Studies of human tumors by MRS: a review

Tumour phospholipid metabolism

Following the impetus of early clinical and experimental investigations, in vivo and in vitro MRS studies of tumours pointed in the eighties to the possible significance of signals arising from phospholipid (PL) precursors and catabolites as novel biochemical indicators of in vivo tumour progression and response to therapy. In the present decade, MRS analyses of individual components contributing to the 31P PME (phosphomonoester) and PDE (phosphodiester) resonances, as well as to the 1H 'choline peak', have reinforced some of these expectations. Moreover, the absolute quantification of these signals provided the basis for addressing more specific (although still open) questions on the biochemical mechanisms responsible for the formation of intracellular pools of PL derivatives in tumours, under different conditions of cell proliferative status and/or malignancy level. This article is aimed at providing an overview on: (a) quantitative MRS measurements on the contents of phosphocholine (PCho), phosphoethanolamine (PEtn) and their glycerol derivatives ģlycerol 3-phosphocholine (GPC) and glycerol 3-phosphoethanolamine (GPE)[ in human tumours and cells (with particular attention to breast and brain cancer and lymphomas), as well as in normal mammalian tissues (including developing organs and rapidly proliferating tissues); (b) possible correlations of MRS parameters like PEtn/PCho and PCho/GPC ratios with in vitro cell growth status and/or cell tumorigenicity; and (c) current and new hypotheses on the role and interplay of biosynthetic and catabolic pathways of the choline and ethanolamine cycles in modulating the intracellular sizes of PCho and PEtn pools, either in response to mitogenic stimuli or in relation to malignant transformation.

Cerebral (1)H MRS alterations in recreational 3, 4-methylenedioxymethamphetamine (MDMA, "ecstasy") users

3,4-methylenedioxymethamphetamine (MDMA) is an illicit drug that has been associated with serotonergic axonal degeneration in animals. This study evaluates neurochemical abnormalities in recreational MDMA users. Twenty-two MDMA users and 37 normal subjects were evaluated with magnetic resonance imaging (MRI) and proton magnetic resonance spectroscopy ((1)H MRS) in the mid-frontal, mid-occipital, and parietal brain regions. (1)H MRS showed normal N-acetyl (NA) compounds in all brain regions. The myo-inositol (MI) concentration (+16.3%, P = 0.04) and the MI to creatine (CR) ratio (+14.1%, P = 0. 01) were increased in the parietal white matter of MDMA users. The cumulative lifetime MDMA dose showed significant effects on [MI] in the parietal white matter and the occipital cortex. The normal NA concentration suggests a lack of significant neuronal injury in recreational MDMA users. However, the usage-related increase in MI suggests that exposure to MDMA, even at recreational doses, may cause increased glial content. J. Magn. Reson. Imaging 1999;10:521-526.

Molecular aspects of magnetic resonance imaging and spectroscopy

Magnetic resonance imaging (MRI) is a well known diagnostic tool in radiology that produces unsurpassed images of the human body, in particular of soft tissue. However, the medical community is often not aware that MRI is an important yet limited segment of magnetic resonance (MR) or nuclear magnetic resonance (NMR) as this method is called in basic science. The tremendous morphological information of MR images sometimes conceal the fact that MR signals in general contain much more information, especially on processes on the molecular level. NMR is successfully used in physics, chemistry, and biology to explore and characterize chemical reactions, molecular conformations, biochemical pathways, solid state material, and many other applications that elucidate invisible characteristics of matter and tissue. In medical applications, knowledge of the molecular background of MRI and in particular MR spectroscopy (MRS) is an inevitable basis to understand molecular phenomenon leading to macroscopic effects visible in diagnostic images or spectra. This review shall provide the necessary background to comprehend molecular aspects of magnetic resonance applications in medicine. An introduction into the physical basics aims at an understanding of some of the molecular mechanisms without extended mathematical treatment. The MR typical terminology is explained such that reading of original MR publications could be facilitated for non-MR experts. Applications in MRI and MRS are intended to illustrate the consequences of molecular effects on images and spectra.

Metabolic changes in neuronal migration disorders: evaluation by combined MRI and proton MR spectroscopy

PURPOSE

To assess the role of 1H-magnetic resonance spectroscopy (MRS) in detecting biochemical abnormalities in neuronal migration disorders (NMDs).

METHODS

We performed 1H-MRS studies on 17 brain NMD areas [five polymicrogyria, eight subcortical heterotopia, and four cortical dysplasia on magnetic resonance imaging (MRI)]. The study group consisted of 15 patients, all but one affected by partial epileptic seizures. Spectra were acquired from volumes of interest localized on NMDs and contralateral sides and compared with those obtained on gray and white matter of 18 neurologic controls.

RESULTS

NMD lesions were characterized by lower N-acetylaspartate to creatine (NAA/Cr) and choline to Cr (Cho/Cr) ratios than those of the white (p = 0.002 and p = 0.004) and gray matter (p = 0.03 and p = 0.06) of neurologic controls. In addition, the normal-appearing contralateral sides to the NMD lesions showed a significant decrease of Cho/Cr ratio when compared with those of white (p = 0.003) and gray matter (p = 0.05) of neurologic controls. No relation was found between NAA/Cr decrease, EEG abnormalities, and NMD sides, or between NAA/Cr ratios, duration of epilepsy, and frequency of seizures. Lactate signal was detected in the spectra of four patients who had an epileptic seizure a short time before MR examination.

CONCLUSIONS

NAA/Cr decrease may be related more to structural and functional alteration of the NMD sides than to epileptic activity in these lesions. Low Cho/Cr may be related to a more extensive diffuse hypomyelination than suggested by the MRI findings. An activation of anerobic glycolysis during and after seizures could account for the presence of lactate. These data confirm that H-MRS is an advanced technique that may provide useful biochemical information in vivo on neurobiologic processes underlying NMDs.

Enhancement of chemotherapy by manipulation of tumour pH

The extracellular (interstitial) pH (pHe) of solid tumours is significantly more acidic compared to normal tissues. In-vitro, low pH reduces the uptake of weakly basic chemotherapeutic drugs and, hence, reduces their cytotoxicity. This phenomenon has been postulated to contribute to a 'physiological' resistance to weakly basic drugs in vivo. Doxorubicin is a weak base chemotherapeutic agent that is commonly used in combination chemotherapy to clinically treat breast cancers. This report demonstrates that MCF-7 human breast cancer cells in vitro are more susceptible to doxorubicin toxicity at pH 7.4, compared to pH 6.8. Furthermore 31P-magnetic resonance spectroscopy (MRS) has shown that the pHe of MCF-7 human breast cancer xenografts can be effectively and significantly raised with sodium bicarbonate in drinking water. The bicarbonate-induced extracellular alkalinization leads to significant improvements in the therapeutic effectiveness of doxorubicin against MCF-7 xenografts in vivo. Although physiological resistance to weakly basic chemotherapeutics is well-documented in vitro and in theory, these data represent the first in vivo demonstration of this important phenomenon.

