APPLICATION OF BIOMODELS FOR SURGICAL PLANNING BY USING RAPID PROTOTYPING: A REVIEW & CASE STUDIES

The application of rapid prototyping (RP) to surgical planning came as a natural extension of the development of the technology. Current high technology scanners analyzing biological samples present their data in a layered format providing a straightforward interface to the RP technologies. The highest spatial resolutions are available from CT and MRI scan data, but other modalities also provide valuable diagnostic information. Presenting the results in a physical 3D model, either scaled 1:1 or magnified, provides the medical user with invaluable insights beyond 2D data. Depth is a critical parameter in planning procedures. These techniques allow one to reproduce human anatomical objects as 3D physical models, which give the surgeon a practical impression of complex structures before a surgical intervention. This paper will focus on surgical planning and the development of prostheses in advance of invasive procedures. Biomodelling is an perceptive, user-friendly technology that facilitated diagnosis and operative planning. Biomodels allowed surgeons to rehearse procedures readily and improved communication between colleagues and patients. The paradigm shift from the visual to the visual-tactile representation of anatomical objects introduces a new kind of interface. The RP models are very well suited for use in the opinion and the precise preoperative simulations. The case studies included cover applications like the fabrication of custom implants & models for preoperating surgical planning. Keywords—Rapid Prototyping; Rapid Manufacturing; Biomodelling; Medical applications. INTRODUCTION Prior studies have recommended that biomodels increase patient education. The usefulness of biomodels for preoperative planning and intra-operative surgery compared to regular imaging modalities such as x-ray, CT and MRI has not been quantified. The aim of this study was to quantify surgeon’s perceptions on the usefulness of biomodels compared to standard visualization modalities for pre-operative planning and intra-operative anatomical reference. Additive fabrication (AF) is a relatively new concept that emerged during the last decade in order to describe a set of new or under development manufacturing methods, processes and technologies that function through material addition, in contrast to the established traditional cutting, forming or casting methods. Rapid Prototyping (RP) technologies are the most widely applied and known fabrication methods that are based on additive fabrication principles. Some of the major RP technologies used worldwide are Stereo lithography (SLS), Selective Laser Sintering (SLS), Fused Deposition Modelling (FDM), 3D printing (3DP), Laminated Object Manufacturing (LOM). Main applications of RP include the fabrication of various kinds of models and prototypes for concept evaluation and presentation as well as functional testing of new products, early in the product development process [1]. The continuous improvement of RP systems accuracy and materials, expand gradually their applications to other areas like medical applications. What makes RP particularly appealing for the above applications is the fact that compared to alternative manufacturing technologies, like for instance CNC machining, RP systems can fabricate parts of almost any geometrical complexity in relatively lower time and with reduced cost and without significant requirements in technical expertise. This kind of geometric flexibility, which is mostly a consequence of their additive nature, is the main reason that RP technologies are increasingly used. The medical branch in particular has attracted the attention of many researchers and scientists since the first introduction of RP technologies. The reported medical applications of RP technologies can be classified to the following categories:  Biomodelling, which involves the fabrication of physical models of parts of the human anatomy and biological structures in general, for surgery planning or testing.  Design and fabrication of customized implants for prosthetic operations, rehabilitation and plastic surgery  Fabrication of porous implants and tissue engineering Despite of their great flexibility and potential, RP technologies have not yet been widely adopted in the medical and health-care sector. International Journal of Innovative Research in Advanced Engineering (IJIRAE) ISSN: 2349-2163 Volume 1 Issue 6 (July 2014) http://ijirae.com _________________________________________________________________________________________________ © 2014, IJIRAEAll Rights Reserved Page 264 This can be attributed to the high cost and time required for the fabrication of corresponding models which at present can only be justified in relatively complex medical cases [2]. Besides time and cost, there is the issue of accuracy of RP systems, which is not sufficient for some applications due to poor or inaccurate medical imaging data. Nevertheless, RP