Showing papers in "NMR in Biomedicine in 1998"

Simultaneous in vivo spectral editing and water suppression

Abstract: Water suppression is typically performed in vivo by exciting the longitudinal magnetization in combination with dephasing, or by using frequency-selective coherence generation. MEGA, a frequency-selective refocusing technique, can be placed into any pulse sequence element designed to generate a Hahn spin-echo or stimulated echo, to dephase transverse water coherences with minimal spectral distortions. Water suppression performance was verified in vivo using stimulated echo acquisition mode (STEAM) localization, which provided water suppression comparable with that achieved with four selective pulses in 3,1-DRYSTEAM. The advantage of the proposed method was exploited for editing J-coupled resonances. Using a double-banded pulse that selectively inverts a J-coupling partner and simultaneously suppresses water, efficient metabolite editing was achieved in the point resolved spectroscopy (PRESS) and STEAM sequences in which MEGA was incorporated. To illustrate the efficiency of the method, the detection of gamma-aminobutyric acid (GABA) was demonstrated, with minimal contributions from macromolecules and overlying singlet peaks at 4 T. The estimated occipital GABA concentration was consistent with previous reports, suggesting that editing for GABA is efficient when based on MEGA at high field strengths.

Development of a model for classification of toxin-induced lesions using 1H NMR spectroscopy of urine combined with pattern recognition.

Abstract: Pattern recognition approaches were developed and applied to the classification of 600 MHz 1 H NMR spectra of urine from rats dosed with compounds that induced organ-specific damage in either the liver or kidney Male rats were separated into groups (n = 5) and each treated with one of the following compounds; adriamycin, allyl alcohol, 2-bromoethanamine hydrobromide, hexachlorobutadiene, hydrazine, lead acetate, mercury II chloride, puromycin aminonucleoside, sodium chromate, thioacetamide, 1,1,2-trichloro-3,3,3-trifluoro-1-propene or dose vehicle Urine samples were collected over a 7 day time-course and analysed using 600 MHz 1 H NMR spectroscopy Each NMR spectrum was data-reduced to provide 256 intensity-related descriptors of the spectra Data corresponding to the periods 8-24 h, 24-32 h and 32-56 h post-dose were first analysed using principal components analysis (PCA) In addition, samples obtained 120-144 h following the administration of adriamycin and puromycin were included in the analysis in order to compensate for the late onset of glomerular toxicity Having established that toxin-related clustering behaviour could be detected in the first three principal components (PCs), three-quarters of the data were used to construct a soft independent modelling of class analogy (SIMCA) model The remainder of the data were used as a test set of the model Only three out of 61 samples in the test set were misclassified Finally as a further test of the model, data from the 1 H NMR spectra of urine from rats that had been treated with uranyl nitrate were used Successful prediction of the toxicity type of the compound was achieved based on NMR urinalysis data confirming the robust nature of the derived model © 1998 John Wiley & Sons, Ltd

Restricted diffusion and exchange of intracellular water: theoretical modelling and diffusion time dependence of 1H NMR measurements on perfused glial cells.

Abstract: Intracellular diffusion properties of water in F98 glioma cells immobilized in basement membrane gel threads, are investigated with a pulsed-field-gradient spin-echo NMR technique at diffusion times from 6 to 2000 ms and at different temperatures. In extended model calculations the concept of 'restricted intracellular diffusion at permeable boundaries' is described by a combined Tanner-Karger formula. Signal components in a series of ct experiments (constant diffusion time) are separated due to different diffusion properties (Gaussian and restricted diffusion), and physiological as well as morphological cell parameters are extracted from the experimental data. The intracellular apparent diffusion coefficients strongly depend on the diffusion time and are up to two orders of magnitude smaller than the self diffusion constant of water. Propagation lengths are found to be in the range of 4-7 microns. Hereby intracellular signals of compartments with a characteristic diameter could be selected by an appropriate gradient strength. With cg experiments (constant gradient) a mean intracellular residence time for water is determined to be about 50 ms, and the intrinsic intracellular diffusion constant is estimated to 1 x 10(-3)mm2/s. Studying the water diffusion in glial cells provides basic understanding of the intracellular situation in brain tissue and may elucidate possible influences on the changes in the diffusion contrast during ischemic conditions.

Measurements of human breast cancer using magnetic resonance spectroscopy: a review of clinical measurements and a report of localized 31P measurements of response to treatment.

