Metrologia 54 Tech. Suppl. 06001 with erratum - BIPMII)-K4/BIPM...Metrologia 54 (2017) Tech. Suppl....

Metrologia 54 (2017) Tech. Suppl. 06001 with erratum

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Activity measurements of the radionuclides 18

F and 99m

Tc

for the NMISA, South Africa in the ongoing comparisons BIPM.RI(II)-K4.F-18 and

BIPM.RI(II)-K4.Tc-99m (with erratum)

C. Michotte1, M. Nonis

1, M. W. Van Rooy

2, M. J. Van Staden

2, J. Lubbe

2.

1

Bureau International des Poids et Mesures (BIPM), 2 National Metrology Institute of South Africa (NMISA)

Abstract

In 2015, comparisons of activity measurements of 18

F and 99m

Tc using the

Transfer Instrument of the International Reference System (SIRTI) took

place at the National Metrology Institute of South Africa (NMISA, South

Africa). Ampoules containing about 25 kBq of 18

F and 99m

Tc solutions were

measured in the SIRTI for more than two half-lives. The NMISA

standardized the activity in the ampoules by ionization chamber

measurements traceable to 4(LS) coincidence measurements. The

comparisons, identifiers BIPM.RI(II)-K4.F-18 and BIPM.RI(II)-K4.Tc-

99m, are linked to the corresponding BIPM.RI(II)-K1.F-18 and

BIPM.RI(II)-K1.Tc-99m comparisons and degrees of equivalence with the

respective key comparison reference values have been evaluated.

1. Introduction

Radionuclides are essential for nuclear medicine where very short-lived (much less than one

day) radionuclides are used, particularly for imaging. The use of nuclear medicine is

increasing with the accessibility of these radionuclides which are consequently of great

interest to the National Metrology Institutes (NMIs) in terms of the standardization and SI

traceability. However, sending ampoules of short-lived radioactive material to the Bureau

International des Poids et Mesures (BIPM) for measurement in the International Reference

System (SIR) [1] is only practicable for the NMIs that are based in Europe. Consequently, to

extend the utility of the SIR and enable other NMIs to participate, a transfer instrument

(SIRTI) has been developed at the BIPM with the support of the Consultative Committee for

Ionizing Radiation CCRI(II) Transfer Instrument Working Group [2].

The BIPM ongoing K4 comparisons of activity measurements of 18

F (half-life T1/2 = 1.8288 h;

u = 0.0003 h [3])1 and of

99mTc (half-life of 6.0067(10) h [3]) are based on the SIRTI, a well-

type NaI(Tl) crystal calibrated against the SIR, which is moved to each participating

laboratory. The stability of the system is monitored using a 94

Nb reference source (half-life of

20 300(1 600) a [4]) from the Institute for Reference Materials and Measurements (IRMM,

1 Hereafter, the last digits of the standard uncertainties are given in parenthesis.


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Geel), which also contains the 93m

Nb isotope. The 18

F or 99m

Tc count rate above a low-energy

threshold, defined by the 93m

Nb x-ray peak at 16.6 keV, is measured relative to the 94

Nb count

rate above the same threshold. Once the threshold is set, a brass liner is placed in the well to

suppress the 93m

Nb contribution to the 94

Nb stability measurements. It should be noted that the

uncertainty associated with the 94

Nb decay correction is negligible. The 99m

Tc SIR ampoule is

placed in the detector well with the brass liner to suppress the 99m

Tc x-ray peaks from the

counts. The 18

F SIR ampoule is placed in the detector well in a PVC liner to stop the +

particles while minimizing the production of bremsstrahlung. No extrapolation to zero energy

is carried out as all the measurements are made with the same threshold setting. The live-time

technique using the MTR2 module from the Laboratoire National d’Essais – Laboratoire

National Henri Becquerel, France (LNE-LNHB) [5] is used to correct for dead-time losses,

taking into account the width of the oscillator pulses. The standard uncertainty associated with

the live-time correction, due to the effect of finite frequency of the oscillator, is negligible.

Similarly to the SIR, a SIRTI equivalent activity AE is deduced from the 18

F or 99m

Tc and the 94

Nb counting results and the 18

F or 99m

Tc activity measured by the NMI: AE corresponds to

the inverse of a detection efficiency, i.e. AE is the activity of the source measured by the

participant divided by the 18

F or 99m

Tc count rate in the SIRTI expressed relatively to the 94

Nb

count rate. The possible presence of impurity in the solution should be accounted for using -

spectrometry measurements carried out by the NMI.

