Mississippi Administrative Code › Title 15 - Mississippi Department of Health › Part 21 - Division of Radiological Health › Subpart 78 - Radiological Health › Chapter 1 - REGULATIONS FOR CONTROL OF RADIATION IN MISSISSIPPI › Subchapter 6 - X-Rays In The Healing Arts › Rule 15-21-78-1.6.9 - Computed Tomography X-Ray Systems

Current through June 25, 2024
1. Definitions. In
					 addition to the definitions provided in 1.1.2 and 1.6.2 of these regulations,
					 the following definitions shall be applicable to 1.6.9:
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:
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						Image
where:
z
= Position along a line perpendicular
						to the tomographic plane.
D(z)
= Dose at position z.
T =
Nominal tomographic section
						thickness.
n =
Number of tomograms produced in a
						single scan.
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 CTN relative to water, that is:
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						Image
where:
µ
x = Linear
						attenuation coefficient of the material of interest.
µ
w = Linear
						attenuation coefficient of water.
(
CTN
)x
					 =
CTN
of the material of interest.
(
CTN
)w
					 =
CTN
of water.
c. "CS" (See "Contrast scale").
d. "CT conditions of operation" means all
					 selectable parameters governing the operation of a CT x-ray system including,
					 but not limited to, nominal tomographic section thickness, filtration, and the
					 technique factors as defined in 1.6.2.
e. "CTDI" (See "Computed tomography dose
					 index").
f. "CT gantry" means the
					 tube housing assemblies, beam-limiting devices, detectors, and the supporting
					 structures and frames which hold these components.
g. "CTN" (See "CT number").
h. "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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						Image
where:
k
= A
						constant31
µ
x = Linear
						attenuation coefficient of the material of interest.
µ
w = Linear
						attenuation coefficient of water.
i. "Dose profile" means the dose as a
					 function of position along a line.
j. "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").
k. "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.
l. "Noise" means the
					 standard deviation of the fluctuations in
CTN
expressed as a
					 percentage of the attenuation coefficient of water. Its estimate
					 (
S
n) is calculated using the following
					 expression:
Click Here To View
						Image
where:
CS
= Contract scale.
µ
w = Linear
						attenuation coefficient of water.
s
= Estimated standard deviation of the
CTN
of picture elements in a specified area of the CT
						image.
m. "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.
n. "Picture element" means an elemental area
					 of a tomogram.
o. "Reference plane"
					 means a plane which is displaced from and parallel to the tomographic
					 plane.
p. "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.
q. "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.
r.
					 "Scan sequence" means a preselected set of two or more scans performed
					 consecutively under preselected CT conditions of operation.
s. "Scan time" means the period of time
					 between the beginning and end of x-ray transmission data accumulation for a
					 single scan.
t. "Single tomogram
					 system" means a CT x-ray system which obtains x-ray transmission data during a
					 scan to produce a single tomogram.
u. "Tomographic plane" means that geometric
					 plane which is identified as corresponding to the output tomogram.
v. "Tomographic section" means the volume of
					 an object whose x-ray attenuation properties are imaged in a tomogram.
2
Requirement for Equipment.
a. Termination of Exposure.
i. Means shall be provided to terminate the
					 x-ray exposure automatically by either de-energizing the x-ray source or
					 shuttering the x-ray beam in the event of equipment failure affecting data
					 collection. Such termination shall occur within an interval that limits the
					 total scan time to no more than 110 percent of its preset value through the use
					 of either a backup timer or devices which monitor equipment function.
ii. A visible signal shall indicate when the
					 x-ray exposure has been terminated through the means required by
					 1.6.9(2)(a)(i).
iii. The operator
					 shall be able to terminate the x-ray exposure at any time during a scan, or
					 series of scans under CT x-ray system control, of greater than one-half second
					 duration.
b. Tomographic
					 Plane Indication and Alignment.
i. For any
					 single tomogram system, means shall be provided to permit visual determination
					 of the tomographic plane or a reference plan offset from the tomographic
					 plane.
