ISO/IEC 3532-1:2023

Information technology - Medical image-based modelling for 3D printing - Part 1: General requirements

This document specifies the requirements for medical image-based modelling for 3D printing for medical applications. It concerns accurate 3D data modelling in the medical field using medical image data generated from computed tomography (CT) devices. It also specifies the principal considerations for the general procedures of medical image-based modelling. It excludes soft tissue modelling from magnetic resonance image (MRI).

Technologies de l'information — Modélisation médicale à base d'images pour l'impression 3D — Partie 1: Exigences générales

General Information

• Status: Published
• Publication Date: 08-Jun-2023
• ICS: 25.030 - Additive manufacturing
• ICS: 35.240.80 - IT applications in health care technology
• Technical Committee: ISO/IEC JTC 1 - Information technology
• Drafting Committee: ISO/IEC JTC 1/WG 12 - 3D Printing and scanning
• Current Stage: 6060 - International Standard published
• Start Date: 09-Jun-2023
• Due Date: 24-Aug-2023
• Completion Date: 09-Jun-2023

Overview

ISO/IEC 3532-1:2023 - Information technology - Medical image-based modelling for 3D printing - Part 1: General requirements provides high-level requirements for producing accurate 3D data models from medical imaging for additive manufacturing in medical applications. The standard focuses on medical image-based modelling using CT (computed tomography) data, specifying principal considerations for general procedures (image acquisition, segmentation, 3D reconstruction, calibration and validation, and file formats). It explicitly excludes soft-tissue modelling from MRI.

Key topics and technical requirements

• Scope and terminology: Defines terms (voxel, segmentation, surface/volume models, Hounsfield unit, MPR, etc.) and abbreviated terms (CT, DICOM, STL, AMF, PACS, HU).
• Process flow overview: Breaks the 3D printing workflow into phases - image acquisition, segmentation, 3D modelling, and 3D printing - and outlines recommended reporting items (Annex A).
• Medical image acquisition (CT): Addresses requirements for acquiring CT image data suitable for modelling, emphasizing the need for consistent, high-quality source images.
• Segmentation: Requires clear documentation and control of the segmentation process used to isolate anatomy or implants from surrounding tissues.
• 3D reconstruction and visualization: Covers conversion of segmented raster/voxel data to surface/volume models suitable for visualization and additive manufacturing.
• Calibration and validation: Calls for calibration and validation of 2D-to-3D conversion workflows to ensure model accuracy for clinical use.
• File formats and data exchange: Discusses acceptable formats for 3D model exchange (e.g., STL, AMF) and the need to maintain traceability of source medical images (DICOM/PACS).
• Quality control and reporting: Emphasizes documentation, QC measures, and traceability throughout the imaging-to-printing pipeline.

Practical applications and target users

Applications enabled by ISO/IEC 3532-1:2023 include:

• Patient-specific surgical implants and prosthetics
• Surgical guides and fixtures
• Anatomical models for preoperative planning and simulation
• Educational models and device design validation

Primary users and stakeholders:

• Biomedical engineers and 3D printing technicians
• Clinical teams (surgeons, radiologists) involved in patient-specific device workflows
• Medical device manufacturers and service bureaus
• Software developers of segmentation and modelling tools
• Regulatory and quality assurance professionals seeking standard-aligned processes

Related standards

• ISO/IEC 2382 (Information technology - Vocabulary) - terminology used in the standard
• ISO/ASTM 52900 (Additive manufacturing - Fundamentals and Vocabulary) - additive manufacturing concepts referenced
• ISO/ASTM TR 52916 (informative reference for optimized medical image data for additive manufacturing) is noted in the Introduction as helpful complementary guidance.

This standard helps ensure consistent, traceable, and clinically appropriate workflows for converting CT medical images into accurate 3D models for additive manufacturing, supporting safer and more reliable patient-specific medical devices.