The present K4 comparisons are linked to the corresponding BIPM.RI(II)-K1 comparisons

through the calibration of the SIRTI against the SIR at the BIPM and consequently degrees of

equivalence with the K1 key comparison reference value (KCRV) can be evaluated. The K4 99m

Tc comparison results based on primary measurements carried out by the NMI, or

ionization chamber measurements traceable to primary 99m

Tc measurements made within one

year prior to the K4 comparison, are eligible to be included in the KCRV.

The protocol [6] and previous comparison results for the BIPM.RI(II)-K4 comparisons are

available in the key comparison database of the CIPM Mutual Recognition Arrangement [7].

Publications concerning the details of the SIRTI and its calibration against the SIR can be

found elsewhere [8, 9].

2. Participants

As detailed in the protocol, participation in the BIPM.RI(II)-K4 comparisons mainly concerns

member states that are located geographically far from the BIPM and that have developed a

primary measurement method for the radionuclide of concern. However, at the time of the

comparison the National Metrology Institute (NMI) may decide for convenience to use a

secondary method, for example a calibrated ionization chamber. In this case, the traceability

of the calibration needs to be clearly identified.

The present comparisons took place at the National Metrology Institute of South Africa

(NMISA), South Africa, in November 2015, who used an ionization chamber calibrated by

the 4(LS) coincidence method one and two months prior to the comparison to

standardize the 18

F and 99m

Tc solutions, respectively.


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3. The SIRTI at the NMISA

The reproducibility and stability of the SIRTI at the NMISA were checked by measuring the

count rate produced by the reference 94

Nb source No. 3, the threshold position (defined by the 93m

Nb x-ray peak), the background count rate, the frequency of the oscillator No. 1 for the

live-time correction and the room temperature as shown in Figure 1. The plots shown in the

Figure represent the differences from the values indicated in the figure caption, using the

appropriate units, as given, for each quantity measured.

Figure 1: Fluctuation of the SIRTI at the NMISA. Black squares:

94Nb No.1 count rate / s

–1

above 7600 s–1

; circle: threshold position / channel above 90 channels; stars: room

temperature / °C above 15 °C; open squares: background count rate / s–1

above

70 s–1

; triangles: frequency of the oscillator No.1 / Hz above 999 960 Hz.

The SIRTI was very stable during the comparison, except maybe a slight increase in the 94

Nb

count rate on the last days and a corresponding slight decrease of the threshold position.

However, the 99m

Tc measurements are almost insensitive to the threshold position [8].

Consequently, it was decided to use the mean 94

Nb count rate to normalize the 99m

Tc

measurements (instead of individual 94

Nb results for the 18

F comparison) so that the small

fluctuations observed in the 94

Nb results do not influence the 99m

Tc comparison results. The

mean 94

Nb No. 3 count rate, corrected for live-time, background and decay, measured at the

NMISA is 7632.8(5) s–1

which is in agreement with the weighted mean since the set-up of the

system in March 2007, 7632.14(25) s–1

. Finally, the 94

Nb count rate was checked on the return

of the SIRTI to the BIPM after the NMISA comparison, giving a value of 7631.8(13) s–1

in

agreement within standard uncertainty with the mean since 2007.

17/11/2015 19/11/2015 21/11/2015 23/11/2015 25/11/2015

0

5

10

15

20

25

30

35

40

45

50

Nb-94 Background

Threshold Oscillator freq.

Temperature

Date

99mTc

18F


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4. The 18

F and 99m

Tc solutions standardized at the NMISA

The 18

F and 99m

Tc solutions measured in the SIRTI consisted in saline solutions diluted with

de-ionized water. Two SIR ampoules were prepared from each diluted solution. Details are

shown in Table 1, including any impurities, when present, as identified by the laboratory. The

density and volume of the solutions in the ampoules conformed to the K4 protocol

requirements. Drops (max. 3 mm diameter) of solution were observed in the cylindrical part

of the ampoules (max. 1 cm above the solution). For the 18

F ampoules, many bubbles were

observed in the solution and condensation in the upper part of the ampoule was noted (see

Figure 2). The total volume of the bubbles was estimated in the range of 10 mm3,

corresponding to an effective solution density of 0.997 g cm–3

. For the condensation, a

hypothetic 500 nm thick layer would correspond to a solution volume in the range of

0.1 mm3. Monte-Carlo simulations indicate that the drops, bubbles and condensation observed

should have a negligible effect on the SIRTI measurement result. The 99m

Tc ampoules were

not sealed, but closed with Parafilm®.

