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Peripheral Nerve Diffusion Tensor Imaging: Assessment of Axon and Myelin Sheath Integrity.

Heckel A, Weiler M, Xia A, Ruetters M, Pham M, Bendszus M, Heiland S, Baeumer P - PLoS ONE (2015)

Bottom Line: FA correlated with dml (r=-0.63, p=0.002, Bonf. corr.) and sNCV (r=0.68, p=0.001, Bonf. corr.) but not with markers of axon integrity.DTI is particularly sensitive, since these findings are observed in healthy participants.Our results encourage future studies to evaluate the potential of DTI in differentiating axon from myelin sheath injury in patients with manifest peripheral neuropathies.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroradiology, Heidelberg University Hospital, Heidelberg, Germany; Department of Diagnostic Radiology, Freiburg University Hospital, Freiburg, Germany.

ABSTRACT

Purpose: To investigate the potential of diffusion tensor imaging (DTI) parameters as in-vivo biomarkers of axon and myelin sheath integrity of the median nerve in the carpal tunnel as validated by correlation with electrophysiology.

Methods: MRI examinations at 3T including DTI were conducted on wrists in 30 healthy subjects. After manual segmentation of the median nerve quantitative analysis of fractional anisotropy (FA) as well as axial, radial and mean diffusivity (AD, RD, and MD) was carried out. Pairwise Pearson correlations with electrophysiological parameters comprising sensory nerve action potential (SNAP) and compound muscle action potential (CMAP) as markers of axon integrity, and distal motor latency (dml) and sensory nerve conduction velocity (sNCV) as markers of myelin sheath integrity were computed. The significance criterion was set at P=0.05, Bonferroni corrected for multiple comparisons.

Results: DTI parameters showed a distinct proximal-to-distal profile with FA, MD, and RD extrema coinciding in the center of the carpal tunnel. AD correlated with CMAP (r=0.50, p=0.04, Bonf. corr.) but not with markers of myelin sheath integrity. RD correlated with sNCV (r=-0.53, p=0.02, Bonf. corr.) but not with markers of axon integrity. FA correlated with dml (r=-0.63, p=0.002, Bonf. corr.) and sNCV (r=0.68, p=0.001, Bonf. corr.) but not with markers of axon integrity.

Conclusion: AD reflects axon integrity, while RD (and FA) reflect myelin sheath integrity as validated by correlation with electrophysiology. DTI parameters consistently indicate a slight decrease of structural integrity in the carpal tunnel as a physiological site of median nerve entrapment. DTI is particularly sensitive, since these findings are observed in healthy participants. Our results encourage future studies to evaluate the potential of DTI in differentiating axon from myelin sheath injury in patients with manifest peripheral neuropathies.

No MeSH data available.


Related in: MedlinePlus

DTI parameter values of the median nerve at the wrist from proximal to distal.X-axis denotes the distance from the reference structure (hamulus of the hamate bone) in millimeters. Negative/positive values indicate position proximal/distal to that reference, respectively. Errorbars denote the standard error of the mean. FA: fractional anisotropy; AD: axial diffusivity; MD: mean diffusivity; RD: radial diffusivity.
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pone.0130833.g002: DTI parameter values of the median nerve at the wrist from proximal to distal.X-axis denotes the distance from the reference structure (hamulus of the hamate bone) in millimeters. Negative/positive values indicate position proximal/distal to that reference, respectively. Errorbars denote the standard error of the mean. FA: fractional anisotropy; AD: axial diffusivity; MD: mean diffusivity; RD: radial diffusivity.

Mentions: Fig 2 displays proximal-to-distal DTI parameter values of the median nerve at the wrist (Fig 2). The FA profile is u-shaped with a minimum at -4 mm, i.e. four millimeters proximal to the hamulus of the hamate bone in the center of the carpal tunnel (Fig 2a). The RD profile appears as an inverted FA profile with the maximum again at -4 mm (Fig 2d). The MD and RD profiles appear similar with both maxima at -4 mm (Fig 2c and 2d). The extrema of FA, RD and MD are all distinct from the mean parameter baseline (t≥4.7(df = 29), p<0.001 for all parameters). Specifically, FA minimum was at -6.3% of mean baseline, and MD and RD maxima were at +8.0% and +15.3% of mean baseline, respectively. The AD profile differs markedly showing an almost linearly increasing proximal-to-distal gradient (Fig 2b). Example DTI parameter images of the median nerve within the carpal tunnel are shown in S1 Fig.


