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Spectral counting, a promising method for quantifying relative changes in protein abundance in mass spectrometry-based proteomic analysis, was compared to metabolic stable isotope labeling using 15N/14N “heavy/light” peptide pairs. The data were drawn primarily from a Methanococcus maripaludis experiment comparing a wild-type strain with a mutant deficient in a key enzyme relevant to energy metabolism. The dataset contained both proteome and transcriptome measurements. The normalization technique used previously for the isotopic measurements was inappropriate for spectral counting, but a simple adjustment for sampling frequency was sufficient for normalization. This adjustment was satisfactory both for M. maripaludis, an organism that showed relatively little expression change between the wild-type and mutant strains, and Porphyromonas gingivalis, an intracellular pathogen that has demonstrated widespread changes between intracellular and extracellular conditions. Spectral counting showed lower overall sensitivity defined in terms of detecting a two-fold change in protein expression, and in order to achieve the same level of quantitative proteome coverage as the stable isotope method, it would have required approximately doubling the number of mass spectra collected.

For the archaeon Methanococcus maripaludis, a fully sequenced and annotated model species of hydrogenotrophic methanogen, we report validation of quantitative protein level expression ratios on a proteome-wide basis. Using an approach based on quantitative multidimensional capillary HPLC and quadrupole ion trap mass spectrometry, coverage of gene expression approached that currently achievable with transcription microarrays. Comprehensive mass spectrometry-based proteomics and spotted cDNA arrays were used to compare global protein and mRNA levels in a wild-type (S2) and mutant strain (S40) of M. maripaludis. Using linear regression with 652 expression ratios generated by both the proteomic and microarray methods, a product moment correlation coefficient of 0.24 was observed. The correlation improved to 0.61 if only genes showing significant expression changes were included. A novel two-stage method of outlier detection was used for the protein measurements when Dixon’s Q-test by itself failed to give satisfactory results. The log2transformations of the number of peptides or isotopic peptide pairs associated with each ORF, divided by the predicted molecular weight, were found to have moderately positive correlations with two bioinformatic predictors of gene expression based on codon bias. We detected peptides derived from 939 proteins or 55% of the genome coding capacity. Of these, 60 were overexpressed, and 34 were underexpressed in the mutant. Of the 1722 ORFs encoded in the genome, 1597 or 93% were probed by cDNA arrays. Of these, 50 were more highly expressed, and 45 showed lower expression levels in the mutant relative to the wild type. 15 ORFs were shown to be overexpressed by both methods, and two ORFs were shown to be overexpressed by proteomics and underexpressed by microarray.

For the archaeon Methanococcus maripaludis, a fully sequenced and annotated model species of hydrogenotrophic methanogen, we report validation of quantitative protein level expression ratios on a proteome-wide basis. Using an approach based on quantitative multidimensional capillary HPLC and quadrupole ion trap mass spectrometry, coverage of gene expression approached that currently achievable with transcription microarrays. Comprehensive mass spectrometry-based proteomics and spotted cDNA arrays were used to compare global protein and mRNA levels in a wild-type (S2) and mutant strain (S40) of M. maripaludis. Using linear regression with 652 expression ratios generated by both the proteomic and microarray methods, a product moment correlation coefficient of 0.24 was observed. The correlation improved to 0.61 if only genes showing significant expression changes were included. A novel two-stage method of outlier detection was used for the protein measurements when Dixon’s Q-test by itself failed to give satisfactory results. The log2 transformations of the number of peptides or isotopic peptide pairs associated with each ORF, divided by the predicted molecular weight, were found to have moderately positive correlations with two bioinformatic predictors of gene expression based on codon bias. We detected peptides derived from 939 proteins or 55% of the genome coding capacity. Of these, 60 were overexpressed, and 34 were underexpressed in the mutant. Of the 1722 ORFs encoded in the genome, 1597 or 93% were probed by cDNA arrays. Of these, 50 were more highly expressed, and 45 showed lower expression levels in the mutant relative to the wild type. 15 ORFs were shown to be overexpressed by both methods, and two ORFs were shown to be overexpressed by proteomics and underexpressed by microarray.

There is continued debate in the literature concerning the location and magnitude of reflections in the arterial vasculature. We present an alternative approach to investigating these wave reflections. This technique utilizes the Fourier transform of the input impedance to yield the ideal impulse response of the arterial system in the time domain. We demonstrate theoretically and with computer simulations that this technique allows the determination of location of significant reflection sites and the magnitude of the reflected waves. This analysis may be better suited for studying reflections in the human arterial system than traditional analysis.

