C. Bohm

Automated blood sampling systems for positron emission tomography

An automated blood sampling system has been constructed and evaluated for use with positron-emission tomography (PET). The dispersion functions of two different detector units in the blood sampling system are compared. One is a plastic scintillator, and the other is a coincidence detector. No significant differences were found. Results from studies of blood-brain barrier transfer of a C-11 labelled receptor antagonist are discussed. >

Measurement Of The Anisotropy Of Cosmic-Ray Arrival Directions With Icecube

We report the first observation of an anisotropy in the arrival direction of cosmic rays with energies in the multi-TeV region in the Southern sky using data from the IceCube detector. Between 2007 June and 2008 March, the partially deployed IceCube detector was operated in a configuration with 1320 digital optical sensors distributed over 22 strings at depths between 1450 and 2450 m inside the Antarctic ice. IceCube is a neutrino detector, but the data are dominated by a large background of cosmic-ray muons. Therefore, the background data are suitable for high-statistics studies of cosmic rays in the southern sky. The data include 4.3 billion muons produced by downward-going cosmic-ray interactions in the atmosphere; these events were reconstructed with a median angular resolution of 3 degrees and a median energy of similar to 20 TeV. Their arrival direction distribution exhibits an anisotropy in right ascension with a first-harmonic amplitude of (6.4 +/- 0.2 stat. +/- 0.8 syst.) x 10(-4).

A Four Ring Positron Camera System for Emission Tomography of the Brain

The exciting possibilities of regional, noninvasive and quantitative metabolic studies of the brain with positron emission tomography, have initiated the construction of a second generation positron camera system at the Department of Physics, University of Stockholm, in collaboration with the Departments of Neuroradiology, Clinical Neurophysiology and Radiation Physics at the Karolinska Hospital and Institute, and the Instrument AB Scanditronix. The camera is a four ring system with 96 bismuth germanate (BGO) detectors per ring. The spatial resolution is 7.7 mm FWHM and the sensitivity per ¿Ci per ml for a 20 cm diameter cylinder phantom is 25000 c/s for direct slices and 35000 c/s for cross slices.

A Computer Assisted Ringdector Positron Camera System for Reconstruction Tomography of the Brain

A ring detector positron camera system for brain metabolism studies is being constructed at the Institute of Physics, University of Stockholm, in collaboration with the Departments of Neuroradiology and clinical Neurophysiology, Karolinska Sjukhuset, Stockholm, Sweden. The instrument utilizes 95 NaI(Tl) detectors and will simultaneously record coincidences from 1900 detector combinations. Each detector is coupled in coincidence with forty detectors on the opposite side of the ring. In the conventional stationary mode of operation the experimental system resolution is 10.5 mm. A new sampling technique has been developed to reduce the system resolution. Based on this technique, an experimental system resolution of 7 mm has been obtained.

The ATLAS Level-1 Calorimeter Trigger

The ATLAS Level-1 Calorimeter Trigger uses reduced-granularity information from all the ATLAS calorimeters to search for high transverse-energy electrons, photons, τ leptons and jets, as well as high missing and total transverse energy. The calorimeter trigger electronics has a fixed latency of about 1 μs, using programmable custom-built digital electronics. This paper describes the Calorimeter Trigger hardware, as installed in the ATLAS electronics cavern.

Transformations and algorithms in a computerized brain atlas

The computerized brain atlas constructed at the Karolinska Hospital, Stockholm, Sweden has been further developed. This atlas was designed to be employed in different fields of neuro imaging such as positron emission tomography (PET), single photon emission computed tomography (SPECT), computerized tomography (CT), and magnetic resonance imaging (MR). The main objectives with the atlas are to aid the interpretation of functional images by introducing anatomical information, to serve as a tool in the merging of data from different imaging modalities, and to facilitate the comparisons of data from different individuals by allowing for anatomical standardization of individual data. The authors describe the algorithms and transformations used in the implementation of the atlas software. >

SPECIFICATION AND SELECTION OF REGIONS OF INTEREST (ROIS) IN A COMPUTERIZED BRAIN ATLAS

The computerized individually adjustable brain atlas (CBA) has been further developed. The atlas was primarily designed for anatomical localization and quantitative evaluation of data in positron emission tomography (PET), but may also be employed for other neuroimaging modalities, such as transmission computed tomography (CT) and magnetic resonance imaging (MRI). The atlas is based on anatomical information obtained from digitized cryosectioned brains. Using spatially standardized and then averaged MRI images, we demonstrate the high localization accuracy and precision of the brain atlas. This is a prerequisite for obtaining accuracy when using the atlas in the localization and the quantitative evaluation of PET data. The specification and the selection of region of interests (ROIs) by the CBA are presented and discussed.

A study of the possibility of using multi-slice PET systems for 3D imaging

Two PET (positron emission tomography) system configurations have been studied by Monte Carlo simulations, one with and one without interplane septa. The basic tomograph configuration studied is a 50-cm-diameter brain system, using 2048 6-mm-wide and 12-mm-tall detectors. The detectors are arranged in eight rings with 256 detectors in each ring. It is shown that with the removal of the interplane septa and using all 64 possible ring combinations, the efficiency can be increased by a factor of about 6. This number is an average over the whole sensitive volume. In the central regions the increase can be as much as a factor of 8. The removal of the septa also increases the number of detected scattered events which have to be corrected for, for example, by a deconvolution algorithm. The accidental coincidence rate will increase by a factor of 17, limiting this mode of operation to studies with low-activity administrations less than 20 mCi. However, even for such a low administration of activity, the efficiency gain of true unscattered events with the removal of the septa is still higher than in the case where septa are used with a higher dose administration. >

A computerized adjustable brain atlas

AbstractA computerized brain atlas, adjustable to the patients anatomy, has been developed. It is primarily intended for use in positron emission tomography, but may also be employed in other fields utilizing neuro imaging, such as stereotactic surgery, transmission computerized tomography (CT) and magnetic resonance imaging (MRI). The atlas is based on anatomical information obtained from a digitized cryosectioned brain. It can be adjusted to fit a wide range of images from individual brains with normal anatomy. The corresponding transformation is chosen so that the modified atlas agrees with a set of CT or NMR images of the patient. The computerized atlas can be used to improve the quantification and evaluation of PET data by:- Aiding and improving the selection of regions of interests.- Facilitating comparisons of functional image data from different individuals or groups of individuals.- Facilitating the comparison of different examinations of the same patient, thus reducing the need of reproducible fixation systems.- Providing external a priori anatomical information to be used in the image reconstruction.- Improving the attenuation and scatter corrections.- Aiding in selecting a suitable patient orientation during the PET study. By applying the inverse atlas transformation to PET data set it is possible to relate the PET information to the anatomy of the reference atlas. Thus reformatted PET data from different patients can be averaged, and averages from different categories of patients can be compared. This procedure will facilitate the identification of statistically significant differences in the PET information from different groups of patients.

Design Studtes of Two Possible Detector Blocks for High Resolution Positron Emission Tomography of the Brain

Two possible detector designs for high resolution positron camera systems have been investigated. The goal is to achieve an instrument that can measure the whole brain with a spatial resolution of 5 mm FWHM in all directions. For both detectors BGO crystals are used, with the dimension 4.5*9.5*25 mm. One detector scheme utilizes the Anger principle for crystal identification with 16 crystals mounted on two dual PMT:s via a 3 mm light guide. The other detector scheme utilizes position sensitive PMT:s. The figures of merit for these two configurations are discussed in terms of high count rate capabilities and identification reliability.