Prospects for increasing the accessibility of MRI.
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California↗
Biomedical subjects
J Hoenninger
Publications and source records attributed to J Hoenninger.
Magnetic resonance imaging the velocity vector components of fluid flow.
Encoding the precession phase angle of proton nuclei for Fourier analysis has produced accurate measurement of fluid velocity vector components by MRI. A pair of identical gradient pulses separated in time by exactly 1/2 TE, are used to linearly encode the phase of flow velocity vector components without changing the phase of stationary nuclei. Two-dimensional Fourier transformation of signals gave velocity density images of laminar flow in angled tubes which were in agreement with the laws of vector addition. These velocity profile images provide a quantitative method for the investigation of fluid dynamics and hemodynamics.
Fourier Analysis↗
Thin-section definition in magnetic resonance imaging. Technical concepts and their implementation.
In multisection magnetic resonance imaging, gradient strength and earliest desired echo time (TE) set a limit to the thinnest section achievable. Offset radio-frequency irradiation techniques and phase encoding within a thick section make possible the production of thin sections of clinically useful quality in practical imaging times.
Brain↗
Magnetic resonance imaging performance: a comparison of sodium and hydrogen.
Although many nuclei can be used to produce magnetic resonance (MR) images, technical considerations dictate the choice of certain of these. Hydrogen is the most favorable, followed by sodium. We present an evaluation of the imaging performance of sodium MR imaging based on imager performance and biologic factors. Because it is hampered by high operating fields, low signal-to-noise levels, and radiofrequency power deposition constraints, careful clinical comparisons will be needed to identify a diagnostic niche that could take advantage of the large sodium differences known to exist within biologic systems.
Brain Neoplasms↗
High-resolution magnetic resonance imaging. Technical concepts and their implementation.
In magnetic resonance (MR) imaging manipulating spatial resolution, contrast resolution, and imaging time separately results in improvement in some parameters without degradation of others. The authors have found that MR imaging of the head with a repetition time TR = 2.0 seconds produces images with high signal-to-noise levels and excellent sensitivity to demyelinating disease and brain water content. In the body, a long TR yields large signal levels that permit delineation of low-intensity structures such as patent vessels and bone. The long TR technique can be used in a high-resolution mode (256 X 256 data acquisition elements, each 0.8 X 0.8 mm) while maintaining image times of 50 or 100 sec/section. For normal resolution (1.7 X 1.7 mm), imaging time is 25 or 50 sec/section. It is concluded that the combination of slow-imaging techniques with simultaneous multisection imaging will prove practical for clinical MR.
Brain↗
Magnetic resonance imaging: effects of magnetic field strength.
Magnetic resonance images of the head, abdomen, and pelvis of normal adult men were obtained using varying magnetic field strength, and measurements of T1 and T2 relaxations and of signal-to-noise (SN) ratios were determined. The T1 relaxation of gray matter, white matter, and muscle increases and T2 decreases with field strength, while T1 of fat remains relatively constant and T2 increases. As a consequence, for any one spin echo sequence, gray/white matter contrast decreases and muscle/fat contrast increases with field. SN levels rise rapidly up to 3.0 kgauss and then change more slowly, actually dropping for muscle. The optimum field for magnetic resonance imaging depends on tissue type, body part, and imaging sequence, so that it does not have a unique value. Magnetic resonance systems that operate in the 3.0-5.0 kgauss range achieve most or all of the gains that can be achieved by higher magnetic fields.
Abdomen↗
Pulsatile blood velocity in human arteries displayed by magnetic resonance imaging.
The authors describe a new method for magnetic resonance (MR) imaging of flowing protons which can illustrate relative blood velocity in the arteries supplying the brain. The magnetic gradient pulse sequence was synchronized to the cardiac cycle at 100-msec. increments to track pulsatile blood flow perpendicular to the image plane. The magnitude of the signal increased with the velocity of blood in major arteries flowing in the direction of the spatially offset refocusing plane. The blood velocity in the vertebral and internal carotid arteries varied as a function of the phase of the cardiac cycle, and the velocity profiles across the vascular lumina were compatible with laminar flow.
Blood Flow Velocity↗
Nuclear magnetic resonance imaging of mammary adenocarcinomas in the rat.
A study of 24 rats implanted in the hind leg with mammary adenocarcinomas and five sham-implanted rats, followed from the second to the eight week postimplantation, showed nuclear magnetic resonance imaging capable of detecting all the tumors without yielding any false-positives in the control rats. The T1 relaxation time of tumors overlapped that of muscle, and the T2 times overlapped fat, but the combination was unique when comparing tumors to muscle and fat. Necrotic regions of the tumor and the bladder contents tended to have very long T1 and T2 relaxation times. The difference in relaxation time between tumors and muscle could be accounted for in terms of water content, which was approximately 8% higher for the tumors. The study corroborates data from previous studies indicating that NMR imaging is a highly sensitive modality, although T1 and T2 times are not exclusive indicators of malignancy.
