An extension of the 16th Hilbert problem for continuous piecewise linear-quadratic centers separated by a non-regular line.

In the last few decades, there has been much interest in studying piecewise differential systems. This is mainly due to the fact that these differential systems allow us to modelize many natural phenomena. In order to describe the dynamics of a differential system, we need to control its periodic orbits and, especially, its limit cycles. In particular, providing an upper bound for the maximum number of limit cycles that such differential systems can exhibit would be desirable, that is solving the extended 16th Hilbert problem. In general, this is an unsolved problem. In this paper, we give an upper bound for the maximum number of limit cycles that a class of continuous piecewise differential systems formed by an arbitrary linear center and an arbitrary quadratic center separated by a non-regular line can exhibit. So for this class of continuous piecewise differential systems, we have solved the extended 16th Hilbert problem, and the upper bound found is seven. The question whether this upper bound is sharp remains open.

A novel range telescope concept for proton CT.

Proton beam therapy can potentially offer improved treatment for cancers of the head and neck and in paediatric patients. There has been a sharp uptake of proton beam therapy in recent years as improved delivery techniques and patient benefits are observed. However, treatments are currently planned using conventional x-ray CT images due to the absence of devices able to perform high quality proton computed tomography (pCT) under realistic clinical conditions. A new plastic-scintillator-based range telescope concept, named ASTRA, is proposed here to measure the proton's energy loss in a pCT system. Simulations conducted using GEANT4 yield an expected energy resolution of 0.7%. If calorimetric information is used the energy resolution could be further improved to about 0.5%. In addition, the ability of ASTRA to track multiple protons simultaneously is presented. Due to its fast components, ASTRA is expected to reach unprecedented data collection rates, similar to 108protons/s. The performance of ASTRA has also been tested by simulating the imaging of phantoms. The results show excellent image contrast and relative stopping power reconstruction.

The 16th Hilbert problem for discontinuous piecewise isochronous centers of degree one or two separated by a straight line.

In this paper, we deal with discontinuous piecewise differential systems formed by two differential systems separated by a straight line when these two differential systems are linear centers (which always are isochronous) or quadratic isochronous centers. It is known that there is a unique family of linear isochronous centers and four families of quadratic isochronous centers. Combining these five types of isochronous centers, we obtain 15 classes of discontinuous piecewise differential systems. We provide upper bounds for the maximum number of limit cycles that these fifteen classes of discontinuous piecewise differential systems can exhibit, so we have solved the 16th Hilbert problem for such differential systems. Moreover, in seven of the classes of these discontinuous piecewise differential systems, the obtained upper bound on the maximum number of limit cycles is reached.

Safety and Efficacy of Ultrasound-Guided Radiofrequency Ablation of Recurrent Colorectal Cancer Liver Metastases after Hepatectomy.

INTRODUCTION: To assess the results and outcome of radiofrequency ablation in the treatment of recurrent colorectal liver metastases. PATIENTS AND METHODS: Between January 2005 and September 2012, we treated 59 patients with recurrent colorectal metastases not amenable to surgery with 77 radiofrequency ablation procedures. Radiofrequency was indicated if oncologic resection was technically not possible or the patient was not fit for major surgery. A total of 91 lesions were treated. The mean number of liver tumors per patient was 1.5, and the mean tumor diameter was 2.3 cm. In 37.5% of the cases, lesions had a subcapsular location, and 34% were close to a vascular structure. RESULTS: The morbidity rate was 18.7%, and there were no post-procedural deaths. Distant extrahepatic recurrence appeared in 50% of the patients. Local recurrence at the site of ablation appeared in 18% of the lesions. Local recurrence rate was 6% in lesions less than 3 cm and 52% in lesions larger than 3 cm. The size of the lesions (more than 3 cm) was an independent risk factor for local recurrence (p < 0.05). Survival rates at 1, 3, and 5 years were 94.5%, 65.3%, and 21.7%, respectively. DISCUSSION: Radiofrequency ablation is a safe procedure and allows local tumor control in lesions less than 30 mm (local recurrence of 6%) and provides survival benefits in patients with recurrent colorectal liver metastases.

Enlarged lymph nodes in the upper abdomen after liver transplantation: imaging features and clinical significance.

