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P R Moran

Publications and source records attributed to P R Moran.

At least 19 recordsLinked to original sources
PubMed1991

Observations on maximum entropy processing of MR images.

A maximum entropy (MAXENT) criteria for MR image processing optimizations has previously shown poor performance, but this note observes that there are two entirely different kinds of "data transmission" applications which appear to have been intermixed. In the two cases, "image entropy" actually refers to different kinds of data variables. The previous literature formulations are for transfer of data in which pixel-locations are the transmitted variable, and these pixels may be neither uniform nor constant. The second application concerns the MRI data set for display. Its data variables are image pixel-values of magnetization intensity, and the data transfer mode has the sense of visual display. When MAXENT criteria are modified to address an array of pixel-value intensities, and use a pixel-value information entropy rather than pixel-locations entropy, then successful data processing results. Restoring display visualization from highly nonuniform surface coils for lumbar spine scans are demonstrated, as an example of MAXENT usefulness.

Image Processing, Computer-Assisted↗
PubMed1991

Spatially resolved flow velocity measurements and projection angiography by adiabatic passage.

This paper describes the basic principles of gradient modulated adiabatic passage using a CW radiofrequency excitation. The possible applications of this technique include a direct assessment of in-plane and oblique directional flow velocities, and visualization of flow velocity profiles. Flow angiography based on the time-of-flight technique is also discussed with experimental results.

Angiography↗
PubMed1991

Experiments for two MR imaging theories of motion phase sensitivity.

Two theories of motion-sensitive phase shifts in magnetic resonance (MR) imaging result in different mathematical predictions of the observed effects of gradient modulation-induced motion artifacts. The consequences are critical for gradient waveform designed to minimize motion artifact contaminations from time-dependent motion sensitivity. To resolve this discrepancy with a test case (the monopolar waveform of a commonly used, discretely pulsed encoding phase gradient), computer integration of the fundamental Bloch equations for MR imaging with motion was performed. Simulation images for constant and erratic motion showed almost complete agreement with the predictions of the transport integral solutions for motion phase sensitivity; the artifact was solely time-of-flight oblique flow misregistration. Conventional method-of-moments gradient moment nulling compensations produced greater motion artifacts in experiments than did use of no waveform compensation at all. Transport equation solutions implied second-integral zeroing instead; these modifications eliminated the artifacts.

Magnetic Resonance Imaging↗
PubMed1986

Tissue contrast enhancement: image reconstruction algorithm and selection of TI in inversion recovery MRI.

It is clearly demonstrated that the proper application of the inversion recovery imaging pulse sequence is dependent on the method of image reconstruction and the selection of TI for optimum tissue contrast. There are two methods of 2DFT image reconstruction of IR sequence time-domain raw data. The first is a modulus-image reconstruction algorithm (contrast-obliterating option), and the second is a phase-correction routine for reconstructing "phase-sensitive" true IR-images. The second option generates proper "in-phase" images, retains proper scale of contrast, but can invert the algebraic sign of image-values under certain conditions. A series of "phase-sensitive" and "modulus" reconstructed brain images, obtained with conventional and optimized new IR pulse sequences, are shown to demonstrate these effects. They illustrate the considerable advantages gained, in practical clinical situations, if one generates "phase-sensitive" true IR-images from IR-sequence raw data at optimum TI for tissue contrast enhancement.

Algorithms↗
PubMed1986

Paramagnetic macrocyclic complexes as contrast agents for MR imaging: proton nuclear relaxation rate enhancement in aqueous solution and in rat tissues.