Standards Content (Sample)

INTERNATIONAL ISO/IEC
STANDARD 3532-1
First edition
2023-06
Information technology — Medical
image-based modelling for 3D
printing —
Part 1:
General requirements
Technologies de l'information — Modélisation médicale à base
d'images pour l'impression 3D —
Partie 1: Exigences générales
Reference number
© ISO/IEC 2023
© ISO/IEC 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
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CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
© ISO/IEC 2023 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and abbreviated terms . 1
3.1 Terms and definitions . 1
3.2 Abbreviated terms . 4
4 Overview of image processing for the medical industry . 5
4.1 Process flow . 5
4.1.1 3D printing process for medical applications . 5
4.1.2 Explanation of a typical use case (cranial implant case) . 5
5 General requirements . 6
6 Requirements of data processing .7
6.1 Medical image data flow . 7
6.2 Medical image acquisition/computed tomography scan . 8
6.3 Segmentation . 9
6.4 3D reconstruction and visualization . 11
6.5 Calibration and validation of 2D and 3D conversion .12
6.6 File format . 13
Annex A (informative) Reporting .14
Bibliography .15
iii
© ISO/IEC 2023 – All rights reserved

Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that are
members of ISO or IEC participate in the development of International Standards through technical
committees established by the respective organization to deal with particular fields of technical
activity. ISO and IEC technical committees collaborate in fields of mutual interest. Other international
organizations, governmental and non-governmental, in liaison with ISO and IEC, also take part in the
work.
The procedures used to develop this document and those intended for its further maintenance
are described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria
needed for the different types of document should be noted. This document was drafted in
accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives or
www.iec.ch/members_experts/refdocs).
Attention is drawn to the possibility that some of the elements of this document may be the subject
of patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent
rights. Details of any patent rights identified during the development of the document will be in the
Introduction and/or on the ISO list of patent declarations received (see www.iso.org/patents) or the IEC
list of patent declarations received (see https://patents.iec.ch).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see
www.iso.org/iso/foreword.html. In the IEC, see www.iec.ch/understanding-standards.
This document was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology.
A list of all parts in the ISO/IEC 3532 series can be found on the ISO and IEC websites.
Any feedback or questions on this document should be directed to the user’s national standards
body. A complete listing of these bodies can be found at www.iso.org/members.html and
www.iec.ch/national-committees.
iv
© ISO/IEC 2023 – All rights reserved

Introduction
This document was developed in response to the need for customization of 3D scanning and 3D printing
technology within the medical industry, which can be achieved by taking full advantage of information
and communication technology (ICT).
This document addresses the overview of medical image processing and requirements for image-
based modelling. 3D printing technology has caused a revolution in health care delivery. New classes
of medical devices embody the true meaning of personalized medicine. Medical device designers and
practitioners are able to practically and efficiently create devices that were very difficult or impossible
to create before. In addition to using 3D printing technology to create standard medical devices with
features like intricate lattice structures, clinicians and engineers work in conjunction to produce what
are known as patient-specific devices or patient-matched devices. These are medical devices designed
to fit a specific patient’s anatomy, typically using medical imaging from that patient. Anatomically
matched devices have very complex geometrical contours and shapes. Several challenges exist in the
design process between the input data and the final device design. Most of these steps definitely depend
on software-based management of medical images.
Overall, the world revenue from 3D printing technology in the healthcare industry is expected to grow
exponentially, yet very few guides exist for 3D printing for medical practice. Medical images from the
human body are different from solid objects due to the non-geometric nature of the human body. To
perform 3D printing for medical practice, an accurate and consistent approach for image processing and
data creation from medical images is needed. Standardization for 3D printing processes in medicine
is urgently required for education, diagnosis, neurosurgical treatment, developing simulation models,
medical equipment (including surgical guides) and surgical implantable devices in the clinical fields.
Regulatory bodies from several countries (US, Republic of Korea, etc.) have already published their
own guidelines for approval. However, those guidelines are not specifically designed for 3D printing
technology.
Applications of 3D printing in medicine are thriving, and include surgical simulation models, surgical
guides, educational models, surgical implants, etc. Those which are manufactured by 3D printing
technology require patient- and/or procedure-specific data (e.g. planned surgical technique and others)
and medical image data acquisition processing. Most of the processing of medical images for 3D printing
medical devices is software-based. In order to accurately and consistently visualize human body
anatomy, appropriate software-based modelling for 3D printing is needed. This document provides
requirements for software-based medical image processing for the purpose of producing 3D models for
3D printing. Valuable information related to optimized medical image data for additive manufacturing
can be found in ISO/ASTM TR 52916.
v
© ISO/IEC 2023 – All rights reserved

