Biomedical subjects

M Viallon

Publications and source records attributed to M Viallon.

9 recordsLinked to original sources

PubMed2002

3He-MRI-based vs. conventional determination of lung volumes in patients after unilateral lung transplantation: a new approach to regional spirometry.

BACKGROUND: To use 3Helium (3He)-MRI in patients with unilateral lung grafts to assess the contributions of graft and native lung to total ventilated lung volume, and second to compare conventional measurements of intrapulmonary gas volume (spirometry, body plethysmography) with image-based volumetry of ventilated lung parenchyma visualized by hyperpolarized 3He-MRI. METHODS: With Ethics Committee approval, five patients with single lung transplantation (SLTX) for idiopathic pulmonary fibrosis (IPF) underwent both conventional pulmonary function testing (PFT) and 3He-MRI of the lung. Intrapulmonary gas volume (GV) during the inspiratory breathhold for 3He-MRI was calculated from measured functional residual capacity (corrected for supine position) and inspired tidal volume. Image-based global and regional lung volumetries (LV) were performed in three-dimensionally reconstructed 3He-MR images (corrected for the fraction of tissue and blood). RESULTS: Transplanted lungs were characterized by a homogeneous distribution of signal intensity, whereas the native lungs of the patients suffering from IPF displayed an inhomogeneous signal distribution pattern with numerous round or wedge-shaped ventilation defects. Total ventilated lung volume determined by 3He-MRI correlated well with PFT-based measurements, but with a systematic overestimation of the 3He-based lung volumetry of approximately 20%. Functioning lung grafts contributed 66+/-6% and their corresponding native IPF lungs 34+/-6% to total ventilated volume (P<0.05; mean+/-SD). CONCLUSION: 3Helium-MRI of the lung offers a novel approach to regional determination of ventilated lung volume, including its blood and tissue compartments. The advantage of this technique over computed tomography or ventilation scintigraphy is the lack of radiation exposure, and hence its repeatability. Follow up of SLTX patients with this new technique may allow the monitoring of functional and structural developments of grafted lungs with better sensitivity and specificity than PFT.

Female↗

PubMed2001

MR perfusion imaging using encapsulated laser-polarized 3He.

In this work, the use of a new carrier agent for intravascular laser-polarized 3He imaging is reported. Lipid-based helium microbubbles were investigated. Their average diameter of 3 microm, which is smaller than that of the capillaries, makes it possible to conduct in vivo studies. The NMR relaxation parameters T1, T2, and T2* of a microbubble suspension were measured as 90 s, 300 ms, and 4.5 ms, respectively, and in vivo images of encapsulated 3He with signal-to-noise ratios (SNRs) larger than 30 were acquired. Dynamic cardiac images and vascular images of encapsulated 3He were obtained in rats using intravenous injections of microbubble suspensions. Excellent preservation of 3He polarization through the lung capillaries and heart cavities was observed. The first images of 3He microbubble distributions in the lungs were obtained. Additionally, the potential of this technique for lung perfusion assessment was validated through an experimental embolism model with the visualization of perfusion defects.

Animals↗

PubMed2001

Vascular and perfusion imaging using encapsulated laser-polarized helium.

In this work, the use of hyperpolarized (HP) 3He for in vivo intravascular imaging on animal is reported. To overcome the problem of the low solubility of helium in blood, we propose an approach based on helium encapsulation in lipid-based carrier agents. The mean diameter of the 3He microbubbles, measured equal to 3.0+/-0.2 microm, makes it possible to conduct in vivo studies. In vitro spectroscopy yielded a longitudinal relaxation time T(1) equal to 90 s and an apparent transverse relaxation time T(2)(*) of 4.5 ms. Angiographic imaging (venous and cardiac cavity visualization), as well as lung perfusion imaging, were demonstrated in rats using intravenous injections of microbubble suspensions. Suitable signal and spatial resolution were achieved. The potential of this technique for lung perfusion assessment was assessed using an experimental animal embolism model. Lung perfusion defects and recovery towards a normal perfusion state were visualized. This study was completed with the demonstration of a new ventilation-perfusion lung exploration method based entirely on HP 3He.

Animals↗

PubMed2001

[Dynamic imaging of the nasal cavity and the paranasal sinuses with polarized 3helium MRI].

PURPOSE: Reduced or blocked ventilation of the paranasal sinuses is probably the most important factor in the development of sinusitis. Recently, the use of optically polarized noble gas isotopes has attracted increasing interest for use in a variety of promising MR applications. The aim of this study was to test the feasibility of imaging and visualization ventilation of the nasal cavity and paranasal sinus in MR by inhalation of hyperpolarized (3)helium. The goal was to evaluate ventilation defects of the paranasal sinuses. VOLUNTEERS AND METHODS: Three volunteers were enrolled in the study. (3)Helium was polarized to 40 - 50 % by direct optical pumping. 300 ml of 100 % (3)helium were administered in the left nasal vestibule through a glass tube. With a closed contralateral nasal vestibule, the Valsalva maneuver was performed twice. Using a dedicated application unit, which is also used in MR imaging of the lung, an exact amount of (3)helium gas was administered at the beginning of inspiration. Measurements were carried out on a clinical 1.5 T scanner. Coronal images of the nasal cavity and paranasal sinuses were acquired using ultrafast gradient-echo pulse sequence (TR = 2 ms, TE = 0.7 ms, FA < 2 degrees, 75 x 128, FOV = 500) with an image aquisition time of 130 ms. RESULTS: The oral cavity and nasal cavities display a very high signal intensity after inhalation of polarized (3)helium gas. The signal intensity in the left maxillary sinus was higher compared to the right one. The mean signal intensity on the left side was 526 +/- 86 and on the right side 336 +/- 102. The left and right frontal sinus and ethmoid sinus only show signal of hyperpolarized (3)helium after two Valsalva maneuvers. Because of the low signal intensity of the frontal and ethmoid cells their visualization was incomplete. The signal to noise ratio was 14.1 for the left maxillary sinus, 8.9 for the right side, 6.3 for the left ethmoid sinus, 5.8 for the right side and 6.6 for the left frontal sinus and 7.8 for the right side. CONCLUSION: (3)Helium MR allows imaging of the nasal cavity and the paranasal sinuses. Perhaps this method could be a new tool to visualize the ventilation of the maxillary sinus without ionizing radiation. Interpretations about the ventilation of the frontal and ethmoid cells remain speculative.

