Measuring myotube thickness is a physiological and unbiased approach for screening therapeutic compounds that prevent skeletal muscle atrophy or induce hypertrophy. However, an accurate cell thickness estimate is often quite challenging because of the extreme heterogeneity of the myotube cellular population and therefore the lack of a regular distribution of perturbed myotubes. Here the authors present a novel method to evaluate changes in myotube thickness via measuring cellular electrical impedance. They demonstrate that both qualitative and quantitative changes in electrical impedance as a function of cellular adhesion in real time correlate well with variation in myotube thickness caused by atrophy or hypertrophy agents. Conversely, pharmacologically blocking myotube hypertrophy prevents changes in electrical impedance. Thus, impedance can be used as a reliable and sensitive biomarker for myotube atrophy or hypertrophy. Application of this technique to drug screening might be beneficial in finding novel treatments preventing muscle atrophy and other diseases associated with any morphological change in cell shape.

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The Multiband Imaging Photometer for Spitzer (MIPS) provides long wavelength capability for the mission, in imaging bands at 24, 70, and 160µm and measurements of spectral energy distributions between 52 and 100µm at a spectral resolution of about 7%. By using true detector arrays in each band, it provides both critical sampling of the Spitzer point spread function and relatively large imaging fields of view, allowing for substantial advances in sensitivity, angular resolution, and efficiency of areal coverage compared with previous space far-infrared capabilities. The Si:As BIB 24µm array has excellent photometric properties, and measurements with rms relative errors of 1% or better can be obtained. The two longer wavelength arrays use Ge:Ga detectors with poor photometric stability. However, the use of 1.) a scan mirror to modulate the signals rapidly on these arrays, 2.) a system of on-board stimulators used for a relative calibration approximately every two minutes, and 3.) specialized reduction software result in good photometry with these arrays also, with rms relative errors of less than 10%.

The Multiband Imaging Photometer for SIRTF (MIPS) provides the Space Infrared Telescope Facility (SIRTF) with imaging, photometry, and total power measurement capability in broad spectral bands centered at 24, 70, and 160tm, and with low resolution spectroscopy between 50 and 95p.m. The optical train directs the light from three zones in the telescope focal plane to three detector arrays: l28x128 Si:As BIB, 32x32 Ge:Ga, and 2x20 stressed Ge:Ga. A single axis scan mirror is placed at a pupil to allow rapid motion of the field of view as required to modulate above the 1/f noise in the germanium detectors. The scan mirror also directs the light into the different optical paths of the instrument and makes possible an efficient mapping mode in which the telescope line of sight is scanned continuously while the scan mirror freezes the image motion on the detector arrays. The instrument is designed with pixel sizes that oversample the telescope Airy pattern to operate at the diffraction limit and, through image processing, to allow superresolution beyond the traditional Rayleigh criterion.The instrument performance and interface requirements, the design concept, and the mechanical, optical, thermal, electrical, software, and radiometric aspects of MIPS are discussed in this paper. Solutions are shown to the challenge of operating the instrument below 3K, with focal plane cooling requirements down to 1.5K. The optical concept allows the versatile operations described above with only a single mechanism and includes extensive self-test and on-board calibration capabilities. In addition, we discuss the approach to cryogenic end-to-end testing and calibration prior to delivery of the instrument for integration into SIRTF.