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Three-dimensional virtual model and animation of penile lengthening surgery
Journal of Plastic, Reconstructive & Aesthetic Surgery (2012) 65, e281ee285
Three-dimensional virtual model and animation of penile lengthening surgery Ruiheng Wang, Dongyun Yang, Shirong Li* Department of Plastic and Reconstructive Surgery, Southwest Hospital, Third Military Medical University, 30 Gaotanyan Main Street, Chongqing 400038, China Received 20 October 2011; accepted 8 April 2012
KEYWORDS Penile lengthening surgery; Three-dimensional model; Computer simulation; Magnetic resonance imaging; Surgical education; Patient tutorial
Summary Background: Three-dimensional digital models, animations, and simulations have been used in the plastic surgical field for surgical education and training and patient education. In penile lengthening surgery, proper patient selection and well-designed surgical interventions are necessary; however, no such surgical or patient education tool exists. Methods: Using magnetic resonance images as references, a preliminary three-dimensional digital model of the penis with its adjacent structures was constructed using Amira 5. This preliminary model was imported into Maya 2009, a computer modeling and animation software program, for processing to correct many defects. The refined model was used to create digital animation of penile lengthening surgery, including ordered steps of the procedure, using Maya 2009 and Adobe After Effects CS4. Results: A three-dimensional digital animation was created to illustrate penile lengthening surgery. All major surgical steps were demonstrated, including exposure, transversal incision of the fundiform ligament, partial division and release of the suspensory ligament. Conclusions: Three-dimensional digital models and animations of penile lengthening surgery may serve as resources for patient education to facilitate patient selection and resident education outside the operating room. ª 2012 British Association of Plastic, Reconstructive and Aesthetic Surgeons. Published by Elsevier Ltd. All rights reserved.
Introduction Although various penile lengthening procedures have been described,1 the most widely used technique is division of the penile ligaments in combination with an advancement
flap at the penile base. Penile ligaments are composed of the fundiform ligament and the suspensory ligament.2 Surgical division of these ligaments allows the penis to lie in a more dependent position and therefore gives the appearance that penile length has increased.3 Patients with
* Corresponding author. Tel.: þ86 13896181743; fax: þ86 (0)23 68765851. E-mail address: [email protected] (S. Li). 1748-6815/$ - see front matter ª 2012 British Association of Plastic, Reconstructive and Aesthetic Surgeons. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.bjps.2012.04.015
e282 a truly short penis would be candidates for penile lengthening surgery (e.g., patients with an erect penile length < 8 cm are recommended for the surgical intervention in our department).4 However, patients with normal-sized penises usually have unrealistic expectations regarding the outcome of surgery, and thus the satisfaction rates were lower in these patients.3 Therefore, for patients requiring penile lengthening surgery, an effective patient tutorial for correct information about the surgical procedure that could facilitate proper patient selection and a well-designed surgical intervention are necessary. Virtual reality techniques have been used in the plastic surgical field for patient education5 and surgical training and education.6 Virtual reality techniques enable surgeons to construct anatomically accurate, virtual models of human structures, on which surgical procedure animation and interactive surgical simulators can be developed.7 Animation can be used for patient5 and surgical education.8 Surgical simulators can provide opportunities for plastic surgery training6 or patient-specific, anatomically correct information which help surgeons visualize and plan procedures by viewing the predicted outcomes.9,10 As we have performed penile lengthening surgery for more than 10 years4,11 and have struggled with the problem of proper patient selection and resident education, we wanted to develop a virtual surgical animation with the aim of developing a tutorial aid for patients and a surgery education tool for residents. The quality of the animation or simulation is dependent on the fidelity of the digital model, as the digital models are the working materials on which these methods are constructed.7 Computed tomography (CT) images7,12 and photographs of histologic sections13,14 are two major data types used for reconstructing virtual human models with high fidelity. In this study, the authors constructed a threedimensional, high-fidelity virtual model of the penis with its adjacent structures using patient-specific magnetic resonance (MR) images. Based on this model, an animation of penile lengthening surgery was subsequently created for teaching surgical residents and providing patients with more comprehensible information about the surgery.
