Equipment Ops & QC Flashcards
(104 cards)
Digital fluoroscopy units use which of the following devices in lieu of a television camera tube?
photomultiplier tube
EXPLANATION: In a digital fluoroscopy unit, a charge-coupled device (CCD) (A) is mounted on the output phosphor of the image intensifier tube and is coupled via fiber optics or a lens system. The sensitive layer of crystalline silicon within the CCD responds to the light from the output phosphor, creating an electrical charge. The charges are sampled, pixel by pixel, and then manipulated to produce a digital image. A photometer (B) is used to measure luminance response and uniformity of monitors used in digital imaging. Two types are commonly used: near-range and telescopic. Near-range photometers are used for measuring a monitor’s luminance at close range, whereas telescopic photometers measure this from a distance of one meter. Background ambient light should be kept constant when either photometer is used. A photomultiplier tube (C) receives light energy from the scanned IP in a CR reader and converts it into an electrical (analog) signal that can then be converted to a binary signal in the analog-to-digital convertor (ADC). This binary signal is then processed by a computer to develop a diagnostic image. Newer CR readers may use a charged-coupled device (CDC) to convert the light energy in to an electrical signal. The light gate (or channeling guide) (D) in a CR reader channels the light energy released by the image plate as it is scanned by the laser beam to the photomultiplier tube (D). (Bushong, 9th ed., p. 439).
All the following statements regarding three-phase current are true except
three-phase current is constant-potential direct current.
EXPLANATION: Three-phase current is obtained from three individual alternating currents superimposed on, but out of step with, one another by 120 degrees. The result is an almost constant potential current, with only a very small voltage ripple (4%–13%), producing more x-rays per milliampere-second. (Bushong, 10th ed., p. 243)
Tungsten alloy is the usual choice of target material for radiographic equipment because it
- has a high atomic number
- has a high melting point
- can readily dissipate heat
1, 2, and 3
EXPLANATION: The x-ray anode may be a molybdenum disk coated with a tungsten–rhenium alloy. Tungsten, with a high atomic number (74), produces high-energy x-rays quite efficiently. Since a great deal of heat is produced at the target, its high melting point (3410°C) helps to avoid damage to the target surface. Heat produced at the target should be dissipated readily, and tungsten’s conductivity is similar to that of copper. Therefore, as heat is applied to the focus, it can be conducted throughout the disk to equalize the temperature and thus avoid pitting, or localized melting, of the focal track. (Selman, 9th ed., p. 138)
Digital fluoroscopy units use which of the following devices in lieu of a television camera tube?
charge-coupled device (CCD)
EXPLANATION: In a digital fluoroscopy unit, a charge-coupled device (CCD) (A) is mounted on the output phosphor of the image intensifier tube and is coupled via fiber optics or a lens system. The sensitive layer of crystalline silicon within the CCD responds to the light from the output phosphor, creating an electrical charge. The charges are sampled, pixel by pixel, and then manipulated to produce a digital image. A photometer (B) is used to measure luminance response and uniformity of monitors used in digital imaging. Two types are commonly used: near-range and telescopic. Near-range photometers are used for measuring a monitor’s luminance at close range, whereas telescopic photometers measure this from a distance of one meter. Background ambient light should be kept constant when either photometer is used. A photomultiplier tube (C) receives light energy from the scanned IP in a CR reader and converts it into an electrical (analog) signal that can then be converted to a binary signal in the analog-to-digital convertor (ADC). This binary signal is then processed by a computer to develop a diagnostic image. Newer CR readers may use a charged-coupled device (CDC) to convert the light energy in to an electrical signal. The light gate (or channeling guide) (D) in a CR reader channels the light energy released by the image plate as it is scanned by the laser beam to the photomultiplier tube (D). (Bushong, 9th ed., p. 439).
