Methods for calculating Size Specific Dose Estimate (SSDE) on Computed Tomography (IEC 62985:2019)

This document applies to - CT SCANNERS that are able to display and report CTDIVOL in accordance with IEC 60601-2-44, and - RADIATION dose index monitoring software (RDIMS) for the purpose of calculating, displaying and recording the SIZE SPECIFIC DOSE ESTIMATE (SSDE) and its associated components. Specifically, this document provides standardized methods and requirements for calculating, displaying, or recording of SSDE, SSDE(z), WATER EQUIVALENT DIAMETER (DW), and DW(z), where z represents a specific longitudinal position of the scanned object. This document provides a method of determining a reference WATER EQUIVALENT DIAMETER, DW,REF(z), using CT scans of two cylindrical water PHANTOMS and one or more anthropomorphic PHANTOM(S), which conform to the specifications defined in this document. The method of calculating the WATER EQUIVALENT DIAMETER that is implemented by the MANUFACTURER, DW,IMP(z), is tested and validated against DW,REF(z) using the TEST OBJECTS and methods defined within this document. This document also describes the methods for calculating SSDE and DW, which represent the average values of SSDE(z) and DW(z) over the RECONSTRUCTION LENGTH.

Verfahren für die Berechnung größenspezifischer Dosisschätzungen (SSDE) für die Computertomographie (IEC 62985:2019)

Méthodes de calcul de l’estimateur de dose morphologique (SSDE) en tomodensitométrie (IEC 62985:2019)

L'IEC 62985:2019 s’applique: – aux TOMODENSITOMETRES qui sont capables d’afficher et de notifier CTDIVOL conformément à l’IEC 60601-2-44, et – au logiciel de surveillance de l’indice de dose de RAYONNEMENT (RDIMS - RADIATION Dose Index Monitoring Software) pour les besoins de calcul, d’affichage et d’enregistrement de l’ESTIMATEUR DE DOSE MORPHOLOGIQUE (SSDE) et de ses composantes associées. Plus spécifiquement, le présent document fournit des méthodes et des exigences normalisées pour le calcul, l’affichage ou l’enregistrement du SSDE, du SSDE(z), du DIAMETRE EQUIVALENT EAU (DW), et de DW(z), où z représente une position longitudinale spécifique de l’objet balayé. Le présent document fournit une méthode permettant de déterminer un DIAMETRE EQUIVALENT EAU de référence, DW,REF(z), par balayage TOMOGRAPHIQUE de deux FANTOMES d’eau cylindriques et d’un ou plusieurs FANTOMES anthropomorphiques conformes aux spécifications définies dans le présent document. La méthode de calcul du DIAMETRE EQUIVALENT EAU appliquée par le FABRICANT, DW,IMP(z), est vérifiée par essai et validée par rapport à la valeur DW,REF(z) en utilisant les OBJETS D’ESSAI et les méthodes définis dans le présent document. Le présent document décrit également les méthodes de calcul du SSDE et DW, qui représentent les valeurs moyennes du SSDE(z) et du DW(z) sur l’ensemble de la LONGUEUR DE RECONSTRUCTION.

Metode za izračun doze obsevanja glede na velikost obsevanca (SSDE) pri računalniški tomografiji (IEC 62985:2019)

Ta dokument se uporablja za: – NAPRAVE CT, ki lahko prikazujejo in poročajo CTDIVOL v skladu s standardom IEC 60601-2-44; in – programsko opremo za spremljanje indeksa odmerka OBSEVANJA (RDIMS) za namene izračunavanja, prikazovanja ter beleženja DOZE OBSEVANJA GLEDE NA VELIKOST OBSEVANCA (SSDE) in njenih povezanih komponent. Natančneje, ta dokument podaja standardizirane metode in zahteve za izračunavanje, prikazovanje ali beleženje SSDE, SSDE(z), VODNEGA EKVIVALENTNEGA PREMERA (DW) in DW(z), pri čemer z označuje določen vzdolžni položaj slikanega objekta. Ta dokument določa metodo za določevanje referenčnega VODNEGA EKVIVALENTNEGA PREMERA, DR,REF(z), s slikanji CT dveh valjastih vodnih FANTOMOV in enega ali več antropomorfnih FANTOMOV, ki so skladni s specifikacijami, določenimi v tem dokumentu. Metoda za izračun VODNEGA EKVIVALENTNEGA PREMERA, ki jo uporablja PROIZVAJALEC, DW,IMP(z), se preskuša in potrdi glede na DW,REF(z) z uporabo PRESKUSNIH OBJEKTOV in metod, določenih v tem dokumentu. Ta dokument opisuje tudi metode za izračun SSDE in DW, ki predstavljata povprečni vrednosti SSDE(z) in DW(z) na DOLŽINI REKONSTRUKCIJE.

