Pulmonary function in men after repeated sessions of oxygen breathing at 0.25 MPa for 90 min

HYPOTHESIS: We wanted to evaluate the pulmonary effects of discontinuous oxygen breathing (15 min O2, 2 min air breaks, 15:2), at 0.25 MPa once a day for 90 min O2 (6 sequences) over 10 d. This sequence, which has never been evaluated, is currently used in our hyperbaric therapy center. METHODS: Clinical and functional pulmonary status (questionnaire, spirometry, flow/volume loop, pulmonary diffusing capacity for carbon monoxide) was assessed in 10 non-smoking healthy volunteers after one exposure at 0.25 MPa consisting of 90 min of discontinuous oxygen breathing (15:2) and in 10 non-smoking patients who received a hyperbaric treatment consisting of 90 min of the same discontinuous O2 breathing (15:2) once a day over 10 d. The patients received daily intravenous methylprednisolone (1 mg x kg(-1)) and nicergoline (60 mg). RESULTS: There were no respiratory symptoms in either group. As expected, for a single exposure of that duration, lung function did not change in volunteers; however, a significant decrease in maximal expiratory flows (MEF) at 50 (-15%) and 25% (-33%) of forced vital capacity (p < 0.05) without change in forced vital capacity (FVC) appeared in patients treated over 10 d. CONCLUSION: Repetition of the 15:2 oxygen breathing sequence for 90 min once a day over 10 d led to greater flow limitation in peripheral airways than reported after continuous oxygen breathing of 210 min at 0.3 MPa which showed a 7% decrement in MEF50 and a 12% decrement in MEF25. No studies reporting these indexes were found in the 0.2-0.25 MPa range. Similar decrements in MEF50 and MEF25 with steady FVC have been reported after 14 d of daily hyperbaric therapy (0.24 MPa) with 30:5 sequence (-9% and -13%, respectively), 80% of the patients were symptom free. Similarily, our patients were all symptom free and remained so 1 yr after the study, hence, this toxicity is of weak clinical significance in subjects free of inflammatory lung diseases. HBO therapy, though safe, is not totally without effect on the lung.     

Magnetic resonance imaging of lung tissue: influence of body positioning, breathing and oxygen inhalation on signal decay using multi-echo gradient-echo sequences

PURPOSE: To assess susceptibility related signal decay in lung tissue and to measure the influence of body positioning, together with inspiration and expiration, as well as oxygen inhalation. T2* maps and line shape maps of lung parenchyma were derived from datasets acquired at 0.2 T and compared with findings at 1.5 T. The line shape maps allow for a visualization of the intravoxel frequency distribution of lung parenchyma. MATERIALS AND METHODS: A multiecho spoiled gradient-echo sequence with 16 echoes was implemented both on a 0.2 T [repetition time (TR) = 100 milliseconds, echo time (TE)1 = 2.15 milliseconds, DeltaTE = 2.94 milliseconds, flip angle 30 degrees] and on a 1.5 T magnetic resonance scanner (TR = 100 milliseconds, TE1 = 1.25 milliseconds, DeltaTE = 1.65 milliseconds, flip angle 30 degrees). Sagittal datasets were recorded in 8 healthy volunteers at 0.2 T in supine position under maximal expiration and inspiration and during oxygen breathing. Additional measurements were performed after 20 minutes inside the scanner in supine position and after prone repositioning. In 2 volunteers, further datasets were acquired at 1.5 T. Color-encoded T2* maps and full-width-at-half-maximum (FWHM) maps of the frequency distribution were computed on a pixel-by-pixel basis. T2* maps were generated by mono-exponential fitting and, additionally, with an extended nonexponential fitting approach. The FWHM maps were calculated with a model-free approach using a discrete Fast Fourier Transformation. RESULTS: A notably slower T2* decay was found at 0.2 T (T2*: 5.9-11.8 milliseconds) when compared with 1.5 T (T2*: 1.0-1.4 milliseconds), allowing for the measurement of up to 6 to 8 gradient echoes above the noise level. The T2* maps and the FWHM maps computed from the datasets acquired at 0.2 T allowed regional comparison of the derived parameters. If volunteers were positioned in supine position, expiration resulted in a T2* of 10.9 +/- 1.0 milliseconds and a FWHM of 47.1 +/- 4.0 Hz in the dorsal lung. Significant changes (P < 0.05) were found, eg, in the ventral lung in expiration (T2*: 7.5 +/- 0.8, FWHM: 76.7 +/- 11.2) versus dorsal lung in expiration, in the dorsal lung in inspiration (T2*: 8.4 +/- 1.0, FWHM: 67.8 +/- 12.5) versus dorsal lung in expiration, in the dorsal lung during oxygen breathing (T2*: 8.7 +/- 1.1, FWHM: 52.2 +/- 5.2) versus dorsal lung while breathing room air, and in the dorsal lung in prone position (T2*: 8.5 +/- 0.6, FWHM: 67.0 +/- 9.2) versus dorsal lung in supine position. CONCLUSION: The proposed method allows for the computation of color-encoded T2* maps and FWHM maps of lung parenchyma in good image quality using datasets acquired at 0.2 T. The technique is robust and sensitive to physiological changes of lung magnetic resonance properties, eg, due to the type of body positioning or oxygen breathing.     

