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Biomedical subjects

N Chandrakumar

Publications and source records attributed to N Chandrakumar.

5 recordsLinked to original sources
PubMed2006

Optimized 1D double quantum filter NMR experiments.

We propose and demonstrate a 1D pulse sequence to convert double quantum coherence (DQC) of y phase with optimal efficiency, relying on single transition selection. Our sequence has a larger high-sensitivity bandwidth with respect to the coupling, compared to other reconversion strategies. A modified version of the new pulse sequence provides the missing chemical shift and coupling information, at minor cost in sensitivity. Application to 1D 13C INADEQUATE is demonstrated. Our new sequence is also applied to quadrupole coupled spin-1 systems, such as 2H in lyotropic phase. Performance of the sequence may be fine-tuned by pulse flip angle optimization, taking into account relaxation effects.

Journal Article↗
PubMed1999

PRAWN: mixing sequences for selective heteronuclear J cross polarization.

In this work, we present a family of pulse sequences for selective heteronuclear J cross-polarization (JCP), which we have developed especially for indirect 13C imaging using JCP, for example in the CYCLCROP environment. The sequences are straightforward to implement and operate reliably. Results of an average Hamiltonian analysis are given for the basic sequence, which we term PRAWN (pulsed rotating frame transfer sequence with windows). It is shown experimentally that the pulse sequence, which operates efficiently with low RF duty cycles down to a few percent, has a useful tolerance range to absolute Hartmann-Hahn mismatch and generates coherence transfer spectra in close correspondence with the JCP average Hamiltonian. Computer simulation of the performance of the basic sequence on a heteronuclear spin-(1/2) AX system is also presented. The mismatch compensation of PRAWN may be markedly enhanced further by issuing a pi pulse to each spin halfway through the basic PRAWN train and in phase quadrature to it. A simple analysis of this modified sequence, PRAWN-pi, is given under conditions of mismatch and off-resonance irradiation.

Carbon Isotopes↗
PubMed1988

Proton relaxation times in cancer diagnosis.

Proton nuclear magnetic resonance relaxation parameters (T1, T2) were measured for over 100 malignant and normal tissue samples of various organs of the human body. The purpose of this study was to estimate the reliability of the NMR technique in discriminating normal from malignant tissues. Breast and cervix samples were analyzed by using the malignancy index concept and we were able to distinguish malignant and normal tissue in 17 out of 18 breast samples and 5 out of 7 cervix samples. Since the relaxation data of a normal control population of the other organs were not available, the data for these are reported without any further analysis. The distinction between carcinomas and sarcomas was also made by using the estimated relaxation parameters. Malignancy indices of breast tissue samples for linear least-squares and nonlinear two-parameter and three-parameter least-squares procedures were calculated and used to evaluate the relative efficiencies in discriminating malignant from normal tissues.

Breast Neoplasms↗