13C-NMR glutamate isotopomer analysis, pioneered by Malloy and colleagues at the University of Texas-Southwestern (Malloy et al. 1990), is a powerful method for the study of substrate selection and utilization in biological systems. It is also based on measurements of ¹³C-label incorporation from ¹³C-labeled substrates into glutamate. However, instead of determining the time course of enrichment, the method is based on analyzing the complex line-splitting pattern of ¹³C-glutamate resonances observed in high-resolution ¹³C-NMR spectra of tissue or cell extracts. This approach is clearly invasive in that it requires the preparation of tissue extracts; however, it has several advantages over traditional radioisotope methods, including the fact that the contributions of up to four different substrates to energy production can be determined in a single experiment. The analysis of spectra from simple experiments can be carried out by hand readily. The analysis of more complex experiments is simplified by software developed by Mark Jeffrey from the University of Texas-Southwestern and is available free of charge. (For more information, their Website is listed in Table 1.) This approach has been used to study intermediary metabolism in a variety of systems, including cells in culture (Hall et al. 2001), heart (Chatham and Forder 1997; Chatham et al. 1999a,b; Jeffrey et al. 1995), skeletal muscle (Bertocci and Lujan 1999; Bertocci et al. 1997), and vascular smooth muscle (Allen and Hardin 1998).

Although the focus of many ¹³C-NMR studies is on glycolytic and oxidative metabolism, it is possible to investigate other metabolic pathways by the appropriate choice of ¹³C-labeled precursors. For example, as shown in Figure 6, glutathione synthesis was measured in a line of adriamycin-resistant human mammary adenocarcinoma cells (MCF7adr). The cells had been grown on a collagen sponge matrix and perfused as previously described (Gamcsik et al. 1996). After switching to perfusion medium containing [3,3'-¹³C₂]-cystine, resonances from ¹³C-labeled glutathione began to appear, which reflected the metabolism of the ¹³C-labeled cystine through the gamma-glutamyl cycle and the resulting synthesis of glutathione. From such experiments, it is possible to determine the rate of glutathione synthesis and turnover. Because glutathione is a major intracellular antioxidant that plays a central role in the protection of cells from oxidative stress, it is possible that alterations in glutathione metabolism may contribute to different sensitivities to drug therapy or radiation. Thus, by judiciously choosing ¹³C-labeled precursors, it is possible to use ¹³C-NMR spectroscopy to determine metabolic fluxes noninvasively through a variety of different metabolic pathways.

The most sensitive NMR nucleus is the proton ¹H. Given the large number of metabolites that contain protons, one would anticipate that ¹H-NMR spectroscopy would be widely used to study metabolism in biological samples; however, several factors have limited its widespread use. The main obstacle in the use of ¹H-NMR spectroscopy is that the resonances from water and lipids are several orders of magnitude greater than that of the potential metabolites of interest. The first step in obtaining a ¹H-NMR spectrum of metabolites in biological systems is the suppression of the very intense water signals. A variety of methods for achieving this suppression have been documented (Duyn et al. 1993; Ernst and Hennig 1995; Moonen et al. 1989); however, these methods are usually motion sensitive and thus limited to stationary samples. Even with excellent water suppression, the presence of large lipid signals can also obscure much of the spectral region of interest. Consequently, ¹H-NMR spectroscopy has been applied primarily in the brain (Anderson et al. 1994; Barker et al. 1993, 1994; Monsein et al. 1993) and prostate (Kurhanewicz et al. 1993; Narayan and Kurhanewicz 1992; Narayan et al. 1989), which are relatively stationary and have negligible endogenous lipids. To a lesser extent, ¹H-NMR spectroscopy has also been used in metabolic studies of perfused cells (Pilatus et al. 1997) and tumors (Bhujwalla et al. 1996; Shungu et al. 1992). Among the few investigations of the heart that have used ¹H-NMR spectroscopy, most have focused on investigations of lipid metabolism (Balschi et al. 1992, 1997). However, a few reports have documented the ability to measure other metabolites in the heart with this technique (Bottomley et al. 1997; Ugurbil et al. 1984).

In ¹H spectra, besides the large water resonance, which is usually suppressed, the major resonances observed in the brain are NAA, creatine, and choline. Lactate is evident in many diseases and can be detected very early in stroke models (Monsein et al. 1993). NAA in the brain is thought to be present predominantly in neuronal cell bodies, where it acts as a neuronal marker; and choline increases are indicative of increased membrane synthesis. Future work may result in detection of smaller resonances arising from lower-concentration metabolites, and the limits of detection are being explored at increasingly higher level field strengths.

Imaging

As with spectroscopy, the range of studies used for MRI is very large. In this section, examples of these capabilities are given in the context of this review. For the most part, the applications of MRI on animals have paralleled similar developments in clinical studies, and both have been intimately tied to technological developments. Magnetic resonance (MR¹) technology is still evolving and continues to operate with increasingly high levels of field strength. Ancillary hardware, which includes radiofrequency and gradient coils used for spatial encoding, are still undergoing improvements; consequently, the applications of MRI continue to grow and evolve.

Like clinical MR studies, MR on animal models is immediately effective as a standard radiological technique that, compared with other modalities, provides exquisite anatomical pictures of soft tissues. The application of these images for assessing tissue structure and damage is obvious. The images of animals shown in Figure 7 indicate this potential. It is important to restate that the size of the radiofrequency coil used to detect the NMR signal dictates the signal-to-noise ratio that can be attained; thus, higher levels of resolutions are feasible on smaller samples. Additionally, animal studies have often utilized excised tissues to provide improved access and control. The examples in Figure 7 indicate the wide applicability of MRI on samples as small as single cells (spatial resolutions of 10-20 μm) through excised (fixed or perfused) tissues (with resolutions of 20-100 μm), through live whole animal models (resolutions of 100-300 μm). The figure also includes two examples of pathology in rats. The choice of animal model of course is dependent on the biological questions being addressed. Mice, rats, and rabbits are commonly used; however, in principle, any animal can be imaged. This principle has also led to MRI's use as a diagnostic tool in clinical veterinary medicine; however, this potential is beyond the scope of this article and is therefore not explored.

Signal differences (contrast) observed in images between tissues are caused by variations in tissue water content, T₁ and T₂. By varying the imaging sequence, the image contrast can be controlled and varied, allowing MRI to discern a wide range of pathologies, including stroke (ischemia) from blood vessel rupture or blockage, cancer, multiple sclerosis, and muscle atrophy. Image contrast can also be improved with the use of injectable contrast agents, mainly Gd-diethylenetriamine penta-acetic acid, which has the effect of changing the local magnetic field (hence, T₁ or T₂ in the tissue), leading to changes in signal and contrast. Contrast agents, in particular, are especially effective in highlighting regions in the brain where the blood brain barrier has broken down, thus identifying tumors that would otherwise be difficult to see. By using multislice or volume acquisition MR imaging sequences, three-dimensional information may be obtained. Thus, the size and extent of normal or pathological tissues can be extracted and followed over time in multiple studies.

The amount of information required will dictate the data acquisition time required. The higher the spatial resolution required, the larger the sample volume and number of different sequences with different contrast required, and the longer a single study will be. These choices are modulated by the temporal resolution required and the ability to maintain the animal under anesthesia (which in turn is related to the health of the animal). Although the length of studies can range from minutes to many hours, depending on the specific nature of the experiment, typical total data acquisition times are approximately 1 hr. The sensitivity of the animal to repeated anesthesia will also affect the time difference and frequency of subsequent studies on the same animal.

