Papers by Eric Mauricio Lopez Diaz
Revista Cubana De Oftalmologia, Feb 13, 2014
Los científicos han estado interesados en el estudio de las secreciones de las glándulas de Meibo... more Los científicos han estado interesados en el estudio de las secreciones de las glándulas de Meibomio desde hace muchos años. Enfermedades asociadas, como los cánceres y la blefaritis posterior, se han observado en la literatura médica, desde la primera parte del siglo XX. Sin embargo, el término "disfunción de las glándulas de Meibomio" fue introducida por Korb y Henríquez en 1980. No existía una definición establecida publicada en la literatura hasta que más de 50 expertos internacionales participaron en un taller, que tuvo lugar durante un período de dos años, donde se llegó a definir como una anormalidad crónica y difusa de estas glándulas, comúnmente caracterizada por la obstrucción del conducto terminal y cambios cualitativos/cuantitativos en la secreción de esta. Esto puede resultar en la alteración de la película lagrimal, síntomas de irritación ocular, inflamación clínicamente aparente y enfermedad de la superficie ocular. Es en el mismo Taller Internacional, donde se decide clasificar de acuerdo con los cambios anatómicos, fisiopatológicos, o la gravedad de la enfermedad, donde la forma obstructiva fue la más generalizada. Constituye una afección frecuente con disminución de la calidad de vida y perjuicios potencialmente graves para el bienestar humano.
Revista Cubana De Oftalmologia, Jun 18, 2014
RESUMEN Objetivo: determinar la efectividad de la biometría de inmersión para el cálculo del lent... more RESUMEN Objetivo: determinar la efectividad de la biometría de inmersión para el cálculo del lente intraocular. Métodos: se realizó un estudio observacional descriptivo, prospectivo. El universo estuvo constituido por los pacientes operados de catarata en el Instituto Cubano de Oftalmología "Ramón Pando Ferrer", entre enero y septiembre de 2011. La muestra estuvo conformada por 39 ojos de 34 pacientes que cumplieron con los criterios de inclusión establecidos para la investigación y fueron operados por la técnica de facoemulsificación con previo cálculo del lente intraocular por biometría de inmersión e interferometría de coherencia óptica. Resultados: el promedio de edad fue de 72,33 años, con un predominio del sexo femenino. La diferencia de longitud axial promedio entre los pacientes calculados por inmersión y los de IOL Máster fue de 0,09 mm, mientras que la diferencia de profundidad de la cámara anterior fue de 0,19 mm. Se obtuvo una diferencia de 0,13 D y no existió diferencia significativa en cuanto al cálculo del poder del lente intraocular entre ambos métodos. Conclusiones: los valores de longitud axial y de profundidad de cámara anterior obtenidos mediante biometría de inmersión pueden ser utilizados para calcular con efectividad el poder del lente intraocular de los pacientes que serán sometidos a cirugía de cataratas, lo que demuestra ser una alternativa en ausencia del IOL Máster. Palabras clave: biometría de inmersión, interferometría de coherencia óptica, cálculo del lente intraocular, facoemulsificación.
PURPOSE To provide a non-invasive quantitative means of evaluating Achilles tendon T2* values usi... more PURPOSE To provide a non-invasive quantitative means of evaluating Achilles tendon T2* values using 3T MR UTE techniques in asymptomatic volunteers. METHOD AND MATERIALS Left ankles of 10 asymptomatic volunteers (43±14.2 yrs, mean±sd) underwent MR imaging at 3T. Measurements were taken from 1.5 to 6 cm above the posterior superior margin of the calcaneus in the region of the mid-tensile tendon. A constant TR–variable TE 2D ultrashort TE (UTE) sequence with a minimum TE of 8 us was employed to image and quantify the Achilles tendon of asymptomatic volunteers. Typical imaging parameters included: field of view (FOV)=10 cm, slice thickness = 2 mm, readout = 512, 355 projections, TR = 200 ms, number of excitation=2, bandwidth=±62.5 kHz, flip angle=45°, scan time=2.4 min (x4 scans total). T2* was quantified using Matlab, employing voxel-wise mono exponential fitting of fat saturated axial UTE images taken at 4 TEs (8 us, 600 us, 2.2 ms, 6.6 ms). For each sample, the region of interest wa...
