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Biomedical subjects

Ignacio Rodriguez

Publications and source records attributed to Ignacio Rodriguez.

14 recordsLinked to original sources
PubMed2006

Noninvasive measurement of myocardial tissue volume change during systolic contraction and diastolic relaxation in the canine left ventricle.

In coronary circulation the flow in epicardial arteries and veins is observed to be pulsatile and out of phase with each other. Theoretical considerations predict that this phenomenon extends to all levels of the vascular tree and leads to a cyclic fluctuation of regional tissue volume. Intramyocardial tissue volume change between end-systole and end-diastole was measured noninvasively with MRI in 10 closed-chest beagles. The displacement encoding with stimulated-echo technique was used to obtain pixel-by-pixel tissue displacement field between end-diastole and end-systole and vice versa in the midlevel left ventricle, from which the 3D strain matrix and volume changes were calculated. The volume change was between 0.8+/-0.5% (mean+/-STD) in the epicardial layer and 1.5+/-0.6% in the subendocardial layer of the left ventricle. Tissue volume fluctuation reflects the amount of arterial inflow in a heartbeat under the assumption that regional arterial inflow and venous outflow have little time overlap. The corresponding perfusion level was estimated to be from (1.0+/-0.6) ml/min/g in the epicardial layer to (1.7+/-0.6) ml/min/g in the subendocardial layer, in good agreement with microsphere measurements in the same dog model. The result supports the notion of high arterial resistance at the microvascular level from intramyocardial pressure during systole.

Animals↗
PubMed2006

Detection of myocardial capillary orientation with intravascular iron-oxide nanoparticles in spin-echo MRI.

In mammalian hearts the capillaries are closely aligned with the muscle fibers. We report our observation of a main-field direction-dependent contrast in MR spin-echo (SE) images of the heart in the presence of Ferumoxtran-10, an intravascular iron-oxide nanoparticle contrast agent (CA). We describe a novel MRI method for mapping the preferential orientation of capillaries in the myocardial wall. The eigenvector corresponding to the minimum eigen value of the R2 relaxation rate tensor is consistent with the expected orientation of the capillary network. Preliminary results also demonstrate the feasibility of this method for in vivo application to rodent imaging.

Animals↗
PubMed2005

Electromechanical analysis of infarct border zone in chronic myocardial infarction.

To test the hypothesis that alterations in electrical activation sequence contribute to depressed systolic function in the infarct border zone, we examined the anatomic correlation of abnormal electromechanics and infarct geometry in the canine post-myocardial infarction (MI) heart, using a high-resolution MR-based cardiac electromechanical mapping technique. Three to eight weeks after an MI was created in six dogs, a 247-electrode epicardial sock was placed over the ventricular epicardium under thoracotomy. MI location and geometry were evaluated with delayed hyperenhancement MRI. Three-dimensional systolic strains in epicardial and endocardial layers were measured in five short-axis slices with motion-tracking MRI (displacement encoding with stimulated echoes). Epicardial electrical activation was determined from sock recordings immediately before and after the MR scans. The electrodes and MR images were spatially registered to create a total of 160 nodes per heart that contained mechanical, transmural infarct extent, and electrical data. The average depth of the infarct was 55% (SD 11), and the infarct covered 28% (SD 6) of the left ventricular mass. Significantly delayed activation (>mean + 2SD) was observed within the infarct zone. The strain map showed abnormal mechanics, including abnormal stretch and loss of the transmural gradient of radial, circumferential, and longitudinal strains, in the region extending far beyond the infarct zone. We conclude that the border zone is characterized by abnormal mechanics directly coupled with normal electrical depolarization. This indicates that impaired function in the border zone is not contributed by electrical factors but results from mechanical interaction between ischemic and normal myocardium.

Action Potentials↗
PubMed2005

Visualization of tensor fields using superquadric glyphs.

The spatially varying tensor fields that arise in magnetic resonance imaging are difficult to visualize due to the multivariate nature of the data. To improve the understanding of myocardial structure and function a family of objects called glyphs, derived from superquadric parametric functions, are used to create informative and intuitive visualizations of the tensor fields. The superquadric glyphs are used to visualize both diffusion and strain tensors obtained in canine myocardium. The eigensystem of each tensor defines the glyph shape and orientation. Superquadric functions provide a continuum of shapes across four distinct eigensystems (lambda(i), sorted eigenvalues), lambda(1) = lambda(2) = lambda(3) (spherical), lambda(1) < lambda(2) = lambda(3) (oblate), lambda(1) > lambda(2) = lambda(3) (prolate), and lambda(1) > lambda(2) > lambda(3) (cuboid). The superquadric glyphs are especially useful for identifying regions of anisotropic structure and function. Diffusion tensor renderings exhibit fiber angle trends and orthotropy (three distinct eigenvalues). Visualization of strain tensors with superquadric glyphs compactly exhibits radial thickening gradients, circumferential and longitudinal shortening, and torsion combined. The orthotropic nature of many biologic tissues and their DTMRI and strain data require visualization strategies that clearly exhibit the anisotropy of the data if it is to be interpreted properly. Superquadric glyphs improve the ability to distinguish fiber orientation and tissue orthotropy compared to ellipsoids.

