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ABSTRACT: The highly constrained backprojection algorithm (HYPR) has recently been shown to allow accelerated acquisition in various fields of MRI, including angiography, perfusion and diffusion imaging as well as hyperpolarized gas imaging. Increase in temporal resolution is of particular interest in the case of small animal ventilation imaging due to the high respiration rate. In the present study, the two-dimensional HYPR technique and its iterative version (I-HYPR) were applied to (3)He ventilation imaging in rats. Two imaging protocols were used for two separate groups of animals. A single inspiration protocol consisted of (3)He imaging of the lungs during gas inflow and a following apnea. A multiple inspiration protocol involved spontaneous breathing of (3)He contained in a gas reservoir. Series of HYPR frames with four-fold increase in the temporal resolution were obtained in the case of the single inspiration experiment. For the multiple inspiration protocol, series of HYPR images corresponding to four different echo times were obtained and were used to reconstruct T(2)(*) maps at the inspiration and the expiration phases of the breathing cycle. The feasibility of using the two-dimensional HYPR technique for different (3)He ventilation protocols in small animals is demonstrated. Image quality and signal kinetics representations are compared for two variants of the HYPR algorithm.
Contrast Media & Molecular Imaging 09/2010; 5(5):276-85. · 3.33 Impact Factor
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ABSTRACT: To assess the sensitivity of hyperpolarized helium 3 ((3)He) magnetic resonance (MR) imaging for the detection of peripheral airway obstruction in younger cystic fibrosis (CF) patients showing normal spirometric results (mean forced expiratory volume in 1 second [FEV(1)], 112% +/- 14.5 [standard deviation]) and to observe the immediate effects of a single chest physical therapy (CPT) session, thereby comparing two image quantification techniques.
Ten pediatric CF patients (age range, 8-16 years) with normal spirometric results were included in this study after approval from the local research ethics committee. Spirometry followed by proton and hyperpolarized (3)He three-dimensional lung imaging were performed with a 1.5-T MR unit before and after 20 minutes of CPT. The number of ventilation defects per image (VDI) and the ventilated lung fraction (VF), defined as the ratio of ventilated lung volume divided by total lung volume, were quantified.
Ventilation defects were found in all patients (mean VDI, 5.1 +/- 1.9; mean global VF, 78.5% +/- 12.3; and mean peripheral VF, 75.5% +/- 17.1) despite normal spirometric results. After CPT, disparate changes in the distribution of ventilation defects were observed but the average VDI and VF did not change significantly (mean VDI, 5.1 +/- 1.1; mean global VF, 83.5% +/- 12.2; and mean peripheral VF, 80.3% +/- 12.2). There was no correlation between FEV(1) and VDI (rho = -0.041, P = .863) or global VF (rho = -0.196, P = .408) values but peripheral VF and VDI were correlated (rho = -0.563, P = .011).
Although spirometric results indicate normal lung function, the mean VDI in patients (5.1) found in this study is well above the VDI in healthy subjects (1.6) reported in the literature. A single CPT session induces disparate changes in the distribution and extent of ventilation defects.
Radiology 04/2010; 255(1):225-32. · 5.73 Impact Factor
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ABSTRACT: Current clinical hyperpolarized He lung ventilation MR imaging protocols rely on the patient's ability to control inhalation and exhalation and hold their breath on demand. This is impractical for intensive care unit patients under ventilation or for pediatric populations under the age of 3 to 4 years. To address this problem, we propose a free-breathing protocol for hyperpolarized He lung ventilation spiral imaging. This approach was evaluated in vitro and on rabbits.
The protocol was implemented on a clinical 1.5-T magnetic resonance imaging scanner. Ventilation images were acquired using a spiral sequence, in vitro on a lung phantom and in vivo on rabbits, the animal breathing freely from a gas reservoir. Dynamic spiral ventilation images were reconstructed using retrospective Cine synchronization. Magnetic resonance (MR) signal dynamics was modeled taking account of gas inflow and outflow, radiofrequency depolarization and oxygen-induced relaxation.
Cine ventilation images acquired in spontaneously breathing rabbits were reconstructed with a temporal resolution of 50 milliseconds. Gas volume variations and time-to-maximum maps were obtained. The numerical model was validated in vitro and in vivo with various gas mixtures. Ventilation parameters (functional residual capacity, tidal volume, and alveolar pO2) were extracted from the MR signal dynamics.
Ventilation imaging can be performed at tidal volume using a simple experimental protocol, without any ventilation device or breath-hold period. Acquisition time, SNR and pO2 decay can be optimized using the developed numerical model. Free-breathing ventilation images can be obtained without artifacts related to motion or gas flow. Lastly, parametric maps can be derived from the time-resolved ventilation images and physiological parameters extracted from the global signal dynamics.