Abstract: A review of the literature has shown that in human breast tumours, large signals from phosphomonoesters (PME) and phosphodiesters (PDE) are evident. In serial measurements in 19 patients with breast cancer, a decrease in PME was significantly associated with a stable or responding disease (p = 0.017), and an increase in PME was associated with disease progression. Extract studies have shown PME to comprise of phosphoethanolamine (PEth) and phosphocholine (PCho), with the PEth to PCho ratio ranging from 1.3 to 12. The PCho content of high grade tumours was found to be higher than low grade tumours. In some animal models, changes in PCho have been shown to correlate with indices of cellular proliferation, and spheroid studies have shown a decrease in PCho content in spheroids with smaller growth fractions. A serial study of 25 patients with advanced primary breast tumours undergoing hormone, chemotherapy or radiotherapy treatments, showed that in this heterogenous group there were significant changes in metabolites that were seen during the first 3 weeks (range 2-4 weeks) of treatment, that correlated with volume change over this period, employed here as a measure of response. Changes in PME (p = 0.003), total phosphate (TP) (p = 0.008) and total nucleoside tri-phosphate (TNTP) (p = 0.02) over 3 (1) weeks were significantly associated with response, as were the levels of PME (p<0.001), PDE (p = 0.01), TP (p = 0.001) and TNTP (p = 0.007) at week 3 (1). PME at week 3 (1) was also significantly associated with the best volume response to treatment (p = 0.03). A reproducibility analysis of results from the observation of normal breast metabolism in four volunteers showed a mean coefficient of variation of 25%, after correcting for changes resulting from the menstrual cycle. Reproducibility studies in four patients with breast cancer showed a mean coefficient of variation of 33%, with the reproducibility being better in patients measured on different days (difference in TP wasˇ6%) compared with those measured on the same day (difference in TP wasˇ29%). © 1998 John Wiley & Sons, Ltd.

Human magnetic resonance imaging at 8 T.

Abstract: In this work, we present the first human magnetic resonance image (MRI) obtained at ultrahigh field strengths (8 T). We demonstrate that clinical imaging will be possible at 8 T and that reasonable quality head images can be obtained at this field strength. Most importantly, we emphasize that the power required to excite the spins at 8 T is much lower than had previously been predicted by the nuclear magnetic resonance theory. A 90° pulse in the head at 8 T requires only ∼0.085 J of energy (90 W for a 2-lobe 4 ms sinc pulse). Based on measurements at 4 T, 1-2 J of energy should have been utilized to achieve a 90° excitation at 8 T. The fact that the energy required for spin excitation at 8 T is much lower than predicted by the NMR theory, will be extremely important to the viability of ultrahigh field imaging, since concerns related to power absorption and specific absorption rate (SAR) violations at ultrahigh field are alleviated. As such, it will be possible to utilize RF intensive pulse sequences and adiabatic spin excitation at 8 T without significant risk to the subject. © 1998 John Wiley & Sons, Ltd.

Near-optimal region selection for feature space reduction: novel preprocessing methods for classifying MR spectra

Abstract: We introduce a global feature extraction method specifically designed to preprocess magnetic resonance spectra of biomedical origin. Such preprocessing is essential for the accurate and reliable classification of diseases or disease stages manifest in the spectra. The new method is genetic algorithm-guided. It is compared with our enhanced version of the standard forward selection algorithm. Both seek and select optimal spectral subregions. These subregions necessarily retain spectral information, thus aiding the eventual identification of the biochemistry of disease presence and progression. The power of the methods is demonstrated on two biomedical examples: the discrimination between meningioma and astrocytoma in brain tissue biopsies, and the classification of colorectal biopsies into normal and tumour classes. Both preprocessing methods lead to classification accuracies over 97% for the two examples. © 1998 John Wiley & Sons, Ltd.

Towards a method for automated classification of 1H MRS spectra from brain tumours

Abstract: Recent studies have shown that MRS can substantially improve the non-invasive categorization of human brain tumours. However, in order for MRS to be used routinely by clinicians, it will be necessary to develop reliable automated classification methods that can be fully validated. This paper is in two parts: the first part reviews the progress that has been made towards this goal, together with the problems that are involved in the design of automated methods to process and classify the spectra. The second part describes the development of a simple prototype system for classifying H-1 single voxel spectra, obtained at an echo time (TE) of 135 ms, of the four most common types of brain tumour (meningioma (MM), astrocytic (AST), oligodendroglioma (OD) and metastasis (ME)) and cysts. This system was developed in two stages: firstly, an initial database of spectra was used to develop a prototype classifier, based on a linear discriminant analysis (LDA) of selected data points. Secondly, this classifier was tested on an independent test set of 15 newly acquired spectra, and the system was refined on the basis of these results. The system correctly classified all the non-astrocytic tumours. However, the results for the the astrocytic group were poorer (between 55 and 100%, depending on the binary comparison). Approximately 50% of high grade astrocytoma (glioblastoma) spectra in our data base showed very little lipid signal, which may account for the poorer results for this class. Consequently, far the refined system, the astrocytomas were subdivided into two subgroups for comparison against other tumour classes: those with high lipid content and those without

