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RADT 412 (Ch.24, 33)
| Question | Answer |
|---|---|
| Misalignment refers to both: | Off-centering, and off-angling of the tube, part and IR |
| Misalignment generally causes: | Shape distortion |
| Off-centering places the object (the anatomy of interest) in increasingly: | Diverging beams |
| The ___________ (thinner/thicker) the object being radiographed, the greater the resulting distortion | Thicker |
| True or False: Spherical or cubical objects tend to be more distorted | True |
| Examples of spherical or cubical objects that tend to be more distorted | Cranium, femoral condyles, vertebral bodies |
| Examples of wedge-shaped anatomy | Sacrum |
| Examples of tubular | Shafts of the long bones |
| What type of shape distortion occurs when a thin, flat, wedge-shaped or tubular objects are tilted in relation to the IR | Foreshortening |
| What type of shape distortion occurs if the CR is angled perpendicular to the tilted object | Elongation |
| What is Ceiszynski’s Law of Isometry? | That the angle equal to one-half the angle of the part and the IR will eliminate or minimize distortion effects |
| Beam divergence is roughly (40" SID): | 2 degrees per inch |
| Beam divergence is roughly (72" SID) | 1 degree per inch |
| T/F: Off centering of objects cause more severe distortion effects at short SID’s than at long SID’s | True |
| What does affect sharpness of recorded detail? | Focal Spot Size |
| For a fracture, what 2 views should be taken | AP and lateral to visualize displacement |
| For a foreign body, what 2 views should be taken | AP and lateral to visualize exact location (left to right and anterior to posterior or depth of the object) |
| What are the 2 types of motion? | Voluntary and involuntary |
| What is an example of involuntary motion? | Heart and great vessels, peristalsis in GI tract, gall bladder contractions |
| The three available means for controlling motion are: | Patient cooperation (communication), immobilization, short exposure times |
| To nearly freeze motion, how much exposure time in seconds should be used? | Exposure time should not exceed 0.033 or (1/30th) second |
| A ______ image is a new image created by the interaction between the anatomy present and the motion of the x-ray tube itself during a tomographic exposure | False image |
| CR pertains to: | Computed Radiography |
| DR pertains to: | Direct-Capture Digital Radiography |
| Two main advantages of DR over CR are its: | High compatibility with PAC systems, Increased departmental efficiency for work-flow |
| Quantum efficiency (QE) is: | The effectiveness of an imaging device to convert incident photons into electrons |
| The first clinically useful DR system, developed in the 1980s and was called _____________. | Scanned Projection Radiography (SPR) |
| Typical size for modern detector elements (dels) | 100 microns (1/10th mm) |
| __________ is a volume element within the patient. | Voxel |
| __________ is a detector element in the image receptor | Del |
| __________ is a picture element in the final image | Pixel |
| The 3 components of a Del are: | Semiconductor detection surface, Microscopic capacitor, TFT |
| This component of the Del detects the radiation, so the larger the area the more efficient the dexel will be in absorbing x-rays or light | semiconductor layer |
| This component of the Del has the ability to store electric charge that makes direct-capture imaging possible | Microscopic storage capacitor |
| This component of the Del acts as a switching gate to release the electrical charge when the dexel is read out | TFT (Thin Film Transistor) |
| The semiconductor detection surface of a del can be primarily sensitive to either | Xrays (if made of selenium) or Light (if made of silicon) |
| Detective Quantum Efficiency (DQE) is: | The semiconductor’s efficiency with absorbing x-rays or light is described as DQE |
| T/F: A higher fill factor provides both higher contrast resolution and better spatial resolution | True |
| The smaller the del the _______ the fill factor | Lower |
| The lower the fill factor, a _____ (increase/decrease) is needed for technique. | Increase |
| Know how dels work | top electrode (+ charge), "hole drift", del electrode (- charge), the positive charge builds up at the bottom of the semiconductor which is stored in the capacitor |
| Gate lines are controlled by the _______________, which controls the order in which the dels are read out | Address driver |
| Scintillation means: | Emitting light |
| What was developed first with DR, direct or indirect? | Indirect |
| Which DR conversion system must absorb light rather than directly from x-ray photons | Indirect |
| T/F: Final resolution of Indirect Conversion System is not as good as a Direct Conversion System | True |
| ________ conversion produces higher spatial resolution | Direct |
| ________ conversion systems results in less patient dose | Indirect (Because of the amplifying effect of converting x-rays into light) |
| With CR, the active phosphor layer is supported by a firm base, usually made of ____________ | Aluminum |
| The anti-halo layer prevents ______ light from penetrating through to the reflective layer | Red light |
| The anti-halo layer allows ______ light emitted by the phosphor to pass through to it | Blue-violet |
| Why are both the front and back panels of the CR cassette are lined with felt material (2 things) | 1. Back panel may include thin sheet of lead foil to reduce backscatter radiation. 2. Minimizes build-up of static electricity and cushions the plate from jolts |
| The CR receptor plate is a photostimulable phosphor (PSP) with the ability to store a ______ image | Latent |
| A typical PSP plate retains up to ____ of the original image 8 hours after exposure. | 75% |
| _________ allows CR to store a "latent" image | F Centers |
| A ________ laser beam scans the plate, adding energy to the trapped electrons in the F centers | Red |
| How many times does the PSP plate actually glow? | Twice (First, the phosphor fluoresces during exposure), Second, the plate phosphoresces upon later re-stimulation by the laser beam |
| _______________ is the direction in which laser beam scans across the plate | Fast Scan Direction |
| _______________ is the direction of plate movement through the reader | Slow Scan (Subscan) Direction |
| Once the visible light hits the photomultiplier tube, the photomultiplier tube changes light into an _____________ | Electronic signal and converts it into digital data (Analog to Digital Converter - ADC) that can be understood by the computer |
| A bright ________ light is used to completely remove any residual image | White |
| Radiographers should be careful to erase any cassette prior to use if there is any chance it has been in storage for _______ or more | (48 hours) or 2 days |
| Phosphors are used for ________ __________ DR systems | Indirect Conversion |
| ______ __________ DR systems do not employ phosphors | Direct Conversion |
| At 70 kV, typical DQEs are ____ (____) or less for CR phosphor plates | .3 (30%) |
| At 70 kV, typical DQEs are ____ (____) or less for direct-conversion DR receptors | 0.67 (67%) |
| At 70 kV, typical DQEs are ____ (____) or less for indirect-conversion DR receptors | 0.77 (77%) |
| For CR, the most common source of artifacts is the _____________ | Image receptor plate (phosphor plate) |
| CR artifacts that appear consistently on all images are likely the result of _____________ or _____________ problems rather than the plate | Computer hardware or software |
| ______________________ can result from malfunction of the reader transport and scanning systems | Line or column drop-out |
| Dust particles sticking to optical components in the CR reader can cause ______________ | Pixel drop-out |
| ____________ refers to residual images that were not fully erased from a previous exposure | Ghosting |
| An entire line of artifact – most likely a problem within the ________________ | CR reader (dust particles) |
| An artifact that does not create a line across the image – most likely from objects __________ or _________ the cassette | Inside or outside |
Created by:
rdwilliams
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