SIST EN 61675-2:1998
(Main)Radionuclide imaging devices - Characteristics and test conditions -- Part 2: Single photon emission computer tomographs
Radionuclide imaging devices - Characteristics and test conditions -- Part 2: Single photon emission computer tomographs
Specifies terminology and test methods for describing the characteristics of Anger type rotational gamma single photon emission computed tomographs (SPECT), equipped with parallel hole collimators. It is intended that the test methods be carried out by manufacturers thereby enabling them to describe the characteristics of SPECT systems on a common basis.
Bildgebende Systeme in der Nuklearmedizin - Merkmale und Prüfbedingungen -- Teil 2: Einzelphotonen-Emissions-Tomographie
Dispositifs d'imagerie par radionucléides - Caractéristiques et conditions d'essais -- Partie 2: Systèmes de tomographie d'émission à photon unique
L'IEC 61675-2:1998 spécifie la terminologie et les méthodes d'essai relatives à la description des caractéristiques des tomodensitomètres par émission de photons simples des gamma cameras rotatives de type Anger, équipés de collimateurs à trous parallèles. Dans la mesure où ces systèmes sont basés sur les caméras gamma de type Anger, la présente partie de la CEI 61675 doit être utilisée conjointement avec la CEI 60789. Ces systèmes se composent d'un système de portique, de têtes de détecteurs simples ou multiples et d'un système informatique, associés à des dispositifs d'acquisition, d'enregistrement et de visualisation. Les méthodes d'essai spécifiées dans la présente partie de la CEI 61675 ont été sélectionnées afin de refléter autant que possible l'utilisation clinique des tomodensitomètres par émission de photons simples des caméras gamma rotatives de type Anger. L'intention est de faire appliquer ces méthodes d'essai par les constructeurs, leur donnant ainsi les moyens de décrire les caractéristiques des systèmes tomodensitomètres par émission de photons simples des caméras gamma sur la base de critères communs. Aucun essai n'a été spécifié afin de caractériser l'uniformité des images reconstituées, puisque toutes les méthodes connues jusqu'à présent reflèteront principalement le bruit de l'image.
Radionuclide imaging devices - Characteristics and test conditions - Part 2: Single photon emission computer tomographs (IEC 61675-2:1998)
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Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN 61675-2:1998
01-september-1998
Radionuclide imaging devices - Characteristics and test conditions - Part 2: Single
photon emission computer tomographs (IEC 61675-2:1998)
Radionuclide imaging devices - Characteristics and test conditions -- Part 2: Single
photon emission computer tomographs
Bildgebende Systeme in der Nuklearmedizin - Merkmale und Prüfbedingungen -- Teil 2:
Einzelphotonen-Emissions-Tomographie
Dispositifs d'imagerie par radionucléides - Caractéristiques et conditions d'essais --
Partie 2: Systèmes de tomographie d'émission à photon unique
Ta slovenski standard je istoveten z: EN 61675-2:1998
ICS:
11.040.50 Radiografska oprema Radiographic equipment
SIST EN 61675-2:1998 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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INTERNATIONAL
IEC
STANDARD
61675-2
First edition
1998-01
Radionuclide imaging devices –
Characteristics and test conditions –
Part 2:
Single photon emission computed tomographs
Dispositifs d’imagerie par radionucléides –
Caractéristiques et conditions d’essais –
Partie 2:
Systèmes de tomographie d’émission à photon unique
IEC 1998 Droits de reproduction réservés Copyright - all rights reserved
Aucune partie de cette publication ne peut être reproduite ni No part of this publication may be reproduced or utilized in
utilisée sous quelque forme que ce soit et par aucun any form or by any means, electronic or mechanical,
procédé, électronique ou mécanique, y compris la photo- including photocopying and microfilm, without permission in
copie et les microfilms, sans l'accord écrit de l'éditeur. writing from the publisher.
