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120 Cards in this Set
- Front
- Back
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With what frequency must radiographic equipment be checked for linearity and reproducibility? |
Annually. - Examples of tests are focal spot size, linearity, reproducibility, filtration, kVp, and exposure time. |
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Which of the following occurs during Bremsstrahlung (Brems) radiation production? |
An electron approaching a positive nuclear charge changes direction and loses energy. |
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Typical examples of digital imaging include |
MRI CT CR |
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Component parts of a CT gantry include |
High-voltage generator Multidetector array X-ray tube |
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Design characteristics of x-ray tube targets that determine heat capacity include |
The rotation of the anode - target that rotates spreads heat over large area The diameter of the anode - larger the diameter, the longer the focal track, and larger area being heated The size of the focal spot - larger the field, the larger the heat spread |
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If exposure factors of 85 kV, 400 mA, and 12 ms yield an output exposure of 150 mR, what is the milliroentgens per milliampere-seconds (mR/mAs)? |
31. - 150 mR divided by 4.8 mAs = 31.25 mR/mAs |
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If a high voltage transformer has 100 primary turns and 50,000 secondary turns and is supplied by 220 V and 100 A, what are the secondary voltage and current? |
200 mA and 110 kV. - |
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Which of the waveforms below is illustrative of high-frequency current? |
Diagram F. - this shows high frequency current, which is most efficient and produces less than 1% voltage ripple. |
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When using the smaller field in a dual-field image intensifier |
The image is magnified. - The electrostatic focusing lenses are given a greater charge to focus the electron image more tightly, then the focal point moves further from the output phosphor and brightness gain is somewhat diminished. Patient area viewed is smaller and magnified. |
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Light-sensitive AEC devices are known as |
Phototimers. - Small fluorescent screen beneath cassette, when remnant radiation emerging from patient exposes the IR and exits, the fluorescent screen emits light. Once enough light emits to the photocells the exposure terminates. |
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The electron cloud within the x-ray tube is the product of a process called |
Thermionic emission. |
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Which of the following will improve the spatial resolution of image-intensifier images? |
A very thin coating of cesium iodide on the input phosphor & a smaller-diameter input screen. - As layer is made thinner, the detail increases. A smaller diameter creates great detail. |
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Which of the following are characteristics of the x-ray tube? |
The target material should have a high atomic # and a high melting point - to avoid damage to the target surface The useful beam emerges from the port window - Most x-rays generated at the focal spot will pass through the port window The cathode assembly receives both low and high voltages - Low voltage current to heat it to the point of thermionic emission then high voltage is applied to drive electrons across the focal track. |
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A parallel-plate ionization chamber receives a particular charge as x-ray photons travel through it. This is the operating principle of which of the following devices? |
AEC. - This radiolucent chamber beneath the patient terminates exposure once enough photons reach it. |
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Which of the following will serve to increase the effective energy of the x-ray beam? |
Increase in added filtration - lower energy photons are removed and overall energy of wavelength of beam is greater. Increase in kilovoltage - more high energy photons are produced and again, overall energy of beam is greater. |
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Which of the following combinations would pose the least hazard to a particular single phase anode? |
1.2-mm focal spot, 92 kV, 1.5 mAs. - This group is delivering its heat to the large focal spot, thereby decreasing the head load to the anode. |
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Of what material is Number 1 made of? |
Tungsten. This is the filament of the cathode which is made of tungsten and functions to liberate electrons when heated to white hot. |
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Which of the following systems functions to compensate for changing patient/part thicknesses during fluoroscopic procedures? |
Automatic brightness control (ABC). - Functions vary the required mAs. Patient dose varies, and image quality is maintained. |
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Delivery of large exposures to a cold anode or use of exposures exceeding tube limitation can result in |
Cracking of the anode Rotor-bearing damage |
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If the primary coil of high-voltage transformer is supplied by 220 V and has 400 turns and the secondary coil has 100,000 turns, what is the voltage induced in the secondary coil? |
55 kV. |
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What is the relationship between kV and HVL? |
As kV increase, HVL increases. - The higher the kV (energy) the greater the HVL needed to cut its intensity in half. Direct relationship. |
