Adults hospitalized with CAP who had radiological evidence of pneumonia on CT scan but not on concurrent chest radiograph had pathogens, disease severity, and outcomes similar to patients who had signs of pneumonia on chest radiography. These findings support using the same management principles for patients with CT-only pneumonia and those with pneumonia seen on chest radiography.

A survey of biophysical and biomedical applications of free-electron lasers ͑FELs͒ is presented. FELs are pulsed light sources, collectively operating from the microwave through the x-ray range. This accelerator-based technology spans gaps in wavelength, pulse structure, and optical power left by conventional sources. FELs are continuously tunable and can produce high-average and high-peak power. Collectively, FEL pulses range from quasicontinuous to subpicosecond, in some cases with complex superpulse structures. Any given FEL, however, has a more restricted set of operational parameters. FELs with high-peak and high-average power are enabling biophysical and biomedical investigations of infrared tissue ablation. A midinfrared FEL has been upgraded to meet the standards of a medical laser and is serving as a surgical tool in ophthalmology and human neurosurgery. The ultrashort pulses produced by infrared or ultraviolet FELs are useful for biophysical investigations, both one-color time-resolved spectroscopy and when coupled with other light sources, for two-color time-resolved spectroscopy. FELs are being used to drive soft ionization processes in mass spectrometry. Certain FELs have high repetition rates that are beneficial for some biophysical and biomedical applications, but confound research for other applications. Infrared FELs have been used as sources for inverse Compton scattering to produce a pulsed, tunable, monochromatic x-ray source for medical imaging and structural biology. FEL research and FEL applications research have allowed the specification of spin-off technologies. On the horizon is the next generation of FELs, which is aimed at producing ultrashort, tunable x rays by self-amplified spontaneous emission with potential applications in biology.

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1197he science of X-ray production and application is now a little more than a century old [1] but is still an active field of research and development [2].Historically, X rays for imaging and crystallography have generally been produced through the use of bremsstrahlung and line X rays from electrons impinging on a metallic anode. Such sources are inexpensive, simple, and robust but provide little control over the X rays produced. More recently, synchrotron sources have been used for both applications, with good results. Unfortunately, synchrotrons are large, expensive facilities with less than ideal beam geometry and are therefore not entirely practical for routine imaging applications.The excellent results of experiments with monochromatic sources [3][4][5] show the desirability of improving on the current broadband X-ray imaging practice. No alternative has existed for experiments that need to operate at various X-ray energies. The availability of such a source may fundamentally change the practice of X-ray imaging and provide much wider availability of tuned X rays to crystallographers.A compact source of pulsed tunable monochromatic X rays has been designed, built, and tested. This device can deliver "hard" X rays from 10-to 50-keV at narrow bandwidths (1-10%), with a flux of 10 10 photons in each 8-psec pulse. These are produced in a cone-beam area geometry useful for human imaging, small animal imaging, protein crystallography, and nondestructive testing in industry. The machine integrates a laser with a linear accelerator (LINAC) and can be used in an unshielded environment.The source described here is a tabletop-terawatt (T 3 ) laser-based Compton backscattering system, which uses few-joule pulses from a 1,052-nm laser to collide with a 20-to 50-MeV electron beam to produce an intense pulse of narrowband X rays. The entire system footprint is 4 m wide by 10 m long, and it requires no shielding vault. It produces X rays in a smallangle cone-beam geometry in the 10-to 50-keV range, with up to 10 10 photons in an 8-psec pulse, which is sufficient flux for medical and industrial imaging to be performed in a single shot. This source is certainly not the first Compton backscattering or laser-synchrotron X-ray source built. Experiments have been carried out at a number of the large accelerator facilities [6, 7] that have produced modest fluxes of photons over a wide range of interesting energies. Also, sources similar in concept to this one have been proposed [8,9] and operated on a small scale. However, none of these sources has been designed and built in a small practical form and with a high enough flux to be deployed as a common laboratory-scale or clinical resource. Further, most of the current generation of sources produce high levels of background radiation from the linear accelerator and require the source to be embedded in a shielding vault.The source at Vanderbilt University has its roots in a project that was built as an add-on to the free-electron laser at Vanderbilt that was proposed in 1987. It p...