Application unit for the administration of contrast gases for pulmonary magnetic resonance imaging: optimization of ventilation distribution for (3) He-MRI.

PURPOSE: MRI of lung airspaces using gases with MR-active nuclei ((3) He, (129) Xe, and (19) F) 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 (3) He 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 minimal HP losses). The setup was tested in a clinical trial (n = 10 healthy volunteers) according to the German medicinal products law using static and dynamic ventilation HP-(3) He MRI. RESULTS: The required specifications for the AU were successfully realized. Compared to PB-administration, better reproducibility of gas intrapulmonary distribution was observed when using the AU for both static and dynamic ventilation imaging. CONCLUSION: The new AU meets the special requirements for HP gases, which are storage and administration with minimal losses. Our data suggest that gas AU-administration is superior to manual modes for determining the key parameters of dynamic ventilation measurements.

Recycling of 3He from lung magnetic resonance imaging.

We have developed the means to recycle (3) He exhaled by patients after imaging the lungs using magnetic resonance of hyperpolarized (3) He. 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 (3) He, depending on the amount administered and the number of breaths collected to wash out the (3) He gas from the lungs. (3) He 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 (3) He gas features high purity, which is required for repolarization by metastability exchange optical pumping. At present, we achieve a collection efficiency of 80-84% for exhaled gas from healthy volunteers and cryogenic separation efficiency of 95%.

Feasibility of photoelectron sources with sharp lines of stable energy between 20 and 80 keV.

Photo-absorption of γ-rays in thin Al, Co, Ti, and Mo convertors was examined with the aim to produce quasi monoenergetic photoelectrons having an energy spread of 0.5-4.7eV about mean kinetic energies at discrete values between 18632 and 80321eV. The photoelectron rates were estimated for commercial photon sources of (241)Am, (119m)Sn, (125m)Te and (109)Cd with activities of 0.55-3.7GBq. Photoelectrons ejected by (241)Am γ- and X-rays from Co convertors were measured with two different electron spectrometers and obtained energy spectra were compared with Monte Carlo predictions.

Magnetized boxes for housing polarized spins in homogeneous fields.

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 0.1T. With fields of about 1mT, such boxes are being used for shipping spin-polarized (3)He worldwide for MRI purposes. For current powered boxes, we present concepts and realizations of uniaxial and tri-axial shielded magnetic fields which are homogeneous on the level of 10(-4) within the entire shielded volume. This is achieved by inserting tightly fitting solenoids into a box from soft-magnetic material. The flexible tri-axial solution suits in particular laboratory applications, e.g. for establishing a spin quantization axis.

(3) He Spin Filter for Neutrons.

The strongly spin-dependent absorption of neutrons in nuclear spin-polarized (3)He opens up the possibility of polarizing neutrons from reactors and spallation sources over the full kinematical range of cold, thermal and hot neutrons. This paper gives a report on the neutron spin filter (NSF) development program at Mainz. The polarization technique is based on direct optical pumping of metastable (3)He atoms combined with a polarization preserving mechanical compression of the gas up to a pressure of several bar, necessary to run a NSF. The concept of a remote type of operation using detachable NSF cells is presented which requires long nuclear spin relaxation times of order 100 hours. A short survey of their use under experimental conditions, e.g. large solid-angle polarization analysis, is given. In neutron particle physics NSFs are used in precision measurements to test fundamental symmetry concepts.

[Ultrafast MRI of lung ventilation using hyperpolarized helium-3]. / Ultraschnelle MRT der Lungenventilation mittels hochpolarisiertem Helium-3.

OBJECTIVE: Assessment of the temporal and spatial dynamics of hyperpolarized Helium-3 (3He) distribution in the lung with ultrafast gradient-echo magnetic-resonance imaging. MATERIAL AND METHODS: Coronal images of the lung were acquired using ultrafast gradient-echo pulse sequences with TR/TE = 3.3 ms/1.3 ms (slice thickness, 40 mm) and TR/TE = 2.0 ms/0.7 ms (without slice selection). A series of 80 or 160 projection images was obtained with 210 ms or 130 ms temporal resolution, respectively. Imaging was performed during several respiratory cycles after application of a single bolus of 300 mL hyperpolarized 3He. Measurements were performed in six healthy volunteers (spontaneous breathing). RESULTS: Different phases of in- and expiration could be visualized. During the course of consecutive respiratory cycles the 3He signal decreased due to dilution of 3He in residual alveolar gas and by inspired air, relaxation due to oxygen and the RF pulses, and due to Helium-3 washout. The signal of a single bolus of 3He was detected in the lung for up to four respiratory cycles. Anatomical structures were better visualized on slice selective images than on images without slice selection. CONCLUSION: Distribution of inspired 3He within the tracheobronchial tree and alveolar space and its washout can be visualized by ultrafast imaging of a single bolus of hyperpolarized 3He gas. This method may allow for regional analysis of lung function with temporal and spatial resolution superior to conventional methods.

