1. FURI: Honors Thesis Program
fMRI Signal Analysis to Quantify Effects of Therapy on Neurological Disorders
José L. Rios1
, David Frakes1,2
1
School of Biological and Health Systems Engineering
2
School of Electrical, Computer, and Energy Engineering
Quantifying the effects of therapy on neurological disorders is a
challenging problem.
Functional Magnetic Resonance Imaging (fMRI) is a powerful tool
that could be used to quantify the effects of therapy non-invasively.
fMRI signals are time-variant and do not have an absolute baseline.
Evidence suggests that the relationship between motor cortex and
visual cortex activity should not change for normal subjects.
Signal processing techniques were used to establish a relationship
between motor and visual cortex activity.
The relationship between motor and visual cortex activity was
characterized before and after consumption of caffeine.
Introduction
Background Results
Discussion and Conclusion
[1] (2007, March) One billion battling with neurological disorders. [Online]. http://www.news-
medical.net/news/2007/03/01/22314.aspx
[2] (2010) Parkinson's Disease Foundation. [Online]. http://www.pdf.org/en/parkinson_statistics
[3] (2010) Alzheimer's Association. [Online].
http://www.alz.org/alzheimers_disease_facts_figures.asp
[4] Peter Jezzard and Ahmed Toosy, "Functional MRI," MR Imaging in White Matter Diseases
of the Brain and Spinal Cord. Springer Berlin Heidelberg, 2005.
I would like to acknowledge Dr. David Frakes for his guidance and thank Dr. Leslie Baxter for
providing the data. Funding for this research was provided by FURI.
Figure 2: ApEn of the motor tasks and the vision task for the normal and
caffeinated state of a) Patient 1 and b) Patient 2.
Table 1: Ratio between the ApEn of the motor and vision tasks in the normal and
caffeinated states, as well as the difference between ApEn ratios of the two
states.
Figure3: Correlation between motor and vision tasks
(A=normal state, D=caffeinated state).
fMRI data alone is not sufficient to establish a relationship between
motor and visual cortex activity.
Signal analysis methods that are independent of magnitude are
needed to filter changes in the signals’ baselines.
ApEn showed that the relationship between the motor and vision
tasks remained approximately constant after consumption of
caffeine.
The ratio of the ApEn between the motor and vision tasks provides a
quantitative measure of the relationship between motor and visual
cortex activity.
The correlation between the motor and vision tasks remained
approximately constant in Patient 2 and in the right finger tap to
vision task in Patient 1.
ApEn and correlation begin to provide a quantitative relationship
between motor and visual cortex activity.
Further analysis of a bigger population of patients is needed to
establish a standard relationship between motor cortex and visual
cortex activity.
References and Acknowledgements
One billion people suffer from neurological disorders worldwide [1].
In the United States alone, one million people suffer from Parkinson’s
Disease [2] and 5 million people suffer from Alzheimer’s Disease [3].
60,000 new Parkinson’s Disease cases are diagnosed annually in the
United States [2].
The cost of Parkinson’s and Alzheimer’s is $197 billion/year in the
United States [2-3].
Methods
Patients were placed inside an MRI scanner and instructed to
perform a left finger tap, right finger tap, and vision task. The
fMRI data corresponding to the left and right finger taps was
acquired from the motor cortex. The fMRI data corresponding to the
vision task was acquired from the visual cortex.
Approximate Entropy (ApEn) quantifies the complexity of a signal.
The fMRI signals were analyzed with ApEn. ApEn for N data points
is given by the following equation:
where m is the length of compared runs, r is the effective filter and
is a counting vector for compared runs that satisfy r.
•Correlation was used to find the relationship between various signals.
Correlation is given by the following equation:
where x and y are vectors of size n, and are the sample means of X
and Y, and sx and sy are the sample standard deviation of X and Y.
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ln(),,( 1
r
r
rmNApEn
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=
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x y
•ApEn was quantified for the fMRI data from each task and the
results are shown in Figure 2.
•The relationship between the tasks remained approximately constant
between the normal and caffeinated state.
Normal Caffeinated Difference
Left-Vision Right-Vision Left-Vision Right-Vision Left-Vision Right-Vision
Patient 1 1.00 0.95 1.05 0.98 5.71% 3.06%
Patient 2 0.95 0.88 0.94 0.94 1.39% 6.43%
•A quantitative measure of the relationship between the motor and
vision tasks was calculated by taking the ratio of the ApEn.
•The average percent difference was 4.15%.
•The correlations between the fMRI signals of the motor and vision
tasks before and after consumption of caffeine remained
approximately constant in most cases.
•Correlation between the fMRI signals of the left finger task and
vision task for Patient 1 changed significantly from the normal state
to the caffeinated state.
Results (cont.)
a) b)
Figure 1: fMRI data from patient 1 performing a left finger tap in the a) normal
and b) caffeinated states.
•The time-variant nature of fMRI signals makes it impossible to
match the data with a patient’s specific task.
•The fMRI signals from the left finger tap changed in frequency and
magnitude between the normal and caffeinated states.
a) b)