From magnetic resonance spectroscopy to classification of tumors. A review of pattern recognition methods

Abstract: This article reviews the wealth of different pattern recognition methods that have been used for magnetic resonance spectroscopy (MRS) based tumor classification. The methods have in common that the entire MR spectra is used to develop linear and non-linear classifiers. The following issues are addressed: (i) pre-processing, such as normalization and digitization, (ii) extraction of relevant spectral features by multivariate methods, such as principal component analysis, linear discriminant analysis (LDA), and optimal discriminant vector, and (iii) classification by LDA, cluster analysis and artificial neural networks. Different approaches are compared and discussed in view of practical and theoretical considerations.

Volume localized in vivo proton MR spectroscopy of breast carcinoma: variation of water-fat ratio in patients receiving chemotherapy.

Abstract: Results are reported on in vivo volume localized proton magnetic resonance spectroscopy (MRS) of patients (n = 44) suffering from carcinoma of the breast, using a bilateral breast surface coil. Localized proton MR spectra of the unaffected contralateral breast of these patients are dominated by resonances arising from fat and are similar to the breast tissue from normal volunteers (controls, n = 13), while in the malignant breast tissues the water resonance dominates. On the other hand, the water suppressed proton MR spectra of malignant breast tissue reveal several metabolites of low concentration including the choline peak around 3.2 ppm and other resonances attributable to purine and pyrimidine nucleotides, in the 8.5 ppm region. Elevated water- fat (W-F) ratios are measured in the malignant tissues, compared with the normal breast tissue of controls and from the contralateral unaffected breast tissue of the patients (n = 11). In the case of patients receiving chemotherapy resulting in the reduction of primary tumor size, the W-F ratio shows a statistically significant (P < 0.01) decrease compared with the pre-therapy value, thus providing a non-invasive indicator of favourable clinical outcome of neoadjuvant chemotherapy for locally advanced breast cancer. The method provides the potential for non-invasively monitoring and assessing the response of breast cancer to neoadjuvant chemotherapy.

Using pattern analysis of in vivo proton MRSI data to improve the diagnosis and surgical management of patients with brain tumors.

Abstract: We have used pattern analysis of proton magnetic resonance spectroscopic imaging ( 1 H MRSI) data in a variety of situations related to the clinical management of patients with brain tumors and other cerebral space-occupying lesions (SOLs). Here, we review how 'leave-one-out' linear discriminant analyses (LDAs) of in vivo 1 H MRSI spectral patterns have enabled us to quickly, accurately, and non-invasively: (1) discriminate amongst tissue arising from the five most common types of supratentorial tumors found in adults, and (2) use the metabolic heterogeneity of cerebral SOLs to predict certain pathological characteristics that are useful in guiding stereotaxic biopsy and selective tumor resection. These findings suggest that pattern analysis of 1 H MRSI data can significantly improve the diagnostic specificity and surgical management of patients with certain cerebral SOLs.

Nuclear magnetic resonance spectroscopy study of muscle growth, mdx dystrophy and glucocorticoid treatments: correlation with repair.

Abstract: Proton nuclear magnetic resonance spectroscopy (1H NMR) can be used to study skeletal muscle metabolism. The mdx mouse is a unique animal for studies of muscle regeneration, and models the disease of Duchenne muscular dystrophy (DMD). The goals of this study were to determine the potential of 1H NMR spectroscopy as an alternative to conventional histology in monitoring: (1) normal growth in control muscle and the progression of dystrophy in mdx muscle, and (2) beneficial treatments (glucocorticoids) on mdx dystrophy. Ex vivo 1H NMR spectra of limb and diaphragm muscles were obtained from different ages of control and mdx mice, and from mice which were treated with prednisone or deflazacort. Peaks with contributions from creatine, taurine and lipids were examined. Lower levels of taurine and creatine characterized predystrophy and active dystrophy intervals in mdx muscle compared to control. Levels of taurine increased with stabilization of the disease by repair. A measure of accumulated muscle repair, fiber centronucleation and many spectral peaks were highly and significantly correlated. Greater amounts of lipids were found in the diaphragm compared to limb spectra. Treatment of dystrophy, which improved muscle phenotype, resulted in greater levels of taurine and creatine, especially in the limb muscle. Therefore, 1H NMR differentially discriminates: (1) control and mdx muscle; (2) the progression of mdx dystrophy and developmental stages in normal growth; (3) mild and severe dystrophic phenotypes (diaphragm vs limb); and (4) changes associated with improved muscle phenotype and regeneration (due to treatment or injury). The results focus on monitoring muscle repair, not degeneration. We conclude that 1H NMR is a reliable tool in the objective investigation of muscle repair status during muscular dystrophy.