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As window level increases |
Brightness increases. - As window level increases the scale of contrast increases |
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Circuit devices that permit electrons to flow in only one direction are |
Solid-state diodes. - Rectifiers change AC into unidirectional current by allowing current to flow through then in one direction. Solid-state diodes are rectifiers used today in x-ray equipment. |
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Patient dose during fluoroscopy is affected by the |
Distance between the patient and the input phosphor - As SID reduces, the intensity of x-ray photons at the image intensifier's input phosphor increases, ABC then automatically decreases mA & patient dose. Amount of magnification - Moving image intensifier closer, decreases OID, and magnification. Tissue density - As tissue density increases, greater exposure is required. |
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The AEC backup timer functions to |
Protect the patient from overexposure. Protect the x-ray tube from excessive heat. |
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Which of the following devices converts mechanical energy to electrical energy? |
Generator. - As alternating or direct current. |
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The essential function of a phototimer is |
Terminate the x-ray exposure once the IR is correctly exposed. Example: Ionization chamber |
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A slit camera is used to measure |
Focal spot size - Annually tested by slit camera or star pattern or pinhole camera. Spatial resolution - Is affected by the focal spot size. |
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In which of the following examinations would an IP front with very low absorption properties be especially important? |
Mammography. - Mammo uses very low kV levels and any attenuation of beam by the IR front would be undesirable. Low attenuating carbon fibers or special plastics that resist impact/heat softening are used as IR front material. |
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Which of the following causes pitting, or many small surface melts, of the anode's focal track? |
Repeated, frequent overloading. - Exposure in excess of safe values = surface melts, or pits on the focal track. This results in decreased tube output. |
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The advantages of collimators over aperture diaphragms and flare cones include |
The variety of field sizes available. More efficient beam restriction. Collimators are most sufficient and aperture diagrams/cones are good for illuminated crosshairs. |
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The type of x-ray tube designed to turn on and off rapidly, providing multiple short, precise exposure, is |
Grid-controlled. - A grid-controlled tube uses molybdenum focusing cup as switch = very precise control of tube current. |
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Characteristics of the metallic element tungsten include |
Ready dissipation of heat- Tungsten's conductivity is similar to Copper, therefore heat applied to focus can be conducted throughout disk without pitting, melting of focal track High melting point- Helps avoid damage to target surface High atomic #- Produces high energy x-rays more efficiently |
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Which image depicts the phototimer-type automatic exposure control (AEC)? |
Image B. Small fluorescent screen beneath IR that emits light when radiation from patient exposes and hits IR. |
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The voltage ripple associated with a three-phase, 12-pulse rectified generator is about |
13%. Voltage ripple - % drop from maximum voltage each pulse of current experiences. |
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The device that receives the remnant beam, converts it into light, and then increases the brightness of that light is the |
Image intensifier. - Most desirable condition for fluoroscopic viewing is to have a bright enough image to permit cone (daylight) vision for better detail perception. Image intensifiers do this and are converted to TV monitor for viewing. |
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A high-speed electron is decelerated as is attracted to a tungsten atom nucleus. This results in |
Bremsstrahlung radiation. - If positive nucleus of a tungsten atom attract the electron, changing its course, a certain amount of energy is given up in the for of x-ray photon called Brems. or "Braking" radiation. |
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All the following are components of the image intensifier except |
The TV monitor. - Just serves to display image that is transmitted to it from the output phosphor. |
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Components of digital imaging include |
Computer manipulation of the image. Formation of an electronic image on the radiation detector. |
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Which of the following is used in digital fluoroscopy, replacing the image intensifier's television camera tube? |
Charge-coupled device.- CCD They are more sensitive to to light emitted by the output phosphor than analog cameras and are associated with less "noise" |
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Which of the following devices is used to control voltage by varying resistance? |
Rheostat. - Type of variable resistor that is used to change voltage or current values and is found frequently in the filament circuit. |
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The regular measurement and evaluation of radiographic equipment components and their performance is more accurately termed as |