Quantification of regional ventilation-perfusion ratios with PET.

The topographic matching of alveolar ventilation (V(A)) and perfusion (Q) is the main determinant of gas exchange efficiency of the lung. However, no pulmonary functional imaging technique has been shown to predict whole-lung gas exchange in health and disease. This study aims to present a PET-based method to estimate regional alveolar ventilation-to-perfusion ratios (V(A)/Q) predictive of arterial blood gases. METHODS: The method is based on the regional tracer kinetics of (13)N-nitrogen ((13)NN) after an intravenous bolus injection during a breath-hold period and subsequent washout from the lungs with resumption of breathing. The method takes into account the presence of inter- and intraregional nonuniformities at length scales smaller than the imaging spatial resolution. An algorithm used regional tracer washout to classify regional V(A)Q/ uniformity. Intraregional V(A)/Q mismatch in nonuniform regions was described with a 2-compartment model. Regional V(A)/Q estimates were combined into a whole-lung distribution of V(A)/Q ratios and were used to compute global arterial blood gases. The method was applied to 3-dimensional PET data from anesthetized and mechanically ventilated sheep before and after methacholine bronchoconstriction (n = 3) and pulmonary embolism (n = 3) and after saline lung lavage (n = 3). RESULTS: PET images revealed regional changes in ventilation and perfusion consistent with the different disease models. Quantification of the images using PET-derived V(A)Q/ distributions showed unimodal and narrow distributions in control conditions that became wider and unimodal after pulmonary embolism and saline lung lavage and bimodal after bronchoconstriction. Images of regional gas exchange allowed for visualization of regional gas exchange. Arterial blood gases estimated from the PET-based V(A)/Q distributions closely agreed with measured values (partial pressure of oxygen, arterial [PaO(2)]: r(2) = 0.97, P < 0.001; partial pressure of carbon dioxide, arterial [PaCO(2)]: r(2) = 0.96, P < 0.001). CONCLUSION: Tracer kinetics analysis of PET images after an intravenous injection of (13)NN provides a quantitative assessment of regional V(A)/Q heterogeneity including that corresponding to length scales smaller than the spatial resolution of the imaging method. Quantification of V(A)/Q mismatch obtained with the presented technique is directly related to severity of gas exchange impairment as determined by arterial blood gases.     

