Development of a Practical Calibration Procedure for a Clinical SPECT/MRI System Using a Single INSERT Prototype Detector and Multi-Mini Slit-Slat Collimator

In the context of the INSERT project, we have been developing a clinical SPECT insert for an MRI system, in order to perform simultaneous SPECT/MRI of the human brain. This system will consist of 20 CsI:Tl scintillation detectors, 5 cm wide and 10 cm long, with a 72-channel SiPM readout per detector, and a multi-mini slit-slat (MSS) collimator set up in a stationary partial ring. Additionally the system has a custom-built transmit/receive MR coil to ensure compatibility with the SPECT system. Due to the novel design of the system/collimator, existing geometric calibration methods are not suitable. Therefore we propose a novel and practical calibration procedure that consists of a set of specific independent measurements to determine the geometric parameters of the collimator. This procedure was developed utilising a prototype system that consists of a reduced-size single detector with a 36-channel SiPM-based readout and a single MSS collimator module. Validation was performed by reconstructing different imaging phantoms, using a rotating stage to simulate a tomographic acquisition. Regarding uniformity, the COV for the cylinder phantom reconstructed with correct calibration parameters is 6.7%, whereas the COV using incorrect parameters is 9.4%. The quality of the phantom reconstructions provide evidence of the applicability of the proposed method to the calibration of the prototype system. This procedure can be easily adapted for the final INSERT system

The role of preclinical SPECT in oncological and neurological research in combination with either CT or MRI

Preclinical imaging with SPECT combined with CT or MRI is used more and more frequently and has proven to be very useful in translational research. In this article, an overview of current preclinical research applications and trends of SPECT combined with CT or MRI, mainly in tumour imaging and neuroscience imaging, is given and the advan- tages and disadvantages of the different approaches are de- scribed. Today SPECT and CT systems are often integrated into a single device (commonly called a SPECT/CT system), whereas at present combined SPECT and MRI is almost always carried out with separate systems and fiducial markers to combine the separately acquired images. While preclinical SPECT/CT is most widely applied in oncology research, SPECT combined with MRI (SPECT/MRI when integrated in one system) offers the potential for both neuroscience applications and oncological applications. Today CT and MRI are still mainly used to localize radiotracer binding and to improve SPECT quantification, although both CT and MRI have additional potential. Future technology developments may include fast sequential or simultaneous acquisition of (dynamic) multimodality data, spectroscopy, fMRI along with high-resolution anatomic MRI, advanced CT procedures, and combinations of more than two modalities such as combina- tions of SPECT, PET, MRI and CT all together. This will all strongly depend on new technologies. With further advances in biology and chemistry for imaging molecular targets and (patho)physiological processes in vivo, the introduction of new imaging procedures and promising new radiopharmaceu- ticals in clinical practice may be accelerated

Morphometric and functional changes of salivary gland dysfunction after radioactive iodine ablation in a murine model

BACKGROUND: Ablation of the thyroid tissue using radioactive iodine (RAI) after the surgical removal of well-differentiated thyroid cancer can induce radiation-related salivary gland (SG) dysfunction. However, in vivo changes of SGs after RAI administration in appropriate animal models are not well described in the literature. This study was undertaken to document morphometric and functional changes during the 12 months after RAI administration in a murine model of RAI-induced SG dysfunction. METHODS: Four-week-old female C57BL/6 mice (n = 60) were divided into an RAI-treated group (n = 30) that received RAI orally (0.01 mCi/g body weight) and an unexposed control group (n = 30). Mice in both groups were divided into five subgroups (n = 6 per subgroup) and euthanized at 1, 2, 3, 6, and 12 months post-RAI administration. Salivary flow rates and salivary lag times were measured at 1, 2, 3, 6, and 12 months after RAI administration. Morphological and histological examinations and terminal deoxynucleotidyl transferase dUTP nick end labeling assays were performed. In addition, changes in salivary (99m)Tc pertechnetate uptake and excretion were observed by single-photon emission computed tomography. RESULTS: In RAI-treated mice, the SGs were significantly lighter than those of unexposed controls at all study time points. Lag times to salivation in the RAI-treated group were greater than in the unexposed controls, but mean salivary flow rates were lower. Histologic examinations of SGs in the RAI group showed pale cytoplasm, atypical ductal configuration, septal widening, cytoplasmic vacuolization with pleomorphism, lymphocyte infiltration, and increased fibrosis. Furthermore, more apoptotic cells were observed in acini and ducts in the RAI group. In addition, patterns of (99m)Tc pertechnetate uptake and excretion in the RAI group were quite different from those observed in controls at 1 and 12 months post-RAI. CONCLUSION: Various histological alterations were observed in mice exposed to RAI, that is, an increase in apoptotic acini and ductal cells and functional SG deterioration. The murine model of RAI-induced SG dysfunction used in the present study appears to be applicable to preclinical research on RAI-induced sialadenitis in patients with well-differentiated thyroid cancer.ope

Intraoperative Endoscopic Augmented Reality in Third Ventriculostomy

In neurosurgery, as a result of the brain-shift, the preoperative patient models used as a intraoperative reference change. A meaningful use of the preoperative virtual models during the operation requires for a model update. The NEAR project, Neuroendoscopy towards Augmented Reality, describes a new camera calibration model for high distorted lenses and introduces the concept of active endoscopes endowed with with navigation, camera calibration, augmented reality and triangulation modules

Applications of Monte Carlo Methods in Biology, Medicine and Other Fields of Science

This volume is an eclectic mix of applications of Monte Carlo methods in many fields of research should not be surprising, because of the ubiquitous use of these methods in many fields of human endeavor. In an attempt to focus attention on a manageable set of applications, the main thrust of this book is to emphasize applications of Monte Carlo simulation methods in biology and medicine

Experiments and Theory of Induced Optical Magnetization.

