Rolf Lamerichs

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.

1H metabolite relaxation times at 3.0 tesla: Measurements of T1 and T2 values in normal brain and determination of regional differences in transverse relaxation

To measure 1H relaxation times of cerebral metabolites at 3 T and to investigate regional variations within the brain.

Catheter tracking and visualization using 19F nuclear magnetic resonance

This work presents an investigation into catheter visualization and localization using 19F nuclear magnetic resonance (NMR) in conjunction with proton imaging. For this purpose, the imaging capabilities of a standard system were extended to allow for 19F excitation and signal detection. Two modes of operation were implemented: 1) a real‐time tracking mode that provides tip tracking and automatic slice position updates interleaved with real‐time, interactive proton imaging; and 2) a non‐real‐time catheter length visualization mode in which the entire length of a catheter can be assessed. Initial phantom experiments were conducted with the use of an angiographic balloon catheter filled with the blood substitute perfluorooctylbromide (PFOB). Using limited bandwidth excitation centered at the resonances of the CF2 groups of PFOB, we found that sufficient signal could be received to facilitate tip tracking during catheter motion and length visualization for various catheter configurations. The present approach is considered a promising alternative to existing methods, which either are associated with safety concerns (if active markers are employed) or suffer from insufficient, direction‐dependent contrast (if passive visualization is used). Furthermore, our approach enables visualization of the entire length of the catheter. The proposed method provides a safe technique that, unlike electrical or optical devices, does not require modification of commercially available catheters. Magn Reson Med 52:693–697, 2004.

Optimizing PRESS localized citrate detection at 3 Tesla

Analytical methods are used to characterize the response of the strongly coupled two‐spin system of citrate to point‐resolved spectroscopy (PRESS)‐based sequences at 3 T. The signal output is analyzed line by line, as well as in the Cartesian product operator basis. Patterns with a periodicity of 80.9 ms are identified. Furthermore, it is shown that at TE = n · 80.9 ms (n ∈ {0,1,2,…}), the spin evolution can be described without direct reference to strong coupling terms. The theoretical results are found to be in good agreement with in vivo experiments. These results can be used to design protocols for prostate MRS and MRSI at 3 T, and give guidelines for optimizing spin‐echo‐based acquisition schemes for detecting two‐spin systems at arbitrary field strengths. Magn Reson Med 54:51–58, 2005.

Validation of Continuously Tagged MRI for the Measurement of Dynamic 3D Skeletal Muscle Tissue Deformation

PURPOSE Typically spatial modulation of the magnetization (SPAMM) tagged magnetic resonance imaging (MRI) requires many repeated motion cycles limiting the applicability to highly repeatable tissue motions only. This paper describes the validation of a novel SPAMM tagged MRI and post-processing framework for the measurement of complex and dynamic 3D soft tissue deformation following just three motion cycles. Techniques are applied to indentation induced deformation measurement of the upper arm and a silicone gel phantom. METHODS A SPAMM tagged MRI methodology is presented allowing continuous (3.3-3.6 Hz) sampling of 3D dynamic soft tissue deformation using non segmented 3D acquisitions. The 3D deformation is reconstructed by the combination of three mutually orthogonal tagging directions, thus requiring only three repeated motion cycles. In addition a fully automatic post-processing framework is presented employing Gabor scale-space and filter-bank analysis for tag extrema segmentation and triangulated surface fitting aided by Gabor filter bank derived surface normals. Deformation is derived following tracking of tag surface triplet triangle intersections. The dynamic deformation measurements were validated using indentation tests (∼20 mm deep at 12 mm/s) on a silicone gel soft tissue phantom containing contrasting markers which provide a reference measure of deformation. In addition, the techniques were evaluated in vivo for dynamic skeletal muscle tissue deformation measurement during indentation of the biceps region of the upper arm in a volunteer. RESULTS For the phantom and volunteer tag point location precision were 44 and 92 μm, respectively resulting in individual displacements precisions of 61 and 91 μm, respectively. For both the phantom and volunteer data cumulative displacement measurement accuracy could be evaluated and the difference between initial and final locations showed a mean and standard deviation of 0.44 and 0.59 mm for the phantom and 0.40 and 0.73 mm for the human data. Finally accuracy of (cumulative) displacement was evaluated using marker tracking in the silicone gel phantom. Differences between true and predicted marker locations showed a mean of 0.35 mm and a standard deviation of 0.63 mm. CONCLUSIONS A novel SPAMM tagged MRI and fully automatic post-processing framework for the measurement of complex 3D dynamic soft tissue deformation following just three repeated motion cycles was presented. The techniques demonstrate dynamic measurement of complex 3D soft tissue deformation at subvoxel accuracy and precision and were validated for 3.3-3.6 Hz sampling of deformation speeds up to 12 mm/s.

