Showing papers in "Magnetic Resonance in Medicine in 1986"
TL;DR: Based on the principles of echo imaging, a method is proposed to acquire sufficient data for a 256 × 256 image in from 2 to 40s, and the signal amplitudes of structures with long T2 are nearly the same as those in a conventional 2D FT experiment.
Abstract: Based on the principles of echo imaging, we present a method to acquire sufficient data for a 256 X 256 image in from 2 to 40 s. The image contrast is dominated by the transverse relaxation time T2. Sampling all projections for 2D FT image reconstruction in one (or a few) echo trains leads to image artifacts due to the different T2 weighting of the echo. These artifacts cannot be described by a simple smearing out of the image in the phase direction. Proper distribution of the phase-encoding steps on the echoes can be used to minimize artifacts and even lead to resolution enhancement. In spite of the short data acquisition times, the signal amplitudes of structures with long T2 are nearly the same as those in a conventional 2D FT experiment. Our method, therefore, is an ideal screening technique for lesions with long T2.
2,051 citations
TL;DR: The intrinsic and system SNR is applied to predict image SNR and has found satisfactory agreement with measurements on images, which indicates that the initial choice of pixel size is crucial in NMR.
Abstract: The fundamental limit for NMR imaging is set by an intrinsic signal-to-noise ratio (SNR) for a particular combination of rf antenna and imaging subjects. The intrinsic SNR is the signal from a small volume of material in the sample competing with electrical noise from thermally generated, random noise currents in the sample. The intrinsic SNR has been measured for a number of antenna-body section combinations at several different values of the static magnetic field and is proportional to B0. We have applied the intrinsic and system SNR to predict image SNR and have found satisfactory agreement with measurements on images. The relationship between SNR and pixel size is quite different in NMR than it is with imaging modalities using ionizing radiation, and indicates that the initial choice of pixel size is crucial in NMR. The analog of "contrast-detail-dose" plots for ionizing radiation imaging modalities is the "contrast-detail-time" plot in NMR, which should prove useful in choosing a suitable pixel array to visualize a particular anatomical detail for a given NMR receiving antenna.
760 citations
TL;DR: FLASH (Fast Low‐Angle SHot) imaging is a new method for rapid NMR imaging which has been demonstrated to provide abdominal images without artifacts due to respiratory or peristaltic motions.
Abstract: FLASH (Fast Low-Angle SHot) imaging is a new method for rapid NMR imaging which has been demonstrated to provide abdominal images without artifacts due to respiratory or peristaltic motions The sequence typically employs 15° radiofrequency excitation pulses and acquires a free induction decay signal in the form of a gradient echo Here FLASH images are recorded in the presence of dynamic processes with time constants even smaller than the measuring time of about 2 s for an image with a 128 × 128-pixel resolution Experiments are carried out on flow phantoms and on rabbits yielding heart images without gating of the cardiac motion © 1986 Academic Press, Inc
400 citations
TL;DR: Loss of ATP was associated with altered recovery of the muscle: phosphocreatine, Pi, and pH returned more slowly to their pre‐exercise values and the initial rate of oxidative phosphorylation was diminished.
Abstract: The energetics of human muscle have been investigated in vivo during and after fatiguing aerobic, dynamic exercise. Changes in cytoplasmic pH and concentrations of phosphocreatine, ATP and Pi were followed using 31P nuclear magnetic resonance spectroscopy. ATP was significantly depleted in 6 out of 12 experiments and in these 6 experiments decreased to 55 +/- 5% of the pre-exercise concentration. Depleted muscle had a lower phosphocreatine concentration (17 +/- 5% of resting value) and lower pH (6.12 +/- 0.04) than fatigued muscle in which ATP loss was not observed (26 +/- 5% for phosphocreatine and 6.37 +/- 0.09 for pH). The free energy of hydrolysis of ATP was not significantly different in the two groups and was also similar in exhausted and nonexhausted muscle. Loss of ATP was associated with altered recovery of the muscle: [phosphocreatine], [Pi], and pH returned more slowly to their pre-exercise values and the initial rate of oxidative phosphorylation was diminished. The restitution of [ATP] to its pre-exercise value was much slower than that of the other metabolites.
