Jouke Smink

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

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. The first results obtained in nine healthy adult subjects are presented. Magn Reson Med 48:425–429, 2002.

On the performance and accuracy of 2D navigator pulses.

The purpose of this study was to investigate and to optimize the performance of two-dimensional spatially selective excitation pulses used for navigator applications on a clinical scanner. The influence of gradient imperfections, off-resonance effects, and incomplete k-space covering on the pencil beam-shaped spatial excitation profile of the 2D RF pulse was studied. The studies involved experiments performed on phantoms and in vivo. In addition, simulations were carried out by numerical integration of the Bloch equations. The accuracy of positioning of the pencil beam was increased by a factor of three by employing a simple correction scheme for the compensation of gradient distortions. The spatial selectivity of the 2D RF pulse was improved by taking sampling density corrections into account. The 2D RF pulse performance was found to be sufficient to monitor the diaphragm motion even at moderate gradient strength. For applications, where a high spatial resolution is required or a less characteristic contrast is present a strong gradient system is recommended.

Sensitivity-encoded coronary MRA at 3T

Long scan times are still a main limitation in free‐breathing navigator‐gated 3D coronary MR angiography (MRA). Unlike other MRI applications, high‐resolution coronary MRA has not been amenable to acceleration by parallel imaging techniques due to signal‐to‐noise ratio (SNR) concerns. In the present work, mitigating SNR limitations by the transition to higher static magnetic field strength is proposed, thus enabling scan time reduction by the parallel sensitivity encoding (SENSE) technique. The study reports the implementation and evaluation of free‐breathing navigator‐gated 3D coronary MRA with SENSE at 3T. Results from 11 healthy subjects indicate that the approach permits significant scan time reduction in MRA of the left and right coronary systems. Quantitative image analysis and visual grading suggest that two‐fold scan acceleration can be accomplished at nearly preserved image quality. The additional experiments appear to demonstrate that parallel MRA equally permits enhancing volume coverage and spatial resolution while maintaining scan time. Magn Reson Med 52:221–227, 2004.

Respiratory bellows revisited for motion compensation: Preliminary experience for cardiovascular MR

For many cardiac MR applications, respiratory bellows gating is attractive because it is widely available and not disruptive to or dependent on imaging. However, its use is uncommon in cardiac MR, because its accuracy has not been fully studied. Here, in 10 healthy subjects, the bellows and respiratory navigator (NAV) with the displacement of the diaphragm and heart were simultaneously monitored, during single‐shot imaging. Furthermore, bellows‐gated and NAV‐gated coronary MRI were compared using a retrospective reconstruction at identical efficiency. There was a strong linear relationship for both the NAV and the abdominal bellows with the diaphragm (R = 0.90 ± 0.05 bellows, R = 0.98 ± 0.01 NAV, P < 0.001) and the heart (R = 0.89 ± 0.06 bellows, R = 0.96 ± 0.02 NAV, P = 0.004); thoracic bellows correlated less strongly. The image quality of bellows‐gated coronary MRI was similar to NAV‐gated and superior to no‐gating (P < 0.01). In conclusion, bellows provides a respiratory monitor which is highly correlated with the NAV and suitable for respiratory compensation in selected cardiac MR applications. Magn Reson Med, 2010.

Prospective respiratory motion correction for coronary MR angiography using a 2D image navigator.

Respiratory motion remains the major impediment in a substantial amount of patients undergoing coronary magnetic resonance angiography. Motion correction in coronary magnetic resonance angiography is typically performed with a diaphragmatic 1D navigator (1Dnav) assuming a constant linear relationship between diaphragmatic and cardiac respiratory motion. In this work, a novel 2D navigator (2Dnav) is proposed, which prospectively corrects for translational motion in foot–head and left–right direction. First, 1Dnav‐ and 2Dnav‐based motion correction are compared in 2D real time imaging experiments, by evaluating the residual respiratory motion in 10 healthy subjects as well as in a moving vessel phantom. Subsequently, 1Dnav and 2Dnav corrected high‐resolution 3D coronary MR angiograms were acquired, and both objective and subjective image quality were assessed. For a gating window of 10 mm, 1Dnav and 2Dnav performed equally well; however, without any respiratory gating, the 1Dnav had a lower visual score for all coronary arteries compared with 10 mm gating, whereas the 2Dnav without gating performed similar to 1Dnav with 10 mm gating. Magn Reson Med, 2013.

