User Manual
– Technical characteristics
NIMXEN020I
Owandy Radiology SAS
39
6.7
CTDI information
The following dose information are measured using a dosimetry head phantom compliant with the
specifications of CFR 21 1020.33.
The phantom is a circular cylinder of polymethil-methacrylate (PMMA) of density 1.19±0.01 grams
per cubic centimeter. The phantom is 15.0 centimeters high and has a diameter of 16.0
centimeters since the system is designed to image the head (head scanners).
The phantom has holes just large enough for the placement of a dosimeter(s) along its axis of
rotation and along a line parallel to the axis of rotation 1.0 centimeter from the outer surface and
within the phantom.
Values were measured as CTDI
100
as recommended in the FDA Guidance doc. "Provision for
Alternate Measure of the Computed Tomography Dose Index (CDTI) to Assure Compliance with
the Dose Information Requirements of the Federal Performance Standard for Computed
Tomography" of October 20.2006.
1.2.1
Measure conditions
The conditions of operations are set according to the following table:
Quantity
Range
Tube current (mA)
From 2 to 12.5 mA
kV
From 60 to 86 kV
Exposure time
21.2 s
X-ray filtration
≥ 2.5 mm Al eq. @ 86 kV
Nominal Tomographic section thickness
0.175 mm (0.0875 mm in HR)
Image receptor are
144 x 118.6 mm
6.7.1
Measurement procedure
1.
The phantom is placed on the support of the chin rest of the machine.
2.
The dose detector is placed in the phantom in one of the positions at a time.
3.
The default values for adult and normal size (84 kV
– 5 mA) are selected.
4.
An exposure is performed.
5.
The dose measure is recorded.
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