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    Abstract
   Introduction
    Materials and me...
   Results
   Discussion
   Conclusion
   Acknowledgment
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Table of Contents
ORIGINAL ARTICLE  
Year : 2014  |  Volume : 17  |  Issue : 4  |  Page : 279-283
Echocardiography derived three-dimensional printing of normal and abnormal mitral annuli


1 Department of Anesthesia, Critical Care and Pain Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA
2 Department of Anesthesiology, Rhode Island Hospital, Brown Alpert School of Medicine, Providence, RI, USA
3 Division of Cardiac Surgery, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA

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Date of Submission17-Jan-2014
Date of Acceptance17-Aug-2014
Date of Web Publication1-Oct-2014
 

   Abstract 

Aims and Objectives: The objective of this study was to assess the clinical feasibility of using echocardiographic data to generate three-dimensional models of normal and pathologic mitral valve annuli before and after repair procedures. Materials and Methods: High-resolution transesophageal echocardiographic data from five patients was analyzed to delineate and track the mitral annulus (MA) using Tom Tec Image-Arena software. Coordinates representing the annulus were imported into Solidworks software for constructing solid models. These solid models were converted to stereolithographic (STL) file format and three-dimensionally printed by a commercially available Maker Bot Replicator 2 three-dimensional printer. Total time from image acquisition to printing was approximately 30 min. Results: Models created were highly reflective of known geometry, shape and size of normal and pathologic mitral annuli. Post-repair models also closely resembled shapes of the rings they were implanted with. Compared to echocardiographic images of annuli seen on a computer screen, physical models were able to convey clinical information more comprehensively, making them helpful in appreciating pathology, as well as post-repair changes. Conclusions: Three-dimensional printing of the MA is possible and clinically feasible using routinely obtained echocardiographic images. Given the short turn-around time and the lack of need for additional imaging, a technique we describe here has the potential for rapid integration into clinical practice to assist with surgical education, planning and decision-making.

Keywords: Echocardiography; Three-dimensional printing; Mitral valve

How to cite this article:
Mahmood F, Owais K, Montealegre-Gallegos M, Matyal R, Panzica P, Maslow A, Khabbaz KR. Echocardiography derived three-dimensional printing of normal and abnormal mitral annuli. Ann Card Anaesth 2014;17:279-83

How to cite this URL:
Mahmood F, Owais K, Montealegre-Gallegos M, Matyal R, Panzica P, Maslow A, Khabbaz KR. Echocardiography derived three-dimensional printing of normal and abnormal mitral annuli. Ann Card Anaesth [serial online] 2014 [cited 2018 Oct 19];17:279-83. Available from: http://www.annals.in/text.asp?2014/17/4/279/142062



   Introduction Top


Three-dimensional printing, once considered a high-end industrial undertaking, has become increasingly accessible and affordable to users. [1],[2] While there are multiple industrial uses, the medical applications of three-dimensional printing are beginning to be explored. [2] The applications of three-dimensional printing in medicine range from education to manufacturing patient-specific prosthetic materials in plastic surgery, ophthalmology, orthopedics and dentistry. [1] Such three-dimensional models have been generally used for surgical planning, and there are reports of implantation of three-dimensional printed models in patients. [3] In cardiac surgery, three-dimensional printing has so far been used to print models of congenital heart defects, cardiac tumors and aorta for purposes of surgical simulation/planning as well as device development. [4],[5],[6],[7] Currently, such three-dimensional printing is based on volumetric data acquired from computed tomography (CT) and magnetic resonance imaging (MRI). [8],[9] Generally, these techniques are expensive and time-consuming, limiting their clinical feasibility and possibility of ready adoption.

The use of three-dimensional transesophageal echocardiography (TEE) to acquire high-resolution dynamic images of cardiac valves has increased steadily during the past few years. The volumetrically acquired three-dimensional echocardiographic data can be readily geometrically analyzed immediately after acquisition. These echocardiographic data based three-dimensional analyses have demonstrated value in appreciating the static and dynamic conformation of the mitral annulus (MA) before and after repair. However, these are digital reconstructions only, and there is no available technology to provide an actual three-dimensional model of the MA based on these echocardiographic data. Ready availability of a patient-specific model of the MA prior to repair has the potential to aid in surgical planning and decision-making. Since TEE is routinely performed intraoperatively, use of echocardiographic data for three-dimensional printing of MA will bring it a step closer to be a practical technique. Therefore, using three-dimensional echocardiographic data routinely acquired during cardiac surgery, we reconstructed the MA and were able to generate patient-specific three-dimensional models of the MA.