The 18

F and 99m

Tc activities in the SIRTI ampoules were deduced from the measurement at

the NMISA of each master solution in a Vinten Isocal IV well-type ionization chamber (IC)

and a dilution factor of 1/38.424 78 and 1/41.117 13, respectively. The IC had been calibrated

for 18

F and 99m

Tc by the NMISA one and two month, respectively, prior to the K4 comparison

by the 4(LS)β- coincidence method.

The measurement results are summarized in Tables 2 and 3 while the uncertainty budgets of

the NMISA primary measurements are given in appendix 2.

Table 1: Characteristics of the solutions measured in the SIRTI

Radionuclide Solvent

/ mol dm–3

Carrier

/ g g–1

Density at

20 °C

/ g cm–3

Ampoule

number

Mass

/ g Impurity*

18F

(FDG#)

de-ionized

water – 1.0 2 3.543 71 –

3 3.541 34 –

99mTc

de-ionized

water –

1.0

1 3.626 18 –

2 3.594 28 –

* Ratio of the impurity activity to the main radionuclide activity at the reference date # Fluorodesoxyglucose


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Figure 2:

18F ampoule where drops, bubbles and condensation are noted

Table 2: The 18

F and 99m

Tc standardizations by the NMISA

Radionuclide

Measurement

method

ACRONYM*

Activity

conc.

/ kBq g–1

Standard

uncert.

/ kBq g–1

Reference

date YYYY-MM-DD

Half-life

used by the

NMI / h

18F

IC calibrated 4P-IC-GR-00-00-00

in Oct. 2015 by

4(LS)β- coinc. 4P-LS-BP-NA-GR-CO

6.669 0.041 2015-11-24

12:00 UTC 1.828 90(23)

99mTc


in Sept. 2015 by


7.80 0.11 2015-11-23

10:00 UTC 6.0067(10)

* See appendix 1


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Table 3: The NMISA uncertainty budgets for the activity measurement of the 18

F and 99m

Tc ampoules (Nov. 2015)

Uncertainty contributions due to

Evaluation

method

18F

99mTc

Relative

standard

uncert.

104

Comments Relative

sensitivity

factors

Relative

standard

uncert.

104

Comments Relative

sensitivity

factors

Counting statistics A 5

Statist. analysis of

306 values

0.82 7 Statist. analysis of

153 values

0.1

Weighing B 1 Mass for source prep. 1 1 Mass for source prep. 1

Background A 0.2 Statist. analysis of

201 values

0.0003 2 Statist. analysis of

201 values

0.003

Time accuracy of PC clock B 0.1 Accuracy of time

stamping

1 0.1 Accuracy of time

stamping

1

Decay correction B 1.5 From literature value

uncertainty for the

half-life

0.76 0.09 From literature value

uncertainty for the

half-life

0.05

Calibration factor of IC (see

appendix 2) B 35 From primary

standardization

1 134 From primary

standardization

1

IC cyclical variability B 50 IC long term cyclical

behaviour

1 50 IC long term cyclical

behaviour

1

Impurities B 0.0 HPGe measurements – 0.0 HPGe measurements –

Relative combined standard uncertainty

61 143


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5. The 18

F and 99m

Tc measurements in the SIRTI at the NMISA

The maximum count rate corrected for live-time in the NaI(Tl) was 17 000 s–1

which

conforms with the limit of 20 000 s–1

set in the protocol [6]. In addition a relative standard

uncertainty of 2 × 10–4

and 3 × 10–4

for 18

F and 99m

Tc respectively, was added to take account

of a possible drift in the SIRTI at high count rate [8]. The time of each TI measurement was

obtained from the synchronization of the laptop with a local NTP time server.

In principle, the live-time correction should be modified to take into account the decaying

count rate [10]. In the present experiments, the duration of the measurements made at high

rate has been limited to 300 s and 1500 s for 18

F and 99m

Tc respectively, so that the relative

effect of decay on the live-time correction is less than one part in 104.

Two ampoules of each of the 18

F and 99m

Tc solutions were measured alternatively for more

than two half-lives and the results are shown in Figures 3a and 3b. The reduced chi-squared

values evaluated for these series of measurements are 0.83 and 0.71 for 18

F and 99m

Tc,

respectively, showing that the data are consistent. The absence of significant trend confirms

the stability of the SIRTI and the absence of significant impurity in the solutions.

The uncertainty budgets for the SIRTI measurements of the 18

F and 99m

Tc ampoules are given

in Table 4a and 4b. Further details are given in reference [8].

