Three-dimensional Volume Rendering of Spiral CT Data: Theory and Method1
Paul S. Calhoun, BFA,
Brian S. Kuszyk, MD,
David G. Heath, PhD,
Jennifer C. Carley, BS and
Elliot K. Fishman, MD
1 From the Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins Hospital, 600 N Wolfe St, Baltimore, MD 21287 (P.S.C., B.S.K., J.C.C., E.K.F., D.G.H.), and HipGraphics, Baltimore, Md (D.G.H.). Presented as an infoRAD exhibit at the 1997 RSNA scientific assembly. Received June 1, 1998; revision requested August 3 and final revision received October 29; accepted October 30. Address reprint requests to E.K.F.
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Figure 1. Diagram illustrates SSD rendering technique. Numbers represent the voxel values for a sample 2D data set. An algorithm is applied to locate a "surface" within the data set at the margin of a region of voxels with intensities ranging from 6 to 9. Standard computer graphics techniques are then used to generate a surface that represents the defined region of voxel values.
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Figure 2. Diagram illustrates MIP rendering technique. Each voxel along a line from the viewer's eye through the volume of data is evaluated, and the maximum voxel value is selected on the basis of maximum intensity. The resulting displayed value (8) corresponds to this maximum voxel value.
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Figure 3a. Use of volume rendering versus MIP rendering for pulmonary artery mapping. (a) Volume-rendered image clearly depicts pulmonary arteries in the midplane including central vessels. (b) Corresponding MIP image appears to depict more vessels but is actually displaying the entire vascular map of the data set. This is best appreciated by noting the highly opacified superior vena cava and right innominate vein. One limitation of MIP is the inability to clearly define individual structures when they overlap. Interactive volume rendering does not have this limitation.
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Figure 3b. Use of volume rendering versus MIP rendering for pulmonary artery mapping. (a) Volume-rendered image clearly depicts pulmonary arteries in the midplane including central vessels. (b) Corresponding MIP image appears to depict more vessels but is actually displaying the entire vascular map of the data set. This is best appreciated by noting the highly opacified superior vena cava and right innominate vein. One limitation of MIP is the inability to clearly define individual structures when they overlap. Interactive volume rendering does not have this limitation.
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Figure 4. Diagram illustrates volume rendering technique. The upper portion of the diagram represents a histogram of the voxel values in the data "ray" depicted beneath it. An opacity of 0% and 100% are assigned for values of 5 or lower and 9 or higher, respectively. The resulting intermediate opacities for values 6, 7, and 8 are 25%, 50%, and 75%, respectively. The lower portion of the diagram shows the equation and progressive computational results used to determine weighted summation along the "ray" through the volume. The resulting displayed value (6) is affected by both opacity (as determined in the graph at the top) and the value of underlying voxels.
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Figure 5. Clip-plane editing. A clip plane (polygon indicated by straight arrow) can be used to interactively "cut away" the abdominal wall or other superficial structures to allow visualization of anatomic structures and pathologic conditions within the volume. The image demonstrates transitional cell carcinoma of the right renal pelvis (curved arrow).
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Figure 6. Diagram illustrates the effect of adjustments in window width and level with respect to the voxel histogram of a CT data set. Such adjustments alter the attenuation of structures displayed in a reconstructed 3D image. A change in width (slope) alters image contrast, whereas a change in level (shift on the x axis) alters data inclusion and the attenuation of voxels in the resulting image.
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Figure 7. Diagram illustrates fly-through and fly-around display functions. A fly-through reconstructs an image sequence with rotation and dollying similar to what is used for a complex camera shot. A fly-around projects a sequence of views from the surface of a sphere that has the region of interest at its center.
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Figure 8a. Multiple pelvic fractures. Anterior (a), outlet (b), and oblique (c) 3D reconstructions demonstrate fractures of the right femoral neck and left acetabulum. The extent of the fractures is clearly defined. The ability to edit images interactively is particularly helpful in visualizing displacement of the medial wall of the left acetabulum (c).
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Figure 8b. Multiple pelvic fractures. Anterior (a), outlet (b), and oblique (c) 3D reconstructions demonstrate fractures of the right femoral neck and left acetabulum. The extent of the fractures is clearly defined. The ability to edit images interactively is particularly helpful in visualizing displacement of the medial wall of the left acetabulum (c).
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Figure 8c. Multiple pelvic fractures. Anterior (a), outlet (b), and oblique (c) 3D reconstructions demonstrate fractures of the right femoral neck and left acetabulum. The extent of the fractures is clearly defined. The ability to edit images interactively is particularly helpful in visualizing displacement of the medial wall of the left acetabulum (c).
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Figure 9a. Fracture of the tibial plateau. Three-dimensional reconstructions clearly demonstrate a fracture of the lateral aspect of the tibial plateau. (a) Anterior view defines the joint space and its relationship to the fracture. (b) Superior view better defines the orientation of the fragments to the main components of the plateau.