Pulmonary diffusing capacity: assessment with oxygen-enhanced lung MR imaging preliminary findings

PURPOSE: To determine differences in the signal intensity (SI) time courses at oxygen-enhanced magnetic resonance (MR) lung imaging in healthy volunteers and patients with pulmonary diseases and to correlate these differences with pulmonary diffusing capacity. MATERIALS AND METHODS: Seventeen patients with pulmonary diseases and 11 healthy volunteers underwent oxygen-enhanced MR imaging while they breathed room air and 100% oxygen. A turbo spin-echo sequence with global or section-selective inversion pulses was used. For postprocessing, SI slope maps during the breathing of 100% oxygen were calculated. Mean SI slope and SI change values were compared with the diffusing capacity of the lung for carbon monoxide (DLCO). RESULTS: The SI slopes were significantly different for patients and volunteers (P < or = .05, Mann-Whitney U test). Linear correlations were detected between the DLCO and SI slopes for the section-selective inversion pulse (r(2) = 0.81) and the global inversion pulse (r(2) = 0.74). A lower correlation was associated with the SI change for the section-selective pulse (r(2) = 0.04; global pulse, r(2) = 0.81). Regional differences were seen in the SI slope and SI change maps. These differences correlated with findings on radiographs and computed tomographic scans. CONCLUSION: The SI slope during the breathing of 100% oxygen allows spatially resolved assessment of the pulmonary diffusion capacity.     

The use of ECG and respiratory triggering to improve the sensitivity of oxygen-enhanced proton MRI of lung ventilation

Changes in lung signal between normal breathing and breathing pure oxygen is the basis for oxygen-enhanced ventilation MRI. An optimal technique guarantees a significant response to pure oxygen in well-ventilated lung tissue. To improve the sensitivity, we investigated the effect of ECG and respiratory triggering. Centric reordered single-shot rapid acquisition relaxation enhancement sequences (TE 4.2 ms, echo spacing 4.2 ms, bandwidth 650 Hz/pixel), with an inversion recovery preparation pulse (TI 700 ms), were used. Series of 20 measurements were performed with and without ECG and respiratory triggering in five young volunteers. Subsequently, series of 100 images were acquired during breathing normal air and pure oxygen (as "stimulus"). Ventilation maps showed by means of the z-score how far the response deviates from the signal intensities during the normal air condition. The standard deviation of the lung signal intensities was lowest for the cardiac-triggered series. In the ventilation maps, on the other hand, signal changes were statistically more significant in the respiratory than in the cardiac-triggered series. The average z-scores in the right (left) cranial part of the lung were 12.4 (13.0) and 9.2 (9.7) for respiratory and ECG-triggered acquisitions. We propose to use respiratory triggering as a means to improve the sensitivity of MR ventilation studies. Electronic Publication     

The Use of 4DCT to Reduce Lung Dose: A Dosimetric Analysis

Dosimetric studies on respiratory movement suggest several advantages toward the use of 4-dimensional computed tomography (4DCT) in radiation treatment planning. 4DCT is a method to obtain a series of CT scans each representing a different respiratory phase. The use of 4DCT has provided substantial information on tumor movement in the lung, allowing for the creation of custom planning margins explicitly including respiratory motion. These custom motion margins may result in an increase in the amount of normal lung in the field; however, it is believed less normal lung is irradiated than if generic motion margins were used. Clinical data regarding dose to normal lung by using 4DCT remain rather limited. Thus, a study presenting figures on the change in normal lung dose between planned free breathing CT and 4DCT cases would be useful to the dosimetry community. We have generated plans comparing fast spiral CT and 4DCT in regard to tumor coverage and the resulting dose to normal lung for the clinical target volume (CTV) and planning target volume (PTV) expansions used at our institution. These data were analyzed for free breathing and 4D plans of 6 lung cancer patients using intensity modulated radiation therapy (IMRT). We compared doses to normal lung tissue between free breathing and 4DCT plans.     

Magnetic resonance imaging-based spirometry for regional assessment of pulmonary function.

In this work MRI-based spirometry is presented as a method for noninvasively assessing pulmonary mechanical function on a regional basis. A SPAMM tagging sequence was modified to allow continuous dynamic imaging of the lungs during respiration. A motion-tracking algorithm was developed to track material regions from time-resolved grid-tagged images. Experiments were performed to image the lungs during quiet breathing and volumetric strain was calculated from the measured displacement maps. Regional volume calculations, derived from volumetric strain, were integrated over the entire lung and compared to segmented volume calculations with good agreement. Results from this work demonstrate that MRI spirometry has the potential to become a clinically useful tool for measuring regional ventilation and assessing pulmonary diseases that regionally affect the mechanical function of the lung.     

