Review Paper for 3D Bioprinting organs

ORIGINAL ARTICLE

Three-Dimensional Print of a Liver for Preoperative Planning in Living Donor Liver Transplantation Nizar N. Zein,1 Ibrahim A. Hanouneh,1 Paul D. Bishop,2 Maggie Samaan,1 Bijan Eghtesad,3

Cristiano Quintini,3 Charles Miller,3 Lisa Yerian,4 and Ryan Klatte5 1Department of Gastroenterology and Hepatology, Digestive Disease Institute, 2Department of Vascular Surgery, Heart and Vascular Institute, 3Department of Hepato-Pancreato-Biliary and Transplant Surgery, Digestive Disease Institute, 4Department of Anatomic Pathology, Pathology and Laboratory Medicine Institute, and 5Medical Device Solutions, Lerner Research Institute, Cleveland Clinic, Cleveland, OH

The growing demand for liver transplantation and the concomitant scarcity of cadaveric livers have increased the need for living donor liver transplantation (LDLT). Ensuring the safety of donors and recipients is critical. The preoperative identifica- tion of the vascular and biliary tract anatomy with 3-dimensional (3D) printing may allow better preoperative surgical plan- ning, avert unnecessary surgery in patients with potentially unsuitable anatomy, and thereby decrease the complications of liver transplant surgery. We developed a protocol and successfully 3D-printed synthetic livers (along with their complex net- works of vascular and biliary structures) replicating the native livers of 6 patients: 3 living donors and 3 respective recipients who underwent LDLT. To our knowledge, these are the first complete 3D-printed livers. Using standardized preoperative, intraoperative, and postoperative assessments, we demonstrated identical anatomical and geometrical landmarks in the 3D-printed models and native livers. Liver Transpl 19:1304-1310, 2013. VC 2013 AASLD.

Received July 22, 2013; accepted July 26, 2013.

Three-dimensional (3D) printing is a process for mak- ing a solid 3D object of virtually any shape from a dig- ital model. A 3D printer works as an ordinary office printer, but instead of placing a single layer of ink on paper, the machine lays down successive thin layers of a material to form a 3D object that replicates the original one.1

The growing demand for liver transplantation and the concomitant shortage of cadaveric livers have led to a rise in living donor liver transplantation (LDLT), in which resection of the right or left liver lobe is per- formed for the purpose of liver transplantation.2 Liv- ing donors are healthy individuals, so ensuring their safety is of paramount importance. There have been a number of reported donor deaths worldwide and a

substantial number of donor morbidities, so there is a need for measures to optimize donor safety.3 Many of these morbidities are attributable to incomplete pre- operative anatomical characterization of vascular and biliary structures and inaccurate estimates of the liver volume; these data are needed to determine the extent of the resection. This information provides a road map, and its accuracy has improved with the intro- duction of radiological software able to provide 3D visualization of liver structures.4,5

3D imaging has the ability to better demonstrate the 3D relationships between vital vascular and biliary structures and the surrounding parenchyma in com- parison with conventional computed tomography (CT) or magnetic resonance imaging (MRI). 3D imaging

Additional Supporting Information may be found in the online version of this article.

Abbreviations: 2D, 2-dimensional; 3D, 3-dimensional; CT, computed tomography; LDLT, living donor liver transplantation; MRI, magnetic resonance imaging; STL, stereolithography.

The study was supported by the Mikati Foundation Endowed Chair in Liver Diseases (Nizar N. Zein).

Address reprint requests to Nizar N. Zein, M.D., Department of Gastroenterology and Hepatology, Digestive Disease Institute, Cleveland Clinic, 9500 Euclid Avenue, Mail Code A50, Cleveland, OH 44195. Telephone: 1216-444-6126; FAX: 1216-445-5477; E-mail: [email protected]

DOI 10.1002/lt.23729 View this article online at wileyonlinelibrary.com. LIVER TRANSPLANTATION.DOI 10.1002/lt. Published on behalf of the American Association for the Study of Liver Diseases

LIVER TRANSPLANTATION 19:1304–1310, 2013

VC 2013 American Association for the Study of Liver Diseases.

renders volumes as well, and these are essential to the surgical planning and execution process.6-8

Despite these advantages, 3D imaging has its short- comings, including the reality that 3D images are examined through a 2-dimensional (2D) computer screen. Additionally, the intraoperative application of preoperative 3D image findings is still difficult because of the absence of reliable liver surface markers corresponding to hepatic segmentation. Liver deformity after mobilization during surgery has been a major obstacle to the reliable use of preoperative 3D imaging data; hence, intraoperative modalities such as ultrasonography and cholangiography are often used for the localization of vessels and major biliary branches. Our attempt to produce a highly accurate 3D-printed model of a patient’s liver is intended to overcome these obstacles and improve the safety of LDLT. The accurate anatomical reproduction of the donor liver represents progress in existing 3D imaging technology and may enhance patient outcomes.