6. Comparison results and degrees of equivalence

The weighted mean and uncertainty of all the measured AE values is calculated taking into

account correlations. In the case of 18

F, the last 10 measurements shown in Figure 3a were not

considered as the count rate in the SIRTI was lower than the limit of 2000 s–1

set in the

protocol. The standard uncertainty u(AE) is obtained by adding quadratically the SIRTI

combined uncertainty from Tables 4a and 4b and the uncertainty stated by the participant for

the 18

F and 99m

Tc measurements (see Table 2). The correlation between the NMISA and the

BIPM due to the use of the same 99m

Tc half-life is negligible in view of the small contribution

of this half-life to the combined uncertainty of the measurements. The K4 comparison results

are given in Table 5 as well as the linked results Ae in the corresponding BIPM.RI(II)-K1

comparisons which were obtained by multiplying AE by the linking factors L = 1495.1(18) for 18

F and 12 165 (23) for 99m

Tc. The linking factors were obtained through the measurement of 18

F and 99m

Tc ampoules from the LNE-LNHB, the NPL and a commercial company in both

the SIRTI and the SIR [9].


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Figure 3a: The 18

F measurement results in the SIRTI at the NMISA. The uncertainty of the 18

F

activity concentration and of the 94

Nb mean count rate, which are both constant

over all the measurements, are not included in the uncertainty bars shown on the

graph.

Figure 3b: As for Figure 3a, but for the 99m

Tc.


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Table 4a: Uncertainty budgets for the SIRTI measurement of the 18

F ampoules

Uncertainty contributions

due to Comments

Evaluation

method

Relative

standard

uncert. 104

18F meas. including live-

time, background , decay

corrections and threshold

setting

Standard uncertainty of the weighted mean of

30 measurements, taking into account the

correlation due to the 18

F half-life A 1.9

94Nb measurement

including live-time,

background and

threshold setting

Standard deviation of 10 measurements and

sensitivity to threshold setting A/B 1.8

Long-term stability of the

SIRTI Weighted standard deviation of 77 series,

each series consisting of 10 measurements A 0.3

Nb reference source No.3

instead of No.1 Weighted standard deviation of 53 series,


Effect of decay on the

live-time correction Maximum measurement duration evaluated

from [11] B < 1

SIRTI drift at high count

rate Mean possible drift over all

18F measurements

at the NMISA. B 2

Ampoule dimensions From the IRMM report [12] and sensitivity

coefficients from Monte-Carlo simulations B 2*

Ampoule filling height Solution volume is 3.6(1) cm3; sensitivity

coefficients from Monte-Carlo simulations B 2

Solution density Between 1 g/cm3 and 1.01 g/cm

3 as requested

in the protocol; sensitivity coefficients from

Monte-Carlo simulations B 0.7

Unseen droplet on the

walls of the ampoule top Evaluated by Monte-Carlo simulation B 1

Relative combined standard uncertainty 4.2

* Included in the type A uncertainty of the measurements of 2 ampoules of 18

F


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Table 4b: Uncertainty budgets for the SIRTI measurement of the 99m

Tc ampoules

Uncertainty contributions

due to Comments

Evaluation

method

Relative

standard

uncert. 104

99mTc meas. including

live-time, background

and decay corrections

Standard uncertainty of the weighted mean of

36 measurements, taking into account the

correlation due to the 99m

Tc half-life A 1.7

94Nb measurement

including live-time,

background and

threshold setting

Weighted standard deviation of 7 series, each

series consisting of 10 measurements A 0.7

Long-term stability of the

SIRTI Weighted standard deviation of 77 series,


Nb reference source No.3

instead of No.1 Weighted standard deviation of 53 series,


Effect of decay on the

live-time correction Maximum measurement duration evaluated

from [11] B < 1

SIRTI drift at high count

rate Mean possible drift over all

99mTc

measurements at the NMISA. B 3

Ampoule dimensions From the IRMM report [12] and sensitivity

coefficients from Monte-Carlo simulations B 8

Ampoule filling height Solution volume is 3.6(1) cm3; sensitivity

coefficients from Monte-Carlo simulations B 3*

Solution density Between 1 g/cm3 and 1.01 g/cm

3 as requested

in the protocol; sensitivity coefficients from

Monte-Carlo simulations B 0.8

Unseen droplet on the

walls of the ampoule top Evaluated by Monte-Carlo simulation B 2

Relative combined standard uncertainty 9.1

* Included in the type A uncertainty of the measurements of 2 ampoules of 99m

Tc

Table 5: BIPM.RI(II)-K4. comparison results and link to the BIPM.RI(II)-K1 comparisons