Paramagnetic macrocyclic chelates show promise as magnetic resonance (MR) imaging contrast agents due to stability and relaxivity comparable to those of DTPA-type chelates. For the three copper and manganese macrocyclic complexes studied in aqueous solution, T1 and T2 relaxivities ranged from 0.14 to 5.88 mM-1sec-1 at 6.25 MHz. In rats, the intravenous administration of 16 mumol/kg of Mn(cyclam) caused the liver T1 relaxation rate to double at 15 minutes after injection. T1 measurements by pulsed MR imaging and manganese analyses on excised tissue showed that both relaxation rate (1/T1) and manganese content of liver and kidney increase linearly with the dosage of Mn(cyclam). The linear relationship between 1/T1 and manganese content can be considered an "in tissue" relaxivity plot for the agent. The resulting relaxivity is 54 mM-1sec-1 in liver, compared with 3.1 mM-1sec-1 in aqueous solution. Although this work is preliminary, the implication for medical MR imaging applications is that macrocyclic contrast agents can be effective at approximately one-tenth the current typical dose used for gadolinium DTPA.

Animals↗
PubMed1985

Verification and evaluation of internal flow and motion. True magnetic resonance imaging by the phase gradient modulation method.

We report qualitative and quantitative evaluation and verification studies of the bipolar phase gradient modulation method for true MR imaging of internal flow and motion velocities. Velocity encoding modulations provide speed-of-motion and direction-sensitive images using special phase-sensitive reconstructions. True motion MR imaging does not depend upon subject parameters, T1 or T2, nor upon selective active-volume time-of-flight calculations, nor is it limited strictly to fluid-flow velocities. Conventional MR sequences often induce strong accidental phase gradient modulations that can cause severe artifacts in conventional MR scans and limit the useful sensitivities of true motion MR. Multiple steps of velocity encoding allow resolution of separate elements of the velocity spectrum, and enable suppression of all such phase-artifact difficulties. Some view-to-view phase inconsistencies are intrinsic to the subject being scanned, e.g., strong motion variations during the heart cycle; limitations due to such effects require external modifications in the scanning, such as cardiac gating. Since conventional density information remains in the data, independent of velocity encoding modulations, we suggest a multiple encoding sequence and saving the MR raw data. These evaluations and verifications demonstrate exciting potential in clinical application for the phase gradient modulation method of true flow and motion MR imaging.

Biophysical Phenomena↗
PubMed1985

Simultaneous MR imaging of both breasts using a dedicated receiver coil.

We have designed and built a dedicated magnetic resonance (MR) coil that images both breasts simultaneously with the patient in a prone position, incorporates imaging advantages of surface coils, and benefits from having separate transmitter and receiver coils. This coil is compatible with a 0.15-T (6.3 MHz) resistive-magnet unit. It works as a simple plug-in replacement for the standard receiver coil. The unit's triple-coil structure consists of two outer coils that lie close to the lateral surface of the right and left breast and a central coil positioned between the breasts. A two-chambered box supports the coils. Breast-coil image-reception sensitivity is three to seven times greater than values obtained with a whole-body coil and shows a smooth spatial variation without oscillatory or sharply breaking behaviors. Increased sensitivity for breast tissue allows us, with a given imaging time, to use thinner sections (5 mm thick) than are possible with the whole-body coil. Since the coil is insensitive to organs such as heart and lung, motion artifact is eliminated, and image quality and resolution are further increased. Simultaneous imaging of both breasts allows direct comparison and increases patient throughput.

Breast↗
PubMed1977

Thermoluminescent response of LiF (TLD-100) to 5-30 keV electrons and the effect of annealing in various atmospheres.

The response of single crystal and extruded ribbons of TLD-100 to 5-30 keV electrons was investigated. If annealing is done in a vacuum, the sensitivity of TLD-100 single crystals to these electrons and the resultant glow curve are essentially the same as when irradiation are carried out with 137Cs gamma rays. All discrepancies in sensitivity can then be accounted for by the higher LET of electrons. The commonly used 'standard annealing' at 400 degrees C for one hour produced a change in the glow curve shape and a loss in sensitivity in contrast to the vacuum anneal results. Diffusion of hydroxyl ions into the sample during air annealing is believed to be the primary cause for this change. These results explain the source of the 'dead layer' proposed to explain the variation with particle size of the luminescent efficiency of X-ray irradiated TLD-100 powder and the low TL efficiency from low energy electron irradiations. With the use of the vacuum annealing procedure, the same sensitivity and reproducibility can be achieved for the dosimetry of low energy electrons and other shallowly penetrating radiation as is currently achieved for the dosimetry of X-rays.

