Free-breathing variable flip angle balanced SSFP cardiac cine imaging with reduced SAR at 3T.

PURPOSE: To develop a free-breathing variable flip angle (VFA) balanced steady-state free precession (bSSFP) cardiac cine imaging technique with reduced specific absorption rate (SAR) at 3 Tesla. METHODS: Free-breathing VFA (FB-VFA) images in the short-axis and four-chamber views were acquired using an optimal VFA scheme, then compared with conventional breath-hold constant flip angle (BH-CFA) acquisitions. Two cardiac MRI experts used a 5-point scale to score images from healthy subjects (N = 10). The left ventricular ejection fraction, end diastolic volume (LVEDV), end systolic volume, stroke volume (LVSV), and end diastolic myocardial mass (LVEDM) were determined by manual contour analysis for BH-CFA and FB-VFA. A pilot evaluation of FB-VFA was performed in one patient with Duchenne muscular dystrophy. RESULTS: FB-VFA SAR was 25% lower than BH-CFA with similar blood-myocardium contrast. The qualitative FB-VFA score was lower than the BH-CFA for the short-axis (3.1 ± 0.5 versus 4.3 ± 0.8; P < 0.05) and the four-chamber view (3.4 ± 0.4 versus 4.6 ± 0.6; P < 0.05). The LVEDV and the LVSV were 5% and 12% larger (P < 0.05) for FB-VFA compared with BH-CFA. There was no difference in LVEDM. CONCLUSION: FB-VFA bSSFP cardiac cine imaging decreased the SAR at 3T with image quality sufficient to perform cardiac functional analysis. Magn Reson Med 76:1210-1216, 2016. © 2015 Wiley Periodicals, Inc.

Pre- and post-contrast three-dimensional double inversion-recovery MRI in human glioblastoma.

Fluid attenuated inversion recovery (FLAIR) MRI sequences have become an indispensible tool for defining the malignant boundary in patients with brain tumors by nulling the signal contribution from cerebrospinal fluid allowing both regions of edema and regions of non-enhancing, infiltrating tumor to become hyperintense on resulting images. In the current study we examined the utility of a three-dimensional double inversion recovery (DIR) sequence that additionally nulls the MR signal associated with white matter, implemented either pre-contrast or post-contrast, in order to determine whether this sequence allows for better differentiation between tumor and normal brain tissue. T1- and T2-weighted, FLAIR, dynamic susceptibility contrast (DSC)-MRI estimates of cerebral blood volume (rCBV), contrast-enhanced T1-weighted images (T1+C), and DIR data (pre- or post-contrast) were acquired in 22 patients with glioblastoma. Contrast-to-noise (CNR) and tumor volumes were compared between DIR and FLAIR sequences. Line profiles across regions of tumor were generated to evaluate similarities between image contrasts. Additionally, voxel-wise associations between DIR and other sequences were examined. Results suggested post-contrast DIR images were hyperintense (bright) in regions spatially similar those having FLAIR hyperintensity and hypointense (dark) in regions with contrast-enhancement or elevated rCBV due to the high sensitivity of 3D turbo spin echo sequences to susceptibility differences between different tissues. DIR tumor volumes were statistically smaller than tumor volumes as defined by FLAIR (Paired t test, P = 0.0084), averaging a difference of approximately 14 mL or 24 %. DIR images had approximately 1.5× higher lesion CNR compared with FLAIR images (Paired t test, P = 0.0048). Line profiles across tumor regions and scatter plots of voxel-wise coherence between different contrasts confirmed a positive correlation between DIR and FLAIR signal intensity and a negative correlation between DIR and both post-contrast T1-weighted image signal intensity and rCBV. Additional discrepancies between FLAIR and DIR abnormal regions were also observed, together suggesting DIR may provide additional information beyond that of FLAIR.

On the accuracy and computational cost of spiking neuron implementation.

