How is fluoroscopy used to aid in the administration of therapeutic injections for pain management?

Updated: Jun 19, 2018
  • Author: Anthony H Wheeler, MD; Chief Editor: Meda Raghavendra (Raghu), MD  more...
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The fluoroscopy machine is primarily composed of an x-ray tube, image intensifier, C-arm, and control panel. See image below.

C-arm fluoroscopic unit. C-arm fluoroscopic unit.
Typical fluoroscopic instrument panel. Typical fluoroscopic instrument panel.

The electron flow, called tube current, is generated through an electrically heated negatively charged filament (cathode) and is expressed in milliamperes (mA). The x-ray tube fires a beam of electrons through a high voltage vacuum tube forming x-rays that are emitted through a small opening. X-rays are generated by engaging a high-voltage switch with the output expressed as the kilovolt peak (kVp). These x-rays pass into and through human tissue creating electrically charged ions. The image intensifier collects electromagnetic particles that pass through the patient and transforms them into a usable image that can be visualized on a television monitor. X-ray production ceases immediately when the switch is released. For this reason, radiation management in fluoroscopy is best accomplished by keeping the amount of beam-on time as short as possible. [12] See image below.

The fluoroscopic imaging chain. The fluoroscopic imaging chain.

The C-arm facilitates optimal positioning of the fluoroscope for the practitioner to get the most favorable view, (eg, posterior-anterior, oblique, and lateral views of the patient). The control panel allows the technician to manually adjust the quality of the image or leave it to the automatic brightness control (ABC). The quality of the image contrast depends on the balance between the tube voltage and current. A higher kVp setting increases the penetrability of the x-ray beam, but reduces the contrast of the x-ray image, whereas the tube current increases both intensity and penetration. Balance of the tube current and tube voltage (kVp) creates the optimal contrast and image resolution.

This is usually accomplished by the ABC system, whereby the computer automatically analyzes the image contrast and makes the appropriate adjustments to the kVp and mA to achieve the best balance between contrast and brightness of the image with the lowest dose-rate to the patient. Dose-rates are greater depending on the thickness or size of the patient. As patient size increases, image quality decreases, patient dose increases, and exposure rates to personnel increase. The control panel also allows for magnification and collimation of the image. [13]

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