The aim of this novel study was to establish ana- tomical precision and volumetric accuracy in 3D- printed models for donors and recipients undergoing LDLT.

PATIENTS AND METHODS

Patients

After receiving an approval from the Institutional Review Board at the Cleveland Clinic, we prospectively studied 3 consecutive patient pairs (3 donors and 3 recipients) who were evaluated and approved for LDLT at the Cleveland Clinic between November 2012 and May 2013. The donors and the recipients under- went standardized preoperative evaluations, which included contrast-enhanced CT and MRI examina- tions of the abdomen. These standardized images were required for an analysis of morphological charac- teristics and the vascular and biliary anatomy and for an evaluation of the hepatic parenchyma. Addition- ally, CT volumetric measurements of the entire donor liver and both its lobes were taken with CT postpro- cessing software (Medical Image Editor Thomas Lange, B.S., Deutsches Herzzentrum, Berlin, Ger- many). Using information from these imaging modal- ities, we obtained comparative data for the donor and recipient livers, including the volumes, lengths, widths, and heights of the whole livers and their lobes. Anatomical details, including the diameters of the main portal vein, left hepatic vein, right hepatic vein, and biliary tree, were also recorded. Demo- graphic and clinical characteristics of the donors and recipients at the time of surgery (age, sex, ethnicity, weight, height, and body mass index) were also recorded.

3D Printing

The overall process of 3D printing included 3D image reconstruction, digital preparation, 3D printing, and postprinting finishing work. Anatomical structures

(bile ducts, hepatic arteries, hepatic veins, and portal veins) were digitally segmented with MeVis-supplied (MeVis Medical Solutions AG) digital files from the optimal visualization phases of contrast-enhanced CT and MRI imaging. Subsequently, the geometry of each structure was exported to a mesh-type file [stereoli- thography (STL) file] to create a 3D geometry of that structure. Digital preparation of the STL files was accomplished with Magics software (Materialise) in order to (1) evaluate the intersecting vessels and the biliary structures originating from subtle time/posi- tion artifacts between CT/MRI imaging phases and then generate a nonoverlapping geometry, (2) actual- ize hollowed vascular and biliary structures within the liver parenchyma, (3) construct thin-walled exter- nal vessels and biliary structures to accompany the liver model, and (4) divide the liver mesh structure into graft and remnant components on the basis of the proposed surgical resection plane.

The final STL files generated via digital preparation were imported into a Connex 350 3D printer (Stra- tasys), and the 3D model was produced. Materials used for printing included TangoPlus/VeroClearPlus for liver parenchyma, TangoBlackPlus/VeroBlue for hepatic vein structures, and a TangoPlus/VeroClear blend (FLX9995-DM; Shore A hardness �92) for other external vessels (all materials by Stratasys). The post- printing phase involved cleaning of the support mate- rial that formed during the printing process with a water jet, selecting optimal color-coded dye staining for each vascular structure, and clear-coating the liver surfaces with methodologies that we had opti- mized over the past few months; this ensured maxi- mum transparency of the model and vividness of the anatomical structures. Finally, the external vessels and the biliary structures were attached to the liver lobe via a permanent adhesive. This resulted in a life- sized, transparent 3D liver that not only replicated the real one but also allowed detailed visualization of vascular and biliary structures for optimal surgical planning.

The volumes of the native and 3D-printed right or left donor liver lobes were determined by means of liq- uid displacement with a special 6-L cylindrical stain- less steel container that was open at the top and equipped with a stainless steel tube projecting from the top of its sidewall for overflow. The container was filled with saline to the level of the overflow tube. After the immersion of each 3D-printed liver in saline, the saline that escaped via the overflow tube was cap- tured in a graduated cylinder. The volume of the dis- placed saline measured in the graduated cylinder corresponded to the volume of the measured part of the liver.