MRI measurements of cerebral deoxyhaemoglobin concentration [dHb] - correlation with near infrared spectroscopy (NIRS)

Abstract: Changes in physiological parameters such as cerebral blood flow, cerebral blood volume, oxygen extraction, and the size and distribution of cerebral blood vessels, result in changes in the local concentration of deoxyhaemoglobin ([dHb]). The purpose of this study was to quantitatively investigate the dependence of the R2* relaxation rate upon the [dHb] per voxel. Five neonatal piglets were studied in a 7 T/20 cm bore magnet. MRI was conducted using a 2.5 cm diameter surface coil placed over the parietal lobes. Four progressively T2*-weighted images were acquired, allowing the absolute quantitation of R2*. Simultaneous near infrared spectroscopy (NIRS) measurements were made from an area encompassing the MR imaging slice, and allowed the absolute quantitation of [dHb]. The arterial oxygen saturation (SaO2) of the piglet was lowered stepwise by decreasing the fractional inspired oxygen concentration (FiO2), which precipitated a change in [dHb]. NIRS and MRI measurements were made at each FiO2 step. The results demonstrate an extremely strong, linear relationship between R2* as determined by MRI and [dHb], as measured by NIRS. Whereas NIRS can only give us a global measure of [dHb], the results suggest the future use of MRI in producing high resolution relaxation rate maps related to the [dHb] distribution of the brain.

In vivo and in vitro bi-exponential diffusion of N-acetyl aspartate (NAA) in rat brain: a potential structural probe?

Abstract: Diffusion measurements were performed on the N-acetyl aspartate (NAA) signal in in situ brains (in vivo and post-mortem) and on in vitro brain tissue at 37 °C using wide ranges of b-values (from 0 up to 45 10 6 s/cm 2 and 358 10 6 s/cm 2 for the in vivo and the in vitro cases, respectively) In vivo and in vitro NAA signals attenuation due to diffusion was measured at fixed diffusion times (tD) In the in vitro cases the effect of tD on the apparent diffusion coefficients (ADCs) of NAA was evaluated From these experiments the following observations and conclusions were made: (1) NAA signal attenuation both in vivo and in vitro is not mono-exponential and could be fitted by bi-exponential fitting function; (2) analysis of the low b-value range only (up to 05 10 6 s/cm 2 ) gives a mono-exponential decay (r = 0999); (3) in both cases the obtained ADCs are sensitive to the diffusion time; (4) the ADCs of the pre- and post-mortem cases are nearly similar; (5) the ADCs obtained from the bi-exponential fitting function decrease when the diffusion time increases; and (6) both the fast and the slow diffusing components of NAA show a considerable restriction by what seems to be a non-permeable barrier from which two compartments were identified, one having a size of 6-8mm and the other of 1-2mm in size It seems conceivable that the two populations identified in the diffusion experiments represent primarily the NAA in the cell body (soma) and in the neurital space (axons and proximal dendrites) © 1998 John Wiley & Sons, Ltd

Monitoring of cell volume and water exchange time in perfused cells by diffusion-weighted 1H NMR spectroscopy

Abstract: Diffusion of intracellular water was measured in perfused cells embedded in basement membrane gel threads. F98 glioma cells, primary astrocytes, and epithelial KB cells were used and were exposed to osmotic stress, immunosuppressiva, the water channel blocker p-chloromercuriobenzenesulfonate (pCMBS), and apoptotic conditions. With diffusion-weighted 1 H NMR spectroscopy changes in the intracellular signal could be monitored and quantified with single signal (ss), constant diffusion time (ct), and constant gradient strength (cg) experiments. The temporal resolution of the ss monitoring was 3.5 s with a standard deviation of 0.5% of the signal intensity and 32 s (3%) with ct monitoring, respectively. A mean intracellular residence time of water was determined with the cg experiment to about 50 ms. Changes of this exchange time from (51.9 1.0) to (59.0 1.1) ms were observed during treatment with pCMBS. The changes in the diffusion attenuated signal could be simulated analytically varying the intracellular volume fraction and exchange time by combination of restricted diffusion (Tanner model) and water exchange (Karger model). This sensitive and noninvasive NMR method on perfused cells allows to determine changes in the intracellular volume and residence time in a simple and accurate manner. Many further applications as anoxia, volume regulation, ischemia and treatment with various pharmaceuticals are conceiveable to follow up their effect on the cell volume and the exchange time of intracellular water. © 1998 John Wiley & Sons, Ltd.

