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Stereolithography: Turning Computer Models, CT and MRI Data Into Physical Models

By Paul Kakert & Reed Williams, M.D. E-mail:  pk@forensicmedia.com

You’re preparing your next case and have lined up your medical experts. You have poster exhibits of key documents, and have even prepared a realistic 3D computer animation illustrating your expert’s testimony. For many cases, you’re set. In others, you still need something to illustrate that one key issue that is critical for the jury to understand. You need a physical model of a particular part of the affected anatomy that your expert can point to or manipulate, and the jury can hold and view in great detail. With new technology, you can have real, physical models of practically any object represented or created in 3D (three-dimensions) by a computer. The uses in and out of the courtroom are endless.

The process is called Stereolithography. The condensed technical definition states that a computer directed ultra-violet laser solidifies photosensitive polymer in cross-sections, layer-upon-layer, to produce a physical plastic-based model. The fundamental process is based on the fact that liquid can be changed instantaneously into a solid state when exposed to ultraviolet radiation, much as silver changes state in normal photography film when exposed to visible light radiation.

 Medical Applications of Stereolithography

One way this technology is currently being used is in the medical field. Surgeons now use 3D physical models created with stereolithography from that same 2D data. Previously, they relied on 2D (two-dimensional) CT or MRI data to view affected anatomy in preparation for complex surgeries.

Through the process of preparing the computer file with the data to be imaged, the areas of anatomical interest (bone, tumor, soft tissue, or other) are identified. The model is then created in layers of only 0.006 of an inch. Different tissues (e.g. tumor) can be clearly defined by applying a different color to the area. The models can also be transparent, so it is possible to visualize structures within structures.

The majority of the work generated in this fashion is for the surgical fields of craniofacial reconstruction, neuro-surgery, and orthopedic surgery. Typical applications are for surgical reconstruction following severe trauma, tumor, gunshot wounds, birth defect, or revision of previous surgery. One of the key considerations to utilizing stereolithography, is that the final model can only be as accurate as the data provided. There are many factors that determine quality output. Consulting with a firm specializing in stereolithography can identify the areas of importance.

Forensic Applications of Stereolithography

Interpreting data from MRIs and CTs are just two ways of taking 2D information and creating real 3D models. Since the technology is also used for prototyping in the manufacturing and engineering fields, the process readily accepts computer aided drafting (CAD) files. Essentially, models pertaining to construction defects or faulty engineering resulting in product defects, can just as easily be created. Because the techniques used in forensic animations of product liability, accident reconstruction and other areas are so closely related to the CAD process, virtually all models used in forensic animations can be converted to 3D models as well.

Imagine the big picture…and the possibilities. There are techniques that allow accurate scanning of physical objects, such as defective products or equipment, for creation of 3D computer files. These computer files are used to create 3D animations depicting the events surrounding a product failure or other situation.

Stereolithography adds another, real world, dimension to the presentation of evidence. The same information used in creating the animation can be used to create complimentary 3D models for use as exhibits in trial. An effective presentation can now include video and or animation or the events, enhanced by a physical model used to isolate important areas for further discussion with expert witnesses, and to educate and persuade the jury. 

Cost of Creating Stereolithography Models

The cost is greatly affected by the subject and its complexity. For example, a medical model of a human skull is roughly $3,000. Costs can range from a few hundred dollars to a few thousand. The relatively low cost puts stereolithography models in the same category as large poster exhibits used every day in trials throughout the country. The process clearly breaks the 2D to 3D barrier for presentation of evidence.