[Code of Federal Regulations]
[Title 21, Volume 8]
[Revised as of April 1, 2002]
From the U.S. Government Printing Office via GPO Access
[CITE: 21CFR1020.33]
[Page 612-617]
TITLE 21--FOOD AND DRUGS
CHAPTER I--FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN
SERVICES (CONTINUED)
PART 1020--PERFORMANCE STANDARDS FOR IONIZING RADIATION EMITTING PRODUCTS--Table of Contents
Sec. 1020.33 Computed tomography (CT) equipment.
(a) Applicability. (1) The provisions of this section, except for
paragraphs (b), (c)(1), and (c)(2) are applicable as specified herein to
CT x-ray systems manufactured or remanufactured on or after September 3,
1985.
(2) The provisions of paragraphs (b), (c)(1), and (c)(2) are
applicable to CT x-ray systems manufactured or remanufactured on or
after November 29, 1984.
(b) Definitions. As used in this section, the following definitions
apply:
(1) Computed tomography dose index (CTDI) means the integral 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:
[GRAPHIC] [TIFF OMITTED] TC01AP93.003
where:
[[Page 613]]
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.
(2) Contrast scale means the change in linear attenuation
coefficient per CT number relative to water; that is:
[GRAPHIC] [TIFF OMITTED] TC01AP93.000
where:
[mu]w=Linear attenuation coefficient of water.
[mu]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 Sec. 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[plusmn]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 (Sn) is calculated using the following
expression:
[GRAPHIC] [TIFF OMITTED] TC01AP93.001
where:
CS=Contrast scale.
[mu]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.
(11) 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.
(12) Picture element means an elemental area of a tomogram.
(13) Remanufacturing means modifying a CT system in such a way that
the resulting dose and imaging performance become substantially
equivalent to any CT x-ray system manufactured by the original
manufacturer on or after November 29, 1984. Any reference in this
section to ``manufacture'', ``manufacturer'', or ``manufacturing''
includes remanufacture, remanufacturer, or remanufacturing,
respectively.
(14) Scan increment means the amount of relative displacement of the
patient
[[Page 614]]
with respect to the CT x-ray system between successive scans measured
along the direction of such displacement.
(15) Scan sequence means a preselected set of two or more scans
performed consecutively under preselected CT conditions of operations.
(16) Sensitivity profile means the relative response of the CT x-ray
system as a function of position along a line perpendicular to the
tomographic plane.
(17) Single tomogram system means a CT x-ray system which obtains x-
ray transmission data during a scan to produce a single tomogram.
(18) Tomographic plane means that geometric plane which the
manufacturer identifies 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.
(c) Information to be provided for users. Each manufacturer of a CT
x-ray system shall provide the following technical and safety
information, in addition to that required under Sec. 1020.30(h), to
purchasers and, upon request, to others at a cost not to exceed the cost
of publication and distribution of such information. This information
shall be identified and provided in a separate section of the user's
instruction manual or in a separate manual devoted only to this
information.
(1) Conditions of operation. A statement of the CT conditions of
operation used to provide the information required by paragraph (c) (2)
and (3) of this section.
(2) Dose information. The following dose information obtained by
using the CT dosimetry phantom. For any CT x-ray system designed to
image both the head and body, separate dose information shall be
provided for each application. All dose measurements shall be performed
with the CT dosimetry phantom placed on the patient couch or support
device without additional attenuating materials present.
(i) The CTDI at the following locations in the dosimetry phantom:
(a) Along the axis of rotation of the phantom.
(b) Along a line parallel to the axis of rotation and 1.0 centimeter
interior to the surface of the phantom with the phantom positioned so
that CTDI is the maximum obtainable at this depth.
(c) Along lines parallel to the axis of rotation and 1.0 centimeter
interior to the surface of the phantom at positions 90, 180, and 270
degrees from the position in paragraph (c)(2)(i)(b) of this section. The
CT conditions of operation shall be the typical values suggested by the
manufacturer for CT of the head or body. The location of the position
where the CTDI is maximum as specified in paragraph (c)(2)(i)(b) of this
section shall be given by the manufacturer with respect to the housing
of the scanning mechanism or other readily identifiable feature of the
CT x-ray system in such a manner as to permit placement of the dosimetry
phantom in this orientation.