Quality control. Examples: focal-spot size, linearity, reproducibility, collimation, filtration, kV, and exposure time. |
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The procedure whose basic operation involves reciprocal motion of the x-ray tube and IR is |
Tomography. - Blurring everything above and below level of particular body level of interest. |
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In fluoroscopy, the automatic brightness control is used to adjust the |
Kilovoltage (kV) and milliamperage (mA). Also to maintain contrast brightness and contrast of the output screen image. |
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When the radiographer selects kilovoltage on the control panel, which devices is adjusted? |
Autotransformer. - Selecting the amount of voltage to send to the high-voltage transformer to be stepped up (to kilovoltage) |
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Star and wye (delta) configurations are related to |
Three-phase transformers. - Instead of having one single primary coil and single secondary coil, the high-voltage transformer has three primary and three secondary windings = one for each phase. |
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What is the device that directs the light emitted from the image intensifier to various viewing and imaging apparatus? |
Beam splitter. - or objective lens located between the output phosphor and TV camera tube (CCD) The majority of light will go to recording device, whereas small portion goes to the monitor so the procedure can be observed. |
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As electrons impinge on the anode surface, less than 1% of their kinetic energy is changed to |
X-rays. - More than 99% of electron's kinetic energy is changed to heat energy and the 1% into x-ray photon energy. This presents serious heat build up in anode = heat production is directly proportional to tube current. |
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Which of the following contributes to inherent filtration? |
X-ray tube glass envelope. Xray tube port window. Inherent filtration = "built into" the construction of x-ray tube. Before exiting the tube, x-ray photons pass through glass envelope and port window. |
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A quality control (QC) program includes checks on which of the following radiographic equipment conditions? |
Reproducibility - Repeated exposures using given technical factors must provide consistent intensity. Linearity - given a mAs value, using different mA stations with appropriate exposure time adjustments will provide consistent intensity. Positive beam limitation/automatic collimation - automatic collimation and must be accurate to 2% of SID. |
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What x-ray tube component does the Number 7 indicate? |
Rotor. 2 components of an induction motor (stator and rotor) function to rotate the anode. |
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Characteristics of x-ray photons include |
Fluorescent effect on certain phosphors. Physiological effect on living tissue. |
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All the following x-ray circuit devices are located between the incoming power supply and the primary coil of the high-voltage transformer except |
The milliamperage meter. - Connected at the midpoint of secondary col of high-voltage transformer. |
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Congruence of the x-ray beam with the light field is tested using |
Radiopaque objects. - Such as paper clips or a penny placed at the corners of light field. |
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Disadvantages of moving grids over stationary grids include which of the following? |
They can prohibit the use of very short exposure times - Not able to oscillate rapidly enough They increase patient radiation dose - CR point not centered to grid because its moving, lateral decentering occurs and to compensate you must increase exposure |
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The functions of a picture archiving and communication system (PACS) include |
Reception of digital image. Storage of digital images. |
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How many half-value layers will it take to reduce an x-ray beam whose intensity is 78 R/min to an intensity of less than 20 R/min? |
2. First HVL = 39 R/min Second HVL = 19.5 R/min |
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The kV settings on radiographic equipment must be tested annually and must be accurate to within |
+/-4 kV. kV settings can be tested using electronic kV meter. |
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The device used to heat the accuracy of the x-ray timer is the |
Spinning top. A metal disk with small hole in its outer edge placed on pedestal 6in high. An exposure made while top spins. Full-wave-rectifier produces 120 x-ray photon impulses per second, in 0.1 seconds the IR should record 12 dots if timer is accurate. |
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The x-ray tube in a CT imaging system is most likely to be associated with |
A pulsed x-ray beam. (1-5ms & using up to 1,000 mA) CT x-ray tube must have very high short exposure rating and capable of tolerating several million heat units while still having small foal spot for optimal resolution. To help tolerate high production of heat units, anode must be capable of high speed rotation. |
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The image shown was made using an accurately calibrated |
Spinning top is used to test timer efficiency of single phase full wave rectifiers. The result should be a series of dots or dashes = each dot represents a pulse of x-radiation.
