Persona: Santa Marta Pastrana, Cristina María
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Santa Marta Pastrana
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Cristina María
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Publicación Multiresolution Reconstruction for Cone-Beam Tomography from Raw Data Projections Using 3D Ridgelets(Springer Nature, 2011-03-01) Romero, Eduardo C.; Gómez Gómez, Francisco; Santa Marta Pastrana, Cristina MaríaThis paper presents a novel method which reconstructs any desired 3D image resolution from raw cone-beam CT data. X-ray attenuation through the object is approximated using ridgelet basis functions which allow us to have multiresolution representation levels. Since the Radon data have preferential orientations by nature, a spherical wavelet transform is used to compute the ridgelet coefficients from the Radon shell data. The whole method uses the classical Grangeat’s relation for computing derivatives of the Radon data which are then integrated and projected to a spherical wavelet representation and back-reconstructed using a modified version of the well known back-projection algorithm. Unlike previous reconstruction methods, this proposal uses a multiscale representation of the Radon data and therefore allows fast display of low-resolution data level.Publicación A sparse Bayesian representation for super-resolution of cardiac MR images(Elsevier, 2017-02) Velasco, Nelson F.; Rueda Olarte, Andrea del Pilar; Romero, Eduardo C.; Santa Marta Pastrana, Cristina MaríaHigh-quality cardiac magnetic resonance (CMR) images can be hardly obtained when intrinsic noise sources are present, namely heart and breathing movements. Yet heart images may be acquired in real time, the image quality is really limited and most sequences use ECG gating to capture images at each stage of the cardiac cycle during several heart beats. This paper presents a novel super-resolution algorithm that improves the cardiac image quality using a sparse Bayesian approach. The high-resolution version of the cardiac image is constructed by combining the information of the low-resolution series –observations from different non-orthogonal series composed of anisotropic voxels – with a prior distribution of the high-resolution local coefficients that enforces sparsity. In addition, a global prior, extracted from the observed data, regularizes the solution. Quantitative and qualitative validations were performed in synthetic and real images w.r.t to a baseline, showing an average increment between 2.8 and 3.2 dB in the Peak Signal-to-Noise Ratio (PSNR), between 1.8% and 2.6% in the Structural Similarity Index (SSIM) and 2.% to 4% in quality assessment (IL-NIQE). The obtained results demonstrated that the proposed method is able to accurately reconstruct a cardiac image, recovering the original shape with less artifacts and low noise.Publicación Motion estimation of tagged cardiac magnetic resonance images using variational techniques(Elsevier, 2010-09) Carranza Herrezuelo, N.; Bajo, A.; Sroubek, F.; Cristobal, G.; Santos, A.; Ledesma Carbayo, M. J.; Santa Marta Pastrana, Cristina MaríaThis work presents a new method for motion estimation of tagged cardiac magnetic resonance sequences based on variational techniques. The variational method has been improved by adding a new term in the optical flow equation that incorporates tracking points with high stability of phase. Results were obtained through simulated and real data, and were validated by manual tracking and with respect to a reference state-of-the-art method: harmonic phase imaging (HARP). The error, measured in pixels per frame, obtained with the proposed variational method is one order of magnitude smaller than the one achieved by the reference method, and it requires a lower computational cost.Publicación Intraventricular vortex properties in nonischemic dilated cardiomyopathy(American Physiological Society, 2014-03-01) Bermejo, Javier; Benito, Yolanda; Alhama, Marta; Yotti, Raquel; Pérez del Villar, Candelas; Pérez David, Esther; González Mansilla, Ana; Barrio, Alicia; Fernández Avilés, Francisco; Álamo, Juan C. del; Martínez-Legazpi Aguilo, Pablo; Santa Marta Pastrana, Cristina MaríaVortices may have a role in optimizing the mechanical efficiency and blood mixing of the left ventricle (LV). We aimed to characterize the size, position, circulation, and kinetic energy (KE) of LV main vortex cores in patients with nonischemic dilated cardiomyopathy (NIDCM) and analyze their physiological correlates. We used digital processing of color-Doppler images to study flow evolution in 61 patients with NIDCM and 61 age-matched control subjects. Vortex features showed a characteristic biphasic temporal course during diastole. Because late filling contributed significantly to flow entrainment, vortex KE reached its maximum at the time of the peak A wave, storing 26 ± 20% of total KE delivered by inflow (range: 1–74%). Patients with NIDCM showed larger and stronger vortices than control subjects (circulation: 0.008 ± 0.007 vs. 0.006 ± 0.005 m2/s, respectively, P = 0.02; KE: 7 ± 8 vs. 5 ± 5 mJ/m, P = 0.04), even when corrected for LV size. This helped confining the filling jet in the dilated ventricle. The vortex Reynolds number was also higher in the NIDCM group. By multivariate analysis, vortex KE was related to the KE generated by inflow and to chamber short-axis diameter. In 21 patients studied head to head, Doppler measurements of circulation and KE closely correlated with phase-contract magnetic resonance values (intraclass correlation coefficient = 0.82 and 0.76, respectively). Thus, the biphasic nature of filling determines normal vortex physiology. Vortex formation is exaggerated in patients with NIDCM due to chamber remodeling, and enlarged vortices are helpful for ameliorating