(ii) The CTDI in the center location of the dosimetry phantom for
each selectable CT condition of operation that varies either the rate or
duration of x-ray exposure. This CTDI shall be presented as a value that
is normalized to the CTDI in the center location of the dosimetry
phantom from paragraph (c)(2)(i) of this section, with the CTDI of
paragraph (c)(2)(i) of this section having a value of one. As each
individual CT condition of operation is changed, all other independent
CT conditions of operation shall be maintained at the typical values
described in paragraph (c)(2)(i) of this section. These data shall
encompass the range of each CT condition of operation stated by the
manufacturer as appropriate for CT of the head or body. When more than
three selections of a CT condition of operation are available, the
normalized CTDI shall be provided, at least, for the minimum, maximum,
and mid-range value of the CT condition of operation.
(iii) The CTDI at the location coincident with the maximum CTDI at 1
centimeter interior to the surface of the dosimetry phantom for each
selectable peak tube potential. When more than three selections of peak
tube potential are available, the normalized CTDI shall be provided, at
least, for the minimum, maximum, and a typical value of peak tube
potential. The CTDI shall
[[Page 615]]
be presented as a value that is normalized to the maximum CTDI located
at 1 centimeter interior to the surface of the dosimetry phantom from
paragraph (c)(2)(i) of this section, with the CTDI of paragraph
(c)(2)(i) of this section having a value of one.
(iv) The dose profile in the center location of the dosimetry
phantom for each selectable nominal tomographic section thickness. When
more than three selections of nominal tomographic section thicknesses
are available, the information shall be provided, at least, for the
minimum, maximum, and midrange value of nominal tomographic section
thickness. The dose profile shall be presented on the same graph and to
the same scale as the corresponding sensitivity profile required by
paragraph (c)(3)(iv) of this section.
(v) A statement of the maximum deviation from the values given in
the information provided according to paragraph (c)[hairsp](2) (i),
(ii), (iii), and (iv) of this section. Deviation of actual values may
not exceed these limits.
(3) Imaging performance information. The following performance data
shall be provided for the CT conditions of operation used to provide the
information required by paragraph (c)(2)(i) of this section. All other
aspects of data collection, including the x-ray attenuation properties
of the material in the tomographic section, shall be similar to those
used to provide the dose information required by paragraph (c)(2)(i) of
this section. For any CT x-ray system designed to image both the head
and body, separate imaging performance information shall be provided for
each application.
(i) A statement of the noise.
(ii) A graphical presentation of the modulation transfer function
for the same image processing and display mode as that used in the
statement of the noise.
(iii) A statement of the nominal tomographic section thickness(es).
(iv) A graphical presentation of the sensitivity profile, at the
location corresponding to the center location of the dosimetry phantom,
for each selectable nominal tomographic section thickness for which the
dose profile is given according to paragraph (c)(2)(iv) of this section.
(v) A description of the phantom or device and test protocol or
procedure used to determine the specifications and a statement of the
maximum deviation from the specifications provided in accordance with
paragraphs (c)(3) (i), (ii), (iii), and (iv) of this section. Deviation
of actual values may not exceed these limits.
(d) Quality assurance. The manufacturer of any CT x-ray system shall
provide the following with each system. All information required by this
subsection shall be provided in a separate section of the user's
instructional manual.
(1) A phantom(s) capable of providing an indication of contrast
scale, noise, nominal tomographic section thickness, the spatial
resolution capability of the system for low and high contrast objects,
and measuring the mean CT number of water or a reference material.
(2) Instructions on the use of the phantom(s) including a schedule
of testing appropriate for the system, allowable variations for the
indicated parameters, and a method to store as records, quality
assurance data.