The purpose of this study was to determine if chronic fatigue syndrome (CFS) is associated with reduced blood flow and oxidative delivery to skeletal muscle. Patients with CFS according to CDC (Center for Disease Control) criteria (n=19) were compared with normal sedentary subjects (n=11). Muscle blood flow was measured with Doppler ultrasound after cuff ischaemia and exercise. Muscle oxygen delivery was measured as the rate of post-exercise and post-ischaemic oxygen-haem resaturation. Oxygen-haem resaturation was measured in the medial gastrocnemius muscle using continuous wavelength near-IR spectroscopy. Muscle metabolism was measured using 31P magnetic resonance spectroscopy. CFS patients and controls were not different in the peak blood flow after cuff ischaemia, the rate of recovery of phosphocreatine after submaximal exercise, and the rate of recovery of oxygen saturation after cuff ischaemia. In conclusion, CFS patients showed no deficit in blood flow or oxidative metabolism. This suggests that CFS symptoms do not require abnormal peripheral function.

Proton T1ρ‐dispersion MRI is demonstrated for indirect, in vivo detection of 17O in the brain. This technique, which may be readily implemented on any clinical MRI scanner, is applied towards high‐resolution, quantitative mapping of cerebral blood flow (CBF) in the rat by monitoring the clearance of 17O‐enriched water. Strategies are derived and employed for 1) quantitation of absolute H217O tracer concentration from a ratio of high‐ and low‐frequency spin‐locked T1ρimages, and 2) mapping CBF without having to transform the T1ρsignal to H217O tracer concentration. Absolute regional blood flow was mapped in a single 3‐mm brain slice at an in‐plane resolution of 0.4 × 0.8 mm within a 5‐min tracer washout time; these data are consistent with the less localized CBF measurements reported in the literature. T1ρ‐weighted imaging yields excellent signal‐to‐noise ratios, spatiotemporal resolution, and anatomical contrast for mapping CBF. Magn Reson Med 49:479–487, 2003. © 2003 Wiley‐Liss, Inc.

Proton T1ρ-dispersion MRI is demonstrated for indirect, in vivo detection of ¹⁷O in the brain. This technique, which may be readily implemented on any clinical MRI scanner, is applied towards high-resolution, quantitative mapping of cerebral blood flow (CBF) in the rat by monitoring the clearance of ¹⁷O-enriched water. Strategies are derived and employed for 1) quantitation of absolute H2¹⁷O tracer concentration from a ratio of high- and low-frequency spin-locked T1ρ images, and 2) mapping CBF without having to transform the T1ρ signal to H2¹⁷O tracer concentration. Absolute regional blood flow was mapped in a single 3-mm brain slice at an in-plane resolution of 0.4 × 0.8 mm within a 5-min tracer washout time; these data are consistent with the less localized CBF measurements reported in the literature. T1ρ-weighted imaging yields excellent signal-to-noise ratios, spatiotemporal resolution, and anatomical contrast for mapping CBF. Magn Reson Med 49:479–487, 2003. © 2003 Wiley-Liss, Inc.

Perfusion parameters, such as blood flow, are critical properties of tumors related to angiogenesis, drug delivery, radiosensitivity, bioenergetic status, and steady state levels of metabolites, such as lactate, that have been proposed as indices of tumor response to therapy. The existing MR methods for measuring tumor blood flow (TBF) have limitations related to sensitivity, spatial resolution, or dependence on other physiological properties such as vascular permeability. To address many of these difficulties, this study introduces the use of an ¹⁷O-enriched tracer in conjunction with high-resolution, indirect MRI to measure TBF. To demonstrate the advantages of this technique, relative TBF was measured in subcutaneous RIF-1 tumors in C3H mice by monitoring the uptake of H2¹⁷O with a resolution of 0.16 × 0.31 × 3 mm in 13 sec. At this resolution, tumor heterogeneity with respect to blood flow is clearly visible. Measurement of the tracer arterial input function, which is necessary for determination of absolute blood flow, may be facilitated with improved temporal resolution. Magn Reson Med 49:1–6, 2003. © 2003 Wiley-Liss, Inc.

Perfusion parameters, such as blood flow, are critical properties of tumors related to angiogenesis, drug delivery, radiosensitivity, bioenergetic status, and steady state levels of metabolites, such as lactate, that have been proposed as indices of tumor response to therapy. The existing MR methods for measuring tumor blood flow (TBF) have limitations related to sensitivity, spatial resolution, or dependence on other physiological properties such as vascular permeability. To address many of these difficulties, this study introduces the use of an 17O‐enriched tracer in conjunction with high‐resolution, indirect MRI to measure TBF. To demonstrate the advantages of this technique, relative TBF was measured in subcutaneous RIF‐1 tumors in C3H mice by monitoring the uptake of H217O with a resolution of 0.16 × 0.31 × 3 mm in 13 sec. At this resolution, tumor heterogeneity with respect to blood flow is clearly visible. Measurement of the tracer arterial input function, which is necessary for determination of absolute blood flow, may be facilitated with improved temporal resolution. Magn Reson Med 49:1–6, 2003. © 2003 Wiley‐Liss, Inc.

