Abstract-Positron emission tomography (PET) is a relatively lengthy brain imaging method. Because it is difficult for the subject to stay still during the data acquisition, head motion during scans is a source of image degradation. A simple data acquisition technique to reduce the effect of this problem is described. The technique associates the incoming data with the real-space position of the head. During the PET scan, the head position is constantly monitored with two video cameras and compared to its initial position. Every time the displacement for a region within the field of view (FOV) is larger than a specified threshold displacement, the PET data acquisition system starts to save the PET data in a new frame. The total number of frames required for a complete study depends on the magnitude of the head motion during the study and on the threshold displacement. At the end of the study, all the acquired frames are reconstructed independently and each image is rotated and translated to coincide with the initial position. When these images are summed, they produce a final image with fewer motion artefacts.

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We are developing a high specificity technique for detecting the increased metabolic rate of breast tiiinours. The glitcose analog FDG is known to concentrate in breast tiinlours rendering them easily detectable in conventional PET scans. Since PET is a relatively expensive imging technique it has not been used routinely in the detection of breast cancer. Positron emission mtnrnography (PEM) will provide a highly eficient, high sputial resolution, and low cost positron irtulging system whose rnetabolic irnages are co-registered with conventional mnmtnography. Coincidences betweeti hoo BGO blocks CUI into 2 x 2 tnrn squares coitpled to two 7.5 crn square inuiging PMTs are detected and back-projected to form reultirne multiple plane irnages. The design is about 20 tinles more sensitive than a conventional multi-slice PET body scanner, so much less radio-pharmaceiitical can be wed, reducing the patient dose and cost per scan. Protoepe detectors hose been t n d e and extensive rneasurernents done. The device is expected to have an in-plane spatial resolution about 2 intn FWHM. Besides the application as N secondup screening tool the device may be beneficial in rrzeasiiring a tiirrwur's response to ruriio-therapy or cherno-therapy as well as uiding the surgeon in optimizing the removal of inalignant tissue.

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Circular dichroism is a consequence of chirality. However, nonchiral molecules can also exhibit it when the measurement itself introduces chirality, e.g., when measuring molecular-frame photoelectron angular distributions. The few such experiments performed on homonuclear diatomic molecules show that, as expected, circular dichroism vanishes when the molecular-frame photoelectron angular distributions are integrated over the polar electron emission angle. Here we show that this is not the case in resonant dissociative ionization of H2 for photons of 30-35 eV, which is the consequence of the delayed ionization from molecular doubly excited states into ionic states of different inversion symmetry.

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We describe the versatile features of the attosecond beamline recently installed at CEA-Saclay on the PLFA kHz laser. It combines a fine and very complete set of diagnostics enabling high harmonic spectroscopy (HHS) through the advanced characterization of the amplitude, phase, and polarization of the harmonic emission. It also allows a variety of photo-ionization experiments using magnetic bottle and COLTRIMS (COLd Target Recoil Ion Momentum Microscopy) electron spectrometers that may be used simultaneously, thanks to a two-foci configuration. Using both passive and active stabilization, special care was paid to the long term stability of the system to allow, using both experimental approaches, time resolved studies with attosecond precision, typically over several hours of acquisition times. As an illustration, applications to multi-orbital HHS and electron-ion coincidence time resolved spectroscopy are presented.