Since more than a decade ago, three statements about spiking neuron (SN) implementations have been widely accepted: 1) Hodgkin and Huxley (HH) model is computationally prohibitive, 2) Izhikevich (IZH) artificial neuron is as efficient as Leaky Integrate-and-Fire (LIF) model, and 3) IZH model is more efficient than HH model (Izhikevich, 2004). As suggested by Hodgkin and Huxley (1952), their model operates in two modes: by using the α's and ß's rate functions directly (HH model) and by storing them into tables (HHT model) for computational cost reduction. Recently, it has been stated that: 1) HHT model (HH using tables) is not prohibitive, 2) IZH model is not efficient, and 3) both HHT and IZH models are comparable in computational cost (Skocik & Long, 2014). That controversy shows that there is no consensus concerning SN simulation capacities. Hence, in this work, we introduce a refined approach, based on the multiobjective optimization theory, describing the SN simulation capacities and ultimately choosing optimal simulation parameters. We have used normalized metrics to define the capacity levels of accuracy, computational cost, and efficiency. Normalized metrics allowed comparisons between SNs at the same level or scale. We conducted tests for balanced, lower, and upper boundary conditions under a regular spiking mode with constant and random current stimuli. We found optimal simulation parameters leading to a balance between computational cost and accuracy. Importantly, and, in general, we found that 1) HH model (without using tables) is the most accurate, computationally inexpensive, and efficient, 2) IZH model is the most expensive and inefficient, 3) both LIF and HHT models are the most inaccurate, 4) HHT model is more expensive and inaccurate than HH model due to α's and ß's table discretization, and 5) HHT model is not comparable in computational cost to IZH model. These results refute the theory formulated over a decade ago (Izhikevich, 2004) and go more in-depth in the statements formulated by Skocik and Long (2014). Our statements imply that the number of dimensions or FLOPS in the SNs are theoretical but not practical indicators of the true computational cost. The metric we propose for the computational cost is more precise than FLOPS and was found to be invariant to computer architecture. Moreover, we found that the firing frequency used in previous works is a necessary but an insufficient metric to evaluate the simulation accuracy. We also show that our results are consistent with the theory of numerical methods and the theory of SN discontinuity. Discontinuous SNs, such LIF and IZH models, introduce a considerable error every time a spike is generated. In addition, compared to the constant input current, the random input current increases the computational cost and inaccuracy. Besides, we found that the search for optimal simulation parameters is problem-specific. That is important because most of the previous works have intended to find a general and unique optimal simulation. Here, we show that this solution could not exist because it is a multiobjective optimization problem that depends on several factors. This work sets up a renewed thesis concerning the SN simulation that is useful to several related research areas, including the emergent Deep Spiking Neural Networks.

Novel Mathematical Model of Breast Cancer Diagnostics Using an Associative Pattern Classification.

Breast cancer is a disease that has emerged as the second leading cause of cancer deaths in women worldwide. The annual mortality rate is estimated to continue growing. Cancer detection at an early stage could significantly reduce breast cancer death rates long-term. Many investigators have studied different breast diagnostic approaches, such as mammography, magnetic resonance imaging, ultrasound, computerized tomography, positron emission tomography and biopsy. However, these techniques have limitations, such as being expensive, time consuming and not suitable for women of all ages. Proposing techniques that support the effective medical diagnosis of this disease has undoubtedly become a priority for the government, for health institutions and for civil society in general. In this paper, an associative pattern classifier (APC) was used for the diagnosis of breast cancer. The rate of efficiency obtained on the Wisconsin breast cancer database was 97.31%. The APC's performance was compared with the performance of a support vector machine (SVM) model, back-propagation neural networks, C4.5, naive Bayes, k-nearest neighbor (k-NN) and minimum distance classifiers. According to our results, the APC performed best. The algorithm of the APC was written and executed in a JAVA platform, as well as the experimental and comparativeness between algorithms.