MR signals can be modulated to encode information other than T₁, T₂ and proton density in many ways, and these methodologies are in various stages of development. Although some are as close to becoming routine on animal systems as they are on clinical instruments, we believe that with MR technology still improving, the extent to which these techniques can be applied is still evolving and is, in fact, the focus of much of the current developmental research. Furthermore, because of commercial issues, the drive to develop animal machines is understandably not as strong as the drive to develop human clinical instrumentation; thus, technology for animal applications lags behind. Although the increase in field strengths helps improve the signal-to-noise ratio, this increase entails new challenges that must also be met. T₁ and, to a smaller extent, T₂ change with field strength so that the image sequence timings are not the same and must be reevaluated. Artifacts from magnetic field inhomogeneities and sample-induced inhomogeneities (called susceptibility effects) become significant at higher fields and cause image distortions that must be addressed. Radiofrequency coil design and power issues also require much further investigation. In these areas, we are still in a growing phase of MR technology, and we are certain there are surprises yet to come.

MR as described above is rarely quantified in human studies, although some degree of quantification is more prevalent in animal research. Additionally, we do not yet understand the origins of the signals and how they change in tissues---the development of mathematical and physical models is an area of strong research at present. This research, especially using a variety of physical models, will be most effectively pursued on animals systems in which real controls are feasible, and the system may be more accurately perturbed and controlled. It is our long-term hope that MR may to a large extent become quantitative, ultimately leading to improved sensitivity and specificity for the technique. An overview of evolving techniques applied to novel research areas can be found in Gilles (1994), and references to the techniques described briefly below can be found in this and the MRI texts referred to in the Introduction.

As the stability of MR technology has improved, so has the sensitivity of the measurements that can be made. One of the first advances was the realization that moving spins cause the MR signals to change (a spin that moves is not properly rephased by the imaging sequence), which leads to a signal loss that is proportional to the distance the spin has moved. One of the largest (and hence easiest to measure) "movement of spins" arises from blood flow. Images can be sensitized to the blood flow to generate MR angiograms. MR angiography is relatively straightforward, and its clinical use is increasing, particularly as a screening technique. However, it is not yet preferred over the gold standard of invasive x-ray angiography. One of the limiting factors is that spatial resolution restricts the examination to the larger vessels. The method is also sensitive to motion artifacts; thus, application of MR angiography to the heart is problematic. Nevertheless, MR angiography is gaining wider acceptance and is being applied not only to the brain, but also to limbs and the body.

In principle, any moving spin can be encoded in this way; however, the smaller the motion, the less the signal change and the greater the susceptibility to error that will arise from larger confounding motions (such as the animal moving), which could be misinterpreted. Despite these difficulties, the MR signal can be made sensitive to water diffusion. An early application of the technique involved an animal model of stroke in which an ischemic region is clearly well defined in a diffusion-weighted image before any other signal changes can be detected (Lebihan 1995; Mosley et al. 1990). Furthermore, with appropriate encoding, the preferential direction of water diffusion can be quantified, leading to diffusion tensor imaging. These diffusion images are currently being intensively investigated because the anisotropic diffusion thus measured in some way represents the underlying tissue structure. At the time of this writing, the research goal is to identify these structures. However, in more simple cases, the cause of the diffusion anisotropy is clear, leading to the generation of three-dimensional maps of nerve fibers that can be used to track fiber bundles in the central nervous system. Diffusion tensor MRI has also been used to measure fiber organization in the isolated perfused heart and has demonstrated distinct advantages over traditional histological methods for obtaining similar information (Scollan et al. 1998).

MR images also can be sensitized to other physical processes and lead to the generation of, for example, temperature maps (Jolesz et al. 1988; Mulkern et al. 1998; Wang and Plewes 1999), current density maps (Beravs et al. 1997; Bodurka et al. 1999; Joy et al. 1989, 1999), and pH maps (van Sluis et al. 1999). However, great care must be taken in the collection and interpretation of these data. Essentially, they all rely on the same information change in the NMR signal (phase changes); thus, it must be clear that the phase changes result from the variable of interest and not other factors (in particular motion). For the most part, the utility of these methods is still being evaluated.

The development of so-called functional MRI (fMRI) has generated great interest and has stimulated a flurry of activity in the neurological sciences. During the early1990s, when MR systems were sufficiently stable and sensitive, it was realized that MR signals were sensitive to local magnetic field changes induced by the change of oxyhemoglobin to deoxyhemoglobin, compounded by blood flow changes when the brain tissue is required to work. Surprisingly, these signal changes can be observed in the brain in local tissues that undergo activation; for example, image contrast is generated in the occipital cortex when the eyes are visually stimulated. Similar localized brain MR signal changes can be observed after a variety of stimulations, including motor (Baudendistel et al. 1996; Deiber et al. 1999; Miezin et al. 2000; Sadato et al. 1997), verbal (Ojemann et al. 1998; Reichle et al. 2000), acoustic (Belin et al. 2000; Giraud et al. 2000), and emotional stimulation (Schmahmann and Sherman 1998; Sprengelmeyer et al. 1998; Teasdale et al. 1999). These observations have ignited the neurological sciences offering the potential to visualize brain function directly, noninvasively, and repeatedly. However, the interpretation of the subtle signal changes, a few percentages at best, is fraught with danger; and the development of animal models of fMRI is thus desirable, if not essential. However, the use of animal models in fMRI studies is difficult in terms of developing meaningful stimulation paradigms, especially because the animal most often must be anesthetized, which often negates the activation effects. Consequently, although fMRI development in animal models offers great potential for elucidating the mechanisms of basic brain function, as well as validating fMRI against invasive techniques, it is still a "work in progress" rather than a fully developed technique in routine use.

As stated above, the ¹H nucleus is most often used in MRI because the relative signal-to-noise ratio is very large (water in molar quantities) compared with signals from other nuclei (millimeters or less). Consequently, the spatial resolution that can be achieved using other nuclei is very poor. Nevertheless, there have been some attempts to use ²³Na, ³¹P, and ¹³C with imaging techniques. Although we are not yet aware of any significant application of these methodologies, it is still early. Several investigators have speculated that very high fields may have their most significant applications through the studies of nuclei other than the hydrogen nucleus.

Finally, differences between NMR spectroscopy and MRI become less distinct when it is realized that spatially localized spectroscopy is feasible. Although many techniques exist, the most effective techniques involve using imaging methodologies to localize single or multiple regions of tissue spatially and to collect spectra from them. More often it is realized that MR techniques offer the possibility of obtaining structural (MRI), physiological (e.g., diffusion, flow, fMRI), and metabolic (spectroscopy) information on the same tissue, if not simultaneously, at least in an interleaved fashion. The subsequent ability to look at the relations between function, structure, metabolism, and mechanics demonstrates both the flexibility and great potential of MRI.

Simply stated, the use of NMR spectroscopy and imaging as part of a biomedical research program can significantly reduce the number of animals required for a specific project. For example, consider a study in which the goal is to determine the changes in concentration of ATP every 6 min in an isolated perfused organ in response to a physiological stress such as ischemia during a period of 1 hr. Assume the aim is to investigate some new therapy or treatment designed to minimize the effects of the stress, and there will be two experimental groups---control and treatment. Traditional biochemical methods would require measuring individual samples at each time point. Thus, if we require a sample size of five in each of the two experimental groups, we need a total of 100 animals for the study (2 groups ´ 5 samples ´ 10 time points = 100). In contrast, if we use ³¹P-NMR spectroscopy, we require only 10 animals because all of the time points can be measured in each sample (2 groups ´ 5 samples = 10). This total would represent a reduction of 90% in the number of animals required for that project.

The same argument can be used when considering the use of NMR imaging. Consider as an example the impact of knocking out a specific gene on a specific organ system in mice. Using traditional methods, it would be necessary to sacrifice a series of animals at several arbitrary time points to harvest, fix, and examine histologically the organ of interest. However, using MR imaging techniques, it would be possible to monitor the mice as often as one wished without ever having to sacrifice a single animal. Clearly, in most cases, the organs or tissues of interest would be harvested for more detailed analysis; however, by using MRI as a noninvasive imaging tool, it is possible to select specific time points that will yield the most information. Currently, ultrasound is the only other method that is routinely used to image mice noninvasively; and although it is a relatively cheap and quick method, it does not provide the detailed anatomical information that can be obtained with MRI.

