Very heavy solar cosmic rays: energy spectrum and implications for lunar erosion.

The energy spectrum of solar cosmic-ray particles of the iron group has been determined for the first time over the energy range from 1 to 100 million electron volts per nucleon by the use of glass removed from the Surveyor 3 spacecraft. The difference between the observed (energy)(-3) spectrum and the limiting spectrum derived previously from tracks in lunar rocks gives an erosion rate of 0 to 2 angstroms per year. High-energy fission of lead, induced by galactic cosmicray protons and alpha particles, has also been observed.

Particle track identification: application of a new technique to apollo helmets.

The Apollo helmets are being used to record the dose of heavy particles to which astronauts are exposed on space missions. An improved method for examining and identifying the etched tracks of heavy charged particles consists of replicating tracks and measuring the etching rate as a function of position along the track. Tracks have been observed in Apollo helmets that correspond to ionized atoms heavier than iron.

Cosmic-ray tracks in plastics: the apollo helmet dosimetry experiment.

Counts of tracks from heavy cosmic-ray nuclei in helmets from Apollo missions 8 and 12 show variations caused by solar modulation of the galactic cosmic-ray flux. Specific estimates of the biological damage to certain nonreplaceable cells by track-forming particles during these space missions indicate that the fraction of deactivated cells could range from a lower limit of 3 x 10(-7) to an upper limit of 1.4 x 10(-4).

Apollo 14 and apollo 16 heavy-particle dosimetry experiments.

Doses of heavy particles at positions inside the command modules of Apollo missions 8, 12, 14, and 16 correlate well with the calculated effects of solar modulation of the primary cosmic radiation. Differences in doses at different stowage positions indicate that the redistribution of mass within the spacecraft could enhance safety from the biological damage that would otherwise be expected on manned, deep-space missions.

Particle Track, X-ray, Thermal, and Mass Spectrometric Studies of Lunar Material.

Particle tracks in Apollo 11 samples are dominantly of cosmic ray and solar origin: primary galactic and solar flare particles, likely spallation recoil tracks, and possible solar-wind heavy particles. The energy spectrum of irongroup nuclei is inferred from track density gradients in surface layers, and a limit of << 10(-7) centimeter per year is deduced for the surface erosion rate. From cosmic ray tracks in rock and core samples it is clear that the lunar soil is stirred often during each few million years. X-rays reveal augite, anorthite, olivine, ilmenite, troilite, nonmeteoritic iron, and assorted glasses, but no major structural damage. Hydrogen, helium, and other gases in the fines are compatible with expected solar wind ratios.

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.

3D reconstruction of the brain from magnetic resonance images using a connectivity algorithm.

We present high resolution three dimensional (3D) connectivity, surface construction and display algorithms that detect, extract, and display the surface of a brain from contiguous magnetic resonance (MR) images. The algorithms identify the external brain surface and create a 3D image, showing the fissures and surface convolutions of the cerebral hemispheres, cerebellum, and brain stem. Images produced by these algorithms also show the morphology of other soft tissue boundaries such as the cerebral ventricular system and the skin of the patient. For the purposes of 3D reconstruction, our experiments show that T1 weighted images give better contrast between the surface of the brain and the cerebral spinal fluid than T2 weighted images. 3D reconstruction of MR data provides a non-invasive procedure for examination of the brain surface and other anatomical features.

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.

Noninvasive imaging of the normal temporal bone. Comparison of sagittal surface coil magnetic imaging and high-resolution computed tomography.

High-resolution computed tomography (HRCT) is a noninvasive technique for evaluating the middle ear for primary and recurrent cholesteatoma. However, a limitation of HRCT is that it cannot differentiate between cholesteatoma and granulation tissue. Magnetic resonance imaging (MRI) is a noninvasive, nonradiologic technique that has been effective in demonstrating histochemical differences between various soft tissues. We present images from a normal living subject's temporal bone in the sagittal plane obtained with both HRCT and MRI. Anatomic correlates in the same cut planes are presented. The HRCT provided excellent detail of the bony landmarks within the temporal bone and was used as the reference for the MRI. The soft-tissue structures such as cranial nerves, cochlea, vestibule, and semicircular canals were identified.