PURPOSE: Our aim was to review our single-centre experience regarding imaging features and pathological conditions arising from enlarged lymph nodes following orthotopic liver transplantation (OLD) and identify imaging features that may allow narrowing the differential diagnosis. MATERIALS AND METHODS: Between January 1997 and September 2008, 715 OLTs were performed at our Institution in 585 patients. In 19 patients (2.6 %) ultrasound (US) showed enlarged lymph nodes in the upper abdomen, and abdominal computed tomography (CT) was performed RESULTS: Histological results showed posttransplantation lymphoproliferative disorder (PTLD) in six patients (31.5 %), hepatic tumoral disease in six (31.5 %), disseminated systemic tuberculosis in one (5.2%) and sarcoidosis in one (5.2%). Histological results showed nonspecific reactive lymph node hyperplasia in five patients (26%). CONCLUSIONS: Detecting enlarged lymph nodes in the upper abdomen after liver transplantation is and infrequent occurrence; however, thorough imaging is required to detect and characterise a wide variety of disorders. Most of the time, enlarged lymph nodes will be related to posttransplantation lymphoproliferative disorder or tumoral recurrence.

Telomere length is a prognostic factor for overall survival in colorectal cancer.

AIM: The aim of this study was to determine whether telomere length is an independent prognostic factor for the prevention and survival of colorectal cancer. METHOD: Terminal restriction fragment (TRF) length was determined by Southern blot in tumours and paired normal tissue samples from 147 patients with sporadic colorectal cancer who had undergone surgery. The TRF length ratio (TRFLR) was determined as the ratio between the length of the patient's tumour and normal tissue.The classification and regression tree technique was used to determine optimal cut-off values (≤ 1 or > 1). RESULTS: Mean TRF length was 6.79 Kbp (1.19-13.99) in tumour tissue and 7.81 Kbp (3.63-15.70) in normal mucosa (P < 0.001). Mean TRFLR was 0.88. Telomere length and telomere length ratio were not correlated with any clinicopathological factors. In univariate analysis, overall survival was related to N stage (lymph node +/-; P = 0.002), TNM classification (P = 0.019) and TRFLR (≤ 1 or > 1; P = 0.014). In multivariate analysis, overall survival was significantly associated with TRFLR and N stage. Colorectal cancer patients with TRFLR ≤ 1 and negative lymph node involvement had a higher overall survival rate. CONCLUSION: Telomere length ratio is an independent prognostic factor for survival in colorectal cancer patients, and the telomere lengths in the normal and tumour mucosa of the same patient present with parallel behaviour.

Guidelines for the detection and treatment of liver metastases of colorectal cancer.

The spread of the surgical treatment for hepatic metastases have been crucial in the improvement of treatment and survival of metastatic colorectal cancer. The early and accurate diagnosis of metastases and the assessment of their size are essential factors to reach the optimal results with this treatment strategy. The precise indication of the surgical technique with or without the previous administration of neoadjuvant chemotherapy is of significant importance for the choice of R0 surgery and the timing of intervention. Although there is an agreement regarding some parameters related to diagnosis techniques and surgical criteria such as the bilobar extension, the size of the remaining liver post-surgical removal and the indication of pre-operatory chemotherapy, it is necessary to consider all these factors to set up standard criteria and optimize the results. In this article we review all these parameters, from disease follow up to detect metastatic dissemination to the basic criteria for use of neoadjuvant chemotherapy, in order to suggest some general recommendations of evidence level II and recommendation grade A.

Colorectal liver metastases: Radiological diagnosis and staging.

The objective of this paper is to review imaging techniques useful for the diagnosis and staging of colorectal hepatic metastases. Semiological patterns will be reviewed as well as suggestions concerning performance of adequate preoperative staging. Radiological features suggesting non-resectability will be reviewed.

