High‐resolution intracranial and cervical MRA at 3.0T: Technical considerations and initial experience

Abstract

Initial experience with intracranial and cervical MRA at 3.0T is reported. Phantom measurements (corrected for relaxation effects) show S/N (3.0T) ‫؍‬ 2.14 ؎ 0.08 ؋ S/N (1.5T) in identical-geometry head coils. A 3.0T 3DTOF intracranial imaging protocol with higher-order autoshimming was developed and compared to 1.5T 3DTOF in 12 patients with aneurysms. A comparison by two radiologists showed the 3.0T to be significantly better (P < 0.001) for visualization of the aneurysms. The feasibility of cervical and intracranial contrast enhanced MR angiography (CEMRA) at 3.0T is also examined. The relaxivity of the gadolinium contrast agent decreases by only about 4 -7% when the field strength is increased from 1.5 to 3.0T. Cervical 3.0T CEMRA was obtained in eight patients, two of whom had 1.5T studies available for direct comparison. Image comparison suggests 3.0T to be a favorable field strength for cervical CEMRA. Voxel volumes of 0.62-0.73 mm 3 (not including zero-filling) were readily achieved at 3.0T with the use of a single-channel transmitreceive head or cervical coil, a 25 mL 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 3.0T MRA are increased SAR and T* 2 dephasing compared to 1.5T. Image comparison suggests signal loss due to T* 2 dephasing will not be substantially more problematic than at 1.5T. The 1998 revision of the U.S. Food and Drug Administration guidelines (1) states that MRI systems with main static field strengths of 4.0T and less can qualify as nonsignificant risk devices. Moreover, with the advent of actively shielded magnet technology it is now feasible to site a 3.0T scanner in a clinical setting. Much of the prior use of 3.0T and higher field strength MRI systems, however, has been for pure or clinical research, mostly in the fields of functional brain MRI (e.g., 2,3) and spectroscopy (e.g., 4). This is quite logical, since fMRI and spectroscopy benefit not only from the increased S/N of 3.0T, but also from the linear dependence of magnetic susceptibility changes and chemical shift, respectively.We have applied our 3.0T system to both clinical research and routine clinical use. During the period October 1999 to May 2001, 2908 routine clinical brain exams were performed in an outpatient setting (5). The purpose of this article is twofold: 1) to provide an initial comparison of intracranial 3D time of flight (3DTOF) magnetic resonance angiography (MRA) at 1.5 and 3.0T; and 2) to establish the initial feasibility of 3D contrast-enhanced MR angiography (CEMRA) for the cervical and intracranial arteries at 3.0T. CEMRA is already a well-established technique at 1.5T and has been applied previously to study both intracranial aneurysms (6) and the cervical arteries (7). We examined whether the increased S/N available at 3.0T can translate into increased spatial resolution for CEMRA. We believe that the de...

Magnetic resonance imaging protocols for examination of the neurocranium at 3 T

“…Expectedly, also inflow angiographies profit from the higher magnetic field [21,22,23]. Image quality in terms of resolution of small vessels was still inferior to DSA (Fig.…”

High spatial resolution contrast-enhanced MR angiography of the supraaortic arteries using the quadrature body coil at 3.0T: A feasibility study

“…As the signal scales proportionally with the field strength, 3.0T holds potential benefits for cardiovascular MR imaging [6][7][8][9][10][11][12][13][14][15]. The feasibility of higher spatial resolution in MRA of the intracranial and carotid arteries at 3.0T has been the subject of various studies [7][8][9][10].…”

Does black blood MRA have a role in the assessment of intracerebral aneurysms?

“…Studies have shown that the performance of 3D-TOF MRA at 3 T is significantly better than at 1.5 T [38]. However the problems associated with 3D-TOF discussed above remain significant at 3 T also.…”

“…In addition timing problems exist with this technique in order to eliminate venous contamination in the setting of slow flow. In addition, the use of CE-MRA at 3 T introduces specific RF power deposition concerns that need to be addressed [38] through the careful selection of TR and flip angle values.…”