Resumen
Introducción: El diagnóstico del cáncer de próstata (CaP) está basado inicialmente en una combinación del valor del antígeno prostático específico (PSA), el tacto rectal (TR) y los hallazgos de la ecografía transrectal de la próstata (ETR). La ETR ofrece la posibilidad de realizar biopsias aleatorias de la glándula prostática, que a menudo acaban siendo múltiples biopsias repetidas negativas en pacientes con elevación persistente del PSA, debido a la baja especificidad de este marcador. La resonancia magnética (RM) endorrectal es actualmente el mejor método de imagen para la detección del CaP. La espectroscopia por RM endorrectal (RMS) es una técnica no invasiva que complementa el diagnóstico del CaP mediante la detección de metabolitos intracelulares a nivel de la próstata, tales como la colina y el citrato. La RMS combinada con la RM endorrectal mejora de forma significativa la evaluación de la localización del CaP. Método: Se realizó un estudio para determinar la eficacia de la RMS en la detección precoz del CaP en pacientes con elevación del PSA, alteración del TR o ambos, candidatos a biopsia transrectal de próstata. Seleccionamos 51 pacientes entre 50-65 años con PSA entre 4-15 ng/ml con o sin alteración del TR, que debían ser sometidos a biopsia TR de próstata. La sospecha de tumor según la RM y RMS fue clasificada en una escala de 1-4, en la que 1 equivale a normal y 4 a cáncer. Comparamos 306 imágenes (6 por paciente) de RM y 306 curvas espectroscópicas con los valores de PSAt, índice de PSAt/PSAl, TR y la AP de cada uno de los sextantes. Resultados: Diagnosticamos CaP en 23 de 45 pacientes (45%) y en 78 de 306 sextantes (25%). El cociente CC/Ci fue significativamente superior en los pacientes con CaP (1.05 ± 0.41) en comparación con los pacientes en los que no se demostró CaP (0.51 ± 0.21). El índice PSAl/PSAt fue también significativamente inferior en los pacientes con CaP (11.35%) respecto de los pacientes sin CaP (16.55%). Conclusiones: La RMS es en la actualidad el método por imagen probablemente más eficaz para el diagnóstico precoz del CaP, puesto que además del análisis morfológico de la próstata permite realizar un análisis metabólico de toda la glándula prostática.

Palabras clave
espectroscopia, resonancia, cáncer de prostata

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Abstract
Introduction: The diagnosis of PCa is initially based on PSA, digital rectal examination and transrectal ecography findings. The use of PSA has led in the past years to an important rate of localized prostate cancers diagnosed in the screening of the population. Transrectal ecography offers the possibility to perform aleatory biopsies of the prostate in patients with high risk of PCa, with elevated PSA or altered DRE. The lack of specificity of PSA often leads to multiple negative biopsies in patients with persistent elevation of PSA. Morphologic changes in PCa are not always visible despite the fact that metabolic disorders appear in the early stages of PCa. The endorectal MRI is nowadays the best imaging technique available for the diagnosis of PCa, especially in T2 images, where cancer is viewed as hypointense lesions in the normal hyperintensity of the peripheral zone of the prostate. The endorectal MR spectroscopic imaging (RMS) is a non-invasive technique capable to measure the metabolic changes that occur in the prostate, specially citrate and choline. This technique, when combined with the morphological imaging of endorectal MRI, leads to a better evaluation of PCa diagnosis, thus improving the specificity of PSA. Method: Our group performed a study to determine the efficacy of MRS for the early diagnosis of prostate cancer (PCa) in patients with rising PSA and/or abnormal digital rectal examination (DRE), who are elected for transrectal ultrasound and biopsy of the prostate (TRUS biopsy).We have included 200 patients in the study but only 51 of them are actually analyzed in a preliminary result. We selected 51 patients between 50 and 65 years old and PSA ranging from 4 to 15 ng/ml, with or without abnormal digital rectal examination who were elected for TRUS biopsy of the prostate. Before biopsy, they all underwent an endorectal MRI and MRS, which was analyzed individually for each sextant of the prostrate, and the ratio CC/Ci was calculated for each sextant. We considered a pathologic ratio above 0.75. Subsequently, we compared the spectroscopic value of each sextant to the morphological image of MRI, pathology, PSA, free PSA and index fPSA/tPSA. The presence of tumors according to MRI and MRS in each sextant was graded from 1 to 4, in which 1 is normal, 2 probable normal, 3 probable tumor and 4 presence of cancer. We compared 306 resonance images (6 per patient) and 306 spectroscopic curves to PSA values, fPSA/tPSA ratio, DRE and pathologic report of each sextant. Results: We found PCa in 23 out of 45 patients (45%), and in 78 of 306 sextants (25%). The CC/Ci ratio was significantly higher in PCa patients (1.05 ± 0.41) compared to non-PCa patients (0.51 ± 0.21). The ratio fPSA/tPSA was also significantly lower in patients with PCa (11.35%) compared to patient without PCa. (16.55%). But we did not find a significant difference in total PSA of patient with PCa (7.72 ng/ml) compared to patients without PCa (6.42). In this group of patients MRS was highly predictive of PCa because the ratio CC/Ci discriminated better PCa than total PSA. More details of this study will be analyzed in a doctoral thesis and await to be published briefly, together with all data coming from the results of the whole group of patients. Conclusions and clinical implications: The MRS represents nowadays the best imaging technique for viewing and localizing prostate cancer. Besides the morphological study of the prostate it allows a metabolic analysis of the whole gland, and therefore, a simultaneous morphological and functional study of the tissue, that will probably change the diagnostic work up of PCa. Although it is not acceptable to assume the results of the RMS to avoid biopsy, there is a strong belief that it will soon be possible. Can we avoid biopsies in a patient without evidence of lesions suggestive of PCa at the MRS? Several groups have studied that question and we can now say that MRS has a high negative predictive value. MRS will probably help to achieve the so called "selective biopsies", this means, to perform a prostatic biopsy by targeting only the suspicious areas, instead of randomized biopsies of 10-12 cores each. Emerging techniques, such as contrast agents and the study of prostatic diffusion will probably increase the sensitivity and specificity of MRI and MRS, near to 100% in the detection of PCa. Kirkham et al mentioned that endorectal MRI offers a good chance to evaluate all the techniques that would add information in the detection of PCa (morphologic study, spectroscopi-metabolic study, contrast-enhancing and diffusion) in order to analyze the capacity of these techniques to detect Pca.

Key words
spectroscopy, resonance, prostate cancer