Role of short TE 1H-MR spectroscopy in monitoring of post-operation irradiated patients

Post-surgical radiation therapy is a routine procedure in the treatment of primary malignant brain tumors. Along with modest therapeutic effects conventional fractionated radiotherapy, in spite of any modifications, produces damage to non-malignant brain tissues lying within the treatment volume, the extent of which depends on radiation dose. Serial 1H-MRS allows non-invasive investigation of tissue metabolic profiles. In the present study the ratios of resonance signals assigned to the major 1H-MRS-visible metabolites (N-acetylaspartate, choline, creatine, inositol, lactate and lipid methylene group) were evaluated before, during and after post-surgical fractionated radiotherapy in brain regions close to and more distant from the tumor bed, receiving different radiation exposures (60 and < 40 Gy, respectively). The study group consisted of ten patients (aged 28-51). A MRI/MRS system (Elscint 2T Prestige) operating at the field strength of 2 T and the proton resonance frequency of 81.3 MHz has been used and the 1H-MR spectra were acquired using single voxel double-spin-echo PRESS sequence with a short TE. The spectra were post-processed with automatic fitting in the frequency domain. It was found that although the metabolite profiles depend on the dose obtained, but other stress factors (like surgery) seem to contribute to the overall picture of the metabolic status of the brain as well. In studies of early irradiation injuries, an increase of choline related ratios may serve rather as cell proliferation indictors than as cell injury ones, whereas the mI/Cr ratio appears as one of the first indicators of local irradiation injury. In order to establish the prognostic marker for early radiation damage, however, it seems necessary to analyze all visible metabolites as well. None of the metabolites separately may serve as such an indicator due to the complexity of tissue metabolism. Interestingly, MRI reveals no changes during the therapy process, whereas the metabolite ratios are being affected in the course of time, thus supporting the presumption that the 1H-MRS is a valuable method of radiation therapy monitoring.

In vivo imaging of extracellular pH using 1H MRSI

Tumor pH is physiologically important since it influences a number of processes relevant to tumorigenesis and therapy. Hence, knowledge of localized pH within tumors would contribute to understanding these processes. The destructiveness, poor spatial resolution, and poor signal-to-noise ratio (SNR) of current technologies (e.g., microelectrodes, 31P magnetic resonance spectroscopy) have limited such studies. An extrinsic chemical extracellular pH (pHe) probe is described that is used in combination with 1H magnetic resonance spectroscopic imaging to yield pHe maps with a spatial resolution of 1 x 1 x 4 mm3. The principle of the technique is demonstrated on a phantom. Further data are shown to demonstrate its application in vivo, and results agree with previously reported pH values. The accuracy of the reported pH measurements is <0.1 pH units, as derived from a detailed analysis of the errors associated with the technique, the description of which is included.

Cerebral neoplasms in adults

MRI plays a critical role in the diagnosis, management, and follow-up of adult supratentorial neoplasms. However, there is considerable overlap in the imaging findings of these lesions. New imaging methods, such as functional MRI, diffusion imaging, and spectroscopy may further improve diagnostic specificity and surgical management. Knowledge of the pathogenesis of these tumors, imaging characteristics, and available novel imaging tools will aid the radiologist in making meaningful contributions in the evaluation and treatment of these lesions.

Evaluation of the effects of photodynamic therapy with phosphorus 31 magnetic resonance spectroscopy

Magnetic resonance spectroscopy in situ was used to study changes in phosphorus 31 metabolism after photodynamic therapy (PDT) of transplanted HeLa cell tumours. Tumours were irradiated 2 h after administration of ATX-S10 (8-formyloximethylidene-7-hydroxy-3-ethenyl-2,7,12,18, tetramethyl-porphyrin-13,17-bispropionil aspartate), a new photosensitizer and chlorin derivative. Nuclear magnetic resonance spectra were measured prior to illumination and 1, 3, 7, 14, 21 and 28 days after PDT on each mouse. A drastic decrease in adenosine triphosphate (ATP) and a concomitant increase in inorganic phosphate (Pi) were evident on the first day after PDT in all cases. The beta-ATP/total phosphate (P) ratio was 0.64 +/- 0.29% (average +/- s.d.) in complete response, 0.67 +/- 0.30% in recurrence and 2.45 +/- 0.93% in partial response. Comparison of this ratio to the histological findings revealed that the beta-ATP/total P ratio reflects the HeLa cell tumours which survived PDT. In other words, partial response on the one hand was distinguished from complete response and recurrence on the other with this ratio 1 day after PDT (P < 0.05). In addition, the ratio of phosphomonoester (PME) to Pi rose beyond 1.0 when macroscopic recurrence occurred, while it stayed under 1.0 in complete response. This finding suggests that the recurrence of HeLa cell tumours can be detected by the PME/Pi ratio.

Metabolic characterization of AIDS dementia complex by spectroscopic imaging

Prospective proton chemical shift imaging (CSI) of the brain was performed in 30 HIV- 1-seropositive patients and 11 healthy controls. Significant (P < 0.05) reductions in the N-acetyl-L-aspartate (NAA)/total creatine (Cr), and NAA/total choline (Cho) ratios and significant increases in Cho/Cr occurred in patients with 1) AIDS-defining diagnoses; 2) <200 CD4 lymphocyte counts/microl; 3) neurological evidence for an AIDS dementia complex (ADC); 4) magnetic resonance imaging (MRI) signs of cerebral atrophy. The basal ganglia and the insula were affected to approximately the same extent and without indications of spatial variations within these areas. Reduced NAA seems to indicate progressive neuronal injury or loss due to productive HIV infection in the brain and its clinical picture ADC. Spectroscopic abnormalities were, however, also observed in neurologically normal HIV patients or those with normal MRI results. Proton CSI may therefore serve as an early quantitative marker of central nervous system involvement in AIDS.

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

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 was -6%) compared with those measured on the same day (difference in TP was -29%).

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

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.

Feasibility study of lactate imaging of head and neck tumors

A proton spectroscopic imaging sequence was used to investigate the feasibility of lactate imaging in head and neck tumors. The sequence employs a two-shot lactate editing method with inversion recovery for additional lipid suppression, and a restricted field of view to suppress motion artifacts. Variations in acquisition parameters and two different receive coils were investigated on twelve patients. Elevated lactate was detected in three patients, no lactate was observed in seven patients, and two studies were inconclusive because of severe motion or inhomogeneity artifacts. Best results were obtained with an anterior/posterior neck coil at a 288 ms echo time (TE).

Phosphorus MR spectroscopy in the treatment of human extremity sarcomas

The application of 31P MR spectroscopy in the characterization and treatment of malignant human extremity tumors is reviewed and placed in the perspective of results obtained in murine sarcomas. Despite the now widespread acquisition of gradient localized spectral maps, the low spatial resolution that can be achieved at 1.5 or 2 T with 31P MRS, greatly limits its use in the study of tumor heterogeneity. The potential of 31P MRS is in the evaluation and monitoring of large inoperable extremity tumors. There are early spectral changes in human extremity sarcomas monitored after therapy, and recent studies have shown that the 31P MR spectra measured before treatment, and the changes in phosphate metabolites measured shortly thereafter, correlate with the clinical response after 2 or 3 months. Larger clinical studies are needed to confirm whether correlations of, for instance, pretreatment tumor pH with necrosis at resection and Pi decrease with tumor regression, can be used as a predictive test for clinical response.

