Multiple Choice
Identify the choice that best completes the
statement or answers the question.
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1.
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The array size for a 16 slice CT may have more than ____detector elements
laterally across the gantry.
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2.
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What are the advantages of using a higher kVp
i Greater
penetration through the body
ii Higher dose to patient
iii A reduction in beam hardening
artifacts
iv Decrease in quantum noise
v Reduces differences in tissue
densities
a. | i, ii and iii | d. | ii, iii and iv | b. | iii, v and v | e. | i, iv and v | c. | all of the
above | f. | i, iii and
iv |
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3.
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The energies that can be selected on a CT scanner are usually defined by a
limited set of energies such as •A
a. | 100, 200, 300 and 400 kVp | c. | 10, 20, 30 and 40
kVp | b. | 80, 100, 120, and 140kVp |
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4.
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Which of the following is the disadvantages of CT image
reconstruction
a. | Raw data will not be able to be reconstructed | c. | Desired image detail is difficult
to obtain | b. | Multiple reconstructions may be required if significant detail is required from
areas of the study that contain bone and soft tissue | d. | Filters may blur constructed
images |
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5.
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In the 16 slice system, what is the detector design
i Comprised of 2 row
sizes
ii 24 rows total
ii 20mm coverage
a. | i | c. | i, ii and iii | b. | i and ii |
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6.
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How many ways are there to define helical configuration pitch
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7.
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What is the characteristic of high contrast resolution
a. | Better when there is very low noise
| c. | Ability to see a small, dense
lesion in lung tissue
| b. | Differentiate gray matter from white matter in
the brain.
| d. | Visualizing
soft-tissue lesion within the liver.
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8.
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Below are the characteristic X-rays
i These are produced following the
ionization of an atom that leaves an inner shell, typically the K shell, with an electron
vacancy
ii The outer-shell electron that drop in to fill in the inner-shell vacancy must lose
energy
iii The energy lost is released as electromagnetic radiation (x-ray) with a specific or
characteristic energy determined by the energy difference between the two shells
a. | i and ii | c. | none of the above | b. | i, ii and iii | d. | i |
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9.
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The creation of shaded surface displays (SSDs) images is typically done in these
three steps:
Arrange those steps in order
i Render or shade the projected images to
provide depth perception and illumination of the
patient
ii Reconstruct the CT
data from the 2D slices using thin overlapping slices
iii Segment out unwanted data using
thresholding of the CT numbers or cropping or
segmenting out overlying
structures
a. | i, ii, iii | c. | iii, ii, i | b. | ii, iii, i |
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10.
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The typical number range of Kernels in Reconstruction is from
a. | 11000 - 19000 | c. | 1100 - 1900 | b. | 110 - 190 | d. | 10 - 90 |
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Matching
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a. | physiologic parameters | f. | aneurysm | b. | invisible | g. | vascular anatomy | c. | over time
| h. | lower
radiation | d. | morphologic filtering | i. | lax | e. | tissue attenuation | j. | aggressive |
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11.
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Tissue enhancement _______represents the rate and amount of contrast
material
distribution in the vascular space and extravascular, extracellular space.
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12.
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If the thresholding process is too _______, nontissue materials (eg, fluids)
can be rendered as if they were tissue, which can obscure
protruding structures
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13.
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In a case of a cerebellar artery aneurysm, a surface-rendered view is used to
illustrate the location of the _________ relative to a main branch structure
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14.
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The CT acquisition series is centered over the region of interest (eg, infarct
location or lesion location), and a set of images is acquired at that position (without table motion)
over time as contrast material is injected, with a ________ dose than
would be normally
employed
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15.
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CT has recently been applied to measure ___________.
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16.
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In surface rendering, the voxels located on the edge of a structure are
identified, usually by intensity thresholding, and possibly enhanced with _______or
connectivity
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17.
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The remaining voxels in the image are usually _______
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18.
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If the thresholding process is too ________, actual protruding structures can
be lost from view because of partial volume effects.
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19.
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By using various mathematical models adjusted to the arterial
attenuation,
measurement of ______ over time can describe physiologic parameters
such as blood
volume, blood flow rate, tissue permeability, and mean transit time
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20.
