We present the analytical design of an imaging spectrometer based on the three-concentric-mirror (Offner) configuration. The approach presented allows for the rapid design of this class of system. Likewise, high-optical-quality spectrometers are obtained without the use of aberration-corrected gratings, even for high speeds. Our approach is based on the calculation of both the meridional and the sagittal images of an off-axis object point. Thus, the meridional and sagittal curves are obtained in the whole spectral range. Making these curves tangent to each other for a given wavelength results in a significant decrease in astigmatism, which is the dominant residual aberration.RMS spot radii less than 5 mm are obtained for speeds as high as f/2.5 and a wavelength range of 0.4-1.0 microm. A design example is presented using a free interactive optical design tool.

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This paper shows a feasibility study on the use of discrete SiPMs to read out monolithic scintillator-based detectors for use in molecular imaging applications. Monte Carlo simulations are carried out in order to evaluate the basic performance of 8 × 8 arrays of discrete SiPMs with different PDE values and compare it to conventional 64 channel multi-anode PMT (MA-PMT) readout. A detailed optical transport model was incorporated into the Monte Carlo simulation and a detector module based on a monolithic scintillator crystal of 50 × 50 × 4 mm 3 coupled to a MA-PMT was built for experimental validation. The effect of the SiPM dynamic range was also investigated by including a model of the saturation effects into the optical transport simulation. The results show that a detector module based on an array of 8 × 8 discrete SiPM devices (3 × 3 mm 2 and PDE > 32%) is feasible as a replacement of a 64 channel MA-PMT in order to read out large monolithic crystals for MR-compatible gamma cameras.

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where, considering the relation described by equation (1), the relative standard deviation of the SiPM signal due to the fluctuations in the number of photoelectrons can be expressed as (2) (3)ast _ 0.68 [ ( N phe )]1/3 ----exp ---Nf /p p -2.35 J 2 2 FWHM -Nf X (J"phe + (J"st aphe aNphe Nf = p (exp( Nphe) -1) p Considering Poisson statistics, the standard deviation of the number of photoelectrons aNphe = JNphe.