Pennsylvania Code › Title 25 - ENVIRONMENTAL PROTECTION › Part I - Department of Environmental Protection › Subpart D - Environmental Health and Safety › Article V - Radiological Health › Chapter 221 - X-RAYS IN THE HEALING ARTS › COMPUTED TOMOGRAPHY X-RAY SYSTEMS › Section 221.201 - Definitions

Current through Register Vol. 54, No. 28, July 13, 2024
In addition to the definitions in §§
												215.2 and
						  221.2 (relating to definitions),
						  the following words and terms, when used in this section and §§
												221.202-221.205, have the following
						  meanings, unless the context clearly indicates otherwise:
Alert value
-A dose index value (for
						  example, CTDIvol (mGy) or of DLP (mGy-cm)) that is set
						  by the registrant or licensee, or both, to trigger an alert to the operator
						  prior to scanning within an ongoing examination. The alert value represents a
						  value well above the registrant's or licensee's established range for the
						  examination that warrants more stringent review and consideration before
						  proceeding.
CS-Contrast scale
-The change in the
						  linear attenuation coefficient per CT number relative to water; that is:
CS = (Ux -
						  Uw)/((CT)x -
						  (CT)w)
Where:
Ux = Linear attenuation
						  coefficient of the material of interest
Uw = Linear attenuation
						  coefficient of water
(CT)x = CT number of the
						  material of interest
(CT)w = CT number of
						  water
CT-Computed tomography
-The production
						  of a tomogram by the acquisition and computer processing of X-ray transmission
						  data.
CT conditions of operation
-The
						  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 this chapter.
CT dosimetry phantom
-The phantom used
						  for determination of the dose delivered by a CT X-ray system.
CT number
-The number used to represent
						  the X-ray attenuation associated with each elemental area of the CT
						  image:
Click to view image
where:
k = A constant, a normal value of 1,000 when the
						  Hounsfield scale of CTN is used.
µx = Linear attenuation
						  coefficient of the material of interest.
µw = Linear attenuation
						  coefficient of water.
CTDI-Computed tomography dose
						  index
-
(i) 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.
Click to view image
where:
z = Position along a line perpendicular to the
						  tomographic plane.
D(z) = Dose at position z
T = Nominal tomographic section thickness (cm).
N = Number of tomograms produced in a single
						  scan.
(ii) 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.
CTDI100
-An
						  accumulated multiple scan dose at the center of a 100-mm scan that requires
						  integration of the radiation dose profile from a single axial scan over
						  specific integration limits. In the case of CTDI100, the
						  integration limits are +50 mm, which corresponds to the 100-mm length of the
						  commercially available "pencil" ionization chamber.
						  CTDI100 is acquired using a 100-mm long, 3-cc active
						  volume CT "pencil" ionization chamber, one of the two standard CTDI acrylic
						  phantoms (16 and 32 cm diameter) and a stationary patient table.
CTDIvol-Volume Computed
						  Tomography Dose Index
-A radiation dose parameter derived from the
						  CTDIw (weighted or average CTDI given across the field
						  of view), that is:
CTDIvol =
						  (N)(T)(CTDIw)/I,
where:
N = number of simultaneous axial scans per X-ray source
						  rotation,
T = thickness of one axial scan (mm), and
I = table increment per axial scan (mm).
Thus,
CTDIvol = (1 / pitch) x
						  CTDIw
CTDIw-Weighted Computed
						  Tomography Dose Index
-The estimated average
						  CTDI100 across the field of view. The equation
						  is:
CTDIw = 1/3
						  CTDI100.center + 2/3
						  CTDI100.edge
Where 1/3 and 2/3 approximate the relative areas
						  represented by the center and edge values derived using the 16 cm or 32 cm
						  acrylic phantom. CTDIw uses
						  CTDI100 and an f-factor for air (0.87 rad/R for exposure
						  or 1.0 mGy for air kerma measurements).
Detector
-A device that provides a
						  signal or other indication suitable for measuring one or more quantities of
						  incident radiation.
Dose profile
-The dose as a function of
						  position along a line.
Elemental area
-The smallest area
						  within a tomogram for which the X-ray attenuation properties of a body are
						  depicted.
Gantry
-The tube housing assemblies,
						  beam-limiting devices, detectors, transformers, if applicable, and the
						  supporting structures and frames which hold these components.
Lux
-A unit illumination equivalent to
						  1 lumen per square centimeter or 0.0929 foot-candles.
Modulation transfer function
-The
						  modulus of the Fourier transform of the impulse response of the system.
Multiple tomogram system
-A CT X-ray
						  system which obtains X-ray transmission data simultaneously during a single
						  scan to produce more than one tomogram.
Noise
-The standard deviation of the
						  fluctuations in the CT number expressed as a percentage of the attenuation
						  coefficient of water. Its estimate (Sn) is calculated
						  using the following expression:
Sn = 100 x CS x
						  S/Uw
Where:
CS = Contrast scale
Uw = Linear attenuation
						  coefficient of water.
S = Estimated standard deviation of the CT number of
						  picture elements in a specified area of the CT image.
Nominal tomographic section
						  thickness
-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.
Notification value
-A dose index value
						  (for example, CTDIvol (mGy) or DLP (mGy-cm)) that is set
						  by the registrant to trigger a notification to the operator prior to scanning
						  when the dose index exceeds the established range for the examination.
Performance phantom
-A phantom which
						  has a capability of providing an indication of CS, noise, nominal tomographic
						  section thickness, the resolution capability of the CT system for low and high
						  contrast objects, and measuring the mean CT number for water or other reference
						  materials.
Picture element
-See elemental
						  area.
Pixel
-See elemental area.
Reference plane
-A plane which is at a
						  known fixed distance-which could be zero-to the tomographic plane and parallel
						  to it.
Scan
-The complete process of
						  collecting X-ray transmission data for the production of a tomogram. Data may
						  be collected simultaneously during a single scan for the production of one or
						  more tomograms.
Scan increment
-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.
Scan sequence
-A preselected set of two
						  or more scans performed consecutively under preselected CT conditions of
						  operation.
Scan time
-The period of time between
						  the beginning and end of X-ray transmission data accumulation for a single
						  scan.
Sensitivity profile
-The relative
						  response of the CT X-ray system as a function of position along a line
						  perpendicular to the tomographic plane.
Single tomogram system
-A CT X-ray
						  system which obtains X-ray transmission data during a scan to produce a single
						  tomogram.
Technique factors
-The conditions of
						  operation, specified as follows:
(i)
						For CT equipment designed for pulsed operations, peak tube potential, scan time
						in seconds, X-ray pulse width in seconds and the number of X-ray pulses per
						second or per mAs.
(ii) For CT
						equipment not designed for pulsed operation, peak tube potential, and either
						tube current and scan time in seconds or the product of tube current and
						exposure time in mAs.
Tomogram
-The depiction of the X-ray
						  attenuation properties of a section through a body.
Tomographic plane
-The geometric plane
						  which is identified as corresponding to the output tomogram.
Tomographic section
-The volume of an
						  object whose X-ray attenuation properties are imaged in a
						  tomogram.
The provisions of this §
														221.201 issued and amended under
							 sections 301 and 302 of the Radiation Protection Act (35 P.S.
							 §§
															7110.301 and
							 7110.302); and section 1920-A
							 of The Administrative Code of 1929 (71 P.S. §
															510-20); and amended under the Radon
							 Certification Act (63 P.S. §§
															2001-2014).