ii. For any multiple
					 tomogram system, means shall be provided to permit visual determination of the
					 location of a reference plane. This reference plane can be offset from the
					 location of the tomographic planes.
iii. If a device using a light source is used
					 to satisfy 1.6.9(2)(b)(i) or (ii), the light source shall provide illumination
					 levels sufficient to permit visual determination of the location of the
					 tomographic plane or reference plane under ambient light conditions of up to
					 500 lux.
c. Beam-On and
					 Shutter Status Indicators and Control Switches.
i. The CT x-ray control and gantry shall
					 provide visual indication whenever x-rays are produced and, if applicable,
					 whether the shutter is open or closed.
ii. Each emergency button or switch shall be
					 clearly labeled as to its function.
d
Indication of CT Conditions of Operation
The CT x-ray system shall be designed such that the CT conditions of operation
						to be used during a scan or a scan sequence shall be indicated prior to the
						initiation of a scan or a scan sequence. On equipment having all or some of
						these conditions of operation at fixed values, this requirement may be met by
						permanent markings. Indication of CT conditions of operation shall be visible
						from any position from which scan initiation is possible.
e. Extraneous Radiation. When data
					 are not being collected for image production, the radiation adjacent to the
					 tube port shall not exceed that permitted by 1.6.4(3).
f
Maximum Surface CTDI Identification
The
						angular position where the maximum surface CTDI occurs shall be identified to
						allow for reproducible positioning of a CT dosimetry phantom.
g
Additional Requirements Applicable to CT X-Ray
						Systems Containing a Gantry Manufactured After September 3, 1985.
i. The total error in the indicated location
					 of the tomographic plane or reference plane shall not exceed 5
					 millimeters.
ii. If the x-ray
					 production period is less than one-half second, the indication of x-ray
					 production shall be actuated for at least one-half second. Indicators at or
					 near the gantry shall be discernible from any point external to the patient
					 opening where insertion of any part of the human body into the primary beam is
					 possible.
iii. The deviation of
					 indicated scan increment versus actual increment shall not exceed plus or minus
					 1 millimeter with any mass from 0 to 100 kilograms resting on the support
					 device. The patient support device shall be incremented from a typical starting
					 position to the maximum incremented distance or 30 centimeters, whichever is
					 less, and then returned to the starting position. Measurement of actual versus
					 indicated scan increment may be taken anywhere along this travel.
iv. Premature termination of the x-ray
					 exposure by the operator shall necessitate resetting of the CT conditions of
					 operation prior to the initiation of another scan.
3
Facility Design Requirements.
a. Aural Communication. Provision shall be
					 made for two-way aural communication between the patient and the operator at
					 the control panel.
b
Viewing Systems.
i. Windows, mirrors, closed-circuit
					 television, or an equivalent shall be provided to permit continuous observation
					 of the patient during irradiation and shall be so located that the operator can
					 observe the patient from the control panel.
ii. When the primary viewing system is by
					 electronic means, an alternate viewing system (which may be electronic) shall
					 be available for use in the event of failure of the primary viewing system.
4
Surveys, Measurements, Spot Checks and Operating
						Procedures.
a
Surveys.
i. All CT x-ray systems installed after the
					 effective date of these regulations and those systems not previously surveyed
					 shall have a survey made by, or under the direction of, a qualified expert. In
					 addition, such surveys shall be done after any change in the facility or
					 equipment which might cause a significant increase in radiation
					 hazard.
ii. The registrant shall
					 obtain a written report of the survey from the qualified expert, and a copy of
					 the report shall be made available to the Agency upon request.
b
Radiation Measurements.
i. The measurements of the radiation output
					 of the CT x-ray system shall be performed by, or under the direction of, a
					 qualified expert.
ii. The
					 measurement of the radiation output of the CT x-ray system shall be performed
					 annually and after any change or replacement of components which could cause a
					 change in the radiation output.
iii. The measurement of the radiation output
					 of the CT x-ray system shall be performed with a calibrated dosimetry system.
