Generalized flow imaging in NMR : application to angiography of coronary vessel

Abstract

The basic principles of NMR flow imaging is generally discussed to help understanding the concept of the NMR flow imaging and the angiography technique, espeially of the coronary angiography. Two categories of flow imaging method, i.e., phase sensitive method (velocity sensitive method) and in-flow sensitive method (time-of-flight method) are given for flow imaging and angiography. Early study of the phase sensitive techinques such as flow velocity map are presinted together with the improved high-speed NMR flow-velocity measurement technique using a differential phase-encoding. In this thesis, coronary vessel angiography which uses 3-D NMR angiography method with 2-D planar image scanning is suggested and its potential is shown by its experimental results for healthy volunteer. On the basis of the principles of the time-of-flight method and the 3-D angiogram obtainaned by the 2-D planar image scanning technique using glow rehased gradient echo sequence with 90$^\circ$ RF pulse and short repetition time a coronary angiogram has been attempted, In this techinque in order to obtain the maximum constrast between heart wall and blood flow a 90$^\circ$ RF flip angle SSFP techinque has been used in conjunction with thin slice selection. In addition, the cine NMR imaging technique is incorporated in synchronizing ECG R waves to reduce the motion atrifact and at the smae time to induce the satruation effect on the statci samples. Images of the alrge bulk blood flow corresponding to the heart chamber and descending aorta are further removed by the postprocessing using boundary detection and segmentation. The final 3-D angiongram is then formed by stacking the 2-D images with and contrast is fruther enhnaced by maximum ray tracing algorithm. Scan time reduction of 3-D magnetic resonance angiography using a 2-D planar image scanning thchnique based on the time-of flight method and the time-multiplexed multislice acquisition techinque is also proposed. The procedure invlov...