Conventional nuclear ventilation/perfusion (V/Q) scanning is limited in spatial resolution and requires exposure to radioactivity. The acquisition of pulmonary V/Q images using MRI overcomes these difficulties. When inhaled, hyperpolarized helium‐3 (3He) permits MRI of gas distribution. Magnetic labeling of blood (arterial spin‐tagging (AST)) provides images of pulmonary perfusion. Three normal subjects, two patients who had undergone single lung transplantation for emphysema, and one subject with pulmonary embolism (PE), were imaged. 3He distribution and blood perfusion appeared uniform in the normal subjects and throughout the lung allografts. Gas distribution and perfusion in the emphysematous lungs were non‐uniform and paralleled radiographic abnormalities. AST imaging alone revealed a lower‐lobe wedge‐shaped perfusion defect in the patient with PE that corresponded to computed tomography (CT) imaging. Hyperpolarized 3He gas is demonstrated to provide ventilation images of the lung. Blood perfusion information may be obtained during the same examination using the AST technique. The sequential application of these imaging methods provides a novel tool for studying V/Q relationships. Magn Reson Med 47:1073–1076, 2002. © 2002 Wiley‐Liss, Inc.

Methanogenesis, the biological production of methane, plays a pivotal role in the global carbon cycle and contributes significantly to global warming. The majority of methane in nature is derived from acetate. Here we report the complete genome sequence of an acetate-utilizing methanogen, Methanosarcina acetivorans C2A. Methanosarcineae are the most metabolically diverse methanogens, thrive in a broad range of environments, and are unique among the Archaea in forming complex multicellular structures. This diversity is reflected in the genome of M. acetivorans. At 5,751,492 base pairs it is by far the largest known archaeal genome. The 4524 open reading frames code for a strikingly wide and unanticipated variety of metabolic and cellular capabilities. The presence of novel methyltransferases indicates the likelihood of undiscovered natural energy sources for methanogenesis, whereas the presence of single-subunit carbon monoxide dehydrogenases raises the possibility of nonmethanogenic growth. Although motility has not been observed in any Methanosarcineae, a flagellin gene cluster and two complete chemotaxis gene clusters were identified. The availability of genetic methods, coupled with its physiological and metabolic diversity, makes M. acetivorans a powerful model organism for the study of archaeal biology. [Sequence, data, annotations and analyses are available at http://www-genome.wi.mit.edu/.]

A method is presented for the rapid acquisition of temperature maps derived from phase difference maps. The temperature‐dependent chemical shift coefficients (TDCSCs) of various concentrations of aqueous cobalt and dysprosium‐based compounds were measured. The largest TDCSC calculated was for 100 mM DyEDTA, which had a TDCSC of –0.09 PPM/K; 160 mM CoCl2had a TDCSC of –0.04 PPM/K. These temperature‐dependent chemical shifts (TDCSs) result in phase changes in the MR signal with changing temperature. Agarose phantoms were constructed with each paramagnetic metal. A fast gradient‐echo (FGRE) MR image was acquired to serve as the baseline image. A “test” MRI procedure was then performed on the phantom. Immediately afterwards, a second FGRE MR image was acquired, serving as the probing image. Proper image processing as a phase difference map between the probing image and the baseline image resulted in an image which quantitatively described the temperature increase of the phantom in response to a particular “test” imaging experiment. Applications of this technique in assessing the safety of pulse sequences and MR coils are discussed. Magn Reson Med 47:492–498, 2002. © 2002 Wiley‐Liss, Inc.

Continuing advances have rendered the neural control of eye movements one of the best understood motor systems, from molecules to complex behaviors. Nevertheless, new discoveries have required reevaluation of established concepts, from the genetics of disorders that affect extraocular muscles to the way in which the cerebral cortex governs behaviors that encompass several functional classes of eye movements. Curr Opin Neurol 1545–50. © 2002 Lippincott Williams & Wilkins.

