Birdcage coils

The compact MRI system has an advantage for rf coil design because solenoid coils can be used in most applications. The solenoid coil has about three times better SNR than that of the saddle-shaped coil (14). Even if the saddle-shaped or birdcage coil is used in the quadrature mode, the solenoid coil will still have better SNR because an SNR gain of only about 1.4 times is obtained in that mode. 

All experiments were performed in a 1.9-T horizontal bore magnet (Oxford Instruments, Oxford, UK) with a dear bore diameter of 31 cm. Magnetic field gradients were produced by a 12-cm id water-cooled gradient set (Resonance Research, Billerica, MA, USA), capable of a maximum output of 300 mT m-1, and were driven by Techron 7700 amplifiers (Techron Inc., Elkhart, IN, USA). Rf excitation was accomplished using either a quadrature driven birdcage coil (Morris Instruments, Ottawa, ON, Canada), or an 8-tum laboratory-built solenoid coil, driven by an ENI LPI-10 1000 W amplifier or a Matec Model 525 class-C amplifier. 

B as emressed in Eq. (24.18) is maximiun when D = >/2. However, Eq. (24.18) is within 95 percent of its maximum value for > > 0.9. Lcmger birdcage coils result in higher tadio-foequency deposition in patients. Shorter birdcage coils are desirable. TypicaUy, birdcage coils are designed withD = 1. 

Schenck, J. F., E. B. Boskamp, D. J. Schaefer, W. D. Barber, and R. H. Vander Heiden, 1998, Estimating Local SAR Produced by RF Transminer Q>ils Examples Using the Birdcage Coil. Abstracts of the International Society of Magnetic Resonance in Medicine, Sixth Meeting, Sydney, p. 649. 

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