Inadequate collimation in CR imaging can result in an image that is too
- light
- dark
- noisy
1, 2, and 3
EXPLANATION: It is important to note that histogram appearance as well as patient dose can be affected by the radiographer’s knowledge and skill using digital imaging, in addition to his or her degree of accuracy in positioning and centering. Collimation is exceedingly important to avoid histogram analysis errors. Lack of adequate collimation can result in signals outside the anatomical area being included in the exposure data recognition/histogram analysis. This can result in a variety of histogram analysis errors, including excessively light, dark, or noisy images.
Phosphors classified as rare earth include
- lanthanum oxybromide.
- gadolinium oxysulfide.
- cesium iodide.
1 and 2 only
EXPLANATION: Rare earth phosphors have a greater conversion efficiency than do other phosphors. Lanthanum oxybromide is a blue-emitting phosphor, and gadolinium oxysulfide is a green-emitting phosphor. Cesium iodide is the phosphor used on the input screen of image intensifiers; it is not a rare earth phosphor. (Shephard, p. 66)
A three-phase timer can be tested for accuracy using a synchronous spinning top. The resulting image looks like a
solid arc, with the angle (in degrees) representative of the exposure time
EXPLANATION: When a spinning top is used to test the efficiency of a single-phase timer, the result is a series of dots or dashes, with each representing a pulse of radiation. With full-wave-rectified current and a possible 120 dots (pulses) available per second, one should visualize 12 dots at 1/10 s, 24 dots at 1/5 s, 6 dots at 1/20 s, and so on.
However, because three-phase equipment is at almost constant potential, a synchronous spinning top must be used, and the result is a solid arc (rather than dots). The number of degrees formed by the arc is measured and equated to a particular exposure time.
A multitude of small, mesh-like squares describes a screen contact test. An aluminum step wedge (penetrometer) may be used to demonstrate the effect of kilovoltage on contrast (demonstrating a series of gray tones from white to black), with a greater number of grays demonstrated at higher kilovoltage levels. (Selman, 9th ed., p. 106)
Which of the following is most likely to occur as a result of using a 30-in. SID with a 14 x 17 in. IR to radiograph a fairly homogeneous structure?
Density variation between opposite ends of the IR
EXPLANATION: Since x-ray photons are produced at the tungsten target, they more readily diverge toward the cathode end of the x-ray tube. As they try to diverge toward the anode, they interact with and are absorbed by the anode “heel.” Consequently, there is a greater intensity of x-ray photons at the cathode end of the x-ray beam. This phenomenon is known as the anode heel effect. Because shorter SIDs and larger IR sizes require greater divergence of the x-ray beam to provide coverage, the anode heel effect will be accentuated. (Bushong, 8th ed., pp. 138–140)
A star pattern is used to measure
- focal spot resolution.
- intensifying-screen resolution.
- SID resolution.
1 only
EXPLANATION: A quality control program requires the use of a number of devices to test the efficiency of various components of the imaging system. A star pattern is a resolution testing device that is used to test the effect of focal spot size. A parallel-line-type resolution test pattern is used to test the resolving capability of intensifying screens. (Selman, p 210)
Excessive anode heating can cause vaporized tungsten to be deposited on the port window. This can result in
- decreased tube output.
- tube failure.
- electrical sparking.
1, 2, and 3
EXPLANATION: Vaporized tungsten may be deposited on the inner surface of the glass envelope at the tube (port) window. It acts as an additional filter, thereby reducing tube output. The tungsten deposit may also attract electrons from the filament, creating sparking and causing puncture of the glass envelope and subsequent tube failure. (Selman, pp 137–138)
Circuit devices that permit electrons to flow in only one direction are
solid-state diodes
EXPLANATION: 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. Transformers, operating on the principle of mutual induction, change the voltage (and current) to useful levels. Autotransformers, operating on the principle of self-induction, enable us to select the required kilovoltage. (Selman, 9th ed., p. 101)
A device used to ensure reproducible radiographs, regardless of tissue-density variations, is the
phototimer
EXPLANATION: Radiographic reproducibility is an important concept in producing high-quality diagnostic films. Radiographic results should be consistent and predictable not only in terms of positioning accuracy but also with respect to exposure factors. AEC devices (phototimers and ionization chambers) automatically terminate the x-ray exposure once a predetermined quantity of x-rays has penetrated the patient, thus ensuring consistent results. (Shephard, p. 274)
Which of the following are typical sizes of fluoroscopic photospot camera film?