While most proton (1H) spectra acquired in vivoutilize selective suppression of the solvent signal for more sensitive detection of signals from the dilute metabolites, recent reports have demonstrated the feasibility and advantages of collecting in vivodata without solvent attenuation. When these acquisitions are performed at short echo times, the presence of frequency modulations of the water resonance may become an obstacle to the identification and quantitation of metabolite resonances. The present report addresses the characteristics, origin, and elimination of these sidebands. Sideband amplitudes were measured as a function of delay time between gradient pulse and data collection, as a function of gradient pulse amplitude, and as a function of spatial location of the sample for each of the three orthogonal gradient sets. Acoustic acquisitions were performed to demonstrate the correlation between mechanical vibration resonances and the frequencies of MR sidebands. A mathematical framework is developed and compared with the experimental results. This derivation is based on the theory that these frequency modulations are induced by magnetic field fluctuations generated by the transient oscillations of gradient coils.

MR temperature measurements are important for applications such as the evaluation of thermal therapies and radiofrequency (RF) coil heating effects. In this work the spherical mean value (SMV) method has been applied to significantly improve the precision of MR temperature mapping in a homogeneous gel phantom. Temperature‐increase maps of the phantom were obtained with three‐dimensional (3D) MR phase difference mapping after heating with the RF coil. The temperature‐increase distribution in most regions in the phantom is a harmonic function with the mean value property. Based on this property, the precision of temperature‐increase maps was improved up to sixfold with the SMV method. Comparison of this method with conventional smoothing, further precision improvement, and the in vivo application of the SMV method are discussed. Magn Reson Med 4:678–682, 2001. © 2001 Wiley‐Liss, Inc.

Proteoglycan (PG) depletion‐induced changes in T1ρ(spin‐lattice relaxation in rotating frame) relaxation and dispersion in articular cartilage were studied at 4T. Using a spin‐lock cluster pre‐encoded fast spin echo sequence, T1ρmaps of healthy bovine specimens and specimens that were subjected to PG depletion were computed at varying spin‐lock frequencies. Sequential PG depletion was induced by trypsinization of cartilage for varying amounts of time. Results demonstrated that over 50% depletion of PG from bovine articular cartilage resulted in average T1ρincreases from 110–170 ms. Regression analysis of the data showed a strong correlation (R2= 0.987) between changes in PG and T1ρ. T1ρvalues were highest at the superficial zone and decreased gradually in the middle zone and again showed an increasing trend in the region near the subchondral bone. The potentials of this method in detecting early degenerative changes of cartilage are discussed. Also, T1ρ‐dispersion changes as a function of PG depletion are described. Magn Reson Med 46:419–423, 2001. © 2001 Wiley‐Liss, Inc.

The spatial distributions of the static magnetic field components and MR phase maps in space with homogeneous magnetic susceptibility are shown to be harmonic functions satisfying Laplace's equation. A mean value property is derived and experimentally confirmed on phase maps: the mean value on a spherical surface in space is equal to the value at the center of the sphere. Based on this property, a method is implemented for significantly improving the precision of MR phase or field mapping. Three-dimensional mappings of the static magnetic field with a precision of 10−11∼ 10−12T are obtained in phantoms by a 1.5-T clinical MR scanner, with about three-orders-of-magnitude precision improvement over the conventional phase mapping technique. In vivoapplication of the method is also demonstrated on human leg phase maps.

Intermolecular 129Xe–1H nuclear Overhauser effects and 129Xe longitudinal relaxation time measurements were used to demonstrate that the dipole–dipole coupling is the dominant relaxation mechanism for 129Xe in water, at room temperature. 129Xe–1H cross-relaxation rates were derived to be ςXeH∼ 3.2 ± 0.3 × 10−3s−1, independent of xenon pressure (in the range of 1–10 bar) and of the presence of oxygen. Corresponding xenon–proton internuclear distances were calculated to be 2.69 ± 0.12 Å. Using the magnitude of the dipole–dipole coupling and the spin density ratio between dissolved xenon and bulk water, it is estimated that 129Xe–1H spin polarization-induced nuclear Overhauser effects would yield little net proton signal enhancement in water.

The first intermolecular zero‐quantum coherence (iZQC) MR images of the human brain at 4T are presented. To generate iZQC images, a modified echo‐planar imaging pulse sequence was used which included an additional 45° RF pulse and a correlation gradient. The observability and nonconventional contrast of human brain iZQC images at 4T is demonstrated. Axial images are presented for various pulse sequence parameters, and a zero‐quantum relaxation map is obtained. Magn Reson Med 43:627–632, 2000. © 2000 Wiley‐Liss, Inc.

The first intermolecular zero-quantum coherence (iZQC) MR images of the human brain at 4T are presented. To generate iZQC images, a modified echo-planar imaging pulse sequence was used which included an additional 45° RF pulse and a correlation gradient. The observability and nonconventional contrast of human brain iZQC images at 4T is demonstrated. Axial images are presented for various pulse sequence parameters, and a zero-quantum relaxation map is obtained. Magn Reson Med 43:627–632, 2000. © 2000 Wiley-Liss, Inc.