R. Wang et al.
Creation of a preliminary model of the penis and its adjacent structures A preliminary three-dimensional polygonal surface model of the penis with its adjacent structures was created according to the methods described by Flores et al.7 MR images were stored as DICOM format and then imported into Amira 5 (Vistage Imaging, Inc., San Diego, CA). Twodimensional sections from the MR image set were shown in three-dimensional space (Figure 1). Within this software platform, image segmentation and surface reconstruction were performed, and ultimately, a preliminary threedimensional polygonal surface model was obtained as an object file. Image segmentation refers to assigning to each pixel of the MR images a label describing to which structure the pixel belongs. Structures, e.g., lesser pelvis, cavernous body of the penis and urethra, and testis, were segmented manually for each two-dimensional section by two of the authors (Wang RH, Yang DY) using the Brush tool integrated within the Amira Segmentation Editor (Figure 2(a)). Surface reconstruction refers to generating a three-dimensional polygonal surface model for the region of interest after the image segmentation process (Figure 2(b)). The resulting surface model was exported into an object file containing three-dimensional data points of the preliminary polygonal surface model, topographic connectivity, and textural information of the surface model.7
Processing of the preliminary model The object file of the three-dimensional polygonal surface model constructed by Amira was imported into the Maya 2009 (Autodesk, San Raphael, CA) computer modeling and animation software for processing to be usable in an animation or simulation software platform because the preliminary surface model was 1) complex due to its large number of polygons, or dense with data points,7,10 2) absent of many anatomical structures that cannot be identified in MR images, and 3) lacking fidelity
Materials and methods Magnetic resonance imaging (MRI) MR images were obtained using a GE Signa HDx 3.0 Tesla system. A verbal consent was obtained from participant before MR images were taken. The participant was imaged using an axial sectioning plane beginning just above the pubic symphysis and extending below the testis in the rest position. The following MRI parameters were used for the participant: 1) Fast spin-echo pulse sequence 2) T2-weighted imaging (repetition time msec/echo time msec Z 4000/103) 3) Slice thickness Z 3.0 mm 4) Spacing Z 0 mm 5) Field of View Z 44 cm 44 cm 6) NEX Z 4
Figure 1 The utility of Amira as a platform for viewing the MR images. A serial two-dimensional section from the MR image set is shown. A parasagittal section of the penis and testis is circled in red. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
3D model of penile lengthening surgery
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Figure 2 (a): Sample image of the segmented MR image within Amira 5. (b): Preliminary three-dimensional surface model of the penis with its adjacent structures constructed by Amira. Right lesser pelvis is rendered transparent to illustrate underlying anatomical structures. This preliminary model required processing to be usable in an animation or simulation software platform. B Z bladder; CC Z corpora cavernosa; CS Z corpus spongiosum; P Z prostate; R Z rectum; T Z testis.
due to the low quality of its textural surfaces. To correct these defects, Maya 2009 software and Photoshop CS4 (Adobe Systems, Inc., San Jose, CA) were employed. First, the preliminary model was smoothed and simplified in Maya. Using the NEX Quad Draw tool combined with the Slide option integrated within NEX (http://draster. com/nex-1.5/overview.html), a plugin for Maya, meshes of the preliminary surface model were resurfaced. The resulting surface model had a significantly decreased density of data points while still preserving the complex topographic connectivity (Figure 3(a)). After smoothing and simplifying processing, models of the anatomical structures absent in the preliminary model, such as the penile fundiform ligament, penile suspensory ligament, nerves, blood vessels, and other significant structures, were constructed in Maya after a literature review2,15,16 (Figure 3(b, c)). The Chinese Visible Human dataset17 was also used as a reference in creating some of the models. Finally, textures were added to all tissue surfaces to maximize the fidelity of the model. Textures were artistically created de novo in Photoshop CS4 (Figure 3(b, c)).
Creation of surgical animation Surgical animation was created in Maya according to the methods used previously by Flores et al.8 Briefly, a playblast was first constructed, after which incisions of the skin and the penile ligaments were made using Maya’s Split Polygon tool and soft-tissue deformations were made using Maya’s Cluster Deformer tool. Once the playblast was completed, refined adjustments were performed on the camera angle, shading, and light sources. Finally, the rendered frames were composited together to create a completed procedure animation using After Effects CS4 (Adobe Systems; Video 1, Supplemental Digital Content 1, which illustrates an animation of penile lengthening surgery). Supplementary video related to this article can be found at doi:10.1016/j.bjps.2012.04.015.
