DSpace Angular :: Browsing by Author "Tejos, Cristian"

Browsing by Author "Tejos, Cristian"

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A Spatial Off-Resonance Correction in Spirals for Magnetic Resonance Fingerprinting
(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2021) Coronado, Ronal; Cruz, Gastao; Castillo Passi, Carlos; Tejos, Cristian; Uribe, Sergio; Prieto, Claudia; Irarrazaval, Pablo
In MR Fingerprinting (MRF), balanced Steady-State Free Precession (bSSFP) has advantages over unbalanced SSFP because it retains the spin history achieving a higher signal-to-noise ratio (SNR) and scan efficiency. However, bSSFP-MRF is not frequently used because it is sensitive to off-resonance, producing artifacts and blurring, and affecting the parametric map quality. Here we propose a novel Spatial Off-resonance Correction (SOC) approach for reducing these artifacts in bSSFP-MRF with spiral trajectories. SOC-MRF uses each pixel's Point Spread Function to create system matrices that encode both off-resonance and gridding effects. We iteratively compute the inverse of these matrices to reduce the artifacts. We evaluated the proposed method using brain simulations and actual MRF acquisitions of a standardized T1/T2 phantom and five healthy subjects. The results show that the off-resonance distortions in T1/T2 maps were considerably reduced using SOC-MRF. For T2, the Normalized Root Mean Square Error (NRMSE) was reduced from 17.3 to 8.3% (simulations) and from 35.1 to 14.9% (phantom). For T1, the NRMS was reduced from 14.7 to 7.7% (simulations) and from 17.7 to 6.7% (phantom). For in-vivo, the mean and standard deviation in different ROI in white and gray matter were significantly improved. For example, SOC-MRF estimated an average T2 for white matter of 77ms (the ground truth was 74ms) versus 50 ms of MRF. For the same example the standard deviation was reduced from 18 ms to 6ms. The corrections achieved with the proposed SOC-MRF may expand the potential applications of bSSFP-MRF, taking advantage of its better SNR property.
Accelerating dual cardiac phase images using phase encoding trajectories
(ELSEVIER SCIENCE INC, 2016) Letelier, Karis; Urbina, Jesus; Andia, Marcelo; Tejos, Cristian; Irarrazaval, Pablo; Prieto, Claudia; Uribe, Sergio
A three-dimensional dual-cardiac-phase (3D-DCP) scan has been proposed to acquire two data sets of the whole heart and great vessels during the end-diastolic and end-systolic cardiac phases in a single free-breathing scan. This method has shown accurate assessment of cardiac anatomy and function but is limited by long acquisition times. This work proposes to accelerate the acquisition and reconstruction of 3D-DCP scans by exploiting redundant information of the outer k-space regions of both cardiac phases. This is achieved using a modified radial-phase-encoding trajectory and gridding reconstruction with uniform coil combination. The end-diastolic acquisition trajectory was angularly shifted with respect to the end-systolic phase. Initially, a fully-sampled 3D-DCP scan was acquired to determine the optimal percentage of the outer k-space data that can be combined between cardiac phases. Thereafter, prospectively undersampled data were reconstructed based on this percentage. As gold standard images, the undersampled data were also reconstructed using iterative SENSE. To validate the method, image quality assessments and a cardiac volume analysis were performed. The proposed method was tested in thirteen healthy volunteers (mean age, 30 years). Prospectively undersampled data (R = 4) reconstructed with 50% combination led high quality images. There were no significant differences in the image quality and in the cardiac volume analysis between our method and iterative SENSE. In addition, the proposed approach reduced the reconstruction time from 40 min to 1 min. In conclusion, the proposed method obtains 3D-DCP scans with an image quality comparable to those reconstructed with iterative SENSE, and within a clinically acceptable reconstruction time. (C) 2016 Elsevier Inc. All rights reserved.
Chemical species separation with simultaneous estimation of field map and T-2* using a k-space formulation
(WILEY-BLACKWELL, 2012) Luis Honorato, Jose; Parot, Vicente; Tejos, Cristian; Uribe, Sergio; Irarrazaval, Pablo
Chemical species separation techniques in image space are prone to incorporate several distortions. Some of these are signal accentuation in borders and geometrical warping from field inhomogeneity. These errors come from neglecting intraecho time variations. In this work, we present a new approach for chemical species separation in MRI with simultaneous estimation of field map and T?2* decay, formulated entirely in k-space. In this approach, the time map is used to model the phase accrual from off-resonance precession and also the amplitude decay due to T?2*. Our technique fits the signal model directly in k-space with the acquired data minimizing the l2-norm with an interior-point algorithm. Standard two dimensional gradient echo sequences in the thighs and head were used for demonstrating the technique. With this approach, we were able to obtain excellent estimation for the species, the field inhomogeneity, and T?2* decay images. The results do not suffer from geometric distortions derived from the chemical shift or the field inhomogeneity. Importantly, as the T?2* map is well positioned, the species signal in borders is correctly estimated. Considering intraecho time variations in a complete signal model in k-space for separating species yields superior estimation of the variables of interest when compared to existing methods. Magn Reson Med, 2012. (C) 2011 Wiley Periodicals, Inc.
