Designing a 3D Printed Model of the Skull-Base Using Simpleware Software

Posted on 31 May 2022 by Kerim Genc

 

3D printing is becoming increasingly important to neurosurgical applications, including new surgeon training, the simulation of complex anatomical pathways, pre-surgical planning and patient education. A recent paper from the University of Oxford, Oxford University Hospitals, and medical 3D printing specialists 3D LifePrints focuses on how they created a novel, anatomically accurate model of the skull base using Synopsys Simpleware technology. The value of the final model is that it enables the exploration of key neurovascular components and the trajectory of the facial nerve within the temporal bone.

Introduction

With gradual reductions in undergraduate anatomy curricula and access to cadaveric training, 3D printed anatomical models have become increasingly important as adjunctive teaching tools. For skull base surgeries, scanning and printing models offers a valuable resource for reducing the risk of damage from drilling into the temporal bone. The researchers in this paper therefore wanted to create a truly scalable 3D printed model of the skull base, including the relational anatomy of the brainstem, cranial nerves, and the neurovascular network. In addition, the model was designed to visualize the cochlea, labyrinth, and facial nerve within the temporal bone, making it more valuable as a training aid for students and more experienced surgeons.

Figure 1. 3D Reconstruction: three-dimensional rendering of segmented bone (A) and neurovascular structures (B).

Materials and Methods

While the full workflow for the simulation can be found in the researchers' paper, here is a brief summary of the materials and methods used:

  • The skull base and vascular components were reconstructed from CT and CT angiography scans of two separate subjects
  • Anonymized DICOM data was uploaded to Simpleware ScanIP software for semi-automatic registration, and segmentation of bone, cochlea, labyrinth, and the neurovasculature
  • Landmark and automated registration methods were used, with initial manual alignment between scans achieved by matching landmark pairs between images, before the registration was fine-tuned automatically using a greyscale surface matching algorithm
  • The segmentation of the five tissue classes was then achieved using specific Hounsfield Unit (HU) thresholds
  • Results were reviewed iteratively by the director of anatomy and head of neurosurgery to ensure accuracy, and segmented structures reconstructed in 3D images, and the remaining structures digitally constructed in Blender and reviewed by clinicians
  • Changes were made to ensure accurate alignment and a visible bony window to visualize the contents of the Internal Auditory Canal (IAC)
  • Materials were selected for 3D printing to be visually distinctive, durable and haptically representative of the anatomy, and for important cranial nerve trajectories to be visible through the boney structures
  • 3D printing was carried out using polymer jetting in a Stratasys J750 printer, which employs rigid polymers and elastomeric materials to generate functionally graded products
  • Total printing time was 40 hours, while post-processing included cooling, removal of support polymers, washing, coating, and labelling of all twelve cranial nerves

3D Printed Model

The final 3D printed model provides a cost-effective, reproducible resource for medical education, with no complications from successful printing, and accurate representations achieved of the neurovascular contents of the skull base. As the first 3D printed model of the skull base in the researchers' department, it already carries strong value for teaching, and an economical alternative to cadaveric specimens – the 3D printing process cost approximately $1,600 and took three days from printing to finalizing, with no storage or maintenance costs. In contrast, cadaveric specimens cost up to $2,000 to acquire, and a further $4,000-$6,000 to maintain.

Figure 2. Final model: 3D printed skull base model viewed from the medial side (A) and anteriorly (B).

Compared to previous 3D prints of the skull base, this new model is more comprehensive in terms of providing the trajectories of all twelve cranial nerves and their relationship to the anterior circulation within the skull base. The inclusion of a novel modifiable window for training also helps with pre-surgical planning for prospective patients, while the same 3D printing method can be used to generate miniature versions of the model as revision tools for students.

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