Note: Laser-cut molybdenum grids for a retarding field energy analyzer.

A retarding field energy analyzer (RFEA) with grids created by laser-cutting a honeycomb mesh in a 50 µm thick molybdenum foil is presented. The flat grids span an area of 1 cm2 and have high transmission (20 µm wide walls between 150 µm wide meshes). The molybdenum grids were tested in a 3-grid RFEA configuration with an analyzer depth of 0.87 mm.

Constrained Source Space MR Spectroscopy: Multiple Voxels, No Gradient Readout.

BACKGROUND AND PURPOSE: Our goal was to develop a novel technique for measuring a small number of localized spectra simultaneously and in a time-efficient manner. MATERIALS AND METHODS: Using appropriate radiofrequency pulses, the magnetization from multiple voxels is excited simultaneously and then separated (reconstructed) by using the individual coil-sensitivity profiles from a multichannel receiver coil. Because no gradients are used for k-space encoding, constrained source space MR spectroscopy provides a time advantage over conventional spectroscopic imaging and an improved signal-to-noise ratio per square root of unit time over single-voxel spectroscopy applied at each successive location. In the present work, we considered prototype application of constrained source space MR spectroscopy for 2 voxels. RESULTS: Experimental data from healthy volunteers and simulation results showed that constrained source space MR spectroscopy is effective at extracting 2 independent spectra even in the challenging scenario of the voxels being closely spaced. Also, from 6 patients with various types of brain cancer we obtained 2-voxel constrained source space MR spectroscopy data, which showed spectra of clinical quality in half the time required to perform successive single-voxel MR spectroscopy. CONCLUSIONS: Constrained source space MR spectroscopy provides clinical quality spectra and could be used to probe multiple voxels simultaneously in combination with Hadamard encoding for further scan-time reductions.

X-ray coherent scattering form factors of tissues, water and plastics using energy dispersion.

A key requirement for the development of the field of medical x-ray scatter imaging is accurate characterization of the differential scattering cross sections of tissues and phantom materials. The coherent x-ray scattering form factors of five tissues (fat, muscle, liver, kidney, and bone) obtained from butcher shops, four plastics (polyethylene, polystyrene, lexan (polycarbonate), nylon), and water have been measured using an energy-dispersive technique. The energy-dispersive technique has several improvements over traditional diffractometer measurements. Most notably, the form factor is measured on an absolute scale with no need for scaling factors. Form factors are reported in terms of the quantity x = λ(-1)sin (θ/2) over the range 0.363-9.25 nm(-1). The coherent form factors of muscle, liver, and kidney resemble those of water, while fat has a narrower peak at lower x, and bone is more structured. The linear attenuation coefficients of the ten materials have also been measured over the range 30-110 keV and parameterized using the dual-material approach with the basis functions being the linear attenuation coefficients of polymethylmethacrylate and aluminum.