Radionuclide

Measurement

method

ACRONYM*

Solution

volume

(calculated)

/cm3

AE

/kBq

u(AE)

/kBq

Linked Ae

/kBq

u(Ae)

/kBq

18F


in Oct. 2015 by


3.54 10.25 0.06 15 328 96

99mTc


in Sept. 2015 by


3.63 and

3.59 12.83 0.18 156 100 2 200

* See appendix 1


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Every participant in the K4 comparison is entitled to have one result included in the key

comparison database (KCDB) as long as the laboratory is a signatory or designated institute

listed in the CIPM MRA, and the result is valid (i.e., not older than 20 years). Normally, the

most recent result is the one included. Any participant may withdraw its result only if all the

participants agree.

The KCRV for 18

F has been defined in the frame of the BIPM.RI(II)-K1.F-18 comparison

using direct contributions to the SIR, and is equal to 15 276(24) kBq [13]. The key

comparison reference value (KCRV) for 99m

Tc has been defined in the frame of the

BIPM.RI(II)-K1.Tc-99m comparison using direct contributions to the SIR and, as agreed by

the CCRI(II) in 2015, the SIRTI results for NIST, KRISS, NIM, LNMRI/IRD and IFIN-HH,

giving a value of 153 170(310) kBq as detailed in reference [14].

The degree of equivalence of a particular NMI, i, with the KCRV is expressed as the

difference Di with respect to the KCRV

KCRVe ii AD (1)

and the expanded uncertainty (k = 2) of this difference, Ui , known as the equivalence

uncertainty, hence

)(2 ii DuU , (2)

taking correlations into account as appropriate [15].

The degree of equivalence between any pair of NMIs, i and j, is expressed as the difference

Dij in their results

jijiij AADDD ee (3)

and the expanded uncertainty of this difference Uij where

),(2-4)(4 ee

2222

jijiijij AAuuuDuU (4)

where any obvious correlations between the NMIs (such as a traceable calibration) are

subtracted using the covariance u(Aei, Aej), as is the correlation coming from the link of the

SIRTI to the SIR. The covariance between two participants in the K4 comparison is given by

u(Aei, Aej) = Aei Aej (uL /L)2

(5)

where uL is the standard uncertainty of the linking factor L given above. However, the CCRI

decided in 2011 that these pair-wise degrees of equivalence no longer need to be published as

long as the methodology is explained.

Tables 6a and 6b show the matrices of the degrees of equivalence with the KCRV as they will

appear in the KCDB. Only results not older than 20 years are shown. It should be noted that

for consistency within the KCDB, a simplified level of nomenclature is used with Aei replaced

by xi. The introductory text is that agreed for the comparison. The graph of the degrees of

equivalence with respect to the KCRV (identified as xR in the KCDB), is shown in Figure 4a

and Figure 4b. The graphical representation indicates in part the degree of equivalence

between the NMIs but obviously does not take into account the correlations between the

different NMIs.


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Conclusion

The BIPM ongoing key comparisons for 18

F (BIPM.RI(II)-K4.F-18) and 99m

Tc (BIPM.RI(II)-

K4.Tc-99m) currently comprise four and nine results, respectively, and are linked to the

corresponding BIPM.RI(II)-K1 comparisons. The last results in these K4 comparisons, for

NMISA (South Africa), have been analysed with respect to the KCRVs determined for 18

F

and 99m

Tc in the frame of the corresponding K1 comparisons. The degrees of equivalence

have been approved by the CCRI(II) and are published in the BIPM key comparison database.

Other results may be added when other NMIs contribute with 18

F and 99m

Tc activity

measurements to the K4 or K1 comparisons or take part in other linked Regional Metrology

Organization comparisons. It should be noted that the final data in this paper, while correct at

the time of publication, will become out-of-date as NMIs make new comparisons. The formal

results under the CIPM MRA [7] are those available in the KCDB.


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Table 6a. Introductory text and table of degrees of equivalence for 18

F Key comparison BIPM.RI(II)-K1.F-18

MEASURAND :

Equivalent activity of 18

F

Key comparison reference value: the SIR reference value for this radionuclide is xR = 15 276 kBq with a standard uncertainty, uR = 24 kBq (see Final Report). The value xi is the equivalent activity for laboratory i.

The degree of equivalence of each laboratory with respect to the reference value is given by a pair of terms:

Di = (xi - xR) and Ui, its expanded uncertainty (k = 2), both expressed inMBq, and

Ui = 2((1 - 2wi)ui2 + uR

2)1/2

where wi is the weight of laboratory i contributing to the calculation of xR.

