Fluoroscopy

Fluoroscopy is a study of moving body structures similar to an x-ray "movie." A continuous x-ray beam is passed through the body part being examined, and is transmitted to a TV-like monitor so that the body part and its motion can be seen in detail.



History of Fluoroscopy

The fluoroscope was invented by Thomas A. Edison in 1896. Edison quickly discovered that calcium tungstate screens produced brighter images and is credited with designing and producing the first commercially available fluoroscope. In its infancy, many incorrectly predicted that the moving images from fluoroscopy would completely replace the still x-ray radiographs, but the superior diagnostic quality of the earlier radiographs prevented this from occurring.



Purpose of Fluoroscopy

Fluoroscopy enables radiologists and physicians to look at many body systems and is performed to evaluate specific areas of the body, including the bones, muscles, and joints, as well as solid organs such as the heart, lung, or kidneys.





Risks

Because fluoroscopy involves the use of x rays, a form of ionizing radiation, all fluoroscopic procedures pose a potential health risk to the patient. Radiation doses to the patient depend greatly on the size of the patient as well as length of the procedure, with typical skin dose rates quoted as 20-50 mGy/min. Exposure times vary depending on the procedure being performed, but procedure times up to 75 minutes have been documented. Because of the long length of some procedures, in addition to standard cancer-inducing stochastic radiation effects, deterministic radiation effects have also been observed ranging from mild erythema, equivalent of a sun burn, to more serious burns.



Equipment

The first fluoroscopes consisted of an x-ray source and fluorescent screen between which the patient would be placed. As the x rays pass through the patient, they are attenuated by varying amounts as they interact with the different internal structures of the body, casting a shadow of the structures on the fluorescent screen. Images on the screen are produced as the unattenuated x rays interact with atoms in the screen through the photoelectric effect, giving their energy to the electrons. While much of the energy given to the electrons is dissipated as heat, a fraction of it is given off as visible light, producing the images. Early radiologists would adapt their eyes to view the dim fluoroscopic images by sitting in darkened rooms, or by wearing red adaptation goggles.

Image Intensifier Tube




The image-intensifier tube is a complex electronic device that image-forming x-ray beam and converts it into a visible light image of high intensity. The tube components are contained within a glass or metal envelope that provides structural support but more importantly maintains a vacuum.The overall system consists of an x-ray source, input window, input phosphor, photocathode, vacuum and electron optics, accelerating anode, output phosphor and output window,. It allows for lower x-ray doses to be used on patients by magnifying the intensity produced in the output image, enabling the viewer to easily see the structure of the object being imaged.

Linear Tomography

PURPOSE
The purpose of linear tomography is for the clinical staff to make a sectional image through a specific body part. Consequently, structures in the focal plane appear sharper, while structures in other planes appear blurred. By modifying the direction and extent of the movement, operators can select different focal planes which contain the structures of interest.




PRINCIPLE
The principle of linear tomography is that the X-ray tube is moved in a straight line in one direction while the film moves in the opposite direction. As these shifts occur, the X-ray tube continues to emit radiation so that most structures in the part of the body under examination are blurred by motion. Only those objects lying in a plane coinciding with the pivot point of a line.








EQUIPMENT
Linear tomographic equipment is inexpensive and requires shorter exposure times than equipment requiring circular and hypocycloidal motion, however, there is a greater possibility that blurring and streaks will result.


The tomographic object plane contains the fulcrum. The imaginary pivot point from which the tube and the image receptor move. The tomography angle is the angle of movement that determines tomography section thickness. The principal advantage of tomography is its improved radiographic contrast.