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Three-dimensional image display for _______ provides
excellent
anatomic information for surgical planning
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a. | gantry | d. | Ultrafast ceramic detectors | b. | anatomic
section | e. | tissue
densities | c. | 8 bits |
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21.
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________ use rare earth elements such as silicon, germanium, cadmium, yttrium
or gadolinium, which create a semiconducting p-n junction
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22.
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The ____ houses the key components of the scanner
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23.
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CT produces cross-sectional images and also has the ability to differentiate
______
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24.
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Tomography is a term that refers to the ability to view an _____ or slice
through the body.
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25.
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Limitations of CT display is that digital imaging is often limited to ___ of
data
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a. | Bremsstrahlung Radiation | f. | kVp | b. | milliampere | g. | lower quantum | c. | X-rays | h. | Gamma rays | d. | anode | i. | Beam
hardening | e. | Higher-energy | j. | accelerated electrons |
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26.
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______x-ray photons are needed to penetrate large bones of the shoulder, hip
and vertebrae
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27.
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_________ are created by the nuclear forces at the center of the
atom
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28.
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_______occurs when energetic electrons pass very near the nucleus of an
atom.
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29.
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X-ray tubes for CT scanners have an ____ that rotates thousands of revolutions
per minute
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30.
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_____ setting defines the fraction of photons that will successfully reach the
detectors of the scanner
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31.
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There is a proportional increase in the number of x-rays, at all energies, when
the current in is increased
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32.
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More photons reaching the detectors will result in _____ noise in the images,
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33.
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The x-ray tube is a glass envelope that contains a high vacuum so that
____________ from the internal electrodes may move with ease
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34.
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_______ are produced in the electron shell structure of the atom
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35.
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______will create artifacts seen as dark streaks that radiate from the outside
toward the inner part of the body
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Match the definitions.
a. | off-axis views | f. | Filtered
back-projection
| b. | thick | g. | mandible | c. | thin | h. | y and
z directions | d. | sagittal | i. |
interior vessel analysis | e. | transparency
levels | j. | slabs |
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36.
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In volume rendering _______can be more difficult to control
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37.
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Longer helical scans_____slices
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38.
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reformatting process
does not alter the CT voxels in any way; instead
it
uses these voxels in ________
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39.
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The CT scanner acquisition parameters that
have the most direct effect are
_______ and section interval
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40.
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Oblique reformatting is quite similar to_______ or
coronal
reformatting
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41.
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if CT images are acquired at their smallest possible section thickness,
they
can be viewed as _____
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42.
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In curve reformatting the desired curve is generally
defined along some
anatomic structure, such as
the curve of the_______
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43.
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algorithms used to reconstruct CT images:
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44.
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A sagittal view is formed from a stack of CT
images by sampling in
the_________
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45.
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Volume rendering has yet to replace earlier applications
of surface
rendering like___________
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True/False
Indicate whether the statement is true or
false.
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46.
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Helical SSCT slices are reconstructed from data interpolated
between the 4
nearest ray measurements
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47.
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Pitch affects image noise in helical
MSCT if slice measurements are
formed from many
detector samples.
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48.
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The size of the beam penumbra is not related to the collimator
design and the
focal spot size and changes only
moderately at different beam widths.
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49.
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Depending on detector design and element size,
dead space associated with the
dividers can represent up to
25% of the detector surface area
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50.
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Acquiring thin slices increases partial-volume streaks, and they allow
for
the production of high-quality off-axis
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51.
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SSCT detector arrays consist of a large number
(typically 750 or more) of
detector elements in a single
row across the irradiated slice to intercept the
x-ray
fanbeam.
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52.
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A detector design used in one of the first modern MSCT
scanners (Fig. 1)
consisted of 16 rows of detector elements,
each 1.25 mm long in the z-direction, for a total
z-axis
length of 20 mm
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53.
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As beams become even wider for higher-slice-count scanners, the
geometric
efficiency loss associated with the penumbra becomes more of a factor.
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54.
