Magnetized boxes for housing polarized spins in homogeneous fields

Abstract We present novel types of permanently magnetized as well as current powered boxes built from soft-ferromagnetic materials. They provide shielded magnetic fields which are homogeneous within a large fraction of the enclosed volume, thus minimizing size, weight, and costs. For the permanently magnetized solutions, homogenization is achieved either by an optimized distribution of the permanent field sources or by jacketing the field with a soft-ferromagnetic cylindrical shell which is magnetized in parallel to the enclosed field. The latter principle may be applied up to fields of about 0.1 T. With fields of about 1 mT, such boxes are being used for shipping spin-polarized 3 He worldw…

Flip-angle measurement by magnetization inversion: Calibration of magnetization nutation angle in hyperpolarized 3 He magnetic resonance imaging lung experiments

The aim of this work was to establish a new, fast, and robust method of flip-angle calibration for magnetic resonance imaging of hyperpolarized 3He. The method called flip-angle measurement with magnetization inversion is based on acquiring images from periodically inverted longitudinal magnetization created using the spatial modulation of magnetization technique. By measuring the width of the area where the magnetization was inverted by the spatial modulation of magnetization preparation in phase images, the flip angle can be generated using a simple equation. To validate and establish the limits of the proposed method, flip-angle measurement with magnetization inversion acquisitions were …

Pushing the Limit – MRI of the Lung Using Hyperpolarized 3-Helium in Conjunction with Parallel Imaging

Imaging of the lung with hyperpolarized 3He became a well known technique in the last decade. Being able to image ventilation and the microstructure of the lung an increase of SNR and a shortage of scan time is eligible. By using a 32-channel phased array the sensitivity was increased dramatically. High resolution 2D-images with a resolution of 1 × 1 mm2 having a 3 mm slice was realized, showing highly detailed images of the lung. By applying parallel imaging techniques the SNR could be increased and scan time was reduced drastically by using a 2D acceleration of R = 4 × 2 with a 3D-protocol covering the whole lung.

Realization of administration unit for3He with gas recycling

Hyperpolarized (HP) noble gases (3He,129Xe) are used for MR-imaging of the lung. In the majority of case the HP gas is filled in Tedlarbags and directly inhaled by the patients. Starting from an earlier pilot device, an administration unit was built respectively to the Medical Devices Law to administer patients HP noble gas boli in defined quantities and at a predefined time during inspiration with high reproducibility and reliability without reducing MR-quality. The patient's airflows are monitored and recorded. It is possible to use gas admixtures, measure the polarization on-line and collect the exhaled gas for later recycling. The first images with healthy volunteers were taken with thi…

Measurement of gas transport kinetics in high-frequency oscillatory ventilation (HFOV) of the lung using hyperpolarized 3He magnetic resonance imaging

PURPOSE: To protect the patient with acute respiratory distress syndrome from ventilator associated lung injury (VALI) high-frequency oscillatory ventilation (HFOV) is used. Clinical experience has proven that HFOV is an efficient therapy when conventional artificial ventilation is insufficient. However, the optimal settings of HFOV parameters, eg, tidal volumes, pressure amplitudes and frequency for maximal lung protection, and efficient gas exchange are not established unambiguously. METHODS: In this work magnetic resonance imaging (MRI) with hyperpolarized (3)He was employed to visualize the redistribution of gas within the cadaver pig lung during HFOV. The saturated slice method was use…

A polarized 3He target for the photon beam at MAMI

Abstract A polarized 3 He target has been installed for the first time inside the 4 π Crystal Ball detector at the tagged photon beam of the MAinz MIcrotron (MAMI). It has been demonstrated that the system works reliably and that the polarization losses during handling of the polarized gas are under control. Initial polarization values up to 70% and total relaxation times up to 20 h could be obtained during a first test beam time devoted to the measurement of the double polarized photoabsorption cross-section in the Δ ( 1232 ) baryon resonance region.

