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A tracking pulse-sequence, combined with knowledge of the markers' unique geometrical arrangement, is used to measure their positions. Tracking data from the glasses is then used to prospectively update the orientation and position of the image-volume so that it follows the motion of the head. Wireless-marker position measurements were comparable to measurements using traditional wired radio-frequency tracking coils, with the standard deviation of the difference http://www.selleckchem.com/products/AC-220.html with B1 maps and temperature measurements. Prospective motion correction was demonstrated in a 2D spin-echo scan while the subject performed a series of deliberate head rotations. Prospective motion correction using wireless markers enables high quality images to be acquired even during bulk motions. Wireless markers are small, avoid radio-frequency safety risks from electrical cables, are not hampered by mechanical connections to the scanner, and require minimal setup times. These advantages may help to facilitate adoption in the clinic. Magn Reson Med 70:639�C647, 2013. ? 2013 Wiley Periodicals, Inc. ""Disorganization of collagen fibers is a sign of early-stage cartilage degeneration in osteoarthritic knees. Water molecules trapped within well-organized collagen fibrils would be sensitive to collagen alterations. Multicomponent effective transverse relaxation (T2*) http://www.selleckchem.com/products/nutlin-3a.html mapping with ultrashort echo time acquisitions is here proposed to probe short T2 relaxations in those trapped water molecules. Six human tibial plateau explants were scanned on a 3T MRI scanner using a home-developed ultrashort echo time sequence with echo times optimized via Monte Carlo simulations. Time constants and component intensities of T2* decays were calculated at individual pixels, using the nonnegative http://www.selleck.cn/products/Romidepsin-FK228.html least squares algorithm. Four T2*-decay types were found: 99% of cartilage pixels having mono-, bi-, or nonexponential decay, and 1% showing triexponential decay. Short T2* was mainly in 1-6 ms, while long T2* was ?22 ms. A map of decay types presented spatial distribution of these T2* decays. These results showed the technical feasibility of multicomponent T2* mapping on human knee cartilage explants. Magn Reson Med, 2010. ? 2010 Wiley-Liss, Inc. ""Segmented 2D-selective radiofrequency excitations can be used to acquire irregularly shaped target regions, e.g., in single-voxel MR spectroscopy, without involving excessive radiofrequency pulse durations. However, segments covering only outer k-space regions nominally use reduced B1 amplitudes (i.e., smaller flip angles) and yield lower signal contributions, which decreases the efficiency of the measurement.