency units produce a consistent radiation output and are lightweight, but must be plugged into a wall outlet during operation.

Exposure techniques can therefore vary greatly depending on the type of mobile unit and its radiation output for a selected exposure technique. Additionally, care must be taken in manipulating the unit at the patient’s bedside to avoid any damage to the mobile unit or bedside patient care equipment. A radiography suite is a “controlled” and shielded environment specially designed for radiographic imaging. In a mobile environment, however, radiographers must take responsibility for radiation protection for themselves, the patient, and other individuals within close proximity. Radiographers should wear a lead apron during the radiation exposure and stand as far from the patient and x-ray tube as possible (at least 6 feet). Shielding of the patient and other individuals who must remain in the room should be performed as in the radiology department.

Imaging patients using a mobile x-ray unit presents many challenges. Radiographers need to carefully assess the patient’s condition to determine the appropriate alignment of the x-ray tube, patient, and image receptor. The tube-head assembly is freely adjustable and the radiographer must take care to create the correct tube-part-receptor orientation, which is more readily established in a radiographic suite. The ability to obtain a standard source-to-image receptor distance (SID), use of a grid, and automatic exposure control (AEC) device (if available), may be jeopardized during mobile imaging. Obstacles (patient care equipment), patient condition, and the physical room environment may greatly limit or alter the radiographer’s options for obtaining what are otherwise routine images. It is imperative that the radiographer be able to adjust the equipment to maintain proper alignment of the tube and image receptor to achieve a diagnostic-quality image at the patient’s bedside. Therefore additional training and experience is warranted before attempting mobile imaging.

Fluoroscopic Units

C-arm mobile units have fluoroscopic capabilities that are typically used in the operating room when imaging is necessary during surgical procedures. A video unit is also attached, which offers both static and dynamic recording during the procedure. Because it is a fluoroscopic system, many of the features of a fixed fluoroscopic unit are also made available with a C-arm. A C-arm unit is designed with an x-ray tube and image intensifier attached in a C configuration (Figure 15-2). As a result, the unit can be positioned in a variety of planes, enabling viewing from different perspectives. Generally, three sets of locks are provided to move and hold the C-arm in place. One set moves the entire “c” toward or away from the base (the equivalent of moving a table side to side). Another set allows the pivot of the “c” about its axis (the equivalent of angling a general radiographic tube head assembly). The last set allows the “c” to slide along its arc (the equivalent of moving the patient from anteroposterior or posteroanterior to oblique to lateral without having to move the patient).

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The X-ray Tube Structure of the Atom Image Intensified Fluoroscopy Automatic Exposure Control Radiographic Exposure Technique Image Characteristics

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