Peripheral Nerve Diffusion Tensor Imaging: Assessment of Axon and Myelin Sheath Integrity.

Heckel A, Weiler M, Xia A, Ruetters M, Pham M, Bendszus M, Heiland S, Baeumer P - PLoS ONE (2015)

DTI parameter values of the median nerve at the wrist from proximal to distal.X-axis denotes the distance from the reference structure (hamulus of the hamate bone) in millimeters. Negative/positive values indicate position proximal/distal to that reference, respectively. Errorbars denote the standard error of the mean. FA: fractional anisotropy; AD: axial diffusivity; MD: mean diffusivity; RD: radial diffusivity.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4482724&req=5

pone.0130833.g002: DTI parameter values of the median nerve at the wrist from proximal to distal.X-axis denotes the distance from the reference structure (hamulus of the hamate bone) in millimeters. Negative/positive values indicate position proximal/distal to that reference, respectively. Errorbars denote the standard error of the mean. FA: fractional anisotropy; AD: axial diffusivity; MD: mean diffusivity; RD: radial diffusivity.
Mentions: Fig 2 displays proximal-to-distal DTI parameter values of the median nerve at the wrist (Fig 2). The FA profile is u-shaped with a minimum at -4 mm, i.e. four millimeters proximal to the hamulus of the hamate bone in the center of the carpal tunnel (Fig 2a). The RD profile appears as an inverted FA profile with the maximum again at -4 mm (Fig 2d). The MD and RD profiles appear similar with both maxima at -4 mm (Fig 2c and 2d). The extrema of FA, RD and MD are all distinct from the mean parameter baseline (t≥4.7(df = 29), p<0.001 for all parameters). Specifically, FA minimum was at -6.3% of mean baseline, and MD and RD maxima were at +8.0% and +15.3% of mean baseline, respectively. The AD profile differs markedly showing an almost linearly increasing proximal-to-distal gradient (Fig 2b). Example DTI parameter images of the median nerve within the carpal tunnel are shown in S1 Fig.

Bottom Line: FA correlated with dml (r=-0.63, p=0.002, Bonf. corr.) and sNCV (r=0.68, p=0.001, Bonf. corr.) but not with markers of axon integrity.DTI is particularly sensitive, since these findings are observed in healthy participants.Our results encourage future studies to evaluate the potential of DTI in differentiating axon from myelin sheath injury in patients with manifest peripheral neuropathies.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroradiology, Heidelberg University Hospital, Heidelberg, Germany; Department of Diagnostic Radiology, Freiburg University Hospital, Freiburg, Germany.

ABSTRACT

Purpose: To investigate the potential of diffusion tensor imaging (DTI) parameters as in-vivo biomarkers of axon and myelin sheath integrity of the median nerve in the carpal tunnel as validated by correlation with electrophysiology.

Methods: MRI examinations at 3T including DTI were conducted on wrists in 30 healthy subjects. After manual segmentation of the median nerve quantitative analysis of fractional anisotropy (FA) as well as axial, radial and mean diffusivity (AD, RD, and MD) was carried out. Pairwise Pearson correlations with electrophysiological parameters comprising sensory nerve action potential (SNAP) and compound muscle action potential (CMAP) as markers of axon integrity, and distal motor latency (dml) and sensory nerve conduction velocity (sNCV) as markers of myelin sheath integrity were computed. The significance criterion was set at P=0.05, Bonferroni corrected for multiple comparisons.

Results: DTI parameters showed a distinct proximal-to-distal profile with FA, MD, and RD extrema coinciding in the center of the carpal tunnel. AD correlated with CMAP (r=0.50, p=0.04, Bonf. corr.) but not with markers of myelin sheath integrity. RD correlated with sNCV (r=-0.53, p=0.02, Bonf. corr.) but not with markers of axon integrity. FA correlated with dml (r=-0.63, p=0.002, Bonf. corr.) and sNCV (r=0.68, p=0.001, Bonf. corr.) but not with markers of axon integrity.

Conclusion: AD reflects axon integrity, while RD (and FA) reflect myelin sheath integrity as validated by correlation with electrophysiology. DTI parameters consistently indicate a slight decrease of structural integrity in the carpal tunnel as a physiological site of median nerve entrapment. DTI is particularly sensitive, since these findings are observed in healthy participants. Our results encourage future studies to evaluate the potential of DTI in differentiating axon from myelin sheath injury in patients with manifest peripheral neuropathies.

No MeSH data available.


Related in: MedlinePlus