International Electrotechnical Commission 3, rue de Varembé Geneva, Switzerland
Telefax: +41 22 919 0300 e-mail: inmail@iec.ch IEC web site http: //www.iec.ch
CODE PRIX
Commission Electrotechnique Internationale
PRICE CODE T
International Electrotechnical Commission
Pour prix, voir catalogue en vigueur
For price, see current catalogue
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CONTENTS
Page
FOREWORD . . 3
Clause
1 General . 4
1.1 Scope and object . . 4
1.2 Normative references . 4
2 Terminology and definitions . 4
3 Test methods. 9
3.1 Calibration measurements . 9
3.2 Measurement of COLLIMATOR hole misalignment . 10
3.3 Measurement of SPECT system SENSITIVITY . 11
3.4 Scatter. 12
3.5 Measurement of SPECT non-uniformity of response . 14
3.6 SPECT system SPATIAL RESOLUTION . 14
4 ACCOMPANYING DOCUMENTS . 15
Figures
1 Geometry of PROJECTIONS . 16
2 Cylindrical head phantom. 17
3 Phantom insert with holders for the scatter source . 18
4 Evaluation of SCATTER FRACTION. 19
5 Reporting TRANSVERSE RESOLUTION . 20
6 Evaluation of FWHM . 21
7 Evaluation of EQUIVALENT WIDTH (EW) . 22
Annex A – Index of defined terms . 23
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61675-2 © IEC:1998(E) – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
___________
RADIONUCLIDE IMAGING DEVICES –
CHARACTERISTICS AND TEST CONDITIONS –
Part 2: Single photon emission computed tomographs
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of the IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, the IEC publishes International Standards. Their preparation is
entrusted to technical committees; any IEC National Committee interested in the subject dealt with may
participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. The IEC collaborates closely with the International Organization
for Standardization (ISO) in accordance with conditions determined by agreement between the two
organizations.
2) The formal decisions or agreements of the IEC on technical matters express, as nearly as possible, an
international consensus of opinion on the relevant subjects since each technical committee has representation
from all interested National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form
of standards, technical reports or guides and they are accepted by the National Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject
of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61675-2 has been prepared by subcommittee 62C: Equipment for
radiotherapy, nuclear medicine and radiation dosimetry, of IEC technical committee 62:
Electrical equipment in medical practice.
The text of this standard is based on the following documents:
FDIS Report on voting
62C/206/FDIS 62C/215/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
In this standard, the following print types are used:
– TERMS DEFINED IN CLAUSE 2 OF THIS STANDARD OR LISTED IN ANNEX A: SMALL CAPITALS.
The requirements are followed by specifications for the relevant tests.
Annex A is for information only.
A bilingual version of this standard may be issued at a later date.
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RADIONUCLIDE IMAGING DEVICES –
CHARACTERISTICS AND TEST CONDITIONS –
Part 2: Single photon emission computed tomographs
1 General
1.1 Scope and object
This part of IEC 61675 specifies terminology and test methods for describing the character-
istics of Anger type rotational GAMMA CAMERA SINGLE PHOTON EMISSION COMPUTED TOMOGRAPHS
(SPECT), equipped with parallel hole collimators. As these systems are based on Anger type
GAMMA CAMERAS this part of IEC 61675 shall be used in conjunction with IEC 60789. These
systems consist of a gantry system, single or multiple DETECTOR HEADS and a computer system
together with acquisition, recording, and display devices.
The test methods specified in this part of IEC 61675 have been selected to reflect as much as
possible the clinical use of Anger type rotational GAMMA CAMERA SINGLE PHOTON EMISSION
COMPUTED TOMOGRAPHS (SPECT). It is intended that the test methods be carried out by
manufacturers thereby enabling them to describe the characteristics of SPECT systems on a
common basis.
No test has been specified to characterize the uniformity of reconstructed images because all
methods known so far will mostly reflect the noise of the image.
1.2 Normative references
The following normative documents contain provisions which, through reference in this text,
constitute provisions of this part of IEC 61675. At the time of publication, the editions indicated
were valid. All normative documents are subject to revision, and parties to agreements based
on this part of IEC 61675 are encouraged to investigate the possibility of applying the most
recent editions of the normative documents indicated below. Members of IEC and ISO maintain
registers of currently valid International Standards.