Quantification of right to left shunt through pulmonary arteriovenous malformations using 99Tcm albumin microspheres

Calculation of the right-to-left shunt through pulmonary arteriovenous malformations (PAVMs) is important in assessing the effect of therapeutic embolisation or surgical resection. Previously, complicated physiological techniques using radiolabelled inert gases or the 100% oxygen breathing method were required. We describe a new method for quantitating the systemic uptake of intravenously injected 99Tcm albumin microspheres (99Tcm MS) which reflects shunt fraction since these particles do not normally traverse the pulmonary capillary bed. Seven patients with PAVMs were studied and shunt values obtained using 99Tcm MS were validated by simultaneous measurement of shunt fraction using the 100% oxygen method. By comparing radioactive counts in the injection dose to subsequent counts in the right kidney, which was taken as an index of systemic activity, accurate quantification of right-to-left shunt over a wide range of values was obtained (correlation coefficient against 100% oxygen method r = 0.993). The comparison of right kidney counts with total lung counts and total lung counts with injected dose counts, also indicators of shunt fraction, correlated less well with the oxygen method (r = 0.942 and r = 0.88 respectively). Use of 99Tcm labelled microspheres allows simple and precise measurement of right-to-left shunt in patients with PAVMs during routine isotope lung scanning.     

The Use of 4DCT to Reduce Lung Dose: A Dosimetric Analysis

Dosimetric studies on respiratory movement suggest several advantages toward the use of 4-dimensional computed tomography (4DCT) in radiation treatment planning. 4DCT is a method to obtain a series of CT scans each representing a different respiratory phase. The use of 4DCT has provided substantial information on tumor movement in the lung, allowing for the creation of custom planning margins explicitly including respiratory motion. These custom motion margins may result in an increase in the amount of normal lung in the field; however, it is believed less normal lung is irradiated than if generic motion margins were used. Clinical data regarding dose to normal lung by using 4DCT remain rather limited. Thus, a study presenting figures on the change in normal lung dose between planned free breathing CT and 4DCT cases would be useful to the dosimetry community. We have generated plans comparing fast spiral CT and 4DCT in regard to tumor coverage and the resulting dose to normal lung for the clinical target volume (CTV) and planning target volume (PTV) expansions used at our institution. These data were analyzed for free breathing and 4D plans of 6 lung cancer patients using intensity modulated radiation therapy (IMRT). We compared doses to normal lung tissue between free breathing and 4DCT plans.     

Hypoxemia with air breathing periods in U.S. NAVY Treatment Table 6.

Air breathing is used to lessen hyperbaric oxygen (HBO2) toxicity. Hypoxemia could occur during hyperbaric air breathing in patients with lung dysfunction, although this has not been previously reported. We report two cases of hypoxemia during air breathing with two patients treated with the US Navy Table 6. Patient 1 was an 11-year-old male with cerebral gas embolism (during cardiac transplantation), patient 2 was a 66-year-old female with cerebral gas embolism from a central venous catheter accident. Both were mechanically ventilated. We monitored arterial blood gas (ABG) during therapy. In both patients, ABG measurements showed hypoxia during the first air breathing period at 1.9 atm abs (192.5 kPa). If patients require > or = 40% inspired oxygen before HBO2 therapy, oxygenation monitoring is advisable during air breathing periods, especially at lower chamber pressures (< or = 2.0 atm abs).     