Genetic programming for classification and feature selection: analysis of 1H nuclear magnetic resonance spectra from human brain tumour biopsies.

Abstract: Funded by Karen Elise Jensens Fund. Grant Number: CICYT SAF93-0582-C02-01 and SAF96-0147; Conselleria de Sanitat, Generalitat de Catalunya, Spain and EC Concerted Action Biomed-1. Grant Number: PL920432.

New approach for quantitation of short echo time in vivo 1H MR spectra of brain using AMARES

Abstract: Short echo time in vivo STEAM 1H MR spectra (4.7 T, TE = 16 ms) of normal rat brain were fitted in the time domain using a VARPRO-like algorithm called AMARES which allows an inclusion of a large amount of prior knowledge. The prior knowledge was derived from phantom spectra of pure metabolite solutions measured under the same experimental conditions as the in vivo spectra. The prior knowledge for the in vivo spectra was constructed as follows: for each VARPRO-fitted phantom spectrum one peak (the most prominent one in the in vivo spectrum) was chosen and left unconstrained in the AMARES fitting while all the other peaks in the metabolite spectrum (i.e. their corresponding parameters--amplitudes, damping factors, frequencies and phases) were fixed to the parameter values of the unconstrained peak via amplitude and damping ratios and frequency and phase shifts. Including N-acetyl-aspartate, glutamate, total creatine, cholines, glucose and myo-inositol into the fits provided results which were in agreement with published data. An inclusion of glutamine into the set of fitted metabolites was also investigated.

Effects of physiologic motion of the human brain upon quantitative 1H-MRS: analysis and correction by retro-gating.

Abstract: Signal loss and absolute quantitation errors in 1H-MRS (localized proton MR spectroscopy) because of physiologic brain motion are analyzed quantitatively. Cardiac and respiratory related motion lead to substantial phase dispersion when using a standard, short echo-time STEAM sequence. The loss in signal area varies from 6–7% with TM (middle interval time in a STEAM sequence) = 13.7 ms, to 25–39% with TM = 100 ms. The variation in signal area because of motion-related phase dispersion is up to 16% for TM = 100 ms. The signal phase as a function of the position in the cardiac cycle is shown to be reproducible. Maximal differences in the signal phase are over 180° for long TMs. ECG-gating reduces the phase dispersion considerably but introduces problems with variable repetition times. Using a phase calibration curve recorded with the water suppression turned off, it is possible to retrogate subsequent untriggered acquisitions with the water suppression activated, if the time points in the cardiac cycle are recorded for each acquisition. The gain in signal intensity is between 3 and 21%. For absolute quantification via brain water, this phase analysis has the important consequence that reference scans must be phased individually before co-adding, otherwise metabolite concentrations may be severely overestimated. © 1998 John Wiley & Sons, Ltd.

Non-invasive 19F-NMRS of 5-fluorouracil in pharmacokinetics and pharmacodynamic studies.

Abstract: Knowledge of the exact dose and rate at which an antitumor agent is delivered to its target site is postulated to be crucial to proper patient management. It is now possible to obtain such information using non-invasive 19 F-NMRS (nuclear magnetic resonance spectroscopy) following the administration of 5-fluorouracil (5-FU). We have performed such studies in 103 patients with breast, colorectal and other tumors. Measurable 19 F signals were detected in 99 of these patients (92.5%). Estimation of the tumoral t 1/2 of 5-FU in these patients revealed that 51 of them (51.5%) exhibited a tumoral t 1/2 greater than 20 min, a value we had characterized as indicating drug trapping in the tumor. Of these patients, 46 who received regimen bolus 5-FU 600 mg/m 2 with leucovorin for their treatment have been evaluated. In these patients, the association between trapping and response remains very high (p <.000001). None of the non-trappers responded to chemotherapy, whereas 70% of the evaluable trappers responded. Details are presented here on the methodology of NMRS data acquisition and on their pharmacokinetic analysis. The potential mechanisms underlying the trapping effect appear to be predicated primarily on transport processes. Suggestions are presented on how such pharmacokinetic imaging studies may extend both our understanding of the mechanism of action of 5-FU, and how they could be used to optimize patient treatment.