Fraction of radiobiologically hypoxic cells in human melanoma xenografts measured by using single-cell survival, tumour growth delay and local tumour control as end points

Four human melanoma xenograft lines (A-07, D-12, R-18, U-25) grown orthotopically in Balb/c nu/nu mice were characterized with respect to the fraction of radiobiologically hypoxic cells. The purpose of the study was to establish a firm radiobiological basis for future use of the lines in the development and evaluation of non-invasive assays of tumour hypoxia. The hypoxic fractions were assessed using three different assays, the single cell survival assay, the tumour growth delay assay and the local tumour control assay, and the means +/- s.e. were found to be 6 +/- 3%, 3 +/- 1% and 5 +/- 2% respectively (A-07), 26 +/- 5%, 25 +/- 6% and 22 +/- 6% respectively (D-12), 55 +/- 9%, 65 +/- 8% and 48 +/- 7% respectively (R-18) and 52 +/- 8%, 59 +/- 7% and 47 +/- 7% respectively (U-25). The three assays gave numerical values for the hypoxic fraction that were not significantly different for any of the lines. The hypoxic fraction differed significantly among the lines; the R-18 and U-25 lines showed higher hypoxic fractions than the D-12 line (P < 0.05), which in turn showed a higher hypoxic fraction than the A-07 line (P < 0.05), regardless of the assay. The wide range of the hypoxic fractions and the significant differences among the lines suggest that A-07, D-12. R-18 and U-25 tumours should be useful models in future studies attempting to develop non-invasive assays of tumour hypoxia.

Induction of apoptosis in two mammalian cell lines results in increased levels of fructose-1,6-bisphosphate and CDP-choline as determined by 31P MRS

Programmed cell death or apoptosis was induced in human promyelocytic leukemia (HL-60) and Chinese hamster ovary (CHO-K1) cells using several cytotoxic drugs that have different modes of action, including camptothecin, ceramide, chelerythrine, etoposide, farnesol, geranyl geraniol, and hexadecylphosphocholine. The consequent changes in cellular metabolism were monitored using 31P MRS measurements on intact cells and cell extracts. Cells undergoing programmed cell death exhibited characteristic changes in the levels of glycolytic and phospholipid metabolites. The most significant changes were increases in the concentration of the glycolytic intermediate, fructose-1,6-bisphosphate and in the concentration of CDP-choline, which is an intermediate in phosphatidylcholine biosynthesis. In HL-60 cells, the increase in fructose-1,6-bisphosphate levels could be explained by depletion of cellular NAD(H) levels. All of the agents used to induce apoptosis caused the accumulation of CDP-choline. Since the resonances of this compound occur in a relatively well resolved region of tissue spectra, it could provide a marker for apoptosis that would allow the noninvasive detection of the process in vivo using 31P MRS measurements.

Quantitative 1H MRI and MRS microscopy of individual V79 lung tumor spheroids

In this Communication 1H MRI and MRS microscopy experiments of individual V79 lung tumor spheroids with diameters between 550 and 650 micrometer are reported. The results have been used to determine the T1, T2, and D values as well as the concentrations of water, total choline, creatine/phosphocreatine, and mobile lipids in the viable rims and in the necrotic centers.

Choline metabolism in breast cancer; 2H-, 13C- and 31P-NMR studies of cells and tumors

Choline metabolism in breast cancer cells and tumors has been investigated by multinuclear NMR in order to provide the biochemical basis for the presence of high phosphocholine in breast carcinoma relative to benign breast tumors and normal breast tissue. Choline was found to be transported into MCF7 human breast cancer cells and rapidly phosphorylated to phosphocholine which was then accumulated in the cells to high concentrations. The increased level of phosphocholine did not affect the rate of synthesis of phosphatidylcholine, indicating tight regulation of this pathway. The incorporation of [1,2-13C]choline (100 microM) into phosphocholine and phosphatidylcholine after 24 h was 69.5 and 36% of the total respective pools. Incorporation of 2H9-choline to tumors implanted in nude mice was achieved by infusing the deuterated choline to the blood circulation. The metabolism of deuterated choline was then monitored by 2H localized MRS. The blood level of choline before the infusion was 58.6 +/- 10.3 microM (measured by 1H-NMR of plasma samples) and increased approximately 5-fold during the infusion (measured by 2H-NMR). This increase in the blood level resulted in a gradual increase of a signal at 3.2 ppm due to deuterated choline metabolites. It appears that the increased availability of choline in the blood circulation leads to accumulation of phosphocholine in the tumors by the same mechanism as in the cells.

Early radiation effects in highly apoptotic murine lymphoma xenografts monitored by 31P magnetic resonance spectroscopy

PURPOSE

Phosphorus-31 magnetic resonance spectra (31P-MRS) were obtained from highly apoptotic murine lymphoma xenografts before and up to 24 hr following graded doses of radiation ranging from 2 to 30 Gy. Radiation-induced apoptosis was also estimated up to 24 hr by scoring apoptotic cells in tumor tissue.

METHODS AND MATERIALS

Highly apoptotic murine lymphoma cells, EL4, were subcutaneously transplanted into C57/BL mice. At 7 days after transplantation, radiation was given to the tumor with a single dose at 3, 10, and 30 Gy. The beta-ATP/Pi, PME/Pi, and beta-ATP/PME values were calculated from the peak area of each spectrum. Radiation-induced apoptosis was scored with counting apoptotic cells on hematoxylin and eosin stained specimens (% apoptosis).

RESULTS

The values of % apoptosis 4, 8, and 24 hr after radiation were 21.8, 19.6, and 4.6% at 3 Gy, 35.1, 25.6, and 14.8% at 10 Gy, 38.4, 38.0, and 30.6% at 30 Gy, respectively (cf. 4.4% in control). There was no correlation between early change in beta-ATP/Pi and % apoptosis at 4 hr after radiation when most of the apoptosis occurred. An early decrease in PME/Pi was observed at 4 hr after radiation dose at 30 Gy. For each dose, the values of beta-ATP/Pi 24 hr after radiation were inversely related to radiation dose.

CONCLUSION

The increase in beta-ATP/Pi observed by 31P-MRS was linked to the degree of histological recovery from radiation-induced apoptosis.

Proton magnetic resonance spectroscopic imaging in the clinical evaluation of patients with Niemann-Pick type C disease

OBJECTIVES

10 patients with Niemann-Pick disease type C (NP-C) were studied by proton magnetic resonance spectroscopic imaging (1H-MRSI) to assess the biochemical pathology of the brain and to determine whether this method can be useful to clinically evaluate these patients.

METHODS

1H-MRSI permits the simultaneous measurement of N-acetyl aspartate (NA), compounds containing choline (Cho), creatine plus phosphocreatine (Cre), and lactate (Lac) signal intensities from four 15 mm slices divided into 0.84 ml single volume elements. Spectroscopic voxels were identified from seven regions of interest.

RESULTS

In patients with NP-C, NA/Cre was significantly decreased in the frontal and parietal cortices, centrum semiovale, and caudate nucleus; Cho/Cre was significantly increased in the frontal cortex and centrum semiovale. Significant correlations were found between clinical staging scale scores and 1H-MRSI abnormalities.

CONCLUSION

1H-MRSI showed diffuse brain involvement in patients with NP-C consistent with the pathological features of the disease. 1H-MRSI is an objective and sensitive tool to neurologically evaluate patients with NP-C.

