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Raditude19Ch.14

Radiation Dosimetry in CT

QuestionAnswer
What is the second component of the rational use of CT? Minimization of the radiation dose without compromising diagnostic image quality.
What is the maximum energy of the x-ray used in CT? 120 to 140 keV
What is the average energy of the x-ray used in CT? 70keV
What is the unit of x-ray exposure in air? Roentgen (R)
What happens when the x-rays from the CT scanner interact with the tissue of the patient? Most of the energy is absorbed and some of it passes through to the detector.
What is the unit of absorbed dose? rad
What does rad describe? the amount of energy absorbed per unit mass.
What is the newer system that is used internationally in commerce and in science? SI, International System of Units
What is the SI unit of absorbed dose? Gray (Gy)
How many rad equal one Gy? 100rad=1Gy
1 cGy equals how many rad? 1cGy=1rad
What unit of measurement do physicists use to measure fast-moving particles like the ones in x-rays, cosmic rays, and particle accelerators? eV
What is the amount of energy that one electron gains when it is accelerated by an electrical potential of 1 volt? eV
How many eV are 1keV? 1000eV=1keV
What is the conversion factor that accounts for different biologic effects produced from different types of ionizing radiation? Quality Factor
What is the term for the combination of quality factor and radiation absorbed dose? Dose equivalent
What is the unit for dose equivalent? rem
What is the SI unit of the rem? Sievert (Sv)
How many rem are equal to 1 Sv? 100 rem=1 Sv
What is the product of the absorbed dose and a radiation weighting factor? Equivalent dose
What are the units for equivalent dose? rem or Sv
What is the unit that attempts to account for the effects particular to the patient's tissue that has absorbed the radiation dose? Effective dose equivalent
What are the units for effective dose? Sv and rem
What are the two reasons the dose is more uniform in CT than in conventional radiography? Beam is heavily filtered as it exits the x-ray tube.And the CT exposure comes from all directions creating a more uniform exposure.
What happens to the uniformity of the dose as the scan field of view and patient thickness increase? The uniformity of the dose decreases.
Why are body scans less uniform than head scans? As the scan field of view and patient thickness increase the uniformity of the dose decreases.
According to the radiation effects research foundation data doses above what amount in mSv show evidence of statistically significant cancer increase? 100mSv
Which 2 of the following are the main models of radiation exposure risk? nonlinear threshold and linear nonthreshold
If the CTDIW is 35 mGy and the pitch is 1, what is the CTDIVOL is mGy? 35
Which of the following provides the most accurate representation of dose for a defined length of tissue? DLP
What term best describes random variations in CT numbers? noise
Which of the following units relates the radiation exposure to risk and is considered the best method for estimating stochastic radiation risk? mSv
Which 3 of the following are fundamental principles that guide the International System for Radiation Protection and medical imaging? Justification, optimization, dose limits
What is a typical effective dose for a head CT in mSv? 2
Which of the following refers to those effects for which the severity (rather than the probability) increases with radiation dose and for which there is a threshold dose? deterministic
Which of the following terms refers to radiation risk in which the probability increases as the radiation dose increases and for which there's no threshold? stochastic
Created by: amy wiseman