70 mm and 105 mm
EXPLANATION: A photospot camera uses film sizes of 70 mm and 105 mm (B). Answers A, C and D include sizes not used for fluoroscopic photospot camera film. (Bushong, 10th ed., p. 413).
The trend in spot filming in conventional fluoroscopy is to use a:
Photospot camera film
EXPLANATION: Photospot camera film (D) is similar to that used in a movie camera except only one frame is exposed when activated. This film receives its light image from the output phosphor of the image intensifier tube. The photospot camera provides adequate image quality without interruption of the fluoroscopic examination, and can produce up to twelve exposures in one second. A cassette-loaded spot film (A) is positioned in a lead-lined compartment between the patient and the image intensifier. When a spot-film exposure is desired, the radiologist must actuate a control that properly positions the cassette in the X-ray beam and changes the operation of the X-ray tube from low fluoroscopic milliamperes (mA) to high radiographic mA, at which time the rotating anode is energized to a higher rotation speed. A flat panel image receptor (FPIR) (B) composed of cesium iodide and amorphous silicon pixel detectors can be used in place of an image intensifier in digital fluoroscopy for real-time imaging. Images created from this device are digitized and, therefore, can be stored in a PACS, but this device is not considered a recording system in itself. It only generates the image to be recorded. Cine film (C) is almost exclusively used in cardiac catheterization fluoroscopic procedures. Cine film typically comes in 35 mm rolls of 100 and 500 feet in length and is exposed by the light from the output phosphor of the image intensifier tube, similar to that of the photospot camera film, but while rapidly moving to expose each frame of the film strip. The exposed frames can then be played back as a continuous strip of images to produce a dynamic reproduction of the fluoroscopic images, similar to how one would draw various, slightly different images, on the same spot on multiple blank pieces of paper, and then flip these pieces of paper rapidly to produce what appears to be a moving image. Because of the rapid transition to digital imaging, the use of cine film is rapidly declining. (Bushong, 10th ed., p. 413).
Congruence of the x-ray beam with the light field is tested using
radiopaque objects
EXPLANATION: Radiographic results should be consistent and predictable with respect to positioning accuracy, exposure factors, and equipment operation. X-ray equipment should be tested and calibrated periodically as part of an ongoing quality assurance (QA) program. The focal spot should be tested periodically to evaluate its size and its impact on recorded detail; this is accomplished using a slit camera, a pinhole camera, or a star pattern. To test the congruence of the light and x-ray fields, a radiopaque object such as a paper clip or a penny is placed at each corner of the light field before the test exposure is made. After processing, the corners of the x-ray field should be exactly delineated by the radioopaque objects. (Carlton and Adler, 4th ed., p. 484)
All of the following can permanently record the images in conventional fluoroscopy, except a:
Flat panel image receptor
EXPLANATION: A flat panel image receptor (FPIR) (B) composed of cesium iodide and amorphous silicon pixel detectors can be used in place of an image intensifier in digital fluoroscopy for real-time imaging. Images created from this device are digitized and, therefore, can be stored in a PACS, but this device is not considered a recording system in itself. It only generates the image to be recorded. A cassette-loaded spot film (A) is positioned in a lead-lined compartment between the patient and the image intensifier. When a spot-film exposure is desired, the radiologist must actuate a control that properly positions the cassette in the X-ray beam and changes the operation of the X-ray tube from low fluoroscopic milliamperes (mA) to high radiographic mA, at which time the rotating anode is energized to a higher rotation speed. Photospot camera film (C) is similar to that used in a movie camera except only one frame is exposed when activated. This film receives its light image from the output phosphor of the image intensifier tube and therefore requires less patient exposure than that required when using the cassette-loaded spot film image recording method. Cine film (D) is almost exclusively used in cardiac catheterization fluoroscopic procedures. Cine film typically comes in 35 mm rolls of 100 and 500 feet in length and is exposed by the light from the output phosphor of the image intensifier tube, similar to that of the photospot camera film, but while rapidly moving to expose each frame of the film strip. The exposed frames can then be played back as a continuous strip of images to produce a dynamic reproduction of the fluoroscopic images, similar to how one would draw various, slightly different images, on the same spot on multiple blank pieces of paper, and then flip these pieces of paper rapidly to produce what appears to be a moving image. Because of the rapid transition to digital imaging, the use of cine film is rapidly declining. (Bushong, 10th ed., pp. 412-413).