PURPOSE To compare T1ρ measurements using a 2D multi-slice spiral and 3D MAPS technique. METHOD A... more PURPOSE To compare T1ρ measurements using a 2D multi-slice spiral and 3D MAPS technique. METHOD AND MATERIALS Four phantoms (agarose concentration: 1%, 2%, 3%, 4%) and five axially sliced cadaveric patella chips were scanned in a 3T MRI-system using a single-channel, transmit and receive, custom-built quadrature birdcage coil. T1ρ sequences were acquired using a 2D multi-slice spiral technique and 3D MAPS technique. Measurements were performed in the phantoms and in the radial and transitional zones of the cartilage. T1ρ values were compared with respect to the imaging technique, orientation of the cartilage surface compared to the direction of the main magnetic field B0, and localization in the medial or lateral patellar facet. RESULTS On the phantom images (agarose concentration: 1% / 2% / 3% / 4%), average T1ρ values were 75.3 / 30.2 / 22.9 / 21.5 msec using 2D technique, and 61.2 / 46.6 / 27.7 / 18.2 msec using 3D technique. The differences between the measurement techniques wer...
Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine, 2010
In this study, we report the use of a novel ultrashort echo time T(1)rhoT(1) sequence that combin... more In this study, we report the use of a novel ultrashort echo time T(1)rhoT(1) sequence that combines a spin-lock preparation pulse with a two-dimensional ultrashort echo time sequence of a nominal echo time 8 microsec. The ultrashort echo time-T(1)rho sequence was employed to quantify T(1)rho in short T(2) tissues including the Achilles tendon and the meniscus. T(1)rho dispersion was investigated by varying the spin-lock field strength. Preliminary results on six cadaveric ankle specimens and five healthy volunteers show that the ultrashort echo time-T(1)rho sequence provides high signal and contrast for both the Achilles tendon and the meniscus. The mean T(1)rho of the Achilles tendon ranged from 3.06 +/- 0.51 msec for healthy volunteers to 5.22 +/- 0.58 msec for cadaveric specimens. T(1)rho increased to 8.99 +/- 0.24 msec in one specimen with tendon degeneration. A mean T(1)rho of 7.98 +/- 1.43 msec was observed in the meniscus of the healthy volunteers. There was significant T(1)r...
Radiology, 2012
To assess the ability of ultrashort echo time (UTE) magnetic resonance (MR) imaging techniques to... more To assess the ability of ultrashort echo time (UTE) magnetic resonance (MR) imaging techniques to enable morphologic assessment of different types of meniscal calcifications, to compare these sequences with standard clinical sequences, and to perform T2* measurements of meniscal calcifications. This study was exempted by the institutional review board, and informed consent was not required. Ten human cadaveric menisci were imaged with high-spatial-resolution radiography and 3.0-T MR imaging by using morphologic (T1-weighted fast spin-echo [FSE], T2-weighted FSE, proton density [PD]-weighted FSE, two-dimensional [2D] fast spoiled gradient-echo [FSPGR], three-dimensional [3D] FSPGR, and 3D UTE) and quantitative (2D inversion-recovery [IR] UTE and 3D UTE) sequences. The menisci were divided into thirds for regional analysis. Morphologic assessment was performed with MR imaging; MR imaging findings were correlated with radiographs. Calcifications were classified as punctate, linear, or ...
Parasitology Research, 2013
For a deeper understanding of the phylogenetic relationships of Echinococcus genotypes and specie... more For a deeper understanding of the phylogenetic relationships of Echinococcus genotypes and species in different intermediate hosts, we analyzed samples from human and bovine hydatid cysts. For this, segments of the cytochrome oxidase (COX1) and NADH dehydrogenase (ND1) mitochondrial genes were used. To obtain sufficient amounts of the ND1 marker to be sequenced properly, a new variant of the PCR assay was implemented. Phylogenetic analysis with both markers showed that most of the analyzed samples correspond to genotype G1. However, a sample from cysts of a bovine lung (Q21), with the COX1 marker, was grouped in a node together with a sample belonging to genotype G3. In the phylogenetic tree obtained with the ND1 marker, this sample was grouped with sequences of genotypes G3, G2, and G4. Analyzing the single nucleotide polymorphic (SNP) sites of both markers, it was observed that the Q21 sequence is almost identical to the G3 sequence and differ in only one SNP from the G2 sequence, and is completely different from G4. These results are noteworthy, since neither G2 nor G3 genotypes have been described previously in Chile, raising the possibility that the G3 genotype is present in these latitudes. This information is highly relevant; it can be employed to uncover additional unknown details of transmission cycles of this important parasite.