Magnetic resonance angiography.

Pulse sequences that permit selective detection of moving spins in a magnetic resonance image have been developed. Experiments were performed by the authors to produce projected angiographic data without the use of contrast agents, with the intensity of each image pixel determined by the macroscopic velocity of the detected spins. With this method, suppression of nonmoving spins is essentially complete, yielding a high dynamic range in signal intensity for detected vessels. Selective detection of moving spins is not dependent on pulsatile flow. Consequently, not only arterial structures, but also venous structures can easily be visualized. High-resolution angiographic images can be obtained by combining the flow experiment with surface coil techniques.

Magnetic resonance angiography in the head and neck.

Magnetic resonance angiography (MRA) provides a means to visualize vessel structure without the use of contrast agents and consequently without the risks and discomfort associated with contrast media. We have developed a flow encoding procedure which exploits the spatial dependence in the phase of spin magnetization generated by a gradient pulse. This technique yields image information for only those spins having macroscopic motion (i.e. flowing blood). Excellent suppression of non-moving spins can be obtained despite the overwhelming abundance of stationary spins. Data are presented in a projection format similar to that of traditional subtraction angiography.

Rapid scan magnetic resonance angiography.

The change in phase of transverse spin magnetization induced by macroscopic spin motion in the direction of an applied magnetic field gradient is used to generate projection angiograms. The method can provide a quantitative measure of laminar and pulsatile flow. Cardiac synchronization is not required provided that data are acquired at many points in the cardiac cycle. The use of short TR and a large number of excitations provides better suppression of stationary tissue and patient motion artifacts than is possible with cardiac gated studies. In addition to improvements in image quality, a substantial shortening of scan time is obtained.

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.

High resolution magnetic resonance imaging using surface coils.

There is, of course, an intense activity directed at the improvement of MR imaging capabilities. Surface-coil techniques offer the possibility of improving the SNR sufficiently to permit the reduction of pixel sizes to values that would not be possible with conventional head and body coils. The successful application of surface-coil techniques to MR imaging suggests that this technique will be widely used in future MR imaging systems. This provides a fertile field for new research. This includes opportunities for mathematical and physical research into optimizing coil design. It also includes many opportunities for clinical research into the utilization of surface coils and high resolution MR imaging.

Anatomy and metabolism of the normal human brain studied by magnetic resonance at 1.5 Tesla.

Proton magnetic resonance (MR) images were obtained of the human head in magnetic fields as high as 1.5 Tesla (T) using slotted resonator high radio-frequency (RF) detection coils. The images showed no RF field penetration problems and exhibited an 11 (+/- 1)-fold improvement in signal-to-noise ratio over a .12-T imaging system. The first localized phosphorus 31, carbon 13, and proton MR chemical shift spectra recorded with surface coils from the head and body in the same instrument showed relative concentrations of phosphorus metabolites, triglycerides, and, when correlated with proton images, negligible lipid (-CH2-) signal from brain tissue on the time scale of the imaging experiment. Sugar phosphate and phosphodiester concentrations were significantly elevated in the head compared with muscle. This method should allow the combined assessment of anatomy, metabolism, and biochemistry in both the normal and diseased brain.

Ocular and orbital lesions: surface coil MR imaging.

Nine lesions, four ocular (three melanomas, one hemangioma) and five orbital (two perioptic meningiomas, one hemangioma, one pseudotumor, one mucocele), were evaluated by magnetic resonance surface coil imaging at 1.5 T. Small ocular lesions with 3.9-4.5-mm-elevation were demonstrated. The use of two different pulse sequences resulted in separation of melanoma from adjacent retinal detachment. Contrast obtained between orbital lesions and the adjacent normal structures was better than that demonstrated with high-resolution computed tomography.

Magnetic resonance imaging of the temporomandibular joint meniscus.

This report describes early experience with magnetic resonance imaging (MRI) of the temporomandibular joint meniscus in which surface coil technology was used. The results suggest remarkable imaging capabilities and speed with noninvasive methods.