Fast NMR imaging using the SSFP technique and its application to NMR spectroscopic imaging

Abstract

A new fast NMR imaging modality using the steady state free precession (SSFP) technique is proposed. Since the SSFP technique utilizes both longitudinal and transversal spin magnetizations for NMR signal formation, the pulse repetition time in the SSFP technique can be greatly reduced with much bigger NMR signal strength compared with conventional spin echo technique which utilizes only longitudinal spin magnetization for NMR signal formation. With efficient reduction of pulse repetition time using the SSFP technique, the scan time for a 2-dimensional image has been greatly reduced down to less than 10 seconds from several minutes of the conventional spin echo NMR imaging technique. In addition, two different NMR signals, so-called FID and echo signals, are simultaneously generated in the proposed fast NMR imaging technique. The two NMR signals can be used either for the reconstruction of two NMR images with different kinds of contrast or for the precise spatial mapping of magnetic field inhomogeneity. For further reduction of the scan time of 3-dimensional imaging, a new volume selection technique using a radial magnetic field is proposed. By combining the volume selection technique with the proposed fast NMR imaging technique, the scan time of 3-dimensional imaging has been greatly reduced down to several minutes. A scheme for the generation of the radial magnetic field is also proposed and verified by both computer simulations and experiments. The proposed techniques have been implemented in the KAIS 2.0 tesla NMR imaging system and the experimental results are presented with related theoretical works and computer simulation results. The proposed fast NMR imaing technique has been applied to the in-vivo spectroscopic imaging of proton and phosphorus. Experimental results of the spectroscopic imaging are also presented.