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A Hybrid Reconstruction Technique for Improving Image Quality in Single-Shot, Diffusion-Weighted Echo-Planar Imaging

IP.com Disclosure Number: IPCOM000179818D
Original Publication Date: 2009-Mar-16
Included in the Prior Art Database: 2009-Mar-16
Document File: 1 page(s) / 23K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

Single-Shot MR (Magnetic Resonance) EPI (Echo-Planar Imaging) is a reliable technique for acquiring clinical diffusion-weighted images due to its insensitivity to motion-artifacts compared to multi-shot imaging techniques. Due to the long readout time in the EPI sequence a partial Fourier technique is often used, in which a number of raw data lines at one edge of the k-space (temporary image space in which data from digitized MR signals are stored during data acquisition) are not acquired. This allows the data lines at the centre of k-space to be acquired at a shorter echo-time (TE), which is beneficial for the signal-to-noise-ratio of the image. The optimum way to reconstruct images from partial Fourier data is to use a dedicated algorithm, which takes advantage of the Hermitian Symmetry relationship that exists between the acquired data at one side of k-space and the missing data on the other. However, due to CSF (Cerebral Spinal Fluid) pulsation during the cardiac cycle there is some motion of the brain, which causes a positional variation in the phase of the MR signal. These phase perturbations interfere with the partial Fourier image reconstruction procedure and can lead to severe image artifacts.

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A Hybrid Reconstruction Technique for Improving Image Quality in Single- Shot, Diffusion-Weighted Echo-Planar Imaging

Idea: David Porter, Ph.D., DE-Erlangen; Matthew Robson, Ph.D., UK-Oxford

Single-Shot MR (Magnetic Resonance) EPI (Echo-Planar Imaging) is a reliable technique for acquiring clinical diffusion-weighted images due to its insensitivity to motion-artifacts compared to multi-shot imaging techniques. Due to the long readout time in the EPI sequence a partial Fourier technique is often used, in which a number of raw data lines at one edge of the k-space (temporary image space in which data from digitized MR signals are stored during data acquisition) are not acquired. This allows the data lines at the centre of k-space to be acquired at a shorter echo-time (TE), which is beneficial for the signal-to-noise-ratio of the image. The optimum way to reconstruct images from partial Fourier data is to use a dedicated algorithm, which takes advantage of the Hermitian Symmetry relationship that exists between the acquired data at one side of k-space and the missing data on the other. However, due to CSF (Cerebral Spinal Fluid) pulsation during the cardiac cycle there is some motion of the brain, which causes a positional variation in the phase of the MR signal. These phase perturbations interfere with the partial Fourier image reconstruction procedure and can lead to severe image artifacts.

A state of the art technique to address this problem is to use ECG (Electrocardiogram) triggering to synchronize the acquisition with the cardiac cycle and to solely acquire data during the diastolic period when the brain motion due to CSF pulsation is reduced. Under these circumstances good image quality can be obtained using a partial Fourier reconstruction algorithm. However, the acquisition requires a longer time and there is also additional effort required prior to the examination for attaching ECG leads, which are not typically required for examinations of the head. In addition, it is difficult to carry out this type of measurement if the patient is suffering from cardiac arrhythmia.

A second state of the art approach is to replace the dedicated partial Fourier reconstruction by a zero-...