True/False
Indicate whether the
statement is true or false.
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1.
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One benefit of the MSAD is that the average dose for a series of slices, can be
determined by measuring the CTDI from a single slice.
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2.
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The MSAD underestimates the true average dose.
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3.
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Increasing the CTDI increases the dose to the patient.
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4.
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To calculate the CTDI with an ionization chamber, the x-ray beam must be
positioned near the end of the chamber, and the radiation beam is turned on while a single scan
is made.
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5.
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The ionization chamber method for accurate determination of dose from CT
scanners is the easiest and probably most accurate method.
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6.
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1 cGy = 100 rads
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7.
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When the slice width equals the bed index, the MSAD is numerically equal to the
CTDI.
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8.
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Most modern CT Scanners emit a fan shaped x-ray beam.
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9.
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An ionization chamber measures doses.
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10.
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The diameter of the “head” phantom is 32 cm, whereas the diameter of
the “body” phantom is 16 cm.
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11.
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The dose distribution is almost always wider than the nominal slice
width.
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12.
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Multiple Scan Averaged Dose (MSAD) uses a single ionization chamber measurement
and a subsequent simple calculation to determine the peak dose delivered to a patient who has
received a series of scans at a given technique with a specified bed indexing.
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Multiple Choice
Identify the
choice that best completes the statement or answers the question.
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13.
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To standardize the measurements of the dose and provide realistic geometry,
researchers suggest that the ionization chamber be placed in one of two cylindric phantoms during the
radiation measurements. The smaller represents the ______, and the larger represents the
____.
a. | hand, torso | c. | head, feet | b. | head, body | d. | none of the
above |
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14.
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Spiral or Helical CT Scanners use this method for calculating their dose
measurements.
a. | CTDI | c. | TLD | b. | MSAD | d. | Multichannel
Analyzer |
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15.
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As the slice spacing increases, there is a greater likelihood that relevant
tissue will be missed in the scan sequence, thus limiting the amount that the bed indexing can be
increased. This is due to ?
a. | areas of interest falls between slices | c. | slices are too close
together | b. | areas of interest are to large for slices | d. | none of the
above |
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16.
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The ionization chamber receives radiation from all parts of the dose
distribution because
a. | its width is several times the length of the x-ray beam. | c. | is nonproportional
to the area under the curve. | b. | is proportional to the area under the
curve. | d. | its length is
several times the width of the x-ray beam. |
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17.
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The narrow width of the x-ray beam is intercepted by the chamber that is placed
________?
a. | parallel to the longitudinal axis of the patient. | c. | perpendicular to the fan of the
radiation beam. | b. | perpendicular to the horizontal axis of the patient | d. | perpendicular to the longitudinal axis of the
x-ray beam. |
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18.
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In a multiple scan averaged dose of CT is performed on a patient, the doses of
all the scans are summed, the resultant dose is ______ than that from just one scan.
a. | higher | c. | equal to | b. | lower | d. | no different |
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19.
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CT scanners produce approximately how many Grays per Roentgen?
a. | 9.4 Gy/Roentgen | c. | 94 Gy/Roentgen | b. | .94 cGy/Roentgen | d. | 940
cGy/Roentgen |
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20.
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A long ionization chamber is often called a pencil chamber because of its
a. | slenderness | c. | diameter | b. | function | d. | shape and size |
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