Magnetic resonance image segmentation using pattern recognition, and applied to image registration and quantitation

Abstract: This review highlights various magnetic resonance image (MRI) segmentation algorithms that employ pattern recognition. The procedures are grouped into two categories: low- to intermediate-level, and high-level image processing. The former consists of grey level histogram analysis, texture definition, edge identification, region growing, and contour following. The roles of significant prior knowledge, neural networks and cluster analysis are examined by producing objective identification of anatomical structures. The application of the segmented anatomical structures in image registration, to monitor the disease progression or growth of anatomy in normal volunteers and patients, is highlighted. The use of the segmented anatomy in measuring volumes of structures in normals and patients is also examined.

Metabolic changes underlying 31P MR spectral alterations in human hepatic tumours

Abstract: Magnetic resonance spectroscopy (MRS) remains the technique of choice for observing tumour metabolism non-invasively. Although initially 31P MR spectroscopy showed much promise as a non-invasive diagnostic tool, studies of a wide range of hepatic tumours have conclusively shown that this technique cannot be utilized to distinguish between different tumour types. This lack of specificity and sensitivity appears to be a consequence of the fact that hepatic tumours develop with a range of modalities and not as a single abnormal disease process, and also because of the limited availability of MR detectable metabolic markers. This has led, in recent years, to a re-evaluation of the role of 31P MR spectroscopy, re-emerging as a non-invasive tool to follow the efficacy of the treatment regime. Furthermore, since the principal changes observed in tumours by 31P MRS appear to be an elevation in the concentration of phosphorylcholine (PCho) and phosphoethanolamine (PEth), new research using a combination of MRS and tissue culture of cell lines which carry a combination of known inducible oncogenes, are helping to elucidate some of the metabolic pathways that give rise to these metabolic alterations.

NMR spectroscopy and MRI investigation of a potential bioartificial liver.

Abstract: NMR feasibility was established for a coaxial hydrophobic-membrane bioreactor containing isolated rat hepatocytes with features designed to mimic the human liver. A novel triple-tuned NMR probe and a perfusion system controlling temperature, gas concentrations, flow-rate, and pH were used. We determined the optimum coaxial interfiber distance (i.e. diffusion distance) for maintaining hepatocyte viability in two bioreactor prototypes. Prototype no. 1 and no. 2 had diffusion distances of 500 microns and 200 microns, respectively. Cell viability was established by 31P NMR and trypan blue exclusion. Only prototype no. 2 maintained cell viability for more than 6 h, indicating the importance of diffusion distance. 31P spectra obtained over this 6 h time period were similar to in vivo spectra of rat liver. The 31P spectra were found to be more sensitive to subacute cell viability than trypan blue exclusion. In the 1H and 31P spectra, 1H2O and inorganic phosphate signals were split in two at all flow-rates, probably due to bulk magnetic susceptibility effects originating from the three bioreactor compartments. MRI was useful for quality control and determining flow dynamics, fiber integrity, and cell inoculate distribution. MRI revealed that the inner fibers were not centered in either prototype. Although an increased flow-rate did not influence spectral resolution or chemical shifts, significant degradation of MRI quality occurred above 50 mL/min. NMR spectroscopy and imaging provide valuable, real-time information on cell biochemistry and flow dynamics which can be used in development and monitoring of bioreactors designed as artificial livers.

High resolution MRI and MRS: A feasibility study for the investigation of focal cerebral ischemia in mice

Abstract: Combined NMR imaging and spectroscopy have been applied to mouse brain during focal cerebral ischemia. The present study evaluated the feasibility of NMR measurements on mice in order to fine-tune the sequences and experimental setup for systematic investigations on stroke including future studies on transgenic animals. The acquisition of high quality diffusion-weighted, perfusion-weighted, and T2-weighted images (DWI, PWI, T2-WI, respectively) is demonstrated and complemented by measurements of 1H volume-selective spectroscopy and spectroscopic imaging (SI). Despite the small volume of the mouse brain, a satisfactory signal-to-noise ratio can be achieved with reasonably short measurement times. C57black/6J mice with an average body weight of 25 g were studied using state-of-the-art NMR sequences at 4.7 T. After induction of focal cerebral ischemia, the lesion was found clearly distinguishable in all imaging techniques. The apparent diffusion coefficient (ADC) was reduced in the ischemic region, and an expansion of the affected volume was observed with ongoing ischemia time. In the 1H spectra of ischemic animals a distinct change in the concentrations of NAA and lactate was visible. This is the first report on both SI data and perfusion-weighted imaging on mouse brain. It is demonstrated that the perfusion deficit during ischemia can be well demarcated. The spatial resolution of changes in metabolite concentrations allows the clear differentiation of elevated lactate levels in ischemic brain tissue. Copyright © 1998 John Wiley & Sons, Ltd.

