James R. Brookeman

Hyperpolarized 3He MR lung ventilation imaging in asthmatics: Preliminary findings

Asthma is a disease characterized by chronic inflammation and reversible obstruction of the small airways resulting in impaired pulmonary ventilation. Hyperpolarized 3He magnetic resonance (MR) lung imaging is a new technology that provides a detailed image of lung ventilation. Hyperpolarized 3He lung imaging was performed in 10 asthmatics and 10 healthy subjects. Seven asthmatics had ventilation defects distributed throughout the lungs compared with none of the normal subjects. These ventilation defects were more numerous and larger in the two symptomatic asthmatics who had abnormal spirometry. Ventilation defects studied over time demonstrated no change in appearance over 30–60 minutes. One asthmatic subject was studied twice in a three‐week period and had ventilation defects which resolved and appeared in that time. This same subject was studied before and after bronchodilator therapy, and all ventilation defects resolved after therapy. Hyperpolarized 3He lung imaging can detect the small, reversible ventilation defects that characterize asthma. The ability to visualize lung ventilation offers a direct method of assessing asthmatics and their response to therapy. J. Magn. Reson. Imaging 2001;13:378–384.

Dynamic spiral MRI of pulmonary gas flow using hyperpolarized 3He: Preliminary studies in healthy and diseased lungs

An optimized interleaved‐spiral pulse sequence, providing high spatial and temporal resolution, was developed for dynamic imaging of pulmonary ventilation with hyperpolarized 3He, and tested in healthy volunteers and patients with lung disease. Off‐resonance artifacts were minimized by using a short data‐sampling period per interleaf, and gradient‐fidelity errors were compensated for by using measured k‐space trajectories for image reconstruction. A nonsequential acquisition order was implemented to improve image quality during periods of rapid signal change, such as early inspiration. Using a sliding‐window reconstruction, cine‐movies with a frame rate of 100 images per second were generated. Dynamic images demonstrating minimal susceptibility‐ and motion‐induced artifacts were obtained in sagittal, coronal, and axial orientations. The pulse sequence had the flexibility to image multiple slices almost simultaneously. Our initial experience in healthy volunteers and subjects with lung pathology demonstrated the potential of this new tool for capturing the features of lung gas‐flow dynamics. Magn Reson Med 4:667–677, 2001.

Noninvasive medical imaging system and method for the identification and 3-D display of atherosclerosis and the like

There is disclosed an image processing, pattern recognition and computer graphics system and method for the noninvasive identification and evaluation of atheroscelerosis using multidimensional Magnetic Resonance Imaging (MRI). Functional information, such as plaque tissue type, is combined with structure information, represented by the 3-D vessel and plaque structure, into a single composite 3-D display. The system and method is performed with the application of unsupervised pattern recognition techniques and rapid 3-D display methods appropriate to the simultaneous display of multiple data classes. The results are a high information content display which aids in the diagnosis and analysis of the atherosclerotic disease process, and permits detailed and quantitative studies to assess the effectiveness of therapies, such as drug, exercise and dietary regimens.

Probing lung physiology with xenon polarization transfer contrast (XTC)

One of the major goals of hyperpolarized‐gas MRI has been to obtain 129Xe dissolved‐phase images in humans. So far, this goal has remained elusive, mainly due to the low concentration of xenon that dissolves in tissue. A method is proposed and demonstrated in dogs that allows information about the dissolved phase to be obtained by imaging the gas phase following the application of a series of RF pulses that selectively destroy the longitudinal magnetization of xenon dissolved in the lung parenchyma. During the delay time between consecutive RF pulses, the depolarized xenon rapidly exchanges with the gas phase, thus lowering the gas polarization. It is demonstrated that the resulting contrast in the 129Xe gas image provides information about the local tissue density. It is further argued that minor pulse‐sequence modifications may provide information about the alveolar surface area or lung perfusion. Magn Reson Med 44:349–357, 2000.

Merging parametric active contours within homogeneous image regions for MRI-based lung segmentation

Inhaled hyperpolarized helium-3 (/sup 3/He) gas is a new magnetic resonance (MR) contrast agent that is being used to study lung functionality. To evaluate the total lung ventilation from the hyperpolarized /sup 3/He MR images, it is necessary to segment the lung cavities. This is difficult to accomplish using only the hyperpolarized /sup 3/He MR images, so traditional proton (/sup 1/H) MR images are frequently obtained concurrent with the hyperpolarized /sup 3/He MR examination. Segmentation of the lung cavities from traditional proton (/sup 1/H) MRI is a necessary first step in the analysis of hyperpolarized /sup 3/He MR images. In this paper, we develop an active contour model that provides a smooth boundary and accurately captures the high curvature features of the lung cavities from the /sup 1/H MR images. This segmentation method is the first parametric active contour model that facilitates straightforward merging of multiple contours. The proposed method of merging computes an external force field that is based on the solution of partial differential equations with boundary condition defined by the initial positions of the evolving contours. A theoretical connection with fluid flow in porous media and the proposed force field is established. Then by using the properties of fluid flow we prove that the proposed method indeed achieves merging and the contours stop at the object boundary as well. Experimental results involving merging in synthetic images are provided. The segmentation technique has been employed in lung /sup 1/H MR imaging for segmenting the total lung air space. This technology plays a key role in computing the functional air space from MR images that use hyperpolarized /sup 3/He gas as a contrast agent.

