Hisamoto Moriguchi PhD, Presenter: Nothing to Disclose

Jonathan Stuart Lewin MD, Abstract Co-Author: Nothing to Disclose

Jeffrey Lewis Duerk PhD, Abstract Co-Author: Nothing to Disclose

We show scan time can be significantly reduced (practically by a factor of 2 to 4) in MRI if a rapid oscillatory gradient is applied along the phase encoding direction during the data sampling period.

In rectilinear acquisition of MRI, traditionally only a readout gradient and no gradient along the phase encoding direction is applied when k-space data are sampled. In our new technique, a rapid oscillatory gradient is incorporated in the phase encoding direction during data acquisition. The resulting k-space trajectory produces a zig-zag pattern across the readout direction. It can be shown that each zig-zagged k-space trajectory samples more than one phase encoding line (i.e., a ‘bunched phase encoding (BPE)’) and the spacing between these lines is in general smaller than the normal phase encoding step (i.e., 1/FOV). Papoulis’ generalized sampling (GS) theory asserts that it is possible to reconstruct aliasing-artifact free signals if the ‘average’ of sampling density of the Fourier data satisfies the Nyquist criterion. We capitalize on this theoretical construct to reconstruct an image from the data acquired along BPE lines. We applied a BPE technique to a FISP sequence. The sequence consists of 128 TR cycles with 512 data sampled in each TR, thereby enabling us to reconstruct a 256 x 256 image using the GS theory. A standard FISP sequence consisting of 256 TR’s with 256 data sampled per phase encoding was used as a reference. The following parameters were the same for both sequences: TE/TR/FA = 7.4/17.0ms/30deg, FOV 300mm. Both sequences were applied to abdominal images using a 1.5 T Siemens Sonata scanner. SNR was also measured in each image.

The image reconstructed from the data acquired using the BPE technique exhibited no apparent aliasing artifacts. The scan time of BPE technique was half of that of the standard method. The measured SNR for BPE technique and the standard method were 29.3 and 42.3, respectively.

The BPE technique requires only minor modification of a gradient and leads to significant scan time reduction while the reconstructed image shows no apparent aliasing artifacts. BPE technique is a new, quite useful acquisition method for fast MRI.

J.S.L.,J.L.D.,H.M.: This work was supported by Siemens Medical Solutions. Our methods were developed under Grants R01 CA81431 and R33 CA88144.

Moriguchi, H, Lewin, J, Duerk, J, Bunched Phase Encoding (BPE): A New Fast Data Acquisition Method in Magnetic Resonance Imaging.  Radiological Society of North America 2004 Scientific Assembly and Annual Meeting, November 28 - December 3, 2004 ,Chicago IL. http://archive.rsna.org/2004/4406018.html