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Download Radiologic Technology – Digital Radiography Practice Test 140 Questions & Answers. and more Exams Radiography in PDF only on Docsity!
a To allow some flexibility in centering of the anatomy over different portions of the receptor plate, most fixed DR units have detector cells inthe plate for automatic exposure control (AEC): a.1 b. 3 c.5 d. 6 - ANSWER ****c Whenever there is an insufficient sampling rate for a high-frequency digital image, artifacts may be created: a. pixel drop-out b. halo c. reticulation d. aliasing - ANSWER****d When compared to CR, which of the following is not a disadvantage of DR: a. Tendency to use the bucky grid for distal extremities b. Less flexibility in positioning c. Bulky and cumbersome receptor plates d. Less consistency in image quality - ANSWER****d In the 1980s, the first clinically useful DR system consisted of a bar of large detectors connected to photomultiplier tubes, which swept across the field area during exposure. This system was called: a. computed tomography b. conventional tomography c. linear positron emission tomography d. scanned projection radiography e. direct-scan radiography - ANSWER****d For DR, the size of the individual detector elements (dexels) currently used is closest to: a.1lcm b. 1 mm c. 100 microns (1/10th mm) d. 1 micron (1/1000th mm) e. 1 nanometer - ANSWER****c The Nyquist criterion states that to prevent aliasing, the sampling rate must be the spatial frequency of the image: a. Equal to b. At least twice c. One-half d. Four times - ANSWER****b Which of the following has the highest DQE, at 77%: a. conventional screens and film b. CR phosphor plates c. direct-conversion DR plates d. indirect-conversion DR plates - ANSWER****d Which of the following terms, all contractions, most accurately describes the individual hardware elements of a DR receptor plate that detect radiation inthe remnant x-ray beam? a. the pixel b. the dexel (or del) c. the voxel d. the rexel e. the dynode - ANSWER****b To acomputer expert, a true pixel is a numerical value assigned to a(n): a. small square area in the image b. small circular area in the image c. small square detector surface d. small circular detector surface e. point with no dimensions - ANSWER****e In a DR image receptor, most of the square area of each dexel is dedicated to what portion of the detector element: a. the thin-film transistor b. the semiconductor layer c. the capacitor d. the gate lines - ANSWER****b For CR, the most common source of image artifacts is the: a. patient b. phosphor plate c. reader (processor) d. computer - ANSWER****b Generally, phosphor elements with higher atomic numbers absorb more x-rays; However, an exception to this rule can occur if lowering the atomic number better matches the of the phosphor element to the typical energies in a diagnostic x-ray beam: a. physical density b. electron density c. binding energy of the k-shell d. atomic mass - ANSWER****c In any detector designed to "capture" x-rays, the highest degree of x-ray absorption occurs when the k-edge of the chemical used falls: a. just below the average kV of the x-ray beam c. the amplifier d. the data lines e. photodiodes - ANSWER****a In an individual DR detector element (dexel), the electronic charge built up on the capacitor is positive charge because it is generated by drifting downward through the semiconductor layers to the capacitor: a. x-rays b. electrons c. charge holes d. molecules of amorphous selenium e. top electrodes - ANSWER****c When compared to direct-conversion DR systems, a major reason that indirect-conversion DR systems can save patient dose is that they have higher: a. absorption efficiency b. conversion efficiency c. emission efficiency d. electronic efficiency - ANSWER****a When the signal-to-noise ratio of the output image from a receptor is divided by the signal- tonoise ratio of the signal coming into the receptor, (with both numbers squared), we obtain the overall for the system: a. emission efficiency b. detective quantum efficiency c. contrast-noise ratio d. modulation transfer function - ANSWER****b A reflective backing in a CR phosphor plate improves its: a. absorption efficiency b. conversion efficiency c. emission efficiency d. k-edge effect - ANSWER****c Which of the following increase the absorption efficiency of a CR phosphor plate: a. thicker phosphor layer om . phosphor compounds with high atomic numbers c. compounds that take advantage of the k-edge effect d. all of these e. none of these - ANSWER****d In indirect-conversion DR systems, the dispersion of light emitted from molecules of cesium iodide is reduced by using: a. light guides b. turbid phosphor structure b. the molecule must be suited to absorbing light rather than x-rays c. silicon binds better to the cesium iodide layer above d. silicon is easier to coat into very thin layers - ANSWER****b Magnification of the displayed light image using monitor controls can be accomplished only by: a. Spreading out a single pixel value across several hardware monitor pixels b. Increasing the size of the hardware monitor pixels c. Increasing the displayed image matrix size d. Increasing the displayed image field-of-view (FOV) - ANSWER****a Changing the field-of-view (FOV) can affect the sharpness (spatial resolution) of an image ONLY if it results in: a. Changing the matrix size b. Changing the pixel size c. Changing the pixel value d. Maintaining the matrix size - ANSWER****b Which of the following is a primary advantage of direct-conversion DR receptors over indirectconversion systems? a. improved resolution b. lowered patient exposure c. increased image contrast d. increased system processing speed - ANSWER****a Computed radiography (CR) is a digital imaging technique that acquires image data from: a. an electrostatic image receptor scanned by a CCD b. a magnetic tape that has been scanned by a magnetic