Cervical MRA

Initial experience with intracranial and cervical MRA at 3.0 T was reported. Phantom measurement s (corrected for relaxation effects) show S/N (3.0T) = 2.14 + / - 0.08 x S/N (1.5 T) in identical-geometry head coils [18]. A 3.0 T TOF intracranial imaging protocol with higher-order autoshimming was developed and compared to 1.5 T 3D TOF in 12 patients with aneurysms. A comparison by two radiologists showedthe 3.0 Tto be significantly better (P < 0.001) for visualization of the aneurysms (see Fig. 3.29). The feasibility of cervical and intracranial contrast enhanced MR angiography (CEMRA) at 3.0 T was also examined. The relaxivity of the gadolinium contrast agent decreased by only about 4-7% when the field strength was increased from 1.5 T to 3.0 T. Cervical 3.0 T CEMRA was obtained in eight patients available for direct comparison. Image comparison suggested 3.0 T to be favorable field strength for cervical CEMRA. Voxel volumes of 0.62-0.73 mm3 were readily achieved at 3.0 T with the use of single-channel transmit-receive head or cervical coil, a 25 mL

Figure 3.31: Source images of the 3D TOF MRA of the left carotid artery of a volunteer: (a and b) inferior and (c and d) at the carotid bifurcation. Images were acquired (a and c) without VTE and (b and d) with VTE (16 TE segments). The imaging parameters were as follows: matrix = 256 A~ 256 A~ 32, slice thickness = 1 mm, TR = 24 ms, FOV = 14 cm, and TE = 1.8/2.9 ms for VTE on/off. MT was not applied. The reduced signal indicated by arrows in a and c was much more uniform in images b and d with VTE.

Figure 3.31: Source images of the 3D TOF MRA of the left carotid artery of a volunteer: (a and b) inferior and (c and d) at the carotid bifurcation. Images were acquired (a and c) without VTE and (b and d) with VTE (16 TE segments). The imaging parameters were as follows: matrix = 256 A~ 256 A~ 32, slice thickness = 1 mm, TR = 24 ms, FOV = 14 cm, and TE = 1.8/2.9 ms for VTE on/off. MT was not applied. The reduced signal indicated by arrows in a and c was much more uniform in images b and d with VTE.

bolus of Gadoteridol, and a 3D pulse sequence with a 66% sampling efficiency. This spatial resolution allowed visualization of intracranial aneurysms, carotid dissections, and atherosclerotic disease including ulcerations. Potential drawbacks of 3.0 T MRA are increased SAR and T(*)2 dephasing compared to 1.5 T.

The dependence of RF power deposition on TR for CEMRA was calculated and described.

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