Animals↗
PubMed2005

Virtual vascular endoscopy for acute aortic dissection.

Virtual endoscopy of the aorta is a new three-dimensional reconstruction method from multislice computed tomography or magnetic resonance that offers a virtual navigation through the aorta, and the possibility of having a new preoperative endoluminal vision. We present a case of subacute aortic dissection with a preoperative virtual endoscopy of the aorta.

Aged↗
PubMed2004

Automatic tuning and matching of a small multifrequency saddle coil at 4.7 T.

A new circuit design for automatically tuning and matching a saddle coil for small animal imaging is presented. This design allows working at (1)H, (19)F, and (3)He resonance frequencies in a 4.7 T spectrometer. It is based on a balanced circuit with commercial variable capacity diodes controlled by a computer using digital potentiometers. The change between two different frequencies can be accurately performed in a few seconds. System Q is compared, between 140-210 MHz, to the same coil tuned and matched with high Q variable capacitors. Differences lower than 5% were found with a loaded coil. The proposed design has initially been evaluated in (19)F and (1)H NMR images acquired with a five-tube phantom. An application is also shown for the acquisition of (3)He, (19)F, and (1)H lung images in a control rat.

Analog-Digital Conversion↗
PubMed2003

Computer-assisted enhanced volumetric segmentation magnetic resonance imaging data using a mixture of artificial neural networks.

An accurate computer-assisted method able to perform regional segmentation on 3D single modality images and measure its volume is designed using a mixture of unsupervised and supervised artificial neural networks. Firstly, an unsupervised artificial neural network is used to estimate representative textures that appear in the images. The region of interest of the resultant images is selected by means of a multi-layer perceptron after a training using a single sample slice, which contains a central portion of the 3D region of interest. The method was applied to magnetic resonance imaging data collected from an experimental acute inflammatory model (T(2) weighted) and from a clinical study of human Alzheimer's disease (T(1) weighted) to evaluate the proposed method. In the first case, a high correlation and parallelism was registered between the volumetric measurements, of the injured and healthy tissue, by the proposed method with respect to the manual measurements (r = 0.82 and p < 0.05) and to the histopathological studies (r = 0.87 and p < 0.05). The method was also applied to the clinical studies, and similar results were derived of the manual and semi-automatic volumetric measurement of both hippocampus and the corpus callosum (0.95 and 0.88).

Abscess↗
PubMed2003

Distribution of ventilation in lung transplant recipients: evaluation by dynamic 3He-MRI with lung motion correction.

RATIONALE AND OBJECTIVES: The ability of motion corrected dynamic 3He-magnetic resonance imaging (MRI) to discriminate distributional patterns of inhaled hyperpolarized 3He between different groups of lung transplant recipients was evaluated. METHODS: An ultrafast low-angle shot 2D sequence (temporal resolution 128 ms) was used for ventilation 3He-MRI of 11 single and 6 double lung transplant recipients. After digital motion correction, signal kinetics were evaluated in a tracheal and 7 pulmonary regions of interest. Results from grafts and native lungs as well as from normal and rejected grafts were compared with each other and to reference values from healthy subjects. RESULTS: In emphysema patients, median alveolar rise time, a parameter for increase of alveolar signal, was 0.28 seconds for the graft and 0.48 seconds for the native lung, in fibrosis patients its median was 0.46 seconds for the graft and 0.21 seconds for the native lung. In double lung recipients, alveolar rise time was 0.29 seconds in normal and clinically rejected grafts. CONCLUSIONS: Dynamic ventilation 3He-MRI discriminated normal lung grafts from diseased native lungs in single lung recipients. Graft rejection in double lung recipients could not be discriminated.

Female↗
PubMed2002

Pathway selection by pulsed field gradients.

A method for pathway selection in a multiple spin-echo pulse sequence applying crusher gradients before and after each pi pulse, to dephase unwanted pathways, is described. This method selects the only pathway that would contribute to the measurable signal if the pi pulses were perfect (1,-1,1,-1, em leader ). Good pathway selection is essential in pulse programming, especially when the CPMG condition is not met. An interactive applet was also developed to deal with these calculations.