The examples cited above have focused on the use of isolated organs or small animals; however, NMR imaging and spectroscopy may have even greater impact in studies on larger animals. The cost of purchase and husbandry of larger animals such as dogs and primates has increased dramatically. Clearly, the ability to perform repeated, noninvasive measurements of structure, function, and metabolism in such valuable animals would represent a major cost savings. Furthermore, when using NMR methods, the measurements are made repeatedly in the same sample; thus, the statistical power of the study should also improve. Consequently, in cases in which differences between groups are small, the use of NMR techniques would decrease the number of samples required to obtain statistical significance compared with more traditional methods. Therefore, by including NMR techniques in a biomedical research program, it should be possible to reduce significantly the number of animals used in research thereby also decreasing experimental costs.

The development of stronger NMR magnets will continue at least in the near future. For example, during 2000, a horizontal 11.7-T, 40-cm bore NMR system (first in the world) and a 17.6-T, 9-cm bore magnet (one of three in the world) have been installed at the Advanced Magnetic Resonance Imaging and Spectroscopy facility at the University of Florida, Gainesville, Florida. In addition, the National High Magnetic Field Laboratory in Tallahassee, Florida, is presently constructing the world's first 21.1-T, 11-cm bore magnet. Although the widespread use of such specialized instruments is limited, they will provide a platform for improving our understanding of the fundamental biophysical processes that underlie the characteristics of NMR signals in biological systems. Technological developments, particularly in radiofrequency coil design and high field imaging techniques, will be required to use these instruments effectively so that their potential can be fully realized.

Some potential exists for the development of so-called niche magnets and systems for animal research. Although more of an issue in human studies, real-time interventional studies require easier access to the sample under study than presently feasible with conventional closed cylinder geometry. Open magnet geometry's (e.g., General Electric's [Milwaukee, Wisconsin] double doughnut-shaped system,) or other C-shaped magnets afford some degree of open access and may be applied in animal studies. Additionally, Bruker Instruments Ltd. (Billerica, Massachusetts) has determined a need for high-throughput and low-cost MR studies for the rapid MR evaluation of relatively large numbers of animals aimed at the pharmaceutical industry. In response, they have developed a mid-field low cost (approximately $500K) system designed to perform basic MR scans on rats and mice in just a few minutes. Although more sophisticated and time-consuming MR measurements are thus precluded, the hope is that this use will promote the viability of using MR for drug testing. The practicality and utility of this approach are being evaluated.

Probably the largest expansion in the use and utility of MR will be explored through a multimodality approach. Small-scale CT and PET instruments (called microPET; Cherry and Gambhir 2001) have become available, and there is considerable interest in combining these imaging modalities with MR. The superior spatial resolution of MR already provides localization for PET, CT, and radiation therapy through image overlays and stereotactic procedures. Further integration may be warranted through the construction of multimodality instruments.

We believe the development and application of MR techniques will continue along the lines indicated in this review, particularly through efforts to increase the functional information MR can provide and to examine relations between structure, function, and metabolism. However, some of these areas require the following additional comments.

Our knowledge regarding the regulation of gene expression and our ability to manipulate gene expression in cells and animals are increasing rapidly. As a result, there will be an escalating need to evaluate the relation between alterations in gene and protein expression with cellular function. Such investigations will necessitate the quantitative measurement of a wide range of physiological and metabolic processes in intact biological systems. Thus, in the future, the demands for noninvasive, quantitative measurements of anatomy, physiology, and metabolism in transgenic animals will provide additional impetus for the development and application of novel NMR techniques.

We expect that fMRI techniques, which offer great potential for understanding brain function and connectivity, will continue to be investigated. The successful development and exploration of animal models will be key to an understanding of these issues because they can be perturbed in a controlled fashion. Coupled with access to animal brain atlases presently being developed for availability on the Web, the relations between structure and function can be accurately explored.

Targeted agents are being developed for a variety of applications, and the most exciting are those developed to highlight a particular cell or tissue type (Aime et al. 2000; Kayyem JF et al. 1995; Loui et al, 2000; Sipe et al. 2000; Sipkins et al. 2000). These so-called "smart" contrast agents offer great potential for improving the specificity of MR techniques. However, intrinsic difficulties remain in making the agents nontoxic and particularly in the delivery of the agent. Most agents are restricted to the extracellular space that limits the information they can provide. Efforts are under way to construct agents that can enter particular cells, offering many possibilities for assessing function and detecting abnormal cell populations. Aspects of these studies lead to the concept of molecular imaging with MRI in which contrast agents are attached to molecules such as antibodies targeted to specific molecules and receptors (Sipkins et al., 2000). This kind of molecular imaging is analogous to that used in other diagnostic techniques such as PET (Phelps 2000a,b).

It is clear that MR is still an evolving technology, and a few more surprises are undoubtedly around the corner. Already, MRI is the most versatile and widely applicable imaging modality available today. The combination of MRI and NMR spectroscopy enables us to obtain information from the molecular level through cells, tissues, animal models, and humans. The necessity of animal models in research dictates the development of dedicated animal research systems. With proper use, MR offers the potential for greatly reducing the number of animals that would otherwise be required to move forward in our understanding of biological systems.

We thank Drs.Weiss and Gamcsik for providing Figures 5 and 6, respectively, and Drs. Forder, Beveniste, and Salmon for their contributions to Figure 7. This work has been supported in part by National Institutes of Health (NIH) grants HL48789 and HL67464, an American Heart Association grant-in-aid to J.C.C., and NIH grant NS36992 to S.J.B. Dr. Blackband also gratefully acknowledges the support of the University of Florida Brain Institute and the National High Magnetic Field Laboratory.

¹Abbreviations used in this article: ATP, adenosine triphosphate; CT, computer-assisted tomography; ECG, electrocardiogram; fMRI, functional magnetic resonance imaging; MR, magnetic resonance; MRI, magnetic resonance imaging; NAA, N-acetyl aspartate; NCRR, National Center for Research Resources; NIH, National Institues of Health; NMR, nuclear magnetic resonance; PCr, phosphocreatine; PET, positron emission tomography; P_i, inorganic phosphate; TCA cycle, tricarboxylic acid cycle.

Abragam A. 1961. Principles of Nuclear Magnetism. New York: Oxford University Press.

Ackerman JJ, Bore PJ, Gadian DG, Grove TH, Radda GK. 1980. N.m.r. studies of metabolism in perfused organs. Philos Trans R Soc Lond B Biol Sci 289:425-436.

Aime S, Botta M, Garino E, Crich SG, Giovenzana G, Pagliarin R, Palmisano G, Sisti M. 2000 Non-covalent conjugates between cationic polyamino acids and GdIII chelates: A route for seeking accumulation of MRI contrast agents at tumor targeting sites. Chem Eur J 6:2609-2617.

Allen TM, Hardin CD. 1998. Pattern of substrate utilization in vascular smooth muscle using ¹³C-isotopomer analysis of glutamate. Am J Physiol Heart Circ Physiol 275:H2227-H2235.

Alves PM, McKenna MC, Sonnewald U. 1995. Lactate metabolism in mouse brain astrocytes studied by ¹³C]NMR spectroscopy. Neuroreport 6:2201-2204.

Anderson JH, Strandberg JD, Wong DF, Conti PS, Barker PB, Blackband SJ, Hilton J, Natarajan TK, Dannals RF, Samphilipo MA,Magee CA, Burckhardt DD. 1994. Multimodality correlative study of canine brain tumors. Proton magnetic resonance spectroscopy, positron emission tomography, and histology. Invest Radiol 29:597-605.

Andrew ER, Bottomley PA, Hinshaw WS, Holland GN, Moore WS, Simaroj C. 1977. NMR images by the multiple sensitive point method: Application to larger biological systems. Phys Med Biol 22:971-974.

