(Radiographics. 2002;22:161-172.)
© RSNA, 2002
Volume-rendered 3D CT of the Mesenteric Vasculature: Normal Anatomy, Anatomic Variants, and Pathologic Conditions1
Karen M. Horton, MD and
Elliot K. Fishman, MD
1 From the Department of Radiology, Johns Hopkins Medical Institutions, 601 N Caroline St, Baltimore, MD 21287. Presented as an educational exhibit at the 2000 RSNA scientific assembly. Received April 11, 2001; revision requested July 3 and received July 17; accepted July 18. Address correspondence to E.K.F. (e-mail: efishman@jhmi.edu).
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Abstract
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Multi–detector row computed tomography (CT) offers important advantages over more conventional imaging methods in the evaluation of the mesenteric vasculature. It allows faster scanning, which practically eliminates motion and breathing artifacts, as well as thinner collimation. These advances, coupled with rapid intravenous administration of contrast material, allow excellent opacification of the mesenteric arteries and veins. This improves the quality of the three-dimensional (3D) data sets, which in turn leads to improved 3D vascular maps and more accurate assessment of various conditions such as arterial or venous encasement in patients with pancreatic cancer, mesenteric ischemia, or inflammatory bowel disease. Three-dimensional multi–detector row CT also allows better visualization of arterial and venous branching, thereby improving detection of more distal vascular involvement. In addition, 3D multi–detector row CT may help detect hemodynamic changes in patients with active inflammation and hyperemia of a bowel segment because it can be used to measure bowel wall enhancement over time. Carcinoid tumors that have infiltrated the mesentery have a characteristic CT appearance, and other conditions such as lymphoma or sclerosing mesenteritis can also manifest as an infiltrating mass that envelops mesenteric vessels. Three-dimensional multi–detector row CT represents a significant advance in CT technology and can help ensure prompt, accurate evaluation of the mesenteric vasculature.
© RSNA, 2002
Index Terms: Arteries, mesenteric, 95.1291, 95.92 • Computed tomography (CT), angiography, 95.12916 • Computed tomography (CT), thin-section, 95.1291 Computed tomography (CT), three-dimensional, 95.12917 • Computed tomography (CT), volume rendering, 95.12917 • Veins, mesenteric, 95.1291, 95.92
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Introduction
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Spiral computed tomography (CT) and multi–detector row CT offer distinct advantages over conventional dynamic CT in the imaging of the mesenteric vasculature, including the superior mesenteric artery (SMA), superior mesenteric vein (SMV), inferior mesenteric artery (IMA), and inferior mesenteric vein (IMV) and their major branches. The faster scanning (0.5 sec/rotation) and narrower collimation (0.5–1.25-mm sections) allow data acquisition during optimal opacification of the mesenteric vessels and their branches on both axial and three-dimensional (3D) reformatted images (1). These technologic advances, coupled with rapid intravenous injection of contrast material, improve the quality of the data set available for 3D image reconstruction and manipulation.
Three-dimensional angiographic parameters can be optimized to routinely display, in considerable detail, the mesenteric vasculature. This will likely aid in the assessment of various conditions such as arterial or venous encasement in patients with pancreatic cancer or mesenteric ischemia and in the assessment of disease activity in patients with inflammatory bowel disease.
In this article, we discuss 3D multi–detector row CT technique in the evaluation of the mesenteric vasculature. We also review the normal anatomy and anatomic variants of these vessels, focusing on the most common branching patterns and variations because there is significant anatomic variability. In addition, we discuss and illustrate CT findings in a variety of disease entities involving the mesenteric vessels, including pancreatic cancer, mesenteric ischemia, and Crohn disease.
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Imaging Technique
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Accurate and detailed imaging of the mesenteric vessels requires careful attention to technique. First, optimal opacification of the mesenteric vessels must be achieved. This requires rapid intravenous administration of a bolus of contrast material as well as precise timing of the data acquisition. We routinely use 120 mL of nonionic contrast material injected through a peripheral intravenous catheter at a rate of 3 mL/sec. Scanning is performed during the arterial and venous phases at 25 and 50 seconds after the start of injection, respectively. Because multi–detector row CT can be up to 8 times faster than single-detector CT and allows narrower collimation, it is ideal for this application (2). We use a Siemens Volume Zoom CT scanner (Siemens Medical Systems, Iselin, NJ), which combines multiple rows of detectors and faster gantry rotation. When performing CT angiography of the mesenteric vessels, we use a 4 x 1-mm collimation. This allows us to create 1.25-mm sections, which we reconstruct at 1-mm intervals for high-quality 3D images. Because multi–detector row CT allows the choice of section thickness to be made retrospectively, 3-mm sections can also be created for review on film if desired. The introduction of multi–detector row CT has greatly improved the quality of the CT angiograms and 3D reformatted images by allowing thinner overlapping sections. In addition, the faster scanning practically eliminates motion and breathing artifacts.
