DSpace Angular :: Browsing by Author "Irarrazaval, Pablo"

Browsing by Author "Irarrazaval, Pablo"

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A 3D trajectory for undersampling k-space in MRSI applications
(ELSEVIER SCIENCE INC, 2007) Uribe, Sergio; Guesalaga, Andres; Mir, Roberto; Guarini, Marcelo; Irarrazaval, Pablo
Magnetic resonance spectroscopic imaging (MRSI) is a noninvasive technique for producing spatially localized spectra. MRSI presents the important challenge of reducing the scan time while maintaining the spatial resolution. The preferred approach for this is to use time-varying readout gradients to collect the spatial and chemical-shift information. Fast, three-dimensional (3D) spatial encoded methods also reduce the scan time. Despite the existence of several new and faster 3D encoded methods, or k-space trajectories, for magnetic resonance imaging (MRI), only stack of spirals and echo planar have been studied in 3D MRSI. A novel formulation for designing fast, 3D k-space trajectory applicable to 3D MRSI is presented. This approach is simple and consists of rays expanding from the origin of k-space into a revolving sphere, collecting spectral data of all 3D spatial k-space at different times in the same scan. This article describes this new method and presents some results of its application to 3D MRSI. This technique allows some degree of undersampling; hence, it is possible to reconstruct high-quality undersampled spectroscopic imaging in order to recognize different compounds in short scan times. Additionally, the method is tested in regular 3D MRI. This proposed method can also be used for dynamic undersampled imaging. (c) 2007 Elsevier Inc. All rights reserved.
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
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.
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).
Red wine grape pomace attenuates atherosclerosis and myocardial damage and increases survival in association with improved plasma antioxidant activity in a murine model of lethal ischemic heart disease
(2019) Rivera Vega, Katherine Solange; Salas Pérez, Francisca Lorena; Echeverría Errázuriz, Guadalupe; Urquiaga Reus, Inés; Dicenta, Sara; Pérez Pons, Druso Diego; De La Cerda, Paula; Gonzáles, Leticia; Andía Kohnenkampf, Marcelo Edgardo; Uribe Arancibia, Sergio A.; Tejos Núñez, Cristián Andrés; Martínez, Gonzalo; Busso, Dolores; Irarrazaval, Pablo; Rigotti Rivera, Attilio
Volume visualization using a spatially aware mobile display device
(PERGAMON-ELSEVIER SCIENCE LTD, 2012) Bertelsen, Alvaro; Irarrazaval, Pablo; Cadiz, Rodrigo F.
Volume visualization is a difficult three-dimensional task and a significant amount of research is devoted to the development of a suitable computer input device for it. Most of the proposed models use fixed displays, thus rendering extracted slices in orientations unrelated to their real locations within the volume. We present a new device which takes a different approach, as it leaves the volume in a fixed location and demands the user to change his or her posture to explore it from different angles. To implement this, we built a prototype based on a mobile display equipped with sensors that allows it to track its position, which is related to the location of the slice plane within the volume. Therefore, the user can manipulate this plane by displacing and rotating the display, which is a very intuitive method with minimum learning time. Furthermore, the postural changes required to use the device add a new channel of feedback, which effectively helps to reduce the cognitive load imposed on the user. We built a prototype device and tested it with two groups of volunteers who were asked to use it in a medical imaging application. Statistical analysis of the results shows that explorations made with the proposed device were considerably faster with no penalty in precision. We believe that, with further work, the proposed device can be developed into an useful tool for radiology and neurosurgery. (C) 2011 Elsevier Ltd. All rights reserved.

Browsing by Author "Irarrazaval, Pablo"

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