Design and evaluation of a 32-channel phased-array coil for lung imaging with hyperpolarized 3-helium

Imaging with hyperpolarized 3-helium is becoming an increasingly important technique for MRI diagnostics of the lung but is hampered by long breath holds (>20 sec), which are not always applicable in patients with severe lung disease like chronic obstructive pulmonary disease (COPD) or α-1-anti-trypsin deficiency. Additionally, oxygen-induced depolarization decay during the long breath holds complicates interpretation of functional data such as apparent diffusion coefficients. To address these issues, we describe and validate a 1.5-T, 32-channel array coil for accelerated 3He lung imaging and demonstrate its ability to speed up imaging 3He. A signal-to-noise ratio increase of up to a factor…

Recycling of 3He from lung magnetic resonance imaging

We have developed the means to recycle 3He exhaled by patients after imaging the lungs using magnetic resonance of hyperpolarized 3He. The exhaled gas is collected in a helium leak proof bag and further compressed into a steel bottle. The collected gas contains about 1–2% of 3He, depending on the amount administered and the number of breaths collected to wash out the 3He gas from the lungs. 3He is separated from the exhaled air using zeolite molecular sieve adsorbent at 77 K followed by a cold head at 8 K. Residual gaseous impurities are finally absorbed by a commercial nonevaporative getter. The recycled 3He gas features high purity, which is required for repolarization by metastability ex…

Application unit for the administration of contrast gases for pulmonary magnetic resonance imaging: optimization of ventilation distribution for3He-MRI

Purpose MRI of lung airspaces using gases with MR-active nuclei (3He, 129Xe, and 19F) is an important area of research in pulmonary imaging. The volume-controlled administration of gas mixtures is important for obtaining quantitative information from MR images. State-of-the-art gas administration using plastic bags (PBs) does not allow for a precise determination of both the volume and timing of a 3He bolus. Methods A novel application unit (AU) was built according to the requirements of the German medical devices law. Integrated spirometers enable the monitoring of the inhaled gas flow. The device is particularly suited for hyperpolarized (HP) gases (e.g., storage and administration with m…

POLARIZED 3HE TARGETS FOR REAL AND VIRTUAL PHOTONS

Polarized3He targets in medium energy physics at MAMI

Experiments with polarized 3He targets at the Mainz Microtron (MAMI) involve double polarized photoabsorption or the extraction of the electric form factor of the neutron Ge,n via electron scattering, respectively. Polarized 3He with an initial polarization of up to 70% at the experimental areas is provided by a polarizer based on the principle of metastability exchange optical pumping (MEOP). In this article both target setups for the photon- and the electron beamlines will be described and a status of the data analysis will be given.

Three-dimensional mapping of the B 1 field using an optimized phase-based method: Application to hyperpolarized 3 He in lungs

A novel method is presented for the three-dimensional mapping of the B1-field of a transmit radio-frequency MR coil. The method is based on the acquisition of phase images, where the effective flip angle is encoded in the phase of the nonselective hard pulse excitation. The method involves the application of a rectangular composite pulse as excitation in a three-dimensional gradient recall echo to produce measurable phase angle variation. However, such a pulse may significantly increase the radio-frequency power deposition in excess of the standard acceptable SAR limits, imposing extremely long TRs (>100 msec), which would result in acquisition times significantly greater than a single brea…

A highly polarized target for the electron beam at MAMI

Abstract Polarized He 3 from metastability exchange optical pumping (MEOP) is used as an effective polarized neutron target for electron scattering experiments at the MAinz MIcrotron (MAMI). With the present setup an initial polarization of up to 72% has been obtained at the experimental area. A novel calibration technique will be presented which allows the determination of the absolute polarization within a relative uncertainty of 3%.

Yttria-stabilized zirconia in-flight particle characteristics under vacuum plasma spray conditions

This paper deals with the diagnostic yttria-stabilized zirconia (YSZ) in-flight particles in Vacuum Plasma Spray (VPS) process using an optical measurement device. Particle velocity, temperature and diameter were correlated to spray distance under a fixed chamber pressure of about 14 kPa. Experiments were carried out with a two-color pyrometer. Results show that correlations can be satisfactory described with linear relationships. Particle velocity and temperature decrease when increasing spray distance whereas particle diameter exhibits a linear increase with the spray distance.