We describe the characterization of a 23Na temperature-dependent chemical shift and relaxation rates in the complex, Na4HTm[DOTP]. This is the first characterization of a 23Na temperature-dependent chemical shift in a nonmetallic sample. The 23Na temperature-dependent chemical shift coefficient is ∼−0.5 PPM/°C for both an aqueous solution and a 6% agarose gel of this compound. This is 50 times the magnitude of the temperature-dependent chemical shift coefficient of water protons. The relaxation times, T1, T2f, and T2sincreased by 0.1, 0.01, and 0.05 ms/°C, respectively. Applications of these unique properties for designing an MRI technique for monitoring heat deposition in tissue and tissue phantoms are discussed.

Hyperpolarized gas magnetic resonance imaging has recently emerged as a method to image lungs, sinuses, and the brain. The best lung images to date have been produced using hyperpolarized ³He, which is produced by either spin-exchange or metastability-exchange optical pumping. For hyperpolarized gas MRI, the metastable method has demonstrated higher polarization levels and higher polarizing rates, but it requires compression of the hyperpolarized gas. Prior to this work, compression of hyperpolarized gas had only been accomplished using a large, complex and expensive apparatus. Here, human lung ventilation images are presented that were obtained using a compact compressor that is relatively simple and inexpensive. For this test, 1.1 bar-L of 15% hyperpolarized ³He gas was produced at the National Institute of Standards and Technology using a modified commercial diaphragm pump. The hyperpolarized gas was transported to the University of Pennsylvania in a holding field provided by a portable solenoid. Magn Reson Med 43:290–294, 2000. © 2000 Wiley-Liss, Inc.

Hyperpolarized gas magnetic resonance imaging has recently emerged as a method to image lungs, sinuses, and the brain. The best lung images to date have been produced using hyperpolarized 3He, which is produced by either spin‐exchange or metastability‐exchange optical pumping. For hyperpolarized gas MRI, the metastable method has demonstrated higher polarization levels and higher polarizing rates, but it requires compression of the hyperpolarized gas. Prior to this work, compression of hyperpolarized gas had only been accomplished using a large, complex and expensive apparatus. Here, human lung ventilation images are presented that were obtained using a compact compressor that is relatively simple and inexpensive. For this test, 1.1 bar‐L of 15% hyperpolarized 3He gas was produced at the National Institute of Standards and Technology using a modified commercial diaphragm pump. The hyperpolarized gas was transported to the University of Pennsylvania in a holding field provided by a portable solenoid. Magn Reson Med 43:290–294, 2000. © 2000 Wiley‐Liss, Inc.

Noninvasive methods of detecting cartilage degeneration can have an impact on identifying the early stages of osteoarthritis. Accurate measurement of sodium concentrations within the cartilage matrix provides a means for analyzing tissue integrity. Here a method is described for quantitating sodium concentration and visibility in cartilage, with general applications to all tissue types. The sodium concentration in bovine patellar cartilage plugs was determined by three different methods: NMR spectroscopy of whole cartilage plugs, NMR spectroscopy of liquefied cartilage in concentrated HCl, and inductively coupled plasma emission spectroscopy. Whole bovine patellae were imaged with relaxation normalized calibration phantoms to ascertain sodium concentrations inside the articular cartilage. Sodium concentrations in intact articular cartilage were found to range from ∼200 mM on the edges to ∼390 mM in the center, with an average of ∼320 mM in five separate bovine patellae studied. In essence, we have created sodium distribution maps of the cartilage, showing for the first time, spatial variations of sodium concentration in intact cartilage. This average concentration measurement correlates very well with the values obtained from the spectroscopic methods. Furthermore, sodium was found to be 100% NMR visible in cartilage plugs. Applications of this method in diagnosing and monitoring treatment of osteoarthritis are discussed.

The design of a pressure cell that compresses a cartilage specimen in one dimension within an imaging magnet is presented. One-dimensional projection images in a direction perpendicular to the articular surface of the cartilage specimen were used to generate a uniaxial confined deformation creep curve for normal and trypsin-degraded cartilage specimens during a continuous 0.690 MPa (100 psi) pressure application. The resulting curves are shown to fit a two time constant viscoelastic model well and also indicate that the elastic modulus of cartilage decreases and the deformation rate increases upon trypsin proteolysis. Furthermore, cartilage permeability is shown as a function of cartilage strain for both the normal and trypsin-degraded case. Several two-dimensional slice-selective images were collected both before and after 80 minutes of continuous compression. These images were used to evaluate the relative changes in the spin-lattice, T1, and spin-spin, T2, relaxation time constant maps for both normal and degraded cartilage specimens in response to compression. The results of this study demonstrate the utility of a novel, non-magnetic, cartilage compression device and also support the validity of a simple two-component rheological model of articular cartilage. J. Magn. Reson. Imaging 1999;9:653–662. © 1999 Wiley-Liss, Inc.