Intraoperative Data Acquisition

During surgery, hepatic vein mapping was performed with Doppler ultrasound, whereas the arterial and portal vein anatomy was assessed via surgical dissec- tion. Additionally, after open cholecystectomy and

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ligation of the cystic duct, conventional intraoperative cholangiography was performed for bile duct anat- omy. Anatomical information obtained from these intraoperative studies was used as endpoints for com- parison with the 3D-printed model for accuracy. After proper identification of the vascular and biliary tracts of the donor’s liver, the right or left liver lobe was resected for the purpose of liver transplantation.

A single individual with a standard laboratory scale determined the weight of the resected liver lobe before bench-table graft preparation. In the next step, meas- urements of the resected liver lobe, including the length, width, and height as well as the diameters of the portal vein, left hepatic vein, and right hepatic vein, were obtained by a single operator.

Similarly, measurements of the recipient’s native liver were taken as soon as the liver was explanted, and its volume was determined via liquid displace- ment (as described previously). All measurements were taken by a single operator

Statistical Analysis

We used the results of intraoperative measurements as the gold standard for our study. The accuracy of

the 3D-printed liver models was assessed through the comparison of their preoperatively obtained measure- ments to the gold standard. Data are presented as means and standard deviations. For each subject, the difference in each measure between the 3D print and the native liver was estimated; the mean differences and the corresponding 95% confidence intervals are reported. All analyses were performed with SAS 9.2 (SAS Institute, Cary, NC).

RESULTS

Case 1

The first case was a 42-year-old gentleman with cryp- togenic liver cirrhosis and a 3-cm nodule in segment VI (according to Couinaud’s classification). The nodule was nonenhancing according to contrast-enhanced CT and was consistent with a regenerative nodule. Figure 1A presents the 3D-printed liver and the native liver of the recipient. The 3D model accurately showed the regenerative nodule in segment VI. The geometric characteristics of the 2 livers (the 3D-printed and native recipient livers) were virtually identical, as shown in Table 1. The liquid displacement method

Figure 1. (A) Preoperatively 3D-printed liver and actual explanted liver of a recipient (case 1). The arrows point to a regenerative nodule in segment VI in both the native liver and the 3D-printed liver. (B) Preoperatively 3D-printed right lobe and actual right lobe of a donor (case 1).

TABLE 1. Geometric Characteristics of 3D-Printed Liver Models and Corresponding Donor and Recipient Livers: Case 1

Recipient’s Liver Donor’s Right Liver Lobe

3D Print Native Right Liver Lobe 3D Print Native Right Liver Lobe

Volume (mL) 1175 1215 923 988 Length (cm) 21 23 13 13.5 Width (cm) 13.3 12.5 15.5 15 Height (cm) 10.5 10 10.4 10.5 Portal vein diameter (mm) 1 1.2 0.7 0.9 Right hepatic vein diameter (mm) 0.4 0.5 0.4 0.4 Left hepatic vein diameter (mm) 0.4 0.5 — —

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was used for measuring the volume, and because the native recipient liver volume was considered the refer- ence standard, the 3D liver model provided a more accurate volume measurement than preoperative volu- metric CT (native liver volume 5 1215 mL, 3D-printed liver volume 5 1175 mL, CT volume 5 1267 mL).

The donor was a 46-year-old brother who under- went right lobe hepatectomy (segments V-VIII) without the middle hepatic vein. The 3D-printed model and the native right liver lobe of the donor, as presented in Fig. 1B, appeared to be identical. Table 1 presents the geometric characteristics of the 3D-printed right liver lobe and the native right liver lobe. Intraoperative cholangiography was very difficult and time-

consuming because of the very low insertion of the cystic duct (length 5 4 cm), which caused the contrast to run into the duodenum. This anatomical variation was accurately shown in the 3D liver model, which allowed intraoperative characterization of the biliary anatomy when intraoperative cholangiography was suboptimal (Fig. 2). An accessory left hepatic duct draining directly into the common hepatic duct was also clearly noted in the 3D-printed model (Fig. 2).

Case 2

The second case was a 63-year-old gentleman with liver cirrhosis secondary to nonalcoholic

Figure 2. (A) Intraoperative cholangiogram (case 1). The arrow in panel-B points to an elongated cystic duct. (B) Preoperatively 3D-printed biliary tree.

Figure 3. (A) Preoperatively 3D-printed liver and actual explanted liver of a recipient (case 2). The long arrows point to the hepatic artery, the short arrows point to the hepatic vein, and the double arrows point to the portal vein. (B) Preoperatively 3D-printed right lobe and actual right lobe of a donor (case 2). The single arrows point to the hepatic artery, and the double arrows point to the portal vein.