General Information

Status
Published
Publication Date
24-Nov-2019
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
20-Nov-2019
Due Date
25-Jan-2020
Completion Date
25-Nov-2019

Buy Standard

Standard
SIST EN IEC 62985:2020
English language
24 pages
sale 10% off
Preview
sale 10% off
Preview

e-Library read for
1 day

Standards Content (sample)

SLOVENSKI STANDARD
SIST EN IEC 62985:2020
01-januar-2020
Metode za izračun doze obsevanja glede na velikost obsevanca (SSDE) pri
računalniški tomografiji (IEC 62985:2019)

Methods for calculating Size Specific Dose Estimate (SSDE) on Computed Tomography

(IEC 62985:2019)
Verfahren für die Berechnung größenspezifischer Dosisschätzungen (SSDE) für die
Computertomographie (IEC 62985:2019)
Méthodes de calcul de l’estimateur de dose morphologique (SSDE) en
tomodensitométrie (IEC 62985:2019)
Ta slovenski standard je istoveten z: EN IEC 62985:2019
ICS:
11.040.50 Radiografska oprema Radiographic equipment
SIST EN IEC 62985:2020 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST EN IEC 62985:2020
---------------------- Page: 2 ----------------------
SIST EN IEC 62985:2020
EUROPEAN STANDARD EN IEC 62985
NORME EUROPÉENNE
EUROPÄISCHE NORM
November 2019
ICS 11.040.50
English Version
Methods for calculating size specific dose estimates (SSDE) on
computed tomography
(IEC 62985:2019)

Méthodes de calcul de l’estimateur de dose morphologique Verfahren für die Berechnung größenspezifischer

(SSDE) en tomodensitométrie Dosisschätzungen (SSDE) für die Computertomographie
(IEC 62985:2019) (IEC 62985:2019)

This European Standard was approved by CENELEC on 2019-10-18. CENELEC members are bound to comply with the CEN/CENELEC

Internal Regulations which stipulate the conditions for giving this European Standard 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 CEN-CENELEC

Management Centre or to any CENELEC member.

This European Standard 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 CEN-CENELEC Management Centre has the

same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,

Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the

Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and the United Kingdom.
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2019 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.

Ref. No. EN IEC 62985:2019 E
---------------------- Page: 3 ----------------------
SIST EN IEC 62985:2020
EN IEC 62985:2019 (E)
European foreword

The text of document 62B/1133/FDIS, future edition 1 of IEC 62985, prepared by SC 62B "Diagnostic

imaging equipment" of IEC/TC 62 "Electrical equipment in medical practice" was submitted to the IEC-

CENELEC parallel vote and approved by CENELEC as EN IEC 62985:2019.
The following dates are fixed:

• latest date by which the document has to be implemented at national (dop) 2020-07-18

level by publication of an identical national standard or by endorsement

• latest date by which the national standards conflicting with the (dow) 2022-10-18

document have to be withdrawn

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.

Endorsement notice

The text of the International Standard IEC 62985:2019 was approved by CENELEC as a European

Standard without any modification.
---------------------- Page: 4 ----------------------
SIST EN IEC 62985:2020
EN IEC 62985:2019 (E)
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments)

applies.

NOTE 1 Where an International Publication has been modified by common modifications, indicated by (mod), the relevant

EN/HD applies.

NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is available here:

www.cenelec.eu.
Publication Year Title EN/HD Year
IEC/TR 60788 2004 Medical electrical equipment - Glossary of - -
defined terms
IEC 60601-1 2005 Medical electrical equipment - Part 1: EN 60601-1 2006
General requirements for basic safety and
essential performance
+ A1 2012 + A1 2013
- - + A12 2014
IEC 60601-1-3 2008 Medical electrical equipment - Part 1-3: EN 60601-1-3 2008
General requirements for basic safety and
essential performance - Collateral
Standard: Radiation protection in
diagnostic X-ray equipment
- - + A11 2016

IEC 60601-2-44 2009 Medical electrical equipment - Part 2-44: EN 60601-2-44 2009

Particular requirements for the basic safety
and essential performance of X-ray
equipment for computed tomography
- - + A11 2011
---------------------- Page: 5 ----------------------
SIST EN IEC 62985:2020
---------------------- Page: 6 ----------------------
SIST EN IEC 62985:2020
IEC 62985
Edition 1.0 2019-09
INTERNATIONAL
STANDARD
Methods for calculating size specific dose estimates (SSDE) for computed
tomography
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 11.040.50 ISBN 978-2-8322-7290-9

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 7 ----------------------
SIST EN IEC 62985:2020
– 2 – IEC 62985:2019 © IEC 2019
CONTENTS

FOREWORD ........................................................................................................................... 4

INTRODUCTION ..................................................................................................................... 6

1 Scope .............................................................................................................................. 7

2 Normative references ...................................................................................................... 7

3 Terms and definitions ...................................................................................................... 7

4 Verification of method used to calculate D (z) ................................................................ 9

4.1 General ................................................................................................................... 9

4.2 Characteristics of the water PHANTOMS .................................................................... 9

4.3 Characteristics of the anthropomorphic PHANTOM .................................................. 10

4.4 Generation of D (z) for the water PHANTOMS ................................................ 10

W,REF

4.5 Verification of D for the water PHANTOMS .................................................... 10

W,REF

4.6 Generation of D for the water PHANTOMS ..................................................... 10

W,IMP

4.7 Verification of D (z) against D (z) for the water PHANTOMS .................. 11

W,IMP W,REF

4.8 Generation of D (z) for the anthropomorphic PHANTOM................................. 11

W,REF

4.9 Generation of D (z) for the anthropomorphic PHANTOM ................................. 12

W,IMP
4.10 Verification of D (z) against D (z) for the anthropomorphic
W,IMP W,REF

PHANTOM ............................................................................................................... 12

5 Requirements and limitations ......................................................................................... 12

5.1 Calculation of SSDE and D for CT SCANNERS and RDIMS ................................... 12

5.2 Pre-scan display of SSDE for CT SCANNERs ........................................................... 12

5.3 Post-scan updating of SSDE and D for CT SCANNERS .......................................... 12

5.4 Pre and post-scan display of SSDE and D for CT SCANNERS ............................... 13

5.5 Post-scan recording of SSDE and D for CT SCANNERS ......................................... 13

5.6 Limitations of calculation and display of SSDE and D ........................................ 13

5.7 Requirements for identification of limitations in the ACCOMPANYING

DOCUMENTS ........................................................................................................... 13

5.8 Updating SSDE conversion factors, ƒ ................................................................... 14

Annex A (normative) SSDE conversion factors ..................................................................... 15

A.1 Clarification regarding the use of effective diameter versus D ............................ 15

A.2 Equation for determination of SSDE conversion factor .......................................... 15

Annex B (normative) Language regarding the general limitations of the SSDE

methodology for use in the ACCOMPANYING DOCUMENTS .................................................. 17

Annex C (informative) Estimates of the magnitude of uncertainties from special clinical

scenarios ....................................................................................................................... 18

C.1 General ................................................................................................................. 18

C.2 Neck included in scanned anatomy ....................................................................... 18

C.3 Range of scan projection radiograph exceeded ..................................................... 18

C.4 Single or bilateral extremities scanned .................................................................. 18

C.5 PATIENT not positioned at the centre of rotation along the source/detector

direction ................................................................................................................ 19

C.6 PATIENT anatomy outside the scan field of view ..................................................... 19

