Image restoration from non-uniform magnetic field influence for direct Fourier NMR imaging

Sekihara, Kensuke; Kuroda, M.; Kohno, Hideki

doi:10.1088/0031-9155/29/1/002

Cited by 77 publications

(47 citation statements)

References 6 publications

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“…In the experiments the three marker coils were attached to the instrument head and positioned at a maximum distance of 10 cm. Gradient imperfections can be characterized and corrected by a polynomial expansion of the actual gradient field (23)(24)(25). Near the isocenter, where local changes in the field are typically small, all marker coil positions are shifted predominantly in the same direction.…”

Section: Discussionmentioning

confidence: 99%

Targeted‐HASTE imaging with automated device tracking for MR‐guided needle interventions in closed‐bore MR systems

Zimmermann

Müller

Gutmann³

et al. 2006

Magnetic Resonance in Med

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Percutaneous MR-guided interventions with needles require fast pulse sequences to image the needle trajectory with minimal susceptibility artifacts. Spin-echo pulse sequences are well suited for reducing artifact size; however, even with singleshot turbo spin-echo techniques, such as rapid acquisition with relaxation enhancement (RARE) or half-Fourier acquisition single-shot turbo spin-echo (HASTE), fast imaging remains challenging. In this work we present a HASTE pulse sequence that is combined with inner-volume excitation to reduce the scan time and limit the imaging field of view (FOV) to a small strip close to the needle trajectory (targeted-HASTE). To compensate for signal saturation from fast repeated acquisitions, a magnetization restore pulse (driven equilibrium Fourier transform (DEFT)) is used. The sequence is combined with dedicated active marker coils to measure the position and orientation of the needle so that the targeted-HASTE image slice is automatically repositioned. In an animal experiment the coils were attached to an MR-compatible robotic assistance system for MR- Currently, interventions with MR guidance are primarily performed in open MR systems, which provide better access to the patient. Unfortunately, open clinical systems with field strengths below 1 Tesla suffer from low signalto-noise ratios (SNRs). Furthermore, gradient systems are limited in strength, slew rate, and homogeneity, which affects both image update rates and quality. The main advantage of high-field systems is that the higher SNR allows for faster signal sampling with image update rates of several images per second. For these reasons it is desirable to perform interventions in closed-bore, high-field MR systems.During percutaneous interventions with needles, the closed-bore construction of high-field systems can be partially compensated for by passive or active robotic assistance systems that give mechanical stability to the needle trajectory (1). Commercial breast biopsy systems, for example, use dedicated breast coils with passive markers and grid systems to both hold and position the biopsy needle. Recently a fully MR-compatible robotic assistance system was developed (2) that consists of a pneumatically driven robot arm and a distal instrument holder. With this system the needle trajectory is defined using initial planning images of the target region. The assistance system then places the needle tip at the skin insertion point and aligns the instrument with the planned trajectory. Finally, the operator manually advances the needle to the target point.During advancement of the needle, continuous image guidance can become necessary in anatomical regions where motion is present. For example, if the needle is inserted into a liver lesion, breathing motion will cause a cyclic displacement of tissue in the head-feet direction, which may lead to substantial differences between the planned and the actual needle trajectory. Unfortunately, optimized real-time pulse sequences for needle display, which are less susceptible to n...

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Section: Discussionmentioning

confidence: 99%

Targeted‐HASTE imaging with automated device tracking for MR‐guided needle interventions in closed‐bore MR systems

Zimmermann

Müller

Gutmann³

et al. 2006

Magnetic Resonance in Med

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“…Spatial accuracy in MRI is limited by the inhomogeneity of the static magnetic eld B 0 and the nonlinearity of the imaging gradients G x , G y and G z . The nonlinearity of the gradients is often considered a matter of system and sequence design Bakker et al 1992;O'Donnell and Edelstein 1985;Kawanaka and Takagi 1986 and the inhomogeneity of the static eld is known to stem from the system Bakker et al 1992;Kawanaka and Takagi 1986;Sekihara et al 1984 and from the magnetic properties of the object itself L udeke et al 1985; Edmonds and Wormald 1988;Ericsson et al 1988;Chu et al 1990;Posse and Aue 1990;Bhagwandien et al 1992a. As has been recognized in previous studies L udeke et al 1985, the geometric distortion of MR images is a ected by the strength, direction and polarity of the imaging gradients.…”

