WRITE ANY 4 PROPERTIES OF MAGNETIC LINES OF FORCE.
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Explanation:
in ultra high field environments, e.g. in 7 T MR scanners as used in research applications. The high magnetic fields cause severe magnetohydrodynamic (MHD) effects which disturb the ECG signal. Image synchronization is thus less reliable and yields artefacts in CMR images. A strategy based on Independent Component Analysis (ICA) was pursued in this work to enhance the ECG contribution and attenuate the MHD effect. ICA was applied to 12-lead ed experiments on measuring the magnetic fields of current-carrying wires and permanent magnets using magnetic field probes of various kinds. This paper explains how to use an iPad and the free app MagnetMeter-3D Vector Magnetometer and Accelerometer4 (compass HD) to measure the magnetic fields. Carol; Reeder, Scott B.
2013-01-01
Purpose MR-based quantification of liver magnetic susceptibility may enable field strength-independent measurement of liver iron concentration (LIC). However, susceptibility quantification is challenging, due to non-local effects of susceptibility on the B0 field. The purpose of this work is to demonstrate feasibility of susceptibility-based LIC quantification using a fat-referenced approach. Methods Phantoms consisting of vials with increasing iron concentrations immersed between oil/water layers, and twenty-seven subjects (9 controls/18 subjects with liver iron overload) were scanned. Ferriscan (1.5T) provided R2-based reference LIC. Multi-echo 3D-SPGR (1.5T/3T) enabled fat-water, B0- and R2*-mapping. Phantom iron concentration (mg Fe/l) was estimated from B0 differences (ΔB0) between vials and neighboring oil. Liver susceptibility and LIC (mg Fe/g dry tissue) was estimated from ΔB0 between the lateral right lobe of the liver and adjacent subcutaneous adipose tissue (SAT). Results Estimated phantom iron concentrations had good correlation with true iron concentrations (1.5T:slope=0.86, intercept=0.72, r2=0.98; 3T:slope=0.85, intercept=1.73, r2=0.98). In liver, ΔB0 correlated strongly with R2* (1.5T:r2=0.86; 3T:r2=0.93) and B0-LIC had good agreement with Ferriscan-LIC (slopes/intercepts nearly 1.0/0.0, 1.5T:r2=0.67, slope=0.93±0.13, p≈0.50, intercept=1.93±0.78, p≈0.02; 3T:r2=0.84, slope=1.01±0.09, p≈0.90, intercept=0.23±0.52, p≈0.68). Discussion Fat-referenced, susceptibility-based LIC estimation is feasible at both field strengths. This approach may enable improved susceptibility mapping in the abdomen. PMID:23801540