C.7 Foreign objects within the scanned projection radiograph or scan volume ............. 19

Bibliography .......................................................................................................................... 20

Index of defined terms used in this document ....................................................................... 21

---------------------- Page: 8 ----------------------
SIST EN IEC 62985:2020
IEC 62985:2019 © IEC 2019 – 3 –
Figure A.1 – Visualization of ƒ(D ) versus D for the body and head parameters
w W

provided in Table A.1 ............................................................................................................ 16

Table 1 – Anthropomorphic PHANTOM regions to be scanned ................................................. 11

Table A.1 – SSDE Conversion factor as a function of D ..................................................... 15

---------------------- Page: 9 ----------------------
SIST EN IEC 62985:2020
– 4 – IEC 62985:2019 © IEC 2019
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
METHODS FOR CALCULATING SIZE SPECIFIC DOSE
ESTIMATES (SSDE) FOR COMPUTED TOMOGRAPHY
FOREWORD

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

all national electrotechnical committees (IEC National Committees). The object of 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, IEC publishes International Standards, Technical Specifications,

Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as "IEC

Publication(s)"). 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. 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 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 IEC National Committees.

3) IEC Publications have the form of recommendations for international use and are accepted by IEC National

Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC

Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any

misinterpretation by any end user.

4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications

transparently to the maximum extent possible in their national and regional publications. Any divergence

between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in

the latter.

5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity

assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any

services carried out by independent certification bodies.

6) All users should ensure that they have the latest edition of this publication.

7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and

members of its technical committees and IEC National Committees for any personal injury, property damage or

other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and

expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC

Publications.

8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is

indispensable for the correct application of this publication.

9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of

patent rights. IEC shall not be held responsible for identifying any or all such patent rights.

International Standard IEC 62985 has been prepared by subcommittee 62B: Diagnostic

imaging equipment, of IEC technical committee 62: Electrical equipment in medical practice.

The text of this International Standard is based on the following documents:
FDIS Report on voting
62B/1133/FDIS 62B/1144/RVD

Full information on the voting for the approval of this International Standard can be found in

the report on voting indicated in the above table.

This document has been drafted in accordance with the ISO/IEC Directives, Part 2.

In this document, the following print types are used:
– requirements and definitions: roman type;
---------------------- Page: 10 ----------------------
SIST EN IEC 62985:2020
IEC 62985:2019 © IEC 2019 – 5 –

– informative material appearing outside of tables, such as notes, examples and references: in smaller type.

Normative text of tables is also in a smaller type;
– TERMS DEFINED IN CLAUSE 3, IN CLAUSE 3 OF IEC 60601-1:2005 AND
IEC 60601-1:2005/AMD1:2012, OF THE COLLATERAL STANDARDS, OF IEC TR 60788:2004 OR
AS NOTED: SMALL CAPITALS.

The committee has decided that the contents of this document will remain unchanged until the

stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to

the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.

NOTE The attention of the user of this document is drawn to the fact that equipment MANUFACTURERS and testing

organizations may need a transitional period following publication of a new, amended or revised IEC publication in

which to make products in accordance with the new requirements and to equip themselves for conducting new or

revised tests. It is the recommendation of the committee that the content of this publication be adopted for

implementation nationally not earlier than 3 years from the date of publication.
A bilingual version of this publication may be issued at a later date.
---------------------- Page: 11 ----------------------
SIST EN IEC 62985:2020
– 6 – IEC 62985:2019 © IEC 2019
INTRODUCTION

The SIZE SPECIFIC DOSE ESTIMATE (SSDE) is an estimate of the average ABSORBED DOSE to the

scan volume that takes into account the ATTENUATION of the anatomy being scanned (using

the WATER EQUIVALENT DIAMETER D ) and the RADIATION OUTPUT of the CT SCANNER (using

CTDI ).
VOL

SSDE is intended to provide a dose estimate for PATIENTs of all sizes. SSDE, which is given in

units of mGy, is especially important for small paediatric PATIENTS since the corresponding

applied level of RADIATION (CTDI , also given in units of mGy) does not adequately indicate

VOL
the absorbed RADIATION DOSE.