Askenasy N, Vivi A, Tassini M, Navon G. 1996. The relation between cellular sodium, pH and volumes and the activity of Na/H antiport during hypothermic ischemia: Multinuclear NMR studies of rat hearts. J Mol Cell Cardiol 28:589-601.

Balschi JA, Hai JO, Wolkowicz PE, Straeter-Knowlen I, Evanochko WT, Caulfield JB, Bradley E, Ku DD, Pohost GM. 1997. ¹H NMR measurement of triacylglycerol accumulation in the post-ischemic canine heart after transient increase of plasma lipids. J Mol Cell Cardiol 29:471-480.

Balschi JA, Hetherington HP, Pohost GM. 1992. Water-suppressed one-dimensional ¹H NMR spectroscopic imaging of myocardial metabolites in vivo. Magn Reson Med 25:180-186.

Barker PB, Blackband SJ, Chatham JC, Soher BJ, Samphilipo MA, Magee CA, Hilton JD, Strandberg JD, Anderson JH. 1993. Quantitative proton spectroscopy and histology of a canine brain tumor model. Magn Reson Med 30:458-464.

Barker PB, Breiter SN, Soher BJ, Chatham JC, Forder JR, Samphilipo MA, Magee CA, Anderson JH. 1994. Quantitative proton spectroscopy of canine brain: In vivo and in vitro correlations. Magn Reson Med 32:157-163.

Baudendistel K, Schad LR, Wenz F, Essig M, Schroder J, Jahn T, Knopp MV, Lorenz WJ. 1996. Monitoring of task performance during functional magnetic resonance imaging of sensorimotor cortex at 1.5 T. Magn Reson Imaging 14:51-58.

Belin P, Zatorre RJ, Lafaille P, Ahad P, Pike B. 2000. Voice-selective areas in human auditory cortex. Nature 403:309-312.

Beravs K, White D, Sersa I, Demsar F. 1997. Electric current density imaging of bone by MRI. Magn Reson Imaging 15:909-915.

Berden JA, Cullis PR, Hoult DI, McLaughlin AC, Radda GK, Richards RE. 1974. Frequency dependence of ³¹P NMR linewidths in sonicated phospholipid vesicles: Effects of chemical shift anisotropy. FEBS Lett 46:55-58.

Bertocci LA, Jones JG, Malloy CR, Victor RG, Thomas GD. 1997. Oxidation of lactate and acetate in rat skeletal muscle: Analysis by ¹³C-nuclear magnetic resonance spectroscopy. J Appl Physiol 83:32-39.

Bertocci LA, Lujan BF. 1999. Incorporation and utilization of [3-¹³C]lactate and [1,2-¹³C]acetate by rat skeletal muscle. J Appl Physiol 86:2077-2089.

Bhakoo KK, Williams IT, Williams SR, Gadian DG, Noble MD. 1996. Proton nuclear magnetic resonance spectroscopy of primary cells derived from nervous tissue. J Neurochem 66:1254-1263.

Bhujwalla ZM, Shungu DC, Chatham JC, Wehrle JP, Glickson JD. 1994. Glucose metabolism in RIF-1 tumors after reduction in blood flow: An in vivo ¹³C and ³¹P NMR study. Magn Reson Med 32:303-309.

Bhujwalla ZM, Shungu DC, Glickson JD. 1996. Effects of blood flow modifiers on tumor metabolism observed in vivo by proton magnetic resonance spectroscopic imaging. Magn Reson Med 36:204-211.

Blackband SJ. 1995. Introduction to the physical principles of NMR and MRI. In: Tempany C, ed. MR and Imaging of the Female Pelvis. St. Louis: Mosby-Year Book Inc. p 1-34.

Bloch F, Hansen WW, Packard M. 1946. The nuclear induction experiment. Phys Rev 70:474-485.

Bodurka J, Jesmanowicz A, Hyde JS, Xu H, Estkowski L, Li SJ. 1999. Current-induced magnetic resonance phase imaging. J Magn Reson 137:265-271.

Bottomley PA. 1989. Human in vivo NMR spectroscopy in diagnostic medicine: Clinical tool or research probe? Radiology 170(Pt 1):1-15.

Bottomley PA, Lee Y, Weiss RG. 1997. Total creatine in muscle: Imaging and quantification with proton MR spectroscopy. Radiology 204:403-410.

Brownell AL, Jenkins BG, Elmaleh DR, Deacon TW, Spealman RD, Isacson O. 1998. Combined PET/MRS brain studies show dynamic and long-term physiological changes in a primate model of Parkinson disease. Nat Med 4:1308-1312.

Burns SP, Cohen RD, Iles RA, Bailey RA, Desai M, Germain JP, Going TC. 1999. Zonation of gluconeogenesis, ketogenesis and intracellular pH in livers from normal and diabetic ketoacidotic rats: Evidence for intralobular redistribution of metabolic events in ketoacidosis. Biochem J 343(Pt 1):273-280.

Burt CT, Glonek T, Barany M. 1976a. Analysis of phosphate metabolites, the intracellular pH, and the state of adenosine triphosphate in intact muscle by phosphorus nuclear magnetic resonance. J Biol Chem 251:2584-2591.

Burt CT, Glonek T, Barany M. 1976b. Phosphorus-31 nuclear magnetic resonance detection of unexpected phosphodiesters in muscle. Biochemistry 15:4850-4853.

Cave AC, Ingwall JS, Friedrich J, Liao R, Saupe KW, Apstein CS, Eberli FR. 2000. ATP synthesis during low-flow ischemia: Influence of increased glycolytic substrate. Circulation 101:2090-2096.

Chacko VP, Aresta F, Chacko SM, Weiss RG. 2000. MRI/MRS assessment of in vivo murine cardiac metabolism, morphology, and function at physiological heart rates. Am J Physiol Heart Circ Physiol 279:H2218-H2224.

Chatham JC, Cousins JP, Glickson JD. 1990. The relationship between cardiac function and metabolism in acute adriamycin-treated perfused rat hearts studied by ³¹P and ¹³C NMR spectroscopy. J Mol Cell Cardiol 22:1187-1197.

Chatham JC, Forder JR. 1997. Relationship between cardiac function and substrate oxidation in hearts of diabetic rats. Am J Physiol Heart Circ Physiol 273(Pt 2):H52-H58.

Chatham JC, Forder JR, Glickson JD, Chance EM. 1995. Calculation of absolute metabolic flux and the elucidation of the pathways of glutamate labeling in perfused rat heart by ¹³C NMR spectroscopy and nonlinear least squares analysis. J Biol Chem 270:7999-8008.

Chatham JC, Gao ZP, Bonen A, Forder JR. 1999a. Preferential inhibition of lactate oxidation relative to glucose oxidation in the rat heart following diabetes. Cardiovasc Res 43:96-106.

Chatham JC, Gao ZP, Forder JR. 1999b. Impact of 1 wk of diabetes on the regulation of myocardial carbohydrate and fatty acid oxidation. Am J Physiol Endocrin Metab 277(Pt 1):E342-E351.

Chavin K, Yang S, Lin HZ, Chatham JC, Chacko VP, Hoek J, Chen C-H, Huang C-C, Wu T-C, Lane MD, Diehl AM. 1999. Obesity induces expression of uncoupling protein-2 in hepatocytes and promotes liver ATP depletion. J Biol Chem 274:5692-5700.

Cherry SR, Gambhir SS. 2001. Use of positron emission tomography in animal research. ILAR J 42:219-232.

Cohen SM, Rognstad R, Shulman RG, Katz J. 1981. A comparison of ¹³C nuclear magnetic resonance and ¹⁴C tracer studies of hepatic metabolism. J Biol Chem 256:3428-3432.

