Rowland W. Redington

Human exposure to 4.0‐Tesla magnetic fields in a whole‐body scanner

Details are given for the design, construction, properties, and performance of a large, highly homogeneous magnet designed to permit whole-body magnetic resonance imaging and spectroscopy at 4 T. The magnet has an inductance of 1289 H and a stored energy of 33.4 MJ at rated field. The health of a group of 11 volunteers who had varying degrees of exposure to this field was followed over a 12-month period and no change that could be associated with this exposure was detected. A mild level of sensory experiences, apparently associated with motion within the field of the magnet, was reported by some of the volunteers during some of their exposures. A questionnaire regarding sensory effects associated with magnetic resonance scanners and possibly caused by the static magnetic field of these instruments, was given to nine respondents who had experience within both 1.5-T scanners and this 4-T scanner and to another group of 24 respondents who had experience only within 1.5-T scanners. For the sensations of vertigo, nausea, and metallic taste there was statistically significant (p less than 0.05) evidence for a field-dependent effect that was greater at 4 T. In addition, there was evidence for motion-induced magnetophosphenes caused by motion of the eyes within the static field. These results indicate the practicality of experimental whole-body body scanners operating at 4 T and the possibility of mild sensory effects in humans associated with motion within a static magnetic field. The results also indicate the likelihood of a wide margin of safety for the exposure of noncompromised patients to the static fields of conventional magnetic resonance scanners operated at 1.5 to 2 T and below.

Orbital Magnetic Resonance Imaging

Magnetic resonance images of the eye and orbit performed with surface coils at 1.5 tesla showed anatomic details superior to those of conventional third- and fourth-generation computed tomography.

Resistive NMR of intracranial hematomas.

SummaryComparison between computed tomography and nuclear magnetic resonance imaging in 17 patients with intracranial hematomas indicates a distinct role for NMR in evaluating the stable patient with hematoma. NMR is useful for delineating the extent of the hematoma, the relationship of the hematoma to brain anatomy, and the presence of hematoma at a time when the hematoma is isodense on CT.

Doped Silicon and Germanium Photoconductors as Targets for Infrared Television Camera Tubes

Several doped germanium and silicon photoconductors have been investigated as targets for an infrared television camera tube. The performance of gold-doped silicon is outstanding. Its properties, sensitivity, speed of response, and freedom from various image retention effects are superior to those of a standard vidicon in the visible. It is within an order of magnitude of the maximum performance to be expected of a tube of the vidicon type. The other silicon dopings investigated were gallium, bismuth, and indium. These materials showed very little extrinsic photoconductivity. Copper-, gold-, silver-, and tellurium-doped germanium were also investigated. Targets prepared with all of these germanium dopings showed the development of an insensitive, nonimaging state in a few minutes’ operation. The original imaging state could be recovered by a short change in operating conditions. This nonimaging state has been demonstrated to be due to an induced surface conductivity.

Medical imaging systems

The invention of the stethoscope in 1816 opened a new era in diagnostic medicine. For perhaps the first time the physician, aided by an instrument of science, could obtain information from the inside of the human body without surgical intervention. With the help of this simple instrument the trained practitioner could form an impression of the state of form and function of a variety of internal organs. The stethoscope can be considered a precursor of modern medical imaging systems, systems designed to provide information about the bodys interior with minimum risk to the patient. The 19th century brought two other important medical imaging instruments, the opthalmascope, used to study the retina, and the first x‐ray imagers.

Cerebral NMR: diagnostic evaluation of brain tumors by partial saturation technique with resistive NMR.

SummaryOne hundred and forty patients with cerebral neoplasms were examined in a 0.12-Tesla prototype resistive NMR proton imaging device by partial saturation technique. NMR was superior to CT in tumor and edema localization and equal to CT in tumor and edema detection. NMR, however, was not able to clearly separate tumor from edema, a separation that contrast enhanced CT achieved.

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.

Technical alternatives in nuclear magnetic resonance (NMR) imaging

In this paper we consider the choice of the magnetic field for an imaging system based on the nuclear magnetic resonance of hydrogen. We show by analysis that the quality, or contrast-to-noise ratio, of images based on T1 discrimination increases with field or frequency up to 2 T or 85 MHz. After a brief discussion of potential engineering limitations we present results showing that images of the human head with excellent anatomic detail can be produced at 1.5 T or 64 MHz.

Imaging With Nuclear Magnetic Resonance (NMR) In A 0.12 T Resistive Magnet

Images of the head, torso, and limbs have been obtained using the nuclear magnetic reso-nance (NMR) of hydrogen. Images are presented and the imaging technique and apparatus are described. The mode of imaging, a spin warp 2-D Fourier transform technique with T1 discrimi-nation through partial saturation, is discussed and shown to be less demanding of field homogeneity than other techniques. The radio-frequency (RF) magnetic fields and pulsed field gradients are shown to be below the recommended limits for power deposition and induced electric fields.

Electrostatic optics for camera tubes

Two versions of an electrostatic focusing and deflection system suitable for camera tube applications are described. Focusing properties, resolution and aberrations are discussed.