Sodium multiple quantum (MQ) spectroscopy of the human breast in vivo was performed. Double quantum (DQ) filtered spectra were used to demonstrate the existence of a non-vanishing (residual) quadrupolar interaction in the tissue. Triple quantum (TQ) filtered spectra were used to measure the two time constants associated with the biexponential transverse relaxation times of sodium in biological tissues. The two time constants were found to be 0.64 and 26.57 msec. The potential applications of this finding are discussed. J. Magn. Reson. Imaging 1999;9:391–394. © 1999 Wiley-Liss, Inc.

One of the first effects of degenerative osteoarthritis is the loss of proteoglycans from the matrix of articular cartilage. Using a model of osteoarthritic change where the cartilage has been enzymatically degraded with trypsin, the sodium NMR characteristics of the cartilage were determined as a function of changes in the proteoglycan content. The results demonstrate that the single quantum sodium signal decreases as the proteoglycan content of the cartilage matrix decreases. In addition, the relaxation characteristics of the sodium change such that the T1is longer, the T2sis longer, and the T2fis shorter. Short echo‐time, T1‐weighted sodium images are presented which demonstrate that this information may be utilized to detect the loss of proteoglycans from articular cartilage. Magn Reson Med 41:30‐34, 1999. © 1999 Wiley‐Liss, Inc.

Sodium multiple quantum (MQ) spectroscopy of the human breast in vivo was performed. Double quantum (DQ) filtered spectra were used to demonstrate the existence of a non‐vanishing (residual) quadrupolar interaction in the tissue. Triple quantum (TQ) filtered spectra were used to measure the two time constants associated with the biexponential transverse relaxation times of sodium in biological tissues. The two time constants were found to be 0.64 and 26.57 msec. The potential applications of this finding are discussed. J. Magn. Reson. Imaging 1999;9:391–394. © 1999 Wiley‐Liss, Inc.

1In vivoATP synthesis rates were measured in the human medial gastrocnemius muscle during high intensity exercise using localized 31P‐magnetic resonance spectroscopy (31P‐MRS). Six‐second localized spectra were acquired during and following a 30 s maximal voluntary rate exercise using a magnetic resonance image‐guided spectral localization technique.2During 30 s maximal voluntary rate exercise, ATPase fluxes were predominantly met by anaerobic ATP sources. Maximal in vivoglycogenolytic rates of 207 ± 48 mM ATP min−1were obtained within 15 s, decreasing to 72 ± 34 mM ATP min−1by the end of 30 s. In contrast, aerobic ATP synthesis rates achieved 85 ± 2 % of their maximal capacity within 9 s and did not change throughout the exercise. The ratio of peak glycolytic ATP synthesis rate to maximal oxidative ATP synthesis was 2.9 ± 0.9.3The non‐Pi, non‐CO2buffer capacity was calculated to be 27.0 ± 6.2 slykes (millimoles acid added per unit change in pH). At the cessation of exercise, Pi, phosphomonoesters and CO2were predicted to account for 17.2 ± 1.5, 5.57 ± 0.97 and 2.24 ± 0.34 slykes of the total buffer capacity.4Over the approximately linear range of intracellular pH recovery following the post‐exercise acidification, pHirecovered at a rate of 0.19 ± 0.03 pH units min−1. Proton transport capacity was determined to be 16.4 ± 4.1 mM (pH unit)−1min−1and corresponded to a maximal proton efflux rate of 15.3 ± 2.7 mM min−1.5These data support the observation that glycogenolytic and glycolytic rates are elevated in vivoin the presence of elevated Pilevels. The data do not support the hypothesis that glycogenolysis follows Michealis‐Menten kinetics with an apparent Kmfor [Pi]in vivo.6In vivo‐measured ATP utilization rates and the initial dependence on PCr and glycolysis were similar to those previously reported in in situstudies involving short duration, high intensity exercise. This experimental approach presents a non‐invasive, quantitative measure of peak glycolytic rates in human skeletal muscle.

Principal component analysis (PCA) is a powerful method for quantitative analysis of nuclear magnetic resonance spectral data sets. It has the advantage of being model independent, making it well suited for the analysis of spectra with complicated or unknown line shapes. Previous applications of PCA have required that all spectra in a data set be in phase or have implemented iterative methods to analyze spectra that are not perfectly phased. However, improper phasing or imperfect convergence of the iterative methods has resulted in systematic errors in the estimation of peak areas with PCA. Presented here is a modified method of PCA, which utilizes complex singular value decomposition (SVD) to analyze spectral data sets with any amount of variation in spectral phase. The new method is shown to be completely insensitive to spectral phase. In the presence of noise, PCA with complex SVD yields a lower variation in the estimation of peak area than conventional PCA by a factor of approximately ✓2. The performance of the method is demonstrated with simulated data and in vivo 31P spectra from human skeletal muscle.Magn Reson Med 41:450–455, 1999. © 1999 Wiley‐Liss, Inc.

