Development and evaluation of 3D-printed phantoms for diagnostic and interventional radiography

3D-printed phantom of a pregnant woman in a CT

Background

Quality assurance in medical applications of ionising – i.e. especially high-energy – radiation on humans calls for test bodies, known as phantoms, to allow the measurement of image quality and dose distribution. Anthropomorphic phantoms replicate the human body as realistically as possible in terms of its anatomy and tissue composition. They are therefore a particularly good approximation of human patients. However, commercially available phantoms only represent people with standard body dimensions and are therefore unsuitable for certain groups of people. Especially for overweight individuals, children of different statures or even pregnant patients, the treatment parameters, image quality and dose deviate significantly from the values for standard patients.

Objective

The 3D-printing process used is a filament-based fused deposition modelling (FDM) technique. This offers numerous capabilities for producing phantoms, e.g. using plastic and composite materials that additionally contain stone, metal or wood particles, or for reducing the density of printed objects using suitable printing structures. The available 3D printer can process up to three different filaments at the same time.

Implementation

The project was divided into three stages of work:

• characterisation of tissue equivalence of commercially available 3D-printing materials
• comparison of 3D-printed and conventionally produced phantom parts
• validation of an individualised phantom using computer simulations based on a model of the same phantom.

For the first subproject, over 20 different 3D-printed samples were produced from a wide range of filament types and with different printing configurations (e.g. of the internal density). With regard to X-rays with energies such as those used in radiography, the attenuation and absorption properties of these samples were measured and compared with typical values for human tissue in order to classify suitable materials and printing configurations for the imitation of tissues in phantoms.¹

Parts of the thorax and chest of a conventionally produced phantom were then reproduced using suitable materials on the 3D printer. Examinations on a computed tomography (CT) scanner allowed comparison of the respective imaging properties. Measurements using thermoluminescence dosimeters (TLDs) allowed comparison of the dose distributions inside phantoms manufactured by different methods.²

In the last subproject, the previously developed methods were used to print the phantom of a pregnant woman based on a virtual human model. It was therefore possible to compare the measured dose in the foetus during a CT scan of the mother with results from computer simulations based on the virtual model of the pregnant woman. Simulations of this kind are currently the established method for dose estimations in pregnant women.

Results and summary

3D-printing materials can effectively replicate soft tissue and the internal bone structure in terms of their radiological properties. The only part of the bone for which it wasn’t possible to find a material with similar properties was the denser part (the cortical bone). The 3D-printed phantom parts were largely equivalent to the conventionally produced phantom parts in terms of their geometry, the tissue contrast and the absorbed dose. The measured foetal dose in the 3D-printed phantom of a pregnant woman for a CT scan agreed with the results of the computer simulation based on the corresponding virtual model.

The possibility therefore exists of creating individual phantoms for applications in diagnostic and interventional radiology using 3D-printed techniques. In terms of image quality and dose distributions, the achievable results are equivalent to established methods.

Publications

1. Kunert P, Trinkl S, Giussani A, Reichert D, Brix G. Tissue equivalence of 3D printing materials with respect to attenuation and absorption of X-rays used for diagnostic and interventional imaging. Medical Physics. Dec 2022;49(12):7766-7778.

2. Kunert P, Schlattl H, Trinkl S, Giussani A, Klein, L, Janich, M, Reichert, D, Brix, G. Reproduction of a conventional anthropomorphic female chest phantom by 3D printing: Comparison of image contrasts and absorbed doses in CT. Medical Physics. July 2023, 50(8):4734-4743