Hi Anthony -

Thanks for your input. You have raised very important points. I looked at the literature and found a paper where they look at FBL - fiber bundle length.

Lauren E. Salminen http://www.ncbi.nlm.nih.gov/pubmed/?term=Salminen%20LE%5Bauth%5D,[image: corresponding author] Peter R. Schofield http://www.ncbi.nlm.nih.gov/pubmed/?term=Schofield%20PR%5Bauth%5D, Elizabeth M. Lane http://www.ncbi.nlm.nih.gov/pubmed/?term=Lane%20EM%5Bauth%5D, Jodi M. Heaps http://www.ncbi.nlm.nih.gov/pubmed/?term=Heaps%20JM%5Bauth%5D, Kerrie D. Pierce http://www.ncbi.nlm.nih.gov/pubmed/?term=Pierce%20KD%5Bauth%5D, Ryan Cabeen http://www.ncbi.nlm.nih.gov/pubmed/?term=Cabeen%20R%5Bauth%5D, David H. Laidlaw http://www.ncbi.nlm.nih.gov/pubmed/?term=Laidlaw%20DH%5Bauth%5D, Erbil Akbudak http://www.ncbi.nlm.nih.gov/pubmed/?term=Akbudak%20E%5Bauth%5D, Thomas E. Conturo http://www.ncbi.nlm.nih.gov/pubmed/?term=Conturo%20TE%5Bauth%5D, Stephen Correia http://www.ncbi.nlm.nih.gov/pubmed/?term=Correia%20S%5Bauth%5D, and Robert H. Paul http://www.ncbi.nlm.nih.gov/pubmed/?term=Paul%20RH%5Bauth%5D

Neuronal fiber bundle lengths in healthy adult carriers of the ApoE4 allele: A quantitative tractography DTI study

They call this method quantitative DTI where they looked at Fiber length, volume etc. What they found is intriguing. I quote, "Results suggest that FBL in the UF is influenced by the presence of an ApoE e4 allele (ApoE4) in healthy older adults.

In my study, could it be that shorter FBL in the UF may predispose one to Cannabis addiction? Just thinking out loud.

Thanks,

Alan

On Wed, May 25, 2016 at 10:52 AM, Anthony Dick adick@fiu.edu wrote:

Hello,

I wouldn't mind jumping on this issue more broadly. Diffusion indices like FA, ADC, RD, and AD have more clear physiologic correlates. But what does the length of a tract, the volume of a tract, or the number of streamlines say about physiology? Tract length seems to be very dependent on head size. Or, for example, a person with a long corticospinal tract might simply be taller. At the very least these indices should be included with nuisance variables controlling for brain size. Length and volume measures seem to be very much affected by pulse sequence parameters, further calling into question their utility (see Wang et al., 2012; doi: 10.1016/j.neuroimage.2011.12.062). However, tract volume at least makes more intuitive sense (for example, quantifying Wallerian degeneration in T1 scans is essentially a volume measure). I thought Alan raised an important issue.

Anthony

On 5/25/16 10:34 AM, Alan Francis wrote:

Hi Imagers -

I am looking at the Uncinate fasciculus in a Cannabis use disorder (CUD). I found that CUD subjects have significantly shorter tract length and a significant group x side interaction in comparison with controls. Have you seen this before? What is the interpretation of this finding?

Thank you,

Alan

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