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steatohepatitis who underwent LDLT. Figure 3A presents the 3D-printed liver and the native liver of the recipient. The geometric characteristics of the 2 livers (the 3D-printed and native livers) were identical (Table 2). Using liquid displacement to measure the volume and considering the native recipient liver vol- ume as the reference volume, we found that the 3D liver model provided a more accurate volume mea- surement than preoperative volumetric CT (native liver volume 5 1195 mL, 3D-printed liver vol- ume 5 1235 mL, CT volume 5 851 mL).

The donor was a 27-year-old daughter who under- went right lobe hepatectomy (segments V-VIII) without the middle hepatic vein. Figure 3B presents the 3D- printed model of the native right liver lobe of the donor, which presented with geometric characteristics nearly identical to those of the native right lobe (Table 2). Additionally, the 3D model accurately showed the normal donor biliary anatomy in comparison with preoperative MRI and intraoperative cholangiography (Fig. 4). The biliary anatomy was conventional

because the right posterior duct drained segments VI and VII, and the right anterior duct drained segments V and VIII.

Case 3

The third case was a 63-year-old female with liver cir- rhosis secondary to nonalcoholic steatohepatitis who underwent LDLT. Figure 5A presents a cross-section of the 3D-printed liver along with the corresponding cross-section of the native liver of the recipient. The 3D-printed cross-section of the liver accurately shows the orifices of the portal vein, hepatic vein, and hepatic artery and is consistent with the native liver cross-section. The geometric characteristics of these vascular structures appeared to be identical in the 3D-printed liver and the native liver of the recipient (Table 3). The 3D liver model provided a more accu- rate volume measurement than preoperative volumet- ric CT according to the postoperatively measured volume of the recipient’s explanted liver (native liver

Figure 4. (A) Intraoperative cholangiogram (case 2). No biliary anomalies were noted. (B) Preoperatively 3D-printed biliary tree.

TABLE 2. Geometric Characteristics of 3D-Printed Liver Models and Corresponding Donor and Recipient Livers: Case 2

Recipient’s Liver Donor’s Right Liver Lobe

3D Print Native Right Liver Lobe 3D Print Native Right Liver Lobe

Volume (mL) 1235 1195 715 730 Length (cm) 17.5 17.5 15.4 15.3 Width (cm) 15.4 15.5 10 10.1 Height (cm) 7.5 7.5 9.5 9.5 Portal vein diameter (mm) 11 11.2 12 11.8 Right hepatic vein diameter (mm) 2.4 2.5 1.8 2 Left hepatic vein diameter (mm) 2.1 2 — —

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volume 5 1250 mL, 3D-printed liver volume 5 1458 mL, CT volume 5 1626 mL).

The donor was a 43-year-old daughter who under- went left lateral segmentectomy for living liver dona- tion. The 3D-printed model and the native left liver lobe of the donor are shown in Fig. 5B. Table 3 presents the geometric characteristics of the 3D- printed left liver lobe and the native left liver lobe. Supporting Table 1 presents the differences in each measure of the geometric characteristics between the 3D-printed and native livers.

DISCUSSION

In this study, using 3D printing technology, we have successfully produced prototype models of human liv- ers based on patients’ individual CT scans and MRI imaging. In our experience, 3D organ printing is a val- uable tool for understanding the spatial relationships between vascular and biliary anatomical structures

and ultimately for facilitating surgery and potentially minimizing intraoperative complications.

Through a direct comparative validation protocol, these models were shown to have a very high accu- racy with mean dimensional errors of less than 4 mm for the entire model and less than 1.3 mm for vascu- lar diameters (the portal vein and its main branches, the hepatic veins, and the hepatic artery). To our knowledge, this is the first time that human livers have been synthetically reproduced and validated against actual native livers at the time of surgery.

3D imaging is becoming an important clinical tool for the planning of complex surgeries and is consid- ered superior to conventional 2D imaging for the visu- alization of anatomical structures.4-8 A major disadvantage of 3D imaging is the visualization of images through a 2D computer screen, with which a true sense of depth is limited. Converting these images through 3D printing into a real 3D object with a real indication of depth that can be examined and

Figure 5. (A) Cross-section of a preoperatively 3D-printed liver and corresponding cross-section of the actual explanted liver of a recipient (case 2). The arrows and the arrowheads point to the hepatic vein, and the dotted arrows point to the portal vein. (B) Preoper- atively 3D-printed left lobe and actual left lobe of a donor (case 3). The arrows point to the caudate lobe in both the native liver and the 3D-printed liver.

