MR image-guided P-31 MR spectroscopy in the evaluation of brain tumor treatment

Pre-operative localized in vivo proton spectroscopy in cerebral tumors at 4.0 Tesla--first results

Sixteen patients with prediagnosed cerebral lesions were studied with stimulated echo localized 1H-spectroscopy at 4 Tesla. Initially, CT cerebral angiography and MR investigation at 1.5 Tesla were performed. After selecting a patient and receiving his agreement the high field examination started with the acquisition of an MR image of the known tumor at 4 Tesla using head or surface coil. 1H-spectroscopy was performed by selectively exciting a cubic volume between 8 to 20 cubic centimeters in the center of the tumor, in one case below 4 ccm (pinealoma). If possible, in a second examination the corresponding opposite side of the brain was studied. The extirpation of the tumor followed during the next days. Macroscopic aspects, histology and grading of the investigated lesions were determined. In some cases, specimens of the tumors were cooled in cooking salt solution and in liquid nitrogen, respectively, in order to perform in vitro proton MRS at 8.4 Tesla. The evaluable in vivo spectra showed good resolution and significant differences between corresponding cerebral areas with and without tumor as well as between different types of tumor histologies like medulloblastoma, astrocytoma and meningeomas. Often a good correspondence between in vivo and in vitro spectroscopy was seen. No clinically relevant side effects or complications were observed during the in vivo high field examination.

Experimental approaches to image localized human 31P NMR spectroscopy

Experimental procedures for obtaining localized 31P NMR spectra of humans by means of the ISIS sequence are discussed in detail. The technique is optimized for use with volume coils and with surface coils in order to measure localized 31P NMR spectra of different tissues and organs. Selective frequency-modulated (FM) inversion and excitation pulses are applied for optimal inversion or excitation despite B1 inhomogeneity. Pulse imperfection may lead to spurious signal contributions from outside the selected volume; this contamination is reduced by using long pulse intervals, by properly ordering the ISIS acquisitions, and by using FM excitation pulses. Simultaneous measurement of multiple volumes was implemented by including an additional selective inversion pulse, and an extension of the ISIS addition/subtraction scheme. Localized T1 measurements with surface coils are implemented by using a B1-insensitive inversion pulse in the inversion recovery sequence. The quantitative reproducibility of localized 31P NMR spectra was verified. Absolute metabolite concentration can be determined after a suitable calibration of the 31P NMR spectrum. Localized shimming is required to obtain localized 31P NMR spectra of excellent spectral resolution. This is done by monitoring the 1H NMR signal from water by a single-shot localization technique. The techniques discussed can be applied to obtain spectra of brain, liver, heart, and other organs. 31P NMR spectra of intracranial tumors demonstrate its applicability in the examination of patients.

Magnetic resonance imaging and spectroscopy of intraocular tumors

Proton magnetic resonance imaging (1H MRI) has emerged as a clinically useful tool for the diagnosis of intraocular tumors. During the last four years 1H MRI characteristics, including spin-lattice relaxation times (T1) and spin-spin relaxation times (T2), have been established for several types of tumors. The introduction of surface coils to the imaging process has significantly improved the quality of intraocular MR images, leading some clinicians to suggest that 1H MR images are preferable to CT scans. Another MRI technique, in which sodium-23 (23Na) is imaged rather than protons, is now under development as tool for intraocular diagnosis. The potential of 23Na MRI depends upon the high concentration and "visibility" of sodium in the vitreous body, and upon the apparent differences in sodium behavior in normal cells vs. tumor cells. The metabolism of normal ocular tissues and intraocular tumors may be probed noninvasively with phosphorus-31 MR spectroscopy (31P MRS). Much progress has been made during the last few years in understanding the appearance of 31P MR spectra of many types of healthy and diseased cells and tissues. Clinical application of this technique to the diagnosis and monitoring of intraocular tumors following conservative treatment will be dependent upon the development of spectroscopy techniques that collect information from the volume of interest (tumor) only.

