2008
Fractal properties and critical exponents in tumor
Miguel Martín-Landrove, Démian Pereira
Ciencia 16(2), 203-207, 2008
In general, tumors exhibit irregular borders with geometrical properties which are expected to depend upon their degree of malignancy. To appropriately evaluate these irregularities, it is necessary to apply segmentation procedures on the image that clearly define the active region of the tumor and its border. In the present work, nosologic maps were obtained combining T2-weighted magnetic resonance images with in vivo magnetic resonance spectroscopy information on brain tumors. The image was segmented according to the nosologic map and tumor contours were determined. Several fractal properties were determined on the contour: the capacity or fractal dimension, the correlation dimension for a temporal series constructed from the original contour, and also a critical exponent coming from the contour roughness. The results obtained showed a good correlation between the roughness critical exponent and the degree of malignancy of the tumor.
Metabolic maps obtained by in vivo magnetic resonance spectroscopy
Alvaro Posú, Miguel Martín-Landrove
Ciencia 16(2), 208-212, 2008 [article in spanish]
A methodology for the processing of magnetic resonance in vivo spectroscopy data is presented. The signal, which corresponds to the free induction decay of the nuclear magnetization, is processed by a Fast Fourier Transform algorithm (FFT) to obtain a spectrum. Usually, the real part of the spectrum is taken for the clinical analysis, what means a phase correction. In the present work, it is proposed to use the power spectra for the construction of metabolic maps. The spectra so obtained are denoised using Haar wavelets and the line base is corrected with a third order polynomial. Different tissue types present in the lesion are characterized by specific ratios of spectral peaks. The power spectra so processed are fitted to obtain to obtain the integral of the metabolic peaks and establish within each voxel the tissue property determined by the specific ratio, leading to the construction of a nosologic map o pathology distribution on the image.
Quasi-analytical methods for image segmentation and filtering in T2 and diffusion weighted MRI
Miguel Martín-Landrove, Marco Paluszny, Giovanni Figueroa, Wuilian Torres
Desarrollo y Avances en Métodos Numéricos para Ingeniería y Ciencias Aplicadas, L. Martino, V. Carrera, G. Larrázabal, M. Cerrolaza (Eds.), SVNMI 2008
A quasi-analytical method, previously used for the calculation of transversal relaxation rate distribution functions in T2-weighted MRI images, is proposed for the segmentation of T2 and diffusion – weighted MRI images. The method solves analytically the set of non linear polynomial equations on the assumption that the transversal decay of magnetization can be modeled by a finite number of exponential decay functions, each one corresponding to a particular tissue type. Numerical simulations were performed to validate the method and its application under typical SNR conditions found in MRI images. Distribution functions for transversal relaxation rates and diffusion coefficients were obtained and used for image segmentation and filtering by use of mathematical morphology operators. The results were compared with other segmentation procedures.
Polymer cross-linking and sensitivity enhancement in normoxic polymer gels used for three-dimensional dosimetry
R Martin, J BenComo, M Heard, M Martin, K Kaluarachchi, N Wells,R Sadagopan
Medical Physics, Vol. 35, No. 6, June 2008
Purpose: To discuss the relation between cross-linking and sensitivity enhancement in normoxic polymer gels in a dose range suitable for intensity modulated radiotherapy, based on considerations related to actual sensor preparation methods and a theoretical description of the optical behavior of irradiated polymer gel when dose maps are obtained through optical CT.
Method and Materials: Two set of samples of MAGIC gel (9% in weight of methacrylic acid) were prepared at 370C and 450C and irradiated with a 60Co and 6 MV photon beams to doses in the range from 0.1 to 5 Gy. The samples were scanned in an optical CT. Non-irradiated samples were also scan. A theory based on the number of sites for water solvation, which takes into account polymer cross-linking, is introduced in order to explain the observed changes in the optical density. The slope of the polymer gel response to dose is a measurement of sensitivity and it is analyzed for the actual experimental conditions as well as those for the optimum in connection to cross-linking phenomena. Conclusion: The analysis showed a proper monotonic behavior for the polymer gel response and maximum sensitivity when cross-linking occurs in an important fraction in the preparation process.
Assessment of differential lung function by electrical impedance tomography
J. Bruno de Lema, Ernesto Serrano, Teresa Feixas, Núria Calaf, María del Valle Camacho, Pere J. Riu, Pere Casan
Arch Bronconeumol. 2008;44(8):408-12
OBJECTIVE: To compare differential lung function estimated by 2 methods: electrical impedance tomography (EIT) and ventilation-perfusion lung scintigraphy.
PATIENTS AND METHODS: This prospective clinical study was carried out in the pulmonary function laboratory of a general hospital. Twenty patients diagnosed with lung cancer (17 men and 3 women, ranging in age from 25 to 77 years) who were candidates for lung resection underwent ventilation-perfusion lung scanning breathing radioactive gas. Differential lung function was estimated based on images taken at 2 intercostal spaces in which ventilation and perfusion were represented by changes in bioelectrical impedance. Each lung’s contribution to overall respiratory function was also calculated based on scintigraphy.