High-spatial-resolution contrast-enhanced MR angiography of abdominal arteries with parallel acquisition at 3.0 T: initial experience in 32 patients.

OBJECTIVE: The objective of our study was to evaluate an isotropic high-spatial-resolution 3D contrast-enhanced MR angiography (CE-MRA) protocol with high acceleration parallel acquisition at 3.0 T for the display of the abdominal vasculature. SUBJECTS AND METHODS: Thirty-two consecutive patients (13 men, 19 women; age range, 28-88 years) with suspected abdominal arterial disease underwent abdominal 3D CE-MRA on a 3.0-T MR system, using a high-spatial-resolution (0.7 x 0.82 x 0.8 mm3) 3D gradient-refocused echo (GRE) sequence, integrated with a generalized autocalibrating partially parallel acquisitions (GRAPPA) technique with an acceleration factor of 3. Two vascular radiologists evaluated image quality and the presence and degree of arterial stenoses. Interobserver variability was calculated, using the kappa coefficient. The sensitivity and specificity of the technique were calculated and comparative analysis was performed with those of conventional catheter angiography (in eight patients) as the standard of reference. RESULTS: The abdominal arterial vasculature was visualized with diagnostic image quality in all subjects. Arterial stenoses were detected in 148 and 142 arterial segments by observer 1 and observer 2, respectively, with good interobserver agreement (kappa = 0.75; 95% confidence interval [CI]: 0.69-0.81). The sensitivity and specificity values for CE-MRA for the detection of significant (> 50%) arterial stenoses were 100% and 96% for observer 1 and 100% and 92% for observer 2, respectively. There was a significant correlation between CE-MRA and conventional angiography (R = 0.96 and 0.93 for observers 1 and 2, respectively) for the assessment of the degree of stenosis. CONCLUSION: The outlined MR angiography protocol at 3.0 T combined with parallel acquisition technique renders highly reliable and isotropic high-spatial-resolution imaging of the abdominal vasculature.

Diversidad de árboles en cuatro etapas de sucesión ecológica del bosque tropical montano nuboso del altiplano occidental de Guatemala / Diversity of trees in four stages of ecological succesion of the tropical montane cloud forest in Guatemala ́s western plateau

El objetivo de la investigación fue identificar la riqueza de especies de árboles en etapas de sucesión ecoló-gica de áreas perturbadas del ecosistema bosque tropical montano nuboso (btmn) del altiplano occidental de Guatemala. Con el propósito de generar un registro de referencia para promover acciones de restauración ecológica. El btmn provee de agua para consumo humano a diez etnias mayas y población mestiza. La presión por deforestación y cambio de uso de la tierra por demanda de leña, madera, pastoreo y agricultura, ha generado fragmentación y deterioro de su composición y estructura. Se delimitó como área de estudio el territorio de sierra de Los Cuchumatanes y Cadena Volcánica Occidental con cotas superiores a 2,400 m s. n. m. Se seleccionaron 37 sitios con cuatro etapas de sucesión ecológica denominadas de plántula, brinzal, latizal, fustal y bosque maduro. Se evaluó la presencia y densidad de especies de árboles, en transectos de 2 x 50 m, para definir comunidades florísticas para cada etapa de sucesión ecológica. Se encontró una riqueza de 67 especies de árboles en las 16 comunidades florísticas diferenciadas, de ellas 40 especies promisorias para restauración. Significa que el 60% de la diversidad arbórea del btmn es apta para promover acciones efectivas para su restauración, conocimiento clave para reorientar los planes orientados al establecimiento de plantaciones de coníferas con fines maderables que impulsa el estado guatemalteco para restaurar este ecosistema.