Magnetic Resonance in Medicine, 2011
Biological tissues frequently contain different water compartments, and these often have distinct... more Biological tissues frequently contain different water compartments, and these often have distinct transverse relaxation times. Quantification of these may be problematic on clinical scanners because spin echo sequences usually have initial echo times that are too long to accurately quantify shorter relaxation time components. In this study, an ultrashort echo time pulse sequence was used together with bicomponent analysis to quantify both the short and long T 2 components in tissues of the musculoskeletal system. Feasibility studies were performed using numerical simulation, and on phantoms and in vitro tissues including bovine cortical bone, ligaments, menisci, tendons, and articular cartilage. The simulation and phantom studies demonstrated that this technique can quantify T 2 * and fractions of the short and long T 2 components. The tissues studies showed two distinct components with short T 2 *s ranging from 0.3 ms for bovine cortical bone to 2.1 ms for menisci, and long T 2 *s ranging from 2.9 ms for bovine cortical bone to 35.0 ms for articular cartilage. The short T 2 * fraction ranged from 18.5% for patella cartilage to 80.9% for ligaments. The results show that ultrashort echo time imaging with bicomponent analysis can quantify the short and long T 2 water components in vitro in musculoskeletal tissues. Magn Reson Med 67:645-649, 2012. V
Magnetic Resonance in Medicine, 2007
Cortical bone in the mature skeleton has a short T(2)* and produces no detectable signal with con... more Cortical bone in the mature skeleton has a short T(2)* and produces no detectable signal with conventional MR sequences. A two-dimensional ultrashort echo time (UTE) sequence employing half radio frequency (RF) pulse excitations and radial ramp sampling reduces the effective TE to 8 micros and is capable of detecting signals from cortical bone. We propose a time-efficient UTE spectroscopic imaging (UTESI) technique based on an interleaved variable TE acquisition, preceded by long T(2)* signal suppression using either a 90 degrees pulse and gradient dephasing or an inversion pulse and nulling. The projections were divided into multiple groups with the data for each group being collected with progressively increasing TE and interleaved projection angles. The undersampled projections within each group sparsely covered k-space. A view sharing and sliding window reconstruction algorithm was implemented to reconstruct images at each TE, followed by Fourier transformation in the time domain to generate spectroscopic images. T(2)* was quantified through either exponential fitting of the time domain images or line fitting of the magnitude spectrum. Relative water content and the resonance frequency shift due to bulk susceptibility were also evaluated. The feasibility of this technique was demonstrated with phantom and volunteer studies on a clinical 3T scanner.
Magnetic Resonance in Medicine, 2011
The effects of water loss on the T1 and T2* of bovine cortical bone were investigated using ultra... more The effects of water loss on the T1 and T2* of bovine cortical bone were investigated using ultrashort echo time (UTE) sequences with signals excited either by a short hard pulse or by two longer half pulses. Nine bovine femur samples were prepared and sequentially air and oven dried. On average 3.42% of bone by weight was lost after air-drying for three days, with another 5.98% of bone weight loss after oven-drying at 100 °C for 24 hours. T1 and T2* were measured after every 1% decrease in weight, with 9-10% bone weight loss at the termination of the drying process. After both forms of drying the overall T1 decreased 33% from 153±18 ms to 102±17 ms when measured using the hard pulse and from 186±25 ms to 122±23 ms when using the half pulses. T2* decreased by 45-50% from 368±29 μs to 201±19 μs using the hard pulse and from 379±35 μs to 191±17 μs using the half pulses. A steady decrease of 26-31% was observed in both T1 and T2* with the first 3-4% bone water loss after air-drying. Oven-drying at 100 °C for 24 hours resulted on an additional 4% T1 reduction but 25% T2* reduction.