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

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.

The contribution of lactic acid to acidification of tumours: studies of variant cells lacking lactate dehydrogenase

Solid tumours develop an acidic extracellular environment with high concentration of lactic acid, and lactic acid produced by glycolysis has been assumed to be the major cause of tumour acidity. Experiments using lactate dehydrogenase (LDH)-deficient ras-transfected Chinese hamster ovarian cells have been undertaken to address directly the hypothesis that lactic acid production is responsible for tumour acidification. The variant cells produce negligible quantities of lactic acid and consume minimal amounts of glucose compared with parental cells. Lactate-producing parental cells acidified lightly-buffered medium but variant cells did not. Tumours derived from parental and variant cells implanted into nude mice were found to have mean values of extracellular pH (pHe) of 7.03 +/- 0.03 and 7.03 +/- 0.05, respectively, both of which were significantly lower than that of normal muscle (pHe = 7.43 +/- 0.03; P < 0.001). Lactic acid concentration in variant tumours (450 +/- 90 microg g(-1) wet weight) was much lower than that in parental tumours (1880 +/- 140 microg/g(-1)) and similar to that in serum (400 +/- 35 microg/g(-1)). These data show discordance between mean levels of pHe and lactate content in tumours; the results support those of Newell et al (1993) and suggest that the production of lactic acid via glycolysis causes acidification of culture medium, but is not the only mechanism, and is probably not the major mechanism responsible for the development of an acidic environment within solid tumours.

Magnetic resonance imaging and spectroscopy of combretastatin A4 prodrug-induced disruption of tumour perfusion and energetic status

The effects of combretastatin A4 prodrug on perfusion and the levels of 31P metabolites in an implanted murine tumour were investigated for 3 h after drug treatment using nuclear magnetic resonance imaging (MRI) and spectroscopy (MRS). The area of regions of low signal intensity in spin-echo images of tumours increased slightly after treatment with the drug. These regions of low signal intensity corresponded to necrosis seen in histological sections, whereas the expanding regions surrounding them corresponded to haemorrhage. Tumour perfusion was assessed before and 160 min after drug treatment using dynamic MRI measurements of gadolinium diethylenetriaminepentaacetate (GdDTPA) uptake and washout. Perfusion decreased significantly in central regions of the tumour after treatment. This was attributed to disruption of the vasculature and was consistent with the haemorrhage seen in histological sections. The mean apparent diffusion coefficient of water within the tumour did not change, indicating that there was no expansion of necrotic regions during the 3 h after drug treatment. Localized 31P-MRS showed that there was decline in cellular energy status in the tumour after treatment with the drug. The concentrations of nucleoside triphosphates within the tumour fell, the inorganic phosphate concentration increased and there was a significant decrease in tumour pH for 80 min after drug treatment. The rapid, selective and extensive damage caused to these tumours by combretastatin A4 prodrug has highlighted the potential of the agent as a novel cancer chemotherapeutic agent. We have shown that the response of tumours to treatment with the drug may be monitored non-invasively using MRI and MRS experiments that are appropriate for use in a clinical setting.

31P-magnetic resonance spectroscopy and 2H-magnetic resonance imaging studies of a panel of early-generation transplanted murine tumour models

The objective of this study was first to determine whether three slowly growing early-generation murine transplantable tumours, the T40 fibrosarcoma, T115 mammary carcinoma and T237 lung carcinoma, exhibit patterns of energetics and blood flow during growth that are different from those of the faster growing RIF-1 fibrosarcoma. Serial measurements were made with 31P-magnetic resonance spectroscopy (MRS), relating to nutritive blood flow and 2H-magnetic resonance imaging (MRI), which is sensitive to both nutritive and large-vessel (non-nutritive) flow. All four tumour lines showed a decrease in betaNTP/Pi and pH with growth; however, each line showed a different pattern of blood flow that did not correlate with the decrease in energetics. Qualitative histological analysis strongly correlated with the 2H-MRI. Second, their response to 5 mg kg(-1) hydralazine i.v. was monitored by 31P-MRS. A marked decrease in betaNTP/Pi and pH was observed in both the RIF-1 fibrosarcoma and the third-generation T115 mammary carcinoma after hydralazine challenge. In contrast, the fourth generation T40 fibrosarcoma and T237 lung carcinoma showed no change in 31P-MRS parameters. However, a fifth-generation T237 cohort, which grew approximately three times faster than fourth-generation T237 cohorts, exhibited a significant deterioration in betaNTP/Pi and pH in response to hydralazine. These data are consistent with a decoupling between large-vessel and nutritive blood flow and indicate that early-generation transplants that have a slow growth rate and vascular tone are more appropriate models of human tumour vasculature than more rapidly growing, repeatedly transplanted tumours.

Assessment of glucosylifosfamide mustard biodistribution in rats with prostate adenocarcinomas by means of in vivo 31P NMR and in vitro uptake experiments

A combined in vitro/in vivo study was performed to evaluate the possible application of phosphorus (31P) NMR spectroscopy for therapy monitoring and to investigate glucosylifosfamide mustard (Glc-IPM) transport and biodistribution by radiotracer techniques. Dynamic in vivo 31P NMR measurements were performed in rats with prostate adenocarcinoma after i.v. injection of 1 mmol/kg body weight (bw) of ifosfamide (IFO) (n = 4) and 1 mmol/kg bw (n = 4) or 2.15 mmol/kg bw (n = 9) of Glc-IPM. In a biodistribution study with 14C-labeled Glc-IPM and a final dose of 0.8 mmol Glc-IPM/kg bw, the animals were killed 5, 30, 60, and 120 min after drug administration, an ethanol extraction was performed from several tissues, and the dose per g tissue was calculated. The same tumor cell line was used in saturation and competition experiments to further elucidate the transport mechanism. The 31P NMR signals of IFO and Glc-IPM showed no overlap with the endogenous phosphorus peaks. A rapid washout with a half-life between 25.9 +/- 5.6 min for the lower dose and 34.3 +/- 4.2 min for the higher dose of Glc-IPM was observed in the tumor. No statistically significant change of the pH value was observed during the examination period. The beta-nucleoside 5'-triphosphate (NTP)/inorganic phosphate (Pi) signal intensity ratio showed a tendency to decrease but without statistical significance. A rapid elimination was demonstrated by both the noninvasive NMR technique and the biodistribution study. No saturation was found in vitro for the Glc-IPM uptake, even at the concentration of 5 mM. Furthermore, the Glc-IPM uptake was not inhibited by the presence of 2-deoxyglucose and vice versa. The data show that the pharmacokinetics of Glc-IPM in the tumor can be followed in vivo by 31P NMR. The results presented are evidence for diffusion as the transport mechanism for Glc-IPM in this tumor model. However, the better visualization of Glc-IPM as compared to ifosfamide may be due to metabolic trapping of a negatively charged metabolite after deglycosylation.

31Phosphorus magnetic resonance spectroscopy in the assessment of head and neck tumors

PURPOSE

31Phosphorus magnetic resonance spectroscopy (31P-MRS) provides biochemical information in a noninvasive way. The aim of this work was: (a) to characterize the 31P spectrum of advanced head and neck tumors, and (b) to evaluate the spectral changes after treatment and to correlate them with the pathologic response.

