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HIGH POWER, HIGH DIRECTIVITY DIRECTIONAL COUPLER IN COMPACT SIZE

IP.com Disclosure Number: IPCOM000200883D
Publication Date: 2010-Oct-28
Document File: 4 page(s) / 102K

Publishing Venue

The IP.com Prior Art Database

Abstract

A technique to improve directivity of a coupler in MR system is disclosed. The technique provides a coupler structure that provides high directivity, even at weak coupling application required in MR system, which require high RF power. With this coupler structure in RF chain of the MR system, a more accurate power monitoring is possible in the MR system due to increase in the directivity.

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HIGH POWER, HIGH DIRECTIVITY DIRECTIONAL COUPLER IN COMPACT SIZE

BRIEF ABSTRACT

    A technique to improve directivity of a coupler in MR system is disclosed. The technique provides a coupler structure that provides high directivity, even at weak coupling application required in MR system, which require high RF power. With this coupler structure in RF chain of the MR system, a more accurate power monitoring is possible in the MR system due to increase in the directivity.

KEYWORDS

    Directivity, coupling, MR system, High RF power system, power monitoring, dual directional coupler, high directivity directional coupler, compensating capacitance, coupling line, multi-layer structure

DETAILED DESCRIPTION

    Magnetic resonance (MR) imaging is primarily a noninvasive medical imaging technique used in radiology to visualize detailed internal structure and limited function of the body. MR imaging provides much greater contrast between the different soft tissues of the body, making it especially useful in neurological (brain), musculoskeletal, cardiovascular and oncological (cancer) imaging. MR imaging uses a powerful magnetic field to align the nuclear magnetization of hydrogen atoms in water in the body. Radio frequency (RF) field, especially high RF power field, is used to systematically alter the alignment of this magnetization. This causes the hydrogen nuclei to produce a rotating magnetic field detectable by the scanner. This signal is manipulated by additional


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magnetic fields to build up enough information to construct an image of the body. But for high RF power case, such as MR system, loose coupling coupler is required. However, the directivity becomes worse when coupling decreases. Since the directivity of the coupler is related to the accuracy of the power monitor. More high directivity provides more accurate power monitor.

    In MR system, the forward and reflected power monitor is very important because this is related to the safety of patient. Conventionally, a dual directional coupler is used for this purpose.The dual directional coupler is a passive devices used in the field of radio technology. However, as described above, high RF power case, such as MR system loose coupling coupler is required and unfortunately, directivity becomes worse with coupling decreases and hence accuracy of the power monitor and safety of the patient is compromised. Hence, there is a need of more accurate power monitor in high RF power case, such as MR system and accordingly, there is a need to improve directivity of the coupler in the MR system even at weak coupling application required for high RF power case.

    Efforts have been made in the past, to improve the directivity of the coupler for MR system and to improve the accuracy of RF power monitor. In one such method, a stripline structure was used to improve the directivity of the coupler and the method improves directivity of the stripline coupler with grounding copper【1】【2】. However...