The diffusion coefficient of lipid molecules is usually much smaller than that of water, and it i... more The diffusion coefficient of lipid molecules is usually much smaller than that of water, and it is demonstrated here how this difference can be exploited for robust fat suppression in magnetic resonance imaging (MRI). In contrast to the prevailing methods, diffusion-based fat suppression does not rely on chemical shift differences between water and lipids and can therefore be applied easily in low or inhomogeneous magnetic fields. It is also independent of relaxation times and can therefore be incorporated in experiments requiring conventional T(1)-weighted contrast. Diffusion-based fat suppression (DIFFSUP) consists of subtracting the signals acquired at low and high b-values, where the high b-value is ideally designed to achieve full suppression of the water and negligible attenuation of the lipid signal. Since high b-value images may be particularly affected by motion artifacts, a version of DIFFSUP incorporating first-order velocity compensation is also proposed and demonstrated. Results from phantoms and live mice at field strengths of 4.7 T and 1.0 T are presented.
The diffusion coefficient of lipid molecules is usually much smaller than that of water, and it i... more The diffusion coefficient of lipid molecules is usually much smaller than that of water, and it is demonstrated here how this difference can be exploited for robust fat suppression in magnetic resonance imaging (MRI). In contrast to the prevailing methods, diffusion-based fat suppression does not rely on chemical shift differences between water and lipids and can therefore be applied easily in low or inhomogeneous magnetic fields. It is also independent of relaxation times and can therefore be incorporated in experiments requiring conventional T1-weighted contrast. Diffusion-based fat suppression (DIFFSUP) consists of subtracting the signals acquired at low and high b-values, where the high b-value is ideally designed to achieve full suppression of the water and negligible attenuation of the lipid signal. Since high b-value images may be particularly affected by motion artifacts, a version of DIFFSUP incorporating first-order velocity compensation is also proposed and demonstrated. Results from phantoms and live mice at field strengths of 4.7 T and 1.0 T are presented.
Abstract The diffusion-dependent decay of spin-echo signals from samples distributed over non-uni... more Abstract The diffusion-dependent decay of spin-echo signals from samples distributed over non-uniform field gradients is analyzed. This decay deviates from the linear semilogarithmic dependencies on t 3 or t obtained, respectively, in Hahn spin-echo or Carr-Purcell echo trains from spins in constant field gradients. It is demonstrated here that when the average diffusion distance is small compared to the spatial variation of the gradient, the spin-echo decay can be modeled by a simple superposition of signals from a large number of microdomains, each characterized by a different gradient. This is illustrated by two examples, a water sample in a deliberately created quadratic variation of the external field, and a saturated water/ sand mixture with large internal field gradients.
We have developed boron-11 MRI and MRS techniques of potential use in boron neutron capture thera... more We have developed boron-11 MRI and MRS techniques of potential use in boron neutron capture therapy (BNCT)1,2 for noninvasive quan tification and localization of BNCT agents such as the sodium salt of the dimer of the closododecaboranyl mercaptide anion, B24 H22 S2 4- (BSSB) 3.
The Jerusalem Symposia on Quantum Chemistry and Biochemistry, 1983
In consideration of the importance of conformational flexibility to the functioning of nucleic ac... more In consideration of the importance of conformational flexibility to the functioning of nucleic acids, NMR studies have been carried out to elucidate aspects of dynamics with molecular Mechanics calculations providing supplementary insight. Analysis of 31P and 13C NMR relaxation data in terms of plausible motions in a DNA helix indicate that winding and unwinding, base tilting and base pair propelling are not viable, but sugar repuckering and other limited bond rotations on the nanosecond time scale will account for the data. Molecular mechanics calculations imply that the internal motions are highly localized, not concerted along the length of the DNA helix. 2H and 15N NMR experiments on labeled nucleic acids reveal that the base moieties also eperienci some motions, limited relative to those of the backbone. 31P and 1H NMR studies comparing a closed duplex DNA, pIns36, with linear DNA reveal that segmental motion (apparently bending) occurs two orders of magnitude faster in the cdDNA. The imino proton resonances indicate that there are dynamically-averaged structural differences between linear DNA and supercoiled pIns36 in the A-T base pairs but not the G-C base pairs.
Vestnik Rossiĭskoĭ akademii meditsinskikh nauk / Rossiĭskaia akademiia meditsinskikh nauk, 2005
The subject of the paper is study of optical absorption of sensitizers in biological tissue. The ... more The subject of the paper is study of optical absorption of sensitizers in biological tissue. The study shows that absorbance can be used as a tool that allows studying biodistribution of sensitizers and their interaction with tissue in vivo. The article presents a simple technique of determining biological tissue absorption in vivo, and discusses the results of experimental animal studies of some sensitizers.