The goal in this investigation was to identify the richness species of trees in stages of ecological succesion in perturbed areas of the tropical montane cloud forest (tmcf's) ecosistem in Guatemala ́s western plateau. The intentionally is to generate a reference registration to promote ecological restoration actions, which supply clean water to teen Mayan ethnic groups and mestizo population. However, this forest is being affected due to change of land use for cattle, agriculture, firewood a timber, which has generated fragmentation and deterioration in its composition and structure. The territory of Sierra de los Cuchumatanes and Western Volcanic Chain was de-limited as a study area with dimensions above 2,400 m a. s. l. 37 places with four stages of ecological succession of plantula, brinzal, latizal, fustal and mature forest were selected. The presence and density of trees species was evaluated in 2x50 m transect, to define floristic communities in each stage of ecological succession. In the 16 floristic communities differentiated was found 67 trees species and 40 of them are promising to restoration. This mean that the 60% of the arboreal wealth richness in the tmcf's is suitable to promote effective restoration deeds, this knowledge is the key to update plans to establishment coniferous plantations for timber purposes, promoted by Guatemalan State to assist in the recovery of this ecosystem.

Evaluación de la regeneración natural de tres especies coníferas en áreas de distribución natural en el altiplano occidental de Guatemala / Evaluation of natural regeneration of coniferous species in areas of natural distribution in the western highlands of Guatemala

Los bosques de coníferas del altiplano occidental de Guatemala han sido perturbados por intervenciones humanasy fenómenos naturales, lo cual ha propiciado la ocurrencia del fenómeno de regeneración natural. En esteescenario se evaluó la densidad de la regeneración natural de tres especies coníferas (Pinus oocarpa Schiede, P.pseudostrobus Lindl. y P. tecunumanii Eguiluz & Perry), en 60 sitios distribuidos en espacios de borde y claro. Las variables evaluadas fueron: fuente de disturbio que originó su establecimiento, variación de la densidad respecto de la fuente de semilla y estimación de la distancia de alcance de dispersión de regeneración adecuada, utilizando unidades de muestreo de 25 m2 para regeneración natural y 500 m2 para los árboles fuente de semilla. Las fuentes de disturbio identificadas fueron: extracción forestal 55%, incendios forestales 24%, plagas 8%, agricultura, alud con 5% cada una y huracán 3%. La variación de la densidad de regeneración natural respecto de la fuente de semilla,corresponde a los modelos de J invertida para bordes, y de variable de subpoblaciones para claros. Las distancias de dispersión de regeneración natural establecida para P. oocarpa fue 65 m en borde y 160 m en claro; para P.pseudostrobus fue 75 m en borde y 175 m en claro; y para P. tecunumanii fue 70 m en borde y 170 m en claro.Las distancias de dispersión con densidades aceptables según Instituto Nacional de Bosques-Programa RegionalForestal para Centroamérica, para las tres especies varían de 65-175 m.

Coniferous forests of the western highlands of Guatemala have been disturbed by human intervention and natural phenomena, which has allowed the occurrence of the phenomenon of natural regeneration. In this scenario thedensity of natural regeneration of conifers three species evaluated (Pinus oocarpa Schiede, P. pseudostrobus Lindl.and P. tecunumanii Eguiluz & Perry) in 60 sites distributed in space and clear edge. The variables evaluated were thesource of disturbance that caused its establishment, density variation of the source of seed and distance estimationrange scattering adequate regeneration, using sampling units of 25 m2 for natural regeneration and 500 m2 seedsource trees. Disturbance sources identified were logging 55%, 24% forest fires, pests 8%, agriculture, avalanche5% each and hurricane 3%. The variation of the density of natural regeneration on the seed source, corresponds to the inverted J models for edges, and to clear variable subpopulations. Dispersal distances of natural regenerationwas established for P.oocarpa 65 m in edges, and 160 m in the clears; P. pseudostrobus 75 m in edges, and 175 min the clears; and P. tecunumanii was 70 m in edges, and 170 m in the clears. Dispersal distances with acceptabledensities according National Forestry Institute-Regional Forestry Programme for Central American, for the threespecies vary from 65-175 m.