technologies and AF in general have great potential in the area of medical and health-care applications due to their divergent features. II. LITERATURE REVIEW Muller et al. [3] investigated the usefulness of RP models of the skull in craniofacial and neurosurgical practice. RP biomodels of 52 patients, whose treatment required corrective/reconstructive cranioplasty or involved complex surgical operations, were fabricated. They report that SLS models help in better understanding of the anatomy, increase intraoperative accuracy, support accurate fabrication of implants, facilitate pre-surgical simulation and improve education of trainees. Kermer et al. [4] propose in their study an enhancement of the RP biomodelling approach by investigating the possibility of selectively colored RP biomodels. Their findings indicated that selectively colored models facilitate the management of ablative surgery and reconstructive procedures as well. The value of SLS surgical biomodels has also been shown in the case of reconstructing of complex orbital fractures in a study by Fan et al. [5]. Biomodelling of soft-tissue parts of the human body using RP, are rather rare in practice. This can be mainly attributed to the difficulty of separating the area of interest from the surrounding soft tissues, due to the relatively small differences of grayscale in medical scanned images. D’Urso et al. [6] have studied the possibility of biomodelling of cerebral aneurysms based on data obtained through CT angiography (CTA) and MR angiography (MRA). Their results indicate that the SLS models are sufficiently accurate and can be quite useful for surgical planning in complex cases or when the standard imaging is felt to be equivocal. In a similar study Wurm et al. [7] investigated the usefulness of cerebrovascular biomodels for aneurysm surgery with similar results. The feasibility of RP biomodelling for the replication of soft-tissue parts is shown in the study of Binder et al. [8]. They applied SLS for the construction of replicates of the mitral valve with good results. Although the results of the previous mentioned studies show the usefulness of biomodels for operation planning and rehearsal, the high fabrication cost and time involved is in most cases a major drawback. In particular, SLS and SLS models are very expensive and the associated cost can be justified only in rather complex cases. In order decrease the fabrication cost and time the utilization of 3D-printing is proposed, which is much less expensive and time-consuming [9]. But, biomodels are not only used in the pre-surgical phase but also they can be used in actual surgery, The images obtained by biomodels, can be utilized to guide the operation, assuring the accuracy and the quality of results. D’Urso et al. [10,11] investigated the possibility of using accurate SLS biomodels of the patient in planning and rehearsing stereotactic surgery. The method of stereotaxy is a minimally-invasive form of surgical intervention which uses 3D coordinates in order to locate specific targets and perform on them an operation like removal, implantation or injection. The location of the target is based on MRI/CT data and is determined with respect to a reference frame that is attached to the patient’s body. In order to simplify the method and enhance its accuracy, D’Urso et al. [10,11] employed SLS biomodels in a neurosurgical operation. They report that biomodel-guided stereotaxy offers significant advantages in terms of speed, simplicity, accuracy, and versatility but with the extra cost and time required for biomodel fabrication. Ngan et al. [12] also proposed the use of RP models, fabricated with SLS and 3DP, for preoperative and intraoperative planning of pulmonary atresia surgical treatment. They report that the surgeons found biomodels very useful in visualizing the vascular anatomy, but construction of virtual models was relatively labor intensive and required expert knowledge of the pulmonary vasculature. Another application of SLS models is presented by Starly et al. [13], in which the SLS model is used as a medium for the transfer of the anticipated skull geometry in a surgical guidance system of over-laying images. In this approach the 3D virtual model of the patient’s skull is constructed first through CT data interpolation. The virtual model is then split in two symmetrical parts, the undamaged half and the defective half that contains the suffering. Next, the defective part is discarded and replaced by the mirror image of the other half and a new virtual model of the skull with the required symmetry is constructed and fabricated with SLS. The SLS model is then scanned with CT and the obtained stack of images is transferred to the surgery guidance system, thus providing an image reference that accurately guides the surgeon during operation. SLS has also been used for the fabrication of surgical guides for the placement of dental implants, a restoration process that requires detailed planning and high accuracy. Sarment et al.