A multi-center study has been set up to accurately characterize the optical properties of diffusive liquid phantoms based on Intralipid and India ink at near-infrared (NIR) wavelengths. Nine research laboratories from six countries adopting different measurement techniques, instrumental set-ups, and data analysis methods determined at their best the optical properties and relative uncertainties of diffusive dilutions prepared with common samples of the two compounds. By exploiting a suitable statistical model, comprehensive reference values at three NIR wavelengths for the intrinsic absorption coefficient of India ink and the intrinsic reduced scattering coefficient of Intralipid-20% were determined with an uncertainty of about 2% or better, depending on the wavelength considered, and 1%, respectively. Even if in this study we focused on particular batches of India ink and Intralipid, the reference values determined here represent a solid and useful starting point for preparing diffusive liquid phantoms with accurately defined optical properties. Furthermore, due to the ready availability, low cost, long-term stability and batch-to-batch reproducibility of these compounds, they provide a unique fundamental tool for the calibration and performance assessment of diffuse optical spectroscopy instrumentation intended to be used in laboratory or clinical environment. Finally, the collaborative work presented here demonstrates that the accuracy level attained in this work for optical properties of diffusive phantoms is reliable.

The abnormal, uncontrolled production of blood cells in the bone marrow causes hematological malignancies which are common and tend to have a poor prognosis. These types of cancers may alter the hemodynamics of bone marrow. Therefore, noninvasive methods that measure the hemodynamics in the bone marrow have a potential impact on the earlier diagnosis, more accurate prognosis, and in treatment monitoring. In adults, the manubrium is one of the few sites of bone marrow that is rich in hematopoietic tissue and is also relatively superficial and accessible. To this end we have combined time resolved spectroscopy and diffuse correlation spectroscopy to evaluate the feasibility of the noninvasive measurement of the hemodynamics properties of the healthy manubrium in 32 subjects. The distribution of the optical properties (absorption and scattering) and physiological properties (hemoglobin concentration, oxygen saturation and blood flow index) of this tissue are presented as the first step toward investigating its pathology.

The BabyLux device is a hybrid diffuse optical neuromonitor that has been developed and built to be employed in neonatal intensive care unit for the noninvasive, cot-side monitoring of microvascular cerebral blood flow and blood oxygenation. It integrates time-resolved near-infrared and diffuse correlation spectroscopies in a user-friendly device as a prototype for a future medical grade device. We present a thorough characterization of the device performance using test measurements in laboratory settings. Tests on solid phantoms report an accuracy of optical property estimation of about 10%, which is expected when using the photon diffusion equation as the model. The measurement of the optical and dynamic properties is stable during several hours of measurements within 3% of the average value. In addition, these measurements are repeatable between different days of measurement, showing a maximal variation of 5% in the optical properties and 8% for the particle diffusion coefficient on a liquid phantom. The variability over test/retest evaluation is <3%. The integration of the two modalities is robust and without any cross talk between the two. We also perform in vivo measurements on the adult forearm during arterial cuff occlusion to show that the device can measure a wide range of tissue hemodynamic parameters. We suggest that this platform can form the basis of the next-generation neonatal neuromonitors to be developed for extensive, multicenter clinical testing.

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Diffuse correlation spectroscopy (DCS) can non-invasively and continuously asses regional cerebral blood flow (rCBF) at the cot-side by measuring a blood flow index (BFI) in non-traditional units of cm2/s. We have validated DCS against positron emission tomography using 15 O-labeled water (15O-water PET) in a piglet model allowing us to derive a conversion formula for BFI to rCBF in conventional units (ml/100g/min). Neonatal piglets were continuously monitored by the BabyLux device integrating DCS and time resolved near infrared spectroscopy (TRS) while acquiring 15 O-water PET scans at baseline, after injection of acetazolamide and during induced hypoxic episodes. BFI by DCS was highly correlated with rCBF (R = 0.94, p < 0.001) by PET. A scaling factor of 0.89 (limits of agreement for individual measurement: 0.56, 1.39)×109× (ml/100g/min)/(cm2/s) was used to derive baseline rCBF from baseline BFI measurements of another group of piglets and of healthy newborn infants showing an agreement with expected values. These results pave the way towards non-invasive, cot-side absolute CBF measurements by DCS on neonates.