After the data are acquired, they are transferred to our 3D workstation (Siemens 3D Virtuoso) for volume rendering. Volume rendering is the preferred algorithm for creating vascular maps. Unlike maximum intensity projection, volume rendering maintains spatial relationships and depth. It has been shown to be superior to maximum intensity projection in the evaluation of the renal arteries and peripancreatic vessels (3,4). Our software allows manipulation of parameters such as window width and level, brightness, and opacity so that the vessels can be optimally displayed. Also, this software allows real-time manipulation and editing of the volume, which is essential for displaying the vessels in the proper orientation. In addition, increases in computer power have significantly decreased the time required to create these CT vascular maps. Now, we can routinely perform 3D CT angiography of the mesenteric vessels in approximately 5–10 minutes.
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Normal Anatomy and Anatomic Variants
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Superior Mesenteric Artery
The SMA arises from the abdominal aorta, usually at the level of the L1 vertebral body, and supplies blood to the jejunum, ileum, right colon, and, usually, the transverse colon. It also supplies blood to the duodenum via the pancreaticoduodenal arcade. Typically, the SMA arises less than 1.5 cm below the celiac origin and is just superior to the origin of the renal arteries (Fig 1). The left renal vein is located posterior to the proximal portion of the SMA and anterior to the aorta, unless there is a normal variant such as a retroaortic or circumaortic renal vein. The SMA lies to the left of the SMV as it crosses over the third portion of the duodenum. When the SMA enters the mesentery, it usually lies posterior to the mesenteric vein, although this relationship is variable.
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Figure 1. Sagittal 3D multi-detector row CT scan demonstrates the normal anatomy of the celiac axis (thick solid arrow) and SMA (curved arrow). The SMA courses over the left renal vein (open arrow). The origin of the left renal artery is also visualized (thin solid arrow).
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The jejunal arteries (usually 4–6 arteries) arise from the left side of the SMA (Fig 2). These arteries are quite small and are therefore very difficult to visualize and identify on axial images (Fig 3). The ileocolic artery, which arises from the right side of the SMA, marks the transition from jejunal to ileal arteries. There are usually between eight and 12 ileal arteries (5,6). The branching pattern of the last jejunal artery, ileocolic artery, and ileal arteries varies, sometimes forming a loop or tripod. The ileocolic artery has branches to the terminal ileum, cecum, and lower ascending colon (Figs 2, 4). The right colic artery can arise from the SMA to aid the ileocolic and middle colic arteries in supplying blood to the ascending colon. However, it is absent in up to 80% of individuals (5). The middle colic artery usually arises from the right side of the SMA just before it enters the mesentery (Fig 2). It descends into the right lower quadrant, where it anastomoses with the ileocolic artery (Fig 5). Other branches that may arise from the SMA include an artery for the right angle of the colon and one for the transverse colon. There are also anastomotic connections between the artery to the transverse colon and the left colic artery, which arises from the IMA. Many variations exist (6).
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Figure 2. Coronal 3D multi-detector row CT scan demonstrates the normal anatomy and branching pattern of the SMA. The jejunal branches (straight solid arrows) and ileal branches (curved solid arrows) are well visualized. The ileocolic branch of the SMA arises from the right side of the vessel (curved open arrow). The middle colic artery is also identified (straight open arrow).
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Figure 3. Axial multi-detector row abdominal CT scans obtained at different levels demonstrate the normal appearance of the jejunal arteries (arrow). These vessels are very small and are much better visualized at CT angiography (cf Fig 2).
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Figure 4. Coronal 3D multi-detector row CT scan demonstrates the normal terminal branching pattern of the ileocolic artery (black arrow), which supplies the terminal ileum, cecum, and lower ascending colon. With optimization of technique, even the smallest branches feeding the bowel can be visualized (white arrows). The branches on this image represent the vasa recta.