329 citations
TL;DR: Coronal and sagittal images of a volunteer are presented showing the vertebral and common, internal and external carotid arteries in projection views.
Abstract: A surface coil on the neck causes adiabatic fast passage in blood as it flows by through a magnetic field gradient. This allows separation of blood and stationary tissue images of the head. Coronal and sagittal images of a volunteer are presented showing the vertebral and common, internal and external carotid arteries in projection views. © 1986 Academic Press, Inc.
298 citations
TL;DR: The effects of improper pulse amplitude or duration for nonselective rf pulses on resonance, caused by off‐resonance effects and the use of selective pulses are reported.
Abstract: In principle, multiple-echo magnetic resonance imaging (MRI) can be used to estimate the spin-spin relaxation time, T2, which can then be used for quantitative tissue characterization. Although multiple echoes can be used to enhance the signal-to-noise ratio in an image, by echo addition, rf pulse imperfections modify the echo amplitudes resulting in significant errors in the estimate of T2. Imperfect 180 degree pulses do not completely invert the transverse magnetization so that the magnitude of the transverse component is reduced and a longitudinal component is generated. Successive application of such imperfect pulses generates many components that interact in a complex manner. The amplitudes of successive echoes are affected whenever the transverse components refocus, whereas the longitudinal components may be rotated into the transverse plane by subsequent pulses and may often add to the image signal or give rise to an image artifact. These effects have been analyzed theoretically and have been demonstrated for a wide range of rf pulse imperfections using both simple and composite pulses, through computer simulations based on the numerical solution of the Bloch equations. The theoretical and simulation results have been substantiated through experiments performed on a mineral oil phantom using a resistive prototype MR scanner operating at 6.35 MHz. In this paper we report the effects of improper pulse amplitude or duration for nonselective rf pulses on resonance. We separately describe the other types of imperfections caused by off-resonance effects and the use of selective pulses.
201 citations
TL;DR: Particles of magnetite, Fe3O4, accumulate preferentially in the liver and spleen after intravenous injection, and drastically decrease echo intensities in spinecho proton magnetic resonance imaging sequences, as demonstrated by experiments on dogs injected with 0.05‐μm particles.
Abstract: Particles of magnetite, Fe3O4, accumulate preferentially in the liver and spleen after intravenous injection. Their magnetic fields drastically decrease echo intensities in spinecho proton magnetic resonance imaging sequences, as demonstrated by experiments on dogs injected with 10 mg/kg of 0.05-μm particles. © 1986 Academic Press, Inc.
181 citations
TL;DR: The water relaxation ability of ferromagnetic, albumin‐coated magnetite (Fe3O4) particles has been investigated and these particles are quite effective at reducing both T1 and T2 at relatively low particle concentrations.
Abstract: Most contrast agents used in NMR imaging studies to date have been paramagnetic. However, it is also possible to obtain selective contrast with a ferromagnetic agent, and these agents are potentially more sensitive than paramagnetic compounds because of their large magnetic moments. The water relaxation ability of ferromagnetic, albumin-coated magnetite (Fe3O4) particles has been investigated. These particles are quite effective at reducing both T1 and T2 at relatively low particle concentrations. The potential applications of these particles include improved visualization of the liver, gastrointestinal tract, and genitourinary tract, as well as specific targeting and detection of small tumors or other cells with unique surface receptors. © 1986 Academic Press, Inc.
164 citations
TL;DR: The Gd(DOTA) complex was shown to be a more stable alternative to Gd (DTPA) by serum stability studies and measurement of stability constants, and images of tumors grown in athymic mice were obtained by NMR after injection of Gd
Abstract: Methods have been devised for obtaining gadolinium(III) complexes of the ligands NOTA (1,4,7-triazacyclononane-N,N',N''-triacetic acid), DOTA (1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid), TETA (1,4,8,11-tetraazacyclotetradecane-N,N',N'',N'''-tetraacetic acid), and DTPA (diethylenetriaminepentaacetic acid) as solids for use as pharmaceuticals. Their effectiveness as in vitro and in vivo contrast agents for NMR imaging or T1,2 relaxation agents for spectroscopy has been investigated. The Gd(DOTA) complex was shown to be a more stable alternative to Gd(DTPA) by serum stability studies and measurement of stability constants. Images of tumors grown in athymic mice were obtained by NMR after injection of Gd(DOTA) and Gd(DTPA).