Results A preliminary three-dimensional polygonal surface model of the penis with its adjacent structures was constructed by Amira 5 using MR images as references (Figure 2). As this preliminary model was 1) complex due to its large number of polygons, 2) absent of many anatomical structures that cannot be identified in MR images, and 3) lacking fidelity due to the low quality of its textural surfaces, we employed Maya 2009 and Photoshop CS4 to correct these defects. The refined model contained 1) a decreased number of polygons, 2) high-fidelity textural surfaces, and 3) all major anatomical structures relevant to penile lengthening surgery (Figure 3). According to the findings by Hoznek et al,2 in the refined model, the penile ligaments consist of two separate ligamentous structures: the fundiform ligament, a lax fibrous layer attached above to the linea alba of the anterior abdominal wall that splits into two bands that pass on each side of the penis and unite inferiorly; and the suspensory ligament, which stretches between the pubic symphysis and the tunica albuginea of the corpora cavernosa (Figure 3(b)). The neurovascular bundle (NVB) descends along the posterolateral border of the prostate and has two divisions: cavernous nerve and corpus spongiosum nerve. The branches of the cavernous nerve penetrate the tunica albuginea of the corpora cavernosa around the hilum of the penis, and send connecting fibers to the penile dorsal nerve. The corpus spongiosum nerve is a continuation of the posterolateral NVB, and eventually reaches the corpus spongiosum bulb15,16 (Figure 3(c); Video 2, Supplemental Digital Content 2, which illustrates a model of the penis with its adjacent structures.). Finally, based on the model, a three-dimensional digital animation was developed to illustrate penile lengthening surgery. All major surgical steps that we previously reported4 were observed, including a ‘þ’ shaped skin incision, exposure, transversal incision of the fundiform ligament, partial division and release of the suspensory ligament (Video 1, Supplemental Digital Content 1, which illustrates an animation of penile lengthening surgery.). The suspensory ligament should be divided close to the pubic symphysis to
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R. Wang et al. avoid injuring the nerves and blood vessels which course along the dorsal surface of the penis. It was reported that the border length of suspensory ligament to the pubic symphysis was 2e4 cm.2,18 We have not attempted to cut the suspensory ligament until all midline attachment has been freed as has been described by Li et al.3 From our experience, partial division (1/3 to 1/2 of the length, or 1e1.5 cm) would be acceptable to avoid leading to penile instability or an altered erectile angle4 (Video 1, Supplemental Digital Content 1, which illustrates an animation of penile lengthening surgery.). We propose that the model of the penis with its adjacent structures and the animation of penile lengthening surgery can be used to teach surgical residents and provide patients with more comprehensible information about the surgery to facilitate doctorepatient communication. Supplementary video related to this article can be found at doi:10.1016/j.bjps.2012.04.015.
Discussion
Figure 3 (a): The meshes of the preliminary model were resurfaced using the NEX Quad Draw tool combined with the Slide option integrated within NEX in Maya to decrease the number of polygons. (b): Layers and ligaments of the penis. c: Left posterolateral view of intrapelvic organs, the neurovascular bundle (NVB) descends along the posterolateral border of the prostate (P) and has two divisions: cavernous nerve (CN) and corpus spongiosum nerve (CSN). The CN penetrates the corpora cavernosa and sends connecting fibers to the penile dorsal nerve (DN) which originates from the pudendal nerve (PN). The CSN reaches the corpus spongiosum bulb. CA Z cavernosal artery; DA Z penile dorsal artery;
The use of computer modeling, animation, and simulation is beneficial to plastic surgery, particularly in the area of craniofacial surgery. Three-dimensional model of craniofacial anatomy has been developed, which can be used for anatomical study by medical students. Complex anatomical concepts can be more readily comprehended in dynamic three-dimensional model than from a static, twodimensional textbook.7,19 Animations have been created to illustrate a series of procedures in craniofacial surgery. Transparency was used in these animations to display underlying anatomy that is rarely visible during an operation but is critical to the understanding of the procedure itself.8,12 Animation has also been created to demonstrate the aging process of the face and the associated esthetic surgical procedures.13 In addition, an interactive digital education aid based on virtual animation was developed for breast reconstruction patient. The animation in this aid provides patient with a tutorial regarding the treatment, allowing them to make more informed treatment decisions.5 Concerning surgical simulation, a real-time surgical simulator with haptic feedback has been developed for planning and performing cleft lip repair.10 Simulation also provides residents a means to practice anatomical identification for cleft lip surgery without the risks associated with training on a live patient. However, we believe that many other areas of plastic surgery, such as genital surgery, would also benefit from surgical animation and simulation. Although various penile lengthening procedures have been described, these procedures are still considered highly controversial because questions regarding proper patient selection, methods, and effectiveness exist and the operative techniques and assessment of the results have not yet been standardized.20 As we have performed penile lengthening surgery for more than 10 years,4,11 and have
DDV Z deep dorsal vein; DF Z deep fascia; DN Z penile dorsal nerve; FL Z fundiform ligament of penis; SDV Z superficial dorsal vein; SF Z superficial fascia; SL Z suspensory ligament of penis; U Z urethra.
3D model of penile lengthening surgery faced the problems of proper patient selection and resident education, we created a virtual surgical animation with the aim of developing a tutorial aid for patients and a surgery education tool for residents. With regard to proper patient selection, although Spyropoulos et al21 introduced a novel questionnaire for identifying the most suitable candidates for penile augmentation phalloplasty surgery, busy surgeons may provide insufficient or perhaps overly technical information. As virtual surgical animation can provide comprehensible information about the surgery, the combination of animation with the questionnaire and other specific clinical tools can be a more reasonable strategy for patient selection. For resident surgery education, animation is designed to supplement rather than replace operating room training. By providing efficient training outside the operating room, the surgeon will be well prepared for efficient training inside the operating room.8 To use virtual reality techniques in surgery, Flores et al7,8 described a novel process through which construction of a three-dimensional digital model is the first step, followed by the creation of animation or simulation based on the model. CT scan images7,12 and photographs of histologic sections13,14 can be used for constructing digital models. In this present article, patient-specific MR images were used for creating the digital model because MRI provides more information about soft-tissue structures than CT. The effects of varying slice thickness (1-mm, 3-mm, 5-mm) on the MR images were compared in a preliminary experiment. The images with 1-mm slice thickness have lower signal-tonoise ratio than that with 3- and 5-mm slice thickness. In addition, the anatomical details imaging is better in 3mm images than 5-mm images. Thus, we constructed the preliminary model using 3-mm slice thickness MR images as references. The long-term goals of this research are to create a real-time surgical simulator with haptic feedback for planning and performing penile lengthening surgery and provide residents a means to practice the procedure. The current study focuses on an accurate modeling of the anatomy of the penis with its adjacent structures and the creation of a penile lengthening procedure animation. The development of a penile surgery simulator is expected in future research.