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Figure 5. Three-dimensional multi-detector row CT scan (maximum intensity projection) demonstrates a normal variant anastomotic pathway between the ileocolic and middle colic arteries (arrows).
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The inferior pancreaticoduodenal artery is the pivotal point of embryologic gut rotation. It can arise from either the right or left side of the SMA (5,6) and may arise as one vessel or two (anterior and posterior). This vessel courses behind the SMV and superiorly to anastomose with the superior pancreaticoduodenal artery, which arises from the gastroduodenal artery (Fig 6). The marginal arteries of Dwight and Drummond supply the vasa recta to the small intestine and colon andprovide a continuous channel of potential collateral blood supply to the entire gut (7). The marginal artery is defined as the artery closest to and parallel with the wall of the intestine, supplying the vasa recta. The vasa recta are fine branches that arise from the marginal artery and supply the bowel wall (Fig 4). The middle colic artery is often the marginal artery for the major portion of its distribution. The arc of Riolan is an inconstant artery that courses parallel to a portion of the middle colic artery.
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Figure 6. Coronal 3D multi-detector row CT scan demonstrates the inferior pancreaticoduodenal artery (straight arrow), which arises from the SMA (curved arrow) and connects to the gastroduodenal artery.
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Aberrant branches from the SMA are relatively common (Figs 7–9). They include the common hepatic artery, right hepatic artery, splenic artery, celiac trunk, cystic artery, gastroduodenal artery, right gastroepiploic artery, and left gastric artery (5,7,8).
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Figure 7. Sagittal 3D multi-detector row CT scan demonstrates a normal variant common trunk (straight solid arrow), which gives rise to the celiac axis (curved arrow) and SMA (open arrow).
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Figure 8. Oblique 3D multi-detector row CT scan demonstrates a normal variant origin of the common hepatic artery (straight solid arrow) from the SMA (curved arrow). A biliary stent is present. The portal vein is also seen (open arrow).
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Superior Mesenteric Vein
The SMV is usually a single trunk of variable length (5–50 mm) that is formed by two large intestinal branches (right and left), which receive blood from several veins including the ileocolic, gastrocolic, right colic, and middle colic veins (Fig 10). In some patients, a single trunk may not be present. Instead, there may be large right and left mesenteric branches, both of which join the splenic vein to form the portal vein (7,9).
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Figure 10. Coronal 3D multi-detector row CT scan demonstrates the normal appearance of the SMV (straight solid arrow), which joins the splenic vein (curved arrow) at the portal confluence. The portal vein is also seen (open arrow).
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The SMV lies to the right of the SMA as it crosses over the third portion of the duodenum (Fig 3). When the superior mesenteric vessels enter the mesentery, the SMV usually lies anterior to the SMA, although this relationship is variable, especially in patients with malrotation or nonrotation of the gut (Fig 11). In patients with complete nonrotation of the gut, the relationship between the SMA and SMV will be reversed and the location of the small bowel and colon will be abnormal; typically, the small bowel will be on the right side of the abdomen and the colon on the left side (10,11). In these patients, the duodenum will not cross the spine. However, patients can have a variable degree of malrotation.
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Figure 11a. (a) Axial multi-detector row CT scan demonstrates reversal of the normal relationship between the SMV (straight arrow) and the SMA (curved arrow) due to malrotation. (b) Axial multi-detector row CT scan obtained inferior to a demonstrates abnormal configuration of the intestines. The small bowel is on the right side of the abdomen, and the entire colon is on the left side.
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Figure 11b. (a) Axial multi-detector row CT scan demonstrates reversal of the normal relationship between the SMV (straight arrow) and the SMA (curved arrow) due to malrotation. (b) Axial multi-detector row CT scan obtained inferior to a demonstrates abnormal configuration of the intestines. The small bowel is on the right side of the abdomen, and the entire colon is on the left side.
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Like the SMA, the SMV has jejunal and ileal branches that receive blood from the intestine.