Therapeutic response of breast carcinoma monitored by 31P MRS in situ

In situ phosphorous MRS was employed to study the metabolites of normal and cancerous breasts, and the alterations of tumor response to therapy. In a group of 7 normal volunteers and 12 patients, the total mobile phosphate content of breast carcinomas was found to be at least two to three times higher than that of the normal breast measured off menstruation. The metabolite profiles of normal and tumorous breasts are coarsely similar. In both cases the intracellular pH (pHi) was either neutral or slightly alkaline (pH greater than 7.0). Prior to treatments, the metabolite levels of phosphoryl monoester-to-ATP ratio of breast neoplasms were higher than those of the controls and decreased after the patients received a few treatments while the pHi fluctuated at a value greater than 7.0. The phosphoryl diester-to-ATP ratio also demonstrated to a lesser extent a decreasing trend in response to therapy.

Computer simulation of MRS localization techniques: an analysis of ISIS

Computer simulations were used to evaluate the ISIS localization technique as implemented with both head and surface coils. The effects of chemical shift, B1 inhomogeneity, repetition time, T2 relaxation, a postacquisition saturation pulse, and a B1 insensitive observation pulse were examined. Integrals of ISIS signals over the sample volume showed that significant signal loss from the volume of interest (VOI) and contamination from outside the VOI can occur for both head and surface coil ISIS experiments. The results showed that the saturation pulse, order of the various ISIS acquisitions, and repetition time affect contamination but not signal loss. In addition, short T2 and high RF power can combine synergistically to degrade the selective inversion pulses, causing further contamination and signal loss.

Experimental transplantation gliomas in the adult cat brain. 3. Regional biochemistry

Experimental brain tumours were produced in adult cats by stereotactic xenotransplantation of the rat glioma clone F98. Regional ATP, glucose and lactate were measured after 2-4 weeks on coronal cryostat sections by substrate-induced bioluminescence, potassium content was imaged by the histochemical sodium cobaltinitrite method, and regional pH by incubating cryostat sections with the fluorescent pH-indicator umbelliferone. The regional biochemical alterations were correlated with magnetic resonance imaging and tissue water content. Biochemical changes were heterogeneous in tumours but exhibited a rather uniform pattern in peritumoural oedema. ATP was consistently reduced, glucose and lactate were increased and pH was more alkaline than in normal white matter. The decrease of ATP matched the increase of water, indicating that ATP decline represents fractional dilution in the oedematous tissue rather than break-down of energy metabolism. The increased lactate levels, therefore, may originate from the tumour and not from a metabolic disturbance in the peritumoural oedematous tissue. The implications of this interpretation for the pathogenesis of peritumoural oedema are discussed.

Localized high-resolution proton NMR spectroscopy using stimulated echoes: initial applications to human brain in vivo

Water-suppressed localized proton NMR spectroscopy using stimulated echoes has been successfully applied to detect metabolites in the human brain in vivo. The STEAM spectroscopy sequence allows single-step localization by exciting three intersecting slices. Water suppression is achieved by preceding chemical-shift-selective (CHESS) rf pulses. High-resolution (0.05 ppm) proton NMR spectra of healthy volunteers have been High-resolution (0.05 ppm) proton NMR spectra of healthy volunteers have been obtained on a conventional 1.5-T whole-body MRI system (Siemens Magnetom). Volumes-of-interest (VOI) of 64 ml (4 x 4 x 4 cm3) were localized in the occipital area of the brain and spectra were recorded within measuring times ranging from 1 s (single scan) to about 10 min. The experimental procedure is described in detail. Resonance assignments include acetate, N-acetyl aspartate, gamma-amino butyrate, glutamine, glutamate, aspartate, creatine and phosphocreatine, choline-containing compounds, taurine, and inositols. Cerebral lactate was found to be at a maximum concentration of 0.5 mM when assuming N-acetyl aspartate in white matter to be 6 mM.

