The Design And Realization Of Dual Fast Spin Echo Magnetic Resonance Imaging Pulse Sequence

Magnetic resonance imaging (MRI) is a medical human body imaging technique, which is make use of the property of nuclear magnetic resonance (NMR) and has become one of the most important tools widely used in the clinic medicine diagnosis and research fields now. However, conventional MRI is a time consuming technique, how to improve imaging speed is a hot topic in this area. Because of the restrict of hardware level, now many researchers mainly study in MRI reconstruction method and NMR pulse sequence design to solve the problem. Sequence design has exact requirements mainly in the aspects of magnetic susceptibility weighted, image stability and sensitivity of artifacts. The aim of dual fast spin echo (DFSE) sequence design in this topic is in order to improve the imaging speed and can run in conventional MRI system.The text firstly introduces the national and foreign researching state. After that, expatiating on the basic principle of MRI, special encoding and K-space filling gets ready for the research on the sequence design and image rebuilding. Then, two existing fast the parallel MRI (pMRI) methods based on the partial K-space data SENSE and GRAPPA were investigated in this thesis, which is ready for the combination of sequence and GRAPPA algorithm experiment.The task’s research key is To develop a novel fast spin echo pulse sequence named dual fast spin echo (DFSE). DFSE sequence was developed based on the principle of dual spin echo and fast spin echo. Dual echo sequence and fast spin echo sequence belong to Spin Echo sequences. Dual echo sequence is that two180°RF pulse are supplied after a90°excitation RF pulse to obtain two NMR signals, during a long TR time, the first short time TE signal is sampled to make up one K space, which is used for reconstructing proton density weighted image (PDWI). The second long time TE signal is sampled to make up another K space and reconstruct T2weighted image (T2WI). The FSE pulse sequence many180°RF pulses are supplied after a90°excitation RF pulse to obtain the same number signals, which are used to fill k space at one time. The FSE is a time-efficient method compared to SE pulse sequence. DFSE collects the two above sequence.The first half echoes are used for reconstruct proton density weighted image, and the second half echoes are for T2weighted image, which have different contrast. DFSE sequence can create PDWI and T2WI at one echo train. Special encoding and how to fill the k space is the key and foundation to the sequence design.The detailed job is as follows:based on Visual C++2005language development environment, we programed improved sequence DFSE and compiled to Dynamic Link Library (DLL), then loaded it to MR system for reconstructing images. The detailed steps are as follows:Using VC++platform to design user’s interface and compile the source code of DFSE sequence. Finally, the parameters were set on the MRI interface, The FSE and DFSE were running on an Anke Medical Supervan1.5T MR system respectively to obtain this raw data and reconstruct proton density weighted image (PDWI) and T2weighted image (T2WI) of head and knee. Compared to FSE sequence, the DFSE is a more time-efficient and feasible method. DFSE sequence can create PDWI and T2WI with robust imaging quality at one scan to improve imaging speed significantly, and the quality of the images are adequately satisfied the clinical application. Meanwhile motion artifacts were reduced.Because FSE sequence is one of the most widely used pulse sequences at home and abroad, and FSE sequence has a lot of advantages, such as short sampling time, clear imaging results. We improved this sequence to DFSE, and the result has reached our expectations. We can use the similar method to improve other acquisition sequences such as gradient echo (GE) sequences.At present only Philips’ products has the sequence similar to DFSE. The significance of this article is to provide an important reference on the independent research and development in the pulse sequence on the MR scanner in our country.