The design of a pressure cell that compresses a cartilage specimen in one dimension within an imaging magnet is presented. One‐dimensional projection images in a direction perpendicular to the articular surface of the cartilage specimen were used to generate a uniaxial confined deformation creep curve for normal and trypsin‐degraded cartilage specimens during a continuous 0.690 MPa (100 psi) pressure application. The resulting curves are shown to fit a two time constant viscoelastic model well and also indicate that the elastic modulus of cartilage decreases and the deformation rate increases upon trypsin proteolysis. Furthermore, cartilage permeability is shown as a function of cartilage strain for both the normal and trypsin‐degraded case. Several two‐dimensional slice‐selective images were collected both before and after 80 minutes of continuous compression. These images were used to evaluate the relative changes in the spin‐lattice, T1, and spin‐spin, T2, relaxation time constant maps for both normal and degraded cartilage specimens in response to compression. The results of this study demonstrate the utility of a novel, non‐magnetic, cartilage compression device and also support the validity of a simple two‐component rheological model of articular cartilage. J. Magn. Reson. Imaging 1999;9:653–662. © 1999 Wiley‐Liss, Inc.

Principal component analysis (PCA) is a powerful method for quantitative analysis of nuclear magnetic resonance spectral data sets. It has the advantage of being model independent, making it well suited for the analysis of spectra with complicated or unknown line shapes. Previous applications of PCA have required that all spectra in a data set be in phase or have implemented iterative methods to analyze spectra that are not perfectly phased. However, improper phasing or imperfect convergence of the iterative methods has resulted in systematic errors in the estimation of peak areas with PCA. Presented here is a modified method of PCA, which utilizes complex singular value decomposition (SVD) to analyze spectral data sets with any amount of variation in spectral phase. The new method is shown to be completely insensitive to spectral phase. In the presence of noise, PCA with complex SVD yields a lower variation in the estimation of peak area than conventional PCA by a factor of approximately ✓2. The performance of the method is demonstrated with simulated data and in vivo ³¹P spectra from human skeletal muscle.Magn Reson Med 41:450–455, 1999. © 1999 Wiley-Liss, Inc.

One of the first effects of degenerative osteoarthritis is the loss of proteoglycans from the matrix of articular cartilage. Using a model of osteoarthritic change where the cartilage has been enzymatically degraded with trypsin, the sodium NMR characteristics of the cartilage were determined as a function of changes in the proteoglycan content. The results demonstrate that the single quantum sodium signal decreases as the proteoglycan content of the cartilage matrix decreases. In addition, the relaxation characteristics of the sodium change such that the T1 is longer, the T2s is longer, and the T2f is shorter. Short echo-time, T1-weighted sodium images are presented which demonstrate that this information may be utilized to detect the loss of proteoglycans from articular cartilage. Magn Reson Med 41:30-34, 1999. © 1999 Wiley-Liss, Inc.

Information regarding transcriptional regulation in Archaea has begun to emerge from in vivogenetic studies. Evidence to date suggests a varied repertoire of regulatory mechanisms in Archaea that invokes both bacterial and eukaryal paradigms, as well as some novel features. Overall simplicity of mechanisms may reflect the prokaryotic lifestyle. Sequencing projects suggest the existence of certain classes of regulators, but experimental verification is needed.

Proton T1pdispersion imaging is a recently described method for indirect detection of 17O. However, clinical implementation of this technique is hindered by the requirement for a high‐amplitude spin‐locking field (γB1> 1 kHz) that exceeds current limitations in specific absorption rate (SAR). Here, a strategy is offered for circumventing high SAR in T1pdispersion imaging of 17O through the use of low‐amplitude off‐resonance spin‐locking pulses (γB1< 300 Hz). Proton spin‐lattice relaxation times in the off‐resonance rotating frame were measured in H217O‐enriched tissue phantoms. On‐ and off‐resonance T1pdispersion imaging was implemented at 2 T using a spin‐locking preparatory pulse cluster appended to a standard spin‐echo sequence. On‐ and off‐resonance dispersion images exhibited similar 17O‐based image contrast. Magnetization transfer effects did not depend on 17O concentration and had no effect on image contrast. In conclusion, off‐resonance proton T1pdispersion imaging shows promise as a safe, sensitive technique for generating 17O‐based T1pcontrast without exceeding SAR limitations.

