Developing a New Method for MRI Triggering Using Doppler Ultrasound

Sammanfattning: Purpose: Magnetic Resonance Imaging (MRI) is a medical imaging technique used in radiology to produce high quality images of the anatomy and the physiological processes of the body. Cardiac gating is a triggering system used for the MRI scanner to synchronize the MRI scanner with the cardiac cycle of the patient while imaging. When applying cardiac gating, artifacts that results from small movement in the heart and blood ow are neglected. Recent MRI scanners uses Electrocardiogram (ECG) as a cardiac gating method, but with higher magnetic eld strength the ECG signal get distorted. In this thesis DUS signal will be examined as a replacement cardiac gating method for the MRI scanner. In theory the DUS signal should not be aected by the high magnetic eld strength. Methods: Dierent sets of data were collected from three dierent subjects. The data contain a synchronized ECG and DUS signal without the eect of the MRI magnetic eld. A Filtering and peak detection algorithm were developed in MATLAB to process the DUS signal and the result was compared to the ECG signal as a reference method. Results: The ltering algorithm showed good results in terms of being able to increase the signal to noise ration (SNR) of the signal to enable the processing phase. The peak detection algorithm was able to detect the peaks in the dierent data sets with low false positive (19 out of 24 data sets had lower FP errors then 10%) and false negative errors (17 out of 24 data sets had lower FN errors then 10%). Some data sets had low SNR even after the ltering phase, peak detection on those data sets were not functioning properly. When comparing the DUS signal to the ECG signal, an average delay was detected to be around 0.26 seconds for the forward signal and around 0.5 seconds for the backward signal. Conclusion: The DUS signal shows promising results to be able to be used as a cardiac gating method for the MRI scanner.