Medical Information: Making It Simple

Rapid Prototyping: How It Works

The first and most important step in the process of constructing a model is the procurement of the Computed Tomography Image (CT scan). The ultimate accuracy of the model is dependent on the detail of this initial scan. Next, the relevant data is sent to the service bureau (modeling facility) on a medium, such as a disk or tape containing the data, or over the Internet. In addition, other pertinent patient information and case history should be supplied so that the service bureau can design a model that best highlights the anatomy of interest. For example, models can be built in separate interlocking pieces so that internal anatomy is accessible, with multiple colors to highlight fractures, implants or foreign bodies, and can be scaled up to provide a better view of smaller features.

Rapid prototyping (RP) — sometimes called advanced digital fabrication or layered manufacturing — encompasses several major technologies that produce solid, three-dimensional objects from digital data. Objects are constructed by adding successive layers rather than by removing material in a cutting process. Two examples of RP processes are stereolithography (SLA) and three-dimensional printing (3DP).

SLA (Hull C: Apparatus for Production of Three-Dimensional Objects By Stereolithography. U.S. Pat. 4,575,330. March 11, 1986) involves photocuring of a polymer resin by ultraviolet laser. In general, the machine scans across the surface of a vat of liquid resin in a path described by the input CAD file, solidifying a thin cross-section of the model. As each cross-section is cured, the model is lowered incrementally into the supply vat. Liquid resin is then smoothed over the surface of the model to prepare it for the curing of the adjacent layer by the laser.

The 3DP process, which was developed at the Massachusetts Institute of Technology, can be considered an analog to ink jet printing of text or images on paper. Sachs E, et al.: Three Dimensional Printing: Rapid Tooling and Prototypes Directly from a CAD Model. J. Engin Industry, Vol. 114, Nov. 1992, 481-488. Ink-jet print heads inject a curing agent into a tray of powder stock, solidifying it into layers of approximately one millimeter. After each pass of the print heads, more stock is spread over the machine's print area and the tray is moved downward by the thickness of one layer in order to prepare for the deposit of the next layer.

The latest generation of RP devices enables selective coloration of volumes or surfaces. This allows for the creation of very descriptive models, particularly of objects composed of separate components. Such advancements expand the potential use of medical models into a wider array of application areas. A model provides something that no other imaging study can: a physical object from which to make measurements, a tactile replica about which to bend devices, a simulacrum on which to rehearse procedures, and a tangible aid with which to clearly and precisely communicate the exigencies of a specific case.

A Case Study

William Carpenter, a personal injury attorney in New Mexico, commissioned a medical modeling company to produce models as trial exhibits for one of his cases. Carpenter was representing a plaintiff who sustained a complex fracture of the pelvis as a result of a severe crushing injury. In order to make the CT scans he had on his client more understandable to the jury, he sent them to a service bureau to have a solid scale model of his client's injured pelvis made. The company was able to produce a replica in which the individual fracture fragments — of which there were more than a dozen — were separately colored to highlight the extent of the woman's injuries.

In addition to the physical model, he had the company generate a series of computer images, all based on actual CT scans, which showed the client's injury compared to a virtual model of a normal female pelvis. “The physical model is complemented by side-by-side movie clips of the normal and damaged pelvises rotating in unison,” Carpenter said. “The testifying doctor can then point to specific abnormalities and relate them to the patient's symptoms.”

Conclusion

As every courtroom-experienced attorney knows, demonstrative evidence helps judges and juries to focus on the evidence being presented and to better understand it. High technology image processing of medical scans and rapid prototype manufacturing can be of great help to attorneys on both sides of medical malpractice litigations to prove (or disprove) theories of injury causation, or to show the extent of medical injury a patient has sustained. Unlike artists' depictions of an injury, these models, because they are made from CT scans of the actual anatomy, pose little danger of being interpreted by jury members as overblown exaggerations of the actual injuries. In addition, as a tool already used by physicians in their practices, medical models have a built-in aura of authenticity. Just as models such as these are finding an increasing array of uses in clinical medicine, they will undoubtedly become more common fixtures in the courtroom. As Carpenter notes of the technology, “For the first time, a lay jury can understand a CT scan of the injury since it can be presented in a form that is easily recognizable and familiar to the average person.”

Communicating complicated medical information precisely and simply can make or break a legal case, but imparting this information in a compelling way is no easy task. Descriptions of complex medical procedures and conditions can be difficult for the average person to understand, let alone remember. Advances over the last decade in computer processing of medical images and rapid manufacturing techniques can provide the basis for an important development in medical-legal communication.

Using manufacturing techniques broadly known as rapid prototyping (RP), highly accurate, patient-specific solid replicas of patient anatomy can be created from medical image data. Such three-dimensional models are currently used in clinical applications like pre-surgical planning, customization of devices, and acquisition of informed patient consent. But these models are not only useful for diagnostic and other medical purposes; they can also be effective as demonstrative evidence.