SSDE is calculated using a SSDE CONVERSION FACTOR AT LONGITUDINAL POSITION Z (ƒ) and the

CTDI AT LONGITUDINAL POSITION Z, CTDI (z), where ƒ is a function of the WATER
VOL VOL

EQUIVALENT DIAMETER AT LONGITUDINAL POSITION Z, D (z), and the size of the CTDI PHANTOM

used to report CTDI . ƒ is given in normative Annex A.
VOL

This document provides a methodology (in Clause 4) for a MANUFACTURER to validate their

method for calculating D (z), which is used for the determination of 𝑓𝑓 and the calculation of

SSDE. This method calculates a reference WATER EQUIVALENT DIAMETER AT LONGITUDINAL

POSITION Z, D (z), and compares it against a known PHANTOM dimension and the
W,REF

implemented values of WATER EQUIVALENT DIAMETER AT LONGITUDINAL POSITION Z, D (z).

W,IMP
PHANTOM types and tolerances are also specified.

NOTE 1 The definition of SSDE used in this document differs from that of AAPM Report No. 204 [1] in that

AAPM Report No. 204 estimates the average dose at the centre of the scan volume, whereas in this document,

SSDE estimates the average dose across the whole scan volume.

NOTE 2 CTDI is a dose index that allows quantitation of the RADIATION OUTPUT of CT SCANNERS in terms of one

VOL

of two PMMA test objects. These test objects are 16 cm and 32 cm in diameter. SSDE is calculated by conversion

of one of these PHANTOM-based dose indices to an estimate of the RADIATION dose absorbed by a PATIENT of a

specific size. The magnitude of the difference between SSDE and CTDI values increases as the difference

VOL

between the PATIENT size and the size of the CTDI PHANTOM used to measure the CTDI increases. For infants, the

VOL

calculated SSDE value may be 3 times as much as the corresponding CTDI dose index value. Conversely, the

VOL

CTDI value for large PATIENTs overestimates SSDE, which is representative of the PATIENT's actual absorbed

VOL

RADIATION DOSE. For extra-large adult PATIENTs, the CTDI dose index can overestimate the SSDE by as much as

VOL
40 % [1].
Potential uses of SSDE include the following:
1) evaluating PATIENT ABSORBED DOSE for quality assurance programs;
2) establishing diagnostic reference levels across PATIENT sizes;

3) displaying to the OPERATOR an estimate of PATIENT ABSORBED DOSE prior to initiation of the

CT scan;
4) providing an estimate of ABSORBED DOSE for the DICOM RDSR;

5) developing DOSE NOTIFICATION VALUE and DOSE ALERT VALUES that better take into account

PATIENT size;
6) providing an estimate of PATIENT ABSORBED DOSE for dose registries.
_____________
Numbers in square brackets refer to the Bibliography.
---------------------- Page: 12 ----------------------
SIST EN IEC 62985:2020
IEC 62985:2019 © IEC 2019 – 7 –
METHODS FOR CALCULATING SIZE SPECIFIC DOSE
ESTIMATES (SSDE) FOR COMPUTED TOMOGRAPHY
1 Scope
This document applies to
– CT SCANNERS that are able to display and report CTDI in accordance with
VOL
IEC 60601-2-44, and
– RADIATION dose index monitoring software (RDIMS)
SIZE SPECIFIC DOSE ESTIMATE
for the purpose of calculating, displaying and recording the
(SSDE) and its associated components.

Specifically, this document provides standardized methods and requirements for calculating,

displaying, or recording of SSDE, SSDE(z), WATER EQUIVALENT DIAMETER (D ), and D (z), where

W W
z represents a specific longitudinal position of the scanned object.

This document provides a method of determining a reference WATER EQUIVALENT DIAMETER,

D (z), using CT scans of two cylindrical water PHANTOMS and one or more
W,REF

anthropomorphic PHANTOM(S), which conform to the specifications defined in this document.

The method of calculating the WATER EQUIVALENT DIAMETER that is implemented by the

MANUFACTURER, D (z), is tested and validated against D (z) using the TEST OBJECTS

W,IMP W,REF

and methods defined within this document. This document also describes the methods for

calculating SSDE and D which represent the average values of SSDE(z) and D (z) over the

W, W
RECONSTRUCTION LENGTH.

