Calcium fluoride based multifunctional nanoparticles for multimodal imaging.

New multifunctional nanoparticles (NPs) that can be used as contrast agents (CA) in different imaging techniques, such as photoluminescence (PL) microscopy and magnetic resonance imaging (MRI), open new possibilities for medical imaging, e.g., in the fields of diagnostics or tissue characterization in regenerative medicine.

The potential of nuclear magnetic resonance to track lipids in planta.

Nuclear Magnetic Resonance (NMR) provides a highly flexible platform for non invasive analysis and imaging biological samples, since the manipulation of nuclear spin allows the tailoring of experiments to maximize the informativeness of the data. MRI is capable of visualizing a holistic picture of the lipid storage in living plant/seed. This review has sought to explain how the technology can be used to acquire functional and physiological data from plant samples, and how to exploit it to characterize lipid deposition in vivo.

High isotropic resolution magnetic resonance imaging of the mandibular canal at 1.5 T: a comparison of gradient and spin echo sequences.

Objectives: The precision of localizing the mandibular canal prior to surgical intervention depends on the achievable resolution, whereas identification of the nerve depends on the image contrast. In our study, we developed new protocols based on gradient and spin echo sequences. The results from both sequences were quantitatively compared for their agreement to identify the most suitable approach.

First in vivo traveling wave magnetic particle imaging of a beating mouse heart.

Magnetic particle imaging (MPI) is a non-invasive imaging modality for direct detection of superparamagnetic iron-oxide nanoparticles based on the nonlinear magnetization response of magnetic materials to alternating magnetic fields. This highly sensitive and rapid method allows both a quantitative and a qualitative analysis of the measured signal. Since the first publication of MPI in 2005 several different scanner concepts have been presented and in 2009 the first in vivo imaging results of a beating mouse heart were shown.

Determination of the mesio-distal tooth width via 3D imaging techniques with and without ionizing radiation: CBCT, MSCT, and µCT versus MRI.

Objective: The purpose of this study was to estimate the feasibility and accuracy of mesio-distal width measurements with magnetic resonance imaging (MRI) in comparison to conventional 3D imaging techniques [multi-slice CT (MSCT), cone-beam CT (CBCT), and µCT]. The measured values of the tooth widths were compared to each other to estimate the amount of radiation necessary to enable orthodontic diagnostics.

Material And Methods: Two pig skulls were measured with MSCT, CBCT, µCT, and MRI.

MRI vs. CT for orthodontic applications: comparison of two MRI protocols and three CT (multislice, cone-beam, industrial) technologies.

Objectives: To examine the relative usefulness and suitability of magnetic resonance imaging (MRI) in daily clinical practice as compared to various technologies of computed tomography (CT) in addressing questions of orthodontic interest.

Methods: Three blinded raters evaluated 2D slices and 3D reconstructions created from scans of two pig heads. Five imaging modalities were used, including three CT technologies-multislice (MSCT), cone-beam CT (CBCT), and industrial (µCT)-and two MRI protocols with different scan durations.

Quiet diffusion-weighted head scanning: Initial clinical evaluation in ischemic stroke patients at 1.5T.

Purpose: To compare the quality and diagnostic value of routine single-shot, echo-planar imaging, diffusion-weighted imaging (ss-EPI-DWI) to those of quiet readout segmented EPI-DWI (q-DWI) in magnetic resonance imaging (MRI) of acute stroke.

Materials And Methods: Twenty-six patients with acute stroke underwent a 1.5T MRI including diffusion-weighted ss-EPI and q-DWI.

Desynchronization of Cartesian k-space sampling and periodic motion for improved retrospectively self-gated 3D lung MRI using quasi-random numbers.

Purpose: To demonstrate that desynchronization between Cartesian k-space sampling and periodic motion in free-breathing lung MRI improves the robustness and efficiency of retrospective respiratory self-gating.