Conclusions A three-dimensional digital model of the penis with its adjacent structures and an animation of penile lengthening surgery were constructed. The animation may serve as a resource for patient tutorials to facilitate patient selection and for resident education outside the operating room.
Conflicts of interest The authors have no conflict of interest to disclose.
Funding This work is supported by the National Natural Science Foundation of China, NO. 30973133.
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References 1. Dillon BE, Chama NB, Honig SC. Penile size and penile enlargement surgery: a review. Int J Impot Res 2008;20: 519e29. 2. Hoznek A, Rahmouni A, Abbou C, et al. The suspensory ligament of the penis: an anatomic and radiologic description. Surg Radiol Anat 1998;20:413e7. 3. Li CY, Kayes O, Kell PD, et al. Penile suspensory ligament division for penile augmentation: indications and results. Eur Urol 2006;49:729e33. 4. Shirong L, Xuan Z, Zhengxiang W, et al. Modified penis lengthening surgery: review of 52 cases. Plast Reconstr Surg 2000;105:596e9. 5. Heller L, Parker PA, Youssef A, et al. Interactive digital education aid in breast reconstruction. Plast Reconstr Surg 2008;122:717e24. 6. Rosen JM, Long SA, McGrath DM, et al. Simulation in plastic surgery training and education: the path forward. Plast Reconstr Surg 2009;123:729e38. discussion 739e740. 7. Flores RL, Deluccia N, Grayson BH, et al. Creating a virtual surgical atlas of craniofacial procedures: part I. Threedimensional digital models of craniofacial deformities. Plast Reconstr Surg 2010;126:2084e92. 8. Flores RL, Deluccia N, Oliker A, et al. Creating a virtual surgical atlas of craniofacial procedures: part II. Surgical animations. Plast Reconstr Surg 2010;126:2093e101. 9. Pieper SD, Laub Jr DR, Rosen JM. A finite-element facial model for simulating plastic surgery. Plast Reconstr Surg 1995;96: 1100e5. 10. Schendel S, Montgomery K, Sorokin A, et al. A surgical simulator for planning and performing repair of cleft lips. J Craniomaxillofac Surg 2005;33:223e8. 11. Li S, Tao L, Wang Z, et al. Postoperative hydrophallus after penile lengthening: an experimental and clinical study. Plast Reconstr Surg 2007;119:768e70. 12. Cutting C, Oliker A, Haring J, et al. Use of three-dimensional computer graphic animation to illustrate cleft lip and palate surgery. Comput Aided Surg 2002;7:326e31. 13. Smith DM, Aston SJ, Cutting CB, et al. Applications of virtual reality in aesthetic surgery. Plast Reconstr Surg 2005;116: 898e904. 14. Smith DM, Aston SJ, Cutting CB, et al. Designing a virtual reality model for aesthetic surgery. Plast Reconstr Surg 2005; 116:893e7. 15. Paick JS, Donatucci CF, Lue TF. Anatomy of cavernous nerves distal to prostate: microdissection study in adult male cadavers. Urology 1993;42:145e9. 16. Alsaid B, Bessede T, Diallo D, et al. Division of autonomic nerves within the neurovascular bundles distally into corpora cavernosa and corpus spongiosum components: immunohistochemical confirmation with three-dimensional reconstruction. Eur Urol 2011;59:902e9. 17. Zhang SX, Heng PA, Liu ZJ, et al. Creation of the Chinese visible human data set. Anat Rec B New Anat 2003;275: 190e5. 18. Ding ZH, Zhang QD, Gao CW. Anatomical basis for the lengthening of penis [in Chinese]. Chin J Clin Anat 1993;1:44e6. 19. Smith DM, Oliker A, Carter CR, et al. A virtual reality atlas of craniofacial anatomy. Plast Reconstr Surg 2007;120:1641e6. 20. Vardi Y, Gruenwald I. The status of penile enhancement procedures. Curr Opin Urol 2009;19:601e5. 21. Spyropoulos E, Galanakis I, Dellis A. Augmentation phalloplasty patient selection and satisfaction inventory: a novel questionnaire to evaluate patients considered for augmentation phalloplasty surgery because of penile dysmorphophobia. Urology 2007;70:221e6.
