UNDERSTANDING CHEMICAL-SHIFT INDUCED BOUNDARY ARTIFACTS AS A FUNCTIONOF FIELD-STRENGTH - INFLUENCE OF IMAGING PARAMETERS (BANDWIDTH, FIELD-OF-VIEW, AND MATRIX SIZE)

Objective: To study the importance of chemical shift induced boundary artefact (CSA) at different field strengths and the implications for p ulse sequence design with respect to receiver bandwidth (BW), field-of -view (FOV) and matrix size. Materials and methods: A fat-water phanto m was examined in MR systems of different field strength (1.5 T, 1.0 T and 0.2 T), using pulse sequences with different receiver BW, FOV, an d matrix size. The chemical shift was quantified by measuring the widt h of the bright and dark misregistration rims seen at the planar fat-w ater interface. The measured chemical shift was compared with the theo retically calculated chemical shift. Results: Excellent correlations w ere found between predicted chemical shift and measurement results in our experiments. The width of the CSA (in millimetres) is directly pro portional to field strength, inversely proportional to receiver BW and hence to the strength of the readout gradient, directly proportional to FOV, and inversely proportional to matrix size. Conclusion: CSA occ urs at all magnetic field strengths, but given a certain BW it is more pronounced at higher fields. Although the CSA in Hz is directly propo rtional to field strength, the visible CSA at low-field was slightly h igher than theoretically expected. The relative lack of CSA in low-fie ld strength images permits the application of narrow receiver BW seque nces, resulting in increased signal to noise ratio.