Miquel E. Cabañas

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

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 1H 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 thepoorer results for this class. Consequently, for the refined system, the astrocytomas were subdivided into two subgroups for comparison against other tumour classes: those with high lipid content and those without.

Assignment of the 2.03 ppm resonance in in vivo 1H MRS of human brain tumour cystic fluid: contribution of macromolecules

MRI and MRS are established techniques for the evaluation of intracranial mass lesions and cysts. The 2.03 ppm signal recorded in their 1H-MRS spectra is often assigned to NAA from outer volume contamination, although it has also been detected in non-infiltrating tumours and large cysts. We have investigated the molecular origin of this resonance in ten samples of cystic fluids from human brain tumours. The NMR detected content of the 2.03 ppm resonance in 136 ms echo time spectra, assuming an N- CH3 origin, was 3.19 ± 1.01 mM. Only one third (34 ± 12%) of the N-acetyl containing compound (NAC) signal could be extracted by perchloric acid (PCA) indicating that most of it originated in a macromolecular PCA-insoluble component. Chemical analysis of the cyst fluids showed that sialic acid bound to macromolecules would account for 64.3% and hexuronic containing compounds for 29.2% of the NMR-detectable ex vivo signal, 93.4% of the signal at TE 136 ms. Lactate content measured by NMR (6.4 ± 4.4 mM) and the predominance of NAC originating in sialic acid point to a major origin from tumour rather than from plasma for this 2.03 ppm resonance.

13C-labelling studies indicate compartmentalized synthesis of triacylglycerols in C6 rat glioma cells.

NMR-visible mobile lipid (ML) signals have been detected in (1)H-NMR spectra of tissues in vivo, ex vivo and in vitro, and have been shown to change in apparent intensity in association with pathology (necrosis in brain tumours) and normal processes (cell differentiation, cell growth arrest and apoptosis). Although it is widely accepted that ML signals originate mainly from fatty-acyl chains in triacylglycerols (TAG) contained in cytosolic lipid droplets (LD), the dynamics of TAG in LD is not yet fully understood. In order to better understand the synthesis of cellular TAG and its relationship to ML dynamics we carried out a set of labelling experiments with C6 rat glioma cells in culture. TAG and phospholipid metabolism was monitored by incubating C6 cells with [1-(13)C]-glucose at two time points during cell growth curve -24 h incubation starting at log-phase; 48 h incubation starting at saturation density- and by acquiring the 2D-HMQC NMR spectra of the respective total lipid extracts. The resulting TAG, diacylglycerol (DAG) and phospholipid labelling patterns can only be explained if TAG synthesis takes place in two different subcellular compartments. One compartment would be the endoplasmic reticulum, which is known to be involved in TAG metabolism, while the other compartment could be the plasma membrane and/or the LD. This possible role of LD is further supported by the recent description of diacylglycerolacyltranferase-activity associated with LD. Accordingly, we postulate the existence of a carbon-shuttling mechanism between plasma membrane phospholipids and endoplasmic reticulum by way of LD content. The results we have obtained with C6 cells may also apply to other cellular systems and should be taken into account when interpreting ML dynamics detected by NMR in vivo.

Estudo do metabolismo energético muscular em atletas por 31P-ERM

BACKGROUND: The aim of this study was to characterize the muscular reservoirs of phosphorilated energetic components of athletes using 31P-MRS. METHODS: The sample was formed by 14 elite athletes from the Center for High Sportive Performance (CAR, Sant Cugat del Valles, Spain). The pattern of the phosphorilated metabolites was measured from the muscle vastus medialis by 31P-MRS. Oral supplementation of 20 g of Creatine monohydrate was given during 14 days. Two groups of athletes were formed according to their physical characteristics (weight, height, body mass index, maximum O2 uptake). The first group received a placebo (maltodextrine), while the second group received a diet of creatine supplement. The exercise was performed inside the resonance tunnel with a frequency of 60 RPM with both legs. RESULTS: The results showed that significant decrease occurred in phosphocreatine (PCr), inorganic phosphate (Pi) and intracellular pH after supplementation. CONCLUSION: It was concluded that the exercise performed by the long distance runners recruited in this study, detected by 31P-MRS, reduced the consumption of PCr during exercise owing to creatine supplementation diet.

EFECTO DE LA SUPLEMENTACIÓN ORAL CON MONOHIDRATO DE CREATINA EN EL METABOLISMO ENERGÉRTICO MUSCULAR Y EN LA COMPOSICIÓN CORPORAL DE SUJETOS QUE PRACTICAN ACTIVIDAD FÍSICA

Nos intereso investigar el efecto de la suplementacion oral de creatina en el metabolismo energetico muscular de sujetos activos por medio de espectroscopia de resonancia magnetica de fosforo (31P-RMN) y pruebas de rendimiento en laboratorio. Se estudiaron 13 varones, fisicamente activos de 23,1±5,3 anos (media±sd), los sujetos se distribuyeron de manera aleatoria en tres grupos: placebo (grupo 1, n=4), suplementacion de creatina (grupo 2, n=4) y suplementacion de creatina mas carbohidrato (grupo 3, n=5). La suplementacion se efectuo por via oral, durante 12 dias en forma de: 20 g de fibra de guisante (grupo 1), 20 g de monohidrato de creatina (grupo 2) y 20 g de monohidrato de creatina mas 5,7 g de maltodextrina y 9 g de fructosa (grupo 3). La dosis diaria se repartio en cuatro tomas iguales, disueltas en un vaso de agua. La prueba de rendimiento en laboratorio consistio en ejercicio de pedaleo sobre una bicicleta de freno mecanico a 120 rpm (fuerza de frenado igual al 30% de la fuerza maxima teorica determinada mediante una prueba previa de fuerza-velocidad) llevado hasta el agotamiento seguido, tras 1 minuto de pausa pasiva, se realizo un segun ejercicio de 10 s de pedaleo (fuerza de frenado igual al 50% de la fuerza maxima) a maxima velocidad. Resultados: la relacion PCr/ATP aumento significativamente en los grupos 2 y 3. Esta relacion no vario significativamente entre los grupos 2 y 3. Ambos grupos se consideraron conjuntamente como grupo de suplementacion para el analisis de los resultados del rendimiento en el laboratorio. El grupo suplementado mejoro en forma significativa la velocidad maxima (11,5%), la potencia maxima (12%), y la potencia media (15,7%) desarrolladas durante el esfuerzo de 10 segundos. Se concluye que la suplementacion con creatina incrementa el contenido muscular de fosfocreatina (PCr) y aumenta el rendimiento en una prueba de velocidad realizada en 10 segundos despues de un esfuerzo extenuante