METHODS AND MATERIALS

A total of 20 patients diagnosed with advanced head and neck tumors and 7 healthy controls participated in the study. The tumor mass and its contralateral side were studied by means of 31P-MRS before and after treatment. Neck muscles of a control group were also studied.

RESULTS

Tumors presented ratios of phosphomonoesters (PME), phosphodiesters (PDE), and inorganic phosphate (Pi) with respect to the adenosine triphosphate (ATP), significantly higher and a PCr (phosphocreatine)/ATP ratio lower than the neck muscle of volunteers or the contralateral side. The PDE/ATP and PME/ATP ratio values obtained before therapy were similar, independent of the later response to treatment. However, when there was a complete response, the ratios measured after treatment were decreased.

CONCLUSION

These results show the existence of significant differences between the 31phosphorus spectrum of tumors and neck muscle, but also between the tumors and their contralateral sides. Moreover, 31P-MRS is able to detect metabolic changes after a complete response. These results suggest that 31P-MRS would be useful in the evaluation of the clinical response of head and neck tumors.

3D multivoxel proton spectroscopy of human brain using a hybrid of 8th-order Hadamard encoding with 2D chemical shift imaging

Multivoxel 3D localized proton spectroscopy using a hybrid of 1D 8th-order transverse Hadamard spectroscopic imaging (HSI) with 2D chemical shift imaging (CSI) is demonstrated in human brain. The spatially selective HSI pulse incorporates naturally into the PRESS sequence (TE = 135 ms), which then both excites an 8 x 8 x 6 cm parallelepiped volume of interest (VOI) and subdivides it into eight slices. The planes of these slices are further partitioned into 16 x 16 voxel arrays using 2D CSI to yield 8 x 8 x 8 voxels within the VOI. Simultaneous 3D coverage yields good voxel signal-to-noise (8, 12, and 22 for choline, creatine, and N-acetylaspartate, respectively) from these 0.75-ml voxels, in approximately 45 min. The high spatial isolation allows localization to within less than 1 cm from the skull without fat contamination.

Ethanolamine, but not phosphoethanolamine, potentiates the effects of insulin, phosphocholine, and ATP on DNA synthesis in NIH 3T3 cells--role of mitogen-activated protein-kinase-dependent and protein-kinase-independent mechanisms

NIH 3T3 fibroblasts express a phospholipase D activity hydrolyzing phosphatidylethanolamine (PtdEtn) which produces ethanolamine (Etn) in response to a variety of growth regulating agents. The main objective of this work was to evaluate the effects of Etn on mitogenesis and to determine whether these effects require its metabolism to phosphoethanolamine (PEtn) or PtdEtn. To increase conversion of Etn to PEtn, an Etn-specific kinase derived from Drosophila was highly expressed in NIH 3T3 cells. Overexpression of this Etn kinase resulted in large (10-12.5-fold) increases in PEtn formation, but only in modest (1.2-1.7-fold) increases in PtdEtn synthesis. In both vector control and Etn kinase overexpressor cells, Etn had biphasic effects on insulin-induced DNA synthesis with maximal (approximately 2-fold) potentiating effects being observed at 0.5-1 mM concentrations, followed by an inhibitory phase at higher Etn concentrations. In the Etn kinase overexpressor lines, the inhibitory phase was elicited by lower Etn concentrations and it was partially blocked by 5 mM choline due to decreased formation of PEtn. In both vector control and Etn kinase overexpressor cells, phosphocholine (PCho) and insulin synergistically stimulated DNA synthesis; their effects were further enhanced by physiologically relevant (5-60 microM) concentrations of Etn by a mechanism independent of mitogen-activated protein (MAP) kinase. Concentrations of Etn >50 microM also enhanced the effects of both PCho and the synergistic effects of PCho plus ATP; however, in the latter case 20 microM Etn was inhibitory. The magnitude of both the potentiating and inhibitory effects of Etn on PCho-induced as well as PCho + ATP-induced DNA synthesis were similar in the vector control and Etn kinase overexpressor cells; they were associated with stimulation and inhibition, respectively, of p42 MAP kinase activity. The results indicate that in NIH 3T3 cells Etn exerts significant effects on DNA synthesis which, except inhibition of insulin-induced DNA synthesis by higher concentrations of Etn, do not correlate with the metabolism of Etn to PEtn or PtdEtn.

High spatial resolution and speed in MRSI

The in vivo applications of magnetic resonance spectroscopic imaging (MRSI) have expanded significantly over the past 10 years and have reached the point where clinical trials are underway for a number of different diseases. One of the limiting factors in the widespread use of this technology has been the lack of widely available tools for obtaining data which are localized to sufficiently small tissue volumes to make an impact upon diagnosis and treatment planning. This is especially difficult within the timeframe of a clinical MR examination, which requires that both anatomic and metabolic data are acquired and processed. Recent advances in the hardware and software associated with clinical scanners have provided the potential for improvements in the spatial and time resolution of imaging and spectral data. The two areas which hold the most promise in terms of MRSI data are the use of phased array coils and the implementation of echo planar k-space sampling techniques. These could have immediate impact for 1H MRSI and may prove valuable for future applications of 31P MRSI.

Theoretical evaluation and comparison of fast chemical shift imaging methods

Magnetic resonance chemical shift imaging (CSI) is becoming the method of choice for localized NMR spectroscopic examinations, allowing simultaneous detection of NMR spectra from a large number of voxels. The main limitation of these methods is their long experimental duration. A number of fast CSI experiments have been presented, promising to reduce that duration. In this contribution the criteria for evaluating and optimizing the sensitivity of fast CSI experiments are elaborated. For a typical experiment in the human brain, the performance of various methods is compared. While conventional CSI provides optimal sensitivity per unit time, it is shown in which circumstances fast sequences allow a shorter experimental duration. Using these results, the best method for any experimental requirements can be selected.

Nuclear magnetic resonance spectroscopy of cancer

Nuclear magnetic resonance spectroscopy (MRS) offers a non-invasive approach for studying tumour biochemistry and physiology. This review highlights NMR nuclei (31P, 1H, 19F, 13C, 2H) that have been observed in both pre-clinical and clinical spectroscopic studies of cancer.

Study of the metabolism of choline and phosphatidylcholine in tumors in vivo using phosphonium-choline

The results of an initial study on the feasibility of using the phosphonium analog of choline to follow the metabolism of phosphatidylcholine in tumors in vivo using 31P NMR are reported. C3H/He mice bearing a mammary carcinoma tumor on the foot pad were fed a choline-free diet supplemented with the phosphonium analog of choline. Metabolites of this compound, including the phosphonium analogs of phosphatidylcholine, phosphocholine, glycerophosphocholine, and betaine were observed noninvasively in vivo in tumors by 31P NMR after 2-3 weeks of feeding. Clearance of these phosphonium-labeled metabolites from tumors was measured after a change to a choline-containing diet. Significant decreases were seen in the levels of the analogs of betaine (P < 0.003) and phosphatidylcholine (P < 0.004) by Day 4. A significant increase in the level of authentic phosphocholine (P < 0.003) occurred over the same time period.

