9 research outputs found
Photoacoustic pump-probe tomography of fluorophores in vivo using interleaved image acquisition for motion suppression
In fluorophores, the excited state lifetime can be modulated using pump-probe
excitation. By generating photoacoustic (PA) signals using simultaneous and
time-delayed pump and probe excitation pulses at fluences below the maximum
permissible exposure, a modulation of the signal amplitude is observed in
fluorophores but not in endogenous chromophores. This provides a highly
specific contrast mechanism that can be used to recover the location of the
fluorophore using difference imaging. The practical challenges in applying
this method to in vivo PA tomography include the typically low concentrations
of fluorescent contrast agents, and tissue motion. The former results in
smaller PA signal amplitudes compared to those measured in blood, while the
latter gives rise to difference image artefacts that compromise the
unambiguous and potentially noise-limited detection of fluorescent contrast
agents. To address this limitation, a method based on interleaved pump-probe
image acquisition was developed. It relies on fast switching between
simultaneous and time-delayed pump-probe excitation to acquire PA difference
signals in quick succession, and to minimise the effects of tissue motion. The
feasibility of this method is demonstrated in tissue phantoms and in initial
experiments in vivo
PIXSIC: A Wireless Intracerebral Radiosensitive Probe in Freely Moving Rats
International audienceThe aim of this study was to demonstrate the potential of a wireless pixelated β+-sensitive intracerebral probe (PIXSIC) for in vivo positron emission tomographic (PET) radiopharmacology in awake and freely moving rodents. The binding of [ 11 C]raclopride to D 2 dopamine receptors was measured in anesthetized and awake rats following injection of the radiotracer. Competitive binding was assessed with a cold raclopride injection 20 minutes later. The device can accurately monitor binding of PET ligands in freely moving rodents with a high spatiotemporal resolution. Reproducible time-activity curves were obtained for pixels throughout the striatum and cerebellum. A significantly lower [ 11 C]raclopride tracer–specific binding was observed in awake animals. These first results pave the way for PET tracer pharmacokinetics measurements in freely moving rodents
Potential of the wireless radiosensitive intracerebral probe PIXSIC to monitor PET radiotracers in anaesthetized and awake rat
In neuroscience, functional imaging with positron emission tomography (PET) and behavioural assays in rodents are complementary approaches, despite the fact that they are rarely associated simultaneously because general anaesthesia inherent to PET precludes behavioural studies. To address this methodological limit, we have developped a radiosensitive pixelated intracerebral probe named PIXSIC that provides access to the combination of simultaneous observations of molecular and behavioural parameters on rodents. PIXSIC proposes a novel strategy for in vivo recording of the local time-activity curves of PET radiopharmaceuticals. It relies on a sub-millimetre pixelated probe of Si (200 µm thick, 690 µm wide and 17 mm long hosting 10 pixels with dimension 200 µm x 500 µm) implanted into the brain region of interest by stereotaxic surgery. Positrons resulting from decays of a PET radiotracer are detected by reverse-biased, high-resistivity silicon diodes. The system aims at time-resolved high sensitivity measurements in a volume of a few mm3 defined similarly as for the Beta-Microprobe by the positron range within tissues. The pixelated detection scheme adds "imaging" features as it allows recording of the time-activity curves in different brain regions along the probe position. PIXSIC has a compact and autonomous design based on a radiofrequency data exchange link that allows for full freedom in the animals motion and behavioural activity while limiting stress during acquisition. The first biological validations were performed on anaesthetized rats implanted with two probes, one in the region of interest (hippocampus or striatum, according to the radiotracer) and the other one in a control region (cerebellum). We used [11C]-raclopride for dopamine D2 receptors and [18F]-MPPF for serotonin 5HT1A receptors. According to our previous studies with the Beta-Microprobe (J Nucl Med 2002, 43(2):227-33; Eur J Nucl Med 2002 29(9) 1237-47), the radioactive signals measured with the PIXSIC pixels are reproducible and well-correlated with the distributions of the targeted receptors. The simultaneous measurement of implanted rats in a small animal PET camera confirmed the similarity between PIXSIC and microPET time-activity curves. Moreover, the binding curves highlighted the possibility for PIXSIC to distinguish different tracer kinetics within the structure of interest (cortex/striatum or cortex/hippocampus) in accordance to the stereotaxic location of the pixels. In addition, PIXSIC allowed us to perform the first kinetic measurements of [11C]-raclopride and [18F]-MPPF on awake and freely moving rats. In conclusion, PIXSIC constitutes an unprecedented instrumental methodology for connecting PET molecular imaging and behavioral measurements with freely-moving rodents
PIXSIC, a Pixelated β(+)-Sensitive Probe for Radiopharmacological Investigations in Rat Brain: Binding Studies with [(18)F]MPPF.
International audienc
PIXSIC-Characterisation of a Beta+ Intracerebral Wireless Probe for Functtional Imaging Coupled with Behavioural Studies Performed on Freely Moving Rats
Physical Characterization of a Wireless Radiotracer Detection System Based on Pixelated Silicon for in Vivo Brain Studies in Freely Moving Rats
BLUPS for the four phenotypic traits studied. Each row corresponds to one individual
Physical Characterization of a Wireless Radiotracer Detection System Based on Pixelated Silicon for in Vivo Brain Studies in Freely Moving Rats
An exciting challenge for neuro-physiological investigations remains the combination of brain imaging and behavioral studies, which associates molecular processes of neuronal communications to their related actions. PIXSIC presents novel strategy using a submillimeter pixellated probe for β+ radiotracer detection based on a reverse-biased, high-resistivity silicon diode; This fully autonomous detection system permits local, time resolved measurements of radiotracers in a volume of a few mm3 with the probe dipped into aqueous solutions of [18F] and [11C]. Preliminary implantation tests on a anaesthetized rats proved functionality of the PIXSIC probe in brain tissues. High spatial resolution allows for the visualization of radiotracer concentration in different brain regions with a temporal resolution of less than 2 second
A wireless beta-microprobe based on pixelated silicon for in vivo brain studies in freely moving rats
The investigation of neurophysiological mechanisms underlying the functional specificity of brain regions requires the development of technologies that are well adjusted to in vivo studies in small animals. An exciting challenge remains the combination of brain imaging and behavioural studies, which associates molecular processes of neuronal communications to their related actions. A pixelated intracerebral probe (PIXSIC) presents a novel strategy using a submillimetric probe for beta+ radiotracer detection based on a pixelated silicon diode that can be stereotaxically implanted in the brain region of interest. This fully autonomous detection system permits time-resolved high sensitivity measurements of radiotracerswith additional imaging features in freelymoving rats. An application-specific integrated circuit (ASIC) allows for parallel signal processing of each pixel and enables the wireless operation. All components of the detector were tested and characterized. The beta+ sensitivity of the system was determined with the probe dipped into radiotracer solutions.Monte Carlo simulations served to validate the experimental values and assess the contribution of gamma noise. Preliminary implantation tests on anaesthetized rats proved PIXSIC's functionality in brain tissue. High spatial resolution allows for the visualization of radiotracer concentration in different brain regions with high temporal resolution. (Some figures may appear in colour only in the online journal