Methods: Desynchronization was accomplished by reordering the phase (k ) and partition (k ) encoding of a three-dimensional FLASH sequence according to two-dimensional, quasi-random (QR) numbers. For retrospective respiratory self-gating, the k-space center signal (DC signal) was acquired separately after each encoded k-space line.

Optimization and comparison of two practical dual-tuned birdcage configurations for quantitative assessment of articular cartilage with sodium magnetic resonance imaging.

Background: In this study, two practical dual-tuned birdcage configurations for quantitative assessment of articular cartilage with sodium magnetic resonance imaging (MRI) were designed and compared.

Methods: Two 1.5 T dual-tuned birdcages, a four-ring birdcage (FRB) and an alternating rungs birdcage (ARB), were built and then characterized by bench and MRI measurements.

Comparison of multiple quantitative MRI parameters for characterization of the goat cartilage in an ongoing osteoarthritis: dGEMRIC, T1ρ and sodium.

Rationale And Objectives: Osteoarthritis (OA) is a degenerative joint disease leading to cartilage deterioration by loss of matrix, fibrillation, formation of fissures, and ultimately complete loss of the cartilage surface. Here, three magnetic resonance imaging (MRI) techniques, dGEMRIC (delayed Gadolinium enhanced MRI of cartilage; dG1=T1,post; dG2=1/T1,post-1/T1,pre), T1ρ,and sodium MRI, are compared in a preclinical in vivo study to evaluate the differences in their potential for cartilage characterization and to establish an examination protocol for a following clinical study.

Materials And Methods: OA was induced in 12 caprine knees (6 control, 6 therapy).

Acoustic noise reduction in T 1- and proton-density-weighted turbo spin-echo imaging.

Objective: To reduce acoustic noise levels in T 1-weighted and proton-density-weighted turbo spin-echo (TSE) sequences, which typically reach acoustic noise levels up to 100 dB(A) in clinical practice.

Materials And Methods: Five acoustic noise reduction strategies were combined: (1) gradient ramps and shapes were changed from trapezoidal to triangular, (2) variable-encoding-time imaging was implemented to relax the phase-encoding gradient timing, (3) RF pulses were adapted to avoid the need for reversing the polarity of the slice-rewinding gradient, (4) readout bandwidth was increased to provide more time for gradient activity on other axes, (5) the number of slices per TR was reduced to limit the total gradient activity per unit time. We evaluated the influence of each measure on the acoustic noise level, and conducted in vivo measurements on a healthy volunteer.

Responses of the Human Brain to Mild Dehydration and Rehydration Explored In Vivo by 1H-MR Imaging and Spectroscopy.

Background And Purpose: As yet, there are no in vivo data on tissue water changes and associated morphometric changes involved in the osmo-adaptation of normal brains. Our aim was to evaluate osmoadaptive responses of the healthy human brain to osmotic challenges of de- and rehydration by serial measurements of brain volume, tissue fluid, and metabolites.

Materials And Methods: Serial T1-weighted and (1)H-MR spectroscopy data were acquired in 15 healthy individuals at normohydration, on 12 hours of dehydration, and during 1 hour of oral rehydration.

Diffusion-mediated dephasing in the dipole field around a single spherical magnetic object.

In this work, the time evolution of the free induction decay caused by the local dipole field of a spherical magnetic perturber is analyzed. The complicated treatment of the diffusion process is replaced by the strong-collision-approximation that allows a determination of the free induction decay in dependence of the underlying microscopic tissue parameters such as diffusion coefficient, sphere radius and susceptibility difference. The interplay between susceptibility- and diffusion-mediated effects yields several dephasing regimes of which, so far, only the classical regimes of motional narrowing and static dephasing for dominant and negligible diffusion, respectively, were extensively examined.

Acoustic-noise-optimized diffusion-weighted imaging.

Objective: This work was aimed at reducing acoustic noise in diffusion-weighted MR imaging (DWI) that might reach acoustic noise levels of over 100 dB(A) in clinical practice.

