Name:    MIIWIVQI: Measuring Patient Dose from CT Scanners

True/False
Indicate whether the statement is true or false.

1.

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.

2.

The MSAD underestimates the true average dose.

3.

Increasing the CTDI increases the dose to the patient.

4.

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.

5.

The ionization chamber method for accurate determination of dose from CT scanners is the easiest and probably most accurate method.

6.

7.

When the slice width equals the bed index, the MSAD is numerically equal to the CTDI.

8.

Most modern CT Scanners emit a fan shaped x-ray beam.

9.

An ionization chamber measures doses.

10.

The diameter of the “head” phantom is 32 cm, whereas the diameter of the “body” phantom is 16 cm.

11.

The dose distribution is almost always wider than the nominal slice width.

12.

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.

Multiple Choice
Identify the choice that best completes the statement or answers the question.

13.

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

14.

Spiral or Helical CT Scanners use this method for calculating their dose measurements.
 a. CTDI c. TLD b. MSAD d. Multichannel Analyzer

15.

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

16.

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.

17.

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.

18.

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

19.

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

20.

A long ionization chamber is often called a pencil chamber because of its
 a. slenderness c. diameter b. function d. shape and size