Term
| The principal feature that distinguishes fluoroscopy from radiography. |
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Definition
| Real-time x-ray images with high frame rates and low-dose per image. |
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Term
| Standard fluoroscopy requires how much exposure on the detector? How much does a radiographic CR system require? |
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Definition
Fluoro - 1 to 2 μR, CR system - 0.5 to 1 mR
Fluoro requires about a 1000x less than CR |
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Term
| Four primary components of an II. |
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Definition
| 1) vacuum housing, 2) Input layer - converts x-rays into light into electrons, 3) Electron optics that accelerate and focus the electrons, 4) output phosphor that converts accelerated electrons into visible light |
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Term
| What are the layers of the input screen of the II and what do they do? |
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Definition
| 1) vacuum window - keeps air out 2) support layer - supports the remaining two layers 3) input phosphor - converts x-rays to visible light - 4) photocathode - emits electrons when struck by light |
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Term
| What is the II vacuum window and support layer made of? |
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Definition
| Vacuum window - 1 mm Al, Support layer - 0.5 mm Al |
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Term
| What is the input phosphor made of? |
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Definition
|
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Term
| What is the input photocathode made off? |
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Definition
| Antimony and alkali metals (Sb2S3) |
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Term
| The electronic lens system in the II consists of |
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Definition
| The cathode (input), anode (output), and 3 focusing electrodes (G1, G2, G3) |
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Term
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Definition
| The number of photons generatred at the output phosphor for every photon generated at the input phosphor. Also known as the flux gain. |
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Term
| Pincushion distortion is the result of. |
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Definition
| The input surface of the II being curved and the output surface being flat. |
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Term
| Why is the input surface of the II curved. |
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Definition
| To allow for electronic focusing. |
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Term
| The image at the output phosphor of the II is _______. |
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Definition
|
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Term
| Minification gain of the II |
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Definition
| Ratio of the area of the input phosphor to the area of the output phosphor |
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Term
| Output phosphor of an II is made of |
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Definition
zinc cadmium sulfate doped with silver
ZnCdS: Ag |
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Term
| Each electron that impacts the output phosphor produces about how many light photons? |
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Definition
|
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Term
| What is the size of the output phosphor? |
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Definition
| 2.5 cm (1 inch) diameter circle |
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Term
| What is veiling glare and how is it reduced? |
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Definition
| It is caused by light reflecting inside the output window. The sides of the window are coated in black to absorb the scattered light. |
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Term
| What is coupled to the output screen of the II. |
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Definition
| A light sensitive camera such as an analog vidicon or a solid-state CCD or CMOS. |
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Term
| The amount of light from the output phosphor that gets to the camera is controlled by |
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Definition
|
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Term
| The amount of light reaching the camera is determined by the |
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Definition
|
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Term
|
Definition
| f = focal length / aperture diameter |
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Term
| Increasing the f-number by one f-stop reduces the amount of light passing through by a factor of |
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Definition
|
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Term
| Increasing the gain of the system ______ the exposure rate and the dose, but also ______ the image quality. |
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Definition
|
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Term
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Definition
| Product of the electronic gain and the minification gain |
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Term
| Typical electronic gain of an II |
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Definition
|
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Term
| As the electronic magnification increases (decreasing the effective FOV), the minification gain _______. |
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Definition
|
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Term
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Definition
| Spatial warping of an image into an S shape due to stray magnetic fields or the earth's magnetic field. |
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Term
|
Definition
| flat panel image receptors |
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Term
| Flat panel detectors are made of |
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Definition
| thin film transistors (TFT) |
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Term
| In a flat panel image receptor, each detector element accumulates and stores a charge that is proportional to the _________. |
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Definition
| x-ray flux that is incident on that detector. |
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Term
| Why does a flat panel detector have a higher quantum detection efficiency than an II. |