Contrast-enhanced whole-heart coronary MRI with bolus infusion of gadobenate dimeglumine at 1.5 T

We sought to investigate the T1 kinetics of blood and myocardium after three infusion schemes of gadobenate dimeglumine (Gd‐BOPTA) and subsequently compared contrast‐enhanced whole‐heart coronary MRI after a bolus Gd‐BOPTA infusion with nonenhanced coronary MRI at 1.5 T. Blood and myocardium T1 was measured in seven healthy adults, after each underwent three Gd‐BOPTA infusion schemes (bolus: 0.2 mmol/kg at 2 mL/sec, hybrid: 0.1 mmol/kg at 2 mL/sec followed by 0.1 mmol/kg at 0.1 mL/sec, and slow: 0.2 mmol/kg at 0.3 mL/sec). Fourteen additional subjects underwent contrast‐enhanced coronary MRI with an inversion‐recovery steady‐state free precession sequence after bolus Gd‐BOPTA infusion. Images were compared with nonenhanced T2‐prepared steady‐state free precision whole‐heart coronary MRI in signal‐to‐noise ratio, contrast‐to‐noise ratio, depicted vessel length, vessel sharpness, and subjective image quality. Bolus and slow infusion schemes resulted in similar T1 during coronary MRI, whereas the hybrid infusion method yielded higher T1 values. A bolus infusion of Gd‐BOPTA significantly improved signal‐to‐noise ratio, contrast‐to‐noise ratio, depicted coronary artery length, and subjective image quality, when all segments were collectively compared but not when compared segment by segment. In conclusion, whole‐heart steady‐state free precision coronary MRI at 1.5 T can benefit from a bolus infusion of 0.2 mmol/kg Gd‐BOPTA. Magn Reson Med, 2011.

A new framework for interleaved scanning in cardiovascular MR: Application to image-based respiratory motion correction in coronary MR angiography.

To describe a new framework for interleaving scans and demonstrate its usefulness for image‐based respiratory motion correction in whole heart coronary MR angiography (CMRA).

A new framework for interleaved scanning in cardiovascular MR

To describe a new framework for interleaving scans and demonstrate its usefulness for image‐based respiratory motion correction in whole heart coronary MR angiography (CMRA).

Pulmonary vein inflow artifact reduction for free-breathing left atrium late gadolinium enhancement

Two‐dimensional “pencil‐beam” navigator, placed on the right hemidiaphragm, is used for free‐breathing late gadolinium enhancement of the left atrium in patients with atrial fibrillation. The pencil‐beam navigator creates an inflow artifact in the right pulmonary veins and atrial wall that may obscure local pulmonary vein and left atrium scars. To reduce this artifact, we propose a large slab right hemidiaphragm projection navigator that measures the respiratory motion while reducing the associated inflow artifact. Eighteen subjects underwent pulmonary vein late gadolinium enhancement using the pencil‐beam and projection navigator. Subjective inflow and respiratory motion artifact scores (1 = severe, 2 = moderate, 3 = mild, and 4 = none) from two blinded readers were compared. The artifact scores were 3.8 ± 0.4 and 2.1 ± 0.7 for the projection and pencil‐beam navigators, respectively (P < 0.001). Respiratory motion artifact scores were similar between the two techniques (3.0 ± 0.5 vs. 3.1 ± 0.5 for projection vs. pencil‐beam navigator). The proposed method greatly reduces the inflow artifact in free‐breathing pulmonary vein late gadolinium enhancement while allowing adequate respiratory motion compensation. Magn Reson Med, 2011.

Highly efficient whole-heart imaging using radial phase encoding-phase ordering with automatic window selection

Three dimensional (3D) whole‐heart magnetic resonance imaging (MRI) has become an important imaging modality to assess cardiovascular diseases. The main challenges for 3D whole‐heart MRI are long acquisition times, required to achieve high spatial resolution, and image artefacts due to physiological motion. Here we propose to overcome these problems by the combination of an interleaved Radial Phase Encoding trajectory and the Phase Ordering with Automatic Window Selection method. This Radial Phase Encoding‐Phase Ordering with Automatic Window Selection approach yields fast 3D whole‐heart imaging with a high isotropic resolution and high navigator efficiency even for extremely irregular breathing. Numerical simulations were performed and Radial Phase Encoding‐Phase Ordering with Automatic Window Selection was implemented on a clinical scanner. A comparison between the proposed method and a respiratory gated 3D Cartesian approach was carried out. Radial Phase Encoding‐Phase Ordering with Automatic Window Selection leads to a better depiction of coronary arteries and an increase in navigator efficiency. In addition to a high resolution image, this method also provides dynamic respiratory information without an increase in scan time. Magn Reson Med, 2011.