Multi-coil array

Multiple receive systems with multi-coil arrays have become widely distributed in medical MRI. The benefit is the enhancement of the signal-to-noise ratio per time or a reduction of the acquisition time. This technique is not used in NMR microscopy for objects of intermediate size in standard bore (52-mm id) and wide bore (89-mm id) magnets, which are the most widely distributed magnet types for NMR microscopy. The main reason is the restricted space in such magnets for the shim... 

Fig. 10. (iSR spectrometer DIZITAL for pulsed beam (tSR spectroscopy as used at RAL. The multi-detector arrays are placed within the Helmholtz coils toroidally around the beam. The detector can be turned by 90 degrees in order to switch between longitudinal and transverse field geometry. It can also be moved on rails out of the beam spot position. 

Unlike TIA patients with infarction on DWI, it is not obvious that patients with normal DWI have suffered from ischemia as the cause of their transient symptoms. In these patients, TIA mimics should also be considered (see Chap. 19). However, an ischemic etiology for transient symptoms cannot be excluded by the lack of an associated hyperintense lesion on DWI. A short-lasting episode of ischemia without DWI changes, or with reversible DWI changes as demonstrated in animals (Minematsu et al. 1992 Mintorovitch et al. 1991), might have occurred at the time of symptoms. In addition, DWI may occasionally miss very small infarctions, especially in the brainstem location (Ay et al. 1999 Kuker et al. 2002 Lovblad et al. 1998). This is most likely due to susceptibility artifacts induced by surrounding bones at the skull base. New multi-array head coil systems and parallel imaging techniques promise to overcome this limitation and improve the detection rate of small infarctions in the brainstem. 

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