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The minimum response time of an automatic exposure control (AEC)
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Which of the following will serve to increase the effective energy of the x-ray beam?
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COMPREHENSIVE EQUIPM
| Question | Answer |
|---|---|
| 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 |
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