SIST EN 61675-2:1998/A1:2005
(Amendment)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
Since IEC 61675-2 was first published in 1998, further developments of single photon computer tomographs allow some of the tomographs to be operated in coincidence detection mode as well. To comply with this trend, this amendment describes test conditions in concordance with the test methods established for dedicated PET systems.
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
Naprave za opazovanje radioaktivnih elementov – Karakteristike in preskusni pogoji – 2. del: Računalniška tomografija fotonskega sevanja
General Information
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Standards Content (Sample)
SLOVENSKI SIST EN 61675-2:1998/A1:2005
STANDARD
junij 2005
Naprave za opazovanje radioaktivnih elementov – Karakteristike in preskusni
pogoji – 2. del: Računalniška tomografija fotonskega sevanja
Radionuclide imaging devices - Characteristics and test conditions - Part 2: Single
photon emission computer tomographs
ICS 11.040.50 Referenčna številka
SIST EN 61675-2:1998/A1:2005(en)
© Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljeno
---------------------- Page: 1 ----------------------
EUROPEAN STANDARD EN 61675-2/A1
NORME EUROPÉENNE
EUROPÄISCHE NORM February 2005
ICS 11.040.50
English version
Radionuclide imaging devices -
Characteristics and test conditions
Part 2: Single photon emission computer tomographs
(IEC 61675-2:1998/A1:2004)
Dispositifs d'imagerie par radionucléides - Bildgebende Systeme
Caractéristiques et conditions d'essais in der Nuklearmedizin -
Partie 2: Systèmes de tomographie Merkmale und Prüfbedingungen
d'émission à photon unique Teil 2: Einzelphotonen-Emissions-
(CEI 61675-2:1998/A1:2004) Tomographie
(IEC 61675-2:1998/A1:2004)
This amendment A1 modifies the European Standard EN 61675-2:1998; it was approved by CENELEC
on 2005-02-01. CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations
which stipulate the conditions for giving this amendment the status of a national standard without any
alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the Central Secretariat or to any CENELEC member.
This amendment exists in three official versions (English, French, German). A version in any other language
made by translation under the responsibility of a CENELEC member into its own language and notified to the
Central Secretariat has the same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden,
Switzerland and United Kingdom.
CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
Central Secretariat: rue de Stassart 35, B - 1050 Brussels
© 2005 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 61675-2:1998/A1:2005 E
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EN 61675-2:1998/A1:2005 - 2 -
Foreword
The text of document 62C/378/FDIS, future amendment 1 to IEC 61675-2:1998, prepared by SC 62C,
Equipment for radiotherapy, nuclear medicine and radiation dosimetry, of IEC TC 62, Electrical
equipment in medical practice, was submitted to the IEC-CENELEC parallel vote and was approved
by CENELEC as amendment A1 to EN 61675-2:1998 on 2005-02-01.
The following dates were fixed:
– latest date by which the amendment has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2005-11-01
– latest date by which the national standards conflicting
with the amendment have to be withdrawn (dow) 2008-02-01
__________
Endorsement notice
The text of amendment 1:2004 to the International Standard IEC 61675-2:1998 was approved by
CENELEC as an amendment to the European Standard without any modification.
__________
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INTERNATIONAL IEC
STANDARD
61675-2
1998
AMENDMENT 1
2004-12
Amendment 1
Radionuclide imaging devices –
Characteristics and test conditions –
Part 2:
Single photon emission computed tomographs
� IEC 2004 Droits de reproduction réservés � Copyright - all rights reserved
International Electrotechnical Commission, 3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, Switzerland
Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch Web: www.iec.ch
PRICE CODE
Commission Electrotechnique Internationale U
International Electrotechnical Commission
For price, see current catalogue
---------------------- Page: 4 ----------------------
– 2 – 61675-2 Amend. 1 IEC:2004(E)
FOREWORD
This amendment 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 amendment is based on the following documents:
FDIS Report on voting
62C/378/FDIS 62C/379/RVD
Full information on the voting for the approval of this amendment can be found in the report
on voting indicated in the above table.