Three-dimensional magnetic resonance imaging

A new three-dimensional (3D) MR imaging pulse sequence can produce over 100 high-resolution, high-contrast images in as little as 6 minutes of imaging time. Without additional imaging time, this same image data can be post-processed to yield high-resolution, high-contrast images in any arbitrary orientation. Thus, this new pulse sequence technique provides detailed yet comprehensive coverage. The method of this invention relates to a preparation-acquisition-recovery sequence cycle. The first step is magnetization preparation (MP) period. The MP period can emply a series of RF pulses, gradient field pulses, and/or time delays to encode the desired contrast properties in the form of longitudinal magnetization. A data acquisition period includes at least two repetitions of a gradient echo sequence to acquire data for a fraction of k-space. A magnetization recovery period is provided which allows T1 and T2 relaxation before the start of the next sequence cycle. The MP, data acquisition and magnetization recovery steps are repeated until a predetermined k-space volume is sampled.

Exploring lung function with hyperpolarized 129Xe nuclear magnetic resonance

With the use of polarization‐transfer pulse sequences and hyperpolarized 129Xe NMR, gas exchange in the lung can be measured quantitatively. However, harnessing the inherently high sensitivity of this technique as a tool for exploring lung function requires a fundamental understanding of the xenon gas‐exchange and diffusion processes in the lung, and how these may differ between healthy and pathological conditions. Toward this goal, we employed NMR spectroscopy and imaging techniques in animal models to investigate the dependence of the relative xenon gas exchange rate on the inflation level of the lung and the tissue density. The spectroscopic results indicate that gas exchange occurs on a time scale of milliseconds, with an average effective diffusion constant of about 3.3 × 10−6cm2/s in the lung parenchyma. Polarization‐transfer imaging pulse sequences, which were optimized based on the spectroscopic results, detected regionally increased gas‐exchange rates in the lung, indicative of increased tissue density secondary to gravitational compression. By exploiting the gas‐exchange process in the lung to encode physiologic parameters, these methods may be extended to noninvasive regional assessments of lung‐tissue density and the alveolar surface‐to‐volume ratio, and allow lung pathology to be detected at an earlier stage than is currently possible. Magn Reson Med 51:676–687, 2004.

NMR of hyperpolarized 129Xe in the canine chest: spectral dynamics during a breath-hold

One of the major goals of hyperpolarized‐gas MR imaging has been to obtain 129Xe dissolved‐phase images in humans. Since the dissolved‐phase signal is much weaker than the gas‐phase signal, highly optimized MR pulse sequences are required to obtain adequate images during a single breath‐hold. In particular, a solid understanding of the temporal dynamics of xenon as it passes from the lung gas spaces into the parenchyma, the blood and other downstream compartments is absolutely essential. Spectroscopy experiments were performed in the canine chest to elucidate the behavior of xenon exchange in the lung. The experiments covered a time range from 1 ms to 9 s and therefore considerably extend the data currently available in the literature. It was found that the integrals of the dissolved‐phase resonances approached plateau values within approximately 200 ms, and then increased again after approximately 1 s. This behavior suggests an early saturation of the parenchyma before xenon reaches downstream compartments. Mono‐exponential recovery curves with time constants on the order of 100 ms were fit to the data. These results potentially provide information on several underlying physiological parameters of the lung, including the parenchymal and blood volumes as well as the diffusion properties of lung tissue. Copyright

Assessment of lung development using hyperpolarized helium-3 diffusion MR imaging.

To determine whether hyperpolarized helium‐3 (HHe) diffusion MR can detect the expected enlargement of alveoli that occurs with lung growth during childhood.

Model-based boundary estimation of complex objects using hierarchical active surface templates

A method for the segmentation of complex, three-dimensional objects using hierarchical active surface templates is presented. The templates consist of one or more active surface models which are specified according to a priori knowledge about the expected shape and location of the desired object. This allows complex objects to be naturally modeled as collections of simple subparts which are geometrically constrained. The template is adaptively deformed by the three-dimensional image data in which it is initialized such that the template boundaries are brought into correspondence with the assumed image object. An external energy field is developed based on a vector distance transform such that the surfaces are deformed according to object shape. The method is demonstrated by the segmentation of the human brain from three-dimensional magnetic resonance images of the head given an a priori model of a normal brain.