Golgi staining-like retrograde labeling of brain circuits using rabies virus: Focus onto the striatonigral neurons.

BACKGROUND: The introduction of viral transneuronal tracers in the toolbox of neural tract-tracing methods has been an important addition in the field of connectomics for deciphering circuit-level architecture of the nervous system. One of the added values of viral compared to conventional retrograde tracers, in particular of rabies virus, is to provide a Golgi staining-like view of the infected neurons, revealing the thin dendritic arborizations and the spines that are major post-synaptic seats of neuronal connections. NEWMETHOD: Here, we comparatively illustrate the characteristics of the labeling obtained in the same model system, the basal ganglia circuitry, by different retrograde viral tracing approaches, using the Bartha strain of pseudorabies virus, the SAD and CVS strains of rabies virus and by the conventional retrograde tracer cholera toxin B. To best contrast the differences in the capacity of these tracers to reveal the dendritic morphology in details, we focused on one population of first-order infected neurons in the striatum, which exhibit high spine density, after tracer injection in the substantia nigra. RESULTS AND CONCLUSION: None of the viruses tested allowed to detect as many neurons as with cholera toxin B, but the SAD and CVS strains of rabies virus had the advantage of enabling detailed Golgi-like visualisation of the dendritic trees, the best numerical detection being offered by the transneuronal rCVS-N2c-P-mCherry while poor labeling was provided by rCVS-N2c-M-GFP. Results also suggest that, besides different viral properties, technical issues about constructs and detection methods contribute to apparently different efficiencies among the viral approaches.

Invasive pulmonary aspergillosis in an ICU patient with Legionnaires' disease: A diagnostic challenge.

Aspergillus fumigatus can cause a wide range of diseases, from hypersensitivity to invasive infection. Invasive disease usually occurs in severely immunocompromised patients with deep and prolonged neutropenia. It is a less well-recognized complication in critically ill patients without traditional risk factors. We describe a case of early invasive pulmonary aspergillosis (IPA) secondary to Legionella pneumophila serogroup 1 pneumonia in a patient on an intensive care unit (ICU). In addition to commonly accepted risk factors for IPA in ICU patients, we hypothesis that L. pneumophilia pneumonia could enhance this type of infection. We also reviewed all published cases of coinfection with L. pneumophila and A. fumigatus to assess whether Legionnaires' disease could be a risk factor for IPA.

Reduction of patient radiation dose with a new organ based dose modulation technique for thoraco-abdominopelvic computed tomography (CT) (Liver dose right index).

PURPOSE: To evaluate the radiation dose reduction, image quality and diagnostic confidence with thoraco-abdominopelvic computed tomography (TACT) using a new organ based dose modulation system (liver dose right index [Liver DRI]), compared to TACT using a standard automatic exposure control adjusting mA according to attenuation. METHODS: A total of 37 patients who had two TACT examinations on 2 different CT scanners, one using standard automatic exposure control (combination of a DoseRight automatic current selection and Z modulation) and one using Liver DRI were included. There were 19 men and 18 women with a mean age of 67.6±11.7 (SD) years (range: 36-85 years) For each patient, volume CT dose index (CTDIvol), size-specific dose estimates (SSDE) and signal-to-noise ratio (SNR) were evaluated at each anatomic level (lung, breast, liver and pelvis area) for each protocol. Two radiologists assessed independently image quality, artifacts and diagnostic confidence. RESULTS: The radiation dose decreased significantly using Liver DRI compared to standard automatic exposure control on the total scan length, lung, breast and pelvis area, with a significant CTDIvol reduction of 27% (P=0.0001), 23% (P=0.0002), 24% (P=0.0002) and 31% (P=0.0001), respectively; and a significant SSDE reduction of 23% (P=0.0001), 28% (P=0.0001), 23% (P=0.0002) and 29% (P=0.0001), respectively. No significant SNR reductions were observed in all measured tissues at the level of the aortic arch, celiac trunk and iliac bifurcation, except in the muscle (P=0.0013) and fat tissue (P=0.0052) at the level of the ureteral meatus. No significant differences were noted between both protocols in overall image quality, artifacts and diagnostic confidence with an excellent inter observer agreement between radiologists (Kappa values of 0.83, 0.85 and 0.88, respectively). CONCLUSION: Liver DRI organ based dose modulation technique allows significant dose reduction compared to standard automatic exposure control while preserving diagnostic image quality in all thoraco-abdominopelvic areas.

Lucid dreams, an atypical sleep disturbance in anterior and mediodorsal thalamic strokes.