133 citations
TL;DR: A medium field strength (0.5–1 T) is presented as representing, for general purpose imaging of head and torso, the best current compromise when imaging time is of major importance, with the important caveat that new techniques may always invalidate this conclusion.
Abstract: Some of the factors involved in the choice of field strength for NMR imaging are examined. The influences of relaxation times and chemical shift upon image quality and signal-to-noise ratio are highlighted, and power deposition is introduced as a significant factor which may limit the flexibility and information available at higher fields as long as 180 degrees echo pulses continue to be necessary. Chemical-shift imaging is examined and found wanting as a means of coping with chemical-shift artifacts, and the use of multiple echoes (albeit with research) in conjunction with multiple-slice techniques is advocated as representing an efficient data-gathering scheme which can improve image signal-to-noise ratio. With such use, a medium field strength (0.5-1 T) is presented as representing, for general purpose imaging of head and torso, the best current compromise when imaging time is of major importance, with the important caveat that new techniques may always invalidate this conclusion.
130 citations
TL;DR: The effects of static field inhomogeneities are investigated through computer simulations and analytical solutions of the Bloch equations and a series of experiments performed on a simple tissue phantom using a whole‐body imaging system corroborates the simulation and analytical results.
Abstract: The accurate estimation of the spin-spin relaxation time T2 is an important goal in magnetic resonance imaging particularly because it can be used for quantitative tissue characterization. The spin-spin relaxation time T2 may be estimated using multiecho pulse sequences, but the accuracy of the estimate is dependent on the fidelity of the spin-echo amplitudes, which may be severely compromised by rf pulse and static field imperfections. In this paper, the effects of static field inhomogeneities are investigated. The propagation of the errors introduced by off-resonance effects are analyzed through computer simulations and analytical solutions of the Bloch equations. A series of experiments performed on a simple tissue phantom using a whole-body imaging system operating at 6.35 MHz corroborates the simulation and analytical results. For accurate measurements of T2 using a whole-body imaging system it is necessary to correct for these inhomogeneities. A correction scheme which would enable a more accurate estimate of T2 is currently under investigation.
TL;DR: It is found that, over the field range in which NMR imaging is currently being done, different symmetries of otherwise similar chemical ligands can alter 1/T1 of solvent protons by factors of up to three.
Abstract: The magnetic field dependence of the solvent water proton longitudinal relaxation rate 1/T1 (the NMRD profile) has been measured for solutions of chelates of Gd3+ and Mn2+ ions with two different polyaza macrocyclic ligands: 1, 4, 7-triazacyclononane-N, N′, N″,-triacetic acid (NOTA) and 1, 4, 7, 10-tetraazacyclododecane-N, N′, N″, N‴,-tetraacetic acid (DOTA) Studies were carried out mainly near physiological pH, but the pH dependence was also examined in some cases The results are compared with published data for complexes of Gd3+ and Mn2+ ions with ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetie acid (DTPA) Competition experiments for the NOTA and DOTA chelates with EDTA and DTPA were also performed It is found that, over the field range in which NMR imaging is currently being done, different symmetries of otherwise similar chemical ligands can alter 1/T1 of solvent protons by factors of up to three The ligand environment can influence the relaxation times of the electronic spin moments of the ions, as well as their coordination number, thereby changing both the inner and outer sphere contributions to the relaxivities of the complexes The relevance of these results to questions of efficiency and toxicity of these chelates as agents for enhancement of contrast in NMR images is discussed © 1986 Academic Press, Inc
TL;DR: 1H‐decoupled 13C NMR spectra of the living rabbit brain were collected following the intravenous infusion of [1‐13C]glucose providing information on the rate and extent of blood glucose labeling.
