Preliminary report on in vivo coronary MRA at 3 Tesla in humans

Abstract

Current limitations of coronary magnetic resonance angiography (MRA) include a suboptimal signal-to-noise ratio (SNR), which limits spatial resolution and the ability to visualize distal and branch vessel coronary segments. Improved SNR is expected at higher field strengths, which may provide improved spatial resolution. However, a number of potential adverse effects on image quality have been reported at higher field strengths. The limited availability of high-field systems equipped with cardiac-specific hardware and software has previously precluded successful in vivo human high-field coronary MRA data acquisition. In the present study we investigated the feasibility of human coronary MRA at 3.0T in vivo. Most recent studies suggest that free-breathing 3D coronary magnetic resonance angiography (MRA) at 1.5T is a valuable tool for the noninvasive assessment of significant proximal to mid coronary artery disease (1). Still, the ability to visualize and assess more distal or branching vessels is desirable, and quantitative grading of the stenoses remains an ultimate goal. Limitations of current coronary MRA approaches include residual motion and signal-tonoise (SNR) constraints. In theory, SNR is directly related to the strength (B 0 ) of the static magnetic field. Thus, improved SNR can be expected from the use of magnets with higher magnetic field strength, for which 3.0T systems have recently been approved for clinical use. However, together with the limited availability of higher-field systems equipped for cardiac applications, other potential impediments (2) include increased susceptibility artifacts, reduced T * 2 (3,4), increased T 1 , radiofrequency (RF) field distortions (5), and changed tissue dielectric constants or body dielectric resonances (6,7). Further, at higher field strengths, increased RF deposition may remove flexibility for general sequence design, and efficient myocardial motion suppression (reliable R-wave triggering) becomes more challenging due the amplified magneto-hydrodynamic (MHD) effects (8). Recent progress in 3.0T hardware (vector ECG (VECG) (8), short-bore magnets, dedicated surface receive coils (5), and body send coils) and the adaptation of cardiac-specific software (T 2 Prep (9) and 2D selective real-time navigators (10)) for 3.0T has made it possible to implement analogous 1.5T coronary MRA methodology on a whole-body 3.0T system. Therefore, we sought to investigate the feasibility of coronary MRA data acquisition at 3.0T. The first in vivo results obtained in nine consecutive healthy adult human subjects are presented. METHODSCoronary MRA was implemented on a commercial actively shielded whole-body compact magnet (Intera 3.0T, 157 cm magnet length, 60 cm internal diameter; Philips Medical Systems, Best, The Netherlands) equipped with a MASTER ® gradient system (30 mT; 150 mT/m/ms), a VECG module (8), and Release 8.1.3 cardiac scanner software. A prototype body send coil and a prototype sixelement cardiac synergy receive coil were used. Nine consecutive healthy adult human ...

Detailing the use of magnetohydrodynamic effects for synchronization of MRI with the cardiac cycle: A feasibility study

“…This susceptibility to electromagnetic field (EMF) interference manifests itself in ECG waveform distortions already present in ECG traces acquired at 1.5 T and lower fields (2,5). As high and ultrahigh field MR becomes more widespread, the susceptibility of ECG recordings to MHD effects is further pronounced (6)(7)(8)(9). Artifacts in the ECG trace and severe T-wave elevation might be misinterpreted as R-waves, resulting in misdetection of cardiac activity or erroneous cardiac gating.…”

Toward single breath‐hold whole‐heart coverage coronary MRA using highly accelerated parallel imaging with a 32‐channel MR system

“…Hence appreciable increases in SNR could be obtained through further reductions in the coil size and increases in the density of the array elements. Furthermore, though this study was performed at a field strength of 1.5T, baseline SNR improvements inherent to higher magnetic field strengths have been demonstrated for CMRA (32)(33)(34). Another benefit of high magnetic field strength is the augmentation of the contrast-to-noise ratio (CNR) between the blood pool and the myocardium (32,33).…”

“…Furthermore, though this study was performed at a field strength of 1.5T, baseline SNR improvements inherent to higher magnetic field strengths have been demonstrated for CMRA (32)(33)(34). Another benefit of high magnetic field strength is the augmentation of the contrast-to-noise ratio (CNR) between the blood pool and the myocardium (32,33). It has also been predicted that high field strengths will allow reduced noise amplification in parallel imaging (23,31).…”

Cardiac MR Assessment of Coronary Arteries

“…This is disadvantageous for coronary MRA using SSFP acquisition because of its higher susceptibility to inhomogeneity of magnetic field and the need for higher flip angles to achieve sufficient blood contrast. Coronary MRA acquisition using 3 T was shown to be feasible in humans by Stuber et al [27]. A combination of gradient echo whole heart coronary MRA and gadolinium contrast administration at 3 T produces high-resolution coronary MRA with significantly improved image quality and diagnostic accuracy compared with those at 1.5 T [28,29].…”