Improvement of measurement accuracy in SU(1,1) interferometers

We consider an SU(1,1) interferometer employing four-wave mixers that is fed with two-mode states which are both coherent and intelligent states of the SU(1,1) Lie group. It is shown that the phase sensitivity of the interferometer can be essentially improved by using input states with a large photon-number difference between the modes.Comment: LaTeX, 5 pages, 1 figure (compressed PostScript, available at http://www.technion.ac.il/~brif/graphics/interfer_graph/qopt.ps.gz ). More information on http://www.technion.ac.il/~brif/science.htm

SU(2) and SU(1,1) algebra eigenstates: A unified analytic approach to coherent and intelligent states

We introduce the concept of algebra eigenstates which are defined for an arbitrary Lie group as eigenstates of elements of the corresponding complex Lie algebra. We show that this concept unifies different definitions of coherent states associated with a dynamical symmetry group. On the one hand, algebra eigenstates include different sets of Perelomov's generalized coherent states. On the other hand, intelligent states (which are squeezed states for a system of general symmetry) also form a subset of algebra eigenstates. We develop the general formalism and apply it to the SU(2) and SU(1,1) simple Lie groups. Complete solutions to the general eigenvalue problem are found in the both cases, by a method that employs analytic representations of the algebra eigenstates. This analytic method also enables us to obtain exact closed expressions for quantum statistical properties of an arbitrary algebra eigenstate. Important special cases such as standard coherent states and intelligent states are examined and relations between them are studied by using their analytic representations.Comment: LaTeX, 24 pages, 1 figure (compressed PostScript, available at http://www.technion.ac.il/~brif/abstracts/AES.html ). More information on http://www.technion.ac.il/~brif/science.htm

Chemical exchange saturation transfer MRI in central nervous system tumours on a 1.5 T MR-Linac

Purpose: To describe the implementation and initial results of using Chemical Exchange Saturation Transfer (CEST) for monitoring patients with central nervous system (CNS) tumours treated using a 1.5 tesla MR-guided radiotherapy system. Methods: CNS patients were treated with up to 30 fractions (total dose up to 60 Gy) using a 1.5 T Elekta Unity MR-Linac. CEST scans were obtained in 54 subjects at one or more time points during treatment. CEST metrics, including the amide magnetization transfer ratio (MTRAmide), nuclear Overhauser effect (NOE) MTR (MTRNOE) and asymmetry, were quantified in phantoms and CNS patients. The signal was investigated between tumour and white matter, across time, and across disease categories including high- and low-grade tumours. Results: The gross tumour volume (GTV) exhibited lower MTRAmide and MTRNOE and higher asymmetry compared to contralateral normal appearing white matter. Signal changes in the GTV during fractionated radiotherapy were observed. There were differences between high- and low-grade tumours, with higher CEST asymmetry associated with higher grade disease. Conclusion: CEST MRI using a 1.5 T MR-Linac was demonstrated to be feasible for in vivo imaging of CNS tumours. CEST images showed tumour/white-matter contrast, temporal CEST signal changes, and associations with tumour grade. These results show promise for the eventual goal of using metabolic imaging to inform the design of adaptive radiotherapy protocols

Inversion of the transverse mode calculation problem in laser resonators

No abstract availabl

In-plane visibility of lesions using breast tomosynthesis and digital mammography

Purpose: The purpose of this work was to evaluate the visibility of simulated lesions in 2D digital mammography (DM) and breast tomosynthesis (BT) images of patients. Methods: Images of the same women were acquired on both a DM system (Mammomat Novation, Siemens Healthcare, Erlangen, Germany) and a BT prototype system adapted from the same type of DM system. Using the geometrical properties of the two systems, simulated lesions were projected and added to each DM image as well as to each BT projection image prior to 3D reconstruction. The same beam quality and approximately the same total absorbed dose to the glandular tissue were used for each breast image acquisition on the two systems. A series of four-alternative forced choice human observer experiments was conducted for each of five simulated lesion diameters: 0.2, 1, 3, 8, and 25 mm. An additional experiment was conducted for the 0.2 mm lesion in BT only at twice the dose level (BT2x). Threshold signal was defined as the lesion signal intensity required for a detectability index (d') of 2.5. Four medical physicists participated in all experiments. One experiment, consisting of 60 cases, was conducted per test condition (i.e., lesion size and signal combination). Results: For the smallest lesions (0.2 mm), the threshold signal for DM was 21% lower than for BT at equivalent dose levels, and BT2x was 26% lower than DM. For the lesions larger than 1 mm, the threshold signal increased linearly (in log space) with the lesion diameter for both DM and BT, with DM requiring around twice the signal as BT. The difference in the threshold signal between BT and DM at each lesion size was statistically significant, except for the 0.2 mm lesion between BT2x and DM. Conclusions: The results of this study indicate that low-signal lesions larger than 1.0 mm may be more visible in BT compared to DM, whereas 0.2 mm lesions may be better visualized with DM compared to BT, when compared at equal dose. (C) 2010 American Association of Physicists in Medicine. [DOI: 10.1118/1.3488899

Nodule detection in digital chest radiography: summary of the RADIUS chest trial

As a part of the Europe-wide research project 'Unification of physical and clinical requirements for medical X-ray imaging'-governed by the Radiological Imaging Unification Strategies (RADIUS) Group-a major image quality trial was conducted by members of the group. The RADIUS chest trial aimed at thoroughly examining various aspects of nodule detection in digital chest radiography, such as the effects of nodule location, system noise, anatomical noise, and anatomical background. The main findings of the RADIUS chest trial concerning the detection of a lung nodule with a size in the order of 10 mm can be summarised as: (1) the detectability of the nodule is largely dependent on its location in the chest. (2) the system noise has a minor impact on the detectability at the dose levels used today, (3) the disturbance of the anatomical noise is larger than that of the system noise but smaller than that of the anatomical background and (4) the anatomical background acts as noise to a large extent and is the major image component affecting the detectability of the nodule