Cohen SM, Werrmann JG, Tota MR. 1998. ¹³C NMR study of the effects of leptin treatment on kinetics of hepatic intermediary metabolism. Proc Natl Acad Sci U S A 95:7385-7390.

Colet JM, Makos JD, Malloy CR, Sherry AD. 1998. Determination of the intracellular sodium concentration in perfused mouse liver by ³¹P and ²³Na magnetic resonance spectroscopy. Magn Reson Med 39:155-159.

Constantinidis I, Chatham JC, Wehrle JP, Glickson JD. 1991. In vivo ¹³CNMR spectroscopy of glucose metabolism of RIF-1 tumors. Magn Reson Med 20:17-26.

Cortez-Pinto H, Chatham JC, Chacko VP, Arnold C, Rashid A, Diehl AM. 1999. Alterations in liver ATP homeostasis in human nonalcoholic steatohepatitis---A pilot study. JAMA 282:1659-1664.

Dautry C, Conde F, Brouillet E, Mittoux V, Beal MF, Bloch G, Hantraye P. 1999. Serial ¹H-NMR spectroscopy study of metabolic impairment in primates chronically treated with the succinate dehydrogenase inhibitor 3-nitropropionic acid. Neurobiol Dis 6:259-268.

Dautry C, Vaufrey F, Brouillet E, Bizat N, Henry PG, Conde F, Bloch G, Hantraye P. 2000. Early N-acetylaspartate depletion is a marker of neuronal dysfunction in rats and primates chronically treated with the mitochondrial toxin 3-nitropropionic acid. J Cerebr Blood Flow Metab 20:789-799.

Deiber MP, Honda M, Ibanez V, Sadato N, Hallett M. 1999. Mesial motor areas in self-initiated versus externally triggered movements examined with fMRI: Effect of movement type and rate. J Neurophysiol 81:3065-3077.

Dowd TL, Gupta RK. 1993. NMR studies of the effect of hyperglycemia on intracellular cations in rat kidney. J Biol Chem 268:991-996.

Dowd TL, Gupta RK. 1995. NMR studies of the effect of Mg²⁺ on post-ischemic recovery of ATP and intracellular sodium in perfused kidney. Biochim Biophys Acta 1272:133-139.

Duyn JH, Gillen J, Sobering G, van Zijl PC, Moonen CT. 1993. Multisection proton MR spectroscopic imaging of the brain. Radiology 188:277-282.

Ernst RR, Bodenhausen G, Wokaun A. 1987. Principles of Nuclear Magnetic Resonance in One and Two Dimensions. Oxford: Clarendon Press.

Ernst T, Hennig J. 1995. Improved water suppression for localized in vivo ¹H spectroscopy. J Magn Reson B 106:181-186.

Farrar TC, Becker ED. 1971. Pulse and Fourier Transform NMR. New York: Academic Press.

Foster MA, Hutchinson JMS. 1987. Practical NMR Imaging. Oxford: IRL Press.

Freeman DM, Barker PB, Parivar F, Benninghoven S, Jones LW, Moress EA, Ross B. 1989. Differentiation between renal cortex and medulla in the response to hypotension using localized ³¹P magnetic resonance spectroscopy. Transplantation 48:202-209.

Gadian D. 1995. NMR and Its Applications to Living Systems. New York: Oxford University Press.

Gamcsik MP, Forder JR, Millis KK, McGovern KA. 1996. A versatile oxygenator and perfusion system for magnetic resonance studies. Biotech Bioeng 49:348-354.

Gamcsik MP, Millis KK, Colvin OM. 1995. Noninvasive detection of elevated glutathione levels in MCF-7 cells resistant to 4-hydroperoxycyclophosphamide. Cancer Res 55:2012-2016.

Garlick PB, Radda GK, Seeley PJ. 1977. Phosphorus NMR studies on perfused heart. Biochem Biophys Res Commun 74:1256-1262.

Gilles RJ. 1994. NMR in Physiology and Biomedicine. San Diego: Academic Press.

Giraud AL, Lorenzi C, Ashburner J, Wable J, Johnsrude I, Frackowiak R, Kleinschmidt A. 2000. Representation of the temporal envelope of sounds in the human brain. J Neurophysiol 84:1588-1598.

Gruetter R, Seaquist ER, Kim S, Ugurbil K. 1998a. Localized in vivo ¹³C-NMR of glutamate metabolism in the human brain: Initial results at 4 Tesla. Dev Neurosci 20:380-388.

Gruetter R, Ugurbil K, Seaquist ER. 1998b. Steady-state cerebral glucose concentrations and transport in the human brain. J Neurochem 70:397-408.

Gupta RK, Dowd TL, Spitzer A, Barac-Nieto M. 1989. ²³Na, ¹⁹F, ³⁵Cl and ³¹P multinuclear nuclear magnetic resonance studies of perfused rat kidney. Ren Physiol Biochem 12:144-160.

Hall JL, Chatham JC, Eldar-Finkelman H, Gibbons GH. 2001. Upregulation of glucose metabolism during intimal lesion formation is coupled to the inhibition of vascular smooth muscle cell apoptosis: Role of GSK3b. Diabetes (In press).

Hardin CD, Kushmerick MJ and Roberts TM. 1995. Vascular smooth muscle glycogen metabolism studied by ¹³C-NMR. J Vasc Res 32:293-300.

Harris RK. 1986. Nuclear Resonance Spectroscopy. London: Longmans.

Herman GT. 1980. Image Reconstruction from Projections: The Fundamentals of Computerized Topography. Computer Science and Applied Mathematics. New York: Academic Press.

Hinshaw WS, Bottomley PA, Holland GN. 1977. Radiographic thin-section image of the human wrist by nuclear magnetic resonance. Nature 270:722-723.

Hollis DP, Nunnally RL, Jacobus WE, Taylor GJ. 1977. Detection of regional ischemia in perfused beating hearts by phosphorus nuclear magnetic resonance. Biochem Biophys Res Commun 75:1086-1091.

Hoult DI, Busby SJ, Gadian DG, Radda GK, Richards RE, Seeley PJ. 1974. Observation of tissue metabolites using ³¹P nuclear magnetic resonance. Nature 252:285-287.

Hyder F, Rothman DL, Mason GF, Rangarajan A, Behar KL, Shulman RG. 1997. Oxidative glucose metabolism in rat brain during single forepaw stimulation: A spatially localized ¹H[¹³C] nuclear magnetic resonance study. J Cereb Blood Flow Metab 17:1040-1047.

Jacobus WE, Taylor GJ, Hollis DP, Nunnally RL. 1977. Phorphorus nuclear magentic resonance of perfused working rat hearts. Nature 265:756-758.

Jeffrey FMH, Diczku V, Sherry AD, Malloy CR. 1995. Substrate selection in the isolated working rat heart: Effects of reperfusion, afterload and concentration. Basic Res Cardiol 90:388-396.

Jolesz FA, Bleier AR, Jakab P, Ruenzel PW, Huttl K, Jako GJ. 1988. MR imaging of laser-tissue interactions. Radiology 168:249-253.

Joy ML, Lebedev VP, Gati JS. 1999. Imaging of current density and current pathways in rabbit brain during transcranial electrostimulation. IEEE Trans Biomed Eng 46:1139-1149.

Joy M, Scott G, Henkelman M. 1989. In vivo detection of applied electric currents by magnetic resonance imaging. Magn Reson Imaging 7:89-94.

Jucker BM, Barucci N, Shulman GI. 1999. Metabolic control analysis of insulin-stimulated glucose disposal in rat skeletal muscle. Am J Physiol Endocrin Metab 277(Pt 1):E505-E512.

Jucker BM, Rennings AJ, Cline GW, Petersen KF, Shulman GI. 1997. In vivo NMR investigation of intramuscular glucose metabolism in conscious rats. Am J Physiol Endocrin Metab 273(Pt 1):E139-E148.