Materials And Methods: A diffusion-weighted readout-segmented echo-planar imaging (EPI) sequence was optimized for acoustic noise by utilizing small readout segment widths to obtain low gradient slew rates and amplitudes instead of faster k-space coverage. In addition, all other gradients were optimized for low slew rates.

Optimization of the AC-gradient method for velocity profile measurement and application to slow flow.

This work presents a spectroscopic method to measure slow flow. Within a single shot the velocity distribution is acquired. This allows distinguishing rapidly between single velocities within the sampled volume with a high sensitivity.

Free breathing 1H MRI of the human lung with an improved radial turbo spin-echo.

Objective: To optimize a radial turbo spin-echo sequence for motion-robust morphological lung magnetic resonance imaging (MRI) in free respiration.

Materials And Methods: A versatile multi-shot radial turbo spin-echo (rTSE) sequence is presented, using a modified golden ratio-based reordering designed to prevent coherent streaking due to data inconsistencies from physiological motion and the decaying signal. The point spread function for a moving object was simulated using a model for joint respiratory and cardiac motion with a concomitant T2 signal decay and with rTSE acquisition using four different reordering techniques.

Combined acquisition technique (CAT) for neuroimaging of multiple sclerosis at low specific absorption rates (SAR).

Purpose: To compare a novel combined acquisition technique (CAT) of turbo-spin-echo (TSE) and echo-planar-imaging (EPI) with conventional TSE. CAT reduces the electromagnetic energy load transmitted for spin excitation. This radiofrequency (RF) burden is limited by the specific absorption rate (SAR) for patient safety.

Monitoring of monocyte recruitment in reperfused myocardial infarction with intramyocardial hemorrhage and microvascular obstruction by combined fluorine 19 and proton cardiac magnetic resonance imaging.

Background: Monocytes and macrophages are indispensable in the healing process after myocardial infarction (MI); however, the spatiotemporal distribution of monocyte infiltration and its correlation to prognostic indicators of reperfused MI have not been well described.

Methods And Results: With combined fluorine 19/proton ((1)H) magnetic resonance imaging, we noninvasively visualized the spatiotemporal recruitment of monocytes in vivo in a rat model of reperfused MI. Blood monocytes were labeled by intravenous injection of (19)F-perfluorocarbon emulsion 1 day after MI.

Combined acquisition technique (CAT) for high-field neuroimaging with reduced RF power.

Object: Clinical 3 T MRI systems are rapidly increasing and MRI systems with a static field of 7 T or even more have been installed. The RF power deposition is proportional to the square of the static magnetic field strength and is characterized by the specific absorption rate (SAR). Therefore, there exist defined safety limits to avoid heating of the patient.

Eddy current compensation for delta relaxation enhanced MR by dynamic reference phase modulation.

Object: Eddy current compensation by dynamic reference phase modulation (eDREAM) is a compensation method for eddy current fields induced by B 0 field-cycling which occur in delta relaxation enhanced MR (dreMR) imaging. The presented method is based on a dynamic frequency adjustment and prevents eddy current related artifacts. It is easy to implement and can be completely realized in software for any imaging sequence.

MR safety: fast T₁ thermometry of the RF-induced heating of medical devices.

Determining the MR compatibility of medical implants and devices is becoming increasingly relevant. In most cases, the heating of conductive implants due to radiefrequency (RF) excitation pulses is measured by fluoroptic temperature sensors in relevant tests for approval. Another common method to determine these heating effects is MR thermometry using the proton resonance frequency.

Quantification and localization of contrast agents using delta relaxation enhanced magnetic resonance at 1.5 T.

Object: Delta relaxation enhanced magnetic resonance (dreMR) is a new imaging technique based on the idea of cycling the magnetic field B (0) during an imaging sequence. The method determines the field dependency of the relaxation rate (relaxation dispersion dR (1)/dB). This quantity is of particular interest in contrast agent imaging because the parameter can be used to determine contrast agent concentrations and increases the ability to localize the contrast agent.