Parallel imaging

Parallel images, recorded using different contrast mechanisms, can be directly compared on a pixel-by-pixel basis. Althongh SHG, THG, and MPF images originate... 

MR phased array and parallel imaging, MRI RF-coil development has further blossomed.Phased-array receive coils can provide substantial increases in SNR for spectroscopic applications. Although most phase-array technology has been developed for studies and parallel imaging,... 

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. 

Parallel image aequisition is, in prineiple, possible by two-dimensional multianode PMTs. The anode elements are eonneeted to a standard routing deviee, and the photons are reeorded as deseribed above under Seet. 3.1, page 29. However, the number of amplifiers and diseriminators in the router inereases with the number of anode elements. Power eonsumption and spaee requirements restriet the number of pixels that ean be obtained this way. The praetieal limit is somewhere between 16 and 64. An array of 64 pixels eannot really be eonsidered an image. 

In principle, parallel imaging ean be eombined with multiplexing and sequencing. Of course, the size (or pixel number) of the images, sequeneer steps, and multiplexing channels that can be used simultaneously are limited by the memory space in the TCSPC module. 

McKenzie CA, Lim D, Ransil BJ et al (2004) Shortening MR image acquisition time for volumetric interpolated breath-hold examination with a recently developed parallel imaging reconstruction technique clinical feasibility. Radiology 230 589-594... 

The recent hardware developments of multiple phased-array surface coils and receiver channels combined with parallel imaging offer considerable reduction in data acquisition times, thereby permitting acquisition of a variety of sequences while maintaining acceptable study times. 

Taking all the above-mentioned into account, indications for functional cine MRI still remain controversial. The method itself is not yet standardized, and so far only a 2D approach for functional imaging of the pelvic floor exists. With the advance of fast parallel imaging a stack of two to three slices within the same acquisition time seems possible. 

Edited by G. Maconi and G. Bianchi Porro Parallel Imaging in Clinical MR Applications... 

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