Proceedings of the meeting - Department of Physics - University of ...

T2* weighted and phase imaging at 7 TeslaO11Lei JIANG 1 , Andreas Schaeffer 1 , Penny Gowland 1 and Richard Bowtel 1 .1 Sir Peter Mansfield Magnetic Resonance Centre, University of Nottingham, Nottingham, NG7 2RD, UKIntroductionUltrahigh field offers improved signal to noise ratio and new sourcesof image contrast. In particular spoiled gradient echo sequences provideconsiderable contrast to vessels, and brain areas that have previouslybeen associated with high iron levels ,due to increased T2*decay rates associated with magnetic susceptibility induced fieldperturbations. Furthermore the phase images associated with thissequence provide excellent contrast between the grey and white matter;a similar effect has previously been reported at lower field (1).The aim of this study is to characterise this effect with the future intentionof optimizing the sequences for contrast to noise ratio per unittime in the magnitude and phase images and of investigating thesources of this contrast.Methods and AnalysisData were acquired on a 7 Tesla Philips Intera Achieva scanner. Threehealthy human adult volunteers were studied, who gave their informedconsent. 3D-spoiled gradient echo images were acquired with an echotime of 15 ms, the shortest accessible TR of 27 ms and a flip angle of11 o . The voxel size was 0.4 x 0.4 x 0.7 mm 3 , with a matrix of 512 x512 x 120. The total acquisition time was 11 min. Phase images wereunwrapped in MATLAB (MathWorks, MA) and fitted to a polynomialto remove ‘low spatial frequency’ variations due to inhomogeneitiesin the applied field.Figure 3: Modulus image (left) and corresponding phase map (right)acquired at 7T (TE=15 ms).Results.Figure 4: Maximum intensity projection through a 3D spoiled gradientecho image set, showing the veins (TE=20 ms)The frequency shift between the grey and white matter was found tobe approximately 3 Hz.Figure 1: T2* weighted images through the caudate head, at 7T (left)and 3T (right) (TE=21 ms). Considerably increased contrast can beobserved at 7T.ConclusionWe have demonstrated that gradient echo images provide novel contrastat 7T in both the magnitude and phase data, in regions with largevenous contributions, in deep grey nuclei and in some major whitematter tracts. Possible biophysical explanations for this contrast includedeoxygenated blood in the venules and veins, known differencesin iron content of different brain regions or differences in myelinationbetween brain regions. Experiments are underway to try to understandthis source of contrast, and to improve the processing of the phasedata.References(1) E. Mark Haacke et al. Magn. Reson. Med. 52, 612-618 (2004).(2) Sofic E et al. Jour. Neural Transmission 74 (3), 199-205 (1988).Figure 2: Zoomed version of fig. 1 clearly showing new structurevisible in the caudate head at 7T.Acknowledgements: This work was funded by the Wellcome Trust,MRC, EPSRC and HEFCE, with technical support from Philips MedicalSystems.