   Materials and methods Top


Data from five patients undergoing cardiac surgery were acquired and analyzed as part of an ongoing institutional review board approved protocol of intraoperative echocardiographic data collection. Two patients with normal mitral valves, two with ischemic mitral regurgitation and one with myxomatous valve disease were included.

Echocardiographic technique

All three-dimensional TEE examinations were performed twice, once after induction of general anesthesia and prior to institution of cardiopulmonary bypass (CPB) and the second time after successful separation during a period of hemodynamic stability. All echocardiographic image loops were collected during a brief period of apnea and in the absence of electrical or motion interference over a period of 4-6 heart beats. High-quality data without imaging artifacts were exported in digital imaging for communication in medicine (DICOM) format to an off-line Windows-based desktop computer for geometric analysis.

Geometric analysis

The geometric analysis was performed in the commercial software Image-Arena ® (Tomtec GmbH Munich Germany). Within the Image-Arena ® software, the data were accessed by the 4 D-cardioview programs. The multi-planar sections of the data were displayed in the transverse, sagittal and coronal sections as shown in [Figure 1]. Using the pivot and tilt controls in the coronal section [Figure 1], bottom left], the MA was three-dimensionally marked in the transverse and sagittal windows [Figure 1], top]. This was done in eight successive planes at 45° intervals at end-systole by an experienced echocardiographer [Figure 1]. The resulting three-dimensional point cloud [Figure 1], bottom right] was assumed to be a valid representation of the MA. Cartesian coordinate data in x, y and z planes for these points were exported via comma separated file (CSV) format for geometric reconstruction of a solid model of the MA.
Figure 1: Multi-planar slices of the mitral valve. The transverse and sagittal planes are aligned along the antero-posterior (AP) and anterolateral-posteromedial (ALPM) diameters, with the coronal plane adjusted at the level of the annulus. Four points were identifi ed on the annulus at the origins of the AP and ALPM
lines, and four additional points were identifi ed by rotating the pivot and tilt controls by 45º. The resulting eight points representing the annulus are shown in the bottom right window


Click here to view


Solid model creation

Cartesian coordinates generated in Image-Arena were imported into Solidworks (Dassault Systemes, Waltham MA). The coordinates denoted eight contiguous points, each at 45° interval, representing the entire annulus. A three-dimensional spline curve, which is a polynomial function that takes into account all the points it connects, was then constructed to join the points [Figure 2]. This reconstruction yielded a curve that closely approximated the shape of the actual annulus.
Figure 2: Eight points identifi ed in Cardioview program were joined by a spline curve to yield a three-dimensional representation of the annulus

Click here to view


For this curve to be three-dimensional printable, a 1.75 mm thick, cylindrical surface was constructed along the length of the curve using a perpendicular plane offset [Figure 2]. This was essential to convert the annular model into the STL format that was three-dimensional printable.

Three-dimensional printing

Commercially available MakerBot Replicator 2 (MakerBot Industries, Brooklyn NY, USA) desktop three-dimensional printer was used. STL files generated in solid works were imported into custom software for the Replicator 2. The files were then exported to the printer; average time for printing one annulus was approximately 15 min.


   Results Top


Our initial experience with three-dimensional printing of the MA shows that it is a clinically feasible and practical technique. In our study, the acquired three-dimensional echocardiographic data were exported from the ultrasound system to an off-line workstation equipped with the geometric analytical software. In these cases, we were able to successfully three-dimensional print a MA within 30 min of acquisition of echocardiographic data. The models, which were printed to scale, implying complete conservation of size and measurements, closely resembled the anticipated actual geometric shapes of the tracked mitral annuli [Figure 3] and [Figure 4]. The observed geometric changes in the three-dimensional printed model of the repaired annulus confirmed the known significant changes in the MA after repair [Figure 5], [Figure 6], [Figure 7]. Similarly, the shape of post-repair printed prosthetics conformed to the specific annuloplasty devices used during the surgical procedure [Figure 5], [Figure 6], [Figure 7]. However, the quality of the three-dimensional printed prostheses depends upon the quality of the acquired three-dimensional echocardiographic data. In patients with suboptimal image quality and arrhythmias, the quality of geometric analyses and the subsequent three-dimensional printed model was also suboptimal.
Figure 3: This fi gure shows the anterior and posterior perspectives of a threedimensional printed normal mitral annulus (MA). The anterior and posterior horns of the MA can be easily identifi ed. (A: Anterior horn; P: Posterior horn)

