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COMPREHENSIVE EQUIPM

QuestionAnswer
The minimum response time of an automatic exposure control (AEC) is its shortest possible exposure time
Which of the following will serve to increase the effective energy of the x-ray beam? 1. Increase in added filtration 2. Increase in kilovoltage
The line focus principle refers to the fact that the actual focal spot is larger than the effective focal spot.
In fluoroscopy, the automatic brightness control adjusts the kVp and mA
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
To determine secondary voltage Vsecondary = Iprimmary ~~~~~~~~~~ ~~~~~~~~~ Vprimary = Isecondary
To determine secondary amps Nsecondary = Iprimary Nprimary = I secondary
With full-wave-rectified current and a possible 120 dots (pulses) available per second, one should visualize 12 dots at 1/10 second, 6 dots at 0.05 second, 10 dots at 1/12 second, and 3 dots at 0.025 second
Circuit devices that will conduct electrons in only one direction are 1. valve tubes. 2. solid-state diodes.
Rectifiers change AC into unidirectional current by allowing current to flow through them in only one direction
Valve tubes are vacuum rectifier tubes found in older equipment
Solid-state diodes are the types of rectifiers used in today's x-ray equipment
Rectification systems are found between the secondary coil of the high-voltage transformer and the x-ray tube
Resistors, such as rheostats or choke coils, are circuit devices used to vary voltage or current
What is the device that directs the light emitted from the image intensifier to various viewing and imaging apparatus? Beam splitter
The light image emitted from the output phosphor of the image intensifier is directed to the TV monitor for viewing and sometimes to recording devices such as a spot film camera or cine film
The light is directed to these places by a beam splitter or objective lens located between the output phosphor and the TV camera tube
The majority of the light will go to the recording device, while a small portion goes to the TV so that the procedure may continue to be monitored during filming
Which of the following devices is used to control voltage by varying resistance? Rheostat
The autotransformer operates on the principle of self-induction and functions to select the correct voltage to be sent to the high-voltage transformer to be "stepped up" to kilovoltage
The high-voltage transformer increases the voltage and decreases the current
The rheostat is a type of variable resistor that is used to change voltage or current values
the rheostat is frequently found in the filament circuit
A fuse is a device used to protect the circuit elements from overload by opening the circuit in the event of a power surge
Which of the following will improve the spatial resolution of image-intensified images? 1. A very thin coating of cesium iodide on the input phosphor 2. A smaller-diameter input screen
An image's spatial resolution refers to its recorded detail
The effect of the input screen's phosphor layer is similar to the effect of the phosphor layer thickness in intensifying screens; that is, as the phosphor layer can be made thinner, recorded detail increases
the smaller the input phosphor diameter, the greater the spatial resolution
does a brighter image affect resolution? no
To eject a K shell electron from a tungsten atom, the incoming electron must have an energy of at least 70 keV
Characteristic radiation makes up about what percent of the primary beam? 15%
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
as the focal point moves back 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
To maintain image clarity in an image intensifier system, the path of electron flow from the photocathode to the output phosphor is controlled by electrostatic lenses
The input phosphor of an image intensifier receives remnant radiation emerging from the patient and converts it to a fluorescent light image
Directly adjacent to the input phosphor is the photocathode, which is made of a photoemissive alloy (usually a cesium and antimony compound)
The fluorescent light image strikes the photocathode and is converted to an electron image
The electrons are carefully focused, to maintain image resolution, by the electrostatic focusing lenses, through the accelerating anode and to the output phosphor for conversion back to light
The big advantage of the objective lens is that it allows the use of auxiliary imaging devices such as a cine camera or spot film camera.
Exposures less than the minimum response time of an AEC may be required when 1. using high mA. 2. using fast film-screen combinations.
steep or small target angle= greater heat load, but more anode heel effect
Components of digital imaging include 1. computer manipulation of the image. 2. formation of an electronic image on the radiation detector.
Which of the following x-ray circuit devices operate(s) on the principle of mutual induction? 1. High-voltage transformer 2. Filament transformer
Features of x-ray tube targets that function to determine heat capacity include the 1. rotation of the anode. 2. diameter of the anode. 3. size of the focal spot.
Which of the following is (are) characteristics of the x-ray tube? 1. The target material should have a high atomic number and a high melting point. 2. The useful beam emerges from the port window. 3. The cathode assembly receives both low and high voltages.
in case the AEC fails to terminate the exposure, the backup timer would protect the patient from overexposure and the x-ray tube from excessive heat load.
The brightness gain of image intensifiers is 5000 to 20,000
as the electron image is focused to the output phosphor, it is accelerated by high voltage (this is flux gain)
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.
As the target angle decreases, the effective (projected) focal spot becomes smaller
Off-focus, or extrafocal, radiation may be minimized by restricting the x-ray beam as close to its source as possible.
Off-focus, or extrafocal, radiation is produced as electrons strike metal surfaces other than the focal track and produce x-rays that emerge with the primary beam at a variety of angles
This radiation is responsible for indistinct images outside the collimated field
Mounting a pair of shutters as close to the source as possible minimizes off-focus radiation
The timer, autotransformer, and (prereading) kV meter are all located in the low-voltage circuit
The mA meter is connected at the midpoint of the secondary coil of the high-voltage transformer.
