Additional Resources ❯ Clinical Concerns ❯ Current Clinical Concerns in CT: 3D3

Current Clinical Concerns in CT: Results : 3D Rendering

3D Algorithms

1. I work on a volume zoom in a small hospital. We do very few CTA's of renals, carotids, etc. I have the protocols for scanning, but need more information on MIPS, volume rendering, etc. This is all foreign to me. We had applications come in twice, but it was only touched on. I need printed material that I can follow when I get these cases.

Answer:

1. There is a ton of material and 1000's of cases on www.ctisus.com.
2. You can also link to www.insideinspace.com for more CTA information
3. Next month, the 3rd edition of the Fishman/Jeffrey MDCT book can serve as a good reference

2. RE: settings for volume rendered images. Your volume rendered images are really nice. We are just getting up and running with our new GE Lightspeed 8 and 16 scanners, and TeraRecon workstations. I'm still learning all the capabilities of our workstations, but haven't been able to figure out how to reproduce the images you are publishing. I've asked TeraRecon to look into this, but I also wonder if there are any Mask settings that you may have that would be transferable to other workstations, that you might be able to post? I've learned a great deal from this website, and I applaud the service your are providing to the entire radiologic community.

Answer: Templates are very specific to a workstation and are not simply transferred. I just spoke with Robert Taylor of TeraRecon and he said it might just be best to contact him, and he will get someone to update your system. For the brave, he did list this memo as well: (dated 3/16/03)

Dear All,

The new templates can be installed on a version 3.1 or later system as
follows:

1) You will need to be connected to the Internet

2) Click on this link:
http://zoo.terarecon.com/AquaBin/UnlitTemplates.zip

3) When prompted for a location to save the file, choose one, e.g. C:\

4) Once the download has completed, locate the file in the place where
you
saved it. If you did not download it to the workstation, copy the file
to a
floppy disk, and copy it to C:\ on the workstation.

5) Right click on the saved file, UnlitTemplates.zip, and select WinZip
-
Extract To Folder c:\UnlitTemplates

6) Start the workstation software, and go to the IMPORT tab on the
patient
list.

7) Browse to C:\UnlitTemplates, hit the IMPORT button

8) This should import the templates,and when you go into the 3D viewer,
you
should see them on your templates list. Some are good for soft tissue,
some
for CTA, some for Bone.

===============

Please contact Al Thoman if you have problems, and he'll be able to put
you
in touch with a specialist who can help you through the steps.

If you do not have a version 3.1 system, or if you'd like to do this
manually yourself (this will work on a 3.1 or 3.0 workstation), here are

the steps:

===============

1) Start the 3D viewer on the dataset you wish to process

2) Hit the LIGHT button on the right side of the screen, under the
templates.

3) Move the "AMBIENT" slider all the way to the right

4) Hit the MASK button next to the LIGHT button

5) Hit the ADVANCED button at the top right of the screen

6) Click the button "2" so that it is no longer pressed in.

7) We will now work on the controls next to button "1"

8) Right click on the left end of the slider - set the color to Black or
a
dark gray

9) Right click on the right end of the slider, set the color to White

10) Under the slider, there is a small drop list control, that lets you
control Shape, Opacity, Brightness and Material

11) Set the Brightness to 1.0, set the Shape to "Linear Ramp"

12) Now, adjust the opacity, max and min thresholds, until you see the
image you like

13) The use of the cutplane is a nice way to reveal the interior of the
scan.

14) When you have a setting you like, you can click the TEMPLATE button
next to the ADVANCED button, and then hit SAVE to save your template

===============

Please contact Al Thoman or myself if you have any questions,

Kind regards,

Robert

3. RE: VR for estimation of vascular stenoses. One of my colleagues has reservations using 3D vascular mapping to estimate the % stenosis on CTA. In particular, she is concerned about the effect of changing the windowing or trapezoid parameters on the apparent vessel caliber. We have all seen stenoses made to look like occlusions by changing the display. How do we avoid spuriously over- or under- estimating the degree of stenosis on arteries?

Answer: There is a learning process, but once you master the technique it works well. An article referenced below evaluated the accuracy of volume rendering.

4. We have a Leonardo workstation, but do not have a MINIP tool button. We have an extra effort to do MINIP applications. Is it a general problem for other workstations, or a local problem?

Answer: You must go to www.InsideInspace.com and it will show you where on Inspace the MINIP is. If this doesn't help, let me know.

References
BS Kuszyk, DG Heath, PT Johnson, J Eng, and EK Fishman CT angiography with volume rendering for quantifying vascular stenoses: in vitro validation of accuracy. AJR 1999; 173: 449 - 455.

Summary: In this study, 3 phantoms of vascular stenoses (33%, 67% and 83%) were scanned with single detector helical CT using various acquisition and reconstruction protocols. Volume rendering was conducted to assess diameter and percentage of stenosis. Results showed that vessel orientation significantly impacted the accuracy, with phantoms coursing parallel to the axial plane resulting in a less accurate measured percentage of stenosis. Furthermore, results showed that for 33% and 67% stenosis, the optimal opacity to maximize accuracy at VR was 50%. In the setting of 83% stenosis, an opacity setting of 60% provided the most accurate rendering.

Calhoun PS, Kuszyk BS, Heath DG, Carley JC, and Fishman EK.
Three-dimensional Volume Rendering of Spiral CT Data: Theory and Method.
RadioGraphics, May 1999; 19: 745 - 764.

Summary: This review provides an excellent explanation of different rendering algorithms, including MIP, shaded surface rendering and volume rendering. Such information is essential to those using these algorithms for clinical imaging, so that the strengths and weaknesses of each rendering technique are understood.