While the use of these technologies has become common at hospitals across the country, attorneys are now finding that such imaging studies are routinely admitted into evidence when properly authenticated. Cantor IV: How to Use a SPECT Scan in the Trial of a Traumatic Brain Injury Case. J Virginia Trials Lawyers Assoc., Summer 1998. The technology creates exhibits that clearly illustrate the extent of injuries, results of surgery or the complexity of a congenital abnormality. Created directly from patient scans, physical models can be considered exact replicas of anatomy. Using RP techniques, these models can be built precisely to scale or can be enlarged, preserving relative dimensions, to clarify subtleties. As a result, they can be used as powerful legal demonstrative evidence that clarifies testimony and leaves jurors with a lasting impression.

Rapid Prototyping: How It Works

The first and most important step in the process of constructing a model is the procurement of the Computed Tomography Image (CT scan). The ultimate accuracy of the model is dependent on the detail of this initial scan. Next, the relevant data is sent to the service bureau (modeling facility) on a medium, such as a disk or tape containing the data, or over the Internet. In addition, other pertinent patient information and case history should be supplied so that the service bureau can design a model that best highlights the anatomy of interest. For example, models can be built in separate interlocking pieces so that internal anatomy is accessible, with multiple colors to highlight fractures, implants or foreign bodies, and can be scaled up to provide a better view of smaller features.

Rapid prototyping (RP) — sometimes called advanced digital fabrication or layered manufacturing — encompasses several major technologies that produce solid, three-dimensional objects from digital data. Objects are constructed by adding successive layers rather than by removing material in a cutting process. Two examples of RP processes are stereolithography (SLA) and three-dimensional printing (3DP).

SLA (Hull C: Apparatus for Production of Three-Dimensional Objects By Stereolithography. U.S. Pat. 4,575,330. March 11, 1986) involves photocuring of a polymer resin by ultraviolet laser. In general, the machine scans across the surface of a vat of liquid resin in a path described by the input CAD file, solidifying a thin cross-section of the model. As each cross-section is cured, the model is lowered incrementally into the supply vat. Liquid resin is then smoothed over the surface of the model to prepare it for the curing of the adjacent layer by the laser.

The 3DP process, which was developed at the Massachusetts Institute of Technology, can be considered an analog to ink jet printing of text or images on paper. Sachs E, et al.: Three Dimensional Printing: Rapid Tooling and Prototypes Directly from a CAD Model. J. Engin Industry, Vol. 114, Nov. 1992, 481-488. Ink-jet print heads inject a curing agent into a tray of powder stock, solidifying it into layers of approximately one millimeter. After each pass of the print heads, more stock is spread over the machine's print area and the tray is moved downward by the thickness of one layer in order to prepare for the deposit of the next layer.

The latest generation of RP devices enables selective coloration of volumes or surfaces. This allows for the creation of very descriptive models, particularly of objects composed of separate components. Such advancements expand the potential use of medical models into a wider array of application areas. A model provides something that no other imaging study can: a physical object from which to make measurements, a tactile replica about which to bend devices, a simulacrum on which to rehearse procedures, and a tangible aid with which to clearly and precisely communicate the exigencies of a specific case.

A Case Study

William Carpenter, a personal injury attorney in New Mexico, commissioned a medical modeling company to produce models as trial exhibits for one of his cases. Carpenter was representing a plaintiff who sustained a complex fracture of the pelvis as a result of a severe crushing injury. In order to make the CT scans he had on his client more understandable to the jury, he sent them to a service bureau to have a solid scale model of his client's injured pelvis made. The company was able to produce a replica in which the individual fracture fragments — of which there were more than a dozen — were separately colored to highlight the extent of the woman's injuries.

In addition to the physical model, he had the company generate a series of computer images, all based on actual CT scans, which showed the client's injury compared to a virtual model of a normal female pelvis. “The physical model is complemented by side-by-side movie clips of the normal and damaged pelvises rotating in unison,” Carpenter said. “The testifying doctor can then point to specific abnormalities and relate them to the patient's symptoms.”

Conclusion

As every courtroom-experienced attorney knows, demonstrative evidence helps judges and juries to focus on the evidence being presented and to better understand it. High technology image processing of medical scans and rapid prototype manufacturing can be of great help to attorneys on both sides of medical malpractice litigations to prove (or disprove) theories of injury causation, or to show the extent of medical injury a patient has sustained. Unlike artists' depictions of an injury, these models, because they are made from CT scans of the actual anatomy, pose little danger of being interpreted by jury members as overblown exaggerations of the actual injuries. In addition, as a tool already used by physicians in their practices, medical models have a built-in aura of authenticity. Just as models such as these are finding an increasing array of uses in clinical medicine, they will undoubtedly become more common fixtures in the courtroom. As Carpenter notes of the technology, “For the first time, a lay jury can understand a CT scan of the injury since it can be presented in a form that is easily recognizable and familiar to the average person.”