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Conditions that contribute to x-ray tube damage include |
Lengthy anode rotation - Prolonged rotor time can lead to shortened filament life because early vaporization. Exposures to a cold anode - This will heat the anode surface and the big temperature difference can cause cracking of anode. |
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Exposures less than the minimum response time of an AEC may be required when |
Using high milliamperage. Using fast imaging systems. |
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Which of the following information is necessary to determine the maximum safe kilovoltage using the appropriate x-ray tube rating chart? |
Milliamperage and exposure time - Radiographic rating chart used to determine safe kV for particular exposure. Focal spot size - The heat load an anode will safely accept varies with the size of focal spot & type of rectification. |
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Which of the following statements regarding dual x-ray absorptiometry are true? |
It is a low dose procedure. Two x-ray photon energies are used - One for soft tissue and one for bone. Photon attenuation by bone is calculated - Bone is denser and attenuated x-ray photons readily, attenuation is calculated representing the degree of bone density. |
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A device used to ensure reproducible radiographs, regardless of tissue density variations, is the |
Automatic exposure control (AEC). - Phototimers and ionization chambers automatically terminate exposure once quantity of x-ray has penetrated patient and hit cells in IR. |
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The device used to change alternating current to unidirectional current is |
A solid-state diode. - Rectifiers are solid-state diodes made of semiconductive material hat conduct electricity in only one direction. |
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If the distance from the focal spot to the center of the collimator's mirror is 6 in, what distance should be the illuminator's light bulb be from the center of the mirror? |
6in . In order for projected light light beam to be same size as x-ray beam, focal spot and light bulb must be exactly the same distance from center of the mirror. |
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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. Fluorescent light image strikes the photocathode and is converted to an electron image. Electrons are focused to maintain image resolution by electrostatic lenses through the accelerating anode and to the output phosphor for conversion back to light. |
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The filtering effect of the x-ray tube's glass envelope and its oil coolant are referred to collectively as |
Inherent filtration. Glass envelope and oil coolant provide approximately 0.5 to 1.0-mm Al equivalent filtration, which is called inherent filtration because its "built into" the tube head. |
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Which of the following equipment is mandatory for performance of a myelogram? |
Tilting x-ray table. - Myelograms require contrat be instilled into lumbar subarachnoid space and distributed via gravity with help of tilting x-ray table. |
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Deposition of vaporized tungsten on the inner surface of the x-ray tube glass window |
Acts as additional filtration. - It reduces tube output and the tungsten deposit actually attracts electrons from filament, creating tube current and causes puncture of glass envelope. |
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Which of the following circuit devices operates on the principle of self-induction? |
Autotransformer - Allows radiographer to vary the kV. Choke coil - Type of variable resistor that is used to regulate filament current. |
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Which of the following terms describes the amount of electric charge flowing per second? |
Current. |
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The brightness level of fluoroscopic image can vary with |
Milliamperage - Lower Kilovoltage - Higher Patient thickness - Thicker the part, the less bright |
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Which of the following dose the image represent? |
Bremmstrahlung radiation Or "braking" x-ray production = high-speed electron accelerated toward tungsten atom is attracted and braked or slowed down by positively charged nucleus and is deflected from original course w/ resulting loss of energy. |
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The portion of the remnant x-ray beam representing anatomical details having desirable quality is referred to as |
Signal. Some of the initial x-ray beam is absorbed via photoelectric interaction; some is scattered via Compton scatter creating noise. Signal-to-noise (SNR) is an important factor in all of medical imaging. |
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Component parts of a CT imaging system include an |
High frequency generator. X-ray tube. Operator console. |
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All of the following are associated with the anode except |
Thermionic emission. - The electrons impining on the target have "boiled off" the cathode filament as a result of thermionic emission. |
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Which part of an induction motor is located within the x-ray tube glass envelope? |
Rotor. Induction motor has 2 parts; stator and rotor. The stator consists of series of electromagnets occupying positions around the stem of the anode. The stators electromagnets are supplied with current, and associated magnetic fields function to exert drag or pull on the motor within glass envelope. |
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A technique chart should be prepared for each AEC x-ray unit and should contain which of the following information for each type of examination? |
Photocells used - Correct cells must be selected and the anatomic part of interests must completely cover the cell. Optimum kilovoltage - Penetration must be accurate. Backup time - Always selected on manual timer to prevent patient overexposure and to protect x-ray tube from heat production. |
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Which part of an induction motor is located outside the x-ray tube glass envelope? |