Three-dimensional virtual model and animation of penile lengthening surgery Ruiheng Wang, Dongyun Yang, Shirong Li* Department of Plastic and Reconstructive Surgery, Southwest Hospital, Third Military Medical University, 30 Gaotanyan Main Street, Chongqing 400038, China Received 20 October 2011; accepted 8 April 2012
KEYWORDS Penile lengthening surgery; Three-dimensional model; Computer simulation; Magnetic resonance imaging; Surgical education; Patient tutorial
Summary Background: Three-dimensional digital models, animations, and simulations have been used in the plastic surgical field for surgical education and training and patient education. In penile lengthening surgery, proper patient selection and well-designed surgical interventions are necessary; however, no such surgical or patient education tool exists. Methods: Using magnetic resonance images as references, a preliminary three-dimensional digital model of the penis with its adjacent structures was constructed using Amira 5. This preliminary model was imported into Maya 2009, a computer modeling and animation software program, for processing to correct many defects. The refined model was used to create digital animation of penile lengthening surgery, including ordered steps of the procedure, using Maya 2009 and Adobe After Effects CS4. Results: A three-dimensional digital animation was created to illustrate penile lengthening surgery. All major surgical steps were demonstrated, including exposure, transversal incision of the fundiform ligament, partial division and release of the suspensory ligament. Conclusions: Three-dimensional digital models and animations of penile lengthening surgery may serve as resources for patient education to facilitate patient selection and resident education outside the operating room. ª 2012 British Association of Plastic, Reconstructive and Aesthetic Surgeons. Published by Elsevier Ltd. All rights reserved.
Introduction Although various penile lengthening procedures have been described,1 the most widely used technique is division of the penile ligaments in combination with an advancement
flap at the penile base. Penile ligaments are composed of the fundiform ligament and the suspensory ligament.2 Surgical division of these ligaments allows the penis to lie in a more dependent position and therefore gives the appearance that penile length has increased.3 Patients with
* Corresponding author. Tel.: þ86 13896181743; fax: þ86 (0)23 68765851. E-mail address: [email protected] (S. Li). 1748-6815/$ - see front matter ª 2012 British Association of Plastic, Reconstructive and Aesthetic Surgeons. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.bjps.2012.04.015
e282 a truly short penis would be candidates for penile lengthening surgery (e.g., patients with an erect penile length < 8 cm are recommended for the surgical intervention in our department).4 However, patients with normal-sized penises usually have unrealistic expectations regarding the outcome of surgery, and thus the satisfaction rates were lower in these patients.3 Therefore, for patients requiring penile lengthening surgery, an effective patient tutorial for correct information about the surgical procedure that could facilitate proper patient selection and a well-designed surgical intervention are necessary. Virtual reality techniques have been used in the plastic surgical field for patient education5 and surgical training and education.6 Virtual reality techniques enable surgeons to construct anatomically accurate, virtual models of human structures, on which surgical procedure animation and interactive surgical simulators can be developed.7 Animation can be used for patient5 and surgical education.8 Surgical simulators can provide opportunities for plastic surgery training6 or patient-specific, anatomically correct information which help surgeons visualize and plan procedures by viewing the predicted outcomes.9,10 As we have performed penile lengthening surgery for more than 10 years4,11 and have struggled with the problem of proper patient selection and resident education, we wanted to develop a virtual surgical animation with the aim of developing a tutorial aid for patients and a surgery education tool for residents. The quality of the animation or simulation is dependent on the fidelity of the digital model, as the digital models are the working materials on which these methods are constructed.7 Computed tomography (CT) images7,12 and photographs of histologic sections13,14 are two major data types used for reconstructing virtual human models with high fidelity. In this study, the authors constructed a threedimensional, high-fidelity virtual model of the penis with its adjacent structures using patient-specific magnetic resonance (MR) images. Based on this model, an animation of penile lengthening surgery was subsequently created for teaching surgical residents and providing patients with more comprehensible information about the surgery.