Effect of respiratory motion on pulmonary activity determinations by positron tomography in dogs

The effect of respiratory motion on pulmonary activity determinations by positron emission tomography (PET) was studied in dogs with experimentally created pulmonary emboli (PE). The location of the PE was evaluated by planar 99mTc lung imaging to determine the appropriate sites for transaxial PET scans. PET scans of the lung then were obtained after i.v. injection of 68Ga-labeled microspheres. PET scans were acquired during slow (15 breaths/min) and fast (30 breaths/min) breathing with the same minute ventilation and then postmortem. Lung perfusion patterns were documented by i.v. injection of India ink before sacrifice. Cross sections of the excised lungs were made at the same levels as the PET scans, and eight sections containing 14 perfusion defects were analyzed. The scans obtained during slow breathing consistently showed edge blurring and demonstrated defects less well than scans obtained during fast breathing or postmortem. The normal-to-defect activity ratios during fast breathing and on the postmortem studies were similar and approximately 17% higher (P less than .01) than in scans obtained in the same animals during slow breathing. The results demonstrate the need for motion correction during quantitative analysis of regional lung activity by positron tomography, and suggest that high-frequency respiration at small tidal volumes may be one means for obtaining this correction.     

Proton MRI of lung parenchyma reflects allergen-induced airway remodeling and endotoxin-aroused hyporesponsiveness: a step toward ventilation studies in spontaneously breathing rats.

Proton signals from lung parenchyma were detected with the use of a gradient-echo sequence to noninvasively obtain information on pulmonary function in models of airway diseases in rats. Initial measurements carried out in artificially ventilated control rats revealed a highly significant negative correlation between the parenchymal signal and the partial pressure of oxygen (pO2) in the blood, for different amounts of oxygen administered. The magnitude of the signal intensity variations caused by changes in the oxygen concentration was larger than expected solely from the paramagnetic properties of molecular oxygen. Inhomogeneous line-broadening induced by lung inflation may explain the observed signal amplification. Experiments carried out in spontaneously breathing animals challenged with allergen or endotoxin revealed parenchymal signal changes that reflected the oxygenation status of the lungs and were consistent with airway remodeling or hyporesponsiveness. The results suggest that proton MRI of parenchymal tissue is a sensitive tool for probing the functional status of the lung in rat models of respiratory diseases. The method is complementary to the recently described noninvasive assessment by MRI of pulmonary inflammation in small rodents. Overall, these techniques provide invaluable information for profiling anti-inflammatory drugs in models of airway diseases.     

Lung function in military oxygen divers: a longitudinal study

It is increasingly recognized that professional diving may elicit adverse long-term effects on the lungs, but conflicting results have been reported from distinct diving cohorts. This study reports the longitudinal change in lung function in professional divers who employ closed-circuit oxygen rebreathing apparatuses. All oxygen divers who attended the German Naval Medical Institute between 1994 and 1999 for regular medicals underwent spirometry and were entered if they had at least two follow-up examinations. Forced expiratory flows and volumes at baseline and at maximum follow up were compared. There were 39 divers who presented at least 3 times during a median period of 5.8 (2.7-8) yr. Forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC) amounted to 4.86 +/- 0.62 L and 5.89 +/- 0.67 L at baseline, and 4.83 +/- 0.64 L and 5.87 +/- 0.69 L at maximum follow up, respectively. The change over time was statistically not significant. Substantial exposure to elevated oxygen partial pressure while diving is not associated with an accelerated decline in lung function. Factors other than hyperoxia (e.g., venous gas microemboli and altered breathing gas characteristics) may account for the long-term effects that have been found in professional divers.     