Kayyem JF, Kumar RM, Fraser, SE, Meade TJ, 1995 Receptor-targeted co-transport of DNA and magnetic resonance constrast agents. Chem Biol 2:615-620.

Kinoshita K, Tada E, Matsumoto K, Asari S, Ohmoto T, Itoh T. 1997. Proton MR spectroscopy of delayed cerebral radiation in monkeys and humans after brachytherapy. AJNR 18:1753-1761.

Kohler SJ, Perry SB, Stewart LC, Atkinson DE, Clarke K, Ingwall JS. 1991. Analysis of ²³Na NMR spectra from isolated perfused hearts. Magn Reson Med 18:15-27.

Koutcher JA, Sawyer RC, Kornblith AB, Stolfi RL, Martin DS, Devitt ML, Cowburn D, Young CW. 1991. In vivo monitoring of changes in 5-fluorouracil metabolism induced by methotrexate measured by ¹⁹F NMR spectroscopy. Magn Reson Med 19:113-123.

Kurhanewicz J, Dahiya R, Macdonald JM, Chang LH, James TL, Narayan P. 1993. Citrate alterations in primary and metastatic human prostatic adenocarcinomas: ¹H magnetic resonance spectroscopy and biochemical study. Magn Reson Med 29:149-157.

Kushmerick MJ. 1995. Skeletal muscle: A paradigm for testing principles of bioenergetics. J Bioenerg Biomembr 27:555-569.

Kusuoka H, Kitakaze M, Koretsune Y, Inoue M, Marban E. 1991. Pathophysiology and pathogenesis of contractile failure in stunned myocardium. Jpn Circ J 55:878-884.

Laughlin MR, Petit WA, Jr, Barrett EJ. 1993. The time course of myocardial glycogenolysis stimulated by glucagon. J Mol Cell Cardiol 25:175-183.

Laughlin MR, Taylor J, Chesnick AS, Balaban RS. 1994. Nonglucose substrates increase glycogen synthesis in vivo in dog heart. Am J Physiol Heart Circ Physiol 267(Pt 2):H219-H223.

Laughlin MR, Taylor JF, Chesnick AS, Balaban RS. 1992. Regulation of glycogen metabolism in canine myocardium: Effects of insulin and epinephrine in vivo. Am J Physiol Endocrin Metab 262(Pt 1):E875-E883.

Lauterbur PC. 1973. Image formation by induced local interactions: Examples employing nuclear magnetic resonance. Nature 242:190-191.

Leach RM, Sheehan DW, Chacko VP, Sylvester JT. 1998. Effects of hypoxia on energy state and pH in resting pulmonary and femoral arterial smooth muscles. Am J Physiol 275(Pt 1):L1051-L1060.

Lebihan D, ed. 1995. Diffusion and Perfusion Magnetic Resonance Imaging. Applications to Functional MRI. New York: Raven Press.

Lohmeier-Vogel EM, Hahn-Hagerdal B, Vogel HJ. 1995. Phosphorus-31 and carbon-13 nuclear magnetic resonance study of glucose and xylose metabolism in agarose-immobilized Candida tropicalis. Appl Environ Microbiol 61:1420-1425.

Loui, AY, Huber MM, Ahrens ET, Rothbacher U, Moats R, Jacons RE, Fraser SE, Meade TJ. 2000. In vivo visualization of gene expression using magnetic resonance imaging. Nature Biotech 18:321-325.

Malloy CR, Sherry AD, Jeffrey FM. 1990. Analysis of tricarboxylic acid cycle of the heart using ¹³C isotope isomers. Am J Physiol Heart Circ Physiol 259(Pt 2):H987-H995.

Manor D, Rothman DL, Mason GF, Hyder F, Petroff OA, Behar KL. 1996. The rate of turnover of cortical GABA from [1-¹³C]glucose is reduced in rats treated with the GABA-transaminase inhibitor vigabatrin (gamma- vinyl GABA). Neurochem Res 21:1031-1041.

Mansfield P, Morris PG. 1982. NMR Imaging in Biomedicine. New York: Academic Press.

Marban E, Kitakaze M, Kusuoka H, Poterfield JK, Yue DT, Chacko VP. 1987. Intracellular free calcium concentration measured with NMR spectroscopy in intact ferret hearts. Proc Natl Acad Sci U S A 84:6005-6009.

Mason GF, Gruetter R, Rothman DL, Behar KL, Shulman RG, Novotny EJ. 1995. Simultaneous determination of the rates of the TCA cycle, glucose utilization, alpha-ketoglutarate/glutamate exchange, and glutamine synthesis in human brain by NMR. J Cereb Blood Flow Metab 15:12-25.

Miezin FM, Maccotta L, Ollinger JM, Petersen SE, Buckner RL. 2000. Characterizing the hemodynamic response: Effects of presentation rate, sampling procedure, and the possibility of ordering brain activity based on relative timing. Neuroimage 11(Pt 1):735-759.

Monsein LH, Mathews VP, Barker PB, Pardo CA, Blackband SJ, Whitlow WD, Wong DF, Bryan RN. 1993. Irreversible regional cerebral ischemia: Serial MR imaging and proton MR spectroscopy in a nonhuman primate model. AJNR 14:963-970.

Moon RB, Richards JH. 1973. Determination of intracellular pH by ³¹P magnetic resonance. J Biol Chem 248:7276-7278.

Moonen CT, von Kienlin M, van Zijl PC, Cohen J, Gillen J, Daly P, Wolf G. 1989. Comparison of single-shot localization methods (STEAM and PRESS) for in vivo proton NMR spectroscopy. NMR Biomed 2:201-208.

Mosley, ME, Cohen, Y, Mintorovitch L, Chileuitt L, Shimizu H, Kucharczyk J, Wendland MF, Weinstein PR. 1990 Early Detection of regional cerebral-ischemia in cats---Comparison of diffusion-weighted and T2-weighted MRI and spectroscopy. Magn Reson Med 14:330-346.

Mulkern RV, Panych LP, McDannold NJ, Jolesz FA, Hynynen K. 1998. Tissue temperature monitoring with multiple gradient-echo imaging sequences. J Magn Reson Imaging 8:493-502.

Narayan P, Kurhanewicz J. 1992. Magnetic resonance spectroscopy in prostate disease: Diagnostic possibilities and future developments. Prostate Suppl 4:43-50.

Narayan P, Vigneron DB, Jajodia P, Anderson CM, Hedgcock MW, Tanagho EA, James TL. 1989. Transrectal probe for ¹H MRI and ³¹P MR spectroscopy of the prostate gland. Magn Reson Med 11:209-220.

Ojemann JG, Buckner RL, Akbudak E, Snyder AZ, Ollinger JM, McKinstry RC, Rosen BR, Petersen SE, Raichle ME, Conturo TE. 1998. Functional MRI studies of word-stem completion: Reliability across laboratories and comparison to blood flow imaging with PET. Hum Brain Mapp 6:203-215.

Papas KK, Long RC, Jr., Sambanis A, Constantinidis I. 1999. Development of a bioartificial pancreas: II. Effects of oxygen on long- term entrapped betaTC3 cell cultures. Biotechnol Bioeng 66:231-237.

Partain CL, Price RR, Patton JA, Kulkarni MV, James AE. 1988. Magnetic Resonance Imaging. Philadelphia: WB Saunders.

Phelps ME. 2000a. PET: The merging of biology and imaging into molecular imaging. J Nucl Med 41:661-681.

Phelps ME. 2000b. Positron emission tomography provdies molecular imaging of biological processes. Proc Natl Acad Sci U S A 97:9226-9233.

Pilatus U, Shim H, Artemov D, Davis D, van Zijl PC, Glickson JD. 1997. Intracellular volume and apparent diffusion constants of perfused cancer cell cultures, as measured by NMR. Magn Reson Med 37:825-832.