Adenocarcinoma↗
Clinical efficiency of nuclear magnetic resonance imaging.
Advances in imaging technique have improved the efficiency of clinical nuclear magnetic resonance (NMR) imaging, and will allow total patient examination time that equals or is more favorable than that of x-ray computed tomography (CT). The whole head can be examined with NMR in a 6.5-minute imaging time with a spatial resolution of 1.7 mm. Fifteen sections in the body can be similarly imaged. Quantitative T2 ("spin-spin" relaxation time) information, as well as estimates of T1 ("spin-lattice" relaxation time) can be obtained in this time. Quantitative T1 information requires an additional procedure.
Brain Neoplasms↗
Nuclear magnetic resonance whole-body imager operating at 3.5 KGauss.
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Humans↗
Visualization of cerebral and vascular abnormalities by NMR imaging. The effects of imaging parameters on contrast.
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Brain Diseases↗
Nuclear magnetic resonance imaging of the abnormal live rat and correlations with tissue characteristics.
Nuclear magnetic resonance (NMR) images of live rats with sterile and pyogenic abscesses, hematomas, and various implanted and spontaneous neoplasms demonstrated good contrast differentiation between pathologic and surrounding normal tissues. This differentiation was maximal when both the T1 and T2 tissue relaxation times were used as criteria. Neoplasms have a broad range of T1 and T2 values and may be confused with abscesses or hematomas. Tissue rate constants (1/T1 and 1/T2) are mainly dependent on total water content, the exception being fat, which has a 1/T2 value much shorter than that expected on the basis of water content alone.
Abscess↗
Nuclear magnetic resonance imaging.
NMR imaging is based on the ability to induce and monitor resonance of the magnetic moment of nuclei with an odd number of protons and/or neutrons in the presence of magnetic fields. By the use of magnetic fields whose strength varies with position, it is possible to define both the location and concentration of resonant nuclei, and, thereby, to create images that reflect their distribution in tissue. Hydrogen because it is the most sensitive of the stable nuclei to NMR and because it is also the most abundant nucleus in the body, is ideally suited for NMR imaging.
Animals↗
In vivo imaging of the rat anatomy with nuclear magnetic resonance.
Live rats were imaged by nuclear magnetic resonance (NMR). These images demonstrated fine detail and high object contrast. Motion artifacts are not apparent in 4-minute images, and major blood vessels are demonstrated as regions of low signal intensity because of blood flow. Selective contrast enhancement is possible by varying NMR imager accumulation parameters.
Animals↗
Tomography of hydrogen with nuclear magnetic resonance.
A nuclear magnetic resonance (NMR) imager with a 6.5-cm aperture is described. Spatial resolution is 0.47 X 2.0 mm with a slice thickness of 8.4 mm. Contrast resolution is 3% for a 4-minute image. Because of the excellent spatial resolution and high contrast between soft tissues, the images provide a great deal of detail and reconstruction artifacts due to motion are avoided. Blood flow can be observed, and selected enhancement of lesions thorough the modification of software-controlled operational parameters is demonstrated.
Animals↗
An evaluation of cadmium telluride detectors for computer assisted tomography.
Cadmium telluride (CdTe) presents a set of extremely attractive features as an X-ray detector for computer assisted tomography (CAT). It is stable and easily handled; has a high detection efficiency and very efficient conversion of energy to charge; and permits a high element density in a compact configuration. Unfortunately, effects due to "polarization," "tailing," high and variable leakage currents, and long "memory" are incompatible with the needs of CAT instrumentation. Pulse-processing techniques have allowed us to eliminate these problems in positive-sensitive detectors, thus opening the way for utilization of CdTe in CAT.
Cadmium↗
Imaging characteristics of a small germanium camera.
A high purity germanium gamma-camera has been developed and is currently being evaluated. This camera incorporates unique performance parameters such as a 2 mm full-width spatial response function with rejection of multiple-scatter in the detector, a 2.2% FWHM energy resolution for 99 mTc, a 180 nsec paralyzable dead-time, and a 2 mu sec non-paralyzable dead-time. Imaging studies demonstrate the superior capabilities of this instrument.
Animals↗
An evaluation of HgI2 detectors for x-ray computed tomography.
Mercuric iodide (HgI2) presents a set of attractive features as a semiconductor x-ray detector for computed tomography (CT). Its response is stable, it operates at room temperature, and thin detectors have a high detection efficiency. The properties of HgI2 permit the assembly of high spatial resolution detectors in a compact configuration. On the other hand, HgI2 exhibits a long memory, and some detectors also exhibit polarization effects, both of which are detrimental in CT. A pulse-shaping technique has been used to overcome these effects, thus demonstrating the suitability of HgI2 for use in CT.
Iodides↗