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RationalePaediatric laryngotracheal stenosis (LTS) is often successfully corrected with open airway surgery. However, respiratory and vocal sequelae frequently remain. Clinical care and surgical interventions could be improved with better understanding of these sequelae.ObjectiveThe objective of this cross-sectional study was to develop an upper airway MRI protocol to obtain information on anatomical and functional sequelae post-LTS repair.MethodsForty-eight patients (age 14.4 (range 7.5–30.7) years) and 11 healthy volunteers (15.9 (8.2–28.8) years) were included. Spirometry and static and dynamic upper airway MRI (3.0 T, 30 min protocol) were conducted. Analysis included assessment of postoperative anatomy and airway lumen measurements during static and dynamic (inspiration and phonation) acquisitions.Main resultsGood image quality without artefacts was achieved for static and dynamic images in the majority of MRIs. MRI showed vocal cord thickening in 80.9% of patients and compared with volunteers, a significant decrease in vocal cord lumen area (22.0 (IQR 17.7–30.3) mm2vs 35.1 (21.2–54.7) mm2, p=0.03) but not cricoid lumen area (62.3±27.0 mm2vs 66.2±34.8 mm2, p=0.70). Furthermore, 53.2% of patients had an A-frame deformation at site of previous tracheal cannula, showing lumen collapse during inspiration. Dynamic imaging showed incomplete vocal cord abduction during inspiration in 42.6% and incomplete adduction during phonation in 61.7% of patients.ConclusionsStatic and dynamic MRI is an excellent modality to non-invasively image anatomy, tissue characteristics and vocal cord dynamics of the upper airways. MRI-derived knowledge on postsurgical LTS sequelae might be used to improve surgery.

Improving the resolution in magnetic resonance imaging (MRI) is always done at the expense of either the signal-to-noise ratio (SNR) or the acquisition time. This study investigates whether so-called super-resolution reconstruction (SRR) is an advantageous alternative to direct high-resolution (HR) acquisition in terms of the SNR and acquisition time trade-offs. An experimental framework was designed to accommodate the comparison of SRR images with direct high-resolution acquisitions with respect to these trade-offs. The framework consisted, on one side, of an image acquisition scheme, based on theoretical relations between resolution, SNR, and acquisition time, and, on the other side, of a protocol for reconstructing SRR images from a varying number of acquired low-resolution (LR) images. The quantitative experiments involved a physical phantom containing structures of known dimensions. Images reconstructed by three SRR methods, one based on iterative back-projection and two on regularized least squares, were quantitatively and qualitatively compared with direct HR acquisitions. To visually validate the quantitative evaluations, qualitative experiments were performed, in which images of three different subjects (a phantom, an ex-vivo rat knee, and a post-mortem mouse) were acquired with different MRI scanners. The quantitative results indicate that for long acquisition times, when multiple acquisitions are averaged to improve SNR, SRR can achieve better resolution at better SNR than direct HR acquisitions.

In the current study cell labeling was performed with water-soluble gadolinium (Gd)-DTPA containing liposomes, to allow for cell tracking by MRI. Liposomes were used to assure a highly concentrated intracellular build up of Gd, aiming to overcome the relatively low MRI sensitivity of Gd (compared to T2 contrast agents). Liposomes were positively charged (cationic) to facilitate uptake by binding to anionic charges in the cell membrane of bone marrow-derived mesenchymal stem cells (MSCs). We determined the cellular Gd load by variations in labeling time (1, 4, and 24 h) and liposome concentration (125, 250, 500, 1000 μM lipid), closely monitoring effects on cell viability, proliferation rate, and differentiation ability. Labeling was both time and dose dependent. Labeling for 4 h was most efficient regarding the combination of processing time and final cellular Gd uptake. Labeling for 4 h with low-dose concentration (125 μM lipid, corresponding to 52 ± 3 μM Gd) yielded an intracellular load of 30 ± 2.5 pg Gd cell–1, without any effects on cell viability, proliferation, and cell differentiation. Gd liposomes, colabeled with fluorescent dyes, exhibited a prolonged cellular retention, with an endosomal distribution pattern. In vitro assay over 20 days demonstrated a drop in the average Gd load per cell, as a result of mitosis. However, there was no significant change in the sum of the Gd load in all daughter cells at endpoint (20 days), indicating an excellent cellular retention of Gd. MSCs labeled with Gd liposomes were imaged with MRI at both 1.5T and 3.0T, resulting in excellent visualization both in vitro and in vivo. Prolonged in vivo imaging of 500,000 Gd-labeled cells was possible for at least 2 weeks (3.0T). In conclusion, Gd-loaded cationic liposomes (125 μM lipid) are an excellent candidate to label cells, without detrimental effects on cell viability, proliferation, and differentiation, and can be visualized by MRI.