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Figure 9b. Fracture of the tibial plateau. Three-dimensional reconstructions clearly demonstrate a fracture of the lateral aspect of the tibial plateau. (a) Anterior view defines the joint space and its relationship to the fracture. (b) Superior view better defines the orientation of the fragments to the main components of the plateau.
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Figure 10. Loosening of a hip prosthesis. Three-dimensional reconstruction (anterior view) clearly depicts a left hip prosthesis with loosening of the femoral cup and superior displacement of the femoral component despite substantial artifact on source images.
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Figure 11. Aortic dissection. Three-dimensional reconstruction with an angioscopic perspective shows the intimal flap (arrow) and involvement of the great vessels. The intravascular angioscopic view is ideal for evaluating aortic dissections.
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Figure 12. Figures 12, 13. (12) Carotid artery stenosis. Three-dimensional reconstruction demonstrates significant (>90%) stenosis of the internal carotid artery just past the bifurcation (arrow). (13) Pulmonary embolism. Three-dimensional reconstructions with standard (a) and angioscopic (b) views demonstrate a large thrombus in the right main pulmonary artery (arrow) that subsequently proved to be tumor thrombus from metastatic breast cancer.
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Figure 13a. Figures 12, 13. (12) Carotid artery stenosis. Three-dimensional reconstruction demonstrates significant (>90%) stenosis of the internal carotid artery just past the bifurcation (arrow). (13) Pulmonary embolism. Three-dimensional reconstructions with standard (a) and angioscopic (b) views demonstrate a large thrombus in the right main pulmonary artery (arrow) that subsequently proved to be tumor thrombus from metastatic breast cancer.
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Figure 13b. Figures 12, 13. (12) Carotid artery stenosis. Three-dimensional reconstruction demonstrates significant (>90%) stenosis of the internal carotid artery just past the bifurcation (arrow). (13) Pulmonary embolism. Three-dimensional reconstructions with standard (a) and angioscopic (b) views demonstrate a large thrombus in the right main pulmonary artery (arrow) that subsequently proved to be tumor thrombus from metastatic breast cancer.
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Figure 14a. Renal cell carcinoma. Axial (a), coronal (b), and lateral oblique (c) 3D reconstructions demonstrate a left-sided renal cell carcinoma. The superolateral position of the tumor makes it accessible at partial nephrectomy.
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Figure 14b. Renal cell carcinoma. Axial (a), coronal (b), and lateral oblique (c) 3D reconstructions demonstrate a left-sided renal cell carcinoma. The superolateral position of the tumor makes it accessible at partial nephrectomy.
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Figure 14c. Renal cell carcinoma. Axial (a), coronal (b), and lateral oblique (c) 3D reconstructions demonstrate a left-sided renal cell carcinoma. The superolateral position of the tumor makes it accessible at partial nephrectomy.
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Figure 15. Renal cell carcinoma. Three-dimensional reconstruction demonstrates a 2-cm-diameter, left-sided renal cell carcinoma (arrow). Note that the mass is totally intrarenal.
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Figure 16a. Renal artery anatomy in a potential renal donor. Axial (a) and coronal (b, c) volume-rendered 3D images of spiral CT data clearly demonstrate the anatomy of the renal arteries. This capability obviates classic angiography in such patients.
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Figure 16b. Renal artery anatomy in a potential renal donor. Axial (a) and coronal (b, c) volume-rendered 3D images of spiral CT data clearly demonstrate the anatomy of the renal arteries. This capability obviates classic angiography in such patients.
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Figure 16c. Renal artery anatomy in a potential renal donor. Axial (a) and coronal (b, c) volume-rendered 3D images of spiral CT data clearly demonstrate the anatomy of the renal arteries. This capability obviates classic angiography in such patients.
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Figure 17. Venous enlargement in a potential renal transplant donor. Three-dimensional reconstruction demonstrates an enlarged left gonadal vein (arrow). Definition of this vessel is important in preoperative evaluation prior to laparoscopic nephrec-tomy.
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Figure 18a. Normal vascular anatomy in a potential liver transplant candidate. Volume-rendered 3D reconstruction (a) and MIP image obtained in a similar projection (b) clearly depict the celiac axis and the hepatic artery.
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Figure 18b. Normal vascular anatomy in a potential liver transplant candidate. Volume-rendered 3D reconstruction (a) and MIP image obtained in a similar projection (b) clearly depict the celiac axis and the hepatic artery.
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Figure 19. Splenomegaly in a potential liver transplant candidate. Volume-rendered 3D image demonstrates the hepatic artery (arrow) and marked splenomegaly.
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Copyright © 1999 by the Radiological Society of North America.