Congenital Heart Disease in Children: Coronary MR Angiography during Systole and Diastole with Dual Cardiac Phase Whole-Heart Imaging
(RADIOLOGICAL SOC NORTH AMERICA, 2011) Uribe, Sergio; Hussain, Tarique; Valverde, Israel; Tejos, Cristian; Irarrazaval, Pablo; Fava, Mario; Beerbaum, Philipp; Botnar, Rene M.; Razavi, Reza; Schaeffter, Tobias; Greil, Gerald F.
Purpose: To assess the optimal timing for coronary magnetic resonance (MR) angiography in children with congenital heart disease by using dual cardiac phase whole-heart MR imaging.
Enhancement of Visual Perception with Use of Dynamic Cues
(RADIOLOGICAL SOC NORTH AMERICA, 2009) Andia, Marcelo E.; Plett, Johannes; Tejos, Cristian; Guarini, Marcelo W.; Navarro, Maria E.; Razmilic, Dravna; Meneses, Luis; Villalon, Manuel J.; Irarrazaval, Pablo
Institutional review board approval and signed informed consent were not needed, as medical images included in public databases were used in this study. The purpose of this study was to improve the detection of microcalcifications on mammograms and lung nodules on chest radiographs by using the dynamic cues algorithm and the motion and flickering sensitivity of the human visual system (HVS). Different sets of mammograms from the Mammographic Image Analysis Society database and chest radiographs from the Japanese Society of Radiological Technology database were presented statically, as is standard, and in a video sequence generated with the dynamic cues algorithm. Nine observers were asked to rate the presence of abnormalities with a five-point scale (1, definitely not present; 5, definitely present). The data were analyzed with receiver operating characteristic (ROC) techniques and the Dorfman-Berbaum-Metz method. The video sequence generated with the dynamic cues algorithm increased the rate of detection of microcalcifications by 10.2% (P = .002) compared with that obtained with the standard static method, as measured by the area under the ROC curve. Similar results were obtained for lung nodules, with an increase of 12.3% (P = .0054). The increase in the rate of correct detection did not come just from the image contrast change produced by the algorithm but also from the fact that image frames generated with the dynamic cues algorithm were put together in a video sequence so that the motion sensitivity of the HVS could be used to facilitate the detection of low-contrast objects. (C) RSNA, 2009
Functional Dysconnectivity in Ventral Striatocortical Systems in 22q11.2 Deletion Syndrome
(OXFORD UNIV PRESS, 2021) Tepper, Angeles; Cuiza Vasquez Analia; Alliende, Luz María; Mena, Carlos; Ramirez Mahaluf, Juan Pablo; Iruretagoyena, Barbara; Ornstein, Claudia; Fritsch, Rosemarie; Nachar, Ruben; Gonzalez Valderrama, Alfonso; Undurraga, Juan; Pablo Cruz, Juan; Tejos, Cristian; Fornito, Alex; Repetto, Gabriela; Crossley, Nicolas
22q11.2 deletion syndrome (22q11.2DS) is a genetic neurodevelopmental disorder that represents one of the greatest known risk factors for psychosis. Previous studies in psychotic subjects without the deletion have identified a dopaminergic dysfunction in striatal regions, and dysconnectivity of striatocortical systems, as an important mechanism in the emergence of psychosis. Here, we used resting-state functional MRI to examine striatocortical functional connectivity in 22q11.2DS patients. We used a 2 x 2 factorial design including 125 subjects (55 healthy controls, 28 22q11.2DS patients without a history of psychosis, 10 22q11.2DS patients with a history of psychosis, and 32 subjects with a history of psychosis without the deletion), allowing us to identify network effects related to the deletion and to the presence of psychosis. In line with previous results from psychotic patients without 22q11.2DS, we found that there was a dorsal to ventral gradient of hypo- to hyperstriatocortical connectivity related to psychosis across both patient groups. The 22q11.2DS was additionally associated with abnormal functional connectivity in ventral striatocortical networks, with no significant differences identified in the dorsal system. Abnormalities in the ventral striatocortical system observed in these individuals with high genetic risk to psychosis may thus reflect a marker of illness risk.
