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test 4 rad 255
| Question | Answer |
|---|---|
| What are the two main components of the AEC? | Sensor and Comparator |
| What is the sensor ? | detects the x-rays which have passed through the and the patient produces a corresponding electrical current which is proportional to the amount of x-rays sensed |
| What is the comparator? | a device which “compares” the current flowing from the sensor to a predetermined reference current and terminates the exposure when that amount is reached. |
| What are the two sensing devices used in AEC? | photomultiplier tube and ionization chamber |
| Where is the photomultiplier tube located ? | behind the IR |
| where is the ionization chamber located ? | infront of the IR |
| What are the two main components of the PM tube ? and is it older or newer ? | florescent screen and PM tube, older |
| What is the ionization chamber filled with? | chamber is filled with gas, that is ionized as radiation passes through it |
| What AEC sensing device is an entrance type? | ionization chamber |
| What AEC sensing device is an exit type? | PM tube |
| What is the function of the PM tube? | receives the visible light from the screen and emits electrons which form an electrical current proportional to the amount of light emitted. |
| What sensing device cannot use lead-backed cassette? | PM tube, the image will be over exposed |
| What type of switching allows for very short exposure times in conjucntion with AEC? | forced extinction |
| What is forced extinction? | works with comparator to forcibly terminate exposure when adequate exposure has been accomplished |
| What is MRT? | Minimum response time, it is the time it takes an AEC system to detect and react to radiation received, and then terminate the exposure |
| What is SCR pulsed? | it is a communication systems allow for the exposure to start or stop at any point on the voltage waveform |
| What are the 2 QA tests which should be conducted on all AEC systems periodically ? | repeatability and tissue thickness testing |
| What are the principles of the QA test repeatability? | should reproduce density for all exposures, no more than + or - 10% variation, step wedge is used for the exposure, then a densitometer is then used to measure the variation in densities of the resulting xrays |
| What are the principles of the QA test tissue thickness testing? | should be able to compensate for variations in part thickness, machine should be able to compensate for varying thickness in body parts, and produce radiographs that densities are with 10-15% of one another at all KVP levels |
| What are limitations to the AEC system? | 1. part must be centered to cell 2. ionization chamber increases OID 3. AEC may decrease scatter 4. Capacitor leakage- exposure errors |
| What conditions must be present to be able to produce xrays? | generator- gives power, kilovoltage- high voltage to move electrons toward anode, xray tube- cathode/ anode sides (source of electrons), filament |
| What are the two types of xray production ? | Bremsstrahlung and characteristic |
| Why is brems a continuous radiation ? | because it is heterogeneous it has a non-uniform wavelength because the amount of deceleration varies among electrons |
| What is the KVP requirements for brems radiation ? | 85% of emitted radiation produced at any level KVP |
| What is the KVP requirements for characteristics radiation ? | 10- 15% kvp to be at least 70 kvp |
| what factors govern the strength or energy of brems ? | speed of the projectile electron, how close they approach the nucleus, atomic number of the target |
| what shell is only useful for diagnostic radiation ? | k shell |
| what is the % of heat production to xray production? | 99% heat to only 1% of xrays |
| What happens if the xray tube varies with changed in mA and KVP? | if either of these variables are doubled heat production doubles |
| Is brems continuous or discrete energy level? | continuous |
| Is characteristics continuous or discrete energy level? | discrete |
| how do you calculate the energy of a K-characteristic xray photon? | k shell is 69.5 (subtract from the other shell to get the engery) L shell- 12.1, M shell- 2.8, N shell- .6 |
| What are the various types of mobile generators? | single phase, constant potential, capacitor discharge, high frequency , falling load generators |
| how does a single phase mobile generator obtain its power for the exposure ? | main power supple |
| how does a constant potential mobile generator obtain its power for the exposure ? | series of silicon-controlled rectifiers from the DC voltage of a nickle-cadmium battery (NiCd) |
| how does a capacitor discharge mobile generator obtain its power for the exposure ? | battery |
| how does a high frequency mobile generator obtain its power for the exposure ? | storage batteries and silicon-controlled rectifiers |
| how does a falling load mobile generator obtain its power for the exposure ? | power storage (batttery-powered and capacitor discharge) |
| what is the main impedance compensator? | compensates for main supple fluctuations |
| What is a capacitor? | stores voltage |
| What is a solid-state inverter? | converts DC produced by a battery into AC current |
