EKG-TRIGGERED CIRCUIT DESIGNED FOR CARDIAC MRI IN ANIMALS

Jeffrey A. Belair | James P. Ford

Department of Bioengineering, Pennsylvania State University, University Park, PA

Sponsored by Dr. Andrew G. Webb

EXECUTIVE SUMMARY

Cardiac imaging in animals is important for the future of medical research. Magnetic Resonance Imaging (MRI) offers high resolution images with potential for cardiac imaging. An MRI can take several seconds to perform and is sensitive to the movement of a beating heart. In order to image a beating heart, an MRI image may be created from MRI snapshots taken of the heart during a common point in the cardiac cycle. This proposal is for the design of an electrocardiogram (EKG) circuit that will monitor cardiac signals and trigger an MRI machine to take snapshots at any given time in the heart cycle. This design will be accomplished by creating a typical EKG circuit that utilizes signal filtering to reduce noise and interference from the large magnetic field. Specifically, a band-pass filter will be used to eliminate low frequency and high frequency background noise due to the electrical signals inherently created in magnetic fields, and those induced by movement of charged particles within the blood. All stages of the design will be tested using rabbits in an animal MRI machine located on campus at The Pennsylvania State University. The project will be finished by the end of April 2006 and will require a budget no more than $1000. The final product will be hardwired into a user-friendly device and will come with full design layout and specifications for future use and modifications.

OVERVIEW AND MOTIVATION

Magnetic Resonance Imaging (MRI) provides significantly better images than other imaging modalities, making it an ideal method for cardiovascular imaging of the heart.  However, the significantly slower temporal resolution of MRI makes it challenging to image a beating heart.  It is thus important to consider a system in which an electrocardiogram (EKG) circuit triggers the MRI to acquire an image at regular points in the cardiac cycle.

Animals provide a significant approach for understanding and modeling cardiac disease and function.  Thus, it is important to develop an EKG-triggered circuit for cardiac MRI specifically for animals, as it will provide insight and advantages for the study of cardiovascular disease.

q    MRI provides significantly better images than other imaging modalities, making it an ideal method for cardiovascular imaging.

q    Slow temporal resolution make MRI difficult to image beating heart.

q    Consider a system in which an EKG circuit triggers the MRI to acquire an image at regular points in the cardiac cycle.

DESIGN CRITERIA

q    Construct an EKG circuit that will output a 5 V Transistor-Transistor Logic (TTL) signal at the R-wave of the cardiac cycle to subsequently trigger the MRI machine to acquire an image.

q    Include a second order band pass filter with cutoff frequencies of 0.3 Hz and 80 Hz to filter out noise.

q    Implement the system in the MRI environment using rabbits as test subjects.

q    Overall goal: to successfully create a fully-functional EKG-triggered circuit for cardiac MRI in animals.

ALTERNATIVE DESIGNS

q    Use of a force transducer to quantify the cardiac cycle.

q    Use an ultrasound device to monitor blood flow through an artery or image the heart directly.

q    Use of subcutaneous electrodes.

q    All designs would result in a 5 V output signal to MRI device at a specific point in the cardiac cycle.

RESULTS

Please See the Results Page for more detail.

FINAL DELIVERABLES

1.      Fully functional EKG-triggered circuit for cardiac MRI in animals

2.      Circuit box with easy access for input and output leads

3.      Design specifications and circuit layout diagrams for future modification and use

Please See the Final Deliverables Page for more detail.

TIMELINE

FINAL ITEMIZED BUDGET

ACKNOWLEDGEMENTS

We would like to extend our sincere appreciation to those faculty advisors that helped us throughout this entire project:

v    Dr. Andrew G. Webb

v    Dr. Nadine B. Smith

v    Gene Gerber