The high frequencyk-space data in magnetic resonance imaging is often poorly reproduced due to the finite dynamic range of an analog-to-digital converter. The magnitude of this digitization error can equal and even exceed the magnitude of the thermal noise. Under such conditions, attempts to increase image signal-to-noise ratio via signal averaging meet with diminishing success. Because the relative size of the digitization error increases at higher spatial frequencies, a reduction in image resolution is incurred as well. By adjusting the level of the analog signal sampled by the analog-to-digital converter during the course of an imaging experiment, the magnitude of the digitization artifact can be greatly reduced. The results of simulations and imaging experiments are presented which demonstrate that this strategy improves both the signal-to-noise ratio and resolution of magnetic resonance images.

Detection of H217O with proton T1ρ‐dispersion imaging holds promise as a means of quantifying metabolism and blood flow with MRI. However, this technique requires a priori knowledge of the intrinsic T1ρdispersion of tissue. To investigate these properties, we implemented a T1ρimaging sequence on a 1.9‐T Signa GE scanner. A series of T1ρimages for different locking frequencies and locking durations were obtained from rat brain in vivo and compared with 5 % (wt/vol) gelatin phantoms containing different concentrations of 17O ranging from .037 % (natural abundance) to 2.0 atom%. Results revealed that, although there is considerable T1ρ‐dispersion in phantoms doped with H217O, the T1ρof rat brain undergoes minimal dispersion for spin‐locking frequencies between .2 and 1.5 kHz. A small degree of T1ρdispersion is present below .2 kHz, which we postulate arises from natural‐abundance H217O. Moreover, the signal‐to‐noise ratios of T1ρ‐weighted images are significantly better than comparable T2‐weighted images, allowing for improved visualization of tissue contrast. We have also demonstrated the feasibility of proton T1ρ‐dispersion imaging for detecting intravenous H217O on a live mouse brain. The potential application of this technique to study brain perfusion is discussed.

Mice immunized by excision of a primary, subcutaneously growing SV40-induced mKSA solid tumor which resisted challenge of homologous tumor cells administered at a contralateral site, were found to develop a specific DTH response to SV40 tumor associated transplantation antigens (TATA).

This article has been approved for continuing education credit. Objectives are listed below. Test questions follow at the end of the article along with further directions.

• We randomized 224 patients with resected Dukes' stage B2 or C colorectal cancer to either an untreated control group or to a group receiving 7 days of fluorouracil therapy (500 mg/m2 per day) by portal vein infusion. Randomization was accomplished during surgery after staging by frozen section. Only 5 (2.2%) of our 224 patients were ineligible, but an additional 10 patients assigned to portal vein infusion could not be treated because of technical problems with catheter placement. Toxic reactions were mild. There was only 1 postoperative death on each study arm. At present, the median follow-up for all patients is 5.5 years (range, 1.5 to 9.5 years). Interval to progression and survival curves essentially overlap. The same lack of treatment effect is seen in both the stage B and C subsets.(Arch Surg. 1990;125:897-901)

Triple quantum (TQ) sodium imaging of bovine articular cartilage is presented. True triple quantum imaging sequence was modified to incorporate asymmetric echo acquisition. Triple quantum signal expression in the presence of residual quadrupolar interaction is presented. The filtering capability of the sequence is first demonstrated on an agarose phantom. Both single and triple quantum images of articular cartilage are compared. The TQ image shows non‐zero signal intensity solely from cartilage, indicating complete suppression of signals from bone marrow and saline. The advantages of TQ imaging of articular cartilage, its feasibility in in vivosituations and further improvements in SNR are described.

The authors report, for the first time, sodium properties of human articular cartilage in vivousing sodium multiple‐quantum‐filtered methods with a surface coil. A flip angle‐independent, phase‐cycled pulse sequence was used to obtain triple‐quantum‐filtered spectra as a function of preparation time. Biexponential relaxation rates were calculated by fitting the triple‐quantum‐filtered spectral amplitudes to a theoretical expression. Theoretical analysis of the flip angle dependence of even rank two‐quantum coherence (T22), odd rank two‐quantum coherence (T23), and triple‐quantum coherence are presented and verified against experimental results on a cartilage specimen. Sodium multiple‐quantum‐filtered spectral lineshapes obtained in vivocorrelate well with those observed on in vivospecimens. Relaxation rates obtained from asymptomatic volunteers were found to be: T2rise= 1.0 ± 0.12 ms, T2decay= 12.0 ± 0.75 ms (mean ± SD). The diagnostic potential of this method in detecting early changes in articular cartilage is described.