Magnetic Resonance in Medicine, 2012
We describe the use of ultrashort echo time (UTE) sequences and fast spin echo sequences to asses... more We describe the use of ultrashort echo time (UTE) sequences and fast spin echo sequences to assess cortical bone using a clinical 3T scanner. Regular two-and three-dimensional UTE sequences were used to image both bound and free water in cortical bone. Adiabatic inversion recovery prepared UTE sequences were used to image water bound to the organic matrix. Two-dimensional fast spin echo sequences were used to image free water. Regular UTE sequences were used together with bicomponent analysis to measure T* 2 s and relative fractions of bound and free water components in cortical bone. Inversion recovery prepared UTE sequences were used to measure the T* 2 of bound water. Saturation recovery UTE sequences were used to measure the T 1 of bone water. Eight cadaveric human cortical bone samples and a lower leg specimen were studied. Preliminary results show two distinct components in UTE detected signal decay, a single component in inversion recovery prepared UTE detected signal decay, and a single component in saturation recovery UTE detected signal recovery. Regular UTE sequences appear to depict both bound and free water in cortical bone. Inversion recovery prepared UTE sequences appear to depict water bound to the organic matrix. Two-dimensional fast spin echo sequences appear to depict bone structure corresponding to free water in large pores. Magn Reson Med 000:000-000, 2012. V
Journal of Magnetic Resonance Imaging, 2011
Purpose: To use a tissue specific algorithm to numerically optimize UTE sequence parameters to ma... more Purpose: To use a tissue specific algorithm to numerically optimize UTE sequence parameters to maximize contrast within temporomandibular joint (TMJ) donor tissue. Materials and Methods: A TMJ specimen tissue block was sectioned in a true sagittal plane and imaged at 3 Tesla (T) using UTE pulse sequences with dual echo subtraction. The MR tissue properties (PD, T 2 , T 2 *, and T 1) were measured and subsequently used to calculate the optimum sequences parameters (repetition time [TR], echo time [TE], and y). Results: It was found that the main contrast available in the TMJ could be obtained from T 2 (or T 2 *) contrast. With the first echo time fixed at 8 ms and using TR ¼ 200 ms, the optimum parameters were found to be: y % 60 , and TE2 % 15 ms, when the second echo is acquired using a gradient echo and y % 120 , and TE2 % 15 ms, when the second echo is acquired using a spin echo. Conclusion: Our results show that MR signal contrast can be optimized between tissues in a systematic manner. The MR contrast within the TMJ was successfully optimized with facile delineation between disc and soft tissues.
Bone, 2012
Recent proton magnetic resonance (MR) spectroscopy studies have shown that cortical bone exists a... more Recent proton magnetic resonance (MR) spectroscopy studies have shown that cortical bone exists as different components which have distinct transverse relaxation times (T2s). However, cortical bone shows zero or near zero signal with all conventional MR sequences on clinical scanners and the different water components cannot be assessed with this approach. In order to detect signal in this situation a two-dimensional (2D) non-slice selective ultrashort echo time (UTE) pulse sequence with a nominal TE of 8 μs was used together with bi-component analysis to quantify bound and free water in bovine cortical bone at 3T. Total water concentration was quantified using a 3D UTE sequence together with a reference water phantom. 2D and 3D UTE imaging were performed on 14 bovine bone samples which were subjected to sequential air-drying to evaluate free water loss, followed by oven-drying to evaluate bound water loss. Sequential bone weight loss was measured concurrently using a precision balance. Bone porosity was measured with micro computed tomography (μCT) imaging. UTE measured free water loss was higher than the volume of cortical pores measured with μCT, but lower than the gravimetric bone water loss measured during air-drying. UTE assessed bound water loss was about 82% of gravimetric bone water loss during oven-drying. On average bovine cortical bone showed about 13% free water and 87% bound water. There was a high correlation (R = 0.91; P < 0.0001) between UTE MR measured free water loss and gravimetric bone weight loss during sequential air-drying, and a significant correlation (R = 0.69; P < 0.01) between UTE bound water loss and gravimetric bone weight loss during oven-drying. These results show that UTE bi-component analysis can reliably quantify bound and free water in cortical bone. The technique has potential applications for the in vivo evaluation of bone porosity and organic matrix.
American Journal of Roentgenology, 2011
here has been a growing awareness that osteoarthritis (OA) is a major public health issue; it is ... more here has been a growing awareness that osteoarthritis (OA) is a major public health issue; it is responsible for significant decreases in quality of life, decreases in workforce productivity, and the growing expenditure of health care dollars for treatment. Despite the nearly epidemic proportion of this disease, its pathogenesis remains poorly understood. To this end, techniques that allow the noninvasive detection of early changes in OA, including biochemical alteration in articular cartilage that may occur without changes in its gross morphology, have been emphasized in the literature. Furthermore, the ability for quantitative evaluation that allows these techniques to serve as scientific outcome measures is desirable.
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Papers by Eric Mauricio Lopez Diaz