Nuclear magnetic resonance imaging-guided phosphorus-31 spectroscopy of the human heart

Phosphorus-31 nuclear magnetic resonance spectroscopy can determine the status of high energy phosphates in vivo. However, its application to human cardiac studies requires precise spatial localization without significant contamination from other tissues. Using image-selected in-vivo spectroscopy (ISIS), a technique that allows three-dimensional localization of the volume of interest, 12 subjects were studied to determine the feasibility and reproducibility of phosphorus-31 spectroscopy of the human heart. Nuclear magnetic resonance imaging was performed using a commercial 1.5 tesla system to define the volume of interest. Phosphorus-31 spectra were obtained from the septum and anteroapical region of the left ventricle in 10 studies. Relative peak heights and areas were determined for high energy phosphates. The mean phosphocreatine to adenosine triphosphate ratio was 1.33 +/- 0.19 by height analysis and 1.23 +/- 0.27 by area analysis. Duplicate measurements in four subjects showed a reproducibility of less than or equal to 10% in three of the subjects. All spectra showed significant signal contribution from the 2,3 diphosphoglycerate in chamber red cells without evidence of skeletal muscle contamination. These results demonstrate the feasibility of image-guided phosphorus-31 spectroscopy for human cardiac studies and indicate the potential of this technique to study metabolic disturbances in human myocardial disease.

Cerebral lactate detected by regional proton magnetic resonance spectroscopy in a patient with cerebral infarction

Water-suppressed image-guided localized proton magnetic resonance spectroscopy was performed in a 59-year-old woman with two major brain infarcts. Spectra were measured in the infarcts, in an area between the infarcts, and in the healthy hemisphere. The volumes of interest were selected on the basis of a fast T2-weighted image. A 1331-2662 Hahn spin-echo sequence was used to suppress the water in the 8-cm3 volume that was selected by means of spatially resolved spectroscopy or stimulated echoes. The spectra were obtained in 5 minutes' accumulation time. Spectral editing was applied to separate the resonance of lactate from that of other substances. Our results show no increase of lactate concentration within the infarcts after 6 months; however, a resonance was observed at 1.6 ppm, which is assigned to fatty acids. Peak intensities of brain-specific compounds were decreased. Six months after the onset of clinical symptoms (at the time of bypass surgery), a fivefold increase in lactate concentration compared with normal values was observed in the area between the two infarcts. Four months after bypass surgery, the lactate concentration in this area had decreased to only twice normal. We speculate that lactate is a marker of reversible or impending brain damage.

Phospholipid and energy metabolism of cancer cells monitored by 31P magnetic resonance spectroscopy: possible clinical significance

31P magnetic resonance spectroscopy (MRS) has been established as an excellent noninvasive procedure for studying metabolism in cancer cells. For a full understanding of the results of in vivo MRS studies of metabolism, it is necessary to be able to conduct controlled experiments on the same intact functioning cells in a perfusion apparatus. The specific techniques used for this purpose are described, and the applications to cancer cell bioenergetics and phospholipid metabolism in drug-resistant and drug-sensitive breast cancer cells are illustrated. Spectra of the same cell line grown in a "model tumor" in natural basement membrane gel and in nude mice in vivo are compared. The results indicate a potential for the use of 31P MRS in a clinical setting for monitoring therapy and for diagnosis.

Advances in imaging

The introduction of sonography, x-ray computed tomography, magnetic resonance imaging (MRI), and magnetic resonance spectroscopy (MRS) have enhanced the radiologist's ability to delineate and stage neoplasms in all parts of the human body. Images of excellent quality can be generated within a reasonable time frame and with minimal biologic risk. All of the more sophisticated imaging modalities are costly and none can, isolated from clinical data, provide histologic diagnoses. Within the next few years it is anticipated that the speed of magnetic resonance image acquisition will increase and that contrast agents for MRI will be brought into clinical use. Evaluation of cost-effectiveness will continue and new diagnostic algorithms can be expected to evolve.