Comparison of navigator echo and centroid corrections of image displacement induced by static magnetic field drift on echo planar functional MRI

Liu, Ho-Ling Anthony; Kochunov, Peter; Lancaster, Jack L.; Fox, Peter T.; Gao, Jia

doi:10.1002/1522-2586(200102)13:2<308::aid-jmri1044>3.0.co;2-l

Cited by 14 publications

(4 citation statements)

References 13 publications

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“…Therefore, the detected frequency shift was most likely generated by a small drift of the main magnetic field B 0 , induced by a small temperature increase of the iron plates (passive shim) mounted within the gradient coil. Similar effects have been reported for EPI measurements (21). Apart from these imperfections, Fig.…”

Section: Resultssupporting

confidence: 86%

Update on changes in anemia management

Levy

2007

Dialysis & Transplantation

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Section: Resultssupporting

confidence: 86%

Update on changes in anemia management

Levy

2007

Dialysis & Transplantation

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“…Extensions to higher order polynomial corrections or more extensive prospective corrections may further improve accuracy in cases of more severe background drift. Image shift artifacts over long scanning durations can also be corrected using a retrospective approach, by applying a rigid co-registration of incoming images to the baseline dynamic before subsequent polynomial fitting of phase drift [56,68]. In addition to phase drift, in-vivo implementations of MR thermometry are very sensitive to tissue motion, which may be mitigated using accelerated acquisition with navigators [69] or multi-baseline and referenceless techniques [70,71].…”

Section: Discussionmentioning

confidence: 99%

“…This feature is user-selectable for dynamic acquisitions on 3T Philips MR scanners, but might require customized sequence development on other magnet platforms. With DS enabled, phase shift with respect to the initial resonance frequency is calculated from a small flip-angle, 3-echo acquisition inserted at the beginning of each dynamic [56]. This method also has the effect of counteracting global drift of the B 0 field.…”

Section: Prf Shift Mr Thermometry and Drift Correction Strategiesmentioning

confidence: 99%

Drift correction for accurate PRF-shift MR thermometry during mild hyperthermia treatments with MR-HIFU

Bing

Staruch

Tillander

et al. 2016

International Journal of Hyperthermia

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There is growing interest in performing hyperthermia treatments with clinical MRI-guided high-intensity focused ultrasound (MR-HIFU) therapy systems designed for tissue ablation. During hyperthermia treatment, however, due to the narrow therapeutic window (41–45°C), careful evaluation of the accuracy of PRF shift MR thermometry for these types of exposures is required. Purpose The purpose of this study was to evaluate the accuracy of MR thermometry using a clinical MR-HIFU system equipped with hyperthermia treatment algorithm. Methods Mild heating was performed in a tissue-mimicking phantom with implanted temperature sensors using the clinical MR-HIFU system. The influence of image-acquisition settings and post-acquisition correction algorithms on the accuracy of temperature measurements was investigated. The ability to achieve uniform heating for up to 40 minutes was evaluated in rabbit experiments. Results Automatic center-frequency adjustments prior to image-acquisition corrected the image-shifts on the order of 0.1 mm/min. Zero and first order phase variations were observed over time, supporting the use of a combined drift correction algorithm. The temperature accuracy achieved using both center-frequency adjustment and the combined drift correction algorithm was 0.57 ± 0.58 °C in heated region and 0.54 ± 0.42 °C in unheated region. Conclusion Accurate temperature monitoring of hyperthermia exposures using PRF shift MR thermometry is possible through careful implementation of image-acquisition settings and drift correction algorithms. For the evaluated clinical MR-HIFU system, center-frequency adjustment eliminated image-shifts, and a combined drift correction algorithm achieved temperature measurements with an acceptable accuracy for monitoring and controlling hyperthermia exposures.

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“…For spiral imaging, sidelobes in the blurring point response function become prominent when r/p = 2 ΔfT acq > 1, where r is the radius (9). Geometric distortion corrections have been developed for static off‐resonance conditions occurring because of local variations in magnetic susceptibility (18–20) and corrections have been made using navigator echo phase for magnetic field drift (5, 21). However, to date no corrections have been reported for respiration‐induced dynamic off‐resonance effects.…”

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confidence: 99%

Correction of physiologically induced global off‐resonance effects in dynamic echo‐planar and spiral functional imaging

Pfeuffer

Moortele

Uğurbil

et al. 2002

Magnetic Resonance in Med

203

171

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In functional magnetic resonance imaging, a rapid method such as echo-planar (EPI) or spiral is used to collect a dynamic series of images. These techniques are sensitive to changes in resonance frequency which can arise from respiration and are more significant at high magnetic fields. To decrease the noise from respiration-induced phase and frequency fluctuations, a simple correction of the "dynamic off-resonance in k-space" (DORK) was developed. The correction uses phase information from the center of k-space and a navigator echo and is illustrated with dynamic scans of single-shot and segmented EPI and, for the first time, spiral imaging of the human brain at 7 T. Image noise in the respiratory spectrum was measured with an edge operator. The DORK correction significantly reduced respirationinduced noise (image shift for EPI, blurring for spiral, ghosting for segmented acquisition). While spiral imaging was found to exhibit less noise than EPI before correction, the residual noise after the DORK correction was comparable In functional MRI (fMRI), a time-series of images is collected to monitor changes in the subject's physiology during a challenge, e.g., cognition, exercise, or contrast uptake. Invariably for such techniques, rapid acquisition such as echo-planar imaging (EPI) (1) or spiral imaging (2) is used in order to avoid loss of temporal information and to suppress artifacts from respiration and cardiac functions that are confounds to the challenge being monitored. In the case of blood oxygen level-dependant (BOLD) functional neuroimaging (3), which will be the primary focus of this work, an echo time (TE) comparable toT* 2 is used in order to maximize the sensitivity to small BOLD changes inT* 2 . Unfortunately, the relatively long TE also makes the acquisition sensitive to changes in resonance frequency and other factors, causing various artifacts.NMR phase shifts can arise from instrument instability, bulk motion, or from cardiac and respiratory functions (4 -7). Phase variations between segments cause ghosting and extra noise in the time-series, which degrades functional data and the resulting maps. Zero-order phase (nonevolving in time) corrections using navigator echoes (8 -10) or retrospective modeling of cardiac and respiratory modulations (11-13) have been employed to reduce these effects.A major effect from respiration is that the resonance frequency in the brain region can vary in time even when the head of the subject is immobile (14 -16). These firstorder phase variations (evolving linearly in time) result from respiration-driven movement of organs in the thoracic and abdominal cavities, as well as to changes in the oxygenation state of the respired gas. The field modulations tend to vary weakly in the inferior-superior direction in accordance with relative proximity to the chest, although the dominant effect is a global frequency shift in the whole brain (16,17). In single-shot EPI images, changes in resonance frequency result in positional voxel shifts predominantly in the phase encode ...

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Comparison of navigator echo and centroid corrections of image displacement induced by static magnetic field drift on echo planar functional MRI

Cited by 14 publications

References 13 publications

Update on changes in anemia management

Update on changes in anemia management

Drift correction for accurate PRF-shift MR thermometry during mild hyperthermia treatments with MR-HIFU

Correction of physiologically induced global off‐resonance effects in dynamic echo‐planar and spiral functional imaging

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