Abstract: 1H-decoupled 13C NMR spectra (20.2 MHz) of the living rabbit brain were collected with a surface coil following the intravenous infusion of [1-13C]glucose. Within 15 min of infusion, the α and β anomers of glucose were detected and, shortly thereafter, the carbon atoms at positions C4, C3, and C2 of glutamate and(or) glutamine. After reductions of inspired oxygen from 30 to 5%, lactate C3 was detected. The intensity of the lactate resonance rose progressively during hypoxia and later fell during recovery with oxygen. The 13C fractional isotopic enrichment of arterial blood glucose was measured by 1H NMR providing information on the rate and extent of blood glucose labeling. © 1986 Academic Press, Inc.
TL;DR: It is shown that Gd is in the extracellular space only and is present as rotationally mobile Gd(DTPA), uncomplexed with protein or blood cells; and that the water protons exchange rapidly between the intra‐ and Extracellular regions.
Abstract: The magnetic field dependence of the longitudinal relaxation rates 1/T1 (NMRD profiles) of blood and plasma from rabbits before and after injection of Gd(DTPA) are reported as a function of magnetic field strength from 0.01 to 50 MHz. Over 100 values along the time-dependent magnetization were recorded for each 1/T1 and analyzed for multiple exponentials. From these data, which indicate a single exponential, from the measured Gd content of each sample, and the NMRD profiles, we show that Gd is in the extracellular space only and is present as rotationally mobile Gd(DTPA), uncomplexed with protein or blood cells; and that the water protons exchange rapidly between the intra- and extracellular regions.
TL;DR: A method is proposed for measuring on the bench the NMR signal‐to‐noise ratio of rf probes and also the power deposited in patients during the imaging experiment and is verified by comparison with a direct spectral measure of sensitivity obtained from a small doped water sample placed in NMR imaging equipment.
Abstract: A method is proposed for measuring on the bench the NMR signal-to-noise ratio of rf probes, (over the range 1-100 MHz) and also the power deposited in patients during the imaging experiment. The technique is based on the principle of reciprocity, in that a direct relationship exists between the magnetic field generated (upon transmission) by a matched probe coil and the signal-to-noise ratio delivered by the same coil when used as a receiver. The construction and use of a calibrated sense coil for measuring the field is described, and the precautions and theory necessary for accurate measurement and understanding are outlined. Finally, the method is verified by comparison with a direct spectral measure of sensitivity obtained from a small doped water sample placed in NMR imaging equipment.
TL;DR: Nambu PVA gel which is produced by repeated freezing and thawing of PVA solution has overcome almost all of the problems which present substances have and is close to human soft tissue in MRI parameters.
Abstract: Nambu PVA gel which is produced by repeated freezing and thawing of PVA solution has overcome almost all of the problems which present substances have: (1) It is close to human soft tissue in MRI parameters (2) MRI parameters (1H density, T1, T2) are adjustable to some extent (3) It has appropriate physical characteristics The important problem with PVA gel is long-term stability It is assumed that this problem can be solved by its periodic calibration and replacement © 1986 Academic Press, Inc
TL;DR: It turns out that the nonlinear phases induced by those pulses may compensate each other, that therefore spin‐echo experiments as usual in MR imaging may be performed, and that the required peak power may be reduced by up to a factor of 50.
Abstract: With increasing field strength for whole-body MR scanners there is a need for rf pulses of higher bandwidth to perform selective excitation or inversion. AM pulses will have to become shorter thus leading to an enormous requirement for the peak power of the power amplifier. To reduce these requirements the use of frequency modulation is investigated. The effect of pulses based on a linear frequency sweep on the spin system is analyzed by calculation and computer simulation. It turns out that the nonlinear phases induced by those pulses may compensate each other, that therefore spin-echo experiments as usual in MR imaging may be performed, and that the required peak power may be reduced by up to a factor of 50.
TL;DR: Findings indicate that it may be feasible to develop in vivo NMR contrast agents that selectively will indicate areas of hypoxia and thereby aid in the detection of disease processes such as neoplasia, ischemia, and inflammation.
Abstract: The rate of reduction of nitroxides is shown to be more rapid in hypoxic cells. The rate of reduction and the effect of hypoxia on the reduction rate vary for different nitroxides. These findings indicate that it may be feasible to develop in vivo NMR contrast agents that selectively will indicate areas of hypoxia and thereby aid in the detection of disease processes such as neoplasia, ischemia, and inflammation.