Abnormal cerebral phospholipid metabolism in dyslexia indicated by phosphorus-31 magnetic resonance spectroscopy

It has recently been suggested that many of the features of dyslexia may be explicable in terms of an abnormality of membrane phospholipid metabolism. To investigate this we studied 12 dyslexic and 10 non-dyslexic adults using in vivo cerebral phosphorus-31 magnetic resonance spectroscopy (31P MRS), as the phosphomonoester (PME) and phosphodiester (PDE) peaks include indices of membrane phospholipid turnover. Spectral localization was achieved using four-dimensional chemical shift imaging methods. The PME peak area was significantly elevated in the dyslexic group, as evidenced by higher ratios of PME/total phosphorus (F = 9.5, p < 0.006), PME/beta NTP (F = 17.5, p < 0.001) and PME/PDE (F = 6.9, p < 0.02). No other spectral measurements differed significantly between the groups. These findings are consistent with the hypothesis that membrane phospholipid metabolism is abnormal in dyslexia. The PME peak is multicomponent, but predominantly consists of phosphoethanolamine (PE) and phosphocholine (PC), which are precursors of membrane phospholipids. Our finding of raised PME in dyslexia could therefore reflect reduced incorporation of phospholipids into cell membranes, although definitive interpretation must await further evidence.

Serial proton magnetic resonance spectroscopy imaging of glioblastoma multiforme after brachytherapy

The utility of three-dimensional (3-D) proton magnetic resonance spectroscopy (1H-MRS) imaging for detecting metabolic changes after brain tumor therapy was assessed in a serial study of 58 total examinations of 12 patients with glioblastoma multiforme (GBM) who received brachytherapy. Individual proton spectra from the 3-D array of spectra encompassing the lesion showed dramatic differences in spectral patterns indicative of radiation necrosis, recurrent or residual tumor, or normal brain. The 1H-MRS imaging data demonstrated significant differences between suspected residual or recurrent tumor and contrast-enhancing radiation-induced necrosis. Regions of abnormally high choline (Cho) levels, consistent with viable tumor, were detected beyond the regions of contrast enhancement for all 12 gliomas. Changes in the serial 1H-MRS imaging data were observed, reflecting an altered metabolism following treatment. These changes included the significant reduction in Cho levels after therapy, indicating the transformation of tumor to necrotic tissue. For patients who demonstrated subsequent clinical progression, an increase in Cho levels was observed in regions that previously appeared either normal or necrotic. Several patients showed regional variations in response to brachytherapy as evaluated by 1H-MRS imaging. This study demonstrates the potential of noninvasive 3-D 1H-MRS imaging to discriminate between the formation of contrast-enhancing radiation necrosis and residual or recurrent tumor following brachytherapy. This modality may also allow better definition of tumor extent prior to brachytherapy by detecting the presence of abnormnal metabolite levels in nonenhancing regions of solid tumor.

Assignment of glial brain tumors in humans by in vivo 1H-magnetic resonance spectroscopy and multidimensional metabolic classification

This study presents a simple approach for the noninvasive assignment of glial brain tumors according to malignancy by single-voxel proton magnetic resonance spectroscopy at short echo times (TE < or = 50 milliseconds). Based on peak area ratios, a five-dimensional data set was obtained for each investigated subject. This vector was then projected along metabolic coordinates in a two-dimensional metabolic space. These coordinates had been determined in a previous study (Hagberg G et al., 1995, Magn Reson Med 34: 242-252). Tumor assignment was done without any knowledge of histology by comparing the location of the new cases to the features of the previous study. All 11 investigated glioblastomas multiforme, as well as 4 of 5 astrocytomas grade II, could easily be assigned to the groups of high- and low-grade tumors, respectively. Classification was more difficult in the case of a cystic astrocytoma grade II and one astrocytoma grade III. Two spectra measured in normal-appearing matter of glioblastoma patients were not classified as healthy. Using single-voxel proton magnetic resonance spectroscopy at short echo times with the knowledge of a base study, a straightforward, fast, and noninvasive differential diagnosis of glial brain tumors is possible.

Proton spectroscopy of suprasellar tumors in pediatric patients

OBJECTIVE

Magnetic resonance imaging and computed tomography provide good anatomic detail of suprasellar tumors in pediatric patients but are not able to predict histology in many cases. Proton magnetic resonance spectroscopy provides metabolic data that may add to diagnostic specificity. We preoperatively performed localized proton magnetic resonance spectroscopy on pediatric patients with suprasellar tumors and correlated the results with the histological findings. Cyst fluid obtained from patients with craniopharyngiomas was studied with high-resolution magnetic resonance spectroscopy to better understand the in vivo data.

METHODS

Nineteen patients aged 1 to 21 years underwent spectroscopy. Surgical pathological samples were obtained from 14 patients. In each of five patients, the presence of a solid chiasmatic mass in addition to clinical evidence of neurofibromatosis Type I allowed the presumptive diagnosis of chiasmatic astrocytoma. Thus, the study population included 6 patients with craniopharyngiomas, 10 with chiasmatic/hypothalamic astrocytomas, and 3 with pituitary adenomas. The data obtained were compared with those of healthy brain from age-matched participants.

RESULTS

Spectroscopy was specific for the diagnosis. All craniopharyngiomas showed a dominant peak at 1 to 2 ppm, consistent with lactate or lipids, with trace amounts of other metabolites. This was confirmed using high-resolution spectroscopy. Chiasmatic gliomas showed a profile of choline, N-acetylaspartate, and creatine, and the choline:N-acetylaspartate ratio was 2.6 +/- 1.3, compared with 0.7 +/- 0.3 for samples of healthy brain (t test, P = 0.0003). Pituitary adenomas showed only a choline peak or no metabolites at all.

CONCLUSION

Proton spectroscopy may be helpful in supplementing standard imaging for the preoperative diagnosis of three types of suprasellar tumors that are common in pediatric patients.

Nocturnal 5-fluorouracil infusion to patients with breast cancer prior to surgery: appearance of 5-fluorouracil-induced AgNORs aggregation (FAA)

Between 1994 and 1995, 1 day nocturnal infusion of 5-fluorouracil (5-FU) was performed prior to surgery in 13 primary breast cancer patients; 300 mg/m2 of 5-FU was infused constantly from 2100 h to 0700 h via peripheral vein with a volumetric pump. 5-FU concentration in tissues was measured within surgical specimens by HPLC. The concentrations of 5-FU in tumor tissues ranged from 6 to 49 ng/g (average +/- SEM 25.0 +/- 4.1 ng/g), while in normal breast tissues and adipose tissues 5-FU was below the detection limit (<3 ng/g). The 5-FU concentration was lower in estrogen-receptor-positive tumors (14.4 +/- 4.5 ng/g) than in estrogen-receptor-negative tumors (31.8 +/- 5.0 ng/g). Typical FAA was observed in the tumor tissues of three patients. In these three cases, AgNORs were aggregated to one large spheroidal figure in more than 39% of tumor cells. Appearance of FAA could not be predicted by other clinical features. Nocturnal 5-FU infusion caused FAA changes in certain types of primary breast cancer.

Phosphorus-31 chemical shift imaging of metastatic tumors located in the spine region

RATIONALE AND OBJECTIVES

Phosphorus-31 magnetic resonance spectroscopy was used in 14 cases to examine metastases of known malignant tumors located in the spine region. The purpose was to test the hypothesis that tumor phosphomonoester (PME) is elevated.