Stator. - Consists of electromagnets occupying position around the stem of the anode. They are supplied with current and associated magnetic fields function to exert drag and pull on rotor. |
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Moving the image intensifier closer to the patient during fluoroscopy |
Decreases the SID. Decreases patient dose - Decreases mAs Improves image quality - Less magnification therefore better image quality. |
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The image illustrates the |
Line focus principle. - (focal spot is angled 12-17 degrees to the vertical) |
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Although the stated focal spot size is measured directly under the actual focal spot, focal spot size actually varies along the length of the x-ray beam. At which portion of the x-ray beam is the effective focal spot the smallest? |
At the anode end. - As it is projected toward anode end, and foreshortening becomes more pronounced, the effective focal spot becomes smaller. As it is projected toward cathode, effective focal spot becomes larger and approaches actual size. |
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The total brightness gain of an image intensifier is the product of |
Flux gain - Ratio of # of x-ray photons at input phosphor compared to # light photons at output phosphor. Minification gain - Output phosphor is only a fraction of the size of input phosphor, and this decrease in image size represent brightness gain, termed minification gain. |
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Which of the following are associated with magnification fluoroscopy? |
Higher patient dose than nonmagnification fluoroscopy - mA is increased to compensate for loss in brightness when image intensifier is switched to magnification mode. Higher voltage to the focusing lenses - Image intensifier focal point closer to the input phosphor - |
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Advantages of battery-powered mobile x-ray units include their |
Ability to store a large quantify of energy - 12 hours of full charge. Ability to store energy for extended periods of time - A larger mAs capacity for extended periods of time. |
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Which of the following modes of a trifield image intensifier will result in the highest patient dose? |
Its 12in mode. - When change to a smaller diameter mode is made, the voltage on electrostatic focusing lenses is increases and results in magnified but dimmer image. mAs will increases to compensate for loss in brightness with magnified image = higher patient dose. |
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Off-focus, or extrafocal, radiation is minimized by |
Restricting the x-ray beam as close to its source as possible. - Mounting a pair of shutters as close to the source as possible. |
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Which of the following is of the secondary, or high voltage, side of the x-ray circuit? |
Rectification system. |
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An AEC device can operate on which of the following principles? |
A photomultiplier tube charge by a fluorescent screen - X-ray photons penetrate and emerge from a part, fluorescent IR glows and light chargers phototimer. A parallel-plate ionization chamber charged by x-ray photons - A radiolucent chamber located beneath patient; as photons emerge from patient, they enter chamber and ionize the air within it. Once predetermined charge is met, exposure is terminated. |
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Which of the following functions to increase the milliamperage? |
Increase in heat of the filament. - Thermionic emission then those electrons will become tube current (mA) and as heat is increased, more electrons released, and mA increases. |
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If 92 kV and 15 mAs were used for a particular abdominal exposure with single-phase equipment, what milliamperage-seconds value would be required to produce a similar radiograph with three-phase, 12-pulse equipment? |
7.5 - Only 2/3 original mAs would be used for three-phase, 12-pulse equipment. With three-phase, 12-pulse equipment, original mAs would be cut in half... 15/2 = 7.5 |
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Fractional-focus tubes, with a 0.3-mm focal spot or smaller, have special application in |
Magnification radiography. - Essential to the maintenance of image sharpness in magnification images. Radiographic rating charts should be consulted because the heat load to anode may be critical in magnification radiography. |
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In the radiographic rating charts show, what is the maximum safe kilovoltage that may be used with the 1.0-mm focal spot, single-phase x-ray tube using 400-mA and a 0.02-s exposure? |
80kV. - First find chart with single-phase sine wave in upper right corner and correct focal spot size in upper left corner. (chart c) Located 0.02s on horizontal axis, follow its line up with 400-m |
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In the diagrams, which x-ray tubes permit an exposure of 400 mA, 0.1 s, and 80 kV? |
Tube A & Tube B. Located 0.1s on horizontal axis & follow it up where it intersects w/ 400-mA curve. Chart A permits over 150 kV safely, whereas Chart B permits only 92 kV safely. |
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In the diagrams, what is the maximum safe milliamperage that may be used with a 0.10-s exposure and 120 kV, using the three-phase, 1.0-mm focal spot x-ray tube? |
300 mA. Find chart for three-phase, 1.0-mm focal spot x-ray tube. Locate 0.1s on horizontal axis (seconds) & follow it up where it intersects w/ 120-kV on vertical kV axis. Just about 300-mA curve. |
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Referring to the anode cooling chart, if the anode is saturated with 300,000 heat units (HU), how long will the anode need to cool before another 160,000 HU can be safely applied? |
4 minutes. - Tube is saturated w/ heat at 300,000 HU. In order for another 160,000 HU to safely be applied, x-ray tube must 1st release 160,000 HU which means it has to cool at least to 140,000 HU. Find 140,000 HU on vertical axis and follow across where it intersects with cooling curve. About the 4 minute point. |
