Question 1

What is the easiest and probably the most accurate method used to report dose?

Accepted Answer

The ionization chamber method is the easiest and probably the most accurate, and it is used almost exclusively to report dose.

Question 2

What was the first dose descriptor to be identified?

Accepted Answer

The multiple-scan average dose was the first computed tomography dose descriptor to be identified.

Question 3

Effective mAs can be described as:

Accepted Answer

"Effective mAs" is a term used for multislice computed tomography scanners and denotes the mAs per slice. This is given by the following relationship: Effective mAs = True mAs/pitch.

Question 4

The overall goals of automatic tube current modulation are to: I. provide consistent image quality
II. increase scan speed
III. control dose to the patient

Accepted Answer

The overall goal of automatic tube current modulation is to provide consistent image quality despite the size of the patient and the tissue attenuation differences and to control the dose to the patient compared with manual milliamperage selection techniques.

Question 5

Which of the following are factors of dose that can be controlled by the technologist? 
I. technique factors
II. patient centering
III. x-ray beam collimation

Accepted Answer

The technologist has some degree of control over exposure technique factors, x-ray beam collimation, pitch, patient centering, number of detectors, and overranging (also referred to as z-overscanning).

Question 6

What is the unit of the computed tomography dose index?

Accepted Answer

The CTDI_FDA represents the mean absorbed dose in the scanned object volume and therefore the unit of the computed tomography dose index is the gray (Gy), with relevant submultiples such as the centigray (cGy) and the milligray (mGy).

Question 7

What instrument is used to measure the charge removed from the ionization chamber?

Accepted Answer

The charge is removed from the ionization chamber and measured with a very sensitive instrument known as an electrometer.

Question 8

What term is used to refer to the size and shape of the beam emanating from the x-ray tube and passing through the patient?

Accepted Answer

The term beam geometry refers to the size and shape of the x-ray beam emanating from the x-ray tube and passing through the patient to strike a set of detectors that collects radiation attenuation data.

Question 9

What types of dosimeters have previously been used to measure dose in computed tomography? 
I. film dosimeter
II. thermoluminescent dosimeter
III. ionization chamber

Accepted Answer

In the past, several types of dosimeters were used to measure the dose in computed tomography. These include film dosimeters, thermoluminescent dosimeters, and specially designed ionization chambers.

Question 10

What is the process by which additional rotations before and after the planned length are taken? I. overranging
II. doubling scan
III. z-overscanning

Accepted Answer

Additional rotations before and after the planned length are essential for the image reconstruction process, which is referred to as overranging or z-overscanning.

Question 11

What term refers to the automatic control of the milliamperage in two directions during data acquisition by specific technical procedures?

Accepted Answer

Automatic tube current modulation refers to the automatic control of the milliamperage in two directions of the patient (the x-y axis and the z-axis) during data acquisition (scanning process) by use of specific technical procedures that take into consideration not only the patient size but also the attenuation differences of the various tissues.

Question 12

What technical factor determines the penetrating power of the photons coming from the x-ray tube?

Accepted Answer

The peak kilovoltage determines the penetrating power of the photons coming from the x-ray tube.

Question 13

Which of the following are recommended by the Center for Devices and Radiological Health as computed tomography dose descriptors? 
I. computed tomography dose index
II. multiple-scan average dose
III. dose profile

Accepted Answer

The Center for Devices and Radiological Health introduced and recommend the use of the computed tomography dose index and the multiple-scan average dose in the federal performance standard as the dose descriptors specific to computed tomography.

Question 14

What is the term used to describe the instrumentation and methods used to measure patient dose from a computed tomography scanner?

Accepted Answer

The instrumentation and methods used to measure patient dose from a computed tomography scanner are referred to as computed tomography dosimetry.

Question 15

What is/are the purpose(s) of the use of bowtie filters in computed tomography? 
I. shape the beam intensity
II. produce a more uniform beam
III. increase scan time

Accepted Answer

The use of bowtie filters in computed tomography scanners is intended to mainly serve two purposes: to shape the beam intensity within the scan field of view and to produce a more uniform beam at the detectors.

Question 16

Which technique factor determines the quantity of photons (dose) incident on the patient for the duration of the exposure?

Accepted Answer

The mAs determines the quantity of photons (dose) incident on the patient for the duration of the exposure.

Question 17

What dose descriptor is used to describe a measurement of the total amount of exposure for a series of scans?

Accepted Answer

The dose-length product a dose descriptor used in computed tomography dose studies and reported in the literature; it provides a measurement of the exposure per slice of tissue. The dose-length product provides a measurement of the total amount of exposure for a series of scans.

Question 18

Which factors affecting dose in computed tomography have a direct influence on image quality but no direct effect on radiation dose?

Accepted Answer

The indirect factors are those that factors that have a direct influence on image quality but no direct effect on radiation dose (for example, the reconstruction filter).

Question 19

What is the term used to describe a ratio of the difference the table travels per revolution to nominal beam collimation?

Accepted Answer

The term pitch has been defined by the International Electrotechnical Commission, as a ratio of the distance the table travels per revolution (in millimeters) to the total nominal beam collimation (in millimeters).

Question 20

If the pitch increases, the dose:

Accepted Answer

As the pitch increase the dose decreases. Therefore if the pitch increases by 2, the dose will be reduced to one half.

Quiz 10: Radiation Dose in Computed Tomography