Quantitative regional oxygen transfer imaging of the human lung

PURPOSE: To demonstrate that the use of nonquantitative methods in oxygen-enhanced (OE) lung imaging can be problematic and to present a new approach for quantitative OE lung imaging, which fulfills the requirements for easy application in clinical practice. MATERIALS AND METHODS: A total of 10 healthy volunteers and three non-small-cell lung cancer (NSCLC) patients were examined using a 1.5T scanner. OE imaging was performed using a snapshot fast low-angle shot (FLASH) T(1)-mapping technique (TE = 1.4 msec, TR = 3.5 msec) as well as a series of T(1)-weighted inversion recovery (IR) half- Fourier acquisition single-shot turbo spin-echo (HASTE) (TE(effective) = 43 msec, TE(inter) = 4.2 msec, and inversion time [TI] = 1200 msec) images. Semiquantitative relative signal enhancement ratios (RER) of T(1)-weighted images before and after inhalation of oxygen-enriched gas were compared to the quantitative change in T(1). A hybrid method is proposed that combines the advantages of T(1)-weighted imaging with the quantification provided by T(1)-mapping. To this end, the IR-HASTE images were transformed into quantitative parameter maps. To prevent mismatching and incorrect parameter maps, retrospective image selection was performed using a postprocessing navigator technique. RESULTS: The RER was dependent on the intrinsic values of T(1) in the lung. Quantitative parameters, such as the decrease of T(1) after switching the breathing gas, were more suited to oxygen transfer quantification than to relative signal enhancement. The mean T(1) value during inhalation of room air (T(1,room)) for the volunteers was 1260 msec. This value decreased by about 10% after switching the breathing gas to carbogen. For the patients, the mean T(1,room) value was 1182 msec, which decreased by about 7% when breathing carbogen. The parameter maps generated using the proposed hybrid method deviated, on average, only about 1% from the T(1)-maps. CONCLUSION: For the purpose of intersubject comparison, OE lung imaging should be performed quantitatively. The proposed hybrid technique produced reliable quantitative results in a short amount of time and, therefore, is suited for clinical use.     

Oxygen tension mapping with F-19 echo-planar MR imaging of sequestered perfluorocarbon

The authors used fluorine-19 inversion-recovery (IR) echo-planar imaging (EPI) to map oxygen tension on the basis of the spin-lattice relaxation rate (R1) of sequestered perfluorocarbon. R1 measured with IR-EPI varied as a linear function of oxygen tension and temperature, and the relationship agreed well with earlier spectroscopic findings. Oxygen tension maps of a mouse that had received a dose of perflubron emulsion were acquired before, during, and after the mouse breathed pure oxygen. Results showed low liver oxygen tension during air breathing, which increased during breathing of pure oxygen, with distinct regional heterogeneity, to 8–17%atm (60–130 torr [8.0–17.3 kPa]).     

Effect of unilateral breathing exercises on regional lung ventilation.

We investigated the effect of a unilateral thoracic expansion exercise (TEE), a breathing manoeuvre used by physiotherapists, on regional lung ventilation. Nine trained physiotherapists aged 22-37 years completed the study. Technegas lung ventilation scans were used to determine the effect of a right unilateral TEE performed when sitting. This was compared with a maximal deep breath. Total radioactivity in each lung was determined. Each lung was sectioned into three equal zones (upper, middle and lower) and the ratio of radioactivity for each of the corresponding lung zones calculated. Ventilation was preferentially distributed to the right lung in all participants during both breathing manoeuvres. The mean (+/- S.E.M.) radioactivity ratios (right/left lung) were greater during a unilateral TEE (1.17 +/- 0.02) than during a deep breath (1.07 +/- 0.01). Seven participants achieved significantly greater ventilation to the right middle (1.15 +/- 0.03, P = 0.02) and lower zones (1.34 +/- 0.03, P = 0.02) during a unilateral TEE than to the corresponding zones on the left; this was evident soon after the initiation of the breath. The findings of this study show that relative regional ventilation to the ipsilateral lung can be increased during a unilateral TEE in trained individuals.     

Regional pulmonary distribution of krypton-81m gas delivered by different breathing systems

Regional pulmonary distribution of 81mKr gas delivered by three breathing systems was determined. Data from 18 patients were analyzed. Posterior images were obtained using each breathing system in turn. Distribution of Kr gas was determined in terms of penetration and zonal indices. For penetration indices each lung was divided into a central, intermediate, and peripheral region and these indices, defined as the ratio of counts/cell in the intermediate or the peripheral region over those in the central region, were calculated. For the zonal indices each lung was divided equally into upper and lower zones and the percentage ratio of the counts in each zone to the total counts in both lungs was calculated. For all patients, in addition, the size, height, and width of each lung were determined from computer images. These parameters were compared between the breathing systems using a paired t-test. It was found that there were no statistical differences among the three breathing systems, either in the regional pulmonary distribution of the 81mKr gas or in the overall shapes of the lungs.     