TL;DR: The NMRD profiles (the magnetic field dependence of 1/T1) of solutions of the ternary conjugates differ greatly from those of the corresponding binary ligand‐metal‐ion complexes, both in magnitude and functional form, exhibiting 5‐to 10 fold greater relaxivities and prominent peaks near 20 MHz.
Abstract: Bovine immunoglobulins (IgG) and bovine serum albumin (BSA) were multiply labeled with multidentate ligands, either ethylenediaminetetraacetic acid (EDTA) or diethylene lriaminepentaacetic acid (DTPA), and metal ions were inserted to form the ternary protein ligand-ion conjugates. The NMRD profiles (the magnetic field dependence of 1/T1) of solutions of the ternary conjugates differ greatly from those of the corresponding binary ligand-metal-ion complexes, both in magnitude and functional form, exhibiting 5-to 10 fold greater relaxivities and prominent peaks near 20 MHz. The inference is that the protein-bound chelates are relatively rigidly attached to the macromolecules. The structure and metal ion affinities of these novel conjugates, as well as the relevance to contrast enhancement in NMR imaging, is discussed. © 1986 Academic Press, Inc.
TL;DR: Brain tissue relaxation and spin‐density data were determined using the same protocol in 37 scans performed on 27 normal volunteers, and the positional dependence of the apparent relaxation times appears to be systematic and may be due to variations in the effective field, caused by magnet and rf inhomogeneity.
Abstract: The reproducibility of T1, T2, and proton density, measured in phantoms and the human brain was evaluated by proton imaging techniques. The sequence used to derive T1 and density values was a multiple-saturation recovery which consists of four pairs of 90 degrees pulses, followed by a 180 degrees phase reversal pulse, generating four T1-weighted images. T2 was derived from a multiple-echo sequence, generating four T2-weighted images. The data were analyzed by fitting the pixel intensities to the respective equations by means of nonlinear multiparameter least-squares analysis. Short-term reproducibility between four consecutive scans was evaluated to be 1-4% depending on location with a phantom covering the entire span of physiologic T1 and T2 values. A second phantom containing a series of identical samples served to study the dependence of the apparent T1 and T2 on position, both radially and axially, with respect to magnet isocenter. Reproducibility across the field of view was found to be better than 7% (T1 and T2). This phantom was further used to evaluate effects of long-term reproducibility, which at each location varied from 5-14% (T1) and 2-10% (T2). Finally, interinstrument reproducibility, tested by means of the same protocol on three different instruments, all operating at the same magnetic field and using largely identical hardware for each location, was found to be 1-14% (T1) and 2-10% (T2). The positional dependence of the apparent relaxation times appears to be systematic and may be due to variations in the effective field, caused by magnet and rf inhomogeneity. Finally, brain tissue relaxation and spin-density data were determined using the same protocol in 37 scans performed on 27 normal volunteers. The tissues analyzed were putamen, thalamus, caudate nucleus, centrum semiovale, internal capsule, and corpus callosum. Excellent accordance was further obtained between left and right hemispheres.
TL;DR: Calculations based on the relaxivity of dissolved protein indicate that the use of these methods for the detection of elevated levels of CSF protein would be less sensitive than existing methods.
Abstract: To estimate the feasibility of measuring in vivo CSF protein, oxygen, or other solutes through their effect on proton relaxation times, the T1 and T2 of CSF protons has been measured within the human lateral ventricles. T1 was measured at 6.25, 25.4, and 60.1 MHz with a two-point method. T2 was measured at 6.25 and 25.4 MHz using the CPMG sequence to acquire 8 echo images. The T1 was 4.3 s with no evidence of field dependence. The T2 was 2 s. Although these values approach those for water at the same temperature it is possible that the T1 is influenced by the normal oxygen concentration. Calculations based on the relaxivity of dissolved protein indicate that the use of these methods for the detection of elevated levels of CSF protein would be less sensitive than existing methods.
