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Ann Thorac Surg 2007;83:1854-1857
© 2007 The Society of Thoracic Surgeons

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New Technology

Stereolithographic Models for Surgical Planning in Congenital Heart Surgery

^a Department of Cardiac Surgery, Ludwig-Maximilians-University, Munich, Germany
^b Institute of Micro Technology and Medical Device Technology, Technical University Munich, Garching, Germany

Accepted for publication December 4, 2006.

^_* Address correspondence to PD Dr Sodian, Department of Cardiac Surgery, Ludwig-Maximilians-University, Marchioninistr. 15, Munich, 81377 Germany (Email: ralf.sodian{at}med.uni-muenchen.de).

	Abstract

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Purpose: Currently we are exploring the impact of using rapid prototyping techniques for surgical planning and intraoperative orientation during the correction of complex congenital malformation.

Description: We studied a patient with a left abnormal subclavian artery and right descending aorta as a rare cause of dyspnea and dysphagia. The patient was examined by magnetic resonance imaging angiography. The image data were visualized and reconstructed. Afterward a replica of the malformation was fabricated using a rapid prototyping machine. In addition, a stereolithographic model of an intracardiac lesion (ventricular septal defect) was fabricated with data obtained from a computed tomographic scan.

Evaluation: Using data derived from a magnetic resonance imaging angiography or computed tomographic scan linked to proprietary software, we were able to create three-dimensional reconstructions of complex vascular pathology and intracardiac lesions. In addition, we fabricated replicas of congenital malformations using a rapid prototyping machine. The models could be sterilized and taken to the operating room for orientation during the corrective surgical procedure.

Conclusions: Stereolithographic replicas are helpful for choosing treatment strategies, surgical planning of corrections, and intraoperative orientation, and as demonstrations on life-like models for the patient.

	Introduction

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Complex congenital defects in pediatric patients often require surgical correction [1]. Although the surgical management of most congenital defects is quite straightforward, difficulties are commonly encountered in establishing preoperative data for optimal surgical planning and intraoperative orientation. The actual anatomic structure is sometimes unpredictable and different from that usually found in a particular defect [2].

	Technology

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To overcome this problem, we developed a new technique to fabricate a custom made model to recreate the complex anatomic structure of congenital heart disease using a rapid prototyping technique (ie, stereolithography). Stereolithography is a new technology that was originally used in engineering and industry to generate prototype models. By transferring this method to medicine it is possible to fabricate three-dimensional replicas of anatomic structures from computed tomography or magnetic resonance imaging (MRI) data of patients. This technology is now mainly used for craniofacial and orthopedic surgeries [3, 4].

In our current experiment we used stereolithographic models derived from standard MRI or computed tomography to create accurate and realistic models of complex congenital defects for preoperative assessment and intraoperative orientation. As a proof of the concept, we studied 2 patients. The first was a 16-year-old patient with a left abnormal subclavian artery and right descending aorta as a rare cause of dyspnea and dysphagia in a pediatric patient. Although the defect may require surgical correction, the optimal management of such cases is not clearly established [5]. In addition, we created a stereolithographic model from a 3-month-old patient with a subpulmonary ventricular septal defect showing the exact dimensions of the defect and the surrounding anatomic structures (eg, the pulmonary and aortic valves). In this situation, solid replicas may be helpful in choosing surgical treatment strategies for intraoperative orientation and in demonstrating the planned procedure in lifelike models for the patient.

	Technique

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We studied a patient with a symptomatic aberrant retro-esophageal left subclavian artery and right aortic arch. The patient had already undergone transection of the arterial ligament and showed a severe tracheal stenosis a few months after the initial operation. The patient was symptomatic and suffered from dysphagia and dyspnea. The diagnosis was established by MRI and bronchoscopy, as part of the normal clinical evaluation process (Figs 1A–1C). As indicated by the symptoms and the diagnostic findings, the patient required surgical treatment.

View larger version (56K): [in this window] [in a new window]   Fig 1. (A) Contrast-enhanced magnetic resonance imaging angiography in a patient with symptomatic aberrant retro-esophageal left subclavian artery and right aortic arch (arrow). (B) Three-dimensional segmentation of magnetic resonance imaging data of the patient with symptomatic aberrant retro-esophageal left subclavian artery and right aortic arch (arrow). (C) Tracheobronchoscopy of the patient with symptomatic aberrant retro-esophageal left subclavian artery and right aortic arch demonstrating severe tracheal stenosis.

The data (0.1 to 0.2 mm slices) was entered into the stereolithography machine (ZCorp, Burlington, MA), and a lumen replica of the heart and vascular malformation was created. In this device, the models were produced by inkjet printing technology using a three-dimensional printer. Using data derived from routinely performed MRI or computed tomography linked to the rapid prototype stereolithography equipment, we were able to fabricate a luminal replica of an aberrant retro-esophageal left subclavian artery and right aortic arch (Figs 2A, 2B).

View larger version (113K): [in this window] [in a new window]   Fig 2. (A) Stereolithographic model of the congenital defect (dorsal view): left subclavian artery (1), aortic diverticulum (Kommerell’s) (2), right descending aorta (3), right aortic arch (4), pulmonary vessels (5), right carotid artery (6), brachiocephalic vein (7), and left carotid artery (8). (B) Stereolithographic model of the congenital defect (frontal view): left subclavian artery (1), aortic diverticulum (Kommerell’s) (2), right aortic arch (4), pulmonary vessels (5), right carotid artery (6), left carotid artery (8), right ventricular outflow tract (9), left ventricle (10), left atrium (11), and right atrium (12).

