Alveolar ventilation/perfusion ratio (V A /Q) is a key parameter in functional imaging of the lung. Herein, regional V A /Q was calculated from regional values of alveolar partial pressure of oxygen (P A O 2 ) measured by hyperpolarized 3 He gas MRI (HP 3 He MRI). Yorkshire pigs (n ‫؍‬ 7, mean weight ‫؍‬ 25 kg) were paralyzed and maintained under isoflurane anesthesia. Animals were placed into a birdcage coil, then transferred to the bore of a 1.5 T MRI unit. Prior to imaging, animals were manually ventilated with room air for 5 min, then a 3 He gas mixture was administered during breathhold and imaging performed. P A O 2 was measured based on the decay rate of 3 He signal. Subjects' blood gas concentrations were measured and these values and Imaging techniques for pulmonary disorders have traditionally focused on anatomic and pathologic descriptions of lung parenchyma, airways, and vasculature. Functional imaging of the lung is a relatively recent development in pulmonary imaging that seeks to image physiologic variables. Recent developments in imaging methods for regional measurements of function have generated considerable interest because of the potential for high-resolution, regional distributions of functional variables to enhance detection of lung pathologies. Additionally, regional measurements of function can provide fundamental insights into the pathophysiologic mechanisms of disease.Several methods have been reported recently for imaging of functional variables: local compliance (1-3), local ventilation (4 -6), local perfusion from arterial spin tagging techniques (7-9) and contrast washout kinetics (5,10,11), and regional determinations of the alveolar ventilation/perfusion ratio (V A /Q) by PET (12-16), CT (17), and MRI-based methods (8,18,19). Regional determinations of V A /Q are of particular interest because of the key role of V A /Q in gas exchange (20), and because V A /Q can be disturbed by pathology that affects either ventilation or perfusion. Local measurements and imaging of V A /Q therefore have the potential to serve as a sensitive marker for lung disease.MR-based functional imaging methods offer a unique combination of potentially high spatial resolution and high temporal resolution. Although proton MRI can be used for lung imaging (21), this approach is generally at a disadvantage in that contrast in signal between tissue and gas phases is low (22). Recently, several investigators have used hyperpolarized (HP) 3 He gas for high-resolution imaging of the airways (23,24), and most recently as a method to assess regional ventilation (4). One complicating factor that all HP 3 He methods share is the oxygen-dependent decay of signal due to spin transfer (25).The Mainz group used this oxygen-dependence of polarized spin decay to measure regional alveolar partial pressure of oxygen (P A O 2 ) in the lung, and suggested that these local measurements of P A O 2 and their correlation with decrease rate could reflect matching of ventilation and perfusion (26 -30). It has long been known that the...

Young patients may experience LTE from WPW syndrome without prior symptoms or markers of high-risk on EPS.

Magnetic resonance imaging (MRI) with hyperpolarized 3-helium gas (HP 3 He) 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. Functional lung imaging seeks to image physiological pulmonary variables. Recent developments in imaging techniques offer the possibility of measuring regional pulmonary function. This advancement has generated considerable interest because high-resolution, regional distributions of functional variables can potentially enhance the detection of lung pathologies. In addition, regional measurements of function could provide fundamental insights into the pathophysiologic mechanisms of these diseases.Hyperpolarized helium-3 magnetic resonance imaging (HP 3 He MRI) is ideally suited for functional lung imaging as an imaging modality that is sensitive, regional, quantitative, noninvasive, and nonionizing, and has no known side effects. Recently, several investigators have used HP 3 He gas to perform high-resolution static imaging of the airways (1-6), diffusion measurements (7,8), and regional ventilation studies (9,10), and determine the alveolar partial pressure of oxygen (11-14).The regional alveolar partial pressure of oxygen and oxygen depletion rate are sensitive markers for the efficiency of oxygen transfer between the lung and the blood stream. Lung disorders that mainly affect ventilation (e.g., emphysema) or mainly perfusion (e.g., pulmonary embolism) can severely change these functional parameters (14 -16). Sensitive regional oxygen measurements can help physicians detect early changes in lung function and structure associated with such pulmonary diseases, quantitatively follow the progression of disease, and immediately ascertain response to therapy.The magnetization of initially polarized 3He will gradually decrease in the presence of oxygen because of the interaction between these two gas species (17). The depolarization rate is strongly dependent on the partial pressure of oxygen in the gas mixture. The measurement of this depolarization rate allows for the determination of the partial pressure of oxygen (pO 2 ). The time evolution of pO 2 , and consequently the oxygen depletion rate (R), can be obtained if the evolution of the oxygen-induced depolarization rate can be extracted from a time series of images. However, HP 3 He gas...

Impaired exercise following Fontan is a surrogate of morbidity. Single-center longitudinal data exist, but there is a lack of contemporary multi-center data. Ramp cycle ergometry was re-

In this experiment, Sprague-Dawley rats with elastase-induced emphysema were imaged using hyperpolarized 3 He MRI. Regional fractional ventilation r, the fraction of gas replaced with a single tidal breath, was calculated from a series of images in a wash-in study of hyperpolarized gas. We compared the regional fractional ventilation in these emphysematous rats to the regional fractional ventilations we calculated from a previous baseline study in healthy Sprague-Dawley rats. We found that there were differences in the maps of fractional ventilation and its associated frequency distribution between the healthy and emphysematous rat lungs. Fractional ventilation tended to be much lower in emphysematous rats than in normal rats. Functional lung imaging is a recent trend in diagnostic radiology that seeks to diagnose and/or evaluate disease states based on measurements of functional parameters. Functional parameters of prime importance include the alveolar partial pressure of oxygen (P A O 2 ), oxygen depletion rate (ODR), alveolar ventilation (V A ), alveolar perfusion (Q), and the alveolar ventilation/perfusion ratio (V A /Q) (1). We have recently used hyperpolarized 3 He MRI (HP 3 He MRI) to evaluate P A O 2 , ODR, Q, and V A /Q in healthy and diseased subjects (2-6). Similar regional and quantitative studies have been performed by other researchers (7-10). HP 3 He MRI offers the advantage of measuring these parameters using a noninvasive, nonradiative contrast agent.Chronic obstructive pulmonary disorder (COPD) causes approximately 85,000 deaths annually. It is the fourth leading cause of death in the United States. COPD is also a major cause of disability. It afflicts about 14 million Americans and severely compromises their quality of life. The 3-year mortality rate in ambulatory patients with COPD approaches 23%. Emphysema is a form of COPD that is characterized by the progressive destruction of the lung parenchyma, which leads to a loss of surface area for gas exchange, a reduction in lung elastic recoil, and an irreversible airflow obstruction. Advanced emphysema may result in a 5-year mortality rate of 60%. Patients with emphysema suffer from severe dyspnea and often hypoxemia, due in part to alterations in alveolar ventilation and perfusion.Lung volume reduction surgery (LVRS) is an important and increasingly applied treatment for emphysema (11)(12)(13)(14). LVRS resects portions of the larger, less elastic emphysematous lung in an effort to return some normal function to the patient. A quantitative analysis of normal and emphysematous lung function is necessary to evaluate candidates for LVRS and to assess postoperative results. We hypothesized that HP 3 He MRI measurements of fractional ventilation (based on Deninger's local ventilation method (15)) would identify changes in the lung caused by emphysema (previous studies examined the apparent diffusion coefficient as a means of detecting emphysema (9,16,17)).Fractional ventilation is defined as the amount of gas added to a region of interest during ins...