TL;DR: Electron spin resonance (ESR) spectra from the capsule are sensitive to the concentration of dissolved oxygen and calibration curves are given, and the oxygen concentration was found to rise from a value close to zero when the animal breathes air to a level of 220 μM when theAnimal breaths pure oxygen.
Abstract: Small mice (∼20 g) were anesthetized and placed in a loop-gap resonator of diameter 25 mm resonating at 1.1 GHz. An oxygen-permeable capsule containing 2.5 × 10−2M perdeutero 15N TEMPONE (1-oxyl-2, 2, 6, 6-tetramethyl-4-piperidone) in light paraffin oil was implanted in the peritoneal cavity. Electron spin resonance (ESR) spectra from the capsule are sensitive to the concentration of dissolved oxygen and calibration curves are given. The oxygen concentration was found to rise from a value close to zero when the animal breathes air to a level of 220 μM when the animal breaths pure oxygen. It is speculated that this surprisingly high level is related to the effect of the anesthetic on the cardiovascular system. Encapsulation provides a barrier to spin-label reductants and to paramagnetic metal ions that might confound the spin-label oximetric measurements. © 1986 Academic Press, Inc.
TL;DR: Measuring phantoms with calibrated T2 values, it is shown that the PHAPS imaging sequence leads to an accuracy of quantitative T2 determinations of better than 10%.
Abstract: In 2D Fourier imaging the normal Carr-Purcell multiple-echo sequence generally leads to center line and mirror artifacts caused by imperfect rotations by the rf pulses. We describe a method to avoid these distortions using a phase alternating-phase shift (PHAPS) sequence which also allows multiple-slice and multiple-echo imaging at the same time. Measuring phantoms with calibrated T2 values, we have shown that the PHAPS imaging sequence leads to an accuracy of quantitative T2 determinations of better than 10%. Contrast-enhanced images are presented which we calculated from multiple-echo images and extrapolated to arbitrary echotimes, including negative ones. We believe that these improvements in T2 imaging will result in a significant reduction of patient investigation time in magnetic resonance imaging.
TL;DR: The results suggest that the in vivo phosphodiester resonance has substantial contributions from a fraction of mobile brain phospholipids.
Abstract: The in vivo dog brain 31P NMR spectrum has a large peak in the phosphodiester region accounting for more than 35% of the total observable phosphorus metabolites. It is possible to reduce the intensity of this peak by off-resonance saturation. To characterize the nature of this peak, extracts of dog brain frozen in situ were analyzed by high resolution 31P NMR. ATP, phosphocreatine, inorganic phosphate, and phosphomonoesters were recovered in appropriate amounts in the methanol:HCl extract. However, acid soluble phosphodiesters accounted for only 8% of the observable phosphorus. More NMR observable phosphodiesters were selectively recovered following CHCl3:methanol extraction of phospholipids. These results suggest that the in vivo phosphodiester resonance has substantial contributions from a fraction of mobile brain phospholipids.
TL;DR: A marked increase in 1/T2 is observed at higher iron loadings that the authors are unable to account for within the framework of the theory of outer sphere relaxation, even when the effects arising from inhomogeneities in the local magnetic field are included.
Abstract: The magnetic field dependence of 1/T1 over the range 0.01 to 50 MHz proton Larmor frequency (NMRD profile) is reported for water protons in solutions of horse spleen apoferritin, and of ferritin reconstituted at both low and high iron levels. The apoferritin results are in every way typical of diamagnetic spherical proteins of their size (K. Hallenga and S. H. Koenig, Biochemistry 15, 4255 (1976)). Titration of up to 24 ferrous ions per protein molecule, with subsequent oxidation to ferric, shows a nonlinear saturating contribution to the NMRD profile which is interpreted as arising from a small number of ferric ions (six to eight) bound close to the outside of each ferritin molecule, and a comparable number of interior sites. The latter become multiply occupied as the core grows and do not contribute measurably to 1/T1 in this state. The former sites are never more than singly occupied, and their contribution to the solvent proton relaxation rates is independent of the loading of the core. Measurements of 1/T2 at 20 MHz are quite in accord with theoretical expectations for apoferritin and ferritin with up to 24 ferric ions per molecule. However, a marked increase in 1/T2 is observed at higher iron loadings that we are unable to account for within the framework of the theory of outer sphere relaxation, even when the effects arising from inhomogeneities in the local magnetic field are included. A sample of human spleen hemosiderin was found to have the same 1/T1 NMRD profile as a comparable sample of ferritin.