(3) Representative images obtained with the phantom(s) using the
same processing mode and CT conditions of operation as in paragraph
(c)(3) of this section for a properly functioning system of the same
model. The representative images shall be of two forms as follows:
(i) Photographic copies of the images obtained from the image
display device.
(ii) Images stored in digital form on a storage medium compatible
with the CT x-ray system. The CT x-ray system shall be provided with the
means to display these images on the image display device.
(e) [Reserved]
(f) Control and indication of conditions of operation--(1) Visual
indication. The CT conditions of operation to be used during a scan or a
scan sequence shall be indicated prior to 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 the CT conditions of operation shall be visible
from
[[Page 616]]
any position from which scan initiation is possible.
(2) Timers. (i) Means shall be provided to terminate the x-ray
exposure automatically by either deenergizing 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. A visible signal shall indicate when the x-ray
exposure has been terminated through these means and manual resetting of
the CT conditions of operation shall be required prior to the initiation
of another scan.
(ii) Means shall be provided so that the operator can terminate the
x-ray exposure at any time during a scan, or series of scans under x-ray
system control, of greater than one-half second duration. Termination of
the x-ray exposure shall necessitate resetting of the CT conditions of
operation prior to the initiation of another scan.
(g) Tomographic plane indication and alignment. (1) For any single
tomogram system, means shall be provided to permit visual determination
of the tomographic plane or a reference plane offset from the
tomographic plane.
(2) For any multiple tomogram system, means shall be provided to
permit visual determination of the location of a reference plane. The
relationship of the reference plane to the planes of the tomograms shall
be provided to the user in addition to other information provided
according to Sec. 1020.30(h). This reference plane can be offset from
the location of the tomographic planes.
(3) The distance between the indicated location of the tomographic
plane or reference plane and its actual location may not exceed 5
millimeters.
(4) For any offset alignment system, the manufacturer shall provide
specific instructions with respect to the use of this system for patient
positioning, in addition to other information provided according to
Sec. 1020.30(h).
(5) If a mechanism using a light source is used to satisfy the
requirements of paragraphs (g) (1) and (2) of this section, the light
source shall allow visual determination of the location of the
tomographic plane or reference plane under ambient light conditions of
up to 500 lux.
(h) Beam-on and shutter status indicators. (1) Means shall be
provided on the control and on or near the housing of the scanning
mechanism to provide visual indication when and only when x rays are
produced and, if applicable, whether the shutter is open or closed. If
the x-ray production period is less than one-half second, the indication
of x-ray production shall be actuated for one-half second. Indicators at
or near the housing of the scanning mechanism 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.
(2) For systems that allow high voltage to be applied to the x-ray
tube continuously and that control the emission of x rays with a
shutter, the radiation emitted may not exceed 100 milliroentgens
(2.58x10-5 coulomb/kilogram) in 1 hour at any point 5
centimeters outside the external surface of the housing of the scanning
mechanism when the shutter is closed. Compliance shall be determined by
measurements averaged over an area of 100 square centimeters with no
linear dimensions greater than 20 centimeters.
(i) Scan increment accuracy. The deviation of indicated scan
increment from actual scan increment may not exceed 1 millimeter.
Compliance shall be measured as follows: The determination of the
deviation of indicated versus actual scan increment shall be based on
measurements taken with a mass 100 kilograms or less, on the patient
support device. The patient support device shall be incremented from a
typical starting position to the maximum incrementation 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.
(j) CT number mean and standard deviation. (1) A method shall be
provided to calculate the mean and standard deviation of CT numbers for
an array of picture elements about any location in the image. The number
of elements in this array shall be under user control.
[[Page 617]]
(2) The manufacturer shall provide specific instructions concerning
the use of the method provided for calculation of CT number mean and
standard deviation in addition to other information provided according
to Sec. 1020.30(h).
[49 FR 34712, Aug. 31, 1984; 49 37381, Sept. 24, 1984, as amended at 49
FR 47388, Dec. 4, 1984; 56 FR 36098, Aug. 1, 1991; 67 FR 9587, Mar. 4,
2002]