Analysis of intrapulmonary O(2) concentration by MR imaging of inhaled hyperpolarized helium-3.

Inhalation of hyperpolarized (3)He allows magnetic resonance imaging (MRI) of ventilated airspaces. (3)He hyperpolarization decays more rapidly when interacting with paramagnetic O(2). We describe a method for in vivo determination of intrapulmonary O(2) concentrations ([O(2)]) based on MRI analysis of the fate of measured amounts of inhaled hyperpolarized (3)He in imaged regions of the lung. Anesthetized pigs underwent controlled normoventilation in a 1.5-T MRI unit. The inspired O(2) fraction was varied to achieve different end-tidal [O(2)] fractions (FET(O(2))). With the use of a specifically designed applicator, (3)He (100 ml, 35-45% polarized) was administered at a predefined time within single tidal volumes. During subsequent inspiratory apnea, serial two-dimensional images of airways and lungs were acquired. At least once in each animal studied, the radio-frequency excitation used for imaging was doubled at constant FET(O(2)). Signal intensity measurements in regions of interest of the animals' lungs (volume range, 54-294 cm(3)), taken at two different radio-frequency excitations, permitted calculation of [O(2)] in these regions of interest. The [O(2)] fractions in the regions of interest correlated closely with FET(O(2)) (R = 0.879; P < 0.0001). O(2)-sensitive (3)He-MRI may allow noninvasive study of regional distribution of ventilation and alveolar PO(2) in the lung.

[A new method for imaging ventilation-distribution with 3Helium in magnetic resonance tomography]. / Neue Methode zur Darstellung der Verteilung der Ventilation mittels polarisiertem 3Helium in der Magnetresonanztomographie (MRT).

BACKGROUND: Conventional 1H-MRI of the lung is restricted by susceptibility effects and low proton density: Recently, imaging of lung ventilation in MRI has become feasible using hyperpolarised inert gases with a spin of I = 1/2, such as 3He and 129Xe, as inhalative "contrast agents". New technical developments, preclinical and clinical application of this method are described. MATERIALS AND METHODS: With optical laser pumping high polarisation rates can be achieved, resulting in a high signal-to-noise ratio (S/N). A dedicated application system allows accurate administration of 3He boli at different time points during inspiration. Thus, dynamic ventilation imaging becomes possible. Prerequisites for this method include a dedicated coil as well as a spectroscopy option at the MRI system. Fast sequences and low flip angles are employed to comply with the relaxation of hyperpolarise 3He in vivo. RESULTS: Overall homogeneous signal intensity (SI) represents physiological conditions. Obstructive lung disease is associated with generalised or localised signal inhomogeneity. Different time constants of specific lung regions are probably responsible for this kind of inhomogeneous inspiratory distribution of ventilation. Tumours show a clear ventilation deficit, correlating with non-ventilated lung areas. CONCLUSION: 3He MRI is a promising new modality for the evaluation of ventilation distribution under different pathological conditions. This may include obstructive lung disease and assessment of ventilation distribution before and after thoracic surgery. Furthermore, evaluation of patients with acute lung failure and validation of ventilator settings in anaesthesia may be performed.

Imaging of the lungs using 3He MRI: preliminary clinical experience in 18 patients with and without lung disease.

The purpose of this study was to describe the 3He MRI findings of normal pulmonary ventilation in healthy volunteers and to evaluate abnormalities in patients with different lung diseases. Hyperpolarized 3He gas (300 ml, 3 x 10(5) Pa, polarized to 35-45% by optical pumping, provided in special glass cells) was inhaled by 8 healthy volunteers and 10 patients with different lung diseases. Imaging was performed with a three-dimensional fast low-angle shot (FLASH) sequence (TR = 11.8 msec; TE = 5 msec; transmitter amplitude, 5-8 V; corresponding flip angle, < 5 degrees) in a single breath-hold (22-42 seconds). Clinical and radiological examinations were available for correlation. The studies were performed successfully in eight of eight volunteers and in 8 of 10 patients. The lung parenchyma of volunteers with normal ventilatory function exhibited rather homogeneous intermediate to high signal, whereas patients with chronic obstructive lung disease or bronchiectasis presented with severe signal inhomogeneities with patchy or wedge-shaped defects. The mass effect of bronchogenic carcinoma, chronic empyema, lymphadenopathy, or pleural effusion caused large signal defects, representing the lesion and adjacent hypoventilation, the extent of which had not been presumed from chest x-ray or CT. 3He MRI is a promising new modality for the assessment of pulmonary ventilation and its abnormalities. Additional studies are needed to determine its potential clinical role.

