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41 terms

Fluoroscopic unit

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Using a multifield image intensifier tube, which of the following input phosphor diameters will require the highest patient dose?
12 cm
Multifield image intensifier tubes are usually either dual-field or tri-field and are designed this way in order to permit
magnification imaging
As voltage is applied to the electrostatic focusing lenses, the focal point
moves back—closer to the input phosphor—and a smaller portion of the input phosphor is utilized
As a result, the FOV
decreases and magnification increases, producing better spatial resolution
At the same time, brightness is
decreased requiring an increase in mA (therefore increased patient dose).
This increase in mA increases
image quality; It can be likened to an increase in signal-to-noise ratio (SNR), with mA being the signal.
Using a multifield image intensifier tube, which of the following input phosphor diameters will provide the greatest magnification?
12cm
Which of the following devices is (are) component(s) of a typical fluoroscopic video display system?
1. TV camera
2. TV monitor
The image on the image intensifier's output phosphor may be displayed for viewing through the use of
either a series of lenses or a fiberoptic link.
The two devices needed to view the image are
a TV camera tube and a TV monitor.
The TV camera tube (usually a Plumbicon or Vidicon) converts the output phosphor image into
an electrical signal
The TV monitor (a cathode-ray tube) then converts the electrical signal into
a visible light image
Using a multifield image intensifier tube, which of the following input phosphor diameters will provide the best spatial resolution?
12cm
Which system functions to compensate for changing patient/part thicknesses during fluoroscopic procedures?
Automatic brightness control
The automatic brightness control functions to
vary the required mAs and/or kVp as necessary; with this method, patient dose varies, and image quality is maintained.
Minification and flux gain contribute to
total brightness gain
The brightness level of the fluoroscopic image can vary with
1. milliamperage.
2. kilovoltage.
3. patient thickness.
Fluorescent light is collected from the image intensifier output phosphor and converted to an electronic video signal by the
1. TV camera tube.
2. CCD.
A TV camera tube is found on
older fluoroscopic equipment.
Today's newer fluoroscopic equipment uses
a CCD (charge-coupled device) to accomplish this task
The CCD is a
solid-state device that offers much better spatial resolution and less image noise.
A coaxial cable
follows the TV camera or CCD in the fluoroscopic chain. It is used to connect the TV camera or CCD to the TV monitor.
As the image intensifier's FOV is reduced, how is the resulting image affected?
1. Magnification increases
2. Brightness decreases
3. Quality increases
An image intensifier functions to
provide a brighter fluoroscopic image,
The line voltage compensator
automatically adjusts the incoming line voltage to the x-ray machine to correct for any voltage drops or surges.
Use of a portion of the input phosphor during fluoroscopy, rather than the entire input phosphor, will result in
1. a magnified image.
2. improved spatial resolution.
In fluoroscopy, the automatic brightness control adjusts the
kVp and mA
The ABC functions to
maintain constant brightness and contrast of the output screen image, correcting for fluctuations in x-ray beam attenuation with adjustments in kVp and/or mA.
There are also brightness and contrast controls on the monitor that
the radiographer can regulate
Image quality in digital fluoroscopy is influenced by
1. pixel size.
2. contrast.
3. noise.
The smaller the pixel size and larger the matrix, the better the
image's spatial resolution
Noise can result from a number of causes including
insufficient mA (i.e., signal) causing graininess/mottle, and scattered radiation fog.
The total brightness gain of an image intensifier is a result of
1. flux gain.
2. minification gain.
The brightness gain of image intensifiers is
5000 to 20,000
This increase is accomplished in two ways
First, as the electron image is focused to the output phosphor, it is accelerated by high voltage (this is flux gain). Second, the output phosphor is only a fraction of the size of the input phosphor, and this decrease in image size represents another brightness gain, termed minification gain.
Total brightness gain is equal to
the product of minification gain and flux gain.
Moving the image intensifier closer to the patient during fluoroscopy
1. decreases the source-image distance (SID).
2. decreases patient dose.
3. improves image quality.
Moving the image intensifier closer to the patient during fluoroscopy
reduces the distance between the x-ray tube (source) and the image intensifier (image receptor), that is, the SID.
the distance between the part being imaged (object) and the image intensifier (image receptor), that is, the OID, is
also reduced
The shorter OID produces
less magnification and better image quality
As the SID is reduced,
the intensity of the x-ray photons at the image intensifier's input phosphor increases, stimulating the automatic brightness control (ABC) to decrease the mA and thereby decreasing patient dose