Design and fabrication of a realistic anthropomorphic heterogeneous head phantom for MR purposes

Abstract

Objective: The purpose of this study is to design an anthropomorphic heterogeneous head phantom that can be used for MRI and other electromagnetic applications.

Materials and methods: An eight compartment, physical anthropomorphic head phantom was developed from a 3T MRI dataset of a healthy male. The designed phantom was successfully built and preliminarily evaluated through an application that involves electromagnetic-tissue interactions: MRI (due to it being an available resource). The developed phantom was filled with media possessing electromagnetic constitutive parameters that correspond to biological tissues at ~297 MHz. A preliminary comparison between an in-vivo human volunteer (based on whom the anthropomorphic head phantom was created) and various phantoms types, one being the anthropomorphic heterogeneous head phantom, were performed using a 7 Tesla human MRI scanner.

Results: Echo planar imaging was performed and minimal ghosting and fluctuations were observed using the proposed anthropomorphic phantom. The magnetic field distributions (during MRI experiments at 7 Tesla) and the scattering parameter (measured using a network analyzer) were most comparable between the anthropomorphic heterogeneous head phantom and an in-vivo human volunteer.

Conclusion: The developed anthropomorphic heterogeneous head phantom can be used as a resource to various researchers in applications that involve electromagnetic-biological tissue interactions such as MRI.

Fig 1. A General workflow to design and fabricate an anthropomorphic heterogeneous head phantom using 3D printing.

Fig 2. Medical data acquisition and segmentation.

A 3T MRI scan with 1.0x1.0x1.0mm³ resolution was segmented and divided into eight individual tissues. Each segmented tissue is listed with the corresponding tissue segmentation color within the tissue legend. The pictured MRI dataset and segmented tissues are shown in the mid axial, coronal and sagittal views. Table 1 lists the physiological tissues that were used to classify the tissues in the legend.

Fig 3. Design and fabrication of physical phantom model.

Views of the shelled CAD files (A-C) which were developed in order to make volumetric cavities of the designated biological tissues that were segmented from a 3T MRI dataset. Views of the rapid prototype model (D) show the head phantom printed with stereolithography (SLA) resin. The physical head phantom dimensions are 30.5 cm tall, 25.4 cm long and 14.0 cm wide. The filling-ports are highlighted by arrows indicating the locations at which the fluids, resembling various tissue types, enter the phantom.

Fig 4. Comparison of phantoms to in-vivo volunteer using the scattering parameters of an RF coil.

Fig 5. Comparison of the experimentally mapped magnetic (B₁) field distributions.

Congruent slices of each phantom in comparison with the human volunteer are shown in all planar views. The color bar ranges from 0 to 48.9μT per 500V. The maximum B1 intensity level is set to the highest pixel value among each of the phantoms and the volunteer.

Fig 6. Comparison of phantom to in-vivo volunteer during an EPI stability scan at 7T MRI.