Linking BIPM.RI(II)-K4.F-18 to BIPM.RI(II)-K1.F-18

The value xi is the SIRTI equivalent activity for laboratory i participant in BIPM.RI(II)-K4.F-18 multiplied by the linking factor to BIPM.RI(II)-K1.F-18 (see Final report).

The degree of equivalence of laboratory i participant in BIPM.RI(II)-K4.F-18 with respect to the key comparison reference value is given by a pair of terms: Di = (xi - xR) and Ui, its expanded uncertainty (k = 2), both expressed in MBq.

The approximation Ui = 2(ui2 + uR

2)1/2

is used in the following table as none of these laboratories contributed to the KCRV.

Linking CCRI(II)-K3.F-18 to BIPM.RI(II)-K1.F-18

The value xi is the equivalent activity for laboratory i participant in CCRI(II)-K3.F-18 having been normalized to the value of the NPL and the LNE-LNHB (2002) combined as the link.

The degree of equivalence of laboratory i participant in CCRI(II)-K3. with respect to the key comparison reference value is given by a pair of terms: Di = (xi - xR) and Ui, its expanded uncertainty (k = 2), both expressed in MBq.


2)1/2

is used in the following table as none of these laboratories contributed to the KCRV.

Linking APMP.RI(II)-K3.F-18 to BIPM.RI(II)-K1.F-18

The value xi is the equivalent activity for laboratory i participant in APMP.RI(II)-K3.F-18 having been normalized to the value of the NPL and the LNE-LNHB (2002) combined as the link.


14/22

The degree of equivalence of laboratory i participant in APMP.RI(II)-K3. with respect to the key comparison reference value is given by a pair of terms: Di = (xi - xR) and Ui, its expanded uncertainty (k = 2), both expressed in MBq.


2)1/2

is used in the following table as this laboratory did not contribute to the KCRV.

These statements make it possible to extend the BIPM.RI(II)-K1.F-18 matrices of equivalence to all participants in the CCRI(II)-K3.F-18, the APMP.RI(II)-K3.F-18 and the BIPM.RI(II)-K4.F-18 comparisons.

Lab i Di Ui / MBq IRA 0.04 0.10 BEV 0.11 0.32 CIEMAT -0.06 0.18 PTB 0.04 0.09 LNE-LNHB -0.07 0.11

VNIIM -0.08 0.20 NPL 0.04 0.11 ENEA-INMRI 0.09 0.11 NMISA 0.05 0.20

ANSTO -0.13 0.48 CMI-IIR -0.27 0.24 NIST -0.61 0.32

INER -0.15 0.30


15/22

Figure 4a. Graph of degrees of equivalence with the KCRV for 18

F – NOT VALID, See erratum p. 22 (as it appears in Appendix B of the MRA)

N.B. The right-hand axis gives approximate relative values only


16/22

Table 6b. Table of degrees of equivalence and introductory text for 99m

Tc

Key comparison BIPM.RI(II)-K1.Tc-99m

MEASURAND :

Equivalent activity of 99m

Tc

Key comparison reference value: the SIR reference value for this radionuclide is xR = 153.17 MBq with a standard uncertainty, uR = 0.31 MBq (see Final Report).

The value xi is the equivalent activity for laboratory i.

The degree of equivalence of each laboratory with respect to the reference value is given by a pair of terms: Di = (xi - xR) and Ui, its expanded uncertainty (k = 2), both expressed inMBq, and Ui = 2((1 - 2wi)ui

2 + uR

2)1/2


Linking BIPM.RI(II)-K4.Tc-99m to BIPM.RI(II)-K1.Tc-99m

The value xi is the SIRTI equivalent activity for laboratory i participant in BIPM.RI(II)-K4.Tc-99m multiplied by the linking factor to BIPM.RI(II)-K1.Tc-99m (see Final report).

The degree of equivalence of laboratory i participant in BIPM.RI(II)-K4.Tc-99m with respect to the key comparison reference value is given by a pair of terms: Di = (xi - xR) and Ui, its expanded uncertainty (k = 2), both expressed in MBq,

Ui = 2((1 - 2wi)ui2 + uR

2)1/2


These statements make it possible to extend the BIPM.RI(II)-K1.Tc-99m matrices of equivalence to the other participants in BIPM.RI(II)-K4.Tc-99m.


