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Megha Singh

Publications and source records attributed to Megha Singh.

12 recordsLinked to original sources
PubMed2004

Optical characterization of mammalian tissues by laser reflectometry and Monte Carlo simulation.

The optical characterization of various goat organs/tissues, by measurement of the spatial variation of the diffuse reflectance from the surface by laser multi-probe reflectometer, is carried out. For determination of the optical parameters, these profiles are matched by iterative procedures with that obtained by Monte Carlo simulation by best-fit procedure with chi value 0.99. The first set of measurements is carried out with milk phantom. Thereafter, the absorption and scattering coefficients and anisotropy parameter of goat's heart, lungs, kidney, liver, spleen, skeletal muscle, brain and adipose tissues are measured. These parameters vary over a wide range, which is in agreement with results reported by others. Based on these data, their laser scattering profiles along the depth in terms of depth of penetration (DP) and maximum scattered beam width (MSBW) are determined. These are maximum (0.030 and 0.038 m) for kidney and minimum (0.007 and 0.006 m) for spleen, respectively. The backscattered intensity measured 0.002, 0.004 and 0.006 m away from the beam entry point shows the maximum contribution from the respective depths, irrespective of the nature of the organs/tissues.

Animals↗
PubMed2004

Multislice tomographic imaging and analysis of human breast-equivalent phantoms and biological tissues.

A laser transillumination tomographic system, consisting of electrical, optical, mechanical, and software components, to obtain multislice images of tissue-equivalent breast phantoms and biological tissues, is developed. The tissue-equivalent phantoms are prepared from paraffin wax mixed with wax color pigments by matching their surface backscattered profiles as measured by multiprobe laser reflectometer, with that of respective tissues. The optical parameters of these phantoms are determined by matching their reflectance profiles with that as obtained by Monte Carlo simulation of optical scattering. For multislice tomographic analysis conical breast phantoms of height 80.0 mm and 80.0 mm base diameter with inclusions of different optical properties and dimensions are developed. The resolution of the inclusions in the tomograms depends on their sizes and optical parameters. The minimum size of the inclusion as detected by this procedure in a slice of diameter 50.0 mm is 3.0 mm. The structural variation as observed in the tomograms of phantoms of combination of biological tissues indicates its possible applications in detecting the abnormalities developing in human healthy soft tissues.

Algorithms↗
PubMed2004

Influence of malaria parasite (P. vivax) on erythrocyte aggregation: a study based on dynamic imaging and analysis.

Malaria due to P. vivax (PV) is prevalent in many countries. The present work is aimed to determine the cell-cell interaction through formation of aggregates under dynamic conditions. Blood samples are obtained from patients (n=11) suffering from PV malaria, and the normal subjects (n=10) in test tubes containing citrate phosphate dextrose (10:1.4), as an anticoagulant. The signature analysis of infected erythrocytes shows significant alterations in their shape and membrane. For aggregation analysis, erythrocyte suspension in plasma at hematocrit 5%, was placed in a glass chamber and mounted vertically on the stage of the video-microscope system. The aggregate images thus acquired show erythrocytes adhering with each other to form mash-like structures. With increase in parasitaemia, the erythrocytes show hyper-aggregation compared to that of normal cells. By processing of the sequence of recorded images during sedimentation, the various aggregation parameters are obtained. These parameters show that the formed aggregates are compact which produce distinct changes in sedimentation pattern with significantly higher sedimentation velocity compared to that in healthy blood samples. These changes in malaria could partly be responsible for alteration in blood flow through microcirculatory system.

Animals↗
PubMed2004

Influence of P. vivax malaria on erythrocyte aggregation and deformability.

Malaria due to Plasmodium vivax affects blood flow in cardiovascular system. The present work is aimed to determine the variability of erythrocyte deformability and aggregation in malaria patients in comparison with that of normal subjects. Blood samples of malaria patients (n=16), selected based on occurrence of parasitaemia, are categorized into low (LP), medium (MP) and high parasitaemia (HP), which represent increasing levels of the disease severity. For measurement of aggregation and deformability, by laser aggregometer and optical hemorheometer, the erythrocyte suspensions are prepared in plasma and physiological saline at hematocrit 5%. The results show that the erythrocyte deformability is significantly reduced (p<0.001) with the increasing level of parasitaemia. Despite this decrease in deformability, the aggregation parameters are significantly increased, indicating the occurrence of hyper-aggregation, particularly in MP and HP, due to involvement of various factors. These changes may partly be contributing in the observed changes in blood flow in the microcirculation.

Case-Control Studies↗
PubMed2003

Laser backscattering and transillumination imaging of human tissues and their equivalent phantoms.

Surface backscattering profiles from a human forearm and transmission profiles through a human thumb, of red and near-infrared lasers, were determined. For the preparation of tissue-equivalent phantoms, white paraffin wax mixed with various wax color pigments were used. The surface reflectance profiles of a human forearm were matched with that of the phantom by mixing color pigments in various proportions. The reconstructed surface reflectance image of the phantom prepared by this procedure was similar to that of the human forearm. The transmission tomogram of the human thumb was obtained in fan-beam configuration by a near-infrared laser tomography system. Based on the horizontal scan of this tomogram, a two-layered phantom was made. The color composition of the phantom was so adjusted that its horizontal scan was matched with that of the thumb tomogram. The phantoms of complex tissues, prepared by this procedure, could be used for evaluation and calibration of new optical diagnostic imaging techniques.

Equipment Design↗
PubMed2003

Characterization and imaging of compositional variation in tissues.

