Time filter

Source Type

Chalfont St. Peter, United Kingdom

Chaudhary U.J.,University College London | Chaudhary U.J.,MRI Unit | Duncan J.S.,University College London | Lemieux L.,University College London
Human Brain Mapping | Year: 2013

Functional magnetic resonance imaging (fMRI) is able to detect changes in blood oxygenation level associated with neuronal activity throughout the brain. For more than a decade, fMRI alone or in combination with simultaneous EEG recording (EEG-fMRI) has been used to investigate the hemodynamic changes associated with interictal and ictal epileptic discharges. This is the first literature review to focus on the various fMRI acquisition and data analysis methods applied to map epileptic seizure-related hemodynamic changes from the first report of an fMRI scan of a seizure to the present day. Two types of data analysis approaches, based on temporal correlation and data driven, are explained and contrasted. The spatial and temporal relationship between the observed hemodynamic changes using fMRI and other non-invasive and invasive electrophysiological and imaging data is considered. We then describe the role of fMRI in localizing and exploring the networks involved in spontaneous and triggered seizure onset and propagation. We also discuss that fMRI alone and combined with EEG hold great promise in the investigation of seizure-related hemodynamic changes non-invasively in humans. We think that this will lead to significant improvements in our understanding of seizures with important consequences for the treatment of epilepsy. Hum Brain Mapp, 2013. © 2011 Wiley Periodicals, Inc. Source

Murta T.,University College London | Murta T.,University of Lisbon | Leite M.,University College London | Leite M.,University of Lisbon | And 4 more authors.
Human Brain Mapping | Year: 2015

Electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) are important tools in cognitive and clinical neuroscience. Combined EEG-fMRI has been shown to help to characterise brain networks involved in epileptic activity, as well as in different sensory, motor and cognitive functions. A good understanding of the electrophysiological correlates of the blood oxygen level-dependent (BOLD) signal is necessary to interpret fMRI maps, particularly when obtained in combination with EEG. We review the current understanding of electrophysiological-haemodynamic correlates, during different types of brain activity. We start by describing the basic mechanisms underlying EEG and BOLD signals and proceed by reviewing EEG-informed fMRI studies using fMRI to map specific EEG phenomena over the entire brain (EEG-fMRI mapping), or exploring a range of EEG-derived quantities to determine which best explain colocalised BOLD fluctuations (local EEG-fMRI coupling). While reviewing studies of different forms of brain activity (epileptic and nonepileptic spontaneous activity; cognitive, sensory and motor functions), a significant attention is given to epilepsy because the investigation of its haemodynamic correlates is the most common application of EEG-informed fMRI. Our review is focused on EEG-informed fMRI, an asymmetric approach of data integration. We give special attention to the invasiveness of electrophysiological measurements and the simultaneity of multimodal acquisitions because these methodological aspects determine the nature of the conclusions that can be drawn from EEG-informed fMRI studies. We emphasise the advantages of, and need for, simultaneous intracranial EEG-fMRI studies in humans, which recently became available and hold great potential to improve our understanding of the electrophysiological correlates of BOLD fluctuations. Hum Brain Mapp, 36:391-414, 2015. © 2014 The Authors Human Brain Mapping Published by Wiley Periodicals, Inc. Source

Morgan V.A.,Cancer Research UK Research Institute | Riches S.F.,Cancer Research UK Research Institute | Giles S.,Cancer Research UK Research Institute | Dearnaley D.,Institute of Cancer Research | And 2 more authors.
American Journal of Roentgenology | Year: 2012

OBJECTIVE. The objectives of our study were to establish the apparent diffusion coefficients (ADCs) of tumor and nontumor irradiated tissues in patients with suspected postradiation recurrence of prostate cancer and to determine the sensitivity and specificity of a combination of T2-weighted and diffusion-weighted imaging (DWI) for detecting local recurrence. MATERIALS AND METHODS. Twenty-four patients with rising prostate-specific antigen levels after having completed radiation therapy 30-130 months earlier (median, 62 months) underwent endorectal T2-weighted imaging and DWI (b = 0, 100, 300, 500, and 800 s/mm 2) followed by transrectal ultrasound (TRUS)-guided biopsy. Images were scored prospectively as positive for tumor if a region of low signal intensity on T2-weighted imaging within the prostate corresponded with a focally restricted area on the ADC map. A region of interest (ROI) was drawn around the suspicious lesion on a single slice of the ADC map and a corresponding ROI was drawn around presumed nontumor irradiated peripheral zone and central gland tissues on the opposite side of the prostate. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were determined against TRUS-guided biopsy reference standard (octant, n = 17; sextant, n = 5; two samples, n = 1; 12 samples, n = 1). RESULTS. Sixteen of 24 patients (66.7%) had positive histology findings. The median tumor ROI area was 0.37 cm 2 (quartiles, 0.30 and 0.82 cm 2). The sensitivity, specificity, PPV, and NPV for detecting tumor were 93.8%, 75%, 88.2%, and 85.7%, respectively. A cutoff ADC of 1216 × 10-6 mm 2/s could predict tumor with 100% sensitivity and 96% specificity (area under the receiver operating characteristic curve = 0.992). CONCLUSION. An ADC derived from DWI is a useful adjunct t cm 2 wito T2-weighted MRI for detecting local tumor recurrence larger than 0.4hin the prostate. © American Roentgen Ray Society. Source