Guidelines for the detection and treatment of liver metastases of colorectal cancer

The spread of the surgical treatment for hepatic metastases have been crucial in the improvement of treatment and survival of metastatic colorectal cancer. The early and accurate diagnosis of metastases and the assessment of their size are essential factors to reach the optimal results with this treatment strategy. The precise indication of the surgical technique with or without the previous administration of neoadjuvant chemotherapy is of significant importance for the choice of R0 surgery and the timing of intervention. Although there is an agreement regarding some parameters related to diagnosis techniques and surgical criteria such as the bilobar extension, the size of the remaining liver post-surgical removal and the indication of pre-operatory chemotherapy, it is necessary to consider all these factors to set up standard criteria and optimize the results. In this article we review all these parameters, from disease follow up to detect metastatic dissemination to the basic criteria for use of neoadjuvant chemotherapy, in order to suggest some general recommendations of evidence level II and recommendation grade A (AU)

Preliminary results of treatment with pegylated interferon alpha 2A for chronic hepatitis C virus in kidney transplant candidates on hemodialysis.

INTRODUCTION: At present, there is little published information on the outcome of treatment with pegylated interferon (Peg-IF alpha 2a) in hepatitis C virus (HCV)-infected hemodialysis patients awaiting renal transplantation. The objective of this study was to assess the efficacy and tolerance of Peg-IF alpha 2a in this population. PATIENTS AND METHODS: Twelve noncirrhotic HCV-infected patients (10 men, 50 +/- 8 years of age, genotype 1b 84%), were prescribed Peg-IF alpha 2a, at 135 microg/wk for 48 weeks. Liver biopsy was performed in 11 of 12 cases. RESULTS: Six patients completed 48 weeks of treatment, with one end of treatment response (ETR), two sustained viral responses (SVRs), and three HCV relapses. Treatment was shorter in the six remaining patients: two cases 24 weeks (one due to medical reasons with relapse, one due to nonresponse), one patient chose to discontinue at 14 weeks (with relapse), one patient died of stroke at 10 weeks, and in two additional patients interferon was withdrawn at 18 weeks because of severe anemia (SVR) and at 26 weeks due to prolonged fever (relapse). Other secondary treatment-related events included anemia (requiring transfusion in two patients and major erythropoietin administration in six), and fever in four patients. CONCLUSIONS: Peg-IF had limited efficacy in this group, with ETR in 83%, SVR in only 25%, and recurrence in 50%. Tolerance was moderate, with 4/12 (33%) discontinuing treatment due to adverse events, personal decision, or death. Large randomized controlled studies are needed to determine the role of Peg-IF treatment in this population.

Tumor sólido pseudopapilar de páncreas: diagnóstico y tratamiento curativo / Solid pseudopapillary tumors of the pancreas: diagnosis andcurative treatment

Objetivos: dar a conocer a través de una serie de casos clínicosuna entidad poco frecuente, con una presentación clínica yunos hallazgos radiológicos concretos, que permiten establecer undiagnóstico y un tratamiento que será en la mayoría de los casoscurativo.Pacientes y métodos: se realizó un estudio descriptivo y retrospectivode los casos diagnosticados y tratados quirúrgicamenteen una Unidad Pancreático-Biliar de un hospital universitario, duranteel periodo comprendo entre marzo de 1999 y septiembrede 2005.Resultados: la incidencia fue de 6 pacientes mujeres, con unaedad media de 33,5 años (rango 11-72). La clínica más comúnfue la de dolor y masa abdominal palpable. La tomografía computerizadafue diagnóstica en tres de las pacientes, en las tres restantesse estableció el diagnóstico diferencial con el tumor neuroendocrino.El tratamiento quirúrgico fue individualizado a cadapaciente según los hallazgos y las imágenes visualizadas en la tomografíacomputerizada. El estudio anatomopatológico confirmóel diagnóstico de presunción, informándose de un caso de carcinomasólido-pseudopapilar de páncreas. La estancia hospitalariafue de 18,16 días (rango 8-30). Mortalidad de 0%. En el seguimientocon una media de 46,3 meses (rango 12-76), no existenrecidivas.Conclusiones: la presencia en una mujer joven de una lesiónvoluminosa en el páncreas, debe hacernos pensar en el tumor sólidopseudopapilar. Debido a su bajo potencial de malignidad y ala existencia de unos patrones radiológicos concretos, su diagnósticodebe ser preciso, ya que el tratamiento quirúrgico radical escurativo