RESULTS: The right lung contributed a mean (SD) of 54% (9%) of ventilation (range, 32%-71%) according to EIT. Scintigraphy similarly estimated the right lung’s contribution to be 52% (10%) of total ventilation (range, 31%-80%) and 50% (9%) of perfusion (range, 37%-71%). The difference between the 2 estimates was not significant (t test), and the correlation coefficients between them were r = 0.90 for ventilation and r=0.72 for perfusion (P<.05 in both cases). The analysis of agreement showed that the mean difference between the methods was 1.9% (95% confidence interval [CI], 10.5% to –6.8%) for ventilation
and 3.4% (95% CI, 17.1% to –10.3%) for perfusion.
CONCLUSIONS: EIT is able to estimate differential lung function as accurately as ventilation-perfusion scintigraphy.
Effective radiotherapy of primary tumors and metastasis with 18F-2-deoxy-2-fluoro-D-glucose in C57BL/6 mice
Victoria Caridad, Miriam Arsenak, María Jesús Abad, Rafael Martín, Nilo Guillén, Luís Felipe Colmenter, Peter Taylor
Cancer Biotherapy and Radiopharmaceuticals. June 2008, 23(3): 371-375.
The radiochemical 18F-2-deoxy-2-fluoro-D-glucose (18F-FDG), a positron-emitter, is taken up preferentially by malignant tumors with high metabolic rates. This concentration of 18F-FDG in the tumor permits diagnosis and staging by Positron Emission Tomography (PET) but also may represent a means of targeting radiotherapy. We show that 18F-FDG treatment of C57BL/6 mice significantly reduced the growth of primary tumors of B16/BL6 melanoma cells, by 89% at day 19 post-inoculation and also almost totally inhibited the appearance of lung metastases after intravenous inoculation of the same cells. The advantages and problems of the use of 18F-FDG as a radiotherapeutic agent are discussed.
Visión artificial para detección y ubicación espacial de instrumental laparoscópico [Artificial vision for detection and spatial location of laparoscopic instrumental]
César A. Lizarraga, Luis R. Ortega, Bricelis J. Urbina, Omaira Rodríguez
Mecánica Computacional Vol XXVII, 3627-3637, Alberto Cardona, Mario Storti, Carlos Zuppa. (Eds.) San Luis, Argentina, 10-13 November 2008 [article in spanish]
The Centro de Computación Gráfica (CCG) jointly with the Instituto de Cirugía Experimental (ICE) of the Universidad Central de Venezuela (UCV) and the Instituto Nacional de Bioingeniería (INABIO) are developing a virtual simulator for laparoscopic surgery training. The hardware component of the simulator consists of a mechanical simulator and a tracking subsystem. The tracking subsystem is based on a commercial device called ISOTRAK® II, which sends to the computer the position and rotation of the surgical tool when it is located inside the cavity of the mechanical simulator. Besides the high cost of the equipment, it shows limitations related to the number of objects tracked simultaneously and the interaction with them. In this work it is presented a system based on Artificial Vision, capable to detect and track laparoscopic instrumental using a virtual simulator, showing an alternative way of economic, portable and innovative interaction. The proposed system uses a set of digital cameras to capture the instrumental image within the mechanical simulator. The processed images allows for the relevant characteristics that are used as the input of the system module, obtaining the position and orientation of the instruments within the mechanical simulator.
Morphological eccentricity filter for multidimensional images
Wuilian Torres, Miguel Martín, Marco Paluszny, Giovanni Figueroa
Noveno Congreso Internacional "Aproximación y Optimización en el Caribe" Isla de San Andrés Colombia, 2-7 March 2008 [article in spanish]
In this paper we propose a morphological filter for the identification of tumoral lesions in brain. It is based en magnetic resonance relaxation times and we refer to it as the eccentricity filter. Mathematical morphology is a non-linear technique for the analysis of images where the topological relations and geometric spatial structures are relevant. The morphological operators are functions defined in a complete lattice, i.e. each subset has a supremum and an infimum. In the case of grayscale images the infimum and the supremum are given by the gray intensity. This is not the case for multidimensional images. The eccentricity filter [2] is a morphological filter defined in the multidimensional images where each pixel is represented by a vector in the N space, where N if the dimension of image, namely the number of grayscale images associated to each physical slice. The filter acts on each pixel and his neighbors included in a referenced geometrical space denominated structuring element. The eccentricity of a pixel is calculated by considering the distances between the pixels in the structuring element, the pixel with least eccentricity is close to the centroid of a cloud of pixels. For pixels near the periphery of the cloud the eccentricity is higher. The eccentricity filer was applied to brain multi-echo magnetic resonance T2-weighted that generate a sequence of echo images whose value is dependant of the amount of water in the tissue. This preliminary processing facilitates the segmentation of normal and tumor tissues in the brain.
