scholarly journals Mitigation of susceptibility-induced signal loss in neuroimaging using localized shim coils

2005 ◽  
Vol 53 (2) ◽  
pp. 243-248 ◽  
Author(s):  
Jung-Jiin Hsu ◽  
Gary H. Glover
Keyword(s):  
Signal Loss ◽  
Shim Coils ◽  
Induced Signal

scholarly journals Integrated slice-specific dynamic shimming for whole-body diffusion-weighted MR imaging at 1.5 T

2020 ◽  
Author(s):  
Sarah McElroy ◽  
Jessica M. Winfield ◽  
Olwen Westerland ◽  
Geoff Charles-Edwards ◽  
Joanna Bell ◽  
...  
Keyword(s):  
Spinal Cord ◽  
Image Quality ◽  
Signal Intensity ◽  
Distortion Correction ◽  
Whole Body ◽  
Signal Loss ◽  
Diffusion Weighted ◽  
Average Signal Intensity ◽  
3D Volume ◽  
Induced Signal

Abstract Objective To compare integrated slice-specific dynamic shim (iShim) with distortion correction post-processing to conventional 3D volume shim for the reduction of artefacts and signal loss in 1.5 T whole-body diffusion-weighted imaging (WB-DWI). Methods Ten volunteers underwent WB-DWI using conventional 3D volume shim and iShim. Forty-eight consecutive patients underwent WB-DWI with either volume shim (n = 24) or iShim (n = 24) only. For all subjects, displacement of the spinal cord at imaging station interfaces was measured on composed b = 900 s/mm2 images. The signal intensity ratios, computed as the average signal intensity in a region of high susceptibility gradient (sternum) divided by the average signal intensity in a region of low susceptibility gradient (vertebral body), were compared in volunteers. For patients, image quality was graded from 1 to 5 (1 = Poor, 5 = Excellent). Signal intensity discontinuity scores were recorded from 1 to 4 (1 = 2 + steps, 4 = 0 steps). A p value of < 0.05 was considered significant. Results Spinal cord displacement artefacts were lower with iShim (p < 0.05) at the thoracic junction in volunteers and at the cervical and thoracic junctions in patients (p < 0.05). The sternum/vertebra signal intensity ratio in healthy volunteers was higher with iShim compared with the volume shim sequence (p < 0.05). There were no significant differences between the volume shim and iShim patient groups in terms of image quality and signal intensity discontinuity scores. Conclusion iShim reduced the degree of spinal cord displacement artefact between imaging stations and susceptibility-gradient-induced signal loss.

scholarly journals Reduction of vibration‐induced signal loss by matching mechanical vibrational states: Application in high b ‐value diffusion‐weighted MRS

2019 ◽  
Vol 84 (1) ◽  
pp. 39-51 ◽  
Author(s):  
Dominik Weidlich ◽  
Mark Zamskiy ◽  
Marcus Maeder ◽  
Stefan Ruschke ◽  
Steffen Marburg ◽  
...  
Keyword(s):  
B Value ◽  
Signal Loss ◽  
Vibrational States ◽  
High B Value ◽  
Diffusion Weighted ◽  
Induced Signal

scholarly journals in Vivo Monitoring of Macrophage Infiltration in Experimental Ischemic Brain Lesions by Magnetic Resonance Imaging

2003 ◽  
Vol 23 (11) ◽  
pp. 1356-1361 ◽  
Author(s):  
Christoph Kleinschnitz ◽  
Martin Bendszus ◽  
Marco Frank ◽  
Laszlo Solymosi ◽  
Klaus V Toyka ◽  
...  
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Brain Lesions ◽  
Macrophage Infiltration ◽  
Signal Loss ◽  
Resonance Imaging ◽  
Ischemic Brain ◽  
Induced Signal ◽  
Local Accumulation

Although macrophages represent the major inflammatory cells in cerebral ischemia, the kinetics of macrophage infiltration are largely unknown. To address this issue, we injected superparamagnetic iron oxide (SPIO) particles into the circulation of rats at different time points after focal photothrombotic cerebral infarction and performed magnetic resonance imaging (MRI) 24 hours later. Infarcts appeared as hyperintense lesions on T2-w and CISS MR images during all stages. At days 5.5 and 6, an additional rim of signal loss indicative of local accumulation of SPIO particles appeared at the outer margin of the hyperintense ischemic lesions, which was not present at days 1 to 5. Areas of signal loss corresponded to local accumulation of iron-loaded macrophages in histologic sections. At day 8, signal loss became restricted to the inner core of the lesions and ceased thereafter. Macrophages, however, were still present in late ischemic brain lesions, but they were iron-negative. Thus SPIO-induced signal loss indicates active macrophage transmigration into ischemic infarcts but not their mere presence. SPIO-induced signal loss was independent from the disturbance of the blood-brain barrier. In conclusion, we have shown by in vivo monitoring that macrophages enter photothrombotic infarcts at late stages of infarct development, suggesting a role in tissue remodeling rather than neuronal injury.

scholarly journals On restoring motion-induced signal loss in single-voxel magnetic resonance spectra

2006 ◽  
Vol 56 (4) ◽  
pp. 754-760 ◽  
Author(s):  
Refaat E. Gabr ◽  
Shashank Sathyanarayana ◽  
Michael Schär ◽  
Robert G. Weiss ◽  
Paul A. Bottomley
Keyword(s):  
Magnetic Resonance ◽  
Signal Loss ◽  
Single Voxel ◽  
Induced Signal ◽  
Magnetic Resonance Spectra
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