Atmosphere↗
PubMedDate not supplied

Design modification of dedicated MR breast coil.

We recently reported on a dedicated MR receiver coil for simultaneous breast imaging. We here describe a new design that has increased sensitivity and signal-to-noise ratio and has decreased the spatial variation of reception sensitivity seen with the original design. This breast coil is compatible with a 0.15 T resistive magnet utilizing separate transmit and receive coils and works as a plug-in replacement for the standard receiver coil. As with the original, the modified breast coil uses a triple coil structure. A central coil situated between the breasts consists of an inner loop in vertical plane and two outer loops facing outward at 45 degrees from horizontal. Two outer coils are situated lateral to each breast and consist of an outer loop in vertical plane and an inner loop facing inward at 65 degrees from horizontal plane. A two-chambered clear plastic box supports the coils and allows for accurate patient positioning. The modified coil is insensitive to heart and lung movement, eliminating motion artifacts produced by these organs, and further increasing image quality and resolution.

Breast↗
PubMedDate not supplied

MR flow imaging in projection through a stationary surround.

A magnetic resonance imaging technique is discussed which, by cyclic inversion of the longitudinal magnetization, produces boli of moving material with alternating sign of the magnetization. At periodic spacings along the flow direction, the signal strength from magnetization of positive sign is equal to that of negative sign. This results in a minimum in the intensity distribution. A banded intensity structure results reflecting the distribution of flow velocities across the imaged vessel. The inversion of the longitudinal magnetization causes an inherent suppression of the signal from stationary material allowing the collection of flow images in projection through a stationary surround without the need for image subtraction.

Blood Flow Velocity↗
PubMedDate not supplied

Nuclear magnetic resonance (NMR) relaxation spectroscopy in tissues.

Nuclear magnetic resonance (NMR) techniques have been used to study several in vivo and stabilized tissue samples. The results show that a multicomponent behavior characterizes the magnetization relaxation of all investigated samples. Various specimens were allowed to undergo necrotic processes and then they were examined with the same techniques used in in vivo tissue. A marked approach toward a single-exponential magnetization-decay behavior was observed in these necrotic samples. In addition, large and sometimes irreversible temperature variations have been observed in the relaxation parameters of several preserved and stabilized tissue samples. The most dramatic changes observed throughout these experiments relate to the long-lived magnetization components, and are not observed in in vitro experiments performed solely on necrotic tissues. Meaningful differentiation between normal and neoplastic tissue by NMR techniques is virtually useless unless the roles of the temperature and necrosis on the different magnetization-decay components are well understood.

Animals↗
PubMedDate not supplied

NMR relaxation behavior in living and ischemically damaged tissue.

A study by pulsed NMR techniques in living liver tissue has led to the discovery that the observed longitudinal relaxation decay behavior is strongly multicomponent. After death of the experimental animal, the relaxation decay curves evolve toward a single-component behavior. These changes can also be observed within a few minutes after the liver is excised and placed in a test tube, and they involve a high degree of quantitative and qualitative regularity and reproducibility. An excellent description of all observed NMR behavior is obtained from a dynamic two-compartment model. Rapidly relaxing volumes exchange water molecules with slowly relaxing volumes; associating only an increasing water molecule exchange rate with increasing ischemia accounts in quantitative detail for all observed changes. The exchange-rate values and their variation with tissue deterioration are in good agreement with that estimated for intra- to extracellular water exchange as limited by cell-membrane osmotic permeabilities. Possible applications of these results in different biomedical areas are discussed.

Animals↗