Kansas Administrative Regulations
Agency 28 - DEPARTMENT OF HEALTH AND ENVIRONMENT
Article 35 - RADIATION
Section 28-35-248a - Computed tomography (CT) X-ray systems
Universal Citation: KS Admin Regs 28-35-248a
Current through Register Vol. 43, No. 52, December 26, 2024
(a) Definitions. In addition to the definitions in part 1 of these regulations, the following definitions shall be applicable to this regulation:
(1) "Computed tomography dose index" and
"CTDI" mean the integral from -7T to +7T of the dose profile along a line
perpendicular to the tomographic plane divided by the product of the normal
tomographic section thickness and the number of tomograms produced in a single
scan, as follows:
For Equation see Agnecy.
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.
(2)
"Contrast scale" and "CS" mean the change in the linear attenuation coefficient
per CTN relative to water, as follows:
For Equation see Agnecy.
(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 technique factors.
(4) "CT gantry" means the tube
housing assemblies, beam-limiting devices, and detectors and the supporting
structures and frames that hold these components.
(5) "CT number" and "CTN" mean the number
used to represent the X-ray attenuation associated with each elemental area of
the CT image, as follows:
For Equation see Agnecy.
(6) "Dose profile" means the dose as a
function of position along a line.
(7) "Elemental area" means the smallest area
within a tomogram for which the X-ray attenuation properties of a body are
depicted.
(8) "Multiple tomogram
system" means a computed tomography X-ray system that obtains X-ray
transmission data simultaneously during a single scan to produce more than one
tomogram.
(9) "Noise" means the
standard deviation of the fluctuations in CTN expressed as a percentage of the
attenuation coefficient of water. Noise is estimated using the following
equation:
For Equation see Agnecy.
(10) "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 the X-ray transmission data are
collected.
(11) "Picture element"
means an elemental area of a tomogram.
(12) "Reference plane" means a plane that is
displaced from and parallel to the tomographic plane.
(13) "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.
(14) "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 the displacement.
(15) "Scan sequence" means a preselected set
of two or more scans performed consecutively under preselected CT conditions of
operation.
(16) "Scan time" means
the period of time between the beginning and the end of X-ray transmission data
accumulation for a single scan.
(17) "Single tomogram system" means a CT
X-ray system that obtains X-ray transmission data during a scan to produce a
single tomogram.
(18) "Tomographic
plane" means the geometric plane that is identified as corresponding to the
output tomogram.
(19) "Tomographic
section" means the volume of an object whose X-ray attenuation properties are
imaged in a tomogram.
(b) Requirements for equipment.
(1) Termination of exposure.
(A) A 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 if equipment failure affecting data collection
occurs. This 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 that monitor equipment function.
(B) A visible signal shall indicate when the
X-ray exposure has been terminated as specified in paragraph (b)(1)(A).
(C) Each operator shall be able to
terminate the X-ray exposure at any time during a scan, or series of scans
under CT X-ray systems control, of greater duration than one-half second.
(2) Tomographic plane
indication and alignment.
(A) For any single
tomogram system, a means shall be provided to permit the visual determination
of the tomgraphic plane or a reference plane offset from the tomographic plane.
(B) For any multiple tomogram
system, a means shall be provided to permit the visual determination of the
location of a reference plane. This reference plane can be offset from the
location of the tomographic planes.
(C) If a device using a light source is used,
the light source shall provide illumination levels sufficient to permit the
visual determination of the location of the tomographic plane or reference
plane under ambient light conditions of up to 500 lux.
(3) Beam-on and shutter-status indicators and
control switches.
(A) The CT X-ray control
and gantry shall provide a visual indication whenever X-rays are produced and,
if applicable, whether the shutter is open or closed.
(B) Each emergency button or switch shall be
clearly labeled as to its function.
(4) Indication of CT conditions of operation.
The CT X-ray system shall be designed so that the CT conditions of operation to
be used during a scan or a scan sequence shall be indicated before the
initiation of a scan or a scan sequence. This requirement may be met by
permanent markings on equipment that has all or some of these conditions of
operation at fixed values. An indication of the CT conditions of operation
shall be visible from any position from which scan initiation is possible.
(5) Extraneous radiation. When
data are not being collected for image production, the radiation adjacent to
the tube port shall not exceed the levels permitted in these regulations.
(6) Maximum surface CTDI
identification. The angular position where the maximum surface CTDI occurs
shall be identified to allow for the reproducible positioning of a CT dosimetry
phantom.
(7) Additional
requirements applicable to CT X-ray systems containing a gantry manufactured
after September 3, 1985.