INTERNATIONAL STANDARD ISO/IEC 3532-1:2023(E)
Information technology — Medical image-based modelling
for 3D printing —
Part 1:
General requirements
1 Scope
This document specifies the requirements for medical image-based modelling for 3D printing for
medical applications. It concerns accurate 3D data modelling in the medical field using medical image
data generated from computed tomography (CT) devices. It also specifies the principal considerations
for the general procedures of medical image-based modelling. It excludes soft tissue modelling from
magnetic resonance image (MRI).
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.
ISO/IEC 2382, Information technology — Vocabulary
ISO/ASTM 52900, Additive manufacturing — General principles — Fundamentals and Vocabulary
3 Terms, definitions and abbreviated terms
For the purposes of this document, the terms and definitions given in ISO/IEC 2382, ISO/ASTM 52900
and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1 Terms and definitions
3.1.1
image acquisition
scanning of the structure of interest using computed tomography (CT), magnetic resonance imaging or
other three-dimensional imaging technology
3.1.2
slice distance
slice spacing
distance between the centre of the slices, which is calculated by the difference in the slice locations of
two adjacent slices
3.1.3
hard tissue
tissue which is mineralized and has a firm intercellular matrix (such as bone, tooth enamel, dentin and
cementum)
© ISO/IEC 2023 – All rights reserved

3.1.4
soft tissue
tissue that connects, supports or surrounds other structures and organs of the body, excluding hard
tissue (3.1.3)
3.1.5
solid organ
organ which has firm tissue consistency such as the heart, kidney, liver, lungs, pancreas, etc., excluding
hollow organs (such as the organs of the gastrointestinal tract) and tissue with liquid consistency (such
as blood)
3.1.6
pixel
picture element
smallest two-dimensional element of a display image that can be independently assigned attributes
such as color and intensity
[SOURCE: ISO/IEC 2382:2015, 2125999, modified — Notes to entry have been removed.]
3.1.7
voxel
volume element
smallest three-dimensional element in volume or volumetric (solid) modelling that can be independently
assigned attributes such as colour and intensity
[SOURCE: ISO/IEC 2382:2015, 2126000, modified — Notes to entry have been removed; "solid" has
been replaced by "volume or volumetric (solid)".]
3.1.8
vector data
vector image
vector model
digital description of 2D image or 3D model stored as a series of points and mathematical functions to
describe the geometric figure
[SOURCE: ISO 12651-1:2012, 4.139, modified — "image" has been replaced by "2D image or 3D model”.]
3.1.9
raster data
raster image
raster model
bitmap data
bitmap image
bitmap model
2D image or 3D model data formed by a set of picture elements (3.1.6) or volume elements (3.1.7)
arranged in a grid pattern
3.1.10
volume model
solid model
three-dimensional geometric model which deals with the solid characteristics of an object in order to
represent its internal structure as well as its external shapes
Note 1 to entry: See ISO/IEC 2382 for definitions of volume modelling and solid modelling.
Note 2 to entry: Volume model can be represented with raster model (3.1.9) or vector model (3.1.8).
© ISO/IEC 2023 – All rights reserved

3.1.11
surface model
boundary model
data set of a model which represents the surfaces of objects
Note 1 to entry: See ISO/IEC 2382 for definitions of surfacing and surface modelling.
3.1.12
facet model
faceted model
surface model (3.1.11) of which surfaces consist of group of polygons
Note 1 to entry: A triangle is widely used as a polygon.
3.1.13
segmentation
process of separating the objects of interest from their surroundings
Note 1 to entry: Segmentation can be applicable to 2D, 3D, raster or vector data (3.1.8).
3.1.14
3D visualization
presentation intended for human viewing of a scene on a flat display surface, using graphics techniques
to convey depth information and knowledge of the arrangement and shapes of the visualized scene in a
three-dimensional space
Note 1 to entry: The graphics techniques can include use of perspective, occlusion, stereoscopy, lighting and
environmental effects, and ability to navigate the viewpoint to alternate positions and orientations.
3.1.15
3D modelling
activity intended to create a digital representation of the form and arrangement of one or more 3D
objects in a three-dimensional space
Note 1 to entry: 3D models can contain geometric information such as mesh vertices, appearance, lighting, and
animation information. The created representation is a prerequisite to creating a 3D visualization (3.1.14) of the
modelled objects.
3.1.16
maximum intensity projection
MIP
scientific visualization method for 3D data that projects, in the visualization plane and with maximum
intensity, the voxels that fall in the way of parallel rays traced from the viewpoint to the plane of
projection
3.1.17
minimum intensity projection
MinIP
data visualization method that enables detection of low-density structures in a given volume
Note 1 to entry: The algorithm uses all the data in a volume of interest to generate a single two-dimensional
image. In other words, it consists of projecting the voxel with the lowest attenuation value on every view
throughout the volume onto a 2D image.
© ISO/IEC 2023 – All rights reserved