Click here to view
Figure 4: This fi gure shows a comparison between the three-dimensional printed annulus of a patient without any mitral valve disorder as compared to a patient with chronic signifi cant ischemic mitral regurgitation. As compared to the normal, the ischemic annulus is dilated in the AP axis. Loss of non-planarity can be seen as fl attening and disfi gurement of the saddle shape. (A: Anterior Horn; P: Posterior Horn)

Click here to view
Figure 5: This fi gure shows three-dimensional printed mitral annuli of the same patient with ischemic mitral regurgitation before and after repair with a Physio-II annuloplasty device (Edwards Life sciences Irvine CA USA). In the pre-repair three-dimensional printed model, the mitral annulusis dilated in the AP axis and
fl attened. After repair there is a signifi cant reduction in the mitral annular size and increased non-planarity, which can be visually appreciated as augmentation of the saddle shaped. (A: Anterior Horn; P: Posterior Horn)


Click here to view
Figure 6: This fi gure shows three-dimensional printed mitral annuli of the same patient with ischemic mitral regurgitation before and after repair with a Medtronic Profi le three-dimensional annuloplasty device (Medtronic Minneapolis MN USA). In the pre-repair three-dimensional printed model, the mitral annulus is dilated in the AP axis and fl attened. After repair there is a signifi cant reduction in the mitral annular size and increased non-planarity, which can be visually appreciated as significant augmentation of the saddle-shaped

Click here to view
Figure 7: This fi gure demonstrates an en-face view of a dilated and deformed mitral annulus of a patient with Barlow's myxomatous degeneration of the mitral valve before and after repair. The mitral valve has been repaired annuloplasty performed with a Colvin-Galloway Future ring (Medtronic Minneapolis MN USA)

Click here to view



   Discussion Top


Application of three-dimensional printing has recently gained momentum in clinical practice. However, reports of reconstruction of patient-specific three-dimensional anatomical models have been generally limited to data drawn from CT and MRI. Besides being cumbersome and time-consuming, these techniques are geographically and temporally separated from the operating rooms, making them less feasible for everyday use in cardiac surgery. A significant step forward following Binder et al.'s previous description of three-dimensional printing of cardiac structures using echocardiographic data, our technique allows for enhanced resolution, quicker modeling speed and simplified image processing. [10]

The current mitral valve repair planning is based on initial echocardiographic assessment of pre and intraoperative echocardiographic images and later direct visualization of the valve on surgical exposure, after CPB. The selection of an appropriate size and type of annuloplasty ring for annular support is an integral component of this repair procedure. There are numerous sized rings, with variations in their characteristics, e.g, ring which are rigid, flexible, partially flexible, flat or saddle shaped and bands. The choice of the type of annuloplasty is generally subjective and based on the preexisting structural deformation (ischemic or myxomatous) of the annulus and is supposed to normalize the annular geometric conformation. Similarly, the sizing of the annuloplasty device varies amongst surgeons with little standardization. Currently, based on echocardiographic data, three-dimensional parametric or dynamic virtual models of MV can be generated to assist in surgical decision-making. These digital models are three- dimensional projections on a two-dimensional flat screen with obvious spatial limitations. In contrast, physical three-dimensional models allow haptic perception. Holding a model, turning it around and inspecting it from all angles allows for improved understanding of complex cardiovascular anatomy, making it superior to two-dimensional visualizations on a computer screen.

The ability to manufacture a patient-specific three-dimensional model of the MA prior to surgical repair in a clinically feasible fashion is an important clinical advance. Our technique has expanded the role of intraoperative three-dimensional TEE imaging during mitral valve surgery. The advantage of this technique is in that it is an actual patient-specific model of the MA and based on geometric data, dynamically acquired during the cardiac cycle. Contrarily, the surgical valve analysis and annulus sizing on CPB is performed on an arrested and physiologically un-loaded heart. The three-dimensional printed annular model can also assist in appreciation of changes in annular shape and size after repair. This knowledge can be extrapolated to more objective selection of annuloplasty devices. A specific actual three-dimensional model can provide the spatial orientation and knowledge of geometry to make more informed surgical decisions. This can also be invaluable information for pre-repair surgical planning and education.