R. Wang et al.
Creation of a preliminary model of the penis and its adjacent structures A preliminary three-dimensional polygonal surface model of the penis with its adjacent structures was created according to the methods described by Flores et al.7 MR images were stored as DICOM format and then imported into Amira 5 (Vistage Imaging, Inc., San Diego, CA). Twodimensional sections from the MR image set were shown in three-dimensional space (Figure 1). Within this software platform, image segmentation and surface reconstruction were performed, and ultimately, a preliminary threedimensional polygonal surface model was obtained as an object file. Image segmentation refers to assigning to each pixel of the MR images a label describing to which structure the pixel belongs. Structures, e.g., lesser pelvis, cavernous body of the penis and urethra, and testis, were segmented manually for each two-dimensional section by two of the authors (Wang RH, Yang DY) using the Brush tool integrated within the Amira Segmentation Editor (Figure 2(a)). Surface reconstruction refers to generating a three-dimensional polygonal surface model for the region of interest after the image segmentation process (Figure 2(b)). The resulting surface model was exported into an object file containing three-dimensional data points of the preliminary polygonal surface model, topographic connectivity, and textural information of the surface model.7
Processing of the preliminary model The object file of the three-dimensional polygonal surface model constructed by Amira was imported into the Maya 2009 (Autodesk, San Raphael, CA) computer modeling and animation software for processing to be usable in an animation or simulation software platform because the preliminary surface model was 1) complex due to its large number of polygons, or dense with data points,7,10 2) absent of many anatomical structures that cannot be identified in MR images, and 3) lacking fidelity
Materials and methods Magnetic resonance imaging (MRI) MR images were obtained using a GE Signa HDx 3.0 Tesla system. A verbal consent was obtained from participant before MR images were taken. The participant was imaged using an axial sectioning plane beginning just above the pubic symphysis and extending below the testis in the rest position. The following MRI parameters were used for the participant: 1) Fast spin-echo pulse sequence 2) T2-weighted imaging (repetition time msec/echo time msec Z 4000/103) 3) Slice thickness Z 3.0 mm 4) Spacing Z 0 mm 5) Field of View Z 44 cm 44 cm 6) NEX Z 4
Figure 1 The utility of Amira as a platform for viewing the MR images. A serial two-dimensional section from the MR image set is shown. A parasagittal section of the penis and testis is circled in red. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
3D model of penile lengthening surgery
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Figure 2 (a): Sample image of the segmented MR image within Amira 5. (b): Preliminary three-dimensional surface model of the penis with its adjacent structures constructed by Amira. Right lesser pelvis is rendered transparent to illustrate underlying anatomical structures. This preliminary model required processing to be usable in an animation or simulation software platform. B Z bladder; CC Z corpora cavernosa; CS Z corpus spongiosum; P Z prostate; R Z rectum; T Z testis.
due to the low quality of its textural surfaces. To correct these defects, Maya 2009 software and Photoshop CS4 (Adobe Systems, Inc., San Jose, CA) were employed. First, the preliminary model was smoothed and simplified in Maya. Using the NEX Quad Draw tool combined with the Slide option integrated within NEX (http://draster. com/nex-1.5/overview.html), a plugin for Maya, meshes of the preliminary surface model were resurfaced. The resulting surface model had a significantly decreased density of data points while still preserving the complex topographic connectivity (Figure 3(a)). After smoothing and simplifying processing, models of the anatomical structures absent in the preliminary model, such as the penile fundiform ligament, penile suspensory ligament, nerves, blood vessels, and other significant structures, were constructed in Maya after a literature review2,15,16 (Figure 3(b, c)). The Chinese Visible Human dataset17 was also used as a reference in creating some of the models. Finally, textures were added to all tissue surfaces to maximize the fidelity of the model. Textures were artistically created de novo in Photoshop CS4 (Figure 3(b, c)).
Creation of surgical animation Surgical animation was created in Maya according to the methods used previously by Flores et al.8 Briefly, a playblast was first constructed, after which incisions of the skin and the penile ligaments were made using Maya’s Split Polygon tool and soft-tissue deformations were made using Maya’s Cluster Deformer tool. Once the playblast was completed, refined adjustments were performed on the camera angle, shading, and light sources. Finally, the rendered frames were composited together to create a completed procedure animation using After Effects CS4 (Adobe Systems; Video 1, Supplemental Digital Content 1, which illustrates an animation of penile lengthening surgery). Supplementary video related to this article can be found at doi:10.1016/j.bjps.2012.04.015.