Algorithms↗
PubMed2002

Monitoring acute inflammatory processes in mouse muscle by MR imaging and spectroscopy: a comparison with pathological results.

We have studied an animal model of acute local inflammation in muscle induced by Aspergillus fumigatus by using magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS). We have compared our data to those found using histopathology and segmentation maps obtained by the mathematical processing of three-dimensional T2-weighted MRI data via a neural network. The MRI patterns agreed satisfactorily with the clinical and biological evidence of the phases of acute local infection and its evolution towards chronicity. The MRS results show a statistically significant increase in inorganic phosphate and a significant decrease in phosphocreatine levels in the inflamed region. Image segmentation made with a self-organizing, neural-network map yielded a set of ordered representatives that remained constant for all animals during the inflammatory process, allowing a non-invasive, three-dimensional identification and quantification of the inflamed infected regions by MRI.

Acute Disease↗
PubMed2002

Dynamic ventilation (3)He-magnetic resonance imaging with lung motion correction: gas flow distribution analysis.

RATIONALE AND OBJECTIVES: Software was developed to correct for lung motion to improve the description of hyperpolarized (3)He gas distribution in the lung. METHODS: Five volunteers were studied by dynamic ventilation (3)He-MRI using an ultrafast FLASH 2D sequence with a temporal resolution of 128 milliseconds. Signal kinetics were evaluated in the trachea and seven parenchymal Regions of Interest. Reference ranges for healthy subjects were defined for motion-corrected and uncorrected images. RESULTS: Motion correction was successfully performed. Reference ranges were 0.11-1.21 seconds for tracheal transit time, 0-0.02 seconds for trachea-alveolar interval, 0.22-0.62 seconds for alveolar rise time and 0-76.6 arbitrary units for alveolar amplitude for motion corrected images, and 0-1.09 seconds, 0-0.11 seconds, 0.26-0.85 seconds, 46.4-99.8 arbitrary units for uncorrected images. CONCLUSIONS: Evaluation of (3)He-distribution in the lung using motion correction of dynamic (3)He-ventilation imaging is feasible and gives more narrow reference ranges.

Adult↗
PubMedDate not supplied

Atrial remodeling after mitral valve surgery in patients with permanent atrial fibrillation.

BACKGROUND: Mitral valve pathology is frequently associated with auricular dilatation and atrial fibrillation. Mitral surgery allows an immediate surgical auricular remodeling and besides in those cases in which sinus rhythm is reached, it is followed by a late remodeling. The aim of this study is to investigate the process of postoperative auricular remodeling in patients with permanent atrial fibrillation undergoing mitral surgery. METHODS: In a prospective randomized trial, 50 patients with permanent atrial fibrillation and dilated left atrium, submitted to surgical mitral repair, were divided into two groups: Group I contained 25 patients with left auricular reduction and mitral surgery, and Group II contained 25 patients with isolated valve surgery. Both groups were considered homogeneous in the preoperative assessment. RESULTS: After a mean follow-up of 31 months, 46% of patients included in Group I versus 18% of patients included in Group II restarted sinus rhythm (p = 0.06). An auricular remodeling with size regression occurred in those patients who recovered from sinus rhythm, worthy of remark in Group II (-10.8% of left auricular volume reduction in Group I compared to -21.5% in Group II; p < 0.05). A new atrial enlargement took place in those patients who remained with atrial fibrillation (+16.8% left auricular volume in Group I vs. +8.4% in Group II; p < 0.05). CONCLUSIONS: Mitral surgery produces an atrial postoperative volume that decrease especially when reduction techniques are employed. Late left atrial remodeling depended on the type of atrial rhythm and postoperative surgical volume.

Aged↗
PubMedDate not supplied

Tumor size and lymph node status in multifocal breast cancer.

Tumor size correlates with lymph node metastasis in breast cancer. In multifocal lesions there is controversy about considering the summation of the largest diameter of each tumor. A total of 122 patients with multifocal breast cancer were compared in a retrospective study with 177 patients with unifocal tumors, correlating tumor size with lymph node metastasis. In multifocal tumors, two sizes were considered: the diameter of the largest tumor and the combined diameter of all lesions. Relationship was established by three different logistic models using variables such as age, number of lesions, histologic type, and grade. At a same size of the largest diameter of a unifocal or multifocal lesions and the combined diameter of a multifocal lesion, the latter shows less probability of nodal metastasis indicating that combined diameter is an overestimation of the lesion size. Our results indicate that in multifocal breast cancer, only the diameter of the largest tumor breast cancer has relationship with lymph node metastasis.

Adult↗