Section: In-plane Image Distortions In Echo Planar Imaging Epimentioning

confidence: 93%

“…Field inhomogeneity is known to stem from the MRI scanner and from the magnetic properties of the object itself Bakker et al 1992;Bhagwandien et al 1992a;Ericsson et al 1988;L udeke et al 1985;Schad et al 1987a. The feasibility of measurement and correction of machine-related distortions has been demonstrated before Bakker et al 1992;Schad et al 1987a;Sekihara et al 1984. The magnetic properties of the object induce the chemical shift and the susceptibility artifacts in MR images.…”

Section: Introductionmentioning

confidence: 91%

“…Several measurement and correction methods were applied. In a clinical environment, phantom based methods were most appropriate since they need no pulse sequence modi cations Bakker et al 1992;Cho et al 1988;Kawanaka and Takagi 1986;Maudsley et al 1984;O'Donnell and Edelstein 1985;Sekihara et al 1984;Willcott III et al 1987. Our institute participated in the EEC Concerted Action on Tissue Characterization by magnetic resonance spectroscopy MRS and MRI which i.a.…”

Section: Mr Image Distortionsmentioning

confidence: 99%

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Magnetic resonance imaging in radiotherapy treatment planning

Moerland¹

1997

Medical Physics

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The aim of this study is to investigate the capabilities of magnetic resonance imaging (MRI) in radiotherapy treatment planning (RTP) and to explore the MR image distortions and how these distortions can be reduced or, if necessary, corrected in order to integrate MRI into RTP in a reliable manner. Image distortions and the efficacy of correction methods were evaluated in phantom, volunteer, and patient studies. From the measurement, analysis, and correction of machine‐related geometric distortions in MRI, it was concluded that MR image corrections are necessary in applications which require mm accuracy and that correction methods, based on 3D maps of static field inhomogeneity and gradient nonlinearity, are feasible in clinical practice. From the measurement and numerical analysis of object‐related geometric distortions, it was concluded that these distortions can be reduced to the order of the pixel size by imaging at 0.5 T and using gradients on the order of 3 mT normalm−1. Furthermore, in a study on volunteers, fast MRI scan techniques were used to measure the respiration induced kidney movement and in a study on patients with prostate cancer, the value of MRI for the evaluation of brachytherapy was demonstrated. The MR image artifacts induced by the I‐125 seeds were used to evaluate the dose distributions and dose volume histograms of permanent prostate implants.

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“…Well-known methods can correct mild inhomogeneities (14,15,16), such as those caused by air-tissue interfaces. Most postprocessing algorithms use some a priori knowledge about the object and/or perform field mapping to "unwrap" the images that result from naive reconstruction.…”

mentioning

confidence: 99%

Prepolarized magnetic resonance imaging around metal orthopedic implants

Venook

Matter

Ramachandran

et al. 2006

Magnetic Resonance in Med

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A prepolarized MRI (PMRI) scanner was used to image near metal implants in agar gel phantoms and in in vivo human wrists. Comparison images were made on 1.5-and 0.5-T conventional whole-body systems. The PMRI experiments were performed in a smaller bore system tailored to extremity imaging with a prepolarization magnetic field of 0.4 T and a readout magnetic field of 27-54 mT (1.1-2.2 MHz). Scan parameters were chosen with equal readout gradient strength over a given field of view and matrix size to allow unbiased evaluation of the benefits of lower readout frequency. Results exhibit substantial reduction in metal susceptibility artifacts under PMRI versus conventional scanners. A new artifact quantification technique is also presented, and phantom results confirm that susceptibility artifacts improve as expected with decreasing readout magnetic field using PMRI. This proof-of-concept study demonstrates that prepolarized techniques have the potential to provide diagnostic cross-sectional images for postoperative evaluation of patients with metal implants. Magn Reson Med 56:177-186, 2006.

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Image restoration from non-uniform magnetic field influence for direct Fourier NMR imaging

Cited by 77 publications

References 6 publications

Targeted‐HASTE imaging with automated device tracking for MR‐guided needle interventions in closed‐bore MR systems

Targeted‐HASTE imaging with automated device tracking for MR‐guided needle interventions in closed‐bore MR systems

Magnetic resonance imaging in radiotherapy treatment planning

Prepolarized magnetic resonance imaging around metal orthopedic implants

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