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heat units (HU)
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| Term | Definition |
|---|---|
| heat units (HU) | used by the anode cooling chart to tell the time needed for the anode to cool completely in order to continue making exposures |
| HU formula | kVp (anode speed) x mA x s (technique) x rectification constant (generator factor) |
| generator factor to caculate HU | single phase: 1 three phase 6 pulse: 1.35 3 phase 12/14 pulse: 1.41 high frequency: 1.41 |
| total pixels in a matrix formula | rows x columns |
| pixel size formula | FOV/matrix |
| bit depth determines: | contrast resolution |
| bit depth formula (number of shades) | 2n^2 |
| magnification factor (MF) | Full-size input phosphor diameter / Selected input phosphor diameter |
| What circumstances are most likely to lead to an increase in grid cutoff when using a parallel grid Inc in the exposure time Improper positioning of the grid Large SID Use of sm digital display devices Use of large-area image receptors | improper positioning of the grid, use of large image receptors |
| How much voltage ripple is produced by three-phase, twelve-pulse power 100.0% 4.0% 0.9% 14.0% | 4.0 % |
| Select the factors that influence the amount of beam attenuation. tissue density tissue thickness x-ray beam quality atomic number x-ray beam quantity | tissue density, tissue thickness, xray beam quality, atomic number |
| If the source to image distance is 150 cm, how much variance between the light field and the x-ray beam is acceptable 6 cm from the IR 15 cm from the IR 3 cm from the IR | 3cm, 2% variance |
| A radiograph is made using 40 milliampere seconds (mAs) at a 40-inch SID. If the image must be repeated at a 72-inch SID, what mAs value is necessary to maintain the same exposure Incorrect answer: 120 mAs Correct Answer: 130 mAs 12 mAs | |
| What factors influence receptor exposure Correct answer: SID Incorrect answer: kVp Missed Option - Incorrect Correct answer: Grid Ratio Correct answer: mAs | |
| From the following, select the factor(s) that mAs affect in digital imaging Correct answer: patient dose Incorrect answer: contrast Selected Answer - Incorrect Incorrect answer: spatial resolution Selected Answer - Incorrect Correct | |
| What are the functions of the anode Incorrect answer: Reducing off-focus radiation Selected Answer - Incorrect Answer, Reducing the intensity of leakage radiation Answer, Protecting the x-ray tube from damage Incorrect answer: Pro | |
| Which factors influence image contrast Incorrect answer: IR Missed Option - Incorrect Correct answer: OID Answer, SID Incorrect answer: Alignment of the anatomical part Selected Answer - Incorrect Answer, FSS | |
| The feature of the image intensifier that automatically adjusts kVp and mAs during fluoroscopy is the: automatic gain control. , Not Selected photocathode. , Not Selected electron-focusing lens. , Not Selected Incorrect answer: aut | |
| If a 30/23/15 cm image intensifier is operated in the 23-cm mode, the fluoroscopic image will be magnified by a factor of 1.5 , Not Selected Incorrect answer: 1.3 Correct Answer: 2 1.7 , Not Selected 2 | |
| hen using automatic exposure control (AEC), the radiologic technologist can still select or change which factors Correct answer: Optical Density Correct answer: kVp Correct answer: Backup time Incorrect answer: mA Missed Option | |
| The measure of the imaging system’s ability to display the contrast of anatomic objects varying in size is the: Incorrect answer: spatial frequency. Correct Answer: modulation transfer function. modulation transfer function. , Not Select | |
| If the source to image distance is 150 cm, how much variance between the light field and the x-ray beam is acceptable Higher; larger , Not Selected Incorrect answer: Lower; smaller Correct Answer: Higher; smaller Higher; smaller , | |
| Photoelectric interactions result in the production of Incorrect answer: Secondary photon Missed Option - Incorrect Correct answer: Photoelectron Answer, Compton electron Correct answer: Characteristic radiation | |
| voltage ripple | Voltage ripple is the variation in the output voltage waveform of an X-ray generator. It's expressed as a percentage, calculated as (Vmax - Vmin) / Vmax * 100%, where Vmax is the maximum voltage and Vmin is the minimum voltage during a cycle |
| how voltage ripple affects xrays | affects the energy and intensity of the X-ray beam. Lower voltage values during the cycle produce lower energy X-rays, some of which may be absorbed by the patient or have little diagnostic value |
| Single-phase: | These generators have the highest ripple (100%), as their output voltage fluctuates between the peak voltage and zero |
| Three-phase | Three-phase generators (6-pulse and 12-pulse) have lower ripple (around 13% and 4%, respectively) due to their smoother waveform |
| High-frequency generators | These generators use inverters to produce a nearly constant DC waveform, minimizing ripple to less than 1% |
| half/full wave(rectified) ripple | 100% ripple |
| three phase six pulse ripple | 14% |
| three phase twelve pulse | 4% |
| high frequency | <1% |
| When performing a quality control test to ensure that the penetrating ability of the x-ray beam is accurate, the result must be within this amount of the control panel setting: 5% 4% 2% 10% | 5% |
| exposure indicator | The numerical value that is displayed on the processed image to indicate the level of x-ray exposure received on the digital image receptor |
| sampling frequency. | How often the analog signal is digitized |
| A grid has lead strips 3 mm high and 0.5 mm apart. What is the grid ratio | 6:1 |
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