Portman MA, Ning XH. 1990. Developmental adaptations in cytosolic phosphate content and pH regulation in the sheep heart in vivo. J Clin Invest 86:1823-1828.

Portman MA, Panos AL, Xiao Y, Anderson DL, Alfieris GM, Ning XH, Lupinetti FM. 1997. Influence of the pH of cardioplegic solutions on cellular energy metabolism and hydrogen ion flux during neonatal hypothermic circulatory arrest and reperfusion: A dynamic ³¹P nuclear magnetic resonance study in a pig model. J Thorac Cardiovasc Surg 114:601-608.

Prior MJ, Maxwell RJ, Griffiths JR. 1990. In vivo ¹⁹F NMR spectroscopy of the antimetabolite 5-fluorouracil and its analogues. An assessment of drug metabolism. Biochem Pharmacol 39:857-863.

Purcell EM, Torrey HC, Pound RV. 1946. Resonance absorption by nuclear magnetic moments in a solid. Phys Rev 69:37-38.

Raine AEG, Seymour AML, Roberts AFC, Radda GK, Ledingham JGG. 1993. Impairment of cardiac function and energetics in experimental renal failure. J Clin Invest 92:2934-2940.

Reichle ED, Carpenter PA, Just MA. 2000. The neural bases of strategy and skill in sentence-picture verification. Cog Psychol 40:261-95.

Richards TL, Alvord EC, Jr., Peterson J, Cosgrove S, Petersen R, Petersen K, Heide AC, Cluff J, Rose LM. 1995. Experimental allergic encephalomyelitis in non-human primates: MRI and MRS may predict the type of brain damage. NMR Biomed 8:49-58.

Sadato N, Ibanez V, Campbell G, Deiber MP, Le Bihan D, Hallett M. 1997. Frequency-dependent changes of regional cerebral blood flow during finger movements: Functional MRI compared to PET. J Cereb Blood Flow Metab 17:670-679.

Schlicter CP. 1978. Principles of Magnetic Resonance. New York: Springer-Verlag.

Schmahmann JD, Sherman JC. 1998. The cerebellar cognitive affective syndrome. Brain 121(Pt 4):561-579.

Schwartz GG, Steinman S, Garcia J, Greyson C, Massie B, Weiner MW. 1992a. Energetics of acute pressure overload of the porcine right ventricle. In vivo ³¹P nuclear magnetic resonance. J Clin Invest 89:909-918.

Schwartz GG, Steinman SK, Weiner MW, Matson GB. 1992b. In vivo ³¹P-NMR spectroscopy of right ventricle in pigs. Am J Physiol Heart Circ Physiol 262(Pt 2):H1950-H1954.

Scollan DF, Holmes A, Windslow R, Forder JR. 1998. Histological validation of myocardial microstructure obtained from diffusion tensor magnetic resonance imaging. Am J Physiol Heart Circ Physiol 275: H2308-H2318

Sequin U, Scott AI. 1974. Carbon-13 as a label in biosynthetic studies. Science 186:101-107.

Shungu DC, Bhujwalla ZM, Wehrle JP, Glickson JD. 1992. ¹H NMR spectroscopy of subcutaneous tumors in mice: Preliminary studies of effects of growth, chemotherapy and blood flow reduction. NMR Biomed 5:296-302.

Sibson NR, Dhankhar A, Mason GF, Behar KL, Rothman DL, Shulman RG. 1997. In vivo ¹³C NMR measurements of cerebral glutamine synthesis as evidence for glutamate-glutamine cycling. Proc Natl Acad Sci U S A 94:2699-2704.

Sibson NR, Dhankhar A, Mason GF, Rothman DL, Behar KL, Shulman RG. 1998a. Stoichiometric coupling of brain glucose metabolism and glutamatergic neuronal activity. Proc Natl Acad Sci U S A 95:316-321.

Sibson NR, Shen J, Mason GF, Rothman DL, Behar KL, Shulman RG. 1998b. Functional energy metabolism: In vivo ¹³C-NMR spectroscopy evidence for coupling of cerebral glucose consumption and glutamatergic neuronalactivity. Dev Neurosci 20:321-330.

Sipe JC, Filippi M, Martino G, Furlan R, Rocca MA, Rovaris M, Bergami A, Zyroff J, Scotti G, Comi G. 1999. Method for intracellular magnetic labeling of human mononuclear cells using approved iron contrast agents. Magn Reson Imaging 17:1521-1523.

Sipkins DA, Gijbels K, Tropper FD, Bednarski M, Li KC, Steinman L. 2000. ICAM-1 expression in autoimmune encephalitis visualized using magnetic resonance imaging. J Neuroimmunol 105:1-9.

Sonnewald U, Wang AY, Petersen SB, Westergaard N, Schousboe A, Erikson R, Skottner A. 1995. ¹³C NMR study of IGF-I- and insulin-effects on mitochondrial function in cultured brain cells. Neuroreport 6:878-880.

Sonnewald U, Wang AY, Schousboe A, Erikson R, Skottner A. 1996a. New aspects of lactate metabolism: IGF-I and insulin regulate mitochondrial function in cultured brain cells during normoxia and hypoxia. Dev Neurosci 18:443-448.

Sonnewald U, White LR, Odegard E, Westergaard N, Bakken IJ, Aasly J, Unsgard G, Schousboe A. 1996b. MRS study of glutamate metabolism in cultured neurons/glia. Neurochem Res 21:987-993.

Sorensen V, Jonsson O, Pettersson S, Schersten T, Soussi B. 1998. In vivo ³¹P NMR OSIRIS of bioenergetic changes in rabbit kidneys during and after ischaemia: Effect of pretreatment with an indeno-indole compound. Acta Physiol Scand 162:495-500.

Sprengelmeyer R, Rausch M, Eysel UT, Przuntek H. 1998. Neural structures associated with recognition of facial expressions of basic emotions. Proc R Soc Lond B Biol Sci 265:1927-1931.

Stark DD, Bradley WG, eds. 1999. Magnetic Resonance Imaging. St. Louis: Mosby.

Steenbergen C, Fralix TA, Murphy E. 1993. Role of increased cytosolic free calcium concentration in myocardial ischemic injury. Basic Res Cardiol 88:456-470.

Teasdale JD, Howard RJ, Cox SG, Ha Y, Brammer MJ, Williams SC, Checkley SA. 1999. Functional MRI study of the cognitive generation of affect. Am J Psychiatry 156:209-215.

Ugurbil K, Petein M, Maidan R, Michurski S, Cohn JN, From AH. 1984. High resolution proton NMR studies of perfused rat hearts. FEBS Lett 167:73-78.

Van Emous JG, Schreur JH, Ruigrok TJ, Van Echteld CJ. 1998. Both Na⁺-K⁺ ATPase and Na⁺-H⁺ exchanger are immediately active upon post-ischemic reperfusion in isolated rat hearts. J Mol Cell Cardiol 30:337-348.

van Sluis R, Bhujwalla ZM, Raghunand N, Ballesteros P, Alvarez J, Cerdan S, Galons JP, Gillies RJ. 1999. In vivo imaging of extracellular pH using ¹H MRSI. Magn Reson Med 41:743-750.

Vidal G, Durand T, Canioni P, Gallis JL. 1998. Cytosolic pH regulation in perfused rat liver: Role of intracellular bicarbonate production. Biochim Biophys Acta 1425:224-234.

Wang Y, Plewes DB. 1999. An MRI calorimetry technique to measure tissue ultrasound absorption. Magn Reson Med 42:158-166.

Wehrli FW, Shaw D, Kneeland JB. 1988. Biomedical Magnetic Resonance Imaging. Berlin: Wiley-VCH Weinheim.

Weiss RG, Chacko SM, Aresta F, Chacko VP. 2000. Dynamic magnetic resonance images of murine cardiac function at physiologic heart rates. Circulation (online) 101:E92.