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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. - Because three-phase equipment is almost constant potential, a synchronous spinning top must be used. A solid arc (rather than dots) is formed and the # of degrees is measured and equated to an exposure time. |
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Anode angle will have an effect on the |
Severity of the heel effect - With smaller anode angles, anode heel effect is accentuated and can compromise IR coverage. Focal spot size - As anode angle is decreased (steeper) a larger actual focal spot is used to maintain the same small effective focal spot. Heat load capacity - Since actual focal spot is larger, it can accommodate larger heat load. |
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The minimum response time of an automatic exposure control (AEC) |
It is shortest possible exposure time. - If less than the minimum response time is required for particular exposure, radiograph will exhibit excessive receptor exposure. |
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All the following statements regarding mobile radiographic equipment are true except |
The exposure cord must permit the operator to stand at least 4ft from the patient, x-ray tube, and useful beam. - Must be 6ft or 2 meters. |
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Which of the following is most closely related to the image? |
High kV. - Compton scatter, a high energy (kV) x-ray photon ejects an outer shell electron in tissue or other absorber. Ejected electron is called recoil electron. |
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Which of the following formulas would the radiographer use to determine the total # of heat units produced with a given exposure using three-phase, six-pulsed equipment? |
mA X time X kV X 1.2 |
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The voltage across the x-ray tube in three-phase equipment |
Is 87% to 96% of the maximum value. Is at nearly constant potential - (Direct current) Voltage ripple is small. 13% for three-phase, six-pulse and 3.5% for three-phase, 12-pulse. Therefore, voltage never falls below 87% go 96.8% of its maximum value |
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Images using a particular single-phase, full-wave rectified x-ray unit were made, using known correct exposures. A spinning top test was performed at 200 mA, 0.05 s, and 70 kV, and 8 dots were visualized. Which of the following is indicated? |
The 0.05-s time station is inaccurate. - Single-phase, full-wave rectifiers currents has 120 useful impulses per second, a 1-s exposure of spinning top should demonstrate 120 dots. A 0.05-s exposure should demonstrate six dots. |
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Which of the following combinations will offer the greatest heat-loading capability? |
10 degree target angle, 1.2-mm actual focal spot. - Smaller the focal spot = more limited anode As target angle decreases = actual focal spot increases while maintaining small effective focal spot. |
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Which of the following would be appropriate IP front material? |
Magnesium - (lightest structural metal) Bakelite - (forerunner of today's plastics) IP front should be made of sturdy material w/ low atomic # because attenuation of remnant beam is undesirable. |
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How often are radiographic equipment kV settings required to be evaluated? |
Annually. - kV electronic meter used. Should be within +/-4 kV |
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What x-ray tube component does Number 7 indicate? |
Rotor. Function = rotate anode |
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The image intensifier tube's input phosphor functions to convert |
X-rays to light. - Image intensifier's input phosphor receives remnant radiation emerging from patient and coverts it into fluorescent light image. |
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Accurate operation of the AEC device depends on |
Positioning of the object with respect to the photocell - Must be over cell to achieve exposure desired. Beam restriction - If collimation is inadequate and field size larger than the part is used, excessive scatter from body or tabletop can terminate exposure. |
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The image intensifier's input phosphor generally is composed of |
Cesium iodide. - Much more efficient in this conversion process than was the phosphor used. Helps maintain resolution. |
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The total number of x-ray photons produced at the target is contingent on the |
Tube current - Greater # of electrons in stream = greater of x-ray photons produced. Target material - Higher atomic # of material, denser and more closely packed & greater chance of interaction between high-speed electron and target material. Square of the kilovoltage - Quantity of radiation produced increases as the square of the kilovoltage. |
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A photostimulable phosphor plate is used with |
CR. - Doesn't use intensifying screens or film, the cassette contains photostimulable phosphor that functions as IR. The PSP stores info and is scanned through reader. |
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X-ray tubes used in CT imaging systems must be capable of |
(1.) High short-exposure rating. (2.) Tolerating millions of heat units - To tolerate heat units, anode must be capable of (3.) High-speed anode rotation. |
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An incorrect relationship between the primary beam and the center of a focused grid results in |
Grid cutoff - Absorption of primary radiation causes cutoff and Insufficient receptor exposure. |
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QA was being performed on a three-phase, full-wave-rectified x-ray unit. A synchronous spinning top test was performed using 300 mA, 60 ms, and 70 kV. A 22-degree arc is observed on the test image. Which of the following statements regarding these results is most correct? |
The test results are satisfactory. - Because three-phase, full-wave-rectified current would expose a 360 degree arc each second, a 60-ms (0.06-s) exposure should expose 21.6 degree arc. (360 X 0.06 = 21.6) |
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Which of the following will most likely produce the highest quality radiographic image? |
High SNR. - Noise impairs image resolution. High SNR is desirable. More signal = less noise Less noise = better image contrast resolution |