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Definition
| The II has an aluminum housing and aluminum support layer that absorbs a large fraction of the x-rays. The flat panel detector only has a carbon fiber cover. |
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Term
| What does AERC stand for? What did it used to be called? What is it's purpose? |
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Definition
| Automatic Exposure Rate Control, used to be called ABC - automatic brightness control. It's purpose is to keep the SNR constant when possible. |
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Term
| What parameters does the AERC control? |
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Definition
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Term
| If the AERC increases kVp it will ________ subject contrast, but keeps the dose ________. |
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Definition
| reduce subject contrast, but keeps the dose lower. |
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Term
| If the AERC increases mA, is will ________ subject contrast, but also ________ dose. |
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Definition
| increase subject contrast and also increase dose |
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Term
| What trade-off does the AERC make when adjusting for a thicker patient. |
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Definition
| Having more subject contrast but with a higher dose (increased mA) or having less subject contrast but with a lower dose (increased kVp) |
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Term
| Continuous fluoroscopy typically uses what range of tube current? |
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Definition
|
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Term
| Cameras display images at what frame rate? |
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Definition
|
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Term
| At 30 fps, each image is displayed for how long? |
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Definition
|
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Term
| In pulsed fluoroscopy, exposure times range from |
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Definition
|
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Term
| The shorter exposure times of pulsed fluoroscopy result in |
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Definition
| Reduced blurring from patient motion. |
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Term
| To get the same image quality (same dose) as continous fluroscopy, pulsed fluoroscopy uses |
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Definition
|
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Term
| Typical frame rates for pulsed fluroscopy |
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Definition
| 30, 15, 7.5, and 3.75 fps |
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Term
| Lowering the frame rate in pulsed fluorscopy does what? |
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Definition
| It reduces the temporal resolution which isn't always needed and it reduces the dose. |
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Term
| What determines the largest field of view? |
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Definition
| The physical size of the II. |
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Term
| Magnification modes yield _______ spatial resolution for a ________ field of view. |
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Definition
|
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Term
| Magnification is produced by |
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Definition
| focusing a smaller area of the II input screen onto the entire output phosphor |
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Term
| The brightness gain _______ as magnification increases. |
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Definition
|
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Term
| In mag mode the AERC compensates for reduced brightness gain by increasing the x-ray exposure rate. The increase in exposure rate is given by |
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Definition
| the ratio of the FOV areas. |
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Term
| To reduce patient dose, one should use the _______ magnification and the ________ collimated area. |
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Definition
| least magnification and the smallest collimated area |
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Term
| Advantage and disadvantage of frame averaging. |
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Definition
advantage - lower quantum noise
disadvantage - image lag |
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Term
| DSA - what does it stand for and how does it work |
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Definition
| Digital subtraction angiography - a non-iodinated image is subtracted from an iodinated image leaving just the vascular anatomy |
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Term
| In DSA, the anatomy only image is called |
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Definition
|
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Term
| What is the benefit of DSA? |
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Definition
| It reduces anatomical noise. |
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Term
| What is a typical range for the intrinsic limiting resolution of a fluoroscopy system? |
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Definition
|
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Term
| The limiting resolution of a fluoroscopy system is typically limited by |
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Definition
|
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Term
| The limiting resolution of the fluoroscopy system can be determined by |
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Definition
FOV (mm) / video display matrix (# of pixels) = Δ mm/pixel,
resolution = 1/(2Δ) cycles/mm
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Term
| What does higher magnification modes do to spatial resolution? |
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Definition
|
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Term
| Flat panel detectors in fluoroscopy have ________ spatial resolution than II systems? |
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Definition
|
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Term
| Contrast resolution in fluoroscopy is ______ compared to radiography due to the _______. |
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Definition
|
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Term
| What is the compromise for improved contrast resolution? |