NOTE This standardization is important to ensure that comparisons between reported SSDEs are valid.

2 Normative references

The following documents are referred to in the text in such a way that some or all of their

content constitutes requirements of this document. For dated references, only the edition

cited applies. For undated references, the latest edition of the referenced document (including

any amendments) applies.
IEC TR 60788:2004, Medical electrical equipment – Glossary of defined terms

IEC 60601-1:2005, Medical electrical equipment – Part 1: General requirements for basic

safety and essential performance
IEC 60601-1:2005/AMD1:2012

IEC 60601-1-3:2008, Medical electrical equipment – Part 1-3: General requirements for basic

safety and essential performance – Collateral Standard: Radiation protection in diagnostic X-

ray equipment

IEC 60601-2-44:2009, Medical electrical equipment – Part 2-44: Particular requirements for

the basic safety and essential performance of X-ray equipment for computed tomography

3 Terms and definitions

For the purposes of this document, the terms and definitions of IEC TR 60788, IEC 60601-1,

IEC 60601-1-3, IEC 60601-2-44, and the following apply.
---------------------- Page: 13 ----------------------
SIST EN IEC 62985:2020
– 8 – IEC 62985:2019 © IEC 2019

ISO and IEC maintain terminological databases for use in standardization at the following

addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
CTDI AT LONGITUDINAL POSITION Z
VOL
CTDI (z)
VOL

value quantifying the RADIATION OUTPUT at position z for the selected CT CONDITIONS OF

OPERATION
3.2
RECONSTRUCTION LENGTH

distance between the centre of the first reconstructed image and the centre of the last

reconstructed image, where the centres of the first and last reconstructed images are spaced

as far apart as possible given the CT CONDITIONS OF OPERATION for the PROTOCOL ELEMENT and

the width of the reconstructed images, being essentially the maximum range of reconstructed

images over the scan range for a given reconstruction section thickness
3.3
WATER EQUIVALENT DIAMETER AT LONGITUDINAL POSITION Z
D (z)

diameter, in cm, of a cylinder of water having the same averaged ABSORBED DOSE as the

material contained in an axial plane at longitudinal position z of the object scanned, calculable

for a material of any composition, and quantifying the ATTENUATION of any material in terms of

the ATTENUATION of water

Note 1 to entry: The average ABSORBED DOSE correlates with the average X-ray ATTENUATION. See [2].

Note 2 to entry: If it is not feasible for the RADIATION dose index monitoring software (RDIMS) devices to access

the ATTENUATION-based D (z) from the CT SCANNER or to calculate D (z) from the available reconstructed images,

W W

then estimates of D (z) can be made from the scanned projection radiograph using alternate methods [2] [3].

However, validation of the D (z) implemented by the RDIMS device shall be performed according to Clause 4.

W,IMP
3.4
WATER EQUIVALENT DIAMETER

arithmetic average of D (z) values at equally spaced z position intervals of ≤ 5 mm,

calculated over the RECONSTRUCTION LENGTH, for RDIMS systems or PROTOCOL ELEMENTS in

CT SCANNER where it is not possible to achieve ≤ 5 mm z position intervals, the smallest

the
available image interval
3.5
REFERENCE WATER EQUIVALENT DIAMETER AT LONGITUDINAL POSITION Z
D (z)
W,REF

D (z) calculated using the following equation and being calculated for each of the

reconstructed images for all pixels in the image corresponding to the PHANTOM being scanned

by means of the following equation:
 CT(x,y,z) 
pixel
D (z) = 2 +1 ×
W,REF  
1 000 π
 
x,y
where

CT(x,y,z) is the CT number of the pixel at cross-sectional position x,y and longitudinal

position z;
A is the area of the image pixel
pixel
---------------------- Page: 14 ----------------------
SIST EN IEC 62985:2020
IEC 62985:2019 © IEC 2019 – 9 –

Note 1 to entry: The D (z) is used to validate the suitability of the method implemented by the MANUFACTURER

