Published: March 22nd, 2013
Using modern plastic extrusion and printing technologies, it is now possible to quickly and inexpensively produce physical models of X-ray CT data taken in a laboratory. The three -dimensional printing of tomographic data is a powerful visualization, research, and educational tool that may now be accessed by the preclinical imaging community.
Three-dimensional printing allows for the production of highly detailed objects through a process known as additive manufacturing. Traditional, mold-injection methods to create models or parts have several limitations, the most important of which is a difficulty in making highly complex products in a timely, cost-effective manner.1 However, gradual improvements in three-dimensional printing technology have resulted in both high-end and economy instruments that are now available for the facile production of customized models.2 These printers have the ability to extrude high-resolution objects with enough detail to accurately represent in vivo images generated from a preclinical X-ray CT scanner. With proper data collection, surface rendering, and stereolithographic editing, it is now possible and inexpensive to rapidly produce detailed skeletal and soft tissue structures from X-ray CT data. Even in the early stages of development, the anatomical models produced by three-dimensional printing appeal to both educators and researchers who can utilize the technology to improve visualization proficiency. 3, 4 The real benefits of this method result from the tangible experience a researcher can have with data that cannot be adequately conveyed through a computer screen. The translation of pre-clinical 3D data to a physical object that is an exact copy of the test subject is a powerful tool for visualization and communication, especially for relating imaging research to students, or those in other fields. Here, we provide a detailed method for printing plastic models of bone and organ structures derived from X-ray CT scans utilizing an Albira X-ray CT system in conjunction with PMOD, ImageJ, Meshlab, Netfabb, and ReplicatorG software packages.
2. Image Acquisition and Reconstruction
3. Data Processing
Figure 1. 3D printed models of the lungs and skeletal features of a rat X-ray CT data set. Objects were printed using a ProJet HD 3000 (left), Shapeways Inc. (Center) or a Makerbot Replicator (right). The scale bar denotes 2 cm. Note that the scale bar in panel C is smaller than that of A and B, which reflects that in some cases the Makerbot must print an enlarged object in order to output sufficient detail.
Figure 1 depicts the final products for three methods of printing of the same in vivo rat CT data set. All three models consist of a cropped skeletal structure and removable lungs which were printed independently and pieced together. The model at left is the result of the ProJet HD 3000 high-resolution printer, created using translucent acrylic plastic. The object at center was produced using a third party company, Shapeways Inc., in which the skeletal structure was printed using nylon 12 white plastic while the respiratory structures were fabricated in purple. These first two models were printed to actual scale, measuring approximately 11 cm in length. The object at right was made using the MakerBot. The skeletal structure was printed using natural colored ABS (acrylonitrile butadiene styrene) plastic and the lungs with lime green ABS. Because of the resolution limits of the MakerBot, this model could not be printed to scale without degradation of fine structure like the rib cage. Instead, the model was scaled up by almost 2X using the "fill build space" option to obtain the desired visual detail, resulting in an object of 21 cm in length.
Figure 2. 3D printed models of a an ex vivo rabbit skull data set. The objects displayed were printed using a ProJet HD 3000 (left), Shapeways Inc. (Center) and a Makerbot Replicator (right). The scale bar denotes 1 cm.
Figure 2 shows the final products of each method of printing for the ex vivo rabbit skull CT data set. The model at left is the result from the ProJet HD 3000 high-resolution printer using translucent acrylic plastic. The model at center was printed in white nylon12 plastic through Shapeways Printing. The object at right was printed in white plastic using the MakerBot. All three objects were printed to scale and measure approximately 8.5 cm in length.
Figure 3. 3D printed models of a full rat X-ray CT data set. Objects were printed using a ProJet HD 3000 (left), and Shapeways Inc. (right). The scale bar denotes 1 cm.
Figure 3 depicts the final products for two methods of printing of a full in vivo CT data set of a rat. Both models consist of a complete skeletal structure (minus the tail) and removable lungs. The model at left is the resultant of a high-resolution printer, the ProJet HD 3000, printed using translucent acrylic plastic. The model on the right was printed using Shapeways Printing, with the skeletal structure created using white nylon12 plastic and the lungs in purple. These two models were printed to actual scale, measuring approximately 19 cm in length. Because of the intricate detail required, the full skeleton could not be printed with the MakerBot Replicator.
