Iterative reconstruction of the detector response for medical gamma cameras

Statistical event reconstruction techniques can give better results for gamma cameras than the traditional centroid method. However, implementation of such techniques requires detailed knowledge of the PMT light response functions. Here we describe an iterative technique which allows to obtain the response functions from flood irradiation data without imposing strict requirements on the spatial uniformity of the event distribution. A successful application of the technique for medical gamma cameras is demonstrated using both simulated and experimental data. We show that this technique can be used for monitoring of the photomultiplier gain variations. An implementation of the iterative reconstruction technique capable of operating in real-time is also presented.

From Rates of mixing to recurrence times via large deviations

A classic approach in dynamical systems is to use particular geometric structures to deduce statistical properties, for example the existence of invariant measures with stochastic-like behaviour such as large deviations or decay of correlations. Such geometric structures are generally highly non-trivial and thus a natural question is the extent to which this approach can be applied. In this paper we show that in many cases stochastic-like behaviour itself implies that the system has certain non-trivial geometric properties, which are therefore necessary as well as sufficient conditions for the occurrence of the statistical properties under consideration. As a by product of our techniques we also obtain some new results on large deviations for certain classes of systems which include Viana maps and multidimensional piecewise expanding maps.

Geometry of expanding absolutely continuous invariant measures and the liftability problem

We show that for a large class of maps on manifolds of arbitrary finite dimension, the existence of a Gibbs-Markov-Young structure (with Lebesgue as the reference measure) is a necessary as well as sufficient condition for the existence of an invariant probability measure which is absolutely continuous measure (with respect to Lebesgue) and for which all Lyapunov exponents are positive.

Performances of a Newly High Sensitive Trilayer F/Cu/F GMI Sensor

We have selected stress-annealed nanocrystalline Fe-based ribbons for ferromagnetic/copper/ferromagnetic sensors exhibiting high magneto-impedance ratio. Longitudinal magneto-impedance reaches 400% at 60 kHz and longitudinal magneto-resistance increases up to 1300% around 200 kHz.

Giant Magneto-impedance in stress-annealed Finemet/Copper/Finemet based trilayer structures

The resistive and reactive components of magneto-impedance (MI) for Finemet/Copper/Finemet sandwiched structures based on stress-annealed nanocrystalline Fe75Si15B6Cu1Nb3 ribbons as functions of different fields (longitudinal and perpendicular) and frequencies have been measured and analyzed. Maximum magneto-resistance and magneto-inductance ratios of 700% and 450% have been obtained in 30-600 kHz frequency range respectively. These large magneto-resistance and magneto-inductive ratios are a direct consequence of the large effective relative permeability due to the closed magnetic flux path in the trilayer structure. The influence of perpendicular bias fields (Hper) in the Longitudinal Magneto-impedance (LMI) configuration greatly improves the MI ratios and sensitivities. The maximum MI ratio for the resistive part increases to as large as 2500% for Hper ~ 1 Oe. The sensitivity of the magneto-resistance increases from 48%/Oe to 288%/Oe at 600 kHz frequency with the application of Hper ~ 30 Oe. Such high increase in MI ratios and sensitivities with perpendicular bias fields are due to the formation the favourable (transverse) domain structures.