RF probe

#This invention relates to an RF probe of a magnetic resonance imaging (MRI) apparatus.

#A cross system RF probe using separate transmission and reception coils has ordinarily been used as an RF transmission/reception system for MRI. This is the system which uses exclusive RF coils for RF magnetic field transmission and MR signal reception, respectively. A saddle coil, a slotted tube resonator (hereinafter abbreviated to "STR"), a multiple element resonator (MER; sometimes referred to also as "birdcage resonator"), etc., are used for the transmission coil. A surface coil is used for ultra-high speed imaging of the heart. The STR and the MER are used as the reception coil for imaging the head, and a round coil is used for imaging the spine and a local part. In order to allow the reception coil to stably operate, an inductive coupling system using a pickup coil (PUC) for RF reception is used in a high magnetic field MRI apparatus of 1.5 T, for example. A QD system is used to improve a reception sensitivity, as described, for example, in JP-A-4-17837. The birdcage resonator is described, for example, in JP-A-61-95234 and JP-A-60-132547.

#FIG. 1A of the accompanying drawings illustrates the structure of a cross system RF probe according to the prior art. Reference numerals 101 denotes a transmission coil and reference numeral 100 does a reception coil. The reception coil comprises a resonator 6 and a pickup coil (PUC) 103.

#FIG. 1A is a perspective view showing an RF probe of a cross system as an RF transmission/reception system for MRI according to the prior art;

#FIG. 1B is a circuit diagram showing an example of decoupling device;

#FIG. 2 is a perspective view showing an RF probe according to an embodiment of the present invention;

#A preferred embodiment of the present invention will now be described with reference to FIG. 2. This drawing is a perspective view showing a reception coil 1 having a suitable shape for the present invention. A resonator 6 is a multiple element resonator (MER). The MER generally comprises a pair of conductor loops 2 and 3 spaced apart from each other along a common axis, a plurality of axial direction conductor segments (rungs) 4 for electrically connecting the conductor loops with one another and a plurality of capacitance devices 5 disposed on either the conductor loops or on the segments. This embodiment uses a high-pass type resonator having the capacitance devices disposed on the conductor loops. Feed/reception of the resonator 6 is effected by inductive coupling through a pickup coil (PUC) and is given from a port 8.

#Next, a definite shape of the resonator 6 will be described. The reception coil for the head, for example, has a diameter of 300 mm, a length of 300 mm and the number of segments of 8, 12 or 16. The drawing shows the case where the number of segments is 8 (with the proviso that a part of the segments is omitted). The conductor loops 2, 3 and the segment 4 are constituted by a copper pipe having a diameter of 3 mm. The electrostatic capacity of the capacitance devices 5 is approximately 30 pF. The resonant frequency of the coil, as viewed from the port 8 of the pickup coil 7, can be regulated by finely adjusting the capacitance of the capacitor of the resonator 6, and is adjusted to a desired MRI frequency such as 63.8 MHz in the case of 1.5 T, for example. The impedance as viewed from the port 8 can be easily adjusted to a desired value such as 50 .OMEGA., for example, by changing and regulating the relative positions between the PUC 7 and the resonator 6 so as to adjust their magnetic coupling state.

#Next, the PUC 7 will be explained. The PUC 7 has an 8-shape, and the portion corresponding to the crossing center portion of the 8-shape is constituted in such a manner that coils become parallel to one another. The center parallel portions 21 of the coils are so disposed as to extend along, and in the proximity of, the conductor loops of the resonator 6 (see FIG. 3).