The committee has decided that the contents of this amendment and the base publication will
remain unchanged until the maintenance result date indicated on the IEC web site under
"http://webstore.iec.ch" in the data related to the specific publication. At this date, the
publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
_____________
Introduction to this amendment
Since this International Standard was first published in 1998, further developments of single
photon computer tomographs allow some of the tomographs to be operated in coincidence
detection mode as well. To comply with this trend, this amendment describes test conditions
in concordance with the test methods established for dedicated PET systems.
_____________
Page 2
CONTENTS
Add the title of new subclause 3.7 as follows:
3.7 Test methods for single photon computer tomographs operated in coincidence detection
mode
Add the titles of new Figures 8 to 13 as follows:
8 Phantom insert with hollow spheres
9 Cross-section of body phantom
10 Arm phantom
11 Phantom configuration for COUNT RATE measurements according to 3.7.5.3.1.2
12 Scheme of the evaluation of COUNT LOSS correction
13 Phantom insert for the evaluation of ATTENUATION correction
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61675-2 Amend. 1 IEC:2004(E) – 3 –
Page 4
1.1 Scope and object
Add, after the first paragraph, the following new text:
This part of IEC 61675-2 also specifies test conditions for declaring the characteristics of
single photon computer tomographs operated in coincidence mode as well as in single photon
mode.
The test methods specified for coincidence mode are based on the test methods for dedicated
PET tomographs as described in IEC 61675-1 to reflect as well as possible the clinical use of
coincidence detection. Tests have been modified to reflect the limited sensitivity and COUNT
RATE CHARACTERISTICS of the single photon computer tomographs operated in coincidence
detection mode only when needed.
2 Terminology and definitions
Replace the first sentence by the following:
For the purposes of this part of IEC 61675 the definitions given in IEC 60788, IEC 60789 and
IEC 61675-1 (some of which are repeated in this clause), and the following definitions apply.
Add, at the end of this clause, on page 9, the following new definitions:
2.10
POSITRON EMISSION TOMOGRAPHY
PET
emission computed tomography utilizing the annihilation radiation of positron emitting
radionuclides by coincidence detection
[IEC 61675-1, definition 2.1.3]
2.10.1
POSITRON EMISSION TOMOGRAPH
tomographic device, which detects the annihilation radiation of positron emitting radionuclides
by coincidence detection
[IEC 61675-1, definition 2.1.3.1]
2.10.2
ANNIHILATION RADIATION
IONIZING RADIATION that is produced when a particle and its antiparticle interact and cease to
exist
[IEC 61675-1, definition 2.1.3.2]
2.10.3
LINE OF RESPONSE
LOR
axis of the PROJECTION BEAM
NOTE In PET, it is the line connecting the centres of two opposing detector elements operated in coincidence
[IEC 61675-1, definition 2.1.3.5]
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– 4 – 61675-2 Amend. 1 IEC:2004(E)
2.10.4
TOTAL COINCIDENCES
sum of all coincidences detected
[IEC 61675-1, definition 2.1.3.6]
2.10.4.1
TRUE COINCIDENCE
result of COINCIDENCE DETECTION of two gamma events originating from the same positron
annihilation
[IEC 61675-1, definition 2.1.3.6.1]
2.10.4.2
SCATTERED TRUE COINCIDENCE
TRUE COINCIDENCE where at least one participating PHOTON was scattered before the
COINCIDENCE DETECTION
[IEC 61675-1, definition 2.1.3.6.2]
2.10.4.3
UNSCATTERED TRUE COINCIDENCES
difference between true coincidences and scattered true coincidences
[IEC 61675-1, definition 2.1.3.6.3]
2.10.4.4
RANDOM COINCIDENCE
result of COINCIDENCE DETECTION in which both participating PHOTONS emerge from different
positron annihilations
[IEC 61675-1, definition 2.1.3.6.4]
2.10.5
SINGLES RATE
COUNT RATE measured without COINCIDENCE DETECTION, but with energy discrimination
[IEC 61675-1, definition 2.1.3.7]
2.10.6
TWO-DIMENSIONAL RECONSTRUCTION
in TWO-DIMENSIONAL RECONSTRUCTION, the data are rebinned prior to reconstruction into
sinograms, which are the PROJECTION data of transverse slices, which are considered being
independent of each other and being perpendicular to the SYSTEM AXIS. So, each event will be
assigned, in the axial direction, to that transverse slice passing the midpoint of the
corresponding LINE OF RESPONSE. Any deviation from perpendicular to the SYSTEM AXIS is
neglected. The data are then reconstructed by two-dimensional methods, i.e. each slice is
reconstructed from its associated sinogram, independent of the rest of the data set
NOTE This is the STANDARD method of reconstruction for POSITRON EMISSION TOMOGRAPHS using small axial
acceptance angles, i.e. utilizing septa. For POSITRON EMISSION TOMOGRAPHS using large axial acceptance angles,
i.e. without septa, this method is also called “single slice rebinning”.
