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Advertising↗
Biomedical subjects
P Mansfield
Publications and source records attributed to P Mansfield.
Echo-volumar imaging (EVI) at 0.5 T: first whole-body volunteer studies.
Improvements in the echo-volumar imaging (EVI) technique and its application in whole-body studies are described. Using an in-house built 0.5 T echo-planar imaging system, complete modulus three-dimensional image data are acquired in 102 ms with real-time display. Hardware limitations have restricted the maximum array size achievable to 64 x 32 x 8 voxels. Representative voxel dimensions are x = 6.0 mm; y = 4.0 mm, and z = 10.0 mm. Results on human volunteers are presented, showing cardiac, liver, and bladder images. Also shown are the first EVI gastric filling and emptying results.
Echo-Planar Imaging↗
A microscopic model of fluid transport in porous rocks.
NMR measurements of water velocity flowing through two different porous rocks, Bentheimer and Clashach, have been made using the PEPI sequence. Random changes of localised velocity occur in both materials even though the average velocities across the core cross-sections follow Darcy's Law. The velocity distributions are approximately Gaussian and the velocity variance follows a linear relationship with mean velocity as predicted in the stochastic theory of Mansfield and Issa. The origin of the large fluctuations in localised velocity is thought to be hydrodynamic and a detailed theory of intervoxel coupling is presented, which accounts for such behaviour in a coupled voxel array. In this work the intervoxel coupling is restricted to isolated voxel pairs.
Echo-Planar Imaging↗
Echo-planar microscopy of porous rocks.
A modified version of the echo-planar imaging sequence incorporating multiple 180 degrees RF pulses (PEPI) has been implemented at 11.7 T and used to generate high resolution images of porous solids. By preceding the PEPI sequence with an inversion recovery or flow-encoding sequence, rapid T1, and velocity mapping is possible in the microscopic domain.
Echo-Planar Imaging↗
Transient flow through porous rocks studied by PEPI.
The transient behaviour of fluid flow through porous rocks is examined using the high speed pi-modified echo-planar imaging technique (PEPI). Spatially resolved flow maps show the change in velocity, as the bulk flow rate is increased or decreased in large steps in the approach to steady state for two sandstone samples of different porosity and permeability. Different rise and fall settling times are observed for these rocks. In addition, the area occupied by significant flow and the variance of the velocity distributions are calculated during the transient state.
Echo-Planar Imaging↗
Simulating MRI flow maps in porous rocks: a new approach.
The Mansfield and Issa model of voxel pair coupling is extended using electrical circuit simulation to interacting voxel clusters comprising all configurations of contiguous voxels up to and including four voxels. This information is used to simulate flow through porous rock samples by calculating the expected velocity distributions found in porous rocks using the PEPI rapid NMR imaging technique.
Computer Simulation↗
Structure and behavior in hydrophilic matrix sustained release dosage forms: 4. Studies of water mobility and diffusion coefficients in the gel layer of HPMC tablets using NMR imaging.
PURPOSE: The purpose of this study was to characterise the water mobility in the gel layer of hydrating HPMC tablets. Water mobility in the gel layer of different HPMCs was studied. METHODS: NMR imaging, a non-invasive technique, has been used to measure the spatial distribution of self-diffusion coefficient (SDC) and T2 relaxation times across the gel layer. RESULTS: It has been shown that there is a water mobility gradient across the gel layer of HPMC tablets. Although SDC and T2 relaxation times in the outer parts of the gel layer approached that of free water, in the inner parts they decreased progressively. Water mobility and SDC in the gel layer of different HPMCs appeared to vary with degree of substitution of the polymer and the lowest values were obtained across the gel layer of K4M tablets. CONCLUSIONS: Water mobility varies across the gel layer of hydrating HPMC tablets and it is dependent on the degree of substitution of the polymer.
Chemical Phenomena↗
Cyclosporin A does not reverse clinical resistance to paclitaxel in patients with relapsed non-Hodgkin's lymphoma.