A robust method for estimating regional pulmonary parameters in presence of noise

RATIONALE AND OBJECTIVES: Estimation of regional lung function parameters from hyperpolarized gas magnetic resonance images can be very sensitive to presence of noise. Clustering pixels and averaging over the resulting groups is an effective method for reducing the effects of noise in these images, commonly performed by grouping proximal pixels together, thus creating large groups called "bins." This method has several drawbacks, primarily that it can group dissimilar pixels together, and it degrades spatial resolution. This study presents an improved approach to simplifying data via principal component analysis (PCA) when noise level prohibits a pixel-by-pixel treatment of data, by clustering them based on similarity to one another rather than spatial proximity. The application to this technique is demonstrated in measurements of regional lung oxygen tension using hyperpolarized (3)He magnetic resonance imaging (MRI). MATERIALS AND METHODS: A synthetic dataset was generated from an experimental set of oxygen tension measurements by treating the experimentally derived parameters as "true" values, and then solving backwards to generate "noiseless" images. Artificial noise was added to the synthetic data, and both traditional binning and PCA-based clustering were performed. For both methods, the root-mean-square (RMS) error between each pixel's "estimated" and "true" parameters was computed and the resulting effects were compared. RESULTS: At high signal-to-noise ratios (SNRs), clustering did not enhance accuracy. Clustering did, however, improve parameter estimations for moderate SNR values (below 100). For SNR values between 100 and 20, the PCA-based K-means clustering analysis yielded greater accuracy than Cartesian binning. In extreme cases (SNR<5), Cartesian binning can be more accurate. CONCLUSIONS: The reliability of parameters estimation in imaging-based regional functional measurements can be improved in the presence of noise by utilizing principal component analysis-based clustering without sacrificing spatial resolution compared to Cartesian binning. Results suggest that this approach has a great potential for robust grouping of pixels in hyperpolarized (3)He MRI maps of lung oxygen tension.     

Single-acquisition sequence for the measurement of oxygen partial pressure by hyperpolarized gas MRI.

Magnetic resonance imaging (MRI) with hyperpolarized 3-helium gas (HP 3He) offers the possibility of studying functional lung parameters such as the alveolar oxygen concentration and oxygen depletion rate. Until now, a double-acquisition technique has been utilized to extract these parameters. A complicated single-acquisition technique was previously developed to avoid the necessity of performing two identical breathing maneuvers. The results obtained with this technique were significantly less accurate than the results obtained with the double-acquisition method. In this work, a novel, easily implemented single-acquisition sequence is presented that provides results comparable to those obtained with the established double-acquisition method. This method is demonstrated in a phantom and a pig model on a 1.5 T scanner using a 2D fast low-angle shot (FLASH) gradient-echo sequence. Numerical simulations of the time evolution of the oxygen concentration were performed. Simulation results are presented to support the experimental data. Various parameter regimes were experimentally and numerically investigated.     

Oxygen-enhanced MR imaging of mice lungs.

Inhaled molecular oxygen has been widely used in humans to evaluate pulmonary ventilation using MRI. MR imaging has recently played a greater role in examining the morphologic and physiologic characteristics of mouse models of lung disease where structural changes are highly correlated to abnormalities in respiratory function. The motivation of this work is to develop oxygen-enhanced MR imaging for mice. Conventional human MR techniques cannot be directly applied to mouse imaging due to smaller dimensions and faster cardiac and respiratory physiology. This study examines the development of oxygen-enhanced MR as a noninvasive tool to assess regional ventilation in spontaneously breathing mice. An optimized cardiac-triggered, respiratory-gated fast spin-echo imaging sequence was developed to address demands of attaining adequate signal from the parenchyma, maintaining practical acquisition times, and compensating for rapid physiological motion. On average, a 20% T1-shortening effect was observed in mice breathing 100% oxygen as compared to air. The effect of ventilation was shown as a significant signal intensity increase of 11% to 16% in the mouse parenchyma with 100% oxygen inhalation. This work demonstrates that adequate contrast and resolution can be achieved using oxygen-enhanced MR to visualize ventilation, providing an effective technique to study ventilation defects in mice.