Intake of red wine grape pomace decreased atherosclerosis, attenuated myocardial damage and increased survival in a murine model of lethal coronary heart disease
(MDPI, 2019) Salas Perez, Francisca Lorena; Rivera Vega, Katherine Solange; Echeverria, Guadalupe; Urquiaga, Ines; Dicenta, Sara; Perez, Druso; Andia, Marcelo; Uribe, Sergio; Tejos, Cristian; Busso, Dolores; Irarrazaval Mena, Pablo; Rigotti, Attilio
New Respiratory Gating Technique for Whole Heart Cine Imaging: Integration of a Navigator Slice in Steady State Free Precession Sequences
(WILEY-BLACKWELL, 2011) Uribe, Sergio; Tejos, Cristian; Razavi, Reza; Schaeffter, Tobias
Purpose: To evaluate the performance of a slice navigator sequence integrated into a b-SSFP sequence for obtaining real time respiratory self-gated whole heart cine imaging.
Noise in Magnitude Magnetic Resonance Images
(WILEY, 2008) Cardenas Blanco, Arturo; Tejos, Cristian; Irarrazaval, Pablo; Cameron, Ian
The aims of this article are to review the properties of noise in magnitude MR images to clarify the terminology used when referring to the noise and to discourage the use of the terms Rician noise and Rician noise bias. The distribution of measured MR pixel intensities in the presence of noise is known to be Rician, and the width of this distribution is directly related to the Gaussian noise on the measured real and imaginary signals. It is the pixel magnitude values that follow the Rician distribution, not the noise. The term Rician noise should be used cautiously or, better still, avoided completely since inherent to this terminology is behavior that is not normally associated with noise, such as dependence on signal strength. This terminology is misleading and can lead to conceptual and practical misunderstandings. It is better to relate the image noise to the Gaussian noise on the real and imaginary signals. (C) 2008 Wiley Periodicals. Inc. Concepts Magn Reson Part A 32A: 409-416, 2008.
Prevalence of Advanced Liver Fibrosis and Nonalcoholic Steato-hepatitis Diagnosed by Noninvasive Methods in Chilean Type 2 Diabetic Patients
(2014) Gallego, Consuelo; Valderas, Juan P.; Uribe, Sergio; Tejos, Cristian; Serrano, Cristobal; Huete, Alvaro; Barrera, Francisco; Liberona, Jessica; Labbe, Pilar; Quiroga, Teresa; Irarrazabal, Pablo; Arrese, Marco
Quantification of visceral adipose tissue using magnetic resonance imaging compared with anthropometry, in type 2 diabetic patients
(SOC MEDICA SANTIAGO, 2012) Serrano Garcia, Cristobal; Barrera, Francisco; Labbe, Pilar; Liberona, Jessica; Arrese, Marco; Irarrazaval, Pablo; Tejos, Cristian; Uribe, Sergio
Background: Visceral fat accumulation is associated with the development of metabolic diseases. Anthropometry is one of the methods used to quantify it. aim: to evaluate the relationship between visceral adipose tissue volume (VAT), measured with magnetic resonance imaging (MRI), and anthropometric indexes, such as body mass index (BMI) and waist circumference (WC), in type 2 diabetic patients (DM2). Patients and Methods: Twenty four type 2 diabetic patients aged 55 to 78 years (15 females) and weighting 61.5 to 97 kg, were included. The patients underwent MRI examination on a Philips Intera (R) 1.5T MR scanner. The MRI protocol included a spectral excitation sequence centered at the fat peak. The field of view included from L4-L5 to the diaphragmatic border. VAT was measured using the software Image J (R). Weight, height, BMI, WC and body fat percentage (BF%), derived from the measurement of four skinfolds with the equation of Durnin and Womersley, were also measured. The association between MRI VAT measurement and anthropometry was evaluated using the Pearson's correlation coefficient. Results: Mean VAT was 2478 +/- 758 ml, mean BMI 29.5 +/- 4.7 kg/m(2), and mean WC was 100 +/- 9.7 cm. There was a poor correlation between VAT, BMI (r = 0.18) and WC (r = 0.56). Conclusions: BMI and WC are inaccurate predictors of VAT volume in type 2 diabetic patients. (Rev Med Chile 2012; 140: 1535-1543).
Quantitative description of the morphology and ossification center in the axial skeleton of 20-week gestation formalin-fixed human fetuses using magnetic resonance images
(WILEY, 2012) Chabert, Steren; Villalobos, Manuel; Ulloa, Patricia; Salas, Rodrigo; Tejos, Cristian; San Martin, Sebastian; Pereda, Jaime
Objectives Human tissues are usually studied using a series of two-dimensional visualizations of in vivo or cutout specimens. However, there is no precise anatomical description of some of the processes of human fetal development. The purpose of our study is to develop a quantitative description of the normal axial skeleton by means of high-resolution three-dimensional magnetic resonance (MR) images, collected from six normal 20-week-old human fetuses fixed in formaldehyde.

Browsing by Author "Tejos, Cristian"

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