BACKGROUND: Cognitive, affective, and behavioural disturbances are commonly reported following thalamic strokes. Conversely, sleep disorders are rarely reported in this context. OBSERVATIONS: Herein, we report the cases of two young patients admitted for an ischemic stroke located in the territories of the left pre-mammillary and paramedian arteries. Together with aphasia, memory complaint, impaired attention and executive functions, they reported lucid dreams with catastrophic content or conflicting situations. CONCLUSION: Lucid dreams are an atypical presentation in thalamic strokes. These cases enlarge the clinical spectrum of sleep-wake disturbances potentially observed after an acute cerebrovascular event.

Photon counting spectral CT component analysis of coronary artery atherosclerotic plaque samples.

OBJECTIVE: To evaluate the capabilities of photon counting spectral CT to differentiate components of coronary atherosclerotic plaque based on differences in spectral attenuation and iodine-based contrast agent concentration. METHODS: 10 calcified and 13 lipid-rich non-calcified histologically demonstrated atheromatous plaques from post-mortem human coronary arteries were scanned with a photon counting spectral CT scanner. Individual photons were counted and classified in one of six energy bins from 25 to 70 keV. Based on a maximum likelihood approach, maps of photoelectric absorption (PA), Compton scattering (CS) and iodine concentration (IC) were reconstructed. Intensity measurements were performed on each map in the vessel wall, the surrounding perivascular fat and the lipid-rich and the calcified plaques. PA and CS values are expressed relative to pure water values. A comparison between these different elements was performed using Kruskal-Wallis tests with pairwise post hoc Mann-Whitney U-tests and Sidak p-value adjustments. RESULTS: RESULTS for vessel wall, surrounding perivascular fat and lipid-rich and calcified plaques were, respectively, 1.19 ± 0.09, 0.73 ± 0.05, 1.08 ± 0.14 and 17.79 ± 6.70 for PA; 0.96 ± 0.02, 0.83 ± 0.02, 0.91 ± 0.03 and 2.53 ± 0.63 for CS; and 83.3 ± 10.1, 37.6 ± 8.1, 55.2 ± 14.0 and 4.9 ± 20.0 mmol l(-1) for IC, with a significant difference between all tissues for PA, CS and IC (p < 0.012). CONCLUSION: This study demonstrates the capability of energy-sensitive photon counting spectral CT to differentiate between calcifications and iodine-infused regions of human coronary artery atherosclerotic plaque samples by analysing differences in spectral attenuation and iodine-based contrast agent concentration. ADVANCES IN KNOWLEDGE: Photon counting spectral CT is a promising technique to identify plaque components by analysing differences in iodine-based contrast agent concentration, photoelectric attenuation and Compton scattering.

Impairment of skin blood flow during post-occlusive reactive hyperhemy assessed by laser Doppler flowmetry correlates with renal resistive index.

We lack non-invasive tools for evaluating the coronary and renal microcirculations. Since cutaneous Doppler laser exploration has evidenced impaired cutaneous microvascular responses in coronary artery disease and in impaired renal function, we wanted to find out if there was a link between the impairments in the cutaneous and renal microcirculations. To specify the significance of the rise in the renal resistive index (RI), which is still unclear, we also sought relations between RI and arterial stiffness. We conducted a cross-sectional controlled study in a heterogeneous population including hypertensive patients of various ages with or without a history of cardiovascular disease along with a healthy control group. The cutaneous microcirculation was evaluated by laser Doppler flowmetry of the post-occlusive reactive hyperhemy (PORH) and of the hyperhemy to heat. The renal microcirculation was evaluated by measurement of the RI. Arterial stiffness was evaluated from an ambulatory measurement of the corrected QKD(100-60) interval. We included 22 hypertensives and 11 controls of mean age 60.6 vs 40.8 years. In this population, there was a correlation between RI and basal zero to peak flow variation (BZ-PF) (r=-0.42; P=0.02) and a correlation between RI and rest flow to peak flow variation (RF-PF) (r=-0.44; P=0.01). There was also a significant correlation between RI and the corrected QKD(100-60) (r=-0.47; P=0.01). The significant correlation between PORH parameters and RI indicates that the functional modifications of the renal and cutaneous microcirculations tend to evolve in parallel during ageing or hypertension. The relation between RI and arterial stiffness shows that RI is a compound index of both renal microvascular impairment and the deterioration of macrovascular mechanics.

Image registration and analysis for quantitative myocardial perfusion: application to dynamic circular cardiac CT.

Large area detector computed tomography systems with fast rotating gantries enable volumetric dynamic cardiac perfusion studies. Prospectively, ECG-triggered acquisitions limit the data acquisition to a predefined cardiac phase and thereby reduce x-ray dose and limit motion artefacts. Even in the case of highly accurate prospective triggering and stable heart rate, spatial misalignment of the cardiac volumes acquired and reconstructed per cardiac cycle may occur due to small motion pattern variations from cycle to cycle. These misalignments reduce the accuracy of the quantitative analysis of myocardial perfusion parameters on a per voxel basis. An image-based solution to this problem is elastic 3D image registration of dynamic volume sequences with variable contrast, as it is introduced in this contribution. After circular cone-beam CT reconstruction of cardiac volumes covering large areas of the myocardial tissue, the complete series is aligned with respect to a chosen reference volume. The results of the registration process and the perfusion analysis with and without registration are evaluated quantitatively in this paper. The spatial alignment leads to improved quantification of myocardial perfusion for three different pig data sets.