recorder c. arare earth intensifying screen scanned by a PM tube d. a photostimulable phosphor plate scanned by a laser beam - ANSWER****d Throughout the entire imaging sequence for a CR system, how many times is the photostimulable phosphor plate caused to glow? a. Once b. Twice c. Three times d. A CR plate does not give off light, but conducts electricity - ANSWER****b For a CR image receptor plate, which of the following chemicals makes a good photostimulable phosphor: o . gadolinium oxysulfide b. lanthanium oxybromide c. calcium tungstate d. barium fluorobromide e. silver nitrate - ANSWER****d d. Indirect-conversion DR system - ANSWER****a The CR cassette must be structured soas to protect the phosphor plate inside it from: a. light b. primary x-rays c. static electricity d. heat - ANSWER****c In the structure of a photostimulable phosphor plate, the anti-halo layer prevents: a. back-scattered x-rays from reaching the phosphor layer b. external light from creating artifacts within the phosphor layer c. laser light from penetrating through to the reflective layer d. emitted light from excessive diffusion - ANSWER****c In the CR reader, the release of trapped energy from a meta-stable F-center in a phosphor crystal is triggered by exposure to visible light in the spectrum: a. red b. violet c. green d. ultraviolet - ANSWER****a A photomultiplier tube is incorporated into the CR reader in order to: a. amplify and covert visible light into a measurable electronic signal b. convert laser light into a usable electric signal c. store the exit radiation in multiple conduction bands of the crystal lattice d. convert analog information into a digital signal - ANSWER****a On a liquid-crystal display (LCD) monitor, each intersection of two flat, transparent wires constitutes a: a. Hardware dexel b. Hardware pixel c. "Soft" pixel d. "Soft" dexel - ANSWER****b For a display monitor, which of the following is constant or fixed: a. The displayed field-of-view (FOV) b. The size of the displayed light image pixels c. The size of the hardware pixels d. The matrix size for the displayed light image - ANSWER****c What is the "soft" pixel size for a 205 mm (FOV) image displayed on a monitor screen with a 1024 X 1024 matrix of hardware pixels? a. 0.2 mm b. 2mm c.5mm d. 0.5 mm - ANSWER****a After a photostimulable phosphor plate has been scanned in the CR reader, itis then exposed to high-intensity white light in order to: a. clean the transport system of leftover positive ions b. clearany of the remaining latent image from the phosphor layer c. realign the low density laser mirror to the PM tube d. amplify the electronic signal from the PM tube before it goes to the computer system - ANSWER****b An increase in the voltage applied to the photomultiplier (PM) tube in the CR reader will be associated with a(n): a. increase in spatial resolution b. decrease it the amount of quantum noise c. increase in the system speed d. increase in the amount of scatter radiation - ANSWER****c Because they are NOT subject to change, the pixel size formula is invalidated for: a. the dexels (detector elements) in a DR detector plate b. the pixels in a fixed sampling CR reader c. the hardware pixels of a display monitor d. all of the above - ANSWER****d For CR systems, an upper limit on spatial resolution is imposed by the: a. sampling frequency of the CR reader b. size of crystals in the photostimulable phosphor plate c. geometry of the x-ray beam d. size of the focal spot in the x-ray tube - ANSWER****a The sampling frequency of a CR reader, which determines the number of measurements taken across the phosphor plate, is called the: a. Larmour frequency b. Nyquist frequency c. fast-scan frequency d. aliasing frequency - ANSWER****b The formula relating the field-of-view (FOV) to the pixel size of "soft" pixels is: For a given physical area: a. FOV = PS/M b. FOV = M/PS c. PS = FOV/M d. PS = M/FOV - ANSWER****c During the reading process, the intensity of light emitted by the CR plate phosphor is directly proportional to: a. the amount of quantum mottle present in the image b. the voltage applied to the photomultiplier (PM) tube c. the amount of x-ray energy absorbed in the plate ACR phosphor plate should be erased prior to use if it has been in storage and accumulating background radiation for more than: a. 1 day b. 2 days c. 3 days d. 5 days - ANSWER****b "Pre-fogging" a CR cassette prior to use adds to the overall amount of fed into the computer, which can cause rescaling or gradation errors if it becomes overwhelming. a. CNR b. Data c. Noise d. Signal intensity - ANSWER****c For a DR receptor plate, if the width of the individual detector elements could be reduced to 0.0625 mm (del pitch = 0.0625 mm), what spatial resolution could be achieved? a. 4 LP/mm b. 5 LP/mm c. 6 LP/mm d. 8 LP/mm e. 10 LP/mm - ANSWER****d What "across-the-board" adjustment in radiographic techniques is recommended to allow for CR operation at the 400-speed class, reduce patient exposure, and avoid image mottle? a. double all mAs values b. cut all mAs values in half c. increase all kVp levels by 15 per cent d. reduce all kVp levels by 15 per cent - ANSWER****increase all kVp levels by 15 per cent If adepartment chooses to operate their CR or DR system at the 200-speed class, what general adjustment in techniques must be made in changing from 400-speed rare earth screens: a.an overall doubling b. a four-fold increase overall c. a reduction to one-half d. no change is required - ANSWER****an overall doubling For all digital imaging systems, a lower limit for exposure to the receptor is imposed by: a. the appearance of mottle b. images turning out too light c. the appearance of image fog d. images turning out with excessive contrast - ANSWER****the appearance of mottle Which of the following are essential considerations when using automatic exposure control with a DR or CRsystem? a. the use of high kVp techniques 