[IEC 61675-1, definition 2.1.4.1]
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61675-2 Amend. 1 IEC:2004(E) – 5 –
2.10.7
THREE-DIMENSIONAL RECONSTRUCTION
in THREE-DIMENSIONAL RECONSTRUCTION, the LINES OF RESPONSE are not restricted to being
perpendicular to the SYSTEM AXIS. So, a LINE OF RESPONSE may pass several transverse slices.
Consequently, transverse slices cannot be reconstructed independent of each other. Each
slice has to be reconstructed utilizing the full three-dimensional data set
[IEC 61675-1, definition 2.1.4.2]
2.11
RECOVERY COEFFICIENT
measured (image) ACTIVITY concentration of an active volume divided by the true ACTIVITY
concentration of that volume, neglecting ACTIVITY CALIBRATION FACTORS
NOTE For the actual measurement, the true ACTIVITY concentration is replaced by the measured ACTIVITY
concentration in a large volume.
[IEC 61675-1, definition 2.5]
2.12
NORMALIZED SLICE SENSITIVITY
slice sensitivity divided by the axial slice width (EW) for that slice
[IEC 61675-1, definition 2.6.1.1]
2.12.1
COUNT RATE CHARACTERISTIC
function giving the relationship between observed COUNT RATE and TRUE COUNT RATE
[IEC 60788, definition rm-34-21]
2.12.2
COUNT LOSS
difference between measured COUNT RATE and TRUE COUNT RATE, which is caused by the finite
RESOLVING TIME of the instrument
[IEC 61675-1, definition 2.7.1]
2.12.3
ADDRESS PILE UP
false address calculation of an artificial event which passes the ENERGY
WINDOW, but is formed from two or more events by the PILE UP EFFECT
[IEC 61675-1, definition 2.7.4, modified]
2.12.4
RADIOACTIVE SOURCE
quantity of radioactive material having both an ACTIVITY and a specific ACTIVITY above specific
levels
[IEC 60788, definition rm-20-02]
---------------------- Page: 8 ----------------------
– 6 – 61675-2 Amend. 1 IEC:2004(E)
Page 9
3 Test methods
Add, on page 15, the following subclauses:
3.7 Test methods for single photon computer tomographs operated in coincidence
detection mode
For all measurements, the tomograph shall be set up according to its normal mode of
operation, i.e. it shall not be adjusted specially for the measurement of specific parameters.
If the tomograph is specified to operate in different modes influencing the performance
parameters, for example with different energy windows, different axial acceptance angles,
with and without septa, with TWO-DIMENSIONAL RECONSTRUCTION and THREE-DIMENSIONAL
RECONSTRUCTION, the test results shall be reported in addition. The tomographic configuration
(e.g. energy thresholds, axial acceptance angle, reconstruction algorithm, radius of rotation,
configuration of heads) shall be chosen according to the manufacturer's recommendation and
clearly stated.
If any test cannot be carried out exactly as specified in this standard, the reason for the
deviation and the exact conditions under which the test was performed shall be stated clearly.
The test phantoms shall be centred within the tomograph’s AXIAL FIELD OF VIEW, if not specified
otherwise.
Single photon computer tomographs operated in coincidence mode must also conform to all
planar and SPECT tests (e.g. 3.1 to 3.6).