17/22

Lab i

Di Ui / MBq BEV 2.5 2.7 MKEH 1.2 3.3 PTB -0.5 1.2 LNE-LNHB 0.0 1.5 NPL 0.1 1.6

NIST -0.3 1.4

KRISS 0.9 2.7

NMIJ -0.8 2.3

NIM -0.1 2.3

CNEA 7.0 4.2

LNMRI/IRD 1.5 3.3

IFIN-HH -2.3 2.9

VNIIM 3.4 4.8

ENEA-INMRI -2.4 1.7

NMISA 2.9 4.4


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Figure 4b. Graph of degrees of equivalence with the KCRV for 99m

Tc

(as it appears in Appendix B of the MRA)

N.B. The right-hand axis gives approximate relative values only


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References

[1] Ratel G., 2007, The Système International de Référence and its application in key

comparisons, Metrologia 44(4), S7-S16.

[2] Remit of the CCRI(II) Transfer Instrument Working Group, 2009, CCRI(II) working

document CCRI(II)/09-15.

[3] Bé M.-M., Chisté V., Dulieu C., Browne E., Chechev V., Kuzmenko N., Helmer R.,

Nichols A., Schönfeld E., Dersch R., 2004, Table of radionuclides,

Monographie BIPM-5, volume 1.

[4] NUDAT2.5, National Nuclear Data Center, Brookhaven National Laboratory, based on

ENSDF and the Nuclear Wallet Cards.

[5] Bouchard J., 2000, Appl. Radiat. Isot. 52, 441-446.

[6] SIR Transfer Instrument. Protocol for the ongoing comparisons on site at the NMIs,

BIPM.RI(II)-K4. Published on the CIPM MRA KCDB website.

[7] CIPM MRA: Mutual recognition of national measurement standards and of calibration

and measurement certificates issued by national metrology institutes, International

Committee for Weights and Measures, 1999, 45 pp. http://www.bipm.org/pdf/mra.pdf.

[8] Michotte C. et al., The SIRTI, a new tool developed at the BIPM for comparing activity

measurements of short-lived radionuclides world-wide, Rapport BIPM-2013/02.

[9] Michotte C. et al., Calibration of the SIRTI against the SIR and trial comparison of 18

F

and 99m

Tc at the NPL. In preparation.

[10] Baerg A.P. et al., 1976, Live-timed anti-coincidence counting with extending dead-time

circuitry, Metrologia 12, 77-80.

[11] Fitzgerald R., 2016, Corrections for the combined effects of decay and dead time in live-

timed counting of short-lived radionuclides, Appl. Radiat. Isot. 109, 335-340.

[12] Sibbens G., 1991, A comparison of NIST/SIR-, NPL-, and CBNM 5 ml ampoules,

GE/R/RN/14/91, CEC-JRC Central Bureau for Nuclear Measurements, Belgium.

[13] Michotte C. et al., Update of the BIPM comparison BIPM.RI(II)-K1.F-18 of activity

measurements of the radionuclide 18

F to include the 2010 result of the LNE-LNHB

(France). Metrologia, 2016, 53, Tech. Suppl., 06004.

[14] Michotte C., et al., Activity measurements of the radionuclide 99m

Tc for the VNIIM,

Russia and the ENEA-INMRI, Italy in the ongoing comparison BIPM.RI(II)-K4.Tc-

99m and update of the KCRV of the BIPM.RI(II)-K1.Tc-99m comparison, in

preparation.

[15] Ratel G., 2005, Evaluation of the uncertainty of the degree of equivalence, Metrologia

42, 140-144.

http://stacks.iop.org/0026-1394/44/S7

http://www.bipm.org/en/publications/monographie-ri-5.html

http://www.nndc.bnl.gov/

http://kcdb.bipm.org/appendixB/appbresults/BIPM.RI(II)-K4.Tc-99m/BIPM.RI(II)-K4.Tc-99m_Technical_Protocol.pdf

http://www.bipm.org/pdf/mra.pdf

http://iopscience.iop.org/article/10.1088/0026-1394/53/1A/06004

http://www.iop.org/EJ/abstract/0026-1394/42/2/009/

http://www.iop.org/EJ/abstract/0026-1394/42/2/009/


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Appendix 1. Acronyms used to identify different measurement methods

Each acronym has six components, geometry-detector (1)-radiation (1)-detector (2)-radiation

(2)-mode. When a component is unknown, ?? is used and when it is not applicable 00 is used.

