Peter Boernert

Image‐based tracking of optically detunable parallel resonant circuits

In this work strategies for the robust localization of parallel resonant circuits are investigated. These strategies are based on the subtraction of two images, which ideally differ in signal intensity at the positions of the devices only. To modulate their signal amplification, and thereby generate the local variations, the parallel resonant circuits are alternately detuned and retuned during the acquisition. The integration of photodiodes into the devices permits their fast optical switching. Radial and spiral imaging sequences are modified to provide the data for the two images in addition to those for a conventional image in the same acquisition time. The strategies were evaluated by phantom experiments with stationary and moving catheter‐borne devices. In particular, rapid detuning and retuning during the sampling of single profiles is shown to lead to a robust localization. Moreover, this strategy eliminates most of the drawbacks usually associated with image‐based tracking, such as low temporal resolution. Image‐based tracking may thus become a competitive (if not superior) alternative to projection‐based tracking of parallel resonant circuits. Magn Reson Med 49:1163–1174, 2003.

MR coronary artery imaging with 3D motion adapted gating (MAG) in comparison to a standard prospective navigator technique.

Magnetic resonance coronary angiography (MRCA) has been proven to be feasible for imaging of the proximal and medial portions of the three main coronary arteries. Free breathing techniques allow for high resolution imaging but prolong scan time. This could potentially be shortened by improving the efficiency, robustness and accuracy of the navigator gating algorithm. Aim of this study was to determine the feasibility, efficiency, and image quality of a new motion compensation algorithm (3D-MAG) for coronary artery imaging with navigator techniques. In 21 patients the coronaries were imaged in plane with a 3D k-space segmented gradient echo sequence. A T2 preparation prepulse was used for suppression of myocardial signal, during free breathing and a navigator technique with using real time slice following and a gating window of 5 mm was applied to suppress breathing motion artefacts. Imaging was performed with standard gating and compared to 3D-MAG. Image quality was visually compared, contrast-to-noise and signal-to-noise ratio were calculated, the length of visualized coronary arteries was measured and scan duration and scan efficiency were calculated. Standard navigator imaging was feasible in 19 of 21 (90.5%) patients 3D-MAG in 21/21 (100%). Scan efficiency and duration was significantly improved with 3D-MAG (p < .05) without change in image quality. 3D-MAG is superior to conventional navigator correction algorithms. It improves feasibility and scan efficiency without reduction of image quality. This approach should be routinely used for MR coronary artery imaging with navigator techniques.

Fat suppression for coronary MR angiography at 3T: 2 point Dixon versus Spectral Presaturation with Inversion Recovery (SPIR)

Background The coronary arteries are embedded in epicardial fat. To improve visualization in coronary MR angiography (CMRA) fat suppression techniques such as Spectral Presaturation with Inversion Recovery (SPIR) are often employed. Recently, water-fat separation using the multiecho 2 point Dixon method has gained increasing interest as it allows decomposing the MR signal into a water and fat image during image reconstruction [Eggers, MRM 2011]. While the water image provides a coronary angiogram the fat image may also contain clinically useful information and could be used for epicardial/pericardial fat quantification [Koken, ISMRM, 2011]. The purpose of this study was to compare SPIR and 2 point Dixon for coronary vessel delineation for the first time on a 3T clinical scanner.

Combined high-resolution and real-time imaging: A technical feasibility study on coronary magnetic resonance angiography

To propose a new approach to combining high‐resolution and real‐time imaging and to show its technical feasibility on the example of coronary magnetic resonance angiography.

Simultaneous intracranial angiography and intraplaque hemorrhage imaging using SNAP

Background Intracranial atherosclerotic disease (IAD) accounts for 9-15% of all stroke incidents in the US [1], and the ratio is even higher in some racial groups [2]. Although angiography based imaging remains the prevalent diagnostic tool for IAD detection, it’s unable to detect high risk lesions via direct visualization of the vessel wall. Lesions with intraplaque hemorrhage (IPH) on the carotid arteries have been associated with significantly increased clinical symptoms and plaque progress. An imaging tool that can detect both the luminal stenosis and high risk vessel wall disease is of clinical importance for IAD patient management. In this study, the recently proposed SNAP [3] technique was particularly optimized to simultaneously detect luminal stenosis and IPH for IAD patients.

Using mDixon to remove motion artifacts in carotid artery vessel wall MRI

Background Black blood carotid artery wall imaging can evaluate not just atherosclerotic plaque burden but also high risk components like lipid core and intraplaque hemorrhage. A current limitation in its clinical application, however, is its susceptibility to motion artifacts caused by involuntary motions like swallowing, coughing and breathing. Due to the natural bright signal from subcutaneous fat, unsuppressed fat signal contributes to the majority of motion artifacts in the carotid artery wall region. The fat signal cannot always be properly suppressed using spectrally selective RF pulses due to magnetic field inhomogeneities. Modified Dixon (mDixon) technique, however, is less susceptible to field inhomogeneities because it can separate fat signal without relying on the absolute frequency of the fat spectral. The aim of this study is to explore the feasibility of using mDixon techniques to better separate the strong fat signal and thus reduce motion artifacts near carotid wall region. Methods

iMSDE improves the fat suppression efficiency in vessel wall imaging

Objective To explore the suppression efficiency of spectrally selective fat suppression schemes when different black blood imaging pre-pulses are used. Background Sufficient peri-vascular fat suppression is critical for the outer wall boundary delineation in vessel wall imaging. The MSDE technique has been shown to significantly improve the blood suppression efficiency and measurement reproducibility. A limitation is that, due to the uncompensated eddy currents, undesired frequency shift can be observed after the MSDE prepulse, making the spectrally selective fat suppression ineffective. The aim of this study is to explore whether a previously proposed improved MSDE (iMSDE) technique is more robust against this system imperfection than the conventional MSDE approach, thus improving the fat suppression efficiency in vivo. Methods