Focal-spot blur is greatest
toward the cathode end of the x-ray beam
EXPLANATION: Focal-spot blur, or geometric blur, is caused by photons emerging from a large focal spot. Because the projected focal spot is greatest at the cathode end of the x-ray tube, geometric blur is also greatest at the corresponding part (cathode end) of the radiograph. The projected focal-spot size becomes progressively smaller toward the anode end of the x-ray tube. (Bushong, 8th ed., p. 140)
An automatic exposure control (AEC) device can operate on which of the following principles?
- A photomultiplier tube charged by a fluorescent screen
- A parallel-plate ionization chamber charged by x-ray photons
- Motion of magnetic fields inducing current in a conductor
1 and 2 only
EXPLANATION: A phototimer is one type of automatic exposure control (AEC) that actually measures light. As x-ray photons penetrate and emerge from a part, a fluorescent screen beneath the cassette glows, and the fluorescent light charges a photomultiplier tube. Once a predetermined charge has been reached, the exposure terminates automatically. A parallel-plate ionization chamber is another type of AEC. A radiolucent chamber is beneath the patient (between the patient and the IR). As photons emerge from the patient, they enter the chamber and ionize the air within it. Once a predetermined charge has been reached, the exposure is terminated automatically. Motion of magnetic fields inducing a current in a conductor refers to the principle of mutual induction. (Fauber, 2nd ed., pp. 232–233)
The image-intensifier tube’s input phosphor functions to convert
x-rays to light
EXPLANATION: The image intensifier’s input phosphor receives the remnant radiation emerging from the patient and converts it into a fluorescent light image. Very close to the input phosphor, separated by a thin, transparent layer, is the photocathode. The photocathode is made of a photoemissive alloy, usually an antimony and cesium compound. The fluorescent light image strikes the photocathode and is converted to an electron image that is focused by the electrostatic lenses to the output phosphor. (Bushong, 8th ed., p. 360)
In which type of equipment does kilovoltage decrease during the actual length of the exposure?
- Condenser-discharge mobile equipment
- Battery-operated mobile equipment
- Fixed x-ray equipment
1 only
EXPLANATION: Mobile x-ray machines are compact and cordless and are either the battery-operated type or the condenser-discharge type. Condenser-discharge mobile x-ray units do not use batteries; this type of mobile unit requires that it be charged before each exposure. A condenser (or capacitor) is a device that stores electrical energy. The stored energy is used to operate the x-ray tube only. Because this machine does not carry many batteries, it is much lighter and does not need a motor to drive or brake it. The major disadvantage of the capacitor/condenser-discharge unit is that as the capacitor discharges its electrical charge, the kilovoltage gradually decreases throughout the length of the exposure—therefore limiting tube output and requiring recharging between exposures. (Frank, Long, and Smith, 11th ed., vol. 3, p. 235)
With three-phase equipment, the voltage across the x-ray tube
- drops to zero every 180 degrees
- is 87% to 96% of the maximum value
- is at nearly constant potential
2 and 3 only
EXPLANATION: With single-phase, full-wave-rectified equipment, the voltage is constantly changing from 0% to 100% of its maximum value. It drops to 0 every 180 degrees (of the AC waveform); that is, there is 100% voltage ripple. With three-phase equipment, the voltage ripple is significantly smaller. Three-phase, six-pulse equipment has a 13% voltage ripple, and three-phase, 12-pulse equipment has a 3.5% ripple. Therefore, the voltage never falls below 87% to 96.5% of its maximum value with three-phase equipment, and it closely approaches constant potential [direct current (DC)]. (Carlton and Adler, 4th ed., pp. 91–93)
Which of the following is a device that can be used in lieu of an image intensifier/charge-coupled device combination in digital fluoroscopy?