Proceedings of the National Academy of Sciences of the United States of America, Jan 15, 2014
Mammalian models, and mouse studies in particular, play a central role in our understanding of pl... more Mammalian models, and mouse studies in particular, play a central role in our understanding of placental development. Magnetic resonance imaging (MRI) could be a valuable tool to further these studies, providing both structural and functional information. As fluid dynamics throughout the placenta are driven by a variety of flow and diffusion processes, diffusion-weighted MRI could enhance our understanding of the exchange properties of maternal and fetal blood pools--and thereby of placental function. These studies, however, have so far been hindered by the small sizes, the unavoidable motions, and the challenging air/water/fat heterogeneities, associated with mouse placental environments. The present study demonstrates that emerging methods based on the spatiotemporal encoding (SPEN) of the MRI information can robustly overcome these obstacles. Using SPEN MRI in combination with albumin-based contrast agents, we analyzed the diffusion behavior of developing placentas in a cohort of...
The article is devoted to in vivo investigations of absorption in biological tissue sensitized by... more The article is devoted to in vivo investigations of absorption in biological tissue sensitized by preparations used for diagnostics and therapy of tumors. Efficiency of method of difhse reflectance spectroscopy for in vivo evaluation of accumulation of sensitizers is demonstrated.
Progress in Neutron Capture Therapy for Cancer, 1992
In recent years, efforts have been made to develop boron-11 magnetic resonance imaging (MRI) and ... more In recent years, efforts have been made to develop boron-11 magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) for use in boron neutron capture therapy (BNCT)1–3 for noninvasive quantification and localization of BNCT agents such as the sodium salt of the closodecaboranyl mercaptide anion B12H11SH-2 (BSH) and its dimer B24H22S 2 -4 (BSSB).4 Generation of MR images for fast relaxing nuclei, such as boron-10 and boron-11, is often hampered by the fact that the transverse relaxation times (T2) are considerably shorter than the available time-to-echo (TE). The minimal TE achievable in MR imaging is limited by the need to apply phase-encoding and dephasing/rephasing read-out gradients which have finite rise times imposed by the hardware limitations. Currently, echo times of 2.5 ms are attainable using conventional spin-warp imaging techniques and it may be possible to shorten TE to approximately 1 ms by reducing the resolution requirements. However, the transverse relaxation rate of the BNCT species is so short that even after 1 ms most of the signal has already decayed, resulting in an unacceptably low signal.
The diffusion coefficient of lipid molecules is usually much smaller than that of water, and it i... more The diffusion coefficient of lipid molecules is usually much smaller than that of water, and it is demonstrated here how this difference can be exploited for robust fat suppression in magnetic resonance imaging (MRI). In contrast to the prevailing methods, diffusion-based fat suppression does not rely on chemical shift differences between water and lipids and can therefore be applied easily in low or inhomogeneous magnetic fields. It is also independent of relaxation times and can therefore be incorporated in experiments requiring conventional T(1)-weighted contrast. Diffusion-based fat suppression (DIFFSUP) consists of subtracting the signals acquired at low and high b-values, where the high b-value is ideally designed to achieve full suppression of the water and negligible attenuation of the lipid signal. Since high b-value images may be particularly affected by motion artifacts, a version of DIFFSUP incorporating first-order velocity compensation is also proposed and demonstrated. Results from phantoms and live mice at field strengths of 4.7 T and 1.0 T are presented.
The diffusion coefficient of lipid molecules is usually much smaller than that of water, and it i... more The diffusion coefficient of lipid molecules is usually much smaller than that of water, and it is demonstrated here how this difference can be exploited for robust fat suppression in magnetic resonance imaging (MRI). In contrast to the prevailing methods, diffusion-based fat suppression does not rely on chemical shift differences between water and lipids and can therefore be applied easily in low or inhomogeneous magnetic fields. It is also independent of relaxation times and can therefore be incorporated in experiments requiring conventional T1-weighted contrast. Diffusion-based fat suppression (DIFFSUP) consists of subtracting the signals acquired at low and high b-values, where the high b-value is ideally designed to achieve full suppression of the water and negligible attenuation of the lipid signal. Since high b-value images may be particularly affected by motion artifacts, a version of DIFFSUP incorporating first-order velocity compensation is also proposed and demonstrated. Results from phantoms and live mice at field strengths of 4.7 T and 1.0 T are presented.
Abstract The diffusion-dependent decay of spin-echo signals from samples distributed over non-uni... more Abstract The diffusion-dependent decay of spin-echo signals from samples distributed over non-uniform field gradients is analyzed. This decay deviates from the linear semilogarithmic dependencies on t 3 or t obtained, respectively, in Hahn spin-echo or Carr-Purcell echo trains from spins in constant field gradients. It is demonstrated here that when the average diffusion distance is small compared to the spatial variation of the gradient, the spin-echo decay can be modeled by a simple superposition of signals from a large number of microdomains, each characterized by a different gradient. This is illustrated by two examples, a water sample in a deliberately created quadratic variation of the external field, and a saturated water/ sand mixture with large internal field gradients.