IEC 60788:1984, Medical radiology – Terminology
IEC 60789:1992, Characteristics and test conditions of radionuclide imaging devices – Anger
type gamma cameras
IEC 61675-1, Radionuclide imaging devices – Characteristics and test conditions – Part 1:
Positron emission tomographs
2 Terminology and definitions
For the purpose of this part of IEC 61675 the definitions given in IEC 60788, IEC 60789 and
IEC 61675-1 (see annex A), and the following definitions apply.
Defined terms are printed in small capital letters.
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61675-2 © IEC:1998(E) – 5 –
2.1
SYSTEM AXIS
Axis of symmetry characterized by geometrical and physical properties of the arrangement of
the system
NOTE – The SYSTEM AXIS of a GAMMA CAMERA with rotating detectors is the axis of rotation.
2.1.1
COORDINATE SYSTEMS
2.1.2
FIXED COORDINATE SYSTEM
Cartesian system with axes X, Y, and Z, Z being the SYSTEM AXIS. The origin of the FIXED
COORDINATE SYSTEM is defined by the centre of the TOMOGRAPHIC VOLUME (see figure 1). The
SYSTEM AXIS is orthogonal to all TRANSVERSE SLICES.
2.1.3
COORDINATE SYSTEM OF PROJECTION
Cartesian system of the IMAGE MATRIX of each two-dimensional projection with axes X and Y
p p
(defined by the axes of the IMAGE MATRIX). The Y axis and the projection of the system axis
p
onto the detector front face have to be in parallel. The origin of the COORDINATE SYSTEM OF
PROJECTION is the centre of the IMAGE MATRIX (see figure 1).
2.1.4
CENTRE OF ROTATION (COR)
Origin of that COORDINATE SYSTEM, which describes the PROJECTIONS of a TRANSVERSE SLICE with
respect to their orientation in space
NOTE – The CENTRE OF ROTATION of a TRANSVERSE SLICE is given by the intersection of the SYSTEM AXIS with the
mid-plane of the corresponding OBJECT SLICE.
2.1.5
OFFSET
Deviation of the position of the PROJECTION of the COR (X' ) from X = 0. (See figure 1)
p p
2.2
TOMOGRAPHY (see annex A)
2.2.1
TRANSVERSE TOMOGRAPHY
In TRANSVERSE TOMOGRAPHY the three-dimensional object is sliced by physical methods, e.g.
collimation, into a stack of OBJECT SLICES, which are considered as being two-dimensional and
independent from each other. The transverse image planes are perpendicular to the SYSTEM
AXIS.
2.2.2
EMISSION COMPUTED TOMOGRAPHY (ECT)
Imaging method for the representation of the spatial distribution of incorporated RADIONUCLIDES
in selected two-dimensional SLICES through the object
2.2.2.1
PROJECTION
Transformation of a three-dimensional object into its two-dimensional image or of a two-
dimensional object into its one-dimensional image, by integrating the physical property which
determines the image along the direction of the PROJECTION BEAM
NOTE – This process is mathematically described by line integrals in the direction of projection and called the
Radon-transform.
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2.2.2.2
PROJECTION BEAM
Determines the smallest possible volume in which the physical property which determines the
image is integrated during the measurement process. Its shape is limited by the SPATIAL
RESOLUTION in all three dimensions.
NOTE – In SPECT the PROJECTION BEAM usually has the shape of a long thin diverging cone.
2.2.2.3
PROJECTION ANGLE
Angle at which the PROJECTION is measured or acquired
NOTE – For illustration see figure 1.
2.2.2.4
SINOGRAM
Two-dimensional display of all one-dimensional PROJECTIONS of an object slice, as a function of
the PROJECTION ANGLE
The PROJECTION ANGLE is displayed on the ordinate. The linear PROJECTION coordinate is
displayed on the abscissa.
2.2.2.5
OBJECT SLICE
A slice in the object. The physical property of this slice that determines the measured
information is displayed in the tomographic image.
2.2.2.6
IMAGE PLANE
A plane assigned to a plane in the OBJECT SLICE
NOTE – Usually the IMAGE PLANE is the mid-plane of the corresponding OBJECT SLICE.
