Off-Topic Case Study: Medical Applications of Noncontact 3-D Scanning
Using 3-D scanning in the medical field is becoming more common, and the one thing all medical applications of 3-D scanning have in common (which is the greatest challenge as well) is the difficulty of accurately reproducing organic items typically found in medical applications, such as bones, teeth, or other body parts. They are very complex and amorphous shapes with free-form curves. Measuring such forms is nearly impossible and excruciatingly labor-intensive with manual or contact measurement methods.
However when it comes to amorphous shapes, laser scanners can capture an object’s complete geometry, digitally reproducing a highly accurate model in a very short time. 3-D laser scanning is extremely fast, accurate and thorough, and it is able to digitize the entire topography of whatever shape it sees. If the internal geometry of a part is needed, then computed tomography (CT) scanning fits the bill with its accuracy, ability to “see” inside parts, and nondestructive nature.
These types of noncontact scanning result in precisely digitized “point cloud” versions of the shape from which CAD models are made. The CAD model can be used to replicate, manufacture, fit, assemble, animate, test, demonstrate, simulate, and document the object for a virtually infinite array of innovative medical applications.
Laser Design Inc., a supplier of 3-D laser scanning systems has provided scanning systems specifically designed for customers with medical applications. GKS Inspection Services, Laser Design’s engineering services division, has regularly been called upon to perform scans for medical device or research organizations as well.
As medical devices have become more complex and designed with more internal electronic parts, GKS has acquired the capability to perform CT scans as well. It is an ideal measurement method for inspecting extremely complex parts and assemblies too difficult to measure with conventional touch probe or line-of-sight vision-based scanning technologies. Speed and precision make CT scanning a viable option for nondestructive testing of production line and critical components.
The Main Applications of Noncontact 3-D Scanning1. Device Development
One of the most prevalent uses for noncontact 3-D laser scanning is in creating new life-saving and life-enhancing devices, such as prosthetics. GKS has scanned various body parts for many different applications. In one project, small hand casts were scanned in order to create fully functional finger prosthetic devices.
The devices were body-powered, lightweight, and allowed the users to regain complete control of the flexion and extension movements of an artificial finger. 3-D digital CAD model files were needed to manufacture custom prostheses cost effectively for a larger market.
According to the prosthesis company’s owner, “Compared to manually measuring, the process of laser scanning cut 60% off the amount of time to make enough accurate measurements of the casts to create a CAD model. With more than 600 different variations of each finger-hand configuration, plus six different hand sizes, getting the correct measurements is incredibly labor intensive. I can’t think of an alternative to 3-D laser scanning that would provide similar results. The geometry is too amorphous to capture without laser scanning.”
GKS delivered highly accurate solid models (±.002” or .05 mm) since they are created directly from scan data. In the past, hand prostheses relied heavily on a fabricator’s artistic ability. They were visually realistic, but not functional with articulation and mobility. Today’s prostheses restore not only the look of the hand, but the function as well. Laser scanning is a technology that can capture the fine details of the hand to make the prosthesis fit comfortably and function perfectly.
When the fit of a device is critical to its function, 3-D laser scanning provides highly reliable data. For example, GKS was asked to scan a new mask-like breathing device used to prevent a sleeping disorder. A good seal on the user’s face was critical to the device’s successful function. The mask’s parts were made of different materials based on their purpose in the assembly. The part that made contact with the face was soft and pliable so it would be comfortable and stay in place, while the parts that delivered a stream of air were hard plastic.
Since laser scanning is noncontact, it was able to digitize all the parts of the unit, even the soft ones, without compressing and distorting the shapes. The CAD model was accurate and useful to the engineers so they could make modifications and test the design.
3. Rapid Manufacturing Laser Design created a fully automated laser scanning system to scan the ear impressions of hearing aid users. The ear impressions, created in the field by audiologists, are sent to the hearing aid maker who in the past had manufactured the final product using a manual process.