We have developed boron-11 MRI and MRS techniques of potential use in boron neutron capture thera... more We have developed boron-11 MRI and MRS techniques of potential use in boron neutron capture therapy (BNCT)1,2 for noninvasive quan tification and localization of BNCT agents such as the sodium salt of the dimer of the closododecaboranyl mercaptide anion, B24 H22 S2 4- (BSSB) 3.
The Jerusalem Symposia on Quantum Chemistry and Biochemistry, 1983
In consideration of the importance of conformational flexibility to the functioning of nucleic ac... more In consideration of the importance of conformational flexibility to the functioning of nucleic acids, NMR studies have been carried out to elucidate aspects of dynamics with molecular Mechanics calculations providing supplementary insight. Analysis of 31P and 13C NMR relaxation data in terms of plausible motions in a DNA helix indicate that winding and unwinding, base tilting and base pair propelling are not viable, but sugar repuckering and other limited bond rotations on the nanosecond time scale will account for the data. Molecular mechanics calculations imply that the internal motions are highly localized, not concerted along the length of the DNA helix. 2H and 15N NMR experiments on labeled nucleic acids reveal that the base moieties also eperienci some motions, limited relative to those of the backbone. 31P and 1H NMR studies comparing a closed duplex DNA, pIns36, with linear DNA reveal that segmental motion (apparently bending) occurs two orders of magnitude faster in the cdDNA. The imino proton resonances indicate that there are dynamically-averaged structural differences between linear DNA and supercoiled pIns36 in the A-T base pairs but not the G-C base pairs.
Vestnik Rossiĭskoĭ akademii meditsinskikh nauk / Rossiĭskaia akademiia meditsinskikh nauk, 2005
The subject of the paper is study of optical absorption of sensitizers in biological tissue. The ... more The subject of the paper is study of optical absorption of sensitizers in biological tissue. The study shows that absorbance can be used as a tool that allows studying biodistribution of sensitizers and their interaction with tissue in vivo. The article presents a simple technique of determining biological tissue absorption in vivo, and discusses the results of experimental animal studies of some sensitizers.
Proceedings of the National Academy of Sciences of the United States of America, Jan 15, 2014
Mammalian models, and mouse studies in particular, play a central role in our understanding of pl... more Mammalian models, and mouse studies in particular, play a central role in our understanding of placental development. Magnetic resonance imaging (MRI) could be a valuable tool to further these studies, providing both structural and functional information. As fluid dynamics throughout the placenta are driven by a variety of flow and diffusion processes, diffusion-weighted MRI could enhance our understanding of the exchange properties of maternal and fetal blood pools--and thereby of placental function. These studies, however, have so far been hindered by the small sizes, the unavoidable motions, and the challenging air/water/fat heterogeneities, associated with mouse placental environments. The present study demonstrates that emerging methods based on the spatiotemporal encoding (SPEN) of the MRI information can robustly overcome these obstacles. Using SPEN MRI in combination with albumin-based contrast agents, we analyzed the diffusion behavior of developing placentas in a cohort of...
The article is devoted to in vivo investigations of absorption in biological tissue sensitized by... more The article is devoted to in vivo investigations of absorption in biological tissue sensitized by preparations used for diagnostics and therapy of tumors. Efficiency of method of difhse reflectance spectroscopy for in vivo evaluation of accumulation of sensitizers is demonstrated.
Progress in Neutron Capture Therapy for Cancer, 1992
In recent years, efforts have been made to develop boron-11 magnetic resonance imaging (MRI) and ... more In recent years, efforts have been made to develop boron-11 magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) for use in boron neutron capture therapy (BNCT)1–3 for noninvasive quantification and localization of BNCT agents such as the sodium salt of the closodecaboranyl mercaptide anion B12H11SH-2 (BSH) and its dimer B24H22S 2 -4 (BSSB).4 Generation of MR images for fast relaxing nuclei, such as boron-10 and boron-11, is often hampered by the fact that the transverse relaxation times (T2) are considerably shorter than the available time-to-echo (TE). The minimal TE achievable in MR imaging is limited by the need to apply phase-encoding and dephasing/rephasing read-out gradients which have finite rise times imposed by the hardware limitations. Currently, echo times of 2.5 ms are attainable using conventional spin-warp imaging techniques and it may be possible to shorten TE to approximately 1 ms by reducing the resolution requirements. However, the transverse relaxation rate of the BNCT species is so short that even after 1 ms most of the signal has already decayed, resulting in an unacceptably low signal.
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