TABLE 3. Geometric Characteristics of 3D-Printed Liver Models and Corresponding Donor and Recipient Livers: Case 3

Recipient’s Liver Donor’s Left Liver Lobe

3D Print Native Liver 3D Print Native Left Lobe

Volume (mL) 1458 1250 800 755 Length (cm) 27 26 11.4 11 Width (cm) 17.5 17 14.6 14.2 Height (cm) 6.3 6 13 12.7 Portal vein diameter (mm) 10 10 — — Right hepatic vein diameter (mm) 4.7 4.5 — — Left hepatic vein diameter (mm) 5.6 5.4 12.6 12.3

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altered in a way to be identical to the surgical cutting plane provides additional information that can influ- ence surgical planning and potentially decrease com- plications. Additionally, having the physical model during surgical operations provides greater intuitive navigation for critical areas, and difficulties in orien- tation are overcome because these models can be physically positioned in the most desired fashion. Furthermore, the real-life intraoperative manipulation of the model simulates the changes in orientation experienced during the actual operation (eg, mobiliza- tion and retraction of the liver and exposure of the hepatic hilum), and this allows easy reorientation and identification of critical anatomical landmarks.

Finally, the transparency of the material used for the liver parenchyma in our 3D-printed models and the use of specific color codes for vascular and biliary structures provide detailed information about the vas- cular anatomy and the biliary anatomy, both of which are crucial for surgical outcomes. It may ultimately be possible to replace information provided by intraoper- ative studies (Doppler ultrasound and intraoperative cholangiography) with information provided by a 3D- printed model or to provide additional valuable infor- mation leading to reduced operative times and cold ischemia in liver transplantation. Because of the wide spectrum of materials that can be used in preparing these 3D copies of human livers, it is possible to use a soft material to simulate the mechanical properties of actual liver tissue so that models can be used to rehearse liver resection in LDLT or tumor resection in hepatobiliary and transplant surgery.

Although we have presented potential incremental progress in accurate preoperative and intraoperative surgical planning beyond conventional and 3D imag- ing, certain limitations should be noted. 3D-printed physical models are based on imaging and accord- ingly will be prone to imaging errors. Improved imag- ing resolution will subsequently improve the accuracy of these 3D-printed models. However, according to the present report, the level of accuracy rendered by these 3D models seems to be highly acceptable with small margins of error in comparison with the explanted native livers at the time of surgery. Another potential limitation is the need to control a number of parameters, including the type, quality, and proper-

ties of materials used, in order to achieve a reliable and reproducible model. Finally, the issue of cost is a constant concern when new technologies are being introduced. The production of a single 3D model requires approximately 25 to 40 hours of labor and the cost of materials in addition to the cost of imaging alone. Our group is working on a number of initiatives that will likely improve the efficiency and lower the cost of 3D-printed liver replicas.

In conclusion, we have presented the successful reproduction of human livers via 3D printing technol- ogy. These highly accurate models provide practical and hands-on tools and have a number of possibly unique applications for surgical planning and medical education.

REFERENCES

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3. Soejima Y, Shimada M, Suehiro T, Hiroshige S, Ninomiya M, Shiotani S, et al. Outcome analysis in adult-to-adult living donor liver transplantation using the left lobe. Liver Transpl 2003;9:581-586.

4. Satou S, Sugawara Y, Tamura S, Kishi Y, Kaneko J, Matsui Y, et al. Three-dimensional computed tomography for planning donor hepatectomy. Transplant Proc 2007; 39:145-149.

5. Radtke A, Sgourakis G, Molmenti EP, Schroeder T, Cicinnati VR, Beckebaum S, et al. The "carving" liver par- titioning technique for graft hepatectomy in live donor liver transplantation: a single-center experience. Surgery 2013;153:189-199.

6. Hori M, Suzuki K, Epstein ML, Baron RL. Computed tomography liver volumetry using 3-dimensional image data in living donor liver transplantation: effects of the slice thickness on the volume calculation. Liver Transpl 2011;17:1427-1436.

7. Hiroshige S, Shimada M, Harada N, Shiotani S, Ninomiya M, Minagawa R, et al. Accurate preoperative estimation of liver-graft volumetry using three-dimensional com- puted tomography. Transplantation 2003;75:1561-1564.

8. Frericks BB, Caldarone FC, Nashan B, Savellano DH, Stamm G, Kirchhoff TD, et al. 3D CT modeling of hepatic vessel architecture and volume calculation in living donated liver transplantation. Eur Radiol 2004;14:326-333.

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