North Dakota Administrative Code › Title 33.1 - Department of Environmental Quality › Article 33.1-10 - Radiological Health Rules › Chapter 33.1-10-06 - X-Rays in the Healing Arts › Section 33.1-10-06-11 - Computed tomography x-ray systems

Current through Supplement No. 393, July, 2024
1.
Definitions.
In addition to the definitions provided in sections
				33.1-10-01-04 and
				33.1-10-06-02, the following
				definitions are applicable to this section:
a. "Computed tomography dose index" means the
				integral from -7T to +7T of the dose profile along a line perpendicular to the
				tomographic plane divided by the product of the nominal tomographic section
				thickness and the number of tomograms produced in a single scan, that is:
				where:
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This definition assumes that the dose profile is centered
				  around z = 0 and that, for a multiple tomogram system, the scan increment
				  between adjacent scans is nT.
b. "Contrast scale" means the change in the
				linear attenuation coefficient per computed tomography number relative to
				water, that is:
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c. "CS" (see "contrast scale").
d. "CT" means a radiologic imaging technique
				that produces images of "slices" through a patient's body.
e. "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 section
				33.1-10-06-02.
f. "CTDI" (see "computed tomography dose
				index").
g. "CT gantry" means the
				tube housing assemblies, beam-limiting devices, detectors, and the supporting
				structures and frames which hold these components.
h. "CTN" (see "CT number").
i. "CT number" means the number used to
				represent the x-ray attenuation associated with each elemental area of the CT
				image.
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j. "Dose profile" means the dose as a
				function of position along a line.
k. "Elemental area" means the smallest area
				within a tomogram for which the x-ray attenuation properties of a body are
				depicted. (see also "picture element").
l. "Multiple tomogram system" means a
				computed tomography x-ray system which obtains x-ray transmission data
				simultaneously during a single scan to produce more than one
				tomogram.
m. "Noise" means the
				standard deviation of the fluctuations in computed tomography number expressed
				as a percentage of the attenuation coefficient of water. Its estimate (Sn ) is
				calculated using the following expression:
where:
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n. "Nominal tomographic section thickness"
				means the full width at half maximum of the sensitivity profile taken at the
				center of the cross sectional volume over which x-ray transmission data are
				collected.
o. "Picture element"
				means an elemental area of a tomogram.
p. "Reference plane" means a plane which is
				displaced from and parallel to the tomographic plane.
q. "Scan" means the complete process of
				collecting x-ray transmission data for the production of a tomogram. Data can
				be collected simultaneously during a single scan for the production of one or
				more tomograms.
r. "Scan increment"
				means the amount of relative displacement of the patient with respect to the CT
				x-ray system between successive scans measured along the direction of such
				displacement.
s. "Scan sequence"
				means a preselected set of two or more scans performed consecutively under
				preselected CT conditions of operation.
t. "Scan time" means the period of time
				between the beginning and end of x-ray transmission data accumulation for a
				single scan.
u. "Single tomogram
				system" means a CT x-ray system which obtains x-ray transmission data during a
				scan to produce a single tomogram.
v. "Tomographic plane" means that geometric
				plane which is identified as corresponding to the output tomogram.
w. "Tomographic section" means the volume of
				an object whose x-ray attenuation properties are imaged in a
				tomogram.