3.1.18
Hounsfield value
Hounsfield unit
integer representing the intensity of the image at each image point [pixel (3.1.6)] which originates from
the x-ray scanning process and in turn represents the image intensity, which depends on the density of
the tissue at that location
Note 1 to entry: Hounsfield values rise monotonically with tissue density but are not linearly proportional to
density.
Note 2 to entry: The highest range of biological tissue Hounsfield values is for cortical bone, and they can go even
higher for image artefacts such as metallic implants, metallic sections of a hospital bed included in the image, etc.
3.1.19
multiplanar reformation
MPR
two-dimensional reformatted images that are reconstructed secondarily in arbitrary planes from the
stack of axial image data
Note 1 to entry: Multiplanar reformation (MPR) allows images to be created from the original axial plane in
either the coronal, sagittal or oblique plane.
3.1.20
volume rendering
set of techniques used to display a 2D projection of a 3D discretely sampled data set, typically a 3D
scalar field
3.2 Abbreviated terms
2D two-dimensional
3D three-dimensional
AM additive manufacturing
AMF additive manufacturing file format
ANN artificial neural network
CAD computer aided design
CT computed tomography
DICOM digital imaging and communications in medicine
HU Hounsfield unit
PACS picture archiving communication system
QC quality control
ROI region of interest
STL stereolithography
SVM support vector machine
© ISO/IEC 2023 – All rights reserved

4 Overview of image processing for the medical industry
4.1 Process flow
4.1.1 3D printing process for medical applications
In general, the medical 3D printing processing flow can be divided into eight phases, as shown in
Figure 1.
NOTE Annex A contains a list of recommended items to be noted during the 3D printing process flow.
1) Image acquisition phase
In the image acquisition phase, medical images are acquired from medical imaging devices such as CT.
2) Segmentation phase
In the segmentation phase, the acquired medical images are segmented to fit the design purpose and
are processed to be divided (segmented) to extract a subset that would represent the part(s) of the
anatomy under consideration.
3) 3D modelling phase
In the 3D modelling phase, the segmented data representing the human tissue is converted
(reconstructed) into a 3D model optimized for 3D printing.
4) 3D printing phase
In the 3D printing phase, 3D printing is performed using the 3D model designed. For this phase 3D
model is processed for 3D printing by slicing, assigning build parameters, being oriented and placed
within the build space, and can have support structures generated.
5) Post-processing phase
In the post-processing phase, the 3D printed part is post-processed to become fit for actual medical use.
6) Quality control (QC) phase
In the QC phase, the 3D printed part is finally verified to meet all requirements (user/design/quality/
risk).
7) Clinical application and review phase
In the clinical application and review phase, the 3D printed part is reviewed as applicable to clinical
application by the healthcare practitioner.
8) Post-market phase
In the post-marketing stage, the 3D printed part is managed based on the post-sale market management
policy according to product life cycle issues such as tracking management/recall.
4.1.2 Explanation of a typical use case (cranial implant case)
Computed tomography (CT) is a common imaging modality for medical applications. For instance, for
patients with a skull defect visiting a neurosurgical clinic, CT has been known as the gold standard
for investigating bone-related problems. Figure 1 shows that the CT images are initially transferred to
the PACS server in DICOM file format. DICOM images have been used to reconstruct 3D image through
segmentation and 3D modelling by certain software. This 3D modelled image is transformed and
exported to design software as a stereolithography (STL) file. After completion and confirmation of
3D cranial implant by designing software, a metal AM machine builds this implant as designed. Post-
processing such as heat treatment, machining, cleaning and sanding is performed. Reverse engineering
© ISO/IEC 2023 – All rights reserved

is performed to confirm the completeness of the implant before delivery by 3D scanning and matching
to the original digital blueprint. After QC, the implant is packed, sterilized and delivered. An operation
is performed to cover the defect with the 3D printed cranial implant. For this medical 3D printing
process, accuracy and reproducibility should be considered. The accuracy and reproducibility of the
parts (anatomical model, surgical guides, implant, etc.) from medical 3D printed parts are affected
by the sum of errors introduced in each step during data flow. These steps can be image acquisition,
segmentation and any subsequent post-processing of the segmented images. This document covers
processes 1, 2 and 3 as shown in Figure 1, ending with a 3D model of the relevant patient anatomy for
use in multiple other later processes. Activities related to items for processes 4 - 8 are addressed by
ISO/TC 261.
Figure 1 — Typical workflow of medical 3D printing (example: cranial implant case)
5 General requirements
To conform to this document, all of the following items shall be considered and relevant information
shall be documented.
— The medical image acquisition protocol by
...