I attended an interesting lecture this week. The professor who spoke talked about Diffusion Tensor Imaging (DTI) as well as about a newer technology they are trying to help develop – High Angular Resolution Diffusion Imaging (HARDI). DTI is based on tensor mathematics and physics. The tensor in DTI is basically a 3×3 matrix (x, y, and z planes) of numbers that represent the diffusion per voxel in the brain. A voxel is a volumetric pixel – a 3D portion of the brain in MR imaging. The highest resolution we can typically get with clinical MR scanners is a cubic mm voxel. So with DTI we have a tensor, a matrix, that describes the diffusion of water molecules within each voxel in the brain. Diffusion in a jar of water or in the ventricles of the brain tends to be fast and spherical. It is less spherical in the gray matter and even less so in the white matter. In fact, the diffusion of water is highly directional in white matter (the myelinated axons of neurons). This means that the water molecules tend to diffuse somewhat parallel to the length of the axon. The movements of these water molecules are picked up by the MR scanner (which is technically “focusing” on the hydrogen atoms in water).
The diffusion per voxel can be quantified by measures of fractional anisotropy (how directional is the movement), Mean Diffusivity (total diffusion within the voxel), and by the eigenvalues of the matrix (basically how far the molecules moved in the direction of the eigenvector).
Back to HARDI. HARDI improves upon DTI by allowing for more directions of the white matter fibers to be separated out than is possible with DTI. There are some areas of the brain where there are a lot of crossing fibers and these areas show up as dark spots on DTI (which looks like a hole in the brain). With HARDI, you can see that the fibers are just more complex than is possible to calculate with DTI.
Both of these methods are useful for measuring the overall integrity (and potentially connectivity) of the white matter in the brain.
Dealing with TBIs from the Iraq War
I read a good article on CNN that details some of the problems that veterans and health professionals face when dealing with TBIs acquired during military action. The article provides a good perspective of the “human side” of TBI.
I’ve posted about this topic before but felt that we should revisit it because so many veterans are affected by TBIs (as well as mental health issues). I don’t know the exact number of veterans affected by TBIs but studies have shown that >30% of soldiers and Marines have some sort of psychological issue related to their service in Iraq and/or Afghanistan. The military and the government are realizing how salient this problem is and will be.
“Congress included $900 million in the DoD’s supplemental budget fir fuscal years 2007 and 2008 to fund more mental health services, as well as more research on the effects of traumatic brain injuries (TBI) and treatments for TBI and post-traumatic stress disorder (PTSD)” (Monitor on Psychology, Sep. 2007, pp. 38-39).
Continuing the Introduction to Human Development
I’m now back in the country after my long and very eventful trip. The brain imaging conference was fabulous. Anyway, I just wanted to add a few more of my development lecture slides in PDF format. They are fairly brief and again, just outlines of the material but I tried to fill in a little more info.
I’ll post some more neuroscience material soon – I just have to get caught up on a week’s worth of missed school and related work.
Biological Influences on Development