Objectives: to highlight an infrequent occurrence using a seriesof clinical cases with symptoms and signs, and specific radiologicalfindings allowing its diagnosis and treatment, which is inmost cases successful.Patients and methods: a descriptive and retrospective studyof patients diagnosed by computed tomography scanning andthen treated with surgery in the Pancreas and Biliary Unit of aUniversity Hospital from March 1999 to September 2005.Results: there were 6 female patients with a mean age of33.5 years (range 11-72). Most common signs included pain anda palpable mass in the abdomen. Three patients were diagnosedby computed tomography scanning, and a differential diagnosiswith a neuroendocrine tumor was performed for the remainingthree subjects. Surgical treatment was adapted to each patient accordingto the findings and images seen in their computed tomographyscans. Biopsy results confirmed the presumed diagnoses,and showed one case of solid pseudopapillary carcinoma of thepancreas. Average hospital stay was of 18.16 days (range 8-30).Mortality rate was 0%. No recurrences occurred during follow-upfor 46.3 months on average (range 12-76).Conclusions: the presence of a huge mass in the pancreas ofa young female should prompt suspicion for a solid pseudopapillarytumor. Given its low malignant potential, and the presence ofspecific radiographic patterns, its diagnosis should be accurate, asradical surgical treatment is effective

[Radiofrequency ablation of hepatic tumors]. / Ablación por radiofrecuencia de tumores hepáticos.

This article aims to review the state of the art in ablation techniques for hepatic lesions. In addition to discussing the indications, outcomes, and potential complications of the technique, we illustrate the spectrum of imaging findings after treatment. Recent years have seen the development of a wide variety of minimally invasive techniques to treat liver cancer. These include ethanol injection, and thermal ablation using radiofrequency, laser, microwaves, or cryosurgery. Percutaneous radiofrequency ablation is one of the most promising non-surgical treatments for hepatic neoplasms. The results of several studies show that radiofrequency ablation enables adequate local control of tumors with few complications, achieving acceptable survival rates. Radiofrequency ablation can be performed using any imaging technique, although it is most commonly performed under ultrasound guidance. CT and MRI show the degree of tumor necrosis better and are more frequently employed in follow up. This article reviews the indications and contraindications for the procedure, potential complications, long-term outcome, and imaging findings for percutaneous radiofrequency ablation of hepatic tumors.

[Obstructive Jaundice: diagnostic and therapeutic management]. / L'ictère nu: rôle du radiologue dans la prise en charge diagnostique et thérapeutique.

The purpose of this article is to provide an update on imaging techniques for diagnosis and staging of clinical conditions leading to obstructive jaundice. Clinical and imaging findings of the most frequent diseases presenting as obstructive jaundice will be reviewed in order to optimize imaging strategies. Imaging and treatment strategies will be discussed in order to provide an optimal diagnosis and staging with the least invasive techniques in order to minimize complications in these patients.

Ablación por radiofrecuencia de tumores hepáticos / Radiofrequency ablation of hepatic tumors

El objetivo de este artículo es la revisión del estado actual de las técnicas de ablación hepáticas, sus indicaciones y resultados, además de ilustrar el espectro de hallazgos radiológicos tras un tratamiento adecuado, así como las complicaciones potenciales que pueden producirse. En los últimos años se han desarrollado una gran variedad de tratamientos contra el cáncer mínimamente invasivos, entre los que se incluyen la inyección de etanol, así como técnicas de ablación termal con radiofrecuencia, láser, microondas o criocirugía. La ablación percutánea con radiofrecuencia es uno de los tratamientos no-quirúrgicos de las neoplasias hepáticas más prometedores. Los resultados de varios estudios muestran que la ablación por radiofrecuencia permite un adecuado control local tumoral con pocas complicaciones y que consigue tasas de supervivencia aceptables. La ablación por radiofrecuencia puede realizarse con cualquier técnica de imagen, pero generalmente es la ecografía la más utilizada como guía para el procedimiento mientras que la tomografía computarizada (TC) y la resonancia magnética (RM) valoran más adecuadamente el grado de necrosis tumoral. En este artículo revisaremos las indicaciones y contraindicaciones para la realización del procedimiento, las complicaciones potenciales que pueden producirse, los resultados a largo plazo y los hallazgos por imagen