PURPOSE: Cyclosporin A has been shown to reverse paclitaxel resistance in vitro by inhibiting P-gp function. Therefore, we determined whether addition of cyclosporine to paclitaxel reversed clinical paclitaxel resistance in patients with non-Hodgkin's lymphoma (NHL). PATIENTS AND METHODS: Patients with relapsed NHL were eligible if they had no intervening treatment after failure to respond to paclitaxel (200 mg/m2 over 3 hours), and if they had adequate marrow, renal, and hepatic function, no serious cardiac disease, no CNS involvement, and no antibodies to human immunodeficiency virus-1. A cyclosporin A bolus dose (5 mg/kg over 3 hours) was followed by intravenous infusion (15 mg/kg) over 24 hours. Six hours after the beginning of cyclosporin A, the immediately preceding paclitaxel dose was administered over 3 hours. All patients were premedicated with dexamethasone, diphenhydramine, and cimetidine. Response was assessed after two cycles, and those patients who achieved at least a partial response received a maximum of six courses. RESULTS: All 26 patients entered were assessable for toxicity and 25 were assessable for response. One patient whose disease had progressed during paclitaxel treatment had a partial remission after the addition of cyclosporin A (response rate, 4%; 95% confidence interval, 1% to 20%). Disease progressed in 17 patients (71%) and did not respond in seven (25%). Serum cyclosporin A A levels measured at the time of initiation of paclitaxel infusion were greater than 2,000 ng/mL during 81% of cycles. Treatment toxicity included peripheral neuropathy in 57%, myalgia or arthralgia in 30%, neutropenia in 53%, neutropenic fever in 8%, and thrombocytopenia in 42% of patients. One patient with preexisting asthma had an acute bronchospasm during the first cycle and was removed from the study. There were no renal or hepatic toxicity and no infectious or hemorrhagic deaths. CONCLUSION: Cyclosporin A administered on this schedule did not reverse established clinical resistance to paclitaxel, which suggests that P-gp-mediated drug efflux is unlikely to be the only cause of paclitaxel resistance in this patient population.
Adult↗
Active acoustic screening: reduction of noise in gradient coils by Lorentz force balancing.
We have designed and constructed a quiet gradient set with restricted access for the combined purposes of evaluating the principles of active acoustic screening, recently introduced by Mansfield, Glover, and Bowtell, and for EPI studies of the head at 3.0 T. The design utilizes the return paths of the conductors in a closed arc loop arrangement to eliminate net Lorentz forces thereby attenuating acoustic noise especially at low frequency. This design should significantly reduce the dangers to patients of high noise levels, especially in high field magnetic resonance imaging systems.
Acoustics↗
NMR microscopy of single neurons using spin echo and line narrowed 2DFT imaging.
NMR microimages of single neural cells were acquired at 500 MHz using a conventional spin echo pulse sequence and a line-narrowing sequence that eliminates susceptibility effects. The data show that any contribution to the measured T2 relaxation rate arising from diffusion in local field inhomogeneities using spin echo sequences at high fields and high spatial resolution is relatively small. We conclude that the measured T2 difference between the nucleus and cytoplasm in these cells represents primarily a true T2 relaxation effect arising from the interactions of water with macromolecules in the two compartments and does not result from microsusceptibility differences. These observations have implications regarding water compartmentation in single cells and the interpretation of the MR characteristics of tissues in vivo.
Animals↗
Quiet transverse gradient coils: Lorentz force balanced designs using geometrical similitude.
The principle of active acoustic screening, recently introduced by Mansfield et al. (1) to reduce acoustic noise in gradient coils for MRI, is applied to the design of transverse distributed gradient coils of the fingerprint design. The results indicate that for complete Lorentz force balancing and for exact satisfaction of Kirchoff's law, it is necessary to have a coil system wound on four cylinders if full active magnetic screening of the assembly is required.
Magnetic Resonance Imaging↗
Measurement of fetal liver, brain and placental volumes with echo-planar magnetic resonance imaging.
OBJECTIVE: To quantify accurately in utero fetal liver, brain and placental volumes using echo planar imaging, and to assess whether the technique has the potential to enhance intrauterine fetal assessment. DESIGN: Thirty-two singleton, complicated pregnancies were scanned using echo planar imaging, a form of magnetic resonance imaging. Pregnancies were subdivided on the basis of whether the fetus was found subsequently to have an individualised birthweight ratio above (n = 21) or below (n = 11) the 10th centile. Comparisons of the organ volumes of these two groups were made. RESULTS: The first quantitative in utero measurement of fetal liver volume showed a linear relation between liver volume and gestational age in fetuses where the individualised birthweight ratio was above the 10th centile (the normal growth group). Ten of the 11 liver volume measurements of fetuses subsequently found to have an individualised birthweight ratio below the 10th centile fell on or outside the 95% confidence limits established for the normal growth group. In contrast, no such differences were demonstrated when the brain and placental volumes were considered, with 10 of the 11 brain measurements and all of the 11 placental measurements falling within the 95% confidence limits of the normal growth group. CONCLUSIONS: A single measurement of fetal liver volume using echo planar imaging enabled accurate identification of fetuses subsequently found to have individualised birthweight ratios below the 10th centile. If these findings are repeated in larger, more representative studies, this suggests that the technique has the potential to contribute to intrauterine fetal assessment.