Optimal time spacings for T2 measurements: monoexponential and biexponential systems.

Abstract: We have developed an optimal design strategy, i.e. a choice of times at which the magnetization should be measured, in spin-echo measurements, when the number of measurements is fixed in advance. Results are given for samples whose relaxation is described by either an exponential or biexponential decay curve. The analysis is based on having an initial estimate of the ranges in which the relaxation times are likely to lie. The optimal design consists of a set of easily parameterized non-uniformly spaced measurement times, as opposed to present implementation of spin-echo experiments. Analysis of the biexponential case shows that an order of magnitude greater signal-to-noise is required to achieve T2 estimates of comparable precision to monoexponential measurements with the same number of data points. The optimal designs lead to an improved ability to discriminate between two relatively similar relaxation times. © 1998 John Wiley & Sons, Ltd.

1H MRS markers of tumour growth in intrasplenic tumours and liver metastasis induced by injection of HT-29 cells in nude mice spleen.

Abstract: We have characterized, by in vitro magnetic resonance spectroscopy (MRS), the metabolite pattern of perchloric acid (PCA) extracts of intrasplenic tumours and hepatic metastasis, produced by intra-spleen injection of the human colorectal carcinoma cell line HT-29 and its metastatic variant HT-29 MMM into nude mice. Our aim was to gain further understanding of colorectal tumour metabolism as a basis for future in vivo studies of human colon cancer by 1H MRS. Metabolite PCA extract analysis showed a good reproduction of the spectral pattern observed in human primary colon tumours, while they were very different from the spectral pattern of the host tissues (spleen and liver). The main differences between host and tumour tissues involved taurine, phosphocholine (PC), phosphoethanolamine (PE), creatine, glycogen and glucose. Creatine is the most promising marker to follow tumour growth because of its practical absence in the nude mice host tissues. Detection of variable levels of this compound and of taurine in hepatic foci in man, are suggested as possible diagnostic markers. No correlation could be found between spectral pattern differences and the different ability to metastasize of the two HT-29 cell lines used. Furthermore, indirect evidence for a functional link between taurine and myo-inositol in colon tumour cells is presented. In summary, our data suggest that the nude mice model may be a suitable system for the MRS study of the changes taking place in host tissues upon tumour progression.

Two-compartment model for determination of glycolytic rates of solid tumors by in vivo 13C NMR spectroscopy.

Abstract: Carbon-13 NMR spectroscopy of 13C enriched substrates is useful for non-invasively determining metabolic fluxes of cells and tissues. Our study demonstrates that for RIF-1 tumor cells, examined under monolayer culture with continuous perfusion and also grown as solid subcutaneously (sc) implanted tumors in vivo, the levels of intracellular glucose and intermediates of the glycolytic pathway are below the level of detection by NMR spectroscopy. For these tumors, glucose transport into the cell is the most probable rate limiting step of the glycolytic pathway. Under these limiting conditions a simple two-compartment model of glycolysis applies. This model yields two parameters: the average rate of glycolysis and the rate of lactate clearance through the vasculature. For the RIF-1 tumor these parameters were 0.022 +/- 0.01 and 0.034 +/- 0.006 min(-1), respectively.

Application of self-organizing maps for the detection and classification of human blood plasma lipoprotein lipid profiles on the basis of 1H NMR spectroscopy data.

Abstract: Efficient and relevant classification of clinical findings, i.e. diagnostic decision making, poses a major challenge in medicine. In relation to biomedical NMR spectroscopy the problem of classification is often accompanied by complex, heavily overlapping information. Self-organizing map (SOM) analysis has been successfully applied in many areas of research and was thus also considered as a potential tool for NMR data analysis. In this paper we demonstrate how SOM analysis can be used for automated NMR data classification. Our goal was analysis of plasma lipoprotein lipids, a complex but biochemically well understood and specified system. The results illustrate that clinically relevant lipid classifications can be obtained from the SOM analysis of 1H NMR spectral information alone. The resulting maps were calibrated using independent biochemical lipid analyses and were found to produce excellent clustering of the plasma samples into clinically useful groups: normal, type IIa, IIb and IV hyperlipidaemias. In addition to this traditional classification, we also present results from SOM analysis in which the reference vectors of the map were calibrated for plasma total cholesterol and triglycerides and high and low density lipoprotein C; the plasma lipid parameters that are currently considered as the most useful indicators of coronary heart disease risk. In all, the present results indicate that SOM analysis can cope well with complex NMR spectral information and is thus likely to have an independent role in the area of biomedical NMR data analysis.