[The helium-3 MRT of pulmonary ventilation: the initial clinical applications]. / Helium-3-MRT der Lungenventilation: erste klinische Anwendungen.

PURPOSE: of the study is the visualisation of normal pulmonary ventilation in healthy volunteers and the evaluation of abnormalities in patients with different lung diseases using 3He magnetic resonance imaging (3He-MRI). MATERIAL AND METHODS: Hyperpolarized 3He gas (V = 300 ml, p = 3 x 10(5) Pa, polarised to 35-45% by optical pumping, provided in special glass cells) was inhaled by eight healthy volunteers and ten patients with different lung diseases. A 3D FLASH sequence (TR = 11.8 ms; TE = 5 ms; matrix 144 x 256, FOV 350 mm, section thickness 7-10 mm, coronal orientation) was performed in a single breath-hold (22-42 s). Clinical and radiological examinations were available for correlation. RESULTS: The studies were successfully carried out in 8/8 volunteers and in 8/10 patients. The central airways were constantly visualised with intermediate to high signal intensity. The lung parenchyma of volunteers with normal ventilatory function showed rather homogeneous intermediate to high signal, whereas patients with chronic obstructive lung disease and/or pneumonia presented severe signal inhomogeneities. Space-occupying lesions and pleural effusion caused large areas with little or no signal. The represented the lesion and adjacent ventilatory disturbances whose extent had not been presumed from chest x-ray or CT. The spatial resolution was higher than in ventilation scintigraphy. CONCLUSION: 3He MRI is a promising new modality for the assessment of pulmonary ventilation and its anomalies.

Hyperpolarized gases--a new type of MR contrast agents?

The nuclear spin polarization of noble gases can be strongly enhanced by laser optical pumping followed by electron-nuclear polarization transfer. Direct optical pumping of metastable 3He atoms has been shown to produce enormous polarization in the order of 0.4-0.6. This is about 10(5) times greater than the polarization of water protons at thermal equilibrium used at conventional MR imaging. We demonstrate that hyperpolarized 3He gas can be applied to nuclear MR imaging of human organs with air-filled spaces. In vivo 3He MR experiments were performed in a whole-body MR scanner with a superconducting magnet ramped down to 0.8 T and at 1.5 T using a double resonant Helmholtz coil operating at 63.6 and 48.6 MHz for 1H and 3He, respectively. Anatomical details of the lungs of a volunteer were visualized with the FLASH technique demonstrating the potential of the method for fast imaging of airways in the human body and for pulmonary ventilation studies.

Normal and abnormal pulmonary ventilation: visualization at hyperpolarized He-3 MR imaging.

To assess the feasibility of helium-3 magnetic resonance (MR) imaging with a three-dimensional fast low-angle shot (FLASH) sequence, He-3 gas (volume, 300 mL; pressure, 3 x 10(5) Pa; polarized up to 45% by means of optimal pumping) was inhaled by five healthy volunteers and five patients with pulmonary diseases. All breath-hold examinations (22-42 seconds) were completed successfully. Normal ventilation was depicted with homogeneous high signal intensity, lesions were depicted as causing defects, and obstructive lung disease was depicted with severely inhomogeneous signal intensity.

Nuclear magnetic resonance imaging of airways in humans with use of hyperpolarized 3He.

The nuclear spin polarization of noble gases can be enhanced strongly by laser optical pumping followed by electron-nuclear polarization transfer. Direct optical pumping of metastable 3He atoms has been shown to produce enormous polarization on the order of 0.4-0.6. This is about 10(5) times larger than the polarization of water protons at thermal equilibrium used in conventional MRI. We demonstrate that hyperpolarized 3He gas can be applied to nuclear magnetic resonance imaging of organs with air-filled spaces in humans. In vivo 3He MR experiments were performed in a whole-body MR scanner with a superconducting magnet ramped down to 0.8 T. Anatomical details of the upper respiratory tract and of the lungs of a volunteer were visualized with the FLASH technique demonstrating the potential of the method for fast imaging of airways in the human body and for pulmonary ventilation studies.