NOTE For tomographs with an AXIAL FIELD OF VIEW greater than 16,5 cm, this centring will only produce
performance estimates for the central part. However, if the phantoms were displaced axially in order to cover the
entire AXIAL FIELD OF VIEW, false results could be obtained for the central planes, if the axial acceptance angle of
the detectors was not fully covered with ACTIVITY.
3.7.1 SPATIAL RESOLUTION
3.7.1.1 General
SPATIAL RESOLUTION measurements are used to estimate the ability of a tomograph to
reproduce the spatial distribution of a tracer in an object in a reconstructed image. The
measurement is performed by imaging POINT (or LINE) SOURCES in air and reconstructing
images using a sharp reconstruction filter. Although this does not represent the condition of
imaging a patient, where tissue scatter is present and limited statistics require the use of a
smooth reconstruction filter, the measured SPATIAL RESOLUTION provides a best-case
comparison between tomographs, indicating the highest achievable performance.
3.7.1.2 Purpose
The purpose of this measurement is to characterize the ability of the tomograph to recover
small objects by characterizing the width of the reconstructed TRANSVERSE POINT SPREAD
FUNCTIONS of radioactive POINT SOURCES or of extended LINE SOURCES placed perpendicular to
the direction of measurement. The width of the spread function is measured by the FULL WIDTH
AT HALF MAXIMUM (FWHM) and the EQUIVALENT WIDTH (EW).
To define how well objects can be reproduced in the axial direction, the AXIAL SLICE WIDTH
(commonly referred to as the slice thickness) is used. It is measured with a POINT SOURCE,
which is stepped through the tomograph’s TRANSVERSE FIELD OF VIEW axially in small
increments and is characterized by the EW and the FWHM of the AXIAL POINT SPREAD
FUNCTION for each individual slice.
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61675-2 Amend. 1 IEC:2004(E) – 7 –
The AXIAL RESOLUTION is defined for tomographs with sufficiently fine axial sampling (volume
detectors) and could be measured with a stationary POINT SOURCE. For these systems the
AXIAL RESOLUTION (EW and FWHM) is equivalent to the AXIAL SLICE WIDTH. These systems
(fulfilling the sampling theorem in the axial direction) are characterized by the fact that the
AXIAL POINT SPREAD FUNCTION of a stationary POINT SOURCE would not vary if the position of the
source were varied in the axial direction for half the axial sampling distance.
3.7.1.3 Method
3.7.1.3.1 General
For all systems, the SPATIAL RESOLUTION shall be measured in the transverse IMAGE PLANE in
two directions (i.e. radially and tangentially). In addition, for those systems having sufficiently
fine axial sampling, an AXIAL RESOLUTION also shall be measured.
The TRANSVERSE FIELD OF VIEW and the IMAGE MATRIX size determine the PIXEL size in the
transverse IMAGE PLANE. In order to measure accurately the width of the spread function, its
FWHM should span at least ten PIXELS. A typical imaging study of a brain, however, requires a
260 mm TRANSVERSE FIELD OF VIEW, which together with a 128 x 128 IMAGE MATRIX and 6 mm
SPATIAL RESOLUTION, results in a FWHM of only three PIXELS. The width of the response may
be incorrect if there are fewer than ten PIXELS in the FWHM. Therefore, if possible, the PIXEL
size should be made close to one-tenth of the expected FWHM during reconstruction and
should be indicated as ancillary data for the TRANSVERSE RESOLUTION measurement. For
volume imaging systems, the TRIXEL size, in both the transverse and axial dimensions, should
be made close to one-tenth the expected FWHM, and should be indicated as ancillary data for
the SPATIAL RESOLUTION measurement. For all systems, the AXIAL SLICE WIDTH is measured by
moving the source in fine steps to sample the response function adequately. For the AXIAL
SLICE WIDTH measurement, the step size should be close to one-tenth the expected EW. It is
assumed that a computer-controlled bed will be used for accurate positioning of the
RADIOACTIVE SOURCE.