During the exploration of three-dimensional printing techniques, certain advantages and disadvantages were observed and are outlined in Table 1.
|Method of Printing
|Extremely fast, variety of color options, able to print in two colors, extremely inexpensive
|Lowest level of detail. Removal of support materials is slow (on the order of a couple hours).
|Varity of color options, variety of materials for printing, high level of detail, relatively inexpensive
|Two-week time to process and receive an order
|ProJet HD 3000
|Relatively quick turnaround, highest level of detail, high throughput, easy to remove support materials (wax).
|Most expensive up front cost, only one color option during practical use.
Table 1. Comparison of 3D printing technologies available to print CT data sets.
X-ray CT data sets of a living Lobund-Wistar rat and an ex vivo New Zealand White Rabbit skull were utilized to demonstrate the feasibility of 3D object production from pre-clinical biological data. Models were generated using three difference sources: 1)The popular Makerbot Replicator, 2) The third party company Shapeways Inc, and 3) The high-grade commercial ProJet HD 3000. Each printer was able to generate objects that satisfied the principle goal of enhanced data visualization.
During the process of printing pre-clinical CT data, the advantages and disadvantages of each method of printing were ascertained and summarized for the end user. The MakerBot Replicator is an inexpensive ($1,750) bench top solution that is accessible to virtually any lab around the globe. It can print in multiple colors with inexpensive inputs (a rat CT with lungs used about $3.50 in plastic). However, the Makerbot is limited by resolution, and thus some models will have to be enlarged for proper extrusion and visualization of intended structure. Shapeways Inc. provides an outstanding number of selections with regard to color and material. The models are high resolution, and robust. While their prices are about 10-fold higher than the MakerBot on a per unit basis (a rat CT with lungs was $41.61), a user can execute a limited number of jobs and avoid the upfront cost of purchasing a printer. The two-week lead time from Shapeways is a minor disadvantage. The ProJet HD 3000 provided outstanding models in terms of resolution and strength. We were fortunate enough to contract the printing of our objects on the ProJet HD 3000 at Innovation Park at Notre Dame (about $30 for a rat CT with lungs for labor and materials). Users may have difficulty with access to this type of equipment as they are priced in the range of $80,000, and it is cumbersome to print with multiple colors as well. Since each instrument/manufacturer provides a different metric to describe the resolution for object printing (Shapeways minimum level of detail = 0.2 mm, minimum wall thickness = 0.7 mm, 5 MakerBot slice thickness = 0.2-0.3 mm with a 0.4 mm nozzle, 6ProJet HD 3000 DPI = 656 x 656 x 800 with an accuracy of 0.025-0.05 mm ), a qualitative assessment of relative resolutions between each system suggests that both Shapeways and the ProJet HD system can print in high detail to scale, while some objects must be enlarged for successful use of the MakerBot. Collectively, all three methods are environmentally friendly and provide a convenient means to achieve facile production of highly detailed pre-clinical X-ray CT models.
Gradually, the technology of 3D printing has become more accessible as both costs and complexity have been minimized.8, 9 Now, literally anyone may print high-resolution, three-dimensional objects from digital files. These detailed three-dimensional objects can be useful tools for both educators and researchers alike. Furthermore, they provide a means of visual communication that assists in achieving a clearer understanding.10 For example, medical researchers can use specimen or patient-specific models to improve both communication and comprehension with their colleagues and patients.11 Although representation on 2D screens has come a long way, there is absolutely no replacement for the visual and sensory experience of holding a real object that is able to be held, rotated, examined and moved around. A model paired with an electronic data representation is even more powerful as it allows researchers to examine the physical object for regions of interest, and to find those areas on a computer model for further quantitative analysis. With proper data collection, surface rendering, and stereolithographic editing, it is possible to rapidly produce detailed, relatively inexpensive models from X-ray CT data. Here, we provide a detailed, step by step method for the production of a three-dimensional model from pre-clinical small animal data collected with an X-ray micro-CT. We acquired our in vivo and ex vivo CT data sets using an Albira image station, and performed subsequent processing with PMOD, ImageJ, Meshlab and Netfabb software packages. Finally, we provide detailed instructions to enable three-dimensional model printing with a range of commercial solutions. In each case, the end result is a model that provides a unique, hand-held, physical manifestation of the acquired tomographic data that would normally be restricted to a computer screen.
W. Matthew Leevy is a consultant for Carestream Molecular Imaging. Brian Stamile is a support engineer for MakerBot Industries.
We warmly thank the Nanovic Institute for European Studies, the Glynn Family Honors Program, Notre Dame Integrated Imaging Facility (NDIIF) and Carestream Health for financial support for this project. Research on rabbit cranial development supported by NSF BCS-1029149 to MJR.
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