This thesis reports the results of light scattering experiments at moderate optical intensities (~10^8 W/cm^2) in which the magnetic component of light induces magnetic dipolar response of unprecedented intensity by a novel nonlinear mechanism. Both experimentally and theoretically the amplitude of induced magnetization is found to be as large as electric polarization (M=cP) at intensities above ~10^8 W/cm^2 in different materials, greatly exceeding the conventional bounds of the multipole expansion. The transverse nature of the magnetization, its frequency, and its quadratic dependence on incident light intensity are in agreement with an exact theory which identifies the importance of magnetically-induced torque in achieving 2-photon resonance of this ultrafast process. In this work we report and compare the intensity dependence of cross-polarized scattering in the transparent molecular liquids CCl_4, SiCl_4, SiBr_4, SnCl_4, C_6H_6, C_6D_6, C_6H_5NH_2, and C_6H_5CN and the crystalline solid Gd_3Ga_5O_{12}. Complete radiation patterns of co-polarized and cross-polarized light scattering were recorded as a function of intensity in these homogeneous media and subsequently decomposed into polarized and unpolarized components to provide a more complete picture of scattering dynamics than has been possible in past experiments. The cross-polarized scattering observed from spherical-top molecules CCl_4, SiCl_4, SiBr_4, and SnCl_4 and crystalline GGG is argued to originate from magnetic dipoles induced by a second-order optical nonlinearity driven jointly by the E and B fields of light. Among the spherical top molecular liquids, SnCl_4 developed more intense magnetic scattering at a fixed intensity than CCl_4, in agreement with the predicted dependence on rotational frequency and damping. Cross-polarized scattering in anisotropic molecules C_6H_6, C_6D_6, C_6H_5NH_2, and C_6H_5CN, on the other hand, is known to originate from optical orientation of permanent electric dipole moments in first-order or differential polarizability in third-order. The importance of rotational dynamics to depolarization in all the liquids studied is outlined and confirmed through observation of an isotopic effect in the scattering from C_6H_6 vs. C_6D_6. Finally, the new nonlinear optical process investigated here provides a method for generating oriented rotations of molecules.PhDApplied PhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/120880/1/alxfshr_1.pd

Ultrafast electron dynamics and the role of screening

This thesis focuses on the ultrafast dynamics of electronic excitations in solids and how they are influenced by the screening of the Coulomb interaction between charged particles. The impact of screening on electron dynamics is manifold, ranging from modifications of electron-electron scattering rates over trapping of excess charges to massive renormalisation of electronic band structures. The timescales of these dynamical processes are directly accessible by femtosecond time-resolved photoemission and optical spectroscopy. Three exemplary systems are investigated to shed light onto these fundamental processes: Vanadiumdioxide undergoes a phase transition from a monoclinic insulator to a rutile metal. Apart from temperature, doping and other influences, the insulator-to-metal transition can also be driven by photoexcitation. This, in the past, gave rise to a controversy about the timescales of structural and electronic transition and raised the question which of them constitutes the driving mechanism. Using time-resolved photoelectron spectroscopy, it is shown that the electronic band gap of the insulator collapses instantaneously with photoexcitation and without any structural involvement. The reason is a change of screening due to the generation of photoholes. At the same time, the symmetry of the lattice potential changes, as seen by coherent phonon spectroscopy. This potential change is likely to initiate the structural phase transition from monoclinic to rutile structure. However, the initial non-equilibrium situation can be described by a metallic electronic structure with the atoms still in the monoclinic lattice positions. The SrTiO3/vacuum interface exhibits a two-dimensional electron gas (2DEG), which is delocalised within the surface plane, but localised perpendicular to it. The lower dimensionality changes the form of the screened Coulomb interaction and the phase space within the 2DEG, leading to modified hot carrier lifetimes. These are investigated by time-resolved photoemission spectroscopy: The predicted 2D behaviour is confirmed and two distinct final states within the unoccupied electronic band structure are discovered. Furthermore, the population of the 2DEG is transiently increased by photoexcitation from localised in-gap states into the 2DEG. A different type of screening by dipole moments in amorphous ice layers, is exploited to stabilise and trap electrons within the polar medium in front of a metal surface. Thereby, the mean free path of low energy electrons in amorphous ice is estimated. Moreover, the trapped electrons are used to drive a chemical reaction: A persistent modification of the surface electronic structure of the ice layer is explained via the `dielectron hydrogen evolution reaction'. Understanding the role of screening in these systems allows to explain seemingly unrelated effects, like trapping of excess electrons in ice and the insulator-to-metal transition in VO2, within the same concept