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In vivo MRI of submillisecond T 2 species with two‐dimensional and three‐dimensional radial sequences and applications to the measurement of cortical bone water
Author(s) -
Techawiboonwong Aranee,
Song Hee Kwon,
Wehrli Felix W.
Publication year - 2008
Publication title -
nmr in biomedicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.278
H-Index - 114
eISSN - 1099-1492
pISSN - 0952-3480
DOI - 10.1002/nbm.1179
Subject(s) - pulse sequence , voxel , cartesian coordinate system , nuclear magnetic resonance , pulse (music) , excitation , cortical bone , physics , partial volume , anatomy , biomedical engineering , materials science , chemistry , mathematics , nuclear medicine , geometry , optics , biology , medicine , radiology , quantum mechanics , detector
Water in dense collagenous tissues such as tendons and ligaments, as well as water in cortical bone that occupies the spaces of the lacuno‐canicular system or is tightly bound to collagen, is not ordinarily detectable by MRI. Water proton T 2 in these structures is generally less than 1 ms. Recent advances in instrumentation in conjunction with non‐Cartesian imaging strategies now allow center of k‐space to be scanned 100 µs or less after excitation. We examined the performance of two radial pulse sequences, a 2D sequence with half‐pulse excitation and a new 3D hybrid sequence with variable‐echo Cartesian encoding in the third dimension, on a whole‐body 3 T scanner. Both pulse sequences used long‐ T 2 soft‐tissue suppression pulses. The half‐pulse slice profiles observed experimentally agreed well with those computed on the basis of a numerical solution of Bloch equations. The techniques yielded a signal‐to‐noise ratio of the order of 25 in 9 min scan time at a nominal voxel size of 0.58 × 0.58 × 8 mm 3 and 50–90 µs ‘echo time’ in the cortex of the tibial mid‐shaft. With the use of an external reference, the water volume fraction of cortical bone in four subjects (mean ± SD age 32.25 ± 5.3 years) was found to be 22.5 ± 2.7%, in good agreement with literature values. Copyright © 2007 John Wiley & Sons, Ltd.