convective pressure losses and facilitating transport. These findings can be accurately studied using ultrasound. intraventricular vortex dynamics may have an important role in cardiac hemodynamics. During early filling and atrial contraction, strong jets entering the left ventricle (LV) lead to the formation of vortex rings near the tips of the mitral valve leaflets. Due to the chiral configuration formed by the LV inflow tract, main chamber, and LV outflow tract (LVOT), these vortex rings evolve into large rotational flow structures that occupy a large fraction of the ventricle. Recent clinical data in patients with diastolic dysfunction indicate that LV vortices may facilitate flow from the left atrium to the LV apex (6). Also, vortical structures may increase ejection efficiency by conserving the momentum of blood built up during filling (1). Finally, vortices may contribute to blood mixing inside the ventricle, avoiding stasis (6, 19, 30, 32, 33, 40). Because impaired diastolic function, reduced mechanical efficiency, and risk of thrombosis characteristically concur in patients with nonischemic dilated cardiomyopathy (NIDCM), addressing the physical properties of intraventricular vortices is particularly relevant in this condition. Recent ultrasound (1, 19, 29), computational (28), and phase-contrast magnetic resonance (PC-MR) (3, 6, 11–13) studies have described intraventricular flow characteristics in small numbers of patients with normal and dilated hearts. We hypothesized that significant physiological insights can be gained by comprehensively studying the temporal dynamics and correlates of intraventricular vortex development. We also hypothesized that impaired chamber properties in patients with NIDCM may be associated with modified vortex physiology. Therefore, the present study was designed to characterize the dynamics of vortex position, size, and strength along the cardiac cycle in patients with NIDCM and age-matched healthy control subjects. The physiological relevance of vortices relative to the global LV kinetic energy (KE) balance was also analyzed in detail. We used a custom-developed method that allowed us to measure two-dimensional (2-D) flow using conventional color-Doppler ultrasound (17). Because most previous evidence in this field has been reported using PC-MR, the ultrasound-based method was compared in vivo against this technique in a subset of NIDCM patients.Publicación N-acetyl-aspartate levels in the dorsolateral prefrontal cortex in the early years of schizophrenia are inversely related to disease duration.(Elsevier, 2005-03-01) Molina, Vicente; Reig Redondo, Santiago; Benito, Carlos; Pascau González-Garzón, Javier; Sarramea, Fernando; Gispert, Juan Domingo; Misiego, José M.; Palomo, Tomás; Desco, Manuel; Domínguez Sánchez, Francisco Javier; Sanz Pérez, Javier; Santa Marta Pastrana, Cristina MaríaMagnetic resonance spectroscopy studies in schizophrenia have revealed consistently reduced N-acetyl aspartate (NAA) levels in chronic patients, but not in recent-onset patients. Studies on the relationship between this marker and disease duration have commonly been negative, although it is also true that they have been conducted in patients with long-standing disease. We compared NAA levels in the dorsolateral prefrontal cortex in 16 recent-onset patients (duration: 1.8±0.6 years), 19 chronic patients (duration: 9.7±6.1 years), and 20 healthy controls. We studied the NAA/creatine and choline/creatine ratios in the dorsolateral prefrontal cortex in both hemispheres, controlling for the effect of age. Chronic patients had significantly lower NAA/Cr ratios in the left hemisphere compared to recent-onset patients and healthy controls, with no difference in Cho/Cr ratio. There were no differences between controls and recent-onset patients. There was a significant inverse relationship between left-side NAA/Cr and disease duration, suggesting that prefrontal NAA levels may progressively decrease in schizophrenia. Taken within the context of the existing literature, these results indicate that this process may be limited to the early years following the onset of the disease. Therefore, reduced prefrontal levels of NAA may be limited to chronic schizophrenia patients.Publicación Resolution recovery in Turbo Spin Echo using segmented Half Fourier acquisition.(Elsevier, 2004-04) Lafuente, Javier; Vaquero, Juan José; Garcia Barreno, Pedro; Desco, Manuel; Santa Marta Pastrana, Cristina MaríaTurbo Spin Echo (TSE) is a sequence of choice for obtaining T2-weighted images. TSE reduces acquisition time by acquiring several echoes within each TR, at the cost of introducing an exponential weighting in the k-space that leads to a certain image blurring. This is particularly important for short-T2 structures, which can even disappear if their size in the phase encoding direction is comparable to the degree of blurring. This article suggests the use of a combination of Half Fourier (HF) and segmented (multishot) TSE (sHF-TSE) to recover the original resolution of the SE images. The improved symmetry of the dataset achieved by HF reconstruction is used to increase the resolution of the TSE images. The proposed combination, available in most clinical scanners, reduces the blurring artifact inherent to the TSE sequence without increasing the scan time or the number of acquisitions, but at the cost of a slight reduction of the signal-to-noise ratios (SNR). Qualitative and quantitative results are presented using both numerical simulation and imaging. Significant edge enhancement has been achieved for structures with short T2, (narrowing of the full width at half maximum [FWHM] up to 45%). The proposed sequence is more sensitive to movement artifacts but has proven to be superior to the conventional TSE for imaging static structures.