| How is a single phase mobile generator in terms of reproducibility? | least reliable in reproducibility |
| How is a constant potential mobile generator in terms of reproducibility? | the output is reproducible for every exposure |
| How is a Capacitor Discharge mobile generator in terms of reproducibility? | Good output & good reproducibility |
| How is a High Frequency mobile generator in terms of reproducibility? | great efficiency of x-ray production |
| How is a Falling Load mobile generator in terms of reproducibility? | kV fluctuates slightly |
| What was the first imaging modality to rely solely on a computer to form the image ? | CT - in 1980 |
| How is a Digital image displayed? | x-rays are detected, converted into numerical or digital form by a computer, reconstructed, and then displayed on a monitor as a matrix of pixels, closely resembling a conventional image or electronic image constructed from numerical date by computer |
| What are the factors that will produce a Digital image that most closely resembles an analog image ? | -pixel size should be small -many pixels should comprise the image -there should be many shades of gray available to form the image |
| what are the advantages of digital fluoro over conventional fluoro ? | -Rapid Image acquisition -enhanced image contrast -post processing options - digital subtraction angiography |
| What is the scanned projection radiography? | aaray of radiation detectors, fan shaped beam, pre patient and post patient collimators, detectors measure radiation and send electric signals to computer |
| What is the dual energy imaging ? | X-ray beam is pulsed rapidly during exposure between 140 & 60 kVp Results in two images, one with high contrast and one with low contrast |
| What is the advantages of digital process ? | Faster, less expensive, less scatter, less storage space, manipulation of images, reduce exposure |
| What does PACS stand for and its function? | Picture Archiving and Communication system, A computerized storage and transmission system for digitized images, computer storage replaces hard copy film for filing radiographic images , system can send images to distant sites |
| What is post processing ? and what are some examples | -Post processing is a method of enhancing the computerized image to display diagnostic information more clearly, without re-exposing the patient EX: annotation, image subtraction, windowing (level or width), image rotation image inversion, (ROI), |
| What is hounsfield unit? | "CT #", each voxel is assigned a # by the computer based on its density ? |
| What are the HU's for dense bone, water, air? | -dense bone (+1000) - Water (0) - Air (-1000) |
| What is matrix size? how are spatial res and matrix size related? | Matrix size – number of rows and columns of pixels in image, more pixels the better quality of the image Smaller pixels and large matrix images (high spatial resolution |
| Window level ADJUSTS what ? | Adjusts brightness - increase level - lighter -decrease level- darker |
| Window width ADJUSTS what ? | Adjusts contrast (inverse) -narrowing = increased contrast -wide = decreased contrast |
| What is DR radiography system ? | - DR- Direct Capture Radiography or Direct readout radiography: Very expensive (cassette less), Conventional equipment must be replaced , electronic flat planel image receptor replace the CR imaging plate |
| What is CR radiography system ? | -CR – Computed Radiography (cassette based ): Less expensive than DR ( upfront cost) , Uses existing radiology equipment, imaging plate replace film cassettes |
| What material comprises the photostimulable phosphor in a CR imaging plate? | barium fluorhalide |
| what is indicated by numbers below 25 or above 500, for fugi "S" numbers? | - “S” numbers greater than 500 are considered underexposed Image will have quantum mottle and poor image quality - “S” numbers less than 25 may be grossly overexposed image appears gray or white and need to increase radiation exposure |
| What does DR stand for ? | Direct Radiographgy |
| What does CR stand for ? | Computer Radiography |
| What are the components used to construct a direct conversion detector? | Direct has a capture element, and a collection element |
| What are the components used to construct a indirect conversion detector? | Indirect has a capture element, coupling element, and collection element |
| What does HIS stand for ? | Hospital information system (PT registration) |
| What does RIS stand for ? | Radiology information system |
| What does DICOM stand for? and what does it do ? | Digital Imaging and Communication in Medicine, - A universally adopted standard for interchange of medical imaging |
| What are the 5 interactions with matter? which interactions cause ionization of the atom? | coherent scattering, compton scattering(IONIZING), Photoelectric effect (IONIZING), Pair production, photodisintergration |
| which of the 5 interactions does not occur in Diagnostic Radiology.? | pair production, photodisintergration |
| which interaction causes the image to appear white on the x-ray image? | Photoelectric effect |
| which interaction adds to the image in a negative way? | compton scattering |
| The three-dimensional volume of tissue that is represented in each pixel is known as what? | a voxel |
Created by:
madyep
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