PMID- 16526013
OWN - NLM
STAT- MEDLINE
DCOM- 20060816
LR  - 20150525
IS  - 0740-3194 (Print)
IS  - 0740-3194 (Linking)
VI  - 55
IP  - 4
DP  - 2006 Apr
TI  - Investigation of anomalous estimates of tensor-derived quantities in diffusion 
      tensor imaging.
PG  - 930-6
AB  - The diffusion tensor is typically assumed to be positive definite. However, noise 
      in the measurements may cause the eigenvalues of the tensor estimate to be 
      negative, thereby violating this assumption. Negative eigenvalues in diffusion 
      tensor imaging (DTI) data occur predominately in regions of high anisotropy and 
      may cause the fractional anisotropy (FA) to exceed unity. Two constrained least 
      squares methods for eliminating negative eigenvalues are explored. These methods, 
      the constrained linear least squares method (CLLS) and the constrained nonlinear 
      least squares method (CNLS), are compared with other commonly used algebraic 
      constrained methods. The CLLS tensor estimator can be shown to be equivalent to 
      the linear least squares (LLS) tensor estimator when the LLS tensor estimate is 
      positive definite. Similarly, the CNLS tensor estimator can be shown to be 
      equivalent to the nonlinear least squares (NLS) tensor estimator when the NLS 
      tensor estimate is positive definite. The constrained least squares methods for 
      eliminating negative eigenvalues are evaluated with both simulations and in vivo 
      human brain DTI data. Simulation results show that the CNLS method is, in terms 
      of mean squared error for estimating trace and FA, the most effective method for 
      correcting negative eigenvalues.
CI  - Published 2006 Wiley-Liss, Inc.
FAU - Koay, Cheng Guan
AU  - Koay CG
AD  - Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin, USA. 
      guankoac@mail.nih.gov
FAU - Carew, John D
AU  - Carew JD
FAU - Alexander, Andrew L
AU  - Alexander AL
FAU - Basser, Peter J
AU  - Basser PJ
FAU - Meyerand, M Elizabeth
AU  - Meyerand ME
LA  - eng
GR  - EB002012/EB/NIBIB NIH HHS/United States
GR  - EY07119/EY/NEI NIH HHS/United States
GR  - MH062015/MH/NIMH NIH HHS/United States
PT  - Comparative Study
PT  - Journal Article
PT  - Research Support, N.I.H., Extramural
PL  - United States
TA  - Magn Reson Med
JT  - Magnetic resonance in medicine
JID - 8505245
SB  - IM
MH  - Anisotropy
MH  - Brain Mapping/*methods
MH  - Computer Simulation
MH  - *Diffusion Magnetic Resonance Imaging
MH  - Humans
MH  - Image Processing, Computer-Assisted/*methods
MH  - Least-Squares Analysis
MH  - Models, Theoretical
MH  - Monte Carlo Method
EDAT- 2006/03/10 09:00
MHDA- 2006/08/17 09:00
CRDT- 2006/03/10 09:00
PHST- 2006/03/10 09:00 [pubmed]
PHST- 2006/08/17 09:00 [medline]
PHST- 2006/03/10 09:00 [entrez]
AID - 10.1002/mrm.20832 [doi]
PST - ppublish
SO  - Magn Reson Med. 2006 Apr;55(4):930-6. doi: 10.1002/mrm.20832.