METHODS

Two-dimensional chemical shift imaging was used in combination with a slice-select gradient in the third dimension to obtain true three-dimensional localization.

RESULTS

The spectral maps revealed PME signals increased up to 10 times in voxels containing contrast-enhancing metastatic spine lesions compared with adjacent areas and peripheral muscle voxels. Phosphomonoester increase was significant for all tumors combined (8.6 +/- 5.3 arbitrary units versus 2.4 +/- 0.5 and 2.2 +/- 0.8 arbitrary units in unaffected myelum and corpora; P < 0.001), though smaller than 2 standard deviations in 5 of 14 cases. The latter shared high proportions of phosphocreatine, phosphocreatine > 30% of total phosphate, indicating substantial amounts of muscle tissue included in the tumor voxels (partial volume effect).

CONCLUSIONS

Phosphorus-31 MR spectroscopy can be of value in the recognition of malignant vertebral column abnormalities. Malignant tumor is marked by drastic PME increases-fourfold to tenfold, provided that partial volume effects are small.

Two-dimensional proton chemical-shift imaging of human muscle metabolites

Large lipid signals and strong susceptibility gradients introduced by muscle-bone interfaces represent major technical challenges for in vivo proton MRS of human muscle. Here, the demonstration of two-dimensional proton chemical-shift imaging of human muscle metabolites is presented. This technique utilizes a chemical-shift-selective method for water and lipid suppression and automatic shimming for optimal homogeneity of the magnetic field. The 2D1H CSI technique described facilitates the acquisition of high-spatial-resolution spectra, and allows one to acquire data from multiple muscle groups in a single experiment. A preliminary investigation utilizing this technique in healthy adult males (n = 4) revealed a highly significant difference in the ratio of the creatine to trimethylamine resonance between the fast and slow twitch muscle groups examined. The technique is robust, can be implemented on a commercial scanner with relative ease, and should prove to be a useful tool for both clinical and basic investigators.

3D localized in vivo 1H spectroscopy of human brain by using a hybrid of 1D-Hadamard with 2D-chemical shift imaging

We report acquisition of 3D image-guided localized proton spectroscopy (1H-MRS) in the human brain on a standard clinical imager. 3D coverage is achieved with a hybrid of chemical shift imaging (CSI) and transverse Hadamard spectroscopic imaging (HSI). 16 x 16 x 4 arrays of 3.5 and 1 ml voxels were obtained in 27 min. The spatially selective HSI 90 degrees pulses incorporate naturally into a PRESS double spin-echo sequence to subdivide the VOI into four partitions along its short axis. 2D CSI (16 x 16) is performed along the other long axes. Because the hybrid excites the spins in the entire VOI, a square-root-N signal-to-noise-ratio (SNR) gain per given examination time is realized compared with sequentially interleaving N 2D slices. A two-fold gain in sensitivity is demonstrated in the brain for N = 4.

Alterations of lactate (+lipid) concentration in brain tumors with in vivo hydrogen magnetic resonance spectroscopy during radiotherapy

RATIONALE AND OBJECTIVES

The authors determine whether assessment of the relative lactate(+lipid) concentration ([r-Lac(+lip)]) obtained from hydrogen magnetic resonance (MR) spectroscopy is useful for predicting the outcome of radiotherapy on brain tumors.

METHODS

Fifty-one hydrogen MR spectroscopic studies were performed in eight patients with primary or metastatic brain tumor before and during radiotherapy. The r-Lac(+lip) calculated as the ratio of lactate(+lipid) peak area to total water was compared before and during radiotherapy in each case. The change of tumor volume measured on magnetic resonance images also was compared.

RESULTS

The r-Lac(+lip) substantially decreased in the radiosensitive cases (three lymphomas and one brain cancer) but did not decrease, even at the end of therapy, in the radioresistant cases (two brain cancers and two glioblastomas).

CONCLUSION

Assessment of r-Lac(+lip) may adjunctively contribute to the early prediction of the radiotherapeutic effect on brain tumors.

Quantification of phosphorus metabolites in human calf muscle and soft-tissue tumours from localized MR spectra acquired using surface coils

Metabolite concentrations determined from MR spectra provide more specific information than peak area ratios. This paper presents a method of quantification that allows metabolite concentrations to be determined from in vivo 31P MR spectra acquired using a surface coil and ISIS localization. Corrections for the effects of B1 field inhomogeneity produced by surface coils are based on a measured and calibrated spatial sensitivity field map for the coil. Account is taken of imperfections in pulse performance, coil loading effects and relaxation effects, the latter making use of published metabolite relaxation times. The technique is demonstrated on model solutions. The concentrations of the main 31P metabolites in normal human calf muscle measured using this method are [PCr] = 26.9 +/- 4.1 mM; [Pi] = 3.6 +/- 1.2 mM; [NTP] = 6.8 +/- 1.8 mM. Quantification of spectra acquired from soft-tissue tumours in patients both pre- and post-treatment showed that changes in metabolite concentrations are more sensitive to metabolic changes than changes in peak area ratios.

Diagnosis of brain abscess by magnetic resonance spectroscopy. Report of two cases

Two cases of brain abscess were diagnosed by combining magnetic resonance spectroscopy (MRS) and magnetic resonance (MR) imaging. The resonances observed in vivo were assigned by means of an in vitro MRS study of the exudates extracted during surgical aspiration of the abscesses. The technique of MRS was demonstrated to be very powerful in the differential diagnosis of brain abscesses from other brain pathologies such as neoplasms. Amino acids, probably originating from extracellular proteolysis, and other compounds, such as acetate, arising from bacterial metabolism, were visible in the MRS spectra of the abscess, whereas they are not present in spectra of neoplasms. In this sense, MRS complemented the information provided by MR imaging to achieve a correct diagnosis of brain abscesses and could be added to routine MR examinations with only a small increase in cost and time.

Treatment-induced changes in 31P-MRS (magnetic resonance spectroscopy) spectra of sera from patients with acute leukemia

31P-nuclear magnetic resonance (NMR) spectra were obtained in vitro from sera of 40 healthy volunteers and 30 patients with acute leukemia (AL) at the time of diagnosis and repeated up to 2-13 times during therapy. All spectra consisted of inorganic phosphate (Pi) peak (used as a reference peak) and two peaks from phospholipids (PL): one peak due to phosphatidylethanolamine and sphingomyelin (PE + SM) and second peak due to phosphatidylcholine (PC). Prior to initiation of therapy 31P spectra of sera of patients with acute leukemia differed from spectra of sera of normal individuals. Peak intensities of the PL were low in relation to Pi. During therapy leading to remission, resonance from PL progressively increased approximately to the spectral pattern in normal sera. Contrary to that, in non-responders the intensities of the phospholipids peaks remained unchanged. Long-term follow-up 31P-MRS studies showed not only a good correlation between this 31P-MRS evolution of sera and the response to the therapy but also showed changes in phospholipids' levels in the following days during and after therapy. Moreover, correlations were found between high-density lipoprotein (HDL), cholesterol (CHOL) and low-density lipoprotein (LDL) concentrations measured by conventional techniques and peak intensities of PC and of PE + SM acquired by 31P-MRS.