Inferior Mesenteric Artery
The IMA arises from the aorta approximately 7 cm below the origin of the SMA, usually at the level of L3 (Fig 12). It is a relatively straight vessel with several branches, all of which arise from the left side (8,11). The left colic artery forms an anastomosis with the artery to the transverse colon, which arises from the SMA. It is absent in 12% of individuals, in whom its function is performed by the colosigmoid artery (5,6). The colosigmoid artery also arises from the left side of the IMA and supplies blood to the descending and sigmoid colon. There are usually two to four sigmoid branches that can arise from the IMA, colosigmoid artery, or left colic artery. The next branch off the IMA is the rectosigmoid artery. Finally, after the origin of the rectosigmoid artery, the IMA bifurcates into the superior rectal arteries.
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Figure 12a. (a) Sagittal 3D multi-detector row CT scan demonstrates the normal anatomy of the IMA (arrows). On axial scans, it is very difficult to follow the course of the IMA. With 3D CT angiography, however, the vessel can be seen in its entirety as it enters the pelvis and branches into the superior hemorrhoidal arteries. (b) Coronal 3D multi-detector row CT scan demonstrates the normal branching pattern of the IMA (arrows).
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Figure 12b. (a) Sagittal 3D multi-detector row CT scan demonstrates the normal anatomy of the IMA (arrows). On axial scans, it is very difficult to follow the course of the IMA. With 3D CT angiography, however, the vessel can be seen in its entirety as it enters the pelvis and branches into the superior hemorrhoidal arteries. (b) Coronal 3D multi-detector row CT scan demonstrates the normal branching pattern of the IMA (arrows).
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The colosigmoid artery can arise from the left colic artery or from the angle between the left colic artery and the IMA (Fig 12). The left colic artery can be absent or can arise from the SMA.
Inferior Mesenteric Vein
The major tributaries of the IMV include the superior hemorrhoidal vein, sigmoid vein, and left colic vein. The hemorrhoidal vein and sigmoid vein usually join to form a common trunk before uniting with the left colic vein. The IMV can terminate into the splenic vein or at the splenoportal angle or may drain into the SMV (Figs 13–15) (9).
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Figure 13. Coronal 3D multi-detector row CT scan demonstrates the normal appearance of the mesenteric vessels. The IMV (straight solid arrow) joins the SMV (curved arrow), after which the two vessels join the splenic vein (open arrow) at the portal confluence.
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Figure 14. Coronal 3D multi-detector row CT scan demonstrates a normal variant IMV (straight solid arrow) that joins the splenic vein (open arrow) directly. These vessels then join the SMV (curved solid arrow) at the portal confluence.
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Pathologic Conditions
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Pancreatic Cancer
In addition to detecting liver metastases, a crucial goal of CT in patients with pancreatic cancer is the evaluation of adjacent vascular structures. Involvement of any of the major arterial structures (eg, celiac axis, SMA) or venous structures (eg, portal vein, splenic vein, SMV) will make resection impossible at most institutions (12). Recent articles have described a vessel grading scale based on the percentage of a vessel’s circumference that is involved by tumor. Grades 1–4 indicate 0%–25%, 25%–50%, 50%–75%, and 75%–100% encasement, respectively (13).
In the past, all patients with pancreatic tumors underwent catheter angiography prior to surgery to assess the presence of mesenteric vessel encasement and to provide vascular maps. Several articles have shown similar results with spiral CT and angiography in this setting (4,13,14). CT can also be used to create angiography-style vascular maps and is less expensive than conventional angiography. With the recent introduction of multi–detector row CT, the limitations of earlier CT angiography are eliminated. Multi–detector row CT allows even faster scanning with very thin collimation, which further improves the quality of CT angiography in terms of vessel detail and definition. In addition, unlike conventional angiography, CT is not limited by plane or perspective, and often the "optimal" view can be determined in retrospect.
Invasion of the SMA is one of the contraindications for surgery in pancreatic cancer (Fig 16). Novick and Fishman (15) showed that conventional axial CT was not ideal for imaging the SMA due to the vessel’s oblique course.
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Figure 16a. Pancreatic cancer. (a) Axial oblique 3D multi-detector row CT scan demonstrates tumoral encasement of the SMA (arrows). (b) Sagittal 3D multi-detector row CT scan again demonstrates encasement of the SMA (arrows). Note that the tumor itself causes narrowing of the vessel.
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Figure 16b. Pancreatic cancer. (a) Axial oblique 3D multi-detector row CT scan demonstrates tumoral encasement of the SMA (arrows). (b) Sagittal 3D multi-detector row CT scan again demonstrates encasement of the SMA (arrows). Note that the tumor itself causes narrowing of the vessel.