Brainmapping of alpha-chloralose anesthetized rats with T2*-weighted imaging: distinction between the representation of the forepaw and hindpaw in the somatosensory cortex.

Abstract: T2*-weighted imaging at 4.7 T was used to identify the cortical areas activated by electrical stimulation of the forepaw and hindpaw of alpha-chloralose anesthetized rats. Variation of the coronal slice position relative to the bregma, showed that the forepaw representation in the somatosensory cortex is more frontal and lateral than that of the hindpaw. Overlap between both activation areas was observed only in a small region in the slice at the level of the bregma. Documented localizations of both representations are in good agreement with earlier observations using invasive techniques. The determination of the separate areas of both paws indicates the feasibility of more complex activation studies in anesthetized animals, such as combined stimulations for the investigation of potentiation or depression effects on individual stimuli.

Stimulus dependence of oxygenation-sensitive MRI responses to sustained visual activation

Abstract: Oxygenation-sensitive MRI responses to repetitive and sustained visual activation were compared for stimuli with different temporal, spatial, and luminance contrasts, i.e. reversing checkerboard, flashing diffuse red light, and stationary diffuse gray light with darkness as a control. All paradigms elicited an initial oxygenation 'overshoot' as well as a post-stimulus 'undershoot'. However, whereas flashing and stationary diffuse light resulted in more than a 50% decrease of the initial signal response after 6 min of stimulation, checkerboard responsed remained largely unaffected (less than 20% signal attenuation). The demonstration of a stimulus dependence for sustained visual activation reconciles apparently contradictory reports for stimuli involving checkerboards as opposed to goggles, flickerlight, and movies. It may be caused by stimulus-dependent adjustments of neuronal activity, oxygen consumption, blood flow, or blood volume.

On the correlation between the water diffusion coefficient and oxygen tension in RIF-1 tumors.

Abstract: Water diffusion-coefficient mapping was used in conjunction with 19 F inversion-recovery echo-planar imaging (IR-EPI) of a sequestered perfluorocarbon (PFC) emulsion to investigate the spatial correlation between the diffusion coefficient of water and the tissue oxygen tension (p02) in radiation-induced fibrosarcoma (RIF-1) tumors (n = 11). The diffusion-time-dependent apparent diffusion coefficient, D(t), was determined by acquiring diffusion coefficient maps at 20 different diffusion times. Maps at four representative time points in different regions of the D(t) curve were selected for final analysis. An intravenously administered PFC emulsion, perfluoro-15-crown-5-ether, was used to generate the p02 maps. D(t) and pO 2 data were acquired with the animal breathing either air or carbogen (95% 02 - 5% CO 2 ) to investigate the effects of increased tumor pO 2 on D(t). The average increase in tumor pO 2 was 22 torr when the breathing gas was changed from air to carbogen. Correlation plots generated from pixel data for D(t) (air breathing) vs D(t) (carbogen breathing) show little deviation from a slope of unity. Correlation plots of D(t) vs p02 indicate that no correlation is present between these two parameters. This study also confirmed that necrotic tissue was best differentiated from viable tumor tissue based on D(t) maps at long diffusion times.

A 1H/13C inverse 2D method for the analysis of the polyamines putrescine, spermidine and spermine in cell extracts and biofluids

Abstract: The polyamines putrescine, spermidine and spermine are involved in the regulation of various metabolic processes. It is therefore desirable to detect and quantify the polyamines with NMR. We present the proton and carbon assignments for all polyamine signals obtained from PCA extracts of F98 glioma cells with high resolution using a semi-selective HSQC 2D-experiment. The biosynthesis of the polyamines in cell culture was examined using the labeled substrates [U-13 C]glucose and [U-13 C]glutamate. In such studies the high resolution of the semi-selective HSQC experiment at very high magnetic fields (14–19 T) allows the analysis of carbon-carbon couplings, and isotopomer patterns. The different effects of osmotic stress on the concentrations of polyamines and amino acids are also reported. © 1998 John Wiley & Sons, Ltd.