Adult↗
An assessment of the intrauterine sound intensity level during obstetric echo-planar magnetic resonance imaging.
In order to assess the sound level experienced by the fetal ear during obstetric magnetic resonance imaging, a fluid filled stomach was used as an experimental model of the gravid uterus. A better than 30 dB attenuation in intensity was recorded across the frequency band of interest for all patient orientations. This was enough to reduce acoustic sound pressure from a level close to the instantaneous damage threshold (120 dB), to an acceptable level (< 90 dB). Direct mechanical coupling through the patient table was also shown to increase uterine sound pressure levels by as much as 10 dB. Much higher peak pressures could be obtained by tapping of abdomen with the fingers.
Acoustics↗
Fetal weight estimation by echo-planar magnetic resonance imaging.
Fetal weight was estimated in utero in eleven singleton pregnancies by measurement of fetal volume with echo-planar imaging (EPI), a form of magnetic resonance imaging, and by ultrasound measurements. EPI estimates of fetal volume were closely correlated with actual birthweight (R = 0.97). The median difference (expressed as a percentage of actual birthweight) between actual and EPI-estimated birthweights was 3.0% (range 0.6-9.9); this discrepancy was significantly smaller than that found for ultrasonographic estimates (6.5% [1.7-17.8]; p < 0.01).
Birth Weight↗
A microscope slide probe for high resolution imaging at 11.7 Tesla.
We present details of a novel RF coil for use in NMR microscopy. This coil is an inductively coupled surface coil which is built into a standard microscope slide. The coil is highly sensitive and is also designed so that the sample to be imaged can be viewed under an optical microscope. This facility allows comparison of optical and NMR micrographs, as well as accurate sample positioning. Using the slide coil, images of onion epidermal cells with an in-plane resolution of 4.5 microns have been produced.
Allium↗
Avoiding peripheral nerve stimulation: gradient waveform criteria for optimum resolution in echo-planar imaging.
Adaptation of Mansfield and Harvey's theory of magnetically induced neural stimulation indicates that, for trapezoidal gradient waveforms and at the relatively low modulation frequencies commonly used in echo-planar imaging, an increase in rise time even to the point of creating a triangular waveform can prove advantageous over the use of simple sinusoidal modulation. For example, a higher image resolution is in principle possible before the neural stimulation limit is reached. For higher modulation frequencies and fast ramp trapezoidal waveforms, the peak gradient can be lower than that for a sinusoidal waveform by a factor approaching 2/pi for equal resolution. This means that by using a multimode resonant gradient drive, the amplifier power requirements are greatly relaxed. The signal sampling bandwidth required is also lower, because, due to the trapezoidal nonlinear sample pattern, sample points are spaced linearly during the waveform plateaus.
Echo-Planar Imaging↗
Permeability estimation from T1 mapping.
Fluids permeating a solid matrix can interact strongly with the pores in which they are contained. Enhanced relaxation behaviour over that of the bulk water can ensue due to the presence of paramagnetic centres or to exchange with bound water at the pore surface. In the latter case, the ratio of pore surface to the pore volume is effective in the relaxation behaviour. NMR provides an effective tool for investigating the solid matrix properties (e.g., pore size distribution) via indirect measurement of the fluid NMR parameters. In addition to spin density, we use T1 mapping to provide an estimate of the specific permeability of sandstone for a few samples.
Echo-Planar Imaging↗
Studies of fluid transport in porous rocks by echo-planar MRI.
Attempts to quantify the permeability constant that appears in Darcy's equation in terms of the porosity, tortuosity and surface area have been made by Kozeny and Carman. These results in turn have been translated by Seevers into expressions involving spin-lattice relaxation times. When this work was done originally in the mid-1960s, NMR imaging and spatially localised T1 maps had not been invented. Therefore, bulk T1 average values were used and it is not surprising to see substantial deviations from predicted permeabilities in bore core material. In this paper we re-examine the Kozeny-Carman and Seevers theories in the light of new techniques development for the localised measurement of both T1 maps and fluid velocity maps. New results show spatially correlated T1 and flow maps obtained from Bentheimer sandstone samples. These are discussed in terms of a localised permeability constant. By this means we show that the relationship between T1 and permeability does not hold at the local level for isolated pixels within a larger specimen.
Echo-Planar Imaging↗