The laser scanning system set automatic scan parameters since the ear impressions’ size is quite uniform and then used specialized software to process the scan data of the impressions to make the digital model of the ear shell in a fraction of the time. The model is used to manufacture the ear shell for the hearing aid on a rapid prototyping (SLA or FDM) machine, in effect “mass customizing” the products.
This noncontact process significantly improved the fit of the aids inside the ear canal. A better, more comfortable fit resulted from automated laser scanning and reduced the chronically high return rates for the devices, which saved the hearing aid company a significant amount of money.
4. Device Redesign Another GKS client wanted to modify an existing model of a plastic resin heart to demonstrate a new cardiac device product. The company needed modifications on the unit to fit the new device and then to be able to manipulate it in the CAD software to create the demonstration piece. The design engineer noted that the heart model was a “tricky, amorphous shape which is difficult to scan with a contact process.” It also had an irregular internal, partially open cavity, which needed to be very accurate since that is where the new device would be inserted.
The most difficult challenge in scanning the heart model was the many small venous features. Larry Carlberg, GKS service bureau manager, says, “We received the resin model with the unnecessary items removed, but the intricate small features were still present. The ability to model the many small features and maintain a reasonable budget is a combination of the experience level of our modelers and our software’s advanced tools.”
The modeling process demanded attention to the tiny surface abnormalities. Otherwise the model would generate undesirable ripples on the surfaces. Once imported into CAD, the design company was able to add the necessary features. Then the data was exported to create a rapid prototype SLA model on which they could demonstrate the new cardiac device product to customers.
But the engineers realized that the geometry of the flow path was so complex that they could not be sure that it matched the original CAD model without stringent inspection. They thought about inspecting the part with a coordinate measuring machine (CMM) but realized that the number of points required to fully validate the 3-D surfaces was far more than it would be practical to capture using one-point-at-a-time contact methods.
GKS implemented a laser scanning process that generated a point cloud with the millions of points to accurately define the complex surface geometry of the part. GKS then created a graphical comparison of the manufactured part with the CAD model, while coding differences between the two in colors that indicate the magnitude of the variation from the design intent.
The engineers were able to instantly visualize the differences between the model and the molded part. Based on these laser scans, engineers made a number of modifications to the CAD model to match perfectly to the actual as-built part. The entire process of scanning the part and developing the difference map took less than two days and the cost for the inspection process was minimal. Compared to conventional CMM touch probe-based measurement, the turnaround for laser scanning was much faster and yielded highly accurate and complete results.
6. Training, Simulations and Animations With the advancement of computer-aided instruction (CAI) in the medical field, accurate anatomical models are essential. To train doctors on specific procedures, many body parts have been to create life-like simulations and animations depicting procedures and typical treatments. The realism of the images obtained from the scan data is astounding.
Medical devices can be digitized and procedures for fitting, assembly, and implanting them produced for teaching and training. Demonstrations are easily put together with the scan files, and even FEA studies can be run on the physical properties of the materials and devices.
To preserve and transmit knowledge to a wider base of practitioners, an anatomical library or database (of structures such as the spine, teeth, ears, hip joints, etc.) can be compiled for such training purposes, making life-saving surgeries, routine medical procedures and other manipulations safer for doctors and patients alike.
7. Reverse Engineering a Part with no CAD Data As with any type of physical part that is manufactured, sometimes no CAD data exists for a medical device. The part may be so old that it was originally manufactured in the days before digital models, or the CAD data may have been lost in time when a company was sold or product specifications changed hands. In any case, today’s manufacturing processes, including those that make advanced medical products, require a CAD model for tooling, molds, inspections of parts, and product designs or enhancements.
Laser scanning is a fast, accurate and automated way to acquire 3-D digital data and a CAD model of a part’s geometry when none is available. Re-creating complex free-form shapes is noncontact measurement’s best application. Both the positive and the negative version of a scanned part are easy to create, so no matter what part of a manufacturing process is lacking, 3-D laser scanning can provide the correct type of data file. Also, new features and updates can be integrated into old parts once the modeling is accomplished.
Laser Design / GKS Inspection Services