Capacitor discharge mobile x-ray units 1. use a grid-controlled x-ray tube. 2. provide a direct current output.
the capacitor must be charged just before the exposure is made
Double-focus x-ray tubes have two filaments
TV camera tubes used in image intensification, such as the Plumbicon and Vidicon, function to transfer the output phosphor image to the TV monitor
What parts of the x-ray circuit are on the secondary (high-voltage) side The secondary coil of the step-up transformer, The step-down transformer, or filament transformer, and The rectification system
choke coil operates on the principle of self-induction; it is a type of variable resistor that may be used to regulate filament current.
Which of the following information is necessary to determine the maximum safe kVp, using the appropriate x-ray tube rating chart? 1. mA and exposure time 2. Focal spot size
Because single-phase, full-wave-rectified current has 120 useful impulses per second, a 1-second exposure of the spinning top should demonstrate 120 dots
a 0.05-second exposure should demonstrate six dots
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.
Star and wye configurations are related to three-phase transformers
The part of a CT imaging system made of thousands of solid-state photodiodes is the detector array
A CT imaging system has three component parts a gantry, a computer, and an operating console
The gantry component includes an x-ray tube, a detector array, a high-voltage generator, a collimator assembly, and a patient couch with its motorized mechanism
The CT x-ray tube must have a very high short-exposure rating and must be capable of tolerating several million heat units while still having a small focal spot for optimal resolution
To help tolerate the very high production of heat units, the anode must be capable of high-speed rotation
The x-ray tube produces a pulsed x-ray beam (1–5 ms) using up to about 1000 mA
The scintillation detector array is made of thousands of solid-state photodiodes
These scintillation crystal (cadmium tungstate or rare earth oxide ceramic crystals) photodiode assemblies convert the transmitted x-ray energy into light
That light is then converted into electrical energy and finally into an electronic/digital signal
If the scintillation crystals are packed tightly together so that there is virtually no distance between them, efficiency of x-ray absorption is increased, and patient dose is decreased
Detection efficiency is extremely high approximately 90 percent
The high-voltage generator provides high-frequency power to the CT x-ray tube, enabling the high-speed anode rotation and the production of high-energy pulsed x-ray photons
Similar to the high-frequency x-ray tubes used in projection radiography, conventional 60-Hz full-wave rectified power is converted to a higher frequency of 500–25,000 Hz
The CT high-frequency generator is often mounted in the gantry's rotating wheel
The collimator assembly has two parts
The prepatient, or predetector, collimator is at the x-ray tube that consists of multiple beam restrictions so that the x-ray beam diverges little
This reduces patient dose and reduces the production of scattered radiation, thereby improving the CT image
The postpatient collimator, or predetector collimator, confines the exit photons before they reach the detector array and determines slice thickness
The patient table, or couch, provides positioning support for the patient
Inaccurate indexing can result in missed anatomy and/or double-exposed anatomy
A CT imaging system has three component parts a gantry, a computer, and an operating console
The gantry component includes an x-ray tube, a detector array, a high-voltage generator, a collimator assembly, and a patient couch with its motorized mechanism
The CT x-ray tube must have a very high short-exposure rating and must be capable of tolerating several million heat units while still having a small focal spot for optimal resolution
To help tolerate the very high production of heat units, the anode must be capable of high-speed rotation
The x-ray tube produces a pulsed x-ray beam (1–5 ms) using up to about 1000 mA
The scintillation detector array is made of thousands of solid-state photodiodes
These scintillation crystal (cadmium tungstate or rare earth oxide ceramic crystals) photodiode assemblies convert the transmitted x-ray energy into light
That light is then converted into electrical energy and finally into an electronic/digital signal
If the scintillation crystals are packed tightly together so that there is virtually no distance between them, efficiency of x-ray absorption is increased, and patient dose is decreased
Detection efficiency is extremely high approximately 90 percent
The high-voltage generator provides high-frequency power to the CT x-ray tube, enabling the high-speed anode rotation and the production of high-energy pulsed x-ray photons
Similar to the high-frequency x-ray tubes used in projection radiography, conventional 60-Hz full-wave rectified power is converted to a higher frequency of 500–25,000 Hz
The CT high-frequency generator is often mounted in the gantry's rotating wheel
The collimator assembly has two parts
The prepatient, or predetector, collimator is at the x-ray tube that consists of multiple beam restrictions so that the x-ray beam diverges little
This reduces patient dose and reduces the production of scattered radiation, thereby improving the CT image
The postpatient collimator, or predetector collimator, confines the exit photons before they reach the detector array and determines slice thickness
The patient table, or couch, provides positioning support for the patient
Inaccurate indexing can result in missed anatomy and/or double-exposed anatomy
The advantages of large format spot film cameras, such as 100 mm and 105 mm, over smaller format cameras, such as 70 mm and 90 mm, include improved image quality
The timer, circuit breaker, autotransformer, kilovoltage selector switch, and (prereading) kilovoltage meter are all located in the low-voltage circuit.
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
It follows that 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
Stereoscopy a technique used to produce a radiographic third dimension
Created by: jen. on 2011-04-19



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