Fluoroscopy

FLUOROSCOPY

This is the study of moving body structures. It is very similar to x-rays only that a continuos beam is passed through the body and is projected onto a moniter.

Image intensified fluoroscopy : this is an imaging procedure whereby the radiologist sees images of the internal parts of the patient as he or she is making exposures. Images are projected to a screen to be seen by the radiologist. Fluoroscopy is mainly used in procedures like esophagus, barium enema and so on. In most if not all cases, the patient is given some form of contrast material to enable accurate visualization.

Intensification principles : there are a few terms associated with fluoroscopy;

1.Brightness gain- this is the means by which the fluoroscope gains brightness since it appears darker than usual. This is the minification gain multiplied by the flux gain.

2.Minification gain- the ration of the square of the diameter of the input phosphor to the square of the diameter of the output phosphor. This reduces the size on the input phospher screen.

3.Flux gain- the ration of the number of light photons at the output phosphor to the number of x-rays at the input phosphor.

4. Conversion factor-this is the means by which the image intensifier converts x-rays into visible light.

Automatic Brightness Control: this controls the brightness of the image by automatically differentiating kvp and MA.

Multi-field image intensification: a fluoroscope without magnification is difficult to visualize. The multi-field image intensification makes examinations flexible, this is because the tube comes in many sizes and thus helps in magnifying the image. However, patient dose is increased due to increase in mA. However, magnification of the image causes spatial resolution and contrast to be improved with decrease in phosper diameter which may vary. Distortion and noise is also minimized.

The camera: This camera tube converts the light image from the output phosphor of the image intensifier into an electrical signal. It is then sent to the monitor, where it is reconstructed as an image on the television screen. One way that you can convert the light from the output phosphor into an electrical image is the charge-coupled device (CCD).

The fluoroscopy tube: there are four major principles

1. A vacuum bottle;keeps the air out.
2.An input layer

3. Electronic lens
4.An output phospher

Tomography is a branch of imaging which produces an image called a tomogram which shows a single plane of an object in very specific detail.
The tomographic examination is designed to image only the anatomy that lies in the plane of interest, while blurring structures on either side of that plane. This brings us the sub heading linear tomography.

Linear tomography is the most basic form of tomography which permits the acquisition of x-ray relative to any plane that is parallel to the x-ray table. The main purpose of linear tomography is to blur out objects lying above and below the plane and for object lying in the plane to be properly imaged. This method improves the contrast resolution

the principle of linear tomography is pretty simple. During linear tomography, the x-ray tube is attached mechanically to the image receptor and moves in one direction, while the image receptor moves in the opposite direction. An imaginary pivot point called the fulcrum is the point where the tube and the image receptor move. The position of the fulcrum determines the object plane, and only those anatomical structures lying within this plane are clearly imaged, thus blurring out every other another anatomy below or above the object plane.

In terms of application, linear tomography is used to view parts of the body that have uniform absorption for x-rays (the abdomen is a clear example). It is applied in nephrotomography, which is linear tomography of the kidneys with a relatively large tomographic angle. It basically blurs out any organ blocking the kidneys. Linear tomography is also applied in IVP. The major disadvantage of linear tomography or tomography for that matter is increased patient dose.