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Definition
|
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Term
| What are the range of Bucky factors and grid ratios for grids used in fluoroscopy? |
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Definition
Bucky factor: 2-4
Grid ratio: 6:1 to 12:1 |
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Term
| Maximum permissible entrance exposure rate for normal and high level fluoroscopy? |
|
Definition
normal - 10 R/min (87.3 mGy/min)
high level - 20 R/min (175 mGy/min) |
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Term
| Where are output exposure rates measured in fluoroscopy? |
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Definition
| 1 cm above the table for systems with the tube under the table, 30 cm from the II for C-arms |
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Term
| What is the FDA dose limit for image recording with fluoroscopy? |
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Definition
|
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Term
| An operator standing 1 m from the patient receives about _________ of the entrance exposure. |
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Definition
|
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Term
| The scatter radiation on the entrance side of the patient is about _____ times more than the scatter radiation on the exit side. |
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Definition
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Term
| Dose monitoring can be done with a ________ meter. The units are? |
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Definition
| KAP (Kerma-area-product), mGy*cm2 |
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Term
| How is skin dose calculated from KAP? |
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Definition
|
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Term
| Fluoroscopy systems manufactured after June 10, 2006 are required to display |
|
Definition
| cumulative air kerma (mGy) |
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Term
| For C-arms, the reference point for air kerma rate is |
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Definition
| on the beam axis, 15 cm from the isocenter towards the x-ray tube. |
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Term
| Three reasons why cumulative air kerma may not acurately represent peak skin dose. |
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Definition
| 1) CAK doesn't account for backscatter, 2) the beam may be incident on multiple areas of skin, 3) the skin may be closer or farther away from the x-ray tube than the reference point. |
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Term
| 8 ways to reduce dose in fluoroscopy besides changing technique |
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Definition
| 1) collimate, 2) maximize source to skin distance, 3) remove anti-scatter grids for pediatrics and extremities, 4) use the lowest mag mode possible, 5) vary the location of the entrance field (dose spreading), 6) use low frame rate pulsed fluoroscopy, 7) use last-frame-hold, 8) limit the number of radiographic images |
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Term
| Patient follow-up should occur when cumulative air kerma exceeds |
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Definition
|
|
Term
K-edge of Iodine?
Optimal range of kVp for using Iodine contrast? |
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Definition
|
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Term
| Other names for Equalization Filters. What are they used for? |
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Definition
| Soft filters or soft cones. They are wedge shaped filters used to taper the radiation profile. |
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Term
| What is a virtual collimator? |
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Definition
| White lines that appear on the last hold image. The lines indicate where the collimation will occur next time flouro is used. The results in a dose savings to the patient. |
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Term
Grid ratios used in interventional systems?
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Definition
|
|
Term
| Instead of an ABC, digital image receptor systems use an |
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Definition
| ADRC - Automatic Dose Rate Control |
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Term
| If the noise of a mask image is σ1 and the noise of a contrast image is σ2 what is the noise of the subtracted image? |
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Definition
= √(σ12 + σ22)
The subtracted image will be noisier. |
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Term
| TJC defines a sentinel event in flouroscopy as |
|
Definition
| a cumulative dose of greater than 15 Gray to a single field |
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Term
| Above what patient thickness should a grid be used. |
|
Definition
| 10 cm. The grid should be removed for anatomy that is less than 10 cm thick. |
|
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Term
| Fifty percent of the patient dose is delivered in the first ___ cm of tissue. |
|
Definition
|
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Term
|
Definition
| When the image appears brighter in the center than at the edges. This occurs because the path through the II is farther at the edge of the output phosphor. |
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Term
|
Definition
A measure of the efficiency of an II in converting incident X-ray radiation into light at the output surface.
Units are Cd/m2 per mR/sec |
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Term
| How is contrast ratio measured for an II? What is the range of values? |
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Definition
| A lead disk that covers 10-15% of the II is placed on the input surface. A region adjacent to the disk is compared to the signal behind the disk. It should be 10:1 to 20:1. |
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Term
| What causes the electronic or flux gain? |
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Definition
| The increase in the kinetic energy of the electrons as they are accelerated from the photocathode to the anode. |
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Term
| What is SRDL? What document defines it? |
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Definition
SRDL - Substantial Radiation Dose Level
Defined in NCRP Report No. 168 |
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Term
| What are the values for the SRDL's? |
|
Definition
1. 3 Gy Peak skin dose
2. 5 Gy Cummulative Air Kerma
3. 500 Gy·cm2 KAP (assumes 100 cm2 field)
4. 1 hour of fluoro time |
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