The collision-energy resolved rate coefficient for dissociative recombination of HD + ions in the vibrational ground state is measured using the photocathode electron target at the heavy-ion storage ring TSR. Rydberg resonances associated with ro-vibrational excitation of the HD + core are scanned as a function of the electron collision energy with an instrumental broadening below 1 meV in the low-energy limit. The measurement is compared to calculations using multichannel quantum defect theory, accounting for rotational structure and interactions and considering the six lowest rotational energy levels as initial ionic states. Using thermal equilibrium level populations at 300 K to approximate the experimental conditions, close correspondence between calculated and measured structures is found up to the first vibrational excitation threshold of the cations near 0.24 eV. Detailed assignments, including naturally broadened and overlapping Rydberg resonances, are performed for all structures up to 0.024 eV. Resonances from purely rotational excitation of the ion core are found to have similar strengths as those involving vibrational excitation. A dominant low-energy resonance is assigned to contributions from excited rotational states only. The results indicate strong modifications in the energy dependence of the dissociative recombination rate coefficient through the rotational excitation of the parent ions, and underline the need for studies with rotationally cold species to obtain results reflecting low-temperature ionized media.

A method to map out the energy distribution N(E ʈ ,E Ќ ) of an electron beam as a function of the longitudinal (E ʈ ) and transverse (E Ќ ) energy has been developed and applied to study the photoemission process from GaAs͑Cs, O͒ at 90 K. The method proceeds by ''marking'' electrons with fixed longitudinal energy E ʈ b and a subsequent measurement of the associated differential transverse energy distribution N Ќ (E ʈ b ,E Ќ ), applying an adiabatic magnetic compression technique. The complete energy distribution N(E ʈ ,E Ќ ) of electrons from a GaAs͑Cs, O͒ photocathode obtained by a stepwise variation of E ʈ b provides details about the transfer of electrons through the GaAs͑Cs, O͒-vacuum interface and demonstrates that not only electron energy loss, but also elastic electron scattering is of crucial importance in the escape process.The adsorption of cesium and oxygen on an atomically clean surface of p ϩ -GaAs leads to a state of negative effective electron affinity ͑NEA͒. 1 At this state the vacuum level lies below the bottom of the conduction band in the bulk (E c ) such that electrons with small kinetic energies above E c can escape into vacuum ͑Fig. 1͒. In spite of widespread usage of NEA photocathodes as effective sources of electrons, the physics of the photoelectron escape process is still not well understood. In order to study the mechanisms of photoelectron transport through the GaAs͑Cs, O͒-vacuum interface in more detail, knowledge of the complete twodimensional energy distribution N(E ʈ ,E Ќ ) of the electrons directly after the emission is required, where E ʈ and E Ќ are the energies of electrons associated with their motion parallel and perpendicular to the surface normal, respectively. However, up to now only one-dimensional projections of the complete distributions were measured ͓moreover, in many cases stray electric and ͑or͒ magnetic fields led to an uncontrolled coupling between longitudinal and transverse energies during the transport of the low energy electrons (Ϸ10-300 meV) to the analyzing devices͔, which do not give sufficient information to clarify the relative importance of elastic and inelastic scattering in the emission process. In this work we present a method by which it has become possible to determine the complete energy distribution N(E ʈ ,E Ќ ) in a magnetized electron beam and to obtain detailed information on the energy loss and scattering of the photoelectrons occurring in the escape process from GaAs͑Cs, O͒.We used transmission mode GaAs photocathodes consisting of a two layer heterostructure bonded to a glass substrate. The emitting p ϩ -GaAs͑100͒ layer was Ϸ1.5 m thick and doped with Zn to the hole concentration of about 5 ϫ10 18 cm Ϫ3 . A two-chamber photocathode preparation setup with a base pressure below 10 Ϫ12 mbar allowed us to activate photocathodes with ͑Cs, O͒ to quantum efficiencies of 20%-25% ͑in the reflection mode at 670 nm͒. The photocathode preparation setup and the related procedures are described in detail elsewhere. 2 After the activation the photocathode ...

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