Investigative radiology 03/2009; 44(4):185-91. · 4.85 Impact Factor
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ABSTRACT: As novel engineered nanoparticles such as carbon nanotubes (CNTs) are extensively used in nanotechnology due to their superior properties, it becomes critical to fully understand their biodistribution and effect when accidently inhaled. A noninvasive follow-up study would be beneficial to evaluate the biodistribution and effect of nanotube deposition after exposure directly in vivo. Combined helium-3 and proton magnetic resonance resonance (MRI) were used in a rat model to evaluate the biodistribution and biological impact of raw single-wall CNTs (raw-SWCNTs) and superpurified SWCNTs (SP-SWCNTs). The susceptibility effects induced by metal impurity in the intrapulmonary instilled raw-SWCNT samples were large enough to induce a significant drop in magnetic field homogeneity detected in 3He MR image acquired under spontaneous breathing conditions using a multiecho radial sequence. No MRI susceptibility variation was observed with SP-SWCNT exposition even though histological analysis confirmed their presence in instilled lungs. Proton MRI allowed detection of intravenously injected raw-SWCNTs in spleen and kidneys using gradient echo sequence sensitive to changes of relaxation time values. No signal modifications were observed in the SP-SWCNT injected group. In instilled groups, the contrast-to-noise ratio in liver, spleen, and kidneys stayed unchanged and were comparable to values obtained in the control group. Histological analysis confirms the absence of SWCNTs in systemic organs when SWCNTs were intrapulmonary instilled. In conclusion, the presence of SWCNTs with associated metal impurities can be detected in vivo by noninvasive MR techniques. Hyperpolarized 3He can be used for the investigation of CNT pulmonary biodistribution while standard proton MR can be performed for systemic investigation following injection of CNT solution.
Nano Letters 03/2009; 9(3):1023-7. · 13.20 Impact Factor
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ABSTRACT: Epidemiological and toxicological studies have provided evidence that accidentally inhaled nanosize ultrafine particles can induce chronic or acute health damage. MRI, being noninvasive, is able to assess the biodistribution and clearance of magnetically labeled nanoparticles induced by instillation or inhalation. We report 3He and proton MRI follow-up of lung, liver, spleen, and kidney distribution of USPIO (ultrasmall superparamagnetic iron oxide) in a rat model. The sensitivity of the imaging technique to various concentrations of instilled magnetite suspension was first assessed in vivo (n=12). A 2-week longitudinal imaging study was then performed on animals (n=7) instilled with a 0.5 mg magnetite solution. Hypointense and void signal regions associated with intrapulmonary USPIO were observed in the 3He ventilation images throughout the study, whereas no USPIO-related proton signal intensity changes were found. Intrapulmonary magnetite nanoparticle confinement was confirmed by ex vivo iron assay and histological analysis. This study demonstrates that combined 3He and proton MRI enables noninvasive assessment of the distribution and clearance of magnetically labeled instilled nanoparticles.
Magnetic Resonance in Medicine 07/2008; 59(6):1298-303. · 2.96 Impact Factor
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ABSTRACT: Spatial and temporal variations in oxygen partial pressure (pO(2)) during breath-hold can be exploited to obtain important regional parameters of lung function. In the course of apnea, the oxygen concentration is known to decay exponentially. Therefore, the initial pO(2) (p(0)) can be used to represent local ventilation, and the oxygen depletion time constant can characterize perfusion. The protocol, based on a nonlinear model of pO(2) decay, was validated in six healthy mice. Parametric maps of p(0) and oxygen depletion time constant were obtained for pure (3)He and (3)He/air mixture. The mean measured values of p(0) were 77 +/- 9 mbar for the pure (3)He insufflation and 107 +/- 5 mbar for (3)He/air mixture, in agreement with the predefined p(0) values: 75 +/- 15 mbar and 123 +/- 15 mbar, respectively. The mean measured oxygen depletion time constants were 6.5 +/- 0.2 s for pure (3)He and 7.1 +/- 0.8 s for the (3)He/air mixture, in agreement with physiology.
NMR in Biomedicine 06/2007; 20(3):383-91. · 3.21 Impact Factor
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ABSTRACT: A non-invasive and free-breathing hyperpolarized (HP) (3)He imaging protocol for small animals was implemented and validated on rats for lung function imaging. Animals were allowed to breathe a mixture of air and (3)He from a mask and a gas reservoir fitted to their heads. Radial imaging sequences were used, and MRI signal intensity changes were monitored for retrospective cine image reconstruction. The ventilation cycle of the animals was imaged with a 100 ms temporal resolution. The sliding window imaging technique was applied to reconstruct 5 ms time-shifted image series covering the complete breathing cycle. Image series were processed to extract quantitative ventilation parameters such as the gas arrival time. The reproducibility and the non-invasiveness of this ventilation imaging protocol were evaluated by multiple acquisitions on the same animals.
NMR in Biomedicine 05/2007; 20(2):104-12. · 3.21 Impact Factor
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ABSTRACT: A hyperpolarized 3He ventilation imaging protocol was implemented to assess alveolar pO2 values and the oxygen depletion rate in rats. The imaging protocol, which is based on spiral k-space sampling, was designed to acquire a high signal-to-noise ratio (SNR) T1-weighted ventilation series of images in a single breath-hold. Simulations were performed to estimate the accuracy and dependence of the pO2 imaging protocol on the image SNR and the RF flip-angle determination. The imaging protocol was validated in vitro in phantoms and in vivo in rats. Imaging sessions were carried out for different inhaled O2 concentrations ranging from 20% to 40%. Parametric maps of alveolar pO2 and oxygen depletion rate were generated from the series of images. For each investigated animal, the differences in measured alveolar pO2 values are in agreement with the changes in inhaled O2 concentration. The oxygen depletion rates, ranging between 0.7 and 8.0 mbar s-1, are in close agreement with the published values for healthy rats.
Magnetic Resonance in Medicine 03/2007; 57(2):423-30. · 2.96 Impact Factor
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Investigative Radiology, v.44, 185-191 (2009).
