Maryam Khodaverdi

Combined MRI–PET dissects dynamic changes in plant structures and functions

Unravelling the factors determining the allocation of carbon to various plant organs is one of the great challenges of modern plant biology. Studying allocation under close to natural conditions requires non-invasive methods, which are now becoming available for measuring plants on a par with those developed for humans. By combining magnetic resonance imaging (MRI) and positron emission tomography (PET), we investigated three contrasting root/shoot systems growing in sand or soil, with respect to their structures, transport routes and the translocation dynamics of recently fixed photoassimilates labelled with the short-lived radioactive carbon isotope (11)C. Storage organs of sugar beet (Beta vulgaris) and radish plants (Raphanus sativus) were assessed using MRI, providing images of the internal structures of the organs with high spatial resolution, and while species-specific transport sectoralities, properties of assimilate allocation and unloading characteristics were measured using PET. Growth and carbon allocation within complex root systems were monitored in maize plants (Zea mays), and the results may be used to identify factors affecting root growth in natural substrates or in competition with roots of other plants. MRI-PET co-registration opens the door for non-invasive analysis of plant structures and transport processes that may change in response to genomic, developmental or environmental challenges. It is our aim to make the methods applicable for quantitative analyses of plant traits in phenotyping as well as in understanding the dynamics of key processes that are essential to plant performance.

Radiation Detectors for Medical Applications

Contents. Preface S. Tavernier.-A Look at Medical Imaging Trends through the Eyes of a Medical Doctor S.S. Makeyev.- Introduction.-Historical Aspect of Nuclear Medicine.-Nowadays in Nuclear Medicine.-Perspectives of Nuclear Medicine Imaging.- New Trends in X-Ray CT Imaging R. Deych and E. Dolazza.- Present Status of X-Ray CT.-Detector Instrumentation in Medical CT.- Scintillator.-Photodetectors.-Future Evolution of Data Measurement Systems.- The Evolution of Spect- from Anger to Today and Beyond W.W. Moses, A. Gektin et al.- Introduction.-General Considerations.-SPECT.- The Anger Camera.-Optimizing Positioning in Anger Cameras.- Collimators.-Scintillators for Spect.- Recently Developed Scintillator Materials.- Conclusion.- New Trends in PET Detector Developments P.Lecoq.- Introduction.-PET Based Molecular Imaging.-Improving Sensitivity.- Improving Spatial and Temporal Resolution.-Multimodaility and Multifunctionality.-New Conversion Materials.- New Photodetectors.-Highly Integrated and Low Noise Electronics.-Intelligent and Triggerable Data Acquisition Systems.-Simulation Software.-New Reconstruction and Visualisation Algorithms.-Conclusion.-Semiconductor Detectors in Radiation Medicine: Radiotherapy and related Applcations A.B. Rosenfeld.- Introduction.-Integral Semiconductor Dosimetry in Radiation Therapy.-Mosfet Detectors.-Semiconductor Radiation Detectors in Hadron Therapy.- Semiconductor Radiation Detectors for Microdosimetry in Radiation Therapy.-Application of Scintillator Based Detector in Radiation Therapy.-Conclusion.-First Results with the ClearPET small Animal PET Scanners S. Tavernier et al.- Introduction.-Description of the ClearPET Scanners.-Measured Performance and Comparison with Monte Carlo Simulations.- Image Reconstruction.-Conclusions.-Investigation of Crystal Identification Methods for ClearPETTM Phoswich Detector D. Wisniewski et al.- Introduction.-Measurement Setup.-Crystal Identification Methods.- Experimental Results.- Conclusions.- Directions in Scintillation Materials Research P. Dorenbos.- Introduction.-Historic Developments.- Fundamental Limits.- Directions in Scintillation Materials Research.-Summary and Conclusions.-Scintillation Detectors for Medical and Biology Applications: Materials, Design and Light Collection Conditions M. Globus, B. Grinyov.- Introduction.-2. Some Features and Regularities of Light Collection in Scintillators.- Medical Diagnostics Instrumentation.- Thin Scintillation Films for Biological Microtomography. Conclusions.- Current and Future Use of LSO: CE Scintillators in PET C.L. Melcher et al.- Introduction.-Physical Properties.- Scintillation Properties.-Crystal Growth.-Detector Design.- Future Uses of LSO: CE in PET.-Conclusion.-Inorganic Scintillators in Positron Emission Tomography C.W.E. van Eijk.- Introduction.-Inorganic Scintillators.- Position Resolution and Depth of Interaction.-Coincidence-Time Resolution, Random Coincidences, Time of Flight and Dead Time.-Conclusion.-Crystal Fibers and thin Films for Imaging Applications C. Pedrini and C. Dujardin.-. Introduction.-Single Crystal Fibers.- Scintillating Thin Films Deposited on Substrate.- Scintillation thin Layers created by Irradiation.-Conclusions. Non-Proportionality and Energy Resolution of Scintillation Detectors M. Moszynski.-Introduction.-Outline of the Problem.Study of Energy Resolution and Non-Proportionality.- Discussion and Conclusions.