(A) The total error
in the indicated location of the tomographic plane or reference plane shall not
exceed five millimeters.
(B) 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.
(C) The deviation of the
indicated scan increment versus the actual increment shall not exceed plus or
minus one millimeter for any mass weighing from 0 to 100 kilograms and resting
on the support device. The patient-support device shall be adjusted in
increments from a typical starting position to the maximum 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 range of positions.
(D)
Premature termination of the X-ray exposure by the operator shall necessitate
the resetting of the CT conditions of operation before the initiation of
another scan.
(c) Facility design requirements.
(1) Aural communication. Provision shall be
made for two-way aural communication between the patient and the operator at
the control panel.
(2) Viewing
systems.
(A) Windows, mirrors, closed-circuit
television, or an equivalent shall be provided to permit continuous observation
of the patient during irradiation and shall be located so that the operator can
observe the patient from the control panel.
(B) If the primary viewing system is an
electronic means, an alternate viewing system, which may be electronic, shall
be available for use if the primary viewing system fails.
(d) Surveys, calibrations, spot checks, and operating procedures.
(1)
Surveys.
(A) All CT X-ray systems installed
after the effective date of this regulation and those systems not previously
surveyed shall have a survey performed by, or under the direction of, a
qualified expert. In addition, the surveys shall be performed after each change
in the facility or equipment that might cause a significant increase in
radiation hazard.
(B) Each
registrant shall obtain a written report of the survey from the qualified
expert. The registrant shall make a copy of the report available to the
department upon request.
(2) Radiation calibrations.
(A) The calibration of the radiation output
of the CT X-ray system shall be performed by, or under the direction of, a
qualified expert who is physically present at the facility during the
calibration.
(B) The calibration
of each CT X-ray system shall be performed at the intervals specified by a
qualified expert and after any change or replacement of components that, in the
opinion of the qualified expert, could cause any change in the radiation
output.
(C) The calibration of the
radiation output of each CT X-ray system shall be performed with a calibrated
dosimetry system. The calibration of the system shall be traceable to a
national standard. The dosimetry system shall have been calibrated within the
preceding two years.
(D) One or
more CT dosimetry phantoms shall be used in determining the radiation output of
a CT X-ray system. Each phantom shall meet all of the following requirements
and conditions of use:
(i) Each CT dosimetry
phantom shall consist of right-circular cylinders of polymethyl methacrylate
with a density of 1.19 plus or minus 0.01 grams per cubic centimeter. Each
phantom shall be at least 14 centimeters in length and shall have a diameter 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) Each CT dosimetry phantom shall provide
a means for the placement of one or more dosimeters along the axis of rotation
and along a line parallel to the axis of rotation at 1.0 centimeter from the
outer surface and within the phantom. A means for the placement of dosimeters
or alignment devices at other locations may be provided.
(iii) The 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 by inclusion in the
statement of maximum deviation for the value 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.
(E) Calibration shall be required
for each type of head, body, or whole-body scan performed at the facility.
(F) Calibration shall meet all of
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. If fewer 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 along the two axes shall be
measured. The CT dosimetry phantom shall be oriented so that the measurement
point at 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
required spot checks shall be made.
(G) The calibration procedures shall be in
writing. Records of all calibrations performed shall be maintained for
inspection by the department.
(3) Spot checks.
(A) The spot check procedures shall be in
writing and shall have been developed by a qualified expert.
(B) The spot check procedures shall
incorporate the use of a CT dosimetry phantom that has a capability of
providing an indication of contrast scale, noise, nominal tomographic section
thickness, and the resolution capability of the system for low-contrast and
high-contrast objects, and of measuring the mean CTN for water or other
reference material.
(C) All spot
checks shall be included in the calibration and shall be made at time intervals
and under system conditions specified by a qualified expert.
(D) The spot checks shall include acquisition
of images obtained with the CT dosimetry phantom or phantoms using the same
processing mode and CT conditions of operation that are used to perform
calibrations. The images shall be retained in two forms as follows, until a new
calibration is performed:
(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.
(E) Written records of the spot checks
performed shall be maintained for inspection by the department.
(4) Operating procedures.
(A) The CT X-ray system shall not be operated
except by an individual who has been specifically trained in its operation.
(B) Information shall be available
at the control panel regarding the operation and calibration of the system.
This information shall include the following:
(i) The dates of the latest calibration and
spot checks and the location within the facility where the results of those
tests can be obtained;
(ii)
instructions on the use of the CT dosimetry phantom or phantoms, including the
schedule of spot checks appropriate for the system, the 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 that specifies, for each routine examination,
the CT conditions of operation and the number of scans per examination.
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