Open-Access, Low-Magnetic-Field MRI System for Lung Research

An open-access magnetic resonance imaging (MRI) system is being developed for use in research on orientational/gravitational effects on lung physiology and function. The open-access geometry enables study of human subjects in diverse orientations. This system operates at a magnetic flux density, considerably smaller than the flux densities of typical other MRI systems, that can be generated by resistive electromagnet coils (instead of the more-expensive superconducting coils of the other systems). The human subject inhales air containing He-3 or Xe-129 atoms, the nuclear spins of which have been polarized by use of a laser beam to obtain a magnetic resonance that enables high-resolution gas space imaging at the low applied magnetic field. The system includes a bi-planar, constant-current, four-coil electromagnet assembly and associated electronic circuitry to apply a static magnetic field of 6.5 mT throughout the lung volume; planar coils and associated circuitry to apply a pulsed magnetic-field-gradient for each spatial dimension; a single, detachable radio-frequency coil and associated circuitry for inducing and detecting MRI signals; a table for supporting a horizontal subject; and electromagnetic shielding surrounding the electromagnet coils

Hyperpolarized Xe-129 MRI: A viable functional lung imaging modality?

The majority of researchers investigating hyperpolarized gas MRI as a candidate functional lung imaging modality have used He-3 as their imaging agent of choice rather than Xe-129. This preference has been predominantly due to, He-3 providing stronger signals due to higher levels of polarization and higher gyromagnetic ratio, as well as its being easily available to more researchers due to availability of polarizers (USA) or ease of gas transport (Europe). Most researchers agree, however, that hyperpolarized Xe-129 Will ultimately emerge as the imaging agent of choice due to its unlimited supply in nature and its falling cost. Our recent polarizer technology delivers vast improvements in hyperpolarized Xe-129 output. Using this polarizer, we have demonstrated the unique property of xenon to measure alveolar surface area noninvasively. In this article, we describe our human protocols and their safety, and our results for the measurement of the partial pressure of pulmonary oxygen (pO(2)) by observation of Xe-129 signal decay. We note that the measurement of pO(2) by observation of Xe-129 signal decay is more complex than that for He-3 because of an additional signal loss mechanism due to interphase diffusion of Xe-129 from alveolar gas spaces to septal tissue. This results in measurements of an equivalent pO(2) that accounts for both traditional T-1 decay from pO(2) and that from interphase diffusion. We also provide an update on new technological advancements that form the foundation for an improved compact design polarizer as well as improvements that provide another order-of-magnitude scale-up in xenon polarizer output. (c) 2007 Elsevier Ireland Ltd. All rights reserved

Human pulmonary imaging and spectroscopy with hyperpolarized Xe-129 at 0.2T

Rationale and Objectives: Using a novel Xe-129 polarizer with high throughput (1-2 L/hour) and high polarization (similar to 55%), our objective was to demonstrate and characterize human pulmonary applications at 0.2T. Specifically, we investigated the ability of 129Xe to measure the alveolar surface area per unit volume of gas, S-A/V-gas. Materials and Methods: Variable spin echo time (TE) gradient and radiofrequency (RF) echoes were used to obtain estimates of the lung\u27s contribution to both T-2* and T-2. Standard multislice ventilation images were obtained and signal-to-noise ratio (SNR) determined. Whole-lung, time-dependent measurements of Xe-129 diffusion from gas to septal tissue were obtained with a chemical shift saturation recovery (CSSR) method. Four healthy subjects were studied, and the Butler et al CSSR formalism (J Phys Condensed Matter 2002; 14:L297-L304) was used to calculate S-A/V-gas. A single-breath version of the xenon transfer contrast (SB-XTC) method was implemented and used to image Xe-129 diffusion between alveolar gas and septal tissue. A direct comparison of CSSR and SB-XTC was performed. Results: T-2* = 135 +/- 29 ms amd T-2 = 326.2 +/- 9.5 ms. Maximum SNR = 36 for ventilation images from inhalation of IL 86% Xe-129 and voxel volume = 0.225 mL. CSSR analysis showed S-A/V-gas decreased with increasing lung volume in a manner very similar to that observed from histology measurements; however, the absolute value of S-A/V-gas was similar to 40% smaller than histology values. SB-XTC images in different postures demonstrate gravitationally dependent values. Initial comparison of CSSR with XTC showed fairly good agreement with expected ratios. Conclusions: Hyperpolarized Xe-129 human imaging and spectroscopy are very promising methods to provide functional information about the lung

Quantitative 31P NMR Spectroscopy and 1H MRI Measurements of Bone Mineral and Matrix Density Differentiate Metabolic Bone Diseases in Rat Models

In this study, bone mineral density (BMD) of normal (CON), ovariectomized (OVX) and partially nephrectomized (NFR) rats was measured by 31 P NMR spectroscopy; bone matrix density was measured by 1 H water- and fat-suppressed projection imaging (WASPI); and the extent of bone mineralization (EBM) was obtained by the ratio of BMD/bone matrix density. The capability of these MR methods to distinguish the bone composition of the CON, OVX and NFR groups was evaluated against chemical analysis (gravimetry). For cortical bone specimens, BMD of the CON and OVX groups was not significantly different; BMD of the NFR group was 22.1% (by 31 P NMR) and 17.5% (by gravimetry) lower than CON. For trabecular bone specimens, BMD of the OVX group was 40.5% (by 31 P NMR) and 24.6% (by gravimetry) lower than CON; BMD of the NFR group was 26.8% (by 31 P NMR) and 21.5% (by gravimetry) lower than CON. No significant change of cortical bone matrix density between CON and OVX was observed by WASPI or gravimetry; NFR cortical bone matrix density was 10.3% (by WASPI) and 13.9% (by gravimetry) lower than CON. OVX trabecular bone matrix density was 38.0% (by WASPI) and 30.8% (by gravimetry) lower than CON, while no significant change in NFR trabecular bone matrix density was observed by either method. The EBMs of OVX cortical and trabecular specimens were slightly higher than CON but not significantly different from CON. Importantly, EBMs of NFR cortical and trabecular specimens were 12.4% and 26.3% lower than CON by 31 P NMR/WASPI, respectively; and 4.0% and 11.9% lower by gravimetry. Histopathology showed evidence of osteoporosis in the OVX group and severe secondary hyperparathyroidism (renal osteodystrophy) in the NFR group. These results demonstrate that the combined 31 P NMR/WASPI method is capable of discerning the difference in EBM between animals with osteoporosis and those with impaired bone mineralization

Skeletal Muscle Phosphocreatine Recovery after Submaximal Exercise in Children and Young and Middle-Aged Adults

Context: Elderly subjects have reduced mitochondrial function. However, it remains unclear whether the decline in mitochondrial function begins earlier in the life span