Medical Image Processing

Today the organizers of the 10th international meeting on fully 3-D image reconstruction in radiology and nuclear medicine have announced an extension of the manuscript submission deadline. The new deadline is 17 April 2009. The press release can be found here.

So use the additional time to fine tune your papers …

Yesterday, an algorithmic idea came into my mind which required a specific component:

• Given: Set of discrete delements E(i). Likelihood P(i) for the occurence of an element E(i).
• Goal: A function which returns a random element from E based on the distribution described by P.

What is this useful for? Well, I wanted to implement some kind of stochastic gradient descent algorithm for image registration without gradients but given a certain likelihood for a point to increase the cost function value. However, I think this kind of function comes in handy for many situations.

Matlab Code & Example

I wrote a Matlab function randelement() which solves exactly the problem. It is based on the theory of inverse transform sampling. The link to the download is given below. It is well-documented, that’s why I will only provide a little usage example:

The histogram will then look somehow similar to this:

So … this function seems to do what we wanted - I like it!
The latest version of randelement.m can be downloaded here.

You know what really hurts? A missing round() function if you really need it. Here is a code snippet for all of those with the same problem.

Who said medical imaging is boring? No way! Watch this great video about a Siemens guy who really loves his job with all its facets! Please turn on your sound. Otherwise it won’t be that funny.

Getting CUDA to run on your notebook is not always an easy task even if you have a CUDA enabled graphic card. In my Laptop there is a NVIDIA Quadro FX 570M (256 MB). However, the laptops require you to have a vendor-specific driver otherwise you get the nice error message “no supported hardware detected” when trying to install the latest CUDA driver.

However, NVIDIA seems to realize that this situation is not amusing to any Laptop-Programmer (like me). So yesterday I found on the download site the following item:

Beta Notebook Driver for Developers (181.22)

So downloaded, installed, and same error as with the other drivers. Well, at least it is a step into the right direction.  Maybe it works for others.

Standard alternative

However, there is still the option to install a modified driver for your notebook. This worked for me but is not the clean solution. Those drivers can be found at http://www.laptopvideo2go.com/

My current work includes the evaluation of a parametric motion field which is based on cubic B-splines. Already some time ago I ported the straight forward B-spline evaluation on the graphic card using CUDA. However, it required the evaluation of multiple nested for loops and took even on the graphic card some time.

So the quest of today was: Find a fast way for cubic B-spline evaluation using CUDA!

Of course Google helped me out and pointed meto the following papers:

Daniel Ruijters, Bart M. ter Haar Romeny, and Paul Suetens, “ Accuracy of GPU-based B-Spline Evaluation,” In Proc. Tenth IASTED International Conference on Computer Graphics and Imaging (CGIM), Innsbruck, Austria, pp. 117-122, February 13-15, 2008.

Christian Sigg and Markus Hadwiger, “ Fast Third-Order Texture Filtering,” In GPU Gems 2: Programming Techniques for High-Performance Graphics and General-Purpose Computation, Matt Pharr (ed.), Addison-Wesley; chapter 20, pp. 313-329, 2005.

They showed that a fast and accurate evaluation of B-splines is possible by replacing the nearest neighbor lookups during the B-spline evaulation by linear interpolation which is hard-wired on the GPU.

Finally the best of all: Daniel Ruijters provides some clean CUDA code for download on a website. It helped me out very well. In overall I gained a speed-up factor of 7 in comparison to my first naive implementation!

Sometimes you just need to write macros in your C/C++ code. And sometimes, they get long and you want to split them on multiple lines for reasons of readibility.

I admit, that I only seldomly use multiline macros. But today something new came to my mind. I created a simple multiline macro, e.g. something similar to this:

Nothing difficult or wrong on the first sight! Right? Okay but I got hundreds of compilation errors!
After trying around some time I noticed that it is not allowed to put a space behind the slash, i.e. ” is okay and ‘ ‘ is not.

So if you encounter the same error - welcome to the club …. tststs one never stops learning

Image by: Fraunhofer IPT

At this years JEC trade fair in Paris (Hall 1, Stand T18) from March 24 to 26 a new catheter developed by researchers at the Fraunhofer Institute for Production Technology IPT in Aachen, will be presented. They have developed a guide wire made of glass-fiber-reinforced plastic: Because the guide wire is made of plastic the imaging can be performed by magnetic resonance tomography instead of computer tomography,” says IPT scientist Adrian Schütte.

So will we loose our nice fluoroscopic images from our beloved C-arm systems? We will see …
The complete press release can be found here.