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Involvement of the portal vein, splenic vein, or SMV is also typically a contraindication for surgery, although limited involvement of the portal vein or confluence may not be an absolute contraindication because surgeons may attempt resection with use of a vascular graft (Fig 17). Accurate assessment of the mesenteric veins requires proper timing of the intravenous bolus injection and scanning (16). For maximum opacification of venous structures, scanning should be performed during the portal venous phase (approximately 50 seconds after the start of injection) after obtaining an arterial-phase image. With multi–detector row CT, there is better opacification and visualization of smaller vessels in the venous arcade around the pancreas, which includes the gastrocolic vein and the anterosuperior and posterosuperior portions of the pancreaticoduodenal vein.
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Figure 17a. Pancreatic cancer. (a) Coronal oblique 3D multi-detector row CT scan demonstrates a large mass involving the portal confluence (arrows). (b) Coronal 3D multi-detector row CT scan demonstrates gastroepiploic varices (arrows) resulting from tumoral occlusion of the splenic vein.
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Figure 17b. Pancreatic cancer. (a) Coronal oblique 3D multi-detector row CT scan demonstrates a large mass involving the portal confluence (arrows). (b) Coronal 3D multi-detector row CT scan demonstrates gastroepiploic varices (arrows) resulting from tumoral occlusion of the splenic vein.
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Multi–detector row CT in particular allows better visualization of arterial and venous branching, thereby improving detection of involvement of the more distal portions of the mesenteric vessels. Visualization of the vasculature is greatly improved with 3D volume rendering, which can display a given vessel in the optimal plane; evaluation of the arteries and veins may be limited if only axial images are obtained.
Vascular involvement can be defined as either occlusion or narrowing of a vessel, usually with an associated soft-tissue mass surrounding the area of involvement. Collateral vessels may be present and are a useful secondary sign of vascular involvement.
Mesenteric Ischemia
Small bowel ischemia or infarction presents a diagnostic challenge in that clinical signs and symptoms are usually nonspecific. Common underlying causes of small bowel ischemia include SMA narrowing or occlusion due to atherosclerotic plaque, thrombus or tumoral encasement; mesenteric vein thrombosis or encasement; and hypoperfusion due to low cardiac output or atherosclerotic disease (17,18). Although angiography has historically been the procedure of choice for the diagnosis of mesenteric ischemia, CT (especially 3D multi–detector row CT) can now play a significant role.
Thrombosis of the main vessels can easily be seen at axial imaging, often with associated collateral vessels, depending on its chronicity (Fig 18). For evaluation of more distal branches of the mesenteric vessels and of narrowing or plaque at the origin of the arteries, 3D imaging offers a distinct advantage. Three-dimensional images allow better representation of complex collateral vessels and provide an excellent road map for surgeons (Fig 19).
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Figure 18a. Mesenteric ischemia in a patient who had undergone Whipple surgery for pancreatic cancer. (a) Axial 3D multi-detector row CT scan demonstrates thrombosis of the SMV (arrow). (b) Axial 3D multi-detector row CT scan obtained inferior to a demonstrates thickening of the small bowel, a finding that is compatible with ischemia resulting from thrombosis of the SMV.
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Figure 18b. Mesenteric ischemia in a patient who had undergone Whipple surgery for pancreatic cancer. (a) Axial 3D multi-detector row CT scan demonstrates thrombosis of the SMV (arrow). (b) Axial 3D multi-detector row CT scan obtained inferior to a demonstrates thickening of the small bowel, a finding that is compatible with ischemia resulting from thrombosis of the SMV.
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Figure 19a. Mesenteric ischemia. (a) Sagittal 3D CT angiogram demonstrates occlusion of the SMA. The celiac axis is also seen (arrow). (b) Coronal 3D CT angiogram demonstrates a collateral vessel arising from the gastroduodenal artery (straight arrow) and filling the SMA in a retrograde fashion (curved arrow).
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Figure 19b. Mesenteric ischemia. (a) Sagittal 3D CT angiogram demonstrates occlusion of the SMA. The celiac axis is also seen (arrow). (b) Coronal 3D CT angiogram demonstrates a collateral vessel arising from the gastroduodenal artery (straight arrow) and filling the SMA in a retrograde fashion (curved arrow).