We imaged the protease activity of matrix metalloproteinases (MMPs) upregulated during aneurysm formation, using protease-activatable near-infrared fluorescence probes. We tested whether these protease-activatable sensors can directly report the in vivo activity of the key biomarkers in aneurysm, using our genetically modified fibulin-4 mouse models for aneurysm formation. Mice homozygous for the fibulin-4 reduced-expression allele (fibulin-4RR) show dilatation of the ascending aorta and a tortuous, stiffened aorta resulting from disorganized elastic fiber networks. Strikingly, even a moderate reduction in expression of fibulin-4 in the heterozygous fibulin-4Rmice occasionally results in modest aneurysm formation.

To reduce interstudy variability using long-axis information for correcting short-axis (SA) contours at basal and apical level for left-ventricular analysis by magnetic resonance imaging.

Angiogenesis is a very important process for tumor growth and proliferation. Given its high temporal and spatial resolution, magnetic resonance (MR) imaging is well suited for use in the assessment of angiogenesis. MR angiography can be used clinically and experimentally for identification of tumor feeding and draining vessels, for tumor characterization, and for treatment planning. The morphologic structure of tumor vessels can be investigated in relation to tumor vessel permeability with use of specific contrast agents. To gain insight into tumor angiogenesis in vivo, the authors compared images obtained with digital photography, high-resolution MR angiography, and intravital microscopy through a dorsal skin-fold window in a rodent model. The close correlation between images obtained with these various modalities, with regard to the depiction of the developing tumor vasculature, indicates that noninvasive quantification of angiogenesis may be possible with MR imaging. Future directions in tumor imaging may include so-called four-dimensional MR angiography, in which high-resolution three-dimensional MR angiography is combined with dynamic contrast-enhanced MR imaging. © RSNA, 2005

: The need for better signal-to-noise ratios and resolution has pushed magnetic resonance imaging (MRI) towards high-field MR-scanners for which only little data on MR-related acoustic noise production have been published. The purpose of this study was to validate the theoretical relationship of sound pressure level (SPL) and static magnetic field strength. This is relevant for allowing adequate comparisons of acoustic data of MR systems at various magnetic field strengths. Acoustic data were acquired during various pulse sequences at field strengths of 0.5, 1.0, 1.5 and 2.0 Tesla using the same MRI unit by means of a Helicon rampable magnet. Continuous-equivalent, i.e. time-averaged, linear SPLs and 1/3-octave band frequencies were recorded. Ramping from 0.5 to 1.0 Tesla and from 1.0 to 2.0 Tesla resulted in an SPL increase of 5.7 and 5.2 dB(L), respectively, when averaged over the various pulse sequences. Most of the acoustic energy was in the 1-kHz frequency band, irrespective of magnetic field strength. The relation between field strength and SPL was slightly non-linear, i.e. a slightly less increase at higher field strengths, presumably caused by the elastic properties of the gradient coil encasings.

The purpose of the work was to evaluate the effectiveness of extracellular contrast media in improving MR coronary angiography using breath‐hold segmented echo‐planar imaging (SEPI). Two protocols were designed to optimize the inversion recovery‐prepared contrast‐enhanced SEPI method. In 15 healthy volunteers, significant improvements in signal‐to‐noise ratio (SNR), contrast‐to‐noise ratio (CNR), vessel sharpness, and length of visualization were observed post‐contrast. The method with two targeted scans to cover the left and right arteries, respectively, following separate 20‐mL contrast injections, was found to yield thinner slices and longer right coronary artery (RCA) visualization than a single scan following a 40‐mL contrast injection without compromising SNR and CNR. In conclusion, extracellular contrast media substantially improves the delineation of coronary arteries with SEPI. J. Magn. Reson. Imaging 2001;13:676–681. © 2001 Wiley‐Liss, Inc.

Cardiac and respiratory motion during the long acquisition times required in 3dmagnetic resonance imaging (MRI) can lead to excessive image degradation and consequently poor diagnosis and interpretation in the thoracic region. This paper addresses the issue of obtaining good image quality with 3dgradient echo (GE) imaging in the study of the pulmonary vascular system and its diseases. To study the pulmonary vascular system two approaches have been considered. First, a proton density/inflow weighted scan consisting of a syncopated 3dFLASH acquisition is used to provide a 3dpulmonary angiogram. Secondly, aT1weighted scan using 3dIR-FLASH (inversion recovery FLASH) helps in determining the presence of pulmonary emboli. Multiple acquisitions and rectangular field of view are utilized to pseudogate to the respiratory period in order to reduce motion artifacts while keeping reasonable imaging times. Technical aspects on data collection during the approach to equilibrium and acquisition strategies in the presence of thoracic motion and its impact on vessel resolution are addressed. The method has proven successful for imaging volunteers and, more recently, in obtaining useful clinical information.

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