The material used for three-dimensional printing in our printer is based on a bio-derived plastic, which is rigid and inflexible. In the future, it may be possible to use composite materials for three-dimensional printing which resemble MA in texture and flexibility. This could also open the door to manufacturing patient-specific annuloplasty rings, designed to impart the least amount of geometric distortion and stress, thus prolonging the durability of repair. The commercially available three-dimensional printers currently lack the resolution and technology to print leaflet surfaces satisfactorily. With appropriate materials and due technological advancement in time, it may be possible to three-dimensional print an entire mitral valve apparatus prior to surgery and practice various resection and annuloplasty techniques. The ability to use routinely acquired three-dimensional echocardiographic data is the first step in achieving this ultimate goal.


   Conclusion Top


Three-dimensional printing of the MA is possible and clinically feasible using routinely obtained echocardiographic images. Given the short turn-around time and the lack of need for additional imaging, our technique has the potential for rapid integration into clinical practice to assist with surgical education, planning and decision-making.


   Acknowledgment Top


The authors would like to thank the Ronald M. Weintraub family research fund for their support.

 
   References Top

1.Schubert C, van Langeveld MC, Donoso LA. Innovations in 3D printing: A 3D overview from optics to organs. Br J Ophthalmol 2014;98:159-61.  Back to cited text no. 1
    
2.Rengier F, Mehndiratta A, von Tengg-Kobligk H, Zechmann CM, Unterhinninghofen R, Kauczor HU, et al. 3D printing based on imaging data: Review of medical applications. Int J Comput Assist Radiol Surg 2010;5:335-41.  Back to cited text no. 2
    
3.Zopf DA, Hollister SJ, Nelson ME, Ohye RG, Green GE. Bioresorbable airway splint created with a three-dimensional printer. N Engl J Med 2013;368:2043-5.  Back to cited text no. 3
[PUBMED]    
4.Noecker AM, Chen JF, Zhou Q, White RD, Kopcak MW, Arruda MJ, et al. Development of patient-specific three-dimensional pediatric cardiac models. ASAIO J 2006;52:349-53.  Back to cited text no. 4
    
5.Sodian R, Weber S, Markert M, Loeff M, Lueth T, Weis FC, et al. Pediatric cardiac transplantation: Three-dimensional printing of anatomic models for surgical planning of heart transplantation in patients with univentricular heart. J Thorac Cardiovasc Surg 2008;136:1098-9.  Back to cited text no. 5
    
6.Schmauss D, Schmitz C, Bigdeli AK, Weber S, Gerber N, Beiras-Fernandez A, et al. Three-dimensional printing of models for preoperative planning and simulation of transcatheter valve replacement. Ann Thorac Surg 2012;93:e31-3.  Back to cited text no. 6
    
7.Sodian R, Schmauss D, Schmitz C, Bigdeli A, Haeberle S, Schmoeckel M, et al. 3-dimensional printing of models to create custom-made devices for coil embolization of an anastomotic leak after aortic arch replacement. Ann Thorac Surg 2009;88:974-8.  Back to cited text no. 7
    
8.Kim MS, Hansgen AR, Wink O, Quaife RA, Carroll JD. Rapid prototyping: A new tool in understanding and treating structural heart disease. Circulation 2008;117:2388-94.  Back to cited text no. 8
    
9.Jacobs S, Grunert R, Mohr FW, Falk V. 3D-Imaging of cardiac structures using 3D heart models for planning in heart surgery: A preliminary study. Interact Cardiovasc Thorac Surg 2008;7:6-9.  Back to cited text no. 9
    
10.Binder TM, Moertl D, Mundigler G, Rehak G, Franke M, Delle-Karth G, et al. Stereolithographic biomodeling to create tangible hard copies of cardiac structures from echocardiographic data: In vitro and in vivo validation. J Am Coll Cardiol 2000;35:230-7.  Back to cited text no. 10
    

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Correspondence Address:
Feroze Mahmood
CC-470, West Clinical Center, 1 Deaconess Road, Boston, MA 02215
USA
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0971-9784.142062

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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]

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