This article aims to review the state of the art in ablation techniques for hepatic lesions. In addition to discussing the indications, outcomes, and potential complications of the technique, we illustrate the spectrum of imaging findings after treatment. Recent years have seen the development of a wide variety of minimally invasive techniques to treat liver cancer. These include ethanol injection, and thermal ablation using radiofrequency, laser, microwaves, or cryosurgery. Percutaneous radiofrequency ablation is one of the most promising non-surgical treatments for hepatic neoplasms. The results of several studies show that radiofrequency ablation enables adequate local control of tumors with few complications, achieving acceptable survival rates. Radiofrequency ablation can be performed using any imaging technique, although it is most commonly performed under ultrasound guidance. CT and MRI show the degree of tumor necrosis better and are more frequently employed in follow up. This article reviews the indications and contraindications for the procedure, potential complications, long-term outcome, and imaging findings for percutaneous radiofrequency ablation of hepatic tumors

Solid pseudopapillary tumors of the pancreas: diagnosis and curative treatment.

OBJECTIVES: To highlight an infrequent occurrence using a series of clinical cases with symptoms and signs, and specific radiological findings allowing its diagnosis and treatment, which is in most cases successful. PATIENTS AND METHODS: A descriptive and retrospective study of patients diagnosed by computed tomography scanning and then treated with surgery in the Pancreas and Biliary Unit of a University Hospital from March 1999 to September 2005. RESULTS: There were 6 female patients with a mean age of 33.5 years (range 11-72). Most common signs included pain and a palpable mass in the abdomen. Three patients were diagnosed by computed tomography scanning, and a differential diagnosis with a neuroendocrine tumor was performed for the remaining three subjects. Surgical treatment was adapted to each patient according to the findings and images seen in their computed tomography scans. Biopsy results confirmed the presumed diagnoses, and showed one case of solid pseudopapillary carcinoma of the pancreas. Average hospital stay was of 18.16 days (range 8-30). Mortality rate was 0%. No recurrences occurred during follow-up for 46.3 months on average (range 12-76). CONCLUSIONS: The presence of a huge mass in the pancreas of a young female should prompt suspicion for a solid pseudopapillary tumor. Given its low malignant potential, and the presence of specific radiographic patterns, its diagnosis should be accurate, as radical surgical treatment is effective.

Ictericia obstructiva secundaria a colangitis linfoplasmocitaria. Diagnóstico diferencial con el tumor de Klatskin / Obstructive jaundice secondary to lymphoplasmocytic cholangitis. Differential diagnosis of Klatskin tumors

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Diagnóstico prenatal del retraso de crecimiento intrauterino mediante marcadores bioquímicos / Biochemical markers in the prenatal diagnosis of intrauterine growth retardation

Objetivo: Determinar la relación y capacidad diagnóstica de la IGF-I (insulin-like growth factor I), IGFBP-I (insulin-like growth factor binding protein I), leptina, y alfa-fetoproteína (AFP) en líquido amniótico de 14-18 semanas con el desajuste ponderal del feto al nacer.Sujetos y métodos: Estudio longitudinal y prospectivo. Gestantes con amniocentesis de 14-18 semanas. 86 controles, 18 RCIU (retraso de crecimiento intrauterino) < percentil 10, y 17 RCIU < percentil 5.Resultados: No se demuestra una correlación significativa entre el RCIU y la IGF-I, la IGFBP-I, y la leptina. La AFP cumple una correlación inversa con la severidad del RCIU; en el RCIU < percentil 10 presentó: sensibilidad (S), 65,7 por ciento; especificidad (E), 56,9 por ciento; valor predictivo positivo (VPP), 38,3 por ciento; valor predictivo negativo (VPN), 80,3 por ciento, y una capacidad global del 65,6 por ciento. En el RCIU < percentil 5 se obtuvo: S, 76,4 por ciento; E, 54,8 por ciento; VPP, 21,6 por ciento; VPN, 93,4 por ciento, y una capacidad global del 70,6 por ciento.Conclusión: Los valores elevados de AFP en líquido amniótico de diagnóstico prenatal pueden contribuir a la detección precoz de la población con riesgo de desarrollar un RCIU (AU)