Fluke Biomedical 76-419-4150 User Manual
Page 8
Nuclear Associates 76-419-4150
Operators Manual
2-2
Where:
μ
w
=
Linear attenuation coefficient of water.
μ
x
=
Linear attenuation coefficient of material of interest.
(CT)
w
=
CT number of water.
(CT)
x
=
CT number of material of interest.
3) CT Conditions of Operation Means
All selectable parameters governing the operation of a CT x-ray system including nominal tomographic
section thickness, filtration, and the technique factors as defined in §1020.30(b)(36).
4) CT Number Means
The number used to represent the x-ray attenuation associated with each elemental area of the CT image.
5) [Reserved]
6) CT Dosimetry Phantom Means
The phantom used for determination of the dose delivered by a CT x-ray system. The phantom shall be a
right circular cylinder of polymethl-methacrylate of density 1.19±0.01 grams per cubic centimeter. The
phantom shall be at least 14 centimeters in length and shall have diameters of 32.0 centimeters for testing
any CT system designed to image any section of the body (whole body scanners) and 16.0 centimeters for
any system designed to image the head (head scanners) or for any whole body scanner operated in the
head scanning mode. The phantom shall provide means 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. Means for the placement of a dosimeter(s) or alignment device at other locations may be
provided for convenience. The means used for placement of a dosimeter(s) (i.e., hole size) and the type of
dosimeter(s) used is at the discretion of the manufacturer. Any effect on the doses measured due to the
removal of phantom material to accommodate dosimeters shall be accounted for through appropriate
corrections to the reported data or included in the statement of maximum deviation for the values obtained
using the phantom.
7) Dose Profile Means
The dose as a function of position along a line.
8) Modulation Transfer Function Means
The modulus of the Fourier transform of the impulse response of the system.
9) Multiple Tomogram System Means
A CT x-ray system which obtains x-ray transmission data simultaneously during a single scan to produce
more than one tomogram.
10) Noise Means
The standard deviation of the fluctuations in CT number expressed as a percent of the attenuation
coefficient of water. Its estimate (S
n
) is calculated using the following expression:
Where:
CS = Contrast
scale.
μ
w
=
Linear attenuation coefficient of water.
s
=
Estimated standard deviation of the CT numbers of picture elements in a specified area of the CT
image.
Nominal Tomographic Section Thickness Means