The diffuse surface reflectance profiles of the goat's isolated heart, spleen, and adipose tissues by multiprobe laser reflectometer are measured. The normalized backscattered intensity values for adipose, heart, and spleen tissues at source-detector separation 0.2 cm, are 0.060, 0.021, and 0.003, respectively. The optical parameters of these tissues are determined by the best fit (chi2(0.99)) of their spatial profiles with that as obtained by Monte Carlo simulation by iterative procedure. As the optical parameters of these vary over a wide range, adipose and spleen tissues are treated as inhomogeneity of diameter 0.1, 0.2, or 0.3 cm, and placed inside the control (heart) tissue at different depths. Anisotropic simulation of light backscattering or photon depth distribution is significantly different for various tissues. The surface intensity profiles vary depending on the changes in tissue composition. From the horizontal scans of the subtracted images, the photon backscattering simulated images of control and combination of tissues are obtained. By analysis of peak intensity and full-width at half maximum, the type, location, and size of the tissue compositional variation are determined.

Adipose Tissue↗
PubMed2003

Artificial neural network analysis of malaria severity through aggregation and deformability parameters of erythrocytes.

The erythrocyte aggregation and deformability of blood samples obtained from normal subjects and malaria patients are determined by microscopic imaging and laser aggregometry techniques, and optical hemorheometer, respectively. By these techniques several parameters are determined but four parameters, aggregate sedimentation velocity (ASV), effective number of cells (ENC), process completion time (PCT) and mean filtration time (MFT), show significant variation in malaria patients compared to that of healthy subjects. For malaria severity analysis artificial neural network (ANN), based on feedforward-error back-propagation algorithm in a supervisory training mode is proposed. This network is first trained for different number of epochs ranging from 20 to 50 by set of patterns and at 30 epochs training session the minimum mean square error (MSE) between desired and actual output is obtained. By applying the same procedure the test patterns belonging to normal, non-severe, severe, and highly severe malaria (NSM, SM and HSM) are identified. The results show that malaria with high severity is classified accurately (100%). The success of classification for non-severe and mildly-severe malaria ranges from 60% to 80%.

Equipment Design↗
PubMed2003

Image reconstruction of optical attenuation coefficient variation in biological tissues.

A procedure for non-invasive imaging of the optical attenuation coefficient variation of in vivo thick organs/tissues is developed. The laser back-scattered surface profiles at various locations of human forearm, by multi-probe reflectometer, are measured. These profiles are matched by iterative procedure, with that as obtained by Monte Carlo simulation and the corresponding values of attenuation coefficient (equal to the sum of absorption and reduced scattering coefficients) are determined. By interpolation of this data a 100 x 100 grid is constructed and after median filtering of this data a color-coded image of the variability of the optical attenuation coefficient of the forearm is obtained. These images in different subjects show variation due to change in overall tissue composition and blood pooling. This non-invasive imaging procedure may help in identifying the diseased affected regions in healthy tissues and in application of photodynamic therapy.

Diagnostic Imaging↗
PubMed2002

Influence of temperature variation from 5 degrees C to 37 degrees C on aggregation and deformability of erythrocytes.

Erythrocyte aggregation and elongation index (EI) (deformability) are measured at temperatures ranging from 5 degrees C to 37 degrees C by aggregometer MA1, and diffractometer Rheodyne SSD and the LORCA, respectively. The test samples are prepared from blood obtained from healthy subjects in test tubes containing EDTA as an anticoagulant and prior to measurement are placed in a water bath for 30 min, maintained at respective temperatures. The aggregation process is given in terms of primary aggregation time and indices of aggregation. These show significant to highly significant changes with the increase of temperature compared to that at 5 degrees C. The EI increases with the increase of shear stress but shows significant decrease with the decrease of temperature.

Erythrocyte Aggregation↗
PubMed2002

Digital blood flow analysis from microscopic images of mesenteric microvessel with multiple branching.

Blood flow through frog mesenteric microvessel with multiple branching, at Reynolds number 0.022, is analyzed. After pre-processing the images the velocity and erythrocyte distribution profiles by image velocimetry and axial tomography are obtained, respectively. The vascular parameters and shape descriptors are obtained by image processing techniques. The axial velocity shows the variation around branching areas associated with an increase in radial velocity, which is up to 10% of axial velocity. From the erythrocyte distribution profiles at various locations in the microvessel the tomograms are reconstructed. Based on these the contours of equal concentration are reconstructed. From these contours the point-to-point variation in cell concentration throughout the microvessel is observed and regions where the cellular concentration varies from 3 to 5%, at zero axial velocity, are identified. The change in erythrocyte shape, determined by the shape descriptors, while passing through the capillary is significant. This passage of cells, depending on their orientation, also displaces the capillary walls by 1.5 to 2.5 microm.

Animals↗
PubMed2002

Development of biological tissue-equivalent phantoms for optical imaging.

Optical characteristics of freshly isolated tissues depend on their color and composition. The surface backscattered profile, which account for the tissue compositional variation in fresh excised sheep's heart, lungs, bone and muscle, were measured by multi-probe reflectometer. Optical phantoms were prepared from paraffin wax by mixing a specific combination of wax color materials till the surface backscattered profile of these matched with that of the biological tissues. The optical parameters absorption coefficient (micro(a)), reduced scattering coefficient (micro(s)) and anisotropy factor (g) of these phantoms, are the same as that of biological tissues and are obtained by matching their surface backscattered profiles with that as simulated by Monte Carlo procedure. The maximum and minimum values of absorption coefficient are for the phantoms of lungs (1.0 cm(-1)) and muscle (0.02 cm(-1)), whereas, for scattering coefficient these values are for muscle (21.2 cm(-1)) and bone (13.08 cm(-1)).

Animals↗