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Inflammatory Disease
Detectable changes in mesenteric blood flow may be seen in patients with inflammatory disease of the small bowel. For instance, color Doppler ultrasonography (US) and power Doppler US have been used to differentiate active bowel inflammation (increased blood flow) from chronic wall thickening or fibrosis (no increased flow) in patients with Crohn disease (19). Similarly, Doppler US can demonstrate hemodynamic changes in the mesenteric vessels in patients with active inflammatory bowel disease that are not present in patients with quiescent disease.
With the introduction of multi–detector row CT and improvements in 3D CT, it may now be possible to detect some of these changes in patients with active inflammation and hyperemia of a bowel segment by measuring bowel wall enhancement over time (20). Mesenteric vessels supplying the diseased loops of bowel may be enlarged, indicating increased blood flow to that region compared with adjacent normal regions (Fig 20). In addition, multi–detector row CT with volume data sets obtained at defined enhancement points (eg, arterial phase or venous phase) makes it possible to quantify small bowel enhancement over time and to calculate small bowel perfusion rates. This may help detect hyperemia, even before changes in vessel size or configuration can be detected.
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Figure 20. Crohn disease. Coronal 3D multi-detector row CT scan demonstrates thickening and hyperemia of a small bowel loop on the right side of the abdomen (arrows). There is engorgement of the small vessels feeding this loop, a finding that is compatible with inflammation and hyperemia.
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Other Pathologic Conditions
Other disease entities can occur in the abdomen and involve the mesenteric vessels secondarily. For example, carcinoid tumor is a low-grade neuroendocrine malignancy that represents up to 40% of small bowel neoplasms. Almost 90% of small bowel carcinoid tumors occur in the ileum. Up to 30% will metastasize, the probability of metastasis being related to the size of the primary tumor (21). Although CT typically cannot dem-onstrate the primary mass in the submucosa of the bowel wall, carcinoid tumors that have infiltrated the mesentery have a characteristic CT appearance (Fig 21). Other conditions such as lymphoma or sclerosing mesenteritis (Fig 22) can also manifest as an infiltrating mass that envelops mesenteric vessels. Three-dimensional CT can demonstrate the relationship of the mass to the mesenteric vessels, which aids in surgical planning. CT angiography is also useful in these patients prior to their undergoing biopsy or surgery.
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Figure 21a. Carcinoid tumor in a patient with abdominal pain. (a) Coronal 3D multi-detector row CT scan demonstrates a mesenteric mass (arrows). Minimal small bowel thickening is also seen. (b) Sagittal 3D multi-detector row CT scan demonstrates encasement of the SMA (curved arrow) by the mass (straight arrows).
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Figure 21b. Carcinoid tumor in a patient with abdominal pain. (a) Coronal 3D multi-detector row CT scan demonstrates a mesenteric mass (arrows). Minimal small bowel thickening is also seen. (b) Sagittal 3D multi-detector row CT scan demonstrates encasement of the SMA (curved arrow) by the mass (straight arrows).
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Figure 22a. Sclerosing mesenteritis in a patient with abdominal pain. (a) Coronal 3D multi-detector row CT scan demonstrates an infiltrating mass (arrows) encasing the mesenteric artery and its branches. Significant small bowel thickening is also noted. (b) Axial CT scan again demonstrates encasement of the vessels by the mass (arrows) as well as small bowel thickening and ascites.
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Figure 22b. Sclerosing mesenteritis in a patient with abdominal pain. (a) Coronal 3D multi-detector row CT scan demonstrates an infiltrating mass (arrows) encasing the mesenteric artery and its branches. Significant small bowel thickening is also noted. (b) Axial CT scan again demonstrates encasement of the vessels by the mass (arrows) as well as small bowel thickening and ascites.
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Conclusions
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Multi–detector row CT represents a significant advance in CT technology. By allowing thin collimation (0.5–1.25-mm sections) and rapid scanning, excellent opacification of the mesenteric vessels can routinely be obtained. Better 3D volume sets in turn lead to improved 3D vascular maps, which are useful in cancer staging, surgical planning, and evaluating patients with suspected mesenteric ischemia.
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Footnotes
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Abbreviations: IMA = inferior mesenteric artery,
IMV = inferior mesenteric vein,
SMA = superior mesenteric artery,
SMV = superior mesenteric vein,
3D = three-dimensional
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Abstract
Introduction