Results A preliminary three-dimensional polygonal surface model of the penis with its adjacent structures was constructed by Amira 5 using MR images as references (Figure 2). As this preliminary model was 1) complex due to its large number of polygons, 2) absent of many anatomical structures that cannot be identified in MR images, and 3) lacking fidelity due to the low quality of its textural surfaces, we employed Maya 2009 and Photoshop CS4 to correct these defects. The refined model contained 1) a decreased number of polygons, 2) high-fidelity textural surfaces, and 3) all major anatomical structures relevant to penile lengthening surgery (Figure 3). According to the findings by Hoznek et al,2 in the refined model, the penile ligaments consist of two separate ligamentous structures: the fundiform ligament, a lax fibrous layer attached above to the linea alba of the anterior abdominal wall that splits into two bands that pass on each side of the penis and unite inferiorly; and the suspensory ligament, which stretches between the pubic symphysis and the tunica albuginea of the corpora cavernosa (Figure 3(b)). The neurovascular bundle (NVB) descends along the posterolateral border of the prostate and has two divisions: cavernous nerve and corpus spongiosum nerve. The branches of the cavernous nerve penetrate the tunica albuginea of the corpora cavernosa around the hilum of the penis, and send connecting fibers to the penile dorsal nerve. The corpus spongiosum nerve is a continuation of the posterolateral NVB, and eventually reaches the corpus spongiosum bulb15,16 (Figure 3(c); Video 2, Supplemental Digital Content 2, which illustrates a model of the penis with its adjacent structures.). Finally, based on the model, a three-dimensional digital animation was developed to illustrate penile lengthening surgery. All major surgical steps that we previously reported4 were observed, including a ‘þ’ shaped skin incision, exposure, transversal incision of the fundiform ligament, partial division and release of the suspensory ligament (Video 1, Supplemental Digital Content 1, which illustrates an animation of penile lengthening surgery.). The suspensory ligament should be divided close to the pubic symphysis to
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R. Wang et al. avoid injuring the nerves and blood vessels which course along the dorsal surface of the penis. It was reported that the border length of suspensory ligament to the pubic symphysis was 2e4 cm.2,18 We have not attempted to cut the suspensory ligament until all midline attachment has been freed as has been described by Li et al.3 From our experience, partial division (1/3 to 1/2 of the length, or 1e1.5 cm) would be acceptable to avoid leading to penile instability or an altered erectile angle4 (Video 1, Supplemental Digital Content 1, which illustrates an animation of penile lengthening surgery.). We propose that the model of the penis with its adjacent structures and the animation of penile lengthening surgery can be used to teach surgical residents and provide patients with more comprehensible information about the surgery to facilitate doctorepatient communication. Supplementary video related to this article can be found at doi:10.1016/j.bjps.2012.04.015.
Discussion
Figure 3 (a): The meshes of the preliminary model were resurfaced using the NEX Quad Draw tool combined with the Slide option integrated within NEX in Maya to decrease the number of polygons. (b): Layers and ligaments of the penis. c: Left posterolateral view of intrapelvic organs, the neurovascular bundle (NVB) descends along the posterolateral border of the prostate (P) and has two divisions: cavernous nerve (CN) and corpus spongiosum nerve (CSN). The CN penetrates the corpora cavernosa and sends connecting fibers to the penile dorsal nerve (DN) which originates from the pudendal nerve (PN). The CSN reaches the corpus spongiosum bulb. CA Z cavernosal artery; DA Z penile dorsal artery;
The use of computer modeling, animation, and simulation is beneficial to plastic surgery, particularly in the area of craniofacial surgery. Three-dimensional model of craniofacial anatomy has been developed, which can be used for anatomical study by medical students. Complex anatomical concepts can be more readily comprehended in dynamic three-dimensional model than from a static, twodimensional textbook.7,19 Animations have been created to illustrate a series of procedures in craniofacial surgery. Transparency was used in these animations to display underlying anatomy that is rarely visible during an operation but is critical to the understanding of the procedure itself.8,12 Animation has also been created to demonstrate the aging process of the face and the associated esthetic surgical procedures.13 In addition, an interactive digital education aid based on virtual animation was developed for breast reconstruction patient. The animation in this aid provides patient with a tutorial regarding the treatment, allowing them to make more informed treatment decisions.5 Concerning surgical simulation, a real-time surgical simulator with haptic feedback has been developed for planning and performing cleft lip repair.10 Simulation also provides residents a means to practice anatomical identification for cleft lip surgery without the risks associated with training on a live patient. However, we believe that many other areas of plastic surgery, such as genital surgery, would also benefit from surgical animation and simulation. Although various penile lengthening procedures have been described, these procedures are still considered highly controversial because questions regarding proper patient selection, methods, and effectiveness exist and the operative techniques and assessment of the results have not yet been standardized.20 As we have performed penile lengthening surgery for more than 10 years,4,11 and have
DDV Z deep dorsal vein; DF Z deep fascia; DN Z penile dorsal nerve; FL Z fundiform ligament of penis; SDV Z superficial dorsal vein; SF Z superficial fascia; SL Z suspensory ligament of penis; U Z urethra.
3D model of penile lengthening surgery faced the problems of proper patient selection and resident education, we created a virtual surgical animation with the aim of developing a tutorial aid for patients and a surgery education tool for residents. With regard to proper patient selection, although Spyropoulos et al21 introduced a novel questionnaire for identifying the most suitable candidates for penile augmentation phalloplasty surgery, busy surgeons may provide insufficient or perhaps overly technical information. As virtual surgical animation can provide comprehensible information about the surgery, the combination of animation with the questionnaire and other specific clinical tools can be a more reasonable strategy for patient selection. For resident surgery education, animation is designed to supplement rather than replace operating room training. By providing efficient training outside the operating room, the surgeon will be well prepared for efficient training inside the operating room.8 To use virtual reality techniques in surgery, Flores et al7,8 described a novel process through which construction of a three-dimensional digital model is the first step, followed by the creation of animation or simulation based on the model. CT scan images7,12 and photographs of histologic sections13,14 can be used for constructing digital models. In this present article, patient-specific MR images were used for creating the digital model because MRI provides more information about soft-tissue structures than CT. The effects of varying slice thickness (1-mm, 3-mm, 5-mm) on the MR images were compared in a preliminary experiment. The images with 1-mm slice thickness have lower signal-tonoise ratio than that with 3- and 5-mm slice thickness. In addition, the anatomical details imaging is better in 3mm images than 5-mm images. Thus, we constructed the preliminary model using 3-mm slice thickness MR images as references. The long-term goals of this research are to create a real-time surgical simulator with haptic feedback for planning and performing penile lengthening surgery and provide residents a means to practice the procedure. The current study focuses on an accurate modeling of the anatomy of the penis with its adjacent structures and the creation of a penile lengthening procedure animation. The development of a penile surgery simulator is expected in future research.
