Technique Details

If you have this discussion with Siemens, one of the first things that they will tell you is that cone beam CT imaging requires diluted contrast. However, one thing that they perhaps are overlooking is that there is a large range of contrast concentrations being utilized as a matter of routine in neuroendovascular labs. Visipaque, for example, is sold in the following concentrations: 270 and 320. In our lab, we have had success with Visipaque 270 for both planar angiography and cone beam CT acquisitions without the use of dilution.

No 270? No Problem

For labs utilizing 300 or 320 iodine concentration contrast in a 150 ml contrast injector but aiming to use diluted contrast to a concentration of around 270 mgI/mL, use the following formula: Volume of contrast (mL) = Target concentration (270) × Total volume (150) / Stock concentration

Neuroendovascular requires practitioner dependent imaging. A power injector delivers a more perfect, consistent square wave bolus with each injection. This is simply better than the variability created with hand injected angiography. There are two additional compelling reasons to power inject: removing all physicians from the room during highest radiation usage, and cone beam CT imaging is best acquired when using approximately half the injection rate of planar angiography.

The ICONO machine's interactive reconstruction feature allows users to refine imaging volumes and maximize the information captured in each voxel. Interactive reconstruction processes the acquired volume data into a region of interest defined by the user, resulting in increased detail per voxel—down to 0.1 mm resolution.

Resolution Modes

MicroDynaCT offers 0.05mm resolution, while Interactive Reconstruction achieves 0.1mm resolution for optimal diagnostic clarity.

Aneurysm & Stent Analysis are tools that enable accurate cross sectional measurement of an artery surrounding either an aneurysm or a stenosis. This tool changed the way we practiced with flow diverters. We have found that arteries are often ovalized and the average dimension given by this tool between the long and short diameter has proven to be quite accurate. Additionally, both tools enable implanting of a stent of a specific length superimposed on the 3D volume rendering.

Generally speaking when cone beam CT is acquired most individuals look at the volumetric or 3D image and ignore the three other sequences. MPR stands for multiplanar reconstruction referring to the thinnest section of axial, coronal, and sagittal cross sectional images. MIP, or maximum intensity projection, takes the MPRs and represents the brightest single voxel within a slab of a given width.

This is a technique that we relied on more heavily prior to learning the tools of cone beam CT imaging, nevertheless it remains a powerful and simple way of illustrating the relationship of the devices and the surrounding vessels. Further, it takes very little time to process.

For reasons related to how the human brain processes visual information, it is possible to create a 3D image from two images taken a few degrees apart and fused by crossing ones eyes or using prism glasses. With modern cone beam CT imaging, we find that we use steriography somewhat less, but the ease of acquisition—two planar runs taken six degrees apart—and the decreased radiation compared with a cone beam image still add value in some cases.

Clip planes and VOI Punch are the two ways to eliminate parts of the image that do not add to the diagnostic value. VOI Punch is an erase tool—circle a region and choose whether to eliminate everything inside or outside. Clip Planes are less well known and harder to master, but once you do, add functionality that you cannot get with VOI Punch.

Workflow on the Icono workstation can take time to master. However, it is well worth the time spent given the power of the functionality. There are too many quick commands to list, though all will be covered in our videos.

Key Quick Commands

Folder Stack: Organize and access your reconstructed images efficiently.

Manipulate Tool: Transform and refine your 3D volume with precision controls.

Bookmarking saves the exact state of a post processed 3D image. On older Siemens workstations this tool could be used in conjunction with 3D follows C-arm to reposition to an old working projection.

This tool digitally magnifies the roadmap and the joystick on the control console can be used to pan the magnified roadmap. You only get one mag (2X magnification). Tremendously helpful when you need a larger field of view but want the ease of visualization of a magnified image.

3D Follows C-Arm

You can use the C-Arm to rotate the 3D image, showing you exactly what view you will have on your planar arteriographic run.

C-Arm Follows 3D

You can set up different angles at the workstation and proceed to actuate the C-Arms to obtain the chosen views.

3D windowing is done by holding down the scroll wheel button and moving your mouse. Up/down and side to side adjust the center and width respectively. Preset Gallery is critically important—there are numerous presets set up with the machine, and you can save presets any time you have a window you find valuable.

We have found that setting up projections is time well spent for angiography and intervention. Image Overlay takes a 3D image and shows the angle of the C-arm, the location of the area of interest, and the magnification level that correlates with planar imaging.

The most common fusion is the 4 or 5s DSA where the machine automatically fuses elements of the mask and the subtraction. The workstation also enables fusion of two separate cone beam CT acquisitions. We fuse post contrast to post contrast cone beam CTs to better elucidate angioarchitecture of dural fistulae or brain AVM, and post contrast with pre contrast cone beam acquisitions to understand the relationship between implants and neurovascular disease.