TL;DR: Coupling between large transmit and surface‐receive coils is eliminated using a λ/4 cable, terminated with crossed diodes to ground, inserted between the receive coil and ground.
Abstract: Coupling between large transmit and surface-receive coils is eliminated using a λ/4 cable, terminated with crossed diodes to ground, inserted between the receive coil and ground, and by using a cable of length a little less than λ/2 inserted between the transmit match capacitance and the normal crossed diodes in the transmit input line. © 1986 Academic Press, Inc.
TL;DR: An NMR imaging technique sensitive to slow flow using a conventional imaging gradient strength (0.025 mT/cm) is described and two projections with different spatial magnetic periodicity (determined by the SSFP pulse interval) are subtracted to give signal from flows in a velocity window.
Abstract: An NMR imaging technique sensitive to slow flow (∼ 1 mm/s) using a conventional imaging gradient strength (0.025 mT/cm) is described. Two projections with different spatial magnetic periodicity (determined by the SSFP pulse interval), and thus with different flow sensitivities, are subtracted to give signal from flows in a velocity window. © 1986 Academic Press, Inc.
TL;DR: Large unilamellar liposomes containing the paramagnetic contrast agent manganese chloride were shown to selectively enhance the intensity of the proton NMR signal from the livers of experimental mice, showing that liposome could provide a useful and efficient vehicle for delivering NMR contrast agents to organs like the liver.
Abstract: Large unilamellar liposomes containing the paramagnetic contrast agent manganese chloride were shown to selectively enhance the intensity of the proton NMR signal from the livers of experimental mice. The kinetics of the observed effect indicate that the liposomes are rapidly removed from the circulation and deposited in high concentration within the liver. This process is known to involve the phagocytic activity of macrophages. These results show that liposomes could provide a useful and efficient vehicle for delivering NMR contrast agents to organs like the liver, spleen, and bone marrow. It may also be possible to use liposomes to selectively deliver contrast agents to tissue regions of developing pathology that are rich in macrophage activity. © 1986 Academic Press, Inc.
TL;DR: In this paper, a hybrid technique combining both projection reconstruction and Fourier encoding schemes was proposed for in-vivo imaging of sodium-23 in the human head, where the projection reconstruction was used for the xy plane imaging while the Fourier encoder was used to slice separation.
Abstract: A magnetic resonance imaging pulse sequence featuring a short echo time of 3.6 ms is described and used clinically for in vivo imaging of sodium-23 in the human head. In living tissues, sodium exhibits at least two transverse relaxation constants, namely, (a) a short component T2s = 0.7-3.0 ms and (b) a long component T2e = 16-30 ms. Since our first in vivo imaging of sodium, an echo time of 10-15 ms has been used by us and by other investigators. This echo time is adequate for the observation of the long T2 component of sodium. However, a substantial fraction of the sodium, namely, the short T2 component, representing about 40%, has remained undetected by the imaging method with this echo time and is now observable by the new pulse sequence. The proposed method is a hybrid technique combining both projection reconstruction and Fourier encoding schemes. The projection reconstruction is used for the xy plane imaging while the Fourier encoding is used for slice separation. Sodium MR images of the human head produced with a short and a long TE are presented and analyzed. There is an increase in the MR signal and improved visibility of intraparenchymal sodium with the new scheme of short TE.
TL;DR: Polymeric paramagnetic ion chelate molecules were synthesized and covalently linked to monoclonal antibodies, enabling specifically bound antibody concentrations less than 2.0 μM to significantly reduce proton longitudinal relaxation times.
Abstract: Polymeric paramagnetic ion chelate molecules were synthesized and covalently linked to monoclonal antibodies. The labeled antibodies retained their antigen binding capacity in vitro while carrying up to an average of 50 paramagnetic ion chelates, enabling specifically bound antibody concentrations less than 2.0 microM to significantly reduce proton longitudinal relaxation times.