3.7.1.3.2 RADIONUCLIDE
18
The RADIONUCLIDE for the measurement shall be F, with an ACTIVITY such that the percent
COUNT LOSS is less than 5 % and the RANDOM COINCIDENCE rate is less than 5 % of the TOTAL
COINCIDENCE rate.
3.7.1.3.3 RADIOACTIVE SOURCE distribution
3.7.1.3.3.1 General
POINT SOURCES or LINE SOURCES, respectively, shall be used as described in 3.7.1.3.3.2 to
3.7.1.3.3.4.
3.7.1.3.3.2 TRANSVERSE RESOLUTION
Tomographs shall use LINE SOURCES, suspended in air to minimize scatter, for measurements
of TRANSVERSE RESOLUTION. The sources shall be kept parallel to the long axis of the
tomograph and shall be positioned radially at 100 mm intervals along Cartesian axes in a
plane perpendicular to the long axis of the tomograph i.e. r = 10 mm, 100 mm, 200 mm . up
to the edge of the TRANSVERSE FIELD OF VIEW. The last position shall be not more than 20 mm
from the edge and shall be stated. Each of these positions yields two measurements of
TRANSVERSE RESOLUTION, which shall be distinguished by being in the radial or tangential
direction.
NOTE The SPATIAL RESOLUTION at r = 0 mm may yield artificial values due to sampling, so this measurement is
done at the position r = 10 mm.
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– 8 – 61675-2 Amend. 1 IEC:2004(E)
3.7.1.3.3.3 AXIAL SLICE WIDTH
The AXIAL POINT SPREAD FUNCTION for POINT SOURCES suspended in air shall be measured for
all systems. The POINT SOURCES shall be moved in fine increments along the axial direction
over the length of the tomograph, at radial positions of r = 0 mm, 100 mm, . in 100 mm steps
up to the edge of the TRANSVERSE FIELD OF VIEW. The last position shall be not more than
20 mm from the edge and shall be stated. The source is stepped in the axial direction by one-
tenth of the expected EW of the axial response function. For each radial position, the
measured values shall be corrected for decay. This measurement does not apply to THREE-
DIMENSIONAL RECONSTRUCTION.
3.7.1.3.3.4 AXIAL RESOLUTION
For systems having axial sampling at least three times smaller than the FWHM of the AXIAL
POINT SPREAD FUNCTION the measurement of AXIAL RESOLUTION can be made with stationary
POINT SOURCES. POINT SOURCES suspended in air are positioned at radial intervals of 100 mm,
starting at the centre and extending to a distance which depends on the TRANSVERSE FIELD OF
VIEW, as described in the measurement of AXIAL SLICE WIDTH (3.7.1.3.3.3). Each POINT SOURCE
shall be imaged at axial intervals of ±80 mm, starting at the centre of the tomograph and
extending to within 20 mm from the edge of the AXIAL FIELD OF VIEW.
3.7.1.3.4 Data collection
Data shall be collected for all sources in all of the positions specified above, either singly or in
groups of multiple sources, to minimize the data acquisition time. At least 50 000 counts shall
be acquired in each response function, as defined below.
3.7.1.3.5 Data processing
Reconstruction using a ramp filter with the cut-off at the Nyquist frequency of the PROJECTION
data shall be employed for all SPATIAL RESOLUTION data.
3.7.1.4 Analysis
The RADIAL RESOLUTION and the TANGENTIAL RESOLUTION shall be determined by forming one-
dimensional response functions, which result from taking profiles through the TRANSVERSE
POINT SPREAD FUNCTION in radial and tangential directions, passing through the peak of the
distribution.
The AXIAL RESOLUTION of the POINT SOURCE measurements is determined by forming one-
dimensional response functions (AXIAL POINT SPREAD FUNCTIONS), which result from taking
profiles through the volume image in the axial direction, passing through the peak of the
distribution in the slice nearest the source.
The AXIAL SLICE WIDTH is determined by forming one-dimensional response functions (AXIAL
POINT SPREAD FUNCTIONS), which result from summing the counts per slice collected for each
slice at each axial location of each radial source location.
