Transceive Phased-array Systems for Parallel MRI

Author	Yu Li
Thesis Title	Transceive Phased-array Systems for Parallel MRI
School, Centre or Institute	School of Information Technol and Elec Engineering
Institution	The University of Queensland
Publication date	2010-12
Thesis type	PhD Thesis
Supervisor	Stuart Crozier Feng Liu
Total pages	267
Total colour pages	83
Total black and white pages	184
Subjects	09 Engineering
Abstract/Summary	Abstract This thesis focuses on the transceive phased array designs for magnetic resonance imaging (MRI). With the introduction of phased array technology in MRI, a wide variety of phased array coils have been constructed for human clinical applications or small animal studies. Compared to receive-only phased array coils, transceive phased-arrays combine the function of the transmit coils and receiver coils. They have the capability of generating a homogeneous magnetic field and detecting the MRI signal with a high signal-noise-ration (SNR). Operations at high field have the advantage of being able to enhance the SNR and gain a high spectral resolution. However, to realize the full benefits of high field parallel MRI, current radio frequency (RF) technology still needs improvements and many technical challenges need to be overcome, such as providing an optimized engineering solution which balances the RF magnetic field penetration, coil sensitivity, coupling/decoupling and B1 field homogeneity. Moreover, in some applications, such as in a small animal system, the limited space within small animal systems makes it difficult to incorporate both transmit and receive coils. In this thesis, these issues concerning transceive systems are explicitly optimized for RF performance through a number of proposed novel and effective hardware solutions. An inverse method for the design of phased-array is described and applied to the design of asymmetric, unshielded RF array coils. This method expands the geometry of arrays from conventional cylinders to part-spheres, cone and ellipsoid shapes that conform more closely to the anatomy under study. The research work developed and presented in this thesis has been applied to two specific RF coil applications, human breast imaging and small animal imaging. Firstly, for transceive RF breast coils design, a two-loop array coil has been designed and optimized to improve the homogeneity of the B1 field. Secondly, a hybrid structured design of the breast array coil has been proposed for the improvement of the overall RF field performance, especially the superior-inferior area of the breast, which is a problematic area for the conventional breast coil. Finally, a single-turn solenoidal transceive breast coil design for a bilateral breast MRI has been introduced. For small animal MRI in a high field application, three dedicated, shielded eight-element transceive volume-arrays for large rat MRI applications has been designed and two have been constructed. Several techniques and methods have been proposed and employed for the array design to help to improve the coil RF penetration depth and the signal reception capability, and also to minimize the mutual decoupling between adjacent coil elements. As an important accessory of the phase array system, a high power eight-channel T/R switch unit is also designed and fabricated. Both experimental and theoretical studies have demonstrated the technical potential of the proposed transceive phased-array technology for high-field human and small animal MRI applications.
Keyword	Phased array Inverse Design Hybrid design RF breast coil RF small animal coil Transceive Parallel MRI
Additional Notes	page number of colour page of PDF file p37, p39, p40, p41, p43, p47, p49, p51, p52, p53, p54, p56, p57, p58, p60, p61, p63, p64, p69, p71, p72, p76, p83, p84, p89, p94, p102, p116, p123, p129, p131, p132, p133, p134, p139, p140, p141, p142, p143, p151, p152, p153, p154, p155, p156, p161, p164, p165, p166, p167, p169, p170, p172, p173, p174, p175, p180, p181, p204, p205, p206, p207, p209, p210, p211, p212, p213, p214, p215, p216, p217, p231, p232, p234, p235, p236, p237, p238, p239, p240, p241, p246, p247