Elsevier

Journal of Surgical Education

Volume 71, Issue 1, January–February 2014, Pages 14-17
Journal of Surgical Education

INNOVATIONS
A Low-Cost Surgical Application of Additive Fabrication

https://doi.org/10.1016/j.jsurg.2013.10.012Get rights and content

Objective

This study was used to test the feasibility of using additive fabrication techniques 3-dimensional (3D) printing to create personalized/patient-specific hepatic 3D physical models from clinical radiology studies for surgical resident education.

Design

Patient-specific imaging data from either computed tomography or magnetic resonance imaging scans, in Digital Imaging and Communications in Medicine format, were rendered and manipulated with computer software, translating the medical imaging data sets into useful 3D geometry files in stereo lithography format for 3D printing. A commercial third party was used to print the 3D models in laser sintered nylon, which provided access to expensive, industrial-grade, high-resolution 3-D printers at a low cost.

Results

Multiple patient-specific preoperative 3D physical models were printed of portal and hepatic venous anatomy at a cost of less than $100 per model.

Conclusion

Current 3D printing techniques can be used to create low-cost personalized/patient-specific hepatic 3D models from clinical radiology studies for surgical resident education.

Introduction

The ancients knew of the individual variation in hepatic anatomy. Early Mesopotamian cultures used the anatomical differences seen in the livers of sacrificed animals to divine the future. The Babylonians were famous for this hepatoscopy or haruspicy and the practice is mentioned in the Bible: Ezekiel 21:21. The Babylonians created physical models of the liver to aid this practice (Fig. 1).1

A principle tenet of modern hepatic surgery is a knowledge of the general liver vascular anatomy. Claude Couinaud in the 1950s made physical models of the liver vascular systems using a technique of polyvinyl acetone injected into the hepatic vein, hepatic artery, or portal vein of cadaveric livers and allowed to harden. The liver tissue was then dissolved with a dilute solution of hydrochloric or nitric acid. In 1954, Couinaud described the 8 liver segments in “La Presse Médicale,” also crediting the earlier work of Austrian anatomist Hugo Rex, who had previously described the main plane of the liver and the 4 hepatic sectors.2 Using the physical models, Couinaud saw the regular segmentation pattern that was constant from one liver to another. The different, patient-specific, variations in corrosion cast models have also been used and applied in split liver transplantation techniques.3

The patient-specific variation in liver anatomy can markedly increase the difficulty of major liver operations. The internal hepatic anatomy is complicated, asymmetrical, and variable. Understanding patient-specific spatial relationships among the liver segments and intrahepatic portal and hepatic veins is essential for safe surgical treatment. Intraoperative ultrasound is a useful modality during liver surgery for the localization of the vessels and tumors and confirmation of the dissection line on the liver parenchyma. However, 2-dimensional (2D) intraoperative ultrasound images must be reconstructed in a 3-dimensional (3D) context in the surgeon’s mind. Similar challenges remain in how to appropriately interpret 2D hepatic radiographic images for preoperative planning to visualize the extent of the hepatic veins through the hepatic parenchyma and the arborization of the intrahepatic structures from magnetic resonance imaging (MRI) or computed tomography (CT) scans.

The limitations of 2-dimensional radiologic scans have led to the development of 3D image-processing software tools dedicated to computer assistance in liver surgery.4 The virtual 3D rendering of liver structures was first reported in 1990, before the introduction of multidetector-row CT. The introduction of multidetector-row CT expanded conventional planar information to visually comprehensible 3D images. Automated 3D modeling of the hepatic vessels was first introduced by Marescaux et al. in 1998, and operation planning based on 3D reconstructions of the liver structures was first performed in virtual patients using a volume rendering system in 2000. Subsequently several high-cost software packages are available for computer-assisted liver surgery.4 Complicated liver structures, which surgeons previously had to imagine spatially based on 2D CT or MRI scans, can now be visualized as 3D images on video monitors. However, the advantages of current virtual computer models in education may be more imagined than real. The potential for dynamic display of multiple orientations provided by computer-based anatomy software may offer minimal advantage to some learners and, based on previous research, may disadvantage learners with poorer spatial ability. Learning from virtual objects may be more cognitively and perceptually demanding than learning from real objects. Virtual objects burden students with the need to form 3D mental representations from 2D representations on a computer screen. This burden is compounded by the impoverished sensorimotor cues provided by virtual objects.5, 6 Physical models may be more effective for students than computer-based 3D models or 2D textbooks.7, 8 Real models can provide physical form to digital information and facilitate the direct manipulation of digital data, taking advantage of human abilities to grasp and manipulate physical objects and materials. Our visual sense organs are steeped in digital information, but the windows to the digital world are usually confined to flat, square screens and pixels. Surgeons have developed sophisticated skills for sensing and manipulating their physical environments. However, most of these skills are not employed in interaction with the digital world today. Video representations can be manipulated with generic remote controllers such as mouses and keyboards, but interactions are inconsistent with our interactions with the rest of the physical environment and divorced from the way interaction takes place in the surgical world, being unable to take advantage of our dexterity or use our skills for manipulating physical objects. To take advantage of these haptic, interactive skills that are used in surgery our key idea was to give physical form to digital information to make the digital data directly manipulatable with our hands.9

Despite the ease of use and intuitive nature of real (nonvirtual) physical models, a limiting factor in the use of these physical models has been the lack of patient-specific anatomical accuracy. 3D printing is a relatively new form of data actualization, and the rapidly declining costs are reducing the barrier to entry into this technology. Additive fabrication techniques have already been used in presurgical planning and implant design in craniofacial, cardiovascular, and orthopedic surgery.10 Additive fabrication uses a digital file that describes an object in 3D space, the computer then translates the file over to a “printer” that lays down successive layers of accretive material (metal, plastics, ceramics, etc.) until a physical object is created. This pilot study wished to test the feasibility of creating patient-specific physical hepatic models from Medical imaging files in Digital Imaging and Communications in Medicine (DICOM) format.

Section snippets

Materials and Methods

The raw CT or MRI files (DICOM format) voxel data was accessed using TeraRecon (San Mateo, CA) software for segmentation and rough mesh model creation in stereo lithography format. The 3D models of the intrahepatic structures—portal veins and hepatic veins—were created by extracting neighboring voxels with a similar density. Second- and third-order divisions were modeled of each internal structure. Later, MeshLab (version 1.3.0, open source) software was used to clean up the mesh models, using

Results

Multiple patient-specific preoperative physical models were created of both portal and hepatic venous anatomy from patient data at a cost of less than $100 per model (FIGURE 2, FIGURE 3).The models can be used to demonstrate the operative techniques to educate the junior residents and students in a weekly multidisciplinary divisional conference where the upcoming elective cases are discussed by attending physicians, residents, and medical students.

Discussion

Much current success in elective liver surgery relates to the careful attention to the vascular anatomy of hepatic inflow and outflow. The general vascular anatomy of the liver was first outlined in 1654 by Francis Glisson and rediscovered and clarified by Hugo Rex in Austria and Claude Couinaud in France. However, hepatobilary surgery is also dependent on the understanding of individual, patient-specific variants of the general anatomy.

Medical imaging technologies have made great advances,

Acknowledgment

This project was supported by a UNC University Research Council Grant #3211.

The University of North Carolina Medical Center Institutional Review Board approved all procedures.

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