2.2.2.7
TOMOGRAPHIC VOLUME
Ensemble of all volume elements which contribute to the measured PROJECTIONS for all
PROJECTION ANGLES
NOTE – For a rotating GAMMA CAMERA with a circular field of view the TOMOGRAPHIC VOLUME is a sphere provided
that the radius of rotation is larger than the radius of the field of view. For a rectangular field of view, the
TOMOGRAPHIC VOLUME is a cylinder.
2.2.2.7.1
TRANSVERSE FIELD OF VIEW
Dimensions of a slice through the TOMOGRAPHIC VOLUME, perpendicular to the SYSTEM AXIS. For
a circular TRANSVERSE FIELD OF VIEW it is described by its diameter.
NOTE – For non-cylindrical TOMOGRAPHIC VOLUMES the TRANSVERSE FIELD OF VIEW may depend on the axial position
of the slice.
2.2.2.7.2
AXIAL FIELD OF VIEW
Dimensions of a slice through the TOMOGRAPHIC VOLUME parallel to and including the SYSTEM
AXIS. In practice it is specified only by its axial dimension given by the distance between the
centres of the outermost defined IMAGE PLANES plus the average of the measured AXIAL SLICE
WIDTH measured as EQUIVALENT WIDTH (EW).
2.2.2.7.3
TOTAL FIELD OF VIEW
Dimensions (three-dimensional) of the TOMOGRAPHIC VOLUME
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61675-2 © IEC:1998(E) – 7 –
2.3
IMAGE MATRIX
Arrangement of MATRIX ELEMENTS in a preferentially cartesian coordinate system
2.3.1
MATRIX ELEMENT
Smallest unit of an IMAGE MATRIX, which is assigned in location and size to a certain volume
element of the object (VOXEL)
2.3.1.1
PIXEL
MATRIX ELEMENT in a two-dimensional IMAGE MATRIX
2.3.1.2
TRIXEL
MATRIX ELEMENT in a three-dimensional IMAGE MATRIX
2.3.2
VOXEL
Volume element in the object which is assigned to a MATRIX ELEMENT in the IMAGE MATRIX (two-
dimensional or three-dimensional). The dimensions of the VOXEL are determined by the
dimensions of the corresponding MATRIX ELEMENT via the appropriate scale factors and by
the system's SPATIAL RESOLUTION in all three dimensions.
2.4
POINT SPREAD FUNCTION (PSF)
Scintigraphic image of a POINT SOURCE
2.4.1
PHYSICAL POINT SPREAD FUNCTION
For tomographs, a two-dimensional POINT SPREAD FUNCTION in planes perpendicular to the
PROJECTION BEAM at specified distances from the detector
NOTE – The PHYSICAL POINT SPREAD FUNCTION characterizes the purely physical imaging performance of the
tomographic device independent from, e.g. sampling, image reconstruction and image processing, but dependent
on the COLLIMATOR. A PROJECTION BEAM is characterized by the entirety of all PHYSICAL POINT SPREAD FUNCTIONS as a
function of distance along its axis.
2.4.2
AXIAL POINT SPREAD FUNCTION
Profile passing through the peak of the PHYSICAL POINT SPREAD FUNCTION in a plane parallel to
the SYSTEM AXIS
2.4.3
TRANSVERSE POINT SPREAD FUNCTION
Reconstructed two-dimensional POINT SPREAD FUNCTION in a tomographic IMAGE PLANE
NOTE – In TOMOGRAPHY, the TRANSVERSE POINT SPREAD FUNCTION can also be obtained from a line source located
parallel to the SYSTEM AXIS.
2.5
SPATIAL RESOLUTION
Ability to concentrate the count density distribution in the image of a POINT SOURCE to a point
2.5.1
TRANSVERSE RESOLUTION
SPATIAL RESOLUTION in a reconstructed plane perpendicular to the SYSTEM AXIS
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2.5.1.1
RADIAL RESOLUTION
TRANSVERSE RESOLUTION along a line passing through the position of the source and the
SYSTEM AXIS
2.5.1.2
TANGENTIAL RESOLUTION
TRANSVERSE RESOLUTION in the direction orthogonal to the direction of RADIAL RESOLUTION
2.5.2
AXIAL RESOLUTION
For tomographs with sufficiently fine axial sampling fulfilling the sampling theorem, SPATIAL
RESOLUTION along a line parallel to the SYSTEM AXIS
2.5.3
EQUIVALENT WIDTH (EW)
Width of that rectangle having the same area and the same height as the response function,
e.g. the POINT SPREAD FUNCTION
2.6 Tomographic sensitivity
2.6.1
SLICE SENSITIVITY
Ratio of COUNT RATE as measured on the SINOGRAM to the ACTIVITY concentration in the
phantom
NOTE – In SPECT the measured counts are not numerically corrected for scatter by subtracting the SCATTER
FRACTION
.
