Comparison of coherence measures for assessment of impaired cerebral autoregulation D. De Smet*, J. Vanderhaegen**, G. Naulaers** and S. Van Huffel* KATHOLIEKE UNIVERSITEIT LEUVEN, BELGIUM *DEPARTMENT OF ELECTRICAL ENGINEERING (ESAT-SCD) **NEONATAL INTENSIVE CARE UNIT, UNIVERSITY HOSPITALS LEUVEN
20
Embed
Comparison of coherence measures for assessment of impaired cerebral autoregulation D. De Smet*, J. Vanderhaegen**, G. Naulaers** and S. Van Huffel* KATHOLIEKE.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Comparison of coherence measures for assessment of impaired cerebral
autoregulation
D. De Smet*, J. Vanderhaegen**, G. Naulaers** and S. Van Huffel*
KATHOLIEKE UNIVERSITEIT LEUVEN, BELGIUM
*DEPARTMENT OF ELECTRICAL ENGINEERING (ESAT-SCD)
**NEONATAL INTENSIVE CARE UNIT, UNIVERSITY HOSPITALS LEUVEN
Introduction
Problem : defective cerebrovascular autoregulation
Δ CBF brain injuries
Premature infants : propensity for development because :
• TH acts as a highpass filer• The ratio TH/TC should be in the range of 0.51 or
smaller
REMARK 5The ratio THOver/TH should be equal to 0.5 if a
Hanning window was applied to the H-windows prior to the periodogram average2.
_____________________________________________________[1] De Smet., Unpublished, 2007.[2] Carter, IEEE Trans. on Audio and Electroacoustics, 1973.
Welsh coherence
1. Introduction
2. Datasets
3. Preprocessing
4. Sampling frequency
5. Welsh coherence
6. Critical score value
7. In the practice
8. Conclusion
Consequence : TC= TH(N+1)/2
TH and TH/TC are the sole parameters we really can choose
But … REMARK 6 TH have to satisfy :• TH < TC• TH > 10s1,2
Acronyms :• TC : duration of C-window (calculation window)• TH : duration of H-window (highpass filtering window)• N : number of averages in the Welsh method
_____________________________________________________[1] von Siebenthal et al., Brain & Development, 1999.[2] Urlesberger et al., Neuropediatrics, 1998
Welsh coherence
1. Introduction
2. Datasets
3. Preprocessing
4. Sampling frequency
5. Welsh coherence
6. Critical score value
7. In the practice
8. Conclusion
Critical Score Value
The critical score value (CSV) is the value above which the amplitude of coherence witnesses a significant linear concordance between the input signals.
Possible value for CSV are :• CSV=0.51
• or2
Acronyms : : significance level (e.g. 0.05) : to be chosen• d : 2.83*TC/TH (for Hanning window) : TH to be
chosen• F : F hypothesis testThe significance level greatly influences the CSV, in the case that the remainder parameters are unchanged!!_____________________________________________________[1] De Boer et al., Med. Biol. Eng. Comput., 1985.[2] Taylor et al., Circulation, 1998
1. Introduction
2. Datasets
3. Preprocessing
4. Sampling frequency
5. Welsh coherence
6. Critical score value
7. In the practice
8. Conclusion
Critical Score Value
Problem : this formula doesn’t take into account THOver (and thus N) that also has an influence on the amplitude of the coherence spectrum1
Solution : keep working with CSV=0.5 (two signals based on 50% shared variance),and calibrate2 mean COH (on all infants) on mean correlation coefficient (COR)
+ look at the range of COH and COR._____________________________________________________[1, 2] De Smet., Unpublished
1. Introduction
2. Datasets
3. Preprocessing
4. Sampling frequency
5. Welsh coherence
6. Critical score value
7. In the practice
8. Conclusion
Morren 1 Soul 2 Wong 3 Optimization
fs 6Hz (0.2Hz)
2Hz (O.4Hz)
1Hz >0.1Hz
(von Siebenthal,
Urlesberger)
TC 30min 10min 20min TH(N+1)/2
TCOver 10min 0min 0min E.g. : TC/2
N 217 3 5 close to 8 or calibr.
TH 12min 5min 10min > 2.5min
(von Siebenthal)
THOver 11min55s 2.5min 7.5min TH/2 if Hanning
(Carter)
fCut 0.01Hz 0.04Hz 0.02Hz <0.05Hz
(von Siebenthal,
Urlesberger, Nyq.)
CSV 0.5 0.77
(Taylor)
0.5 0.5 with calibr. or Taylor’s CSV
In the practice
[1] Morren et al., Proc. of the Intern. Conf. of IEEE, 2001.[2] Soul et al., Pediatric Research, 2007.[3] Wong et al., Pediatrics, to be published.
1. Introduction
2. Datasets
3. Preprocessing
4. Sampling frequency
5. Welsh coherence
6. Critical score value
7. In the practice
8. Conclusion
Conclusion
• nice preprocessing but bad consequence on the frequency content of the signals
• the problem of the varying amplitude of COH is solved by another manner Taylor did it. We showed Taylor’s method does not account for the overlap between H-windows
• we proposed optimized parameters to apply the coherence method
1. Introduction
2. Datasets
3. Preprocessing
4. Sampling frequency
5. Welsh coherence
6. Critical score value
7. In the practice
8. Conclusion
Thanks
toPhD grant Fin. ContributorsResearch Council KULeuvenFlemish GovernmentBelgian Federal Science Policy OfficeEUESA WorkgroupProf. Dr. Ir. S. Van HuffelProf Dr. G. NaulaersLic. J. Vanderhaegen