Volume Intensity Projection Fade MIP Joel Neuman, M.D. Zoom Imaging, PA S. Pohlman, M. Meyers M.D, L. Ciancibello E. Dharaiya Philips Medical Systems. Philips Medical systems

Introduction A myriad of post-processing techniques have been explored since the advent of multi-slice CT (MSCT), and in particular CT angiography (CTA). This presentation describes a novel post-processing method for evaluating CTA datasets. This method is called FadeMIP, also known as Volume Intensity Projection (VIP). VR on the left and FadeMIP-VIP on the right. Compare the arteries on the VR with the same arteries on the VIP. Philips Medical systems

Learning Objectives Review common 2D and 3D visualization methods for displaying CT angiography studies. Review the mathematical concepts behind a new 3D visualization method, ‘VIP’. Review several clinical examples of CTA showing the potential advantages of the ‘VIP’ rendering. Philips Medical systems

Comparison of Visualization Methods for Reviewing CTA Traditional Axial slices With axial slices it is generally not possible to view the vessel in its entirety. MS-CTA generates hundreds of slices which can be used to produce three dimensional images of the vessels. MIP Projects a 2D view of the brightest voxels along each ray passing through the volume. Generally shows normal vessels accurately, however, no depth information is provided in the resulting image. Those very dense structures may obscure the vessels. Philips Medical systems

Comparison of Visualization Methods for Reviewing CTA Surface Rendering In surface rendering only the inner or outer surface of organs can be examined. The grading of stenosis tends to be inaccurate due to incorporation of calcium and variable threshold setting. Volume Rendering In volume rendering, opacities and colors are attributed to densities/regions of the dataset allowing them to be rendered opaque, translucent, or invisible. Overlapping, penetrating, and connected tissues can effectively be visualized using Volume Rendering where other rendering techniques may fail. Also, reduce large volume datasets into concise images which are better suited to understanding complex relationships compared with the axial images. Philips Medical systems

Learning Objectives Review common 2D and 3D visualization methods for displaying CT angiography studies. Review the mathematical concepts behind a new 3D visualization method, ‘VIP’. Review several clinical examples of CTA showing the potential advantages of the ‘VIP’ rendering. Philips Medical systems

VIP Principles Like traditional MIP, VIP displays the maximum Hounsfield unit along a particular ray projection, but unlike traditional MIP, it also considers the distance between the voxel and the eye-point. Thus, moderately dense structures, such as contrast filled vessels, can be well depicted even if other higher density structures, such as bone or metal, exist along a particular ray. In such cases the object can be rotated such that the structures of interest are closer to the eye-point and are thus depicted with relatively greater brightness. Philips Medical systems

Schematic Representation The voxels that are closest to the eye-point are given the greatest brightness value and pixels that are farther away are ‘faded’ according to their distance from the eye-point. The images can be rotated such that the structures of interest are displayed closer to the eye-point and appear brighter. Brightest voxels Eye-point Faded voxels Monitor Philips Medical systems

Schematic Representation Eye point Faded front Faded back Gradually darkened voxels Faded voxels in front of the slab Faded voxels in the back of the slab Slab thickness Philips Medical systems

VIP vs. MIP Comparison The slab thickness in both images is the same. The only difference is the rendering used. In this image the vertebral bodies are faded as they are farther away from the eye-point. The density of other regional bones is proportionately decreased. The aorta and its main branches are displayed without being eclipsed by the underlying bone. Conventional MIP simply places the brightest pixel along a particular ray, and ‘paints’ it to the screen. This often results in vessels being obscured by bone, calcium or even other vessels. Regular MIP image VIP Philips Medical systems

VIP vs. MIP Comparison Anatomically, VIP: Compared to MIP, VIP: Has less problems with super-imposition of competing density structures along a particular ray. - Retains excellent low - contrast resolution. Some other characteristics of VIP include: - Rapid processing of large MSCT datasets saves time since bone removal is often unnecessary. - Uses MIP principles with the addition of spatial detail of MPR and volume rendering. Anatomically, VIP: - Helps differentiate spatial relationship of complicated vascular anatomy. - Exceptional visualization of vascular anatomy in spite of overlapping bony or other contrast enhanced structures. Philips Medical systems

VIP vs. MIP Comparison MIP VIP This patient has an aorto-iliac occlusion (LeRiche Syndrome). Using the same slab thickness, conventional MIP masks important information since the denser bone obscures the vessles. With VIP, the extensive collateral pathways reconstituting the femoral arteries are well depicted. Note that even the common femoral arteries are seen in spite of their close relationship to the acetabulum. Philips Medical systems

Learning Objectives Review common 2D and 3D visualization methods for displaying CT angiography studies. Review the mathematical concepts behind a new 3D visualization method, ‘VIP’. Review several clinical examples of CTA showing the potential advantages of the ‘VIP’ rendering. Philips Medical systems

Thoracic CTA With VIP it is possible to see branches of the thoracic aorta crossing in front of the descending thoracic aorta. The artery crossing the descending thoracic is not visualized with a conventional MIP rendering. MIP VIP Philips Medical systems

Circle of Willis This sagital and axial CT view of the circle of Willis using VIP permits rapid and easy identification of the three aneurysms in the circle of Willis. Observe how well the surrounding vessels are displayed. Philips Medical systems

Volume intensity projection Cerebral CTA Volume intensity projection Sagital VIP along with a rotated VIP using a fixed center of rotation. Two aneurysms are clearly seen on the rotated view. Philips Medical systems

Volume intensity projection Cerebral CTA Volume intensity projection CTA-COW showing two contiguous aneurysms Philips Medical systems

Carotid CTA MIP VIP Note on the MIP image the carotid bifurcation is obscured due contrast in the internal jugular vein. However, the VIP image on the right clearly demonstrates the carotid bifurcation in spite of the jugular vein because it is closer to the eye-point. Philips Medical systems

Abdominal CTA VIP MIP Vascular encasement is clearly seen at the origin of the celiac trunk and proximal branch vessels. However, on the MIP projection the mass is not apparent. On the VIP narrowing of the vessels is well depicted as is the lower density of the pancreatic mass. Philips Medical systems

Peripheral CTA Angiogram MIP VIP MIP demonstrating a segment of the posterior tibial artery. VIP show a larger portion of the artery including significant distal disease. Note the calcaneus does not interfere with visualization. DSA barely demonstrates the terminal branches. Philips Medical systems

Cardiac CTA VIP Leak following repair of LV aneurysm. The arrows demonstrate the intact myocardium with thinning of the apex well seen. Philips Medical systems

Cardiac CTA Observe how the LAD is well seen equally in the VR image and VIP. A conventional MIP view would not distinguish the LAD against the background of the LV due to the high density from the contrast in the chamber. VR VIP Philips Medical systems

Thoracic CTA VIP Thoracic aorta dissection type B. True lumen versus false lumen is very well visualized in these VIP views. Philips Medical systems

Thank you Philips Medical systems