Each FWHM shall be determined by linear interpolation between adjacent PIXELS at half the
maximum PIXEL value, which is the peak of the response function (see Figure 6). Values shall
be converted to millimetre units by multiplication with the appropriate PIXEL size.
Each EQUIVALENT WIDTH (EW) shall be measured from the corresponding response function.
---------------------- Page: 11 ----------------------
61675-2 Amend. 1 IEC:2004(E) – 9 –
EW is calculated from the formula
C × PW
i
EW =
∑
C
m
i
where
ΣC is the sum of the counts in the profile between the limits defined by 1/20 cm on either
i
side of the peak;
C is the maximum PIXEL value;
m
PW is the PIXEL width (or axial increment in the case of the AXIAL SLICE WIDTH) in millimetres
(see Figure 7).
3.7.1.5 Report
RADIAL and TANGENTIAL RESOLUTIONS (FWHM and EW) for each radius, averaged over all
slices, shall be calculated and reported as TRANSVERSE RESOLUTION values. AXIAL SLICE WIDTHS
(EW and FWHM) for each radius, averaged over all slices for each type (e.g. odd, even) shall
be reported. Transverse PIXEL dimensions and axial step size shall also be reported.
For systems where AXIAL RESOLUTION is to be measured, AXIAL RESOLUTION (FWHM and EW),
averaged over all slices, shall be reported. For these systems, the axial PIXEL dimension in
millimetres shall also be reported.
For systems utilizing THREE-DIMENSIONAL RECONSTRUCTION, RESOLUTION data as listed above
shall not be averaged. Graphs of TRANSVERSE RESOLUTION and AXIAL RESOLUTION shall be
reported, showing the RESOLUTION values (RADIAL RESOLUTION, TANGENTIAL RESOLUTION, and
AXIAL RESOLUTION) for each radius as a function of slice number.
3.7.2 RECOVERY COEFFICIENT
3.7.2.1 General
The finite RESOLUTION of a tomograph leads to a spreading of image counts beyond the
geometrical boundaries of the object. This effect becomes more important as the object size
decreases. The RECOVERY COEFFICIENT provides an assessment of the ability of the tomograph
to quantify the ACTIVITY concentration as a function of the object size.
3.7.2.2 Purpose
The objective of the following procedures is to quantify the apparent decrease in tracer
concentration in a region of interest (ROI) of an image of spherical sources of different
diameters.
3.7.2.3 Method
18
A number of hollow spheres, filled with an ACTIVITY concentration of F from a stock solution,
are placed in the water-filled head phantom (see Figures 2 and 8), which is in turn placed in
the centre of the TRANSVERSE FIELD OF VIEW. The phantom shall be held in position without
introducing additional attenuating material. At least two samples from this solution are
counted in a well counter. The spheres are arranged to be coplanar.
For systems utilizing THREE-DIMENSIONAL RECONSTRUCTION, the measurements shall be done
at the axial centre of the tomograph and halfway between the axial centre and the edge of the
AXIAL FIELD OF VIEW.
After data acquisition, the spheres are removed and the cylinder filled with a uniform solution
18
of F from which at least two samples are taken for well counting.
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– 10 – 61675-2 Amend. 1 IEC:2004(E)
3.7.2.4 Data collection
The data collection shall be carried out at low COUNT RATES such that the COUNT LOSS is less
than 5 % and the RANDOM COINCIDENCE rate is less than 5 % of the TOTAL COINCIDENCE rate.
Care should be taken to acquire sufficient counts so that statistical variations do not
significantly affect the result. So, for the slice containing the spheres, at least 500 000 counts
shall be acquired. COUNT RATES and scanning times shall be stated.
3.7.2.5 Data processing and analysis
Reconstruction shall be performed using a ramp filter with a cut-off at the Nyquist frequency
and with all corrections applied. The method of ATTENUATION correction shall be by an
analytical calculation. The ATTENUATION coefficient used shall be reported. The scatter
correction method used shall be clearly described.
Circular ROIs of diameter as close as possible to the FWHM as measured in 3.7.1.3.3.3 are
defined centrally on the image of each sphere. The precise ROI diameter should be stated.