					 The calibration of such system shall be traceable to a national standard. The
					 dosimetry system shall have been calibrated within the preceding 2
					 years.
iv. CT dosimetry phantom(s)
					 shall be used in determining the radiation output of a CT x-ray system. Such
					 phantom(s) shall meet the following specifications and conditions of use:
i. CT dosimetry phantom(s) shall be right
					 circular cylinders of polymethyl-methacrylate of density 1.19 plus or minus
					 0.01 grams per cubic centimeter. The phantom(s) shall be at least 14
					 centimeters in length and shall have diameters of 32.0 centimeters for testing
					 CT x-ray systems designed to image any section of the body and 16.0 centimeters
					 for systems designed to image the head or for whole body scanners operated in
					 the head scanning mode.
ii. CT
					 dosimetry phantom(s) shall provide means for the placement of a dosimeter(s)
					 along the 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 dosimeters or alignment devices at other locations may be
					 provided.
iii. Any effects on the
					 doses measured 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.
iv. All dose
					 measurements shall be performed with the CT dosimetry phantom placed on the
					 patient couch or support device without additional attenuation materials
					 present.
v. The measurement of the radiation
					 output shall be required for each type of head, body, or whole-body scan
					 performed at the facility.
vi.
					 Measurement of the radiation output shall meet the following requirements:
i. The dose profile along the center axis of
					 the CT dosimetry phantom for the minimum, maximum, and midrange values of the
					 nominal tomographic section thickness used by the registrant shall be
					 measurable. Where less than three nominal tomographic thicknesses can be
					 selected, the dose profile determination shall be performed for each available
					 nominal tomographic section thickness.
ii. The
CTDI
32 along the two axes specified in
					 1.6.9(4)(b)(iv)(ii) shall be measured. The CT dosimetry phantom shall be
					 oriented so that the measurement point 1.0 centimeter from the outer surface
					 and within the phantom is in the same angular position within the gantry as the
					 point of maximum surface
CTDI
identified. The CT conditions of
					 operation shall correspond to typical values used by the registrant.
iii. The spot checks specified in 1.6.9(4)(c)
					 shall be made.
vii.
					 Procedures for the measurement of radiation output shall be in writing. Records
					 of measurements performed shall be maintained for inspection by the
					 Agency.
c. Spot Checks.
i. The spot-check procedures shall be in
					 writing and shall have been developed by a qualified expert.
ii. The spot-check procedures shall
					 incorporate the use of a CT dosimetry phantom which has a capability of
					 providing an indication of contrast scale, noise, nominal tomographic section
					 thickness, the resolution capability of the system for low and high contrast
					 objects, and measuring the mean
CTN
for water or other
					 reference material.
iii. All spot
					 checks shall be included in the measurement required by 1.6.9(4)(b) and at time
					 intervals and under system conditions specified by a qualified
					 expert.
iv. Spot checks shall
					 include acquisition of images obtained with the CT dosimetry phantom(s) using
					 the same processing mode and CT conditions of operation as are used to perform
					 measurements required by 1.6.9(4)(b). The images shall be retained, until a new
					 measurement is performed, in two forms as follows:
i. photographic copies of the images obtained
					 from the image display device; and
ii. images stored in digital form on a
					 storage medium compatible with the CT x-ray system.
v. Written records of the spot checks
					 performed shall be maintained for inspection by the Agency.
d. Operating Procedures.
i. The CT x-ray system shall not be operated
					 except by an individual who has been specifically trained in its
					 operation.
ii. Information shall be
					 available at the control panel regarding the operation of the system and
					 measurements of radiation output. Such information shall include the following:
					 i. dates of the latest measurements and spot checks and the location within the
					 facility where the results of those tests may be obtained;
ii. instructions on the use of the CT
					 dosimetry phantom(s) including a schedule of spot checks appropriate for the
					 system, allowable variations for the indicated parameters, and the results of
					 at least the most recent spot checks conducted on the system;
iii. the distance in millimeters between the
					 tomographic plane and the reference plane if a reference plane is utilized;
					 and
iv. a current technique chart
					 available at the control panel which specifies for each routine examination the
					 CT conditions of operation and the number of scans per examination.