Administration, Inhalation↗

PubMed2000

Dynamic imaging of hyperpolarized (3)He distribution in rat lungs using interleaved-spiral scans.

The use of spiral scan techniques is investigated for (3)He lung imaging on small animals. Dynamic series of up to 40 high temporal resolution (3)He ventilation images are obtained using a single bolus of gas. General properties of the spiral technique are discussed and compared to those of standard imaging techniques in relation to the specific case of rare gas imaging. To improve temporal resolution of the image series, the efficiency of a sliding window technique, combining data from two consecutive spiral images, is demonstrated. An example of the typical global (3)He signal variation during the (3)He breathing of the animal is shown. Pixel-by-pixel measurements of the (3)He signal derivative during the gas inspiration are performed. A corresponding lung map of the magnetization per time unit entering the lung during gas inflow is presented.

Animals↗

PubMed2000

Laser-polarized (3)He as a probe for dynamic regional measurements of lung perfusion and ventilation using magnetic resonance imaging.

Magnetic resonance imaging (MRI) using laser-polarized noble gases, such as (129)Xe and (3)He, allows unparalleled noninvasive information on gas distribution in lung airways and distal spaces. In addition to pulmonary ventilation, lung perfusion assessment is crucial for proper diagnosis of pathological conditions, such as pulmonary embolism. Magnetic resonance perfusion imaging usually can be performed using techniques based on the detection of water protons in tissues. However, lung proton imaging is extremely difficult due to the low proton density and the magnetically inhomogeneous structure of the lung parenchyma. Here we show that laser-polarized (3)He can be used as a noninvasive probe to image, in a single MRI experiment, not only the ventilation but also the perfusion state of the lungs. Blood volume maps of the lungs were generated based on the (3)He signal depletion during the first pass of a superparamagnetic contrast agent bolus. The combined and simultaneous lung ventilation and perfusion assessments are demonstrated in normal rat lungs and are applied to an experimental animal model of pulmonary embolism. Magn Reson Med 44:1-4, 2000.

Animals↗

PubMed1999

A combined 1H perfusion/3He ventilation NMR study in rat lungs.

The assessment of both pulmonary perfusion and ventilation is of crucial importance for a proper diagnosis of some lung diseases such as pulmonary embolism. In this study, we demonstrate the feasibility of combined magnetic resonance imaging lung ventilation and perfusion performed serially in rat lungs. Lung ventilation function was assessed using hyperpolarized 3He, and lung perfusion proton imaging was demonstrated using contrast agent injection. Both imaging techniques have been implemented using projection-reconstruction sequences with free induction decay signal acquisitions. The study focused on fast three-dimensional (3D) data acquisition. The projection-reconstruction sequences used in this study allowed 3D data set acquisition in several minutes without high-performance gradients. 3D proton perfusion/helium ventilation imaging has been demonstrated on an experimental rat model of pulmonary embolism showing normal lung ventilation associated with lung perfusion defect. Assuming the possibility, still under investigation, of showing lung obstruction pathologies using 3He imaging, these combined perfusion/ventilation methods could play a significant clinical role in the future for diagnosis of several pulmonary diseases.

Animals↗

PubMed1999

Functional MR microscopy of the lung using hyperpolarized 3He.

A new strategy designed to provide functional magnetic resonance images of the lung in small animals at microscopic resolution using hyperpolarized 3He is described. The pulse sequence is based on a combination of radial acquisition (RA) and CINE techniques, referred to as RA-CINE, and is designed for use with hyperpolarized 3He to explore lung ventilation with high temporal and spatial resolution in small animal models. Ventilation of the live guinea pig is demonstrated with effective temporal resolution of 50 msec and in-plane spatial resolution of <100 microm using hyperpolarized 3He. The RA-CINE sequence allows one to follow gas inflow and outflow in the airways as well as in the distal part of the lungs. Regional analysis of signal intensity variations can be performed and can help assess functional lung parameters such as residual gas volume and lung compliance to gas inflow.

Animals↗

PubMed1999

NMR imaging of thermally polarized helium-3 gas.

It is shown that thermally polarized 3He gas can be used to measure important physical parameters and to design, test, and tune imaging sequences. The bulk values of T1, T2, and the diffusion coefficient were measured in a glass cell containing a mixture of helium-3 (0.8 bar) and oxygen (0.2 bar). They were found to be T1 = 7 s, T2 = 2.4 s, and D = 1.6 cm2 s(-1). The relaxation times T2* and T1 and the apparent diffusion coefficient of thermally polarized helium-3 gas were measured in the rat lung, and these parameters were used to design a helium-3 optimized multi-spin-echo sequence which was shown to increase the signal-to-noise ratio sufficiently to obtain the first NMR-images of thermally polarized helium-3 in the rat lung.

Animals↗