Relaxometric studies of gadolinium-functionalized perfluorocarbon nanoparticles for MR imaging

Fluorine MRI ((19) F MRI) is receiving an increasing attention as a viable alternative to proton-based MRI ((1) H MRI) for dedicated application in molecular imaging. The (19) F nucleus has a high gyromagnetic ratio, a 100% natural abundance and is furthermore hardly present in human tissues allowing for hot spot MR imaging. The applicability of (19) F MRI as a molecular and cellular imaging technique has been exploited, ranging from cell tracking to detection and imaging of tumors in preclinical studies. In addition to applications, developing new contrast materials with improved relaxation properties has also been a core research topic in the field, since the inherently low longitudinal relaxation rates of perfluorocarbon compounds result in relatively low imaging efficiency. Borrowed from (1) H MRI, the incorporation of lanthanides, specifically Gd(III) complexes, as signal modulating ingredients in the nanoparticle formulation has emerged as a promising approach to improvement of the fluorine signal. Three different perfluorocarbon emulsions were investigated at five different magnetic field strengths. Perfluoro-15-crown-5-ether was used as the core material and Gd(III)DOTA-DSPE, Gd(III)DOTA-C6-DSPE and Gd(III)DTPA-BSA as the relaxation altering components. While Gd(III)DOTA-DSPE and Gd(III)DOTA-C6-DSPE were favorable constructs for (1) H NMR, Gd(III)DTPA-BSA showed the strongest increase in (19F) R(1). These results show the potential of the use of paramagnetic lipids to increase (19F) R(1) at clinical field strengths (1.5-3 T). At higher field strengths (6.3-14 T), gadolinium does not lead to an increase in (19F) R(1) compared with emulsions without gadolinium, but leads to an significant increase in (19F) R(2). Our data therefore suggest that the most favorable situation for fluorine measurements is at high magnetic fields without the inclusion of gadolinium constructs.

Use of continuously MR tagged imaging for automated motion assessment in the abdomen: A feasibility study

To investigate the feasibility of measuring motion in the abdomen using a continuously tagged magnetic resonance imaging sequence.

Validation of SPAMM tagged MRI based measurement of 3D soft tissue deformation.

PURPOSE This study presents and validates a novel (non-ECG-triggered) MRI sequence based on spatial modulation of the magnetization (SPAMM) to noninvasively measure 3D (quasistatic) soft tissue deformations using only six acquisitions (three static and three indentations). In the current SPAMM tagged MRI approaches, data are typically constructed from many repeated motion cycles. This has so far restricted its application to the measurement of highly repeatable and periodic movements (e.g., cardiac deformation). In biomechanical applications where soft tissue deformation is artificially induced, often by indentation, significant repeatability constraints exist, and for clinical applications, discomfort and health issues generally preclude a large number of repetitions. METHODS A novel (non-ECG-triggered) SPAMM tagged MRI sequence is presented, whereby a single 1-1 (first order) SPAMM set is acquired following a 3D transient field echo acquisition. Full 3D deformation measurement is achieved through the combination of only six acquisitions (three static and three motion cycles). The 3D deformation measurements were validated using quasistatic indentation tests and marker tracking in a silicone gel soft tissue phantom. In addition, the techniques ability to measure 3D soft tissue deformation in vivo was evaluated using indentation of the biceps region of the upper arm in a volunteer. RESULTS Following comparison to marker tracking in the silicone gel phantom, the SPAMM tagged MRI based displacement measurement demonstrated subvoxel accuracy with a mean displacement difference of 72 microm and a standard deviation of 289 microm. In addition, precision of displacement magnitude was evaluated for both the phantom and the volunteer data. The standard deviations of the displacement magnitude with respect to the average displacement magnitude were 75 and 169 microm for the phantom and volunteer data, respectively. CONCLUSIONS The subvoxel accuracy and precision demonstrated in the phantom in combination with the precision comparison between the phantom and the volunteer data provide confidence in the methods presented for measurement of soft tissue deformation in vivo. To the authors knowledge, since only six acquisitions are required, the presented methodology is the fastest SPAMM tagged MRI method currently available for the noninvasive measurement of quasistatic 3D soft tissue deformation.

Noninvasive automated motion assessment of intestinal motility by continuously tagged MR imaging

To evaluate continuously tagged 3 Tesla MRI for monitoring glucagon‐induced bowel motility changes in healthy volunteers.

Optimization of alternating TR‐SSFP for fat‐suppression in abdominal images at 3T

Magnetic resonance imaging is widely used in the work‐up and monitoring of patients with Crohns disease. Balanced steady‐state free precession sequences are an important part of the imaging protocol and until now primarily 1.5T scanners have been used in daily clinical practice. This is largely because running balanced steady‐state free precession sequences in 3T magnets has technical problems related to increased B0 inhomogeneity and specific absorption rate (SAR) deposition. A modified form of alternating repetition time steady‐state free precession sequence is presented to acquire 3D‐isotropic abdominal images with fat‐suppression at 3T within a breath‐hold. The modifications include an adjusted radiofrequency pulse shape, suitable phase‐cycling scheme and TR1/TR2 ratio. Results show that the proposed sequence is successful in obtaining high contrast 3D‐isotropic abdominal images within a breath‐hold. Furthermore, the proposed methodology is easy to implement in a clinical setting and does not require any postprocessing steps. Magn Reson Med, 2012.