Weiss RG, Gloth ST, Kalil-Filho R, Chacko VP, Stern MD, Gerstenblith G. 1992. Indexing tricarboxylic acid cycle flux in intact hearts by carbon-13 nuclear magnetic resonance. Circ Res 70:392-408.

Wiesmann F, Ruff J, Hiller K-H, Rommel E, Haase A, Neubauer S. 2000. Developmental changes of cardiac function and mass assessed with MRI in neonatal, juvenile and adult mice. Am J Physiol Heart Circ Physiol 278:H652-H657.

Yanagida S, Luo CS, Balschi JA, Pohost GM, Pike MM. 1996. Simultaneous multicompartment intracellular Ca²⁺ measurements in the perfused heart using ¹⁹F NMR spectroscopy. Magn Reson Med 35:640-647.

Yu X, White LT, Doumen C, Damico LA, LaNoue KF, Alpert NM, Lewandowski ED. 1995. Kinetic analysis of dynamic ¹³C NMR spectra: Metabolic flux, regulation, and compartmentation in hearts. Biophys J 69:2090-2102.

Zhang J, Murakami Y, Zhang Y, Cho YK, Ye Y, Gong G, Bache RJ, Ugurbil K, From AH. 1999. Oxygen delivery does not limit cardiac performance during high work states. Am J Physiol Heart Circ Physiol 277(Pt 2):H50-H57.

Figure 1 (A) Nuclear dipole equated to a bar magnet. (B) When placed in a magnetic field, B₀, the nuclear moments align with B₀ and generate a net magnetic moment, M. (C) B₁ pushes M away from B₀. When B₁ is removed, M returns to alignment with B₀ and generates an oscillating signal.

Figure 2 Distinct chemical groups emit signals at different frequencies. Signals with multiple frequency components can be decoded into component frequencies using the Fourier transform.

Figure 3 (A) Application of a linear field gradient causes different parts of the sample to resonate at different frequencies. If the gradient is linear, then the frequency spread is linear with space. Hence, the spectrum is a one-dimensional projection of the sample. (B) Left, a series of projections are collected at different projection angles, which, at right, are used to reconstruct the image of the sample. Generally, M projections are required to form an M ´ N digital image, where N is the number of points sampling the signal.

Figure 4 ³¹P nuclear magnetic resonance (NMR) spectrum of an isolated perfused mouse heart collected on a 500-MHz NMR spectrometer. The spectrum required approximately 5 min to acquire. P_i, inorganic phosphate; PCr, phosphocreatine; ATP, adenosine triphosphate; PPM, parts per million.

Figure 5 ¹H- nuclear magnetic resonance (NMR) image of the thorax of a mouse through the heart at end diastole. Selected ³¹P-NMR spectra containing the myocardium (A) and a ³¹P standard adjacent to the chest (B). The spectra and images were obtained using electrocardiogram (ECG) gated imaging sequences. (C) ECG tracing of the mouse during the study. Reprinted with permission from Chacko VP, Aresta F, Chacko SM, Weiss RG. 2000. MRI/MRS assessment of in vivo murine cardiac metabolism, morphology, and function at physiological heart rates. Am J Physiol Heart Circ Physiol 279:H2218-H2224.

Figure 6 Portion of the ¹³C nuclear magnetic resonance spectrum of 9 ´ 10⁷ perfused MCF7adr cells (A) in Dulbecco's modified Eagle's medium/fetal bovine serum; (B) immediately after switching to medium containing [3,3'-¹³C-]-cystine; and (C) 8 hr after switching to the labeled medium. The resonances from cystine (at 39.9 ppm) and glutathione (26.5 ppm) are readily detectable. Each spectrum was acquired in 40 min. Unpublished data courtesy of Dr. Michael P. Gamcsik, The Cancer Center, Duke University, Chapel Hill, North Carolina.

Figure 7 Selection of ¹H images demonstrating the utility of magnetic resonance imaging for assessing tissue structure. (A) Single neuron from Aplysia californica (bright central nucleus surrounded by dark cytoplasm). (B) Isolated perfused rat hippocampal brain slice. (C) Formalin-fixed rat brain (courtesy of Dr. Beneviste, Duke University). (D) Formalin-fixed rabbit heart (courtesy of Dr. Forder, University of Alabama at Birmingham). In vivo (E) axial mouse (courtesy of Dr. Salmon, The University of Florida), (F) saggital rat, (G) axial cat, and (H) saggital monkey brain images. Note that the fields of view (size of the image) increase from ~500 μm in (A) to ~16 cm in (H). (I) Live image of a normal 11-day-old rat pup, and (J) a similar animal with hydrocephalus (note enlarged ventricles). (K) Live image of a normal rat brain, with (L) a diffusion-weighted image after inducement of a stroke, which shows hyperintense on the left.

Biomedical Magnetic Resonance & Technology Center, University of Illinois at Urbana-Champaign
Principal Investigator: Paul C. Lauterbur, PhD TEL: 217-244-0600; FAX: 217-244-1330
E-mail: bmrl@bmrl.med.uiuc.edu; Web-site: bmrl.med.uiuc.edu:8080/

Center for Advanced Magnetic Resonance Technology, Stanford University Medical Center,
Principal Investigator: Gary H. Glover, Ph.D., TEL: 650-723-7577; FAX: 650-723-5795
E-mail: gary@s-word.stanford.edu; Web-site: www-radiology.stanford.edu/research/RR.html

Clinical MR Studies at 4.1T: A Research Resource, University of Alabama at Birmingham,
Principal Investigator: Gerald M. Pohost, M.D, TEL: 205-934-9736; FAX: 205-975-1952
E-mail: nmrcenter@uab.edu; Web-site: www.cnir.uab.edu.

The Center for In Vivo Microscopy, Duke University Medical Center
Principal Investigator: G. Allan Johnson, Ph.D, TEL: 919-684-7755; FAX: 919-684-7122
E-mail: egf@orion.mc.duke.edu; Web-site: wwwcivm.mc.duke.edu/

Pittsburgh NMR Center for Biomedical Research, Carnegie Mellon University
Principal Investigator: Chien Ho, Ph.D., TEL: 412-268-3395 FAX: 412-268-7083
E-mail: chienho@andrew.cmu.edu; Web-site: info.bio.cmu/NMR-Center/NMR.html

Center For Magnetic Resonance Research, University of Minnesota
Principal Investigator: Kamil Ugurbil, Ph.D., TEL: 612-626-2001 ; FAX: 612-626-626-2004
E-mail: kamil@geronimo.drad.umn.edu
Web-site: www.cmrr.drad.umn.edu

Resource for Magnetic Resonance Research & Optical Research,University of Pennsylvania
Principal Investigator: John S. Leigh, Ph.D., TEL: 215-898-9357; FAX: 215-573-2113
E-mail: jack@mail.mmrrcc.upennn.edu; Web-site: www.mmrrcc.upenn.edu

Center for Magnetic Resonance, Massachusetts Institute of Technology
Principal Investigator: Robert G. Griffin, Ph.D., TEL: 617-253-5597; FAX: 617-253-5405
E-mail: rgg@mit.edu; Web-site: web.mit.edu/fbml/cmr/

National Magnetic Resonance Facility at Madison, University of Wisconsin-Madison
Principal Investigator: John L. Markley, Ph.D., TEL: 608-263-9349; FAX: 608-262-3759
E-mail: markely@nmrfam.wisc.edu; Web-site: www.nmrfam.wisc.edu

Rogers Magnetic Resonance Facility, University of Texas Southwestern Medical Center
Principal Investigator: Craig R. Malloy, M.D., TEL: 214-648-5886; FAX: 214-648-5881
E-mail: jthach@mednet.swmed.edu; Web-site: www.swmed.edu/home_pages/rogersmr

^aFrom the 1998 Research Resources Directory published by the NCRR. The Directory contains additional information regarding the capabilities of these resources and is available on-line at the NCRR web site: www.ncrr.nih.gov