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In cardiac imaging CTA examinations are electrocardiographically gated helical
scans with data acquired during the same heart phase over several heartbeats.
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55.
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Helical scanning with MSCT scanners are conceptually
different to that with
SSCT scanners; rotation and table
movement does not occur simultaneously with continuous data
acquisition.
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56.
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In SSCT pitches of
less than 1 were not used.
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57.
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To understand how various factors affect CT image noise, it is easiest
to
consider how many x-ray photons contribute to each
detector measurement.
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58.
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In cardiac imaging, for optimal examination quality, data associated with
the
reconstruction of individual slices should be collected within 3 beats
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59.
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Currently, the fastest rotation times are on
the order of 1/3 s
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60.
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the numbers of images produced by MSCT are not associated with detector
collimation
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61.
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In SSCT the x-ray beam collimation was designed such that the z-axis
width of
the x-ray beam at the isocenter is the same as the desired slice thickness
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62.
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The installation of MSCT scanners providing 16 data
channels for 16
simultaneously acquired slices began in
2002. the detector arrays associated with 16-slice
scanners
did not allow thinner slices to be obtained.
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63.
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In helical SSCT, slice data are interpolated between
equivalent rays
separated by a full rotation (360 apart) or
between parallel opposed rays (180 apart).
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64.
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MSCT examination sizes in terms of image counts are
the same than those for
SSCT
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65.
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The first scanner with more than one row of detectors
and a widened z-axis
x-ray beam was introduced by Godfrey Hounsfield
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66.
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In a fashion analogous to radiographic AEC, CT AEC manually selects scan mA
on
the basis of patient attenuation estimated from scout views
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67.
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Dose efficiency has 2 components: geometric efficiency and absorption
efficiency
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68.
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patient dose tends to be dominated by the higher intensities penetrating through
the patient from the anterior and posterior views.
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69.
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High contrast sensitivity depends on CT image noise
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70.
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Increasing pitch (to reduce either scan time or
x-ray tube heating) increases
distance between interpolated
measurements, so that the likelihood of helical
artifacts
increases.
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71.
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Thinner slices can be combined to form
thicker slices for interpretation
purposes, if necessary
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72.
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In MSCT, the actual x-ray beam
collimation is directly involved in
determining slice
thickness
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73.
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Because of cone beam
effects, some MSCT scanners with 16 channels or
more
only allow the simultaneous acquisition of the maximum
number of slices
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74.
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covering a 40-cm scan range with contiguous 5-mm slices (whether acquired
axially or helically) would
generate 80 images.
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75.
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axial and helical MSCT involves a more
complex data collection process and
measuring and specifying
patient radiation doses in MSCT are different from in
SSCT.
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76.
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Absorption efficiency refers to the fraction of x-rays that exit the
patient
and that enter active detector areas.
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77.
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Some systems now allow mA adjustment not only for each slice or rotation but
also for
individual views (angles) during a single rotation.
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78.
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When a
20-mm-wide x-ray beam is used, 4 slices with a thickness
of 5 mm
are acquired.
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79.
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The closer the distance between the electron and the nucleus, the greater the
acceleration of the electron and the higher the x-ray energy emitted
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80.
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By 2005, 64-slice scanners were announced, and installations
by most
manufacturers began. The approach used by most manufacturers for 64-slice
detector array designs
was to lengthen the arrays in the
z-direction and provide all submillimeter detector
elements
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81.
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dividers must satisfy anti–cross talk and physical separation
requirements,
therefore the width generally remains unchanged as detector
elements are made
smaller
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82.
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‘x-ray beam width’’ always refers to the size of the
x-ray
beam along the z-axis—that is, in the slice thickness direction)
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83.
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The concepts of MSCT and SSCT do not differ
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84.
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For 16-slice scanners (and more), the detector
collimation during helical
scans is 1.5 mm or less (depending
on the model and beam width), with correspondingly
small
differences in the slice profile shape versus pitch.
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85.
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In SSCT, the beam width is taken to be the z-axis dose profile width
measured
at the isocenter between profile points corresponding to 50% of the maximum
intensity
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