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Biomedical subjects

W A Edelstein

Publications and source records attributed to W A Edelstein.

35 records · Page 2Linked to original sources
PubMed1984

Cerebral magnetic resonance: comparison of high and low field strength imaging.

Low field strength (0.12 Tesla resistive) and high field strength (1.0, 1.4, or 1.5 Tesla superconductive) magnetic resonance imagers were compared for their ability to detect central nervous system lesions. Sixteen adult patients with known lesions and three normal volunteers were studied. Contrast-enhanced computed tomography was used as the standard. The data demonstrate that imaging at high magnetic field strength is superior to low field strength imaging for the detection and delineation of lesions. This finding can be explained by the superior signal-to-noise ratio achievable at the higher magnetic field strengths. High field MR imaging was also found to outperform CT in demonstrating anatomic details and relationships. It is predicted that the use of low saturation (e.g., long TR spin echo technique) will make the gain in contrast-to-noise ratio even more significant.

Adenoma↗
PubMed1983

Signal, noise, and contrast in nuclear magnetic resonance (NMR) imaging.

Calculations of the sensitivity of the saturation recovery and inversion recovery pulse sequences used in nuclear magnetic resonance imaging show the former to be superior in discriminating between tissues with the same proton density but different T1's. Two other pulse sequences, which are combinations of the above, have also been analyzed. These have lower T1 discrimination sensitivity, but other considerations, such as self-normalization, may still make them attractive. The calculations are only valid for selective excitation pulse sequences in which the selected slice profiles are approximately rectangular, and thus a sin(bt)/t radiofrequency excitation is desirable. In order to ensure that the saturation recovery sequence gives valid results for pulse repetition times comparable to or shorter than T2, it is necessary to destroy the coherence between pulse applications. For this purpose we use a series of "spoiler" gradient pulses between pulse trains. The saturation recovery pulse sequence also has the advantage that, by the correct choice of interpulse spacing, sensitivity close to the optimum T1 discrimination can be achieved over a wide range of T1 values. This has the potential advantage to the clinician of simplifying his choice of parameters for imaging.

Humans↗
PubMed1983

Nuclear magnetic resonance imaging: contrast-to-noise ratio as a function of strength of magnetic field.

The choice of the strength of the magnetic field for an imaging system based on the nuclear magnetic resonance of hydrogen is considered. It is shown by an analysis based on in vitro data that the quality, or contrast-to-noise ratio, of images based on T1 or T2 discrimination increases with field up to 1.5-2 T. After a brief discussion of potential high-field limitations, results are presented which show that images of the human head with excellent anatomic detail can be produced at 1.5 T or 64 MHz.

Magnetic Resonance Spectroscopy↗
PubMed1982

Head and body imaging by hydrogen nuclear magnetic resonance.

A hydrogen (1H) nuclear magnetic resonance (NMR) imaging study of the normal head, thorax, and limbs is reported. The images are 10 to 15 mm thick transverse slices obtained in 2 to 4 min using a two-dimensional Fourier transform technique. Spatial resolution in the imaging plane is about 2 mm, enabling the optic nerve and many small blood vessels to be observed. Thorax scans show details of the cardiac chambers, aorta wall, and lungs without artefacts arising from physiological motion.

Extremities↗
PubMed1980

In vivo n.m.r. imaging in medicine: the Aberdeen approach, both physical and biological.

A novel magnetic field and radio frequency (1.7 MHz) pulse sequence is described for a whole body n.m.r. imaging machine under construction. Selective excitation is used to obtain signals from successive lines of proton spins(water) across the body to build up an image of a transverse section. The images display spin concentration and spin-lattice relaxation time, T1, separately. For a 50% change in T1 to be discerned in the human trunk, a spatial resolution of 2 cm3 is expected for a 2 min scan and 0.5 cm3 for a 30 min scan. Very preliminary images at the present incomplete stage of development show the geometrical accuracy and T1 discrimination: an in vivo image demonstrates some of the difficulties to be overcome. In vitro measurements of normal rabbit tissue samples have been made at 24 MHz to map the T1 distributions that can be expected from normal subjects. The transposition of this information from rabbit to man, and from 24 MHz to 2.5 MHz have been checked and the comparison shown to be meaningful. Of pathological samples, human breast tumour and human liver metastases offer a good contrast to their surrounding tissue, and an experimental investigation has shown that tissue immediately surrounding a tumour also has an elevated T1 value. A wide range of abnormalities that are associated with abnormal fluid formation in the body may be amenable to imaging by the n.m.r. technique. Potential hazards are believed to be small in the present generation of equipment.

Animals↗
PubMedDate not supplied

Power deposition in whole-body NMR imaging.

The surface radio frequency (rf) power absorption in human head and torso nuclear magnetic resonance (NMR) imaging experiments is estimated. The results are expressed as a function of the NMR frequency, the rf pulse length, and the pulse duty cycle, which are varied over six orders of magnitude for general applicability. The results are compared with average metabolic levels and the limits advised by the National Radiological Protection Broad of the United Kingdom. Heating due to time-dependent magnetic field gradients is discussed.

Biophysical Phenomena↗
PubMedDate not supplied

A signal-to-noise calibration procedure for NMR imaging systems.

A nuclear magnetic resonance (NMR) imaging system signal-to-noise calibration technique based on an NMR projection of distilled water in a cylindrical bottle is proposed. This measurement can characterize any arrangement of rf coils in any magnetic field as signal to noise per ml times root Hz. Inductive losses in a typical patient must be included in the calibration, and such losses can be simulated in a particular system by an externally attached resistor(s) appropriate to that system. Alternatively, an rf inductive damping phantom consisting of a conducting loop of wire containing an appropriate resistor is suggested that can be inserted into any NMR imaging coil to simulate subject Q damping. The same resistor can be used, independent of the details of the coil construction. Furthermore, if the loop inductance is tuned out at each frequency with a series capacitor, then the same loop resistance will serve for all frequencies as a good approximation to human subject damping. This "projection method" signal-to-noise ratio is related to the conventional signal-to-noise ratio measured from a Lorentzian-shaped spectral line as psi P = psi L [2/T2]1/2, where psi stands for signal-to-noise ratio, subscripts P and L stand, respectively, for the projection and "Lorentzian" methods, and T2 is the transverse relaxation time of the spectral line used in the Lorentzian method.

Humans↗
PubMedDate not supplied

NMR imaging in the presence of magnetic field inhomogeneities and gradient field nonlinearities.

The relative merits of the spin-warp method and the multiple-angle projection-reconstruction method are assessed for nuclear magnetic resonance imaging in the presence of magnetic field inhomogeneities. The results of computer modeling studies demonstrate the superiority of the spin-warp method under these conditions. Because the form of the point spread function for the spin-warp approach is insensitive to magnetic field irregularities, simple correction algorithms have been developed to reduce artifacts associated with bias field inhomogeneities. In addition, the formalism developed for magnetic field inhomogeneities can be easily extended to correct for gradient field nonlinearities.

Computers↗