In vivo phosphorus polarization transfer and decoupling from protons in three-dimensional localized nuclear magnetic resonance spectroscopy of human brain

Refocused insensitive nucleus enhancement by polarization transfer (RINEPT) from protons (1H) to a J-coupled phosphorus (31P) has been incorporated into three-dimensional (3D) chemical-shift-imaging (CSI) sequence on a clinical imager. The technique is demonstrated on a phantom and in in vivo human brain. The polarization-transfer efficiency (approximately 1.2) is lower than the theoretical maximum of gamma1H/gamma31P approximately 2.4 resulting from 1H-1H homonuclear J couplings of similar magnitude competing with the 1H --> 31P transfer. Nevertheless, compared with direct 31P Ernst-angle excitation, signal gains of up to x1.8 were obtained mainly as a result of T1 differences between 31P and the 1H. Spectral interpretation is simplified by editing out all non-proton-coupled 31P signals. The duration, approximately 50 min, and power deposition, approximately 1 W x kg(-1), make the application suitable for human studies.

In vivo and ex vivo study of metabolic and cellular effects of 5-fluorouracil chemotherapy in a mouse mammary carcinoma

The effect of 5-fluorouracil (5FU) on the 31P nuclear magnetic resonance (NMR) profile of a mouse mammary carcinoma, implanted on the foot of CH3/He mice, was studied both in vivo and in perchloric acid extracts. In vivo, significant increases in the ratios, nucleotide triphosphate:inorganic phosphate (Pi) (p < 0.02) and phosphocreatine:Pi (p < 0.005), were observed 48 h after 5FU, relative to control. Two readily resolvable peaks were observed in the phosphomonoester region of the in vivo NMR spectrum, phosphocholine (PC) and a peak (denoted PME') comprised of mainly phosphoethanolamine (PE). PME':PC was significantly elevated relative to control from 24 h to 168 h (p < 0.0001 at 48 h). Perchloric acid extract data indicate that the change in this ratio was due to an increase in the PE concentration rather than a decrease in PC. PE increased from 0.56 +/- 0.11 micromol/g tissue in controls to 0.95 +/- 0.29 micromol/g tissue 48 h after 5FU (p < 0.006). Perchloric acid extracts also revealed a significant increase in phosphodiesters. Glycerophosphocholine increased from 0.82 +/- 0.24 micromol/g tissue in controls to 1.82 +/- 0.61 micromol/g tissue in 5FU treated tumors after 48 h (p < 0.002), and glycerophosphoethanolamine increased from 0.25 +/- 0.06 micromol/g tissue in controls to 0.36 +/- 0.10 micromol/g tissue in treated tumors (p < 0.004). These changes suggest that ethanolamine and choline containing metabolites in this tumor may be metabolized via different pathways. Cell cycle analysis showed only relatively small changes in cell cycle distribution and apoptotic fraction following 5FU.

Potential role of in vitro 1H magnetic resonance spectroscopy in the definition of malignancy grading of human neuroepithelial brain tumours

The increasing sensitivity of neuro-imaging in the diagnosis of brain expanding lesions is not directly related to biopathological specificity and new technological approaches are under study. In particular Magnetic Resonance Spectroscopy (MRS) allows evaluation of some biochemical pathways whose metabolic alterations may be correlated with the nature and malignancy grading of primary brain tumours. In the present study the author performed an in vitro high field 1H MRS (9.4 and 14.1 T) analysis of specimens obtained from stereotactic biopsy or microsurgical removal of primary brain tumours. Different samples derived from heterogeneous areas and/or infiltrated perilesional regions were examined. This study was principally focused on malignancy grading of gliomas and its correlation with the ratio (R) between the resonance band arising from choline containing compounds (between 3.14 and 3.35 ppm) and the total creatine signal (3.0 ppm). Analyses allowed significant discrimination between astrocytomas (R = 2.4 +/- 0.6) and glioblastoma (GBM) (R = 4.4 +/- 1.3) [p < 0.002]; however the results did not allow discrimination between differentiated and anaplastic astrocytomas. The GBM showed the largest spread of values corresponding to their higher level of tissue heterogeneity and de-differentiation. Studies on non astrocytic brain tumours indicated that even higher R values were exhibited by oligodendrogliomas, even in well differentiated forms (p < 0.02 with respect to GBM). Moreover, preliminary observations indicated that signals arising from other metabolites may also contribute to a differential diagnosis of different oncotypes. Among these glycine appears particularly relevant, since higher levels were measured for this amino acid in GBM with respect to both astrocytomas and oligodendrogliomas.

In vivo 31P MRS evaluation of ganciclovir toxicity in C6 gliomas stably expressing the herpes simplex thymidine kinase gene

Phosphorus MRS was evaluated as a monitor of tumour therapeutic response to the herpes simplex virus thymidine kinase suicide gene therapy paradigm. In vivo 31P spectra were obtained from subcutaneous rat C6 gliomas constitutively expressing the HSVtk gene post treatment with ganciclovir (GCV, 15 mg/kg i.p., twice-daily). Significant regression (p < 0.1) of tumour volume was observed 10 days after beginning GCV administration. However, no changes in tumour pH or energy metabolites from pre-treatment values were observed. High-resolution 31P spectra of tumour extracts revealed a statistically significant reduction in the phosphocholine to phosphoethanolamine ratio six days post-GCV administration. These results indicate that the HSVtk/GCV-induced killing of tumours is not associated with corresponding changes in 31P MRS-observable energy metabolites and pH. The observed reduction in the PE/PC ratio may provide a non-invasive in vivo indicator of therapeutic efficacy.

An investigation of rat mammary healthy and R3230AC tumor tissues and cells by means of solid-state 13C NMR

The first results are shown of a low temperature 13C solid-state, cross-polarization magic angle spinning (CPMAS) NMR study of R3230AC rat mammary carcinoma transplanted into female Fischer rats. Intact, healthy mammary tissues and tumor tissues, quickly frozen at -78 degrees C after excision, were examined, as were normal epithelial cells and tumor cells extracted from these tissues. The experiments were performed at -100 degrees C and -40 degrees C. The solid-state 13C NMR spectrum of the healthy tissue is dominated by the triacylglycerols present in the adipose tissue. The solid-state spectra of the other compounds differ significantly from the spectrum of the healthy tissue, and are dominated by the phospholipids and the large molecular weight proteins, for a major part present in the membranes. The spectra of the tumor tissues and the tumor cells were very similar, in accordance with the fact that the tumor tissues consisted of 80-90% tumor cells. The spectrum of the normal cells shows the same general features as those of the tumor tissue and tumor cells, but also exhibits some significant differences. The main difference at -100 degrees C is that, in the tumor samples, the relative intensity of the resonance line arising at 30 ppm, which is due to methylene chains, is reduced. At -40 degrees C this intensity is further reduced in the tumor samples, whereas the spectrum of the normal cells remains unaltered. It is tentatively concluded that the spectral differences between the normal and the malignant cells are due to changes in mobilities occurring in the cells after tumorigenesis, and that compared with normal epithelial cells the tumor cells contain an increased amount of mobile methylene chains. These differences virtually disappear if the samples are preserved at temperatures equal to or above 4 degrees C, emphasizing the importance of sample preservation at low temperatures, and hence of the solid-state NMR approach to investigate structures and dynamics in cells before and after tumor formation.