Geometry acronym Detector acronym

4 4P proportional counter PC

defined solid angle SA press. prop. counter PP

2 2P liquid scintillation counting LS

undefined solid angle UA NaI(Tl) NA

Ge(HP) GH

Ge(Li) GL

Si(Li) SL

CsI(Tl) CS

ionization chamber IC

grid ionization chamber GC

Cerenkov light detector LC

calorimeter CA

solid plastic scintillator SP

PIPS detector PS

Radiation acronym Mode acronym

positron PO efficiency tracing ET

beta particle BP internal gas counting IG

Auger electron AE CIEMAT/NIST CN

conversion electron CE sum counting SC

mixed electrons ME coincidence CO

bremsstrahlung BS anti-coincidence AC

gamma rays GR coincidence counting with efficiency tracing

CT

X - rays XR anti-coincidence counting with efficiency tracing

AT

photons (x + ) PH triple-to-double coincidence ratio counting

TD

alpha - particle AP selective sampling SS

mixture of various radiations

MX high efficiency HE

Examples

method acronym

4(PC)-coincidence counting 4P-PC-BP-NA-GR-CO

4(PPC)-coincidence counting eff. trac. 4P-PP-MX-NA-GR-CT

defined solid angle -particle counting with a PIPS detector SA-PS-AP-00-00-00

4(PPC)AX-(Ge(HP))-anticoincidence counting 4P-PP-MX-GH-GR-AC

4 CsI-,AX, counting 4P-CS-MX-00-00-HE

calibrated IC 4P-IC-GR-00-00-00

internal gas counting 4P-PC-BP-00-00-IG


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Appendix 2. Uncertainty budgets for the NMISA primary measurements of 18

F (Oct. 2015) and 99m

Tc (Sept. 2015)

4P-LS-BP-NA-GR-CO

Uncertainty contributions due to

Evaluation

method

18F

99mTc

Comments

Relative

standard

uncert. 104

Relative

sensitivity

factors

Relative

standard

uncert. 104

Relative

sensitivity

factors

Counting statistics A 2 0.18 23 0.23 Statist. analysis of 20 values

Weighing B 5 1 5 1 Mass of sources

Dead time B 2 0.005 5 0.014 D ± 0.05 s

Background A 10 0.0013 6 0.0014 Background square root statist. applied

Coincidence resolving time B 1 0.005 5 0.025 R ± 0.01 s

Counting time B 0.1 1 0.1 1 Calibration of timer

Adsorption B 9 1 0.0 1 18

F : (1) / 99m

Tc : (2)

Decay correction B 2 1.6 7 4.3 From literature value uncert. for the half-life

Extrapolation of effic. curve B 20 1 130 1 Alternative fits to data

Afterpulse correction B 10 0.00012 20 0.02

Beta-plus branching ratio:

0.9686 (19)

B 20 1 – – From literature value uncertainty in Beta-

plus branching ratio

Impurities B 0.0 – 0.0 – HPGe measurements

Relative combined standard uncertainty 34 134

(1) Count rates after multiple rinsings relative to the expected count rates if rinsings were not done

(2) Count rate measurements after multiple rinsings comparable to background count rates


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Erratum

In the present paper, degrees of equivalence for NMISA, South Africa, have been

included in the comparison of 18

F activity measurements BIPM.RI(II)-K4.F-18. The

corresponding Table 6a is correct. However an error in the Graph 4a happened and the

uncertainty bars for the BIPM.RI(II)-K1.F-18 comparison results in red are wrong. The

correct graph is shown below.

Corrected Figure 4a. Graph of degrees of equivalence with the KCRV for 18

F

It should be noted that no error took place in the graph appearing on the Key Comparison

Data Base on line.

http://kcdb.bipm.org/appendixB/KCDB_ApB_result_dtl.asp?cmp_idy=1422&cmp_cod=BIPM%2ERI%28II%29%2DK4%2EF%2D18&search=2&cmp_cod_search=f%2D18&page=1&met_idy=&bra_idy=&epo_idy=&cmt_idy=&ett_idy_org=&lab_idy=&rta_idy=2899&rta=ge

http://kcdb.bipm.org/appendixB/KCDB_ApB_result_dtl.asp?cmp_idy=1422&cmp_cod=BIPM%2ERI%28II%29%2DK4%2EF%2D18&search=2&cmp_cod_search=f%2D18&page=1&met_idy=&bra_idy=&epo_idy=&cmt_idy=&ett_idy_org=&lab_idy=&rta_idy=2899&rta=ge

Metrologia 54 Tech. Suppl. 06001 with erratum - BIPMII)-K4/BIPM...Metrologia 54 (2017) Tech. Suppl....

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