Conclusions A three-dimensional digital model of the penis with its adjacent structures and an animation of penile lengthening surgery were constructed. The animation may serve as a resource for patient tutorials to facilitate patient selection and for resident education outside the operating room.
Conflicts of interest The authors have no conflict of interest to disclose.
Funding This work is supported by the National Natural Science Foundation of China, NO. 30973133.
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References 1. Dillon BE, Chama NB, Honig SC. Penile size and penile enlargement surgery: a review. Int J Impot Res 2008;20: 519e29. 2. Hoznek A, Rahmouni A, Abbou C, et al. The suspensory ligament of the penis: an anatomic and radiologic description. Surg Radiol Anat 1998;20:413e7. 3. Li CY, Kayes O, Kell PD, et al. Penile suspensory ligament division for penile augmentation: indications and results. Eur Urol 2006;49:729e33. 4. Shirong L, Xuan Z, Zhengxiang W, et al. Modified penis lengthening surgery: review of 52 cases. Plast Reconstr Surg 2000;105:596e9. 5. Heller L, Parker PA, Youssef A, et al. Interactive digital education aid in breast reconstruction. Plast Reconstr Surg 2008;122:717e24. 6. Rosen JM, Long SA, McGrath DM, et al. Simulation in plastic surgery training and education: the path forward. Plast Reconstr Surg 2009;123:729e38. discussion 739e740. 7. Flores RL, Deluccia N, Grayson BH, et al. Creating a virtual surgical atlas of craniofacial procedures: part I. Threedimensional digital models of craniofacial deformities. Plast Reconstr Surg 2010;126:2084e92. 8. Flores RL, Deluccia N, Oliker A, et al. Creating a virtual surgical atlas of craniofacial procedures: part II. Surgical animations. Plast Reconstr Surg 2010;126:2093e101. 9. Pieper SD, Laub Jr DR, Rosen JM. A finite-element facial model for simulating plastic surgery. Plast Reconstr Surg 1995;96: 1100e5. 10. Schendel S, Montgomery K, Sorokin A, et al. A surgical simulator for planning and performing repair of cleft lips. J Craniomaxillofac Surg 2005;33:223e8. 11. Li S, Tao L, Wang Z, et al. Postoperative hydrophallus after penile lengthening: an experimental and clinical study. Plast Reconstr Surg 2007;119:768e70. 12. Cutting C, Oliker A, Haring J, et al. Use of three-dimensional computer graphic animation to illustrate cleft lip and palate surgery. Comput Aided Surg 2002;7:326e31. 13. Smith DM, Aston SJ, Cutting CB, et al. Applications of virtual reality in aesthetic surgery. Plast Reconstr Surg 2005;116: 898e904. 14. Smith DM, Aston SJ, Cutting CB, et al. Designing a virtual reality model for aesthetic surgery. Plast Reconstr Surg 2005; 116:893e7. 15. Paick JS, Donatucci CF, Lue TF. Anatomy of cavernous nerves distal to prostate: microdissection study in adult male cadavers. Urology 1993;42:145e9. 16. Alsaid B, Bessede T, Diallo D, et al. Division of autonomic nerves within the neurovascular bundles distally into corpora cavernosa and corpus spongiosum components: immunohistochemical confirmation with three-dimensional reconstruction. Eur Urol 2011;59:902e9. 17. Zhang SX, Heng PA, Liu ZJ, et al. Creation of the Chinese visible human data set. Anat Rec B New Anat 2003;275: 190e5. 18. Ding ZH, Zhang QD, Gao CW. Anatomical basis for the lengthening of penis [in Chinese]. Chin J Clin Anat 1993;1:44e6. 19. Smith DM, Oliker A, Carter CR, et al. A virtual reality atlas of craniofacial anatomy. Plast Reconstr Surg 2007;120:1641e6. 20. Vardi Y, Gruenwald I. The status of penile enhancement procedures. Curr Opin Urol 2009;19:601e5. 21. Spyropoulos E, Galanakis I, Dellis A. Augmentation phalloplasty patient selection and satisfaction inventory: a novel questionnaire to evaluate patients considered for augmentation phalloplasty surgery because of penile dysmorphophobia. Urology 2007;70:221e6.