2.6.2
VOLUME SENSITIVITY
Sum of the individual SLICE SENSITIVITIES
2.6.3
NORMALIZED VOLUME SENSITIVITY
VOLUME SENSITIVITY divided by the AXIAL FIELD OF VIEW of the tomograph or the phantom length,
whichever is the smaller
2.7
SCATTER FRACTION (SF)
Ratio between the number of scattered photons and the sum of scattered plus unscattered
photons for a given experimental set-up
2.8
SINGLE PHOTON EMISSION COMPUTED TOMOGRAPHY (SPECT)
EMISSION COMPUTED TOMOGRAPHY utilizing single photon detection of gamma-ray emitting
RADIONUCLIDES
2.8.1
DETECTOR POSITIONING TIME
Fraction of the total time spent on an acquisition which is not used in collecting data
2.8.2
DETECTOR HEAD TILT
Deviation of the COLLIMATOR axis from orthogonality with the SYSTEM AXIS
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61675-2 © IEC:1998(E) – 9 –
2.8.3
RADIUS OF ROTATION
Distance between the SYSTEM AXIS and the COLLIMATOR front face
2.9
RADIOACTIVE SOURCE
See rm-20-02 of IEC 60788
2.9.1
POINT SOURCE
RADIOACTIVE SOURCE approximating a δ-function in all three dimensions
2.9.2
LINE SOURCE
Straight RADIOACTIVE SOURCE approximating a δ-function in two dimensions and being constant
(uniform) in the third dimension
3 Test methods
All measurements shall be performed with the PULSE AMPLITUDE ANALYZER WINDOW as specified
in table 1 of IEC 60789. Additional measurements with other settings as specified by the
manufacturer can be performed. Before the measurements are performed, the tomographic
system shall be adjusted by the procedure normally used by the manufacturer for an installed
unit and shall not be adjusted specially for the measurement of specific parameters. If any test
cannot be carried out exactly as specified in the standard, the reason for the deviation and the
exact conditions under which the test was performed shall be stated clearly.
Unless otherwise specified, each DETECTOR HEAD in the system shall be characterized by a full
data set covering an angular range of 360°. For multiheaded systems, characterization shall
also be provided for an acquisition covering the minimal rotation required to obtain a complete
set of data (e.g. 120° for a three-headed system). If the tomograph is specified to operate in a
non-circular orbiting mode influencing the performance parameters, test results shall be
reported in addition.
Unless otherwise specified, measurements shall be carried out at COUNT RATES not exceeding
20 000 counts per second.
Measurements of performance parameters in the planar mode of operation are a prerequisite.
A complete set of performance parameters shall be measured as specified in IEC 60789.
3.1 Calibration measurements
3.1.1 Measurement of the CENTRE OF ROTATION (COR)
An error-free reconstruction requires the knowledge of the position of the PROJECTION of the
COR into the coordinate system X , Y for each PROJECTION (i.e. for each PROJECTION angle) of
p p
that slice. For a circular rotation of the DETECTOR and for an ideal system, the PROJECTION of a
POINT SOURCE at the COR will be at the same position X' in the projection matrix for all angles
p
of PROJECTION (see figure 1).
OFFSET
To determine the CENTRE OF ROTATION, the X' has to be measured. POINT SOURCE(S)
p
are used. A minimum of 32 projections equally spaced over 360° are acquired and displayed as
SINOGRAM RADIUS OF ROTATION
a . The shall be set to 20 cm. The source(s) shall be positioned
radially at least 5 cm from the system axis to get SINOGRAMS with a discernible shape of a sine
function. The OFFSET shall be determined for a minimum of three slices with axial positions,
(Z direction), one at the centre of the FIELD OF VIEW and the other two, ±1/3 of the AXIAL FIELD
OF VIEW from the centre.
