Compact MRI

Figure 2.2.3 shows a typical block diagram for a compact MRI system. The square box surrounded by the dotted lines shows the electrical sub-system, which is stored in a single portable rack as shown in Figure 2.2.2. The electrical sub-system is thus often called the (portable) MRI console. In accord with Figure 2.2.3, an MR image acquisition process is described as follows.

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. 

Fig. 2.2.10 Block diagram of the digital system of the compact MRI constructed within a PC.

Figure 2.2.11 shows a typical block diagram of the MRI transceiver used for the compact MRI system. The waveform generator can be replaced by the DA converter on the DSP board described in the previous section. Because the typical input/ output power level for the transmitter and from the preamplifier is about 1 mW, a commercially available transmitter and preamplifier are directly connected. 

Up until now, several tens of compact MRI systems have been constructed and used for various purposes. Among them, two typical systems that use a yoked magnet and a yokeless magnet are described below. 

K. Kose, Y. Matsuda, T. Kurimoto, S. Hashimoto, Y. Yamazaki, T. Haishi, S. Utsuzawa, H. Yoshioka, S. Okada, M. Add, T. Tsuzaki 2004, (Development of a compact MRI system for trabecular bone volume fraction measurements), Magn. Reson. Med. 52, 440—444. 

K. Kose (ed.) 1984, Compact MRI, Kyor-itsu Publishing Company, Tokyo. 

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