Preliminary studies of a micro-CT for a combined small animal PET/CT scanner

We are developing an X-ray computed tomography (CT) system which will be combined with a high resolution animal PET system. This permits acquisition of both molecular and anatomical images in a single machine. In particular the CT will also be utilized for the quantification of the animal PET data by providing accurate data for attenuation correction. A first prototype has been built using a commercially available plane silicon diode detector. A cone-beam reconstruction provides the images using the Feldkamp algorithm. First measurements with this system have been performed on a mouse. It could be shown that the CT setup fulfils all demands for a high quality image of the skeleton of the mouse. It is also suited for soft tissue measurements. To improve contrast and resolution and to acquire the X-ray energy further development of the system, especially the use of semiconductor detectors and iterative reconstruction algorithms are planned.

FIRST RESULTS WITH THE CLEARPET SMALL ANIMAL PET SCANNERS

The Crystal Clear Collaboration has designed and built a family of high resolution small animal PET scanners. These were designed to be used in research laboratories and provide maximum modularity and flexibility. The source code of the data acquisition and reconstruction software is freely available to the users. The design is based on the use of the Hamamatsu R7600-M64 multi-anode photomultiplier tube and an LSO/LuYAP phoswich matrix with one-to-one coupling between the crystals and the photo-detector. A complete system has 80 PMT tubes in four rings with a minimum inner diameter of 137 mm and an axial field of view of 110 mm. The detectors are rotating over 360 degrees so that partially filled ring geometries can be used. This greatly simplifies the combination of PET with other imaging modalities. Single gamma interactions are recorded in list mode format and coincidences are found by software.

Timemark correction for the ClearPET/spl trade/ scanners

The small animal PET scanners developed by the Crystal Clear Collaboration (ClearPETtrade) detect coincidences by analyzing timemarks which are attached to each event. The scanners are able to save complete single list mode data which allows analysis and modification of the timemarks after data acquisition. The timemarks are obtained from the digitally sampled detector pulses by calculating the baseline crossing of the rising edge of the pulse which is approximated as a straight line. But the limited sampling frequency causes a systematic error in the determination of the timemark. This error depends on the phase of the sampling clock at the time of the event. A statistical method that corrects these errors will be presented

High resolution imaging with ClearPET/spl trade/ Neuro - first animal images

The ClearPET/spl trade/ Neuro is the first full ring scanner within the Crystal Clear Collaboration (CCC). It consists of 80 detector modules allocated to 20 cassettes. LSO and LuYAP:Ce crystals in phoswich configuration in combination with position sensitive photomultiplier tubes are used to achieve high sensitivity and realize the acquisition of the depth of interaction (DOI) information. The complete system has been tested concerning the mechanical and electronical stability and interplay. Moreover, suitable corrections have been implemented into the reconstruction procedure to ensure high image quality. We present first results which show the successful operation of the ClearPET/spl trade/ Neuro for artefact free and high resolution small animal imaging. Based on these results during the past few months the ClearPET/spl trade/ Neuro System has been modified in order to optimize the performance.