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At least 10 000 counts per view shall be acquired. The length of PIXEL side shall be less than
4 mm. For the calculation of the centroid (centre of gravity) X (θ) of the source in the X
p p
direction, 50 mm wide strips in the Y direction centred around the Y position of each source
p
shall be used. This shall be done for each projection angle θ. Then the OFFSET is determined
by fitting a sine function to the X (θ) values of each source, where
p
X (θ) = A sin(θ + ϕ) + X'
p
where
θ is the angle of projection;
A is the amplitude;
ϕ is the phase shift of the sine function;
X' is the average OFFSET to be reported for the three different axial positions.
NOTE – If there is a DETECTOR HEAD TILT the position of the image of the POINT SOURCE will move not only in the x
p
direction, but also in the Y direction. To determine the X movement not influenced by the Y movement (for a
p p p
p
reasonable amount of head tilt), the centroid is calculated using the 50 mm wide strip. The subscript refers to the
projection space (see figure 1).
NOTE – If a system uses an automatic OFFSET correction which cannot be switched off, then X' shall be zero.
In addition, the difference between fit and data shall be plotted (showing the error) as a
function of θ. The maximum difference for each axial position shall be reported. The values are
valid only for the COLLIMATOR used and shall be stated in millimetres.
NOTE – Systematic deviations (trends) are indicative of varying OFFSET during rotation of the detector.
3.1.2 DETECTOR HEAD TILT
An error-free reconstruction requires that the direction of the COLLIMATOR holes is orthogonal to
the SYSTEM AXIS for each angle of projection. Deviations from this requirement are called
DETECTOR HEAD TILT.
Using the measurements according to 3.1.1 the DETECTOR HEAD TILT can be determined by
calculating the centroid Y (θ) of the image of the POINT SOURCE in the Y direction, using strips
p p
over the full field-of-view in the X direction. This calculation shall be done for each angle of
p
projection. A sine function is fitted to all those values,
Y (θ)= B sin(θ + ϕ) + D
p
where
θ is the angle of projection;
B is the amplitude;
ϕ is the phase shift of the sine function.
Report the head tilt angle value a = arcsin B/A, where A is the amplitude resulting from the COR
measurement (3.1.1).
NOTE – If there is no DETECTOR HEAD TILT, B must be zero and D must be the Y position of the source.
p
In addition the difference between fit and data shall be plotted (showing the error) as a function
of θ.
3.2 Measurement of COLLIMATOR hole misalignment
If all holes of a parallel hole COLLIMATOR are parallel, the OFFSET is constant for all source
positions within the measuring volume, assuming linearity of the positioning electronics. To
detect possible misalignments of the collimator holes, the OFFSET shall be determined using a
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61675-2 © IEC:1998(E) – 11 –
point source placed at all intersections of an orthogonal positioning grid, lying in the X, Z plane,
covering the field of view. The grid lines shall be 10 cm apart. The radius of rotation shall be at
least 20 cm. The mean value of all measured OFFSETs shall be calculated and the maximum
deviation from that value stated.
3.3 Measurement of SPECT system SENSITIVITY
3.3.1 DETECTOR POSITIONING TIME
DETECTOR POSITIONING TIME
In combination with the acquisition time chosen, the determines
that fraction of the total time spent on an acquisition which is not useful in collecting data.
Therefore it will influence the sensitivity of a tomographic device. This is especially true for a
rotating detector working in "step and shoot" mode.
99m
A POINT SOURCE of Tc shall be placed at the CENTRE OF ROTATION in air. The COUNT RATE
shall be greater than 1 000 cps. Two 360° tomographic acquisitions of a stated number, P
,
j
PROJECTIONS (one with at least 60, the other with at least 120 PROJECTIONS) shall be performed
using an acquisition time ΔT per PROJECTION of 10 s. The subscript j is either "low" or "high"
acq
corresponding to the range of approximately 60 or 120 projections. The time T from the start of
j
acquisition of the first projection to the end of the acquisition of the last projection shall be
measured. A corresponding static acquisition of duration T shall also be performed directly
j
after the tomographic acquisition. The data shall be decay corrected for the different starting
times.