View larger version (117K): [in this window] [in a new window]   Fig 3. Intraoperative use of the stereolithographic model.

The same technique was used to fabricate the model of a 3-month-old patient who was diagnosed with a ventricular septal defect (Fig 4). For this model, the data were obtained from routine preoperative computed tomographic scan. Afterward the cardiac defect was corrected in a routine fashion with a ventricular septal defect patch closure.

View larger version (131K): [in this window] [in a new window]   Fig 4. Stereolithographic model of a patient with an intracardiac lesion (3 months, male, subpulmonary ventricular septal defect): left ventricle (1), ventricular septum (2), right ventricle (3), and subpulmonary ventricular septal defect (probe inside) (4).

	Comment

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Currently there is little experience in using the rapid prototyping technology of stereolithography in the correction of congenital defects [7]. This experiment demonstrates that currently available MRI or computed tomographic technology and accurate three-dimensional models of the live anatomy of patients suffering from congenital defects can be fabricated.

Despite satisfactory long-term results in the correction of congenital heart defects, the surgical planning and intraoperative orientation are often difficult and associated with major limitations, particularly in cases with complex vascular anatomy or reoperations, or both, which are complicated by excessive scar tissue formation and fibrous strands. In such cases it is often not easy to clearly identify the anatomical structures and dimensions. To overcome these shortcomings our group applied rapid prototyping techniques to fabricate models of congenital defects and complex vascular pathology.

We do not believe that these models are necessary in all pediatric cases, but they allow the surgeon to better understand patient-specific three-dimensional anatomy. Moreover, being able to hold a model in one’s hand and examine it from different sides allows the surgeon and the interventionist to develop the optimal surgical approach and anticipate problems that may arise (Fig 3). The dimensions and distances can be easily identified and interventions or surgical procedures can be planned preoperatively. These experiments are proof of the concept and show that it is possible to fabricate stereolithographic models from routine preoperative MRI or computed tomographic scan for patients with intracardiac and extracardiac lesions. It was not expected that the use of the models would change the basic surgical plan or the surgical outcome. Moreover, this technique is currently not established or evaluated in cardiovascular surgery, but learning from other specialities (eg, maxillofacial surgery), stereolithography is useful in studying the pathologic features of the congenital defects and in the simulation of a surgical plan. One difficulty of the technique is the selection of correct segmentation values. This requires a multidisciplinary approach with radiologists, surgeons, and computer specialists cooperating to achieve perfect segmentation and finally a perfect anatomically correct model.

In conclusion, the method described is feasible for patients with complex cardiovascular pathology. The system provides great theoretical and practical advantages for surgeons, interventionists, researchers, and teachers, and may it be used as an explanatory model for demonstration to the patient. Further models of complex cardiovascular malformations are required to fully evaluate the usefulness of this technology in the correction of other congenital defects.

	Disclosures and Freedom of Investigation

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The stereolithographic models were purchased by the Institute of Micro Technology and Medical Device Technology (Technical University Munich). There was no additional funding necessary to perform the study. The authors performed free and independent development and evaluation of this new technology and had full control of the design of the study, methods used, outcome measurements, analysis of data, and production of the written report. The authors have no financial relationship to companies producing stereolithographic models.

	Acknowledgments

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We would like to thank Anne Gale, ELS, of the Deutsches Herzzentrum Berlin for editorial assistance in the preparation of the article.

	Footnotes

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^Disclaimer The Society of Thoracic Surgeons, the Southern Thoracic Surgical Association, and The Annals of Thoracic Surgery neither endorse nor discourage use of the new technology described in this article.

	References

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1. Castaneda A, Jonas R, Mayer JE, Hanley F. Cardiac surgery of the neonate and infant. Philadelphia, PA: W. B. Saunders Co; 1994.
2. Kirklin JW, Barrat-Boyes BG. Cardiac surgery. 3rd edit. New York: Elsevier Science; 2003.
3. Winder J, Bibb R. Medical rapid prototyping technologies: state of the art and current limitations for application in oral and maxillofacial surgery J Oral Maxillofac Surg 2005;63:1006-1015.[Medline]
4. Fukui N, Ueno T, Fukuda A, Nakamura K. The use of stereolithography for an unusual patellofemoral disorder Clin Orthop Relat Res 2003(409):169-174.
5. Loukanov T, Sebening C, Springer W, Ulmer H, Hagl S. Simultaneous management of congenital tracheal stenosis and cardiac anomalies in infants J Thorac Cardiovasc Surg 2005;130:1537-1541.[Abstract/Free Full Text]
6. Winder J, Bibb R. Medical rapid prototyping technologies: state of the art and current limitations for application in oral and maxillofacial surgery J Oral Maxillofac Surg 2005;63:1006-1015.[Medline]
7. Ngan EM, Rebeyka IM, Ross DB, et al. The rapid prototyping of anatomic models in pulmonary atresia J Thorac Cardiovasc Surg 2006;132:264-269.[Abstract/Free Full Text]
8. Poukens J, Haex J, Riediger D. The use of rapid prototyping in the preoperative planning of distraction osteogenesis of the cranio-maxillofacial skeleton Comput Aided Surg 2003;8:146-154.[Medline]

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Ralf Sodian Darius Rassoulian Bruno Reichart Sabine Daebritz Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Sodian, R. Articles by Daebritz, S. Search for Related Content PubMed PubMed Citation Articles by Sodian, R. Articles by Daebritz, S. Related Collections Congenital - cyanotic