Medical Imaging: Applications of Functional Magnetic Resonance Imaging and the Development of a Magnetic Resonance Compatible Ultrasound System

MPhil Thesis


Tang, Mei-yee

Publication Identity

The University of Hong Kong, Department of Electrical and Electronic Engineering, 2006





The thesis presents the results of two related studies in the area of Magnetic Resonance Imaging. The first study is on the application of BOLD fMRI (blood oxygen level dependent functional magnetic resonance imaging) to quantify the usefulness of foot reflexology, a popular complementary medication in Asia.

When humans perform various physical or mental activities, the cerebral blood flow and volume of the corresponding brain cortices changes in responses to the external stimuli. BOLD fMRI is sensitive to the changes in the concentration of oxygenated and deoxygenated blood and serves as a natural contrast in MRI to locate brain activations in the corresponding cerebral cortices. In this study, specific reflex zones of 12 to 14 volunteers were massaged at the feet or stimulated by acupuncture needle and the brain activation signals thereby induced were collected and analyzed. The use of fMRI helped to quantify the effectiveness of the therapies in a scientific manner.

We also demonstrated multi-modality imaging with the use of MRI and Ultrasound (US). Multi-modality imaging benefits medical diagnosis and therapies if the strengths of each modality can be fully appreciated. Diagnostic Ultrasound has high temporal resolution for viewing the dynamic changes of the internal structures of human body, performs real time Doppler flow measurement and is a more readily available imaging technique in medical imaging. MRI has the advantages of providing high resolution images with best tissue contrasts for anatomical details, and allows the evaluation of functional activities such as brain functions and tissue perfusion.

Simultaneous capturing of US and MR images allows information fusion obtained from both modalities. However, the introduction of US into MRI magnet bore introduces noises, thus affecting the image quality captured in both modalities. In a second, we demonstrated the feasibility of simultaneous MR and US imaging by introducing proper shielding and orientation placement of the ultrasound system.

Compatibility tests were performed to quantify the improvements in both modalities. We also presented methods for acquiring MR images in a known orientation with respect to US scan plane, with the use of electro-magnetic active trackers in low field open bore magnet and passive tracking using MR visible markers in close bore magnet. We demonstrated concurrent real-time imaging on two applications: 1) Image Guided Biopsy on a double modality breast phantom in 0.5T open bore and 3T close bore magnet, and 2) vascular wall motion imaging in human carotid arteries in 1.5T close bore magnet.