The total DETECTOR POSITIONING TIME T shall be calculated according to:
pos
NN− T
()jjj
static, total,
T =
pos,j
N
static,j
where
N is the sum of the counts in all PROJECTIONS;
total
N is the number of counts in the static acquisition.
static
The mean positioning time per PROJECTION ΔT is then calculated by dividing T by the
pos pos
number of transitions between PROJECTION steps actually used.
T
pos,j
ΔT =
pos,j
−
P 1
()
j
The correction factor c for the calculation of the VOLUME SENSITIVITY is then given by
j
ΔT
acq, j
c =
j
ΔΔTT+
acq,jjpos,
The correction factor c shall be calculated and reported for the subscript j with corresponding
j
acquisition times per PROJECTION ΔT , of 30 s (low) and 15 s (high), respectively. This
acq j
corresponds to a typical clinical situation of total acquisition time of 30 min.
3.3.2 NORMALIZED VOLUME SENSITIVITY
The measurement shall be carried out using a cylindrical phantom of 200 mm ± 3 mm outside
diameter, of wall thickness 3 mm ± 1 mm, and 190 mm ±3 mm inside length (see figure 2),
99m
filled homogeneously with a water solution of Tc.
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3
The ACTIVITY concentration a (kBq/cm ) shall be accurately determined by counting at least
ave
two samples from that solution in a calibrated well counter and correcting the result for
radioactive decay to the time of measurement (midpoint of acquisition interval).
NOTE – The test is critically dependent upon accurate assays of radioactivity as measured in a dose calibrator or
well counter. It is difficult to maintain an absolute calibration with such devices to accuracies better than 10 %.
Absolute reference standards using appropriate (γ-emitters should be considered if higher degrees of accuracy are
required.
The phantom shall be positioned so that its long axis coincides with the SYSTEM AXIS (parallel to
and as close as possible to the SYSTEM AXIS). The radius of rotation R shall be 20 cm. For each
COLLIMATOR used routinely for SPECT imaging at least one million counts shall be acquired in
static imaging mode and the acquisition time T [sec] recorded. For a rectangular region of
a
interest (ROI) centred on the image of the phantom the number of counts N shall be
ROI
determined. The width of the ROI shall be at most 240 mm to cover the cylinder diameter, and
the length l shall be at least 150 mm in the axial direction and centred to the phantom. The
NORMALIZED VOLUME SENSITIVITY S is then calculated by dividing the number of counts N
norm ROI
registered from the ROI by the activity concentration a , the acquisition time T , the axial
a
ave
length l of the ROI, and by multiplying by the correction factor c (see 3.3.1) according to the
j
following equation:
N
2
ROI
S = c cps / kBq / cm
()
norm j
aTl
ave a
The values shall be specified and stated for the subscript j of low and high respectively.
NOTE – For a given phantom set-up and parallel hole COLLIMATOR, the NORMALIZED VOLUME SENSITIVITY and the
SYSTEM SENSITIVITY measured according to 3.1 of IEC 60789 are related by a fixed ratio and the correction factor c
.
j
3.4 Scatter
The scattering of primary gamma rays results in events with false information for radiation
source localization. Variations in design and implementation cause emission tomographs to
have different sensitivities to scattered radiation. The purpose of this procedure is to measure
the relative system sensitivity to scattered radiation, expressed by the SCATTER FRACTION (SF),
as well as the values of the SCATTER FRACTION in each slice(SFI).
3.4.1 Scatter measurement
The measurements shall be performed by imaging a single line source at three different radial
positions within a water-filled test phantom, using the COLLIMATOR used for SPECT imaging, a
circular orbit and a 20 cm radius of rotation.
Unscattered events are assumed to lie within a 2 × FWHM wide strip centred on the image of the
line source in each SINOGRAM. This width region is chosen because the scatter value is
insensitive to the exact width of the region, and a negligible number of unscattered events lie
m
...
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