A large ROI (diameter: 150 mm) is centred on the image of the uniform cylinder. Calculation
of the RECOVERY COEFFICIENT (RC ) for each sphere is obtained from the equation:
si
C
si
SM
s
RC =
si
C
u
SM
u
where
C are the ROI counts/pixel/s for sphere i;
si
3
SM are the sample counts/s/cm (stock solution spheres);
s
C are the ROI counts/pixel/s (head phantom);
u
3
SM are the sample counts/s/cm (head phantom);
u
C /SM represents a calibration factor for a large reference object.
u u
Care shall be taken to correct for any dead-time and sample volume effects in the well
counter. RC is then plotted against sphere diameter to give recovery curves.
si
3.7.2.6 Report
Graphs of RECOVERY COEFFICIENTS for each axial position described in 3.7.2.3 shall be
reported.
The scatter correction method used shall be clearly described, as well as the ATTENUATION
coefficient used.
3.7.3 Tomographic sensitivity
3.7.3.1 General
Tomographic sensitivity is a parameter that characterizes the rate at which coincidence
events are detected in the presence of a RADIOACTIVE SOURCE in the limit of low ACTIVITY
where COUNT LOSSES and RANDOM COINCIDENCES are negligible. The measured rate of TRUE
COINCIDENCE EVENTS for a given distribution of the RADIOACTIVE SOURCE depends upon many
factors, including the detector material, size, and packing fraction, axial acceptance window
and septa geometry, ATTENUATION, scatter, dead-time, and energy thresholds, radius of
rotation and detector head geometry.
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61675-2 Amend. 1 IEC:2004(E) – 11 –
3.7.3.2 Purpose
The purpose of this measurement is to determine the detected rate of TRUE COINCIDENCE
EVENTS per unit of ACTIVITY concentration for a standard volume source, i.e. a cylindrical
phantom of given dimensions.
3.7.3.3 Method
The tomographic sensitivity test places a specified volume of radioactive solution of known
ACTIVITY concentration in the TOTAL FIELD OF VIEW of the single photon computer tomograph
operated in coincidence detection mode and observes the resulting COUNT RATE. The systems
sensitivity is calculated from these values.
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 finer than 10 %. Absolute reference standards using positron emitters should be
considered if higher degrees of accuracy are required.
3.7.3.3.1 RADIONUCLIDE
18 68
The RADIONUCLIDE used for these measurements shall be F or Ge. The amount of ACTIVITY
used shall be such that the percentage of COUNT LOSSES is less than 5 % and the RANDOM
COINCIDENCE rate is less than 5 % of the TOTAL COINCIDENCE rate.
3.7.3.3.2 RADIOACTIVE SOURCE distribution
The head phantom (Figure 2) shall be filled with a homogeneous solution of known ACTIVITY
concentration. The phantom shall be held in position without introducing additional attenuating
material. It shall be centred both axially and transaxially in the TOTAL FIELD OF VIEW.
3.7.3.3.3 Data collection
Each coincident event between individual detectors shall be taken into account only once.
Data shall be assembled into SINOGRAMS. All events will be assigned to the transverse slice
passing the midpoint of the corresponding LINE OF RESPONSE.
At least 20 000 counts shall be acquired for each slice within the lesser of the AXIAL FIELD OF
VIEW or the central 16,5 cm where the phantom was placed.
3.7.3.3.4 Data processing
The ACTIVITY concentration in the phantom shall be corrected for decay to determine the
average ACTIVITY concentration, a , during the data acquisition time interval, T , by the
ave acq
following equation:
T
A T T −T
1 acq
cal 1/ 2 cal 0
a = exp ln 21− exp − ln2
ave
V ln2 T T T
acq 1/ 2 1/ 2
where
V is the volume of the phantom;
A is the ACTIVITY times branching ratio ("positron activity") measured at time T ;
cal cal
T is the acquisition start time;
0
T is the half life of the RADIONUCLIDE.
1/2
It is not necessary to reconstruct these data. No corrections for detector normalization, COUNT
LOSS, scatter, and ATTENUATION shall be applied. The data shall be corrected for RANDOM
COINCIDENCES.
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