A. Charge-coupled device
B. Flat panel image receptor
C. photometer
D. photomultiplier tube
Flat panel image receptor
EXPLANATION: A flat panel image receptor (FPIR) (B) composed of cesium iodide and amorphous silicon pixel detectors can be used in place of an image intensifier in digital fluoroscopy. There are several advantages of FPIR imaging over image intensifier/CCD imaging, including distortion free images, constant image quality and contrast resolution over the entire image, high detective quantum efficiency (DQE) at all dose levels, a rectangular image area coupled to a similar shaped image monitor, and its immunity to external magnetic fields. A charge-coupled device (CCD) (A) is mounted on the output phosphor of the image intensifier tube and is coupled via fiber optics or a lens system. The sensitive layer of crystalline silicon within the CCD responds to the light from the output phosphor, creating and electrical charge. The charges are sampled, pixel by pixel, and then manipulated to produce a digital image. A photometer (C) is used to measure the luminance response and uniformity of monitors used in digital imaging. A photomultiplier tube receives light energy from the scanned IP plate in a CR reader and converts it into an electrical (analog) signal that can then be converted to a binary signal in the analog-to-digital convertor (ADC). This binary signal is then processed by a computer to develop a diagnostic image. Newer CR readers may use a charged-coupled device (CDC) (D) to convert the light energy into an electrical signal. (Bushong, 9th ed., pp. 441-442).
The advantages of collimators over aperture diaphragms and flare cones include
- the variety of field sizes available
- more efficient beam restriction
- better cleanup of scattered radiation
1 and 2 only
EXPLANATION: There are three types of beam restrictors—aperture diaphragms, cones and cylinders, and collimators. The most practical and efficient type is the collimator. Its design makes available an infinite number of field-size variations that are not available with the other types of beam restrictors. Because aperture diaphragms and flare cones have a fixed aperture size and shape, their beam restriction is not as efficient as that of the variable size collimator. Aperture diaphragms, cones, and cylinders may be placed on a collimator track so that the illuminated crosshairs are visualized. Although the collimator assembly contributes approximately 1.0 mm Al equivalent to the added filtration of the x-ray tube (because of the plastic exit portal and silver-coated reflective mirror), its functions are unrelated to the cleanup of scattered radiation. This is so because the patient is the principal scatterer, and grids function to clean up scattered radiation generated by the patient. (Bushong, 8th ed., pp. 241–243)
Which of the following x-ray circuit devices operate(s) on the principle of mutual induction?
- High-voltage transformer
- Filament transformer
- Autotransformer
1 and 2 only
EXPLANATION: In mutual induction, two coils are in close proximity, and a current is supplied to one of the coils. As the magnetic field associated with every electric current expands and “grows up” around the first coil, it interacts with and “cuts” the turns of the second coil. This interaction, motion between magnetic field and coil (conductor), induces an electromotive force (emf) in the second coil. This is mutual induction, the production of a current in a neighboring circuit. Transformers, such as the high-voltage transformer and the filament (step-down) transformer, operate on the principle of mutual induction. The autotransformer operates on the principle of self-induction. Both the transformer and the autotransformer require the use of alternating current. (Bushong, 8th ed., p. 99)