W,REF
to calculate D (z).
3.6
IMPLEMENTED WATER EQUIVALENT DIAMETER AT LONGITUDINAL POSITION Z
(z)
W,IMP

D (z) calculated with the method implemented by MANUFACTURER for the calculation of SSDE

3.7
SSDE CONVERSION FACTOR AT LONGITUDINAL POSITION Z
f(D (z))

unitless, empirically-derived value relating the RADIATION OUTPUT delivered by the scanner (as

quantified using CTDI ) to the ABSORBED DOSE to soft tissue for a specific size PATIENT or

VOL

PHANTOM, determined for a specific-size CTDI PHANTOM, a specific anatomic region (i.e., head

or body), and a specific z-position within the scanned PATIENT or object, the calculation of

which is performed using the equations provided in Annex A
3.8
SIZE SPECIFIC DOSE ESTIMATE AT LONGITUDINAL POSITION Z
SSDE(z)

estimate of the average ABSORBED DOSE to the material contained in an axial plane at

longitudinal position z within the RECONSTRUCTION LENGTH, expressed in units of mGy:

SSDE(z) f (D (z))×CTDI (z)
w vol
3.9
SIZE SPECIFIC DOSE ESTIMATE
SSDE

arithmetic average of SSDE(z), calculated over the RECONSTRUCTION LENGTH at the same

z-positions as the corresponding D (z) values used to calculate D
W W:
1 n
SSDE × SSDE(z )
∑ i
i=1
where

n is the number of z positions (z , i = 1, 2, …, n) (within the RECONSTRUCTION LENGTH

4 Verification of method used to calculate D (z)
4.1 General

The purpose of Clause 4 is to provide a method to verify a MANUFACTURER's IMPLEMENTED

WATER EQUIVALENT DIAMETER AT LONGITUDINAL POSITION Z, D (z), against the REFERENCE

W,IMP

WATER EQUIVALENT DIAMETER AT LONGITUDINAL POSITION Z D (z). This verification compares

W,REF

a set of D (z) values calculated for water PHANTOMs and an anthropomorphic PHANTOM to

W,IMP
the corresponding set of D (z) values calculated for the same PHANTOMs.
W,REF
4.2 Characteristics of the water PHANTOMS

Each PHANTOM'S structural material thickness shall be the minimum practicable and shall have

a length of at least 10 cm:
• Small water PHANTOM

The small water PHANTOM shall be cylindrical and have an inner water diameter (d) of

14 cm ≤ d ≤ 20 cm.
• Large water PHANTOM
---------------------- Page: 15 ----------------------
SIST EN IEC 62985:2020
– 10 – IEC 62985:2019 © IEC 2019

The larger water PHANTOM shall be cylindrical and have an inner water diameter (d) of

28 cm ≤ d ≤ 34 cm.

These PHANTOM specifications shall apply unless otherwise stated in the ACCOMPANYING

DOCUMENTS, in order to accommodate minor variations from these specifications.
4.3 Characteristics of the anthropomorphic PHANTOM

The anthropomorphic PHANTOM shall be a representative of an average adult human from the

top of the head to the bottom of the pelvis. It shall have a comprehensive set of simulated

internal organs and bones designed to yield the CT NUMBERS of their anatomical counterparts.

The PHANTOM shall include a minimum of simulated soft tissue, lung, and bone.
PHANTOM may be utilized if, as a set, they are representative
More than one anthropomorphic

of average adult head, chest, abdomen and pelvis regions. In addition, verification with a

paediatric PHANTOM(S) may also be performed.
A description of the anthropomorphic PHANTOMS(S) used shall be provided in the
ACCOMPANYING DOCUMENTS.

NOTE If an end user is evaluating the accuracy of D (z) values, differences between D (z) and D (z)

W,IMP W,IMP W,REF

that are larger than the allowed tolerances (4.10) can occur if different PHANTOMS are used compared to those used

by the MANUFACTURER.
4.4 Generation of D (z) for the water PHANTOMS
W,REF

Scans of each water PHANTOM shall be used to obtain the axial images for the calculation of

D (z), generat
...

Questions, Comments and Discussion

Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.