Roldan-Valadez E.,MRI Unit | Favila R.,General Electric | Martinez-Lopez M.,MRI Unit | Uribe M.,Gastroenterology and Liver Unit | And 2 more authors.
Journal of Hepatology | Year: 2010

Background & Aims: The clinical application of liver fat quantification has increased in recent years, paralleling the epidemic increase in nonalcoholic fatty liver disease. The aim of this study was to perform a diagnostic evaluation of spectroscopy by comparing its measurement of total lipid content with that from liver biopsies and morphometry in normal subjects and patients with nonalcoholic fatty liver disease. Methods: Patients with symptomatic cholelithiasis underwent 3T MR cholangiography with spectroscopic quantification of TLC. A laparoscopic cholecystectomy was performed on the day of admission, with liver samples taken during surgery. Microcolorimetric assessment quantified lipid content in liver samples and morphometric evaluation in stained slides. Statistical analysis included bivariate correlation, regression, and ROC analysis. Results: The study was conducted in 18 patients, 5 men (mean age, 35.2 ± 11.03 years; range, 27-54 years) and 13 women (mean age, 46.77 ± 11.77 years; range, 21-61 years). Using a cut-off value >5% for fat content, 8 patients presented with steatosis and 10 patients presented with normal liver fat content. A significant correlation was observed between fat spectroscopy and lipid content (r = 0.876, p <0.001). A lower and non-significant correlation was observed between lipid content and morphometry (r = 0.190, p >0.05). Conclusions: The accuracy of spectroscopy in assessing fat concentration with a cut-off level of 7.48% was 100%. Spectroscopy showed a strong and significant correlation with lipid content. It may reliably replace liver biopsy for the assessment of liver fat content. © 2010 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved. Source

Nogueira L.,Polytechnic Institute of Porto | Brandao S.,MRI Unit | Matos E.,University of Porto | Gouveia Nunes R.,University of Lisbon | And 3 more authors.
European Radiology | Year: 2014

Objectives: To evaluate diffusion-weighted imaging (DWI) and diffusion kurtosis imaging (DKI) in the differentiation and characterisation of breast lesions. Methods: Thirty-six women underwent breast magnetic resonance imaging (MRI) including a DWI sequence with multiple b-values (50-3,000 s/mm 2). Mean values for apparent diffusion coefficient (ADC), mean diffusivity (MD) and mean kurtosis (MK) were calculated by lesion type and histological subtype. Differences and correlation between parameters were determined. Results: Forty-four lesions were found. There were significant differences between benign and malignant lesions for all parameters (ADC, p =0.017; MD, p =0.028; MK, p =0.017). ADC and MD were higher for benign (1.96± 0.41×10-3 and 2.17± 0.42×10 -3 mm2/s, respectively) than for malignant lesions (1.33± 0.18×10-3 and 1.52± 0.50×10 -3 mm2/s). MK was higher for malignant (0.61±0.27) than benign lesions (0.37±0.18). We found differences between invasive ductal carcinoma (IDC) and fibroadenoma (FA) for all parameters (ADC,MDandMK): p =0.016, 0.022 and 0.016, respectively. FA and fibrocystic change (FC) showed differences only in MK (p =0.016). Conclusions: Diffusion in breast lesions follows a non-Gaussian distribution. MK enables differentiation and characterisation of breast lesions, providing new insights into microstructural complexity. To confirm these results, further investigation in a broader sample should be performed. Key Points: • The diffusion kurtosis model provides new information regarding breast lesions • MD and MK are valid parameters to characterise tissue microstructure • MK enables improved lesion differentiation • MK is able to differentiate lesions that display similar ADC values © European Society of Radiology 2014. Source

Discover hidden collaborations