Dose and image quality comparison between prospectively gated axial and retrospectively gated helical coronary CT angiography.

OBJECTIVE: Our aim was to compare image quality, coronary segment assessability and radiation dose in prospectively gated axial (PGA) coronary CT angiography (CTA) and conventional retrospectively gated helical (RGH) coronary CTA. METHODS: Institutional review committee approval and informed consent were obtained. RGH CTA was performed in 41 consecutive patients (33 males, 8 females; mean age 52.6 years), then the PGA CTA technique was evaluated in 41 additional patients (24 males, 17 females; mean age 57.3 years) all with a pre-scan heart rate of ≤70 beats per minute (bpm). Two radiologists, blinded to clinical information, independently scored subjective image quality on a five-point ordinal scale. RESULTS: The mean effective dose in the PGA group was 4.7±0.9 mSv, representing a 69% dose reduction compared with the RGH CTA group (15.1±1.9 mSv, p<0.001). The mean segmental image quality score was significantly higher in the PGA group (3.4 vs 3.2) than in the RGH CTA group (p<0.005). The percentage of assessable segments was 98.1% in the PGA group and 97.3% in the RGH group (p = 0.610). CONCLUSION: PGA CTA offers a significant reduction in radiation dose compared with RGH CTA, with comparable image quality for patients with heart rates below 70 bpm.

Controlled fabrication of Si nanocrystals embedded in thin SiON layers by PPECVD followed by oxidizing annealing.

The controlled fabrication of Si nanocrystals embedded in thin silicon oxynitride films (<15 nm) on top of a silicon substrate has been realized by PPECVD with N(2)O-SiH(4) precursors. The effect of inert and oxidizing annealing processes on the Si nanocrystal spatial and size distributions is studied by coupling ellipsometry measurements and cross-sectional transmission electron microscopy observations. This study gives an interesting insight into the physics underlying the Si nanocrystal nucleation, growth and oxidation mechanisms. In particular, it evidences the presence in the as-deposited films of a high density of small amorphous Si particles that crystallize after high temperature thermal annealing. Annealing under oxidizing conditions is shown to be a powerful way to create tunnel oxides of good quality and controlled thickness needed to design future memory devices.

High-k Hf-based layers grown by RF magnetron sputtering.

Structural and chemical properties of Hf-based layers fabricated by RF magnetron sputtering were studied by means of x-ray diffraction, transmission electron microscopy and attenuated total reflection infrared spectroscopy versus the deposition parameters and annealing treatment. The deposition and post-deposition conditions allow us to control the temperature of the amorphous-crystalline phase transition of HfO(2)-based layers. It was found that silicon incorporation in an HfO(2) matrix plays the main role in the structural stability of the layers. It allows us not only to decrease the thickness of the film/substrate interfacial layer to 1 nm, but also to conserve the amorphous structure of the layers after an annealing treatment up to 900-1000 degrees C.

Si nanocrystal synthesis in HfO2/SiO/HfO2 multilayer structures.

The synthesis of two-dimensional arrays of Si nanocrystals in an HfO2 matrix has been achieved by deposition of HfO2/SiO/HfO2 multilayer structures followed by high temperature (1100 degrees C) thermal treatment in nitrogen atmosphere. Silicon out-diffusion from the SiO layer through the HfO2 films has been shown to be the limiting factor in the formation of the Si nanocrystals. Suitable strategies have been identified in order to overcome this limitation. Si nanocrystal formation has been achieved by properly adjusting the thickness of the SiO layer.

Thalamic afferent activation of supragranular layers in auditory cortex in vitro: a voltage sensitive dye study.

We studied auditory thalamocortical interactions in vitro, using an auditory thalamocortical brain slice preparation. Cortical activity evoked by electrical stimulation of the medial geniculate nucleus (MGN) was investigated through field potential recordings and voltage sensitive dyes. Experiments were performed in slices obtained from adult mice (9-14 weeks). Stimulus evoked activity was detected in the granular and supragranular layers after a short latency (5-6 ms). In 9-14 weeks old mice infragranular activity was detected in 10 of 24 preparations and was found to be increased in younger mice (p 31-64). In 14 of 24 slices a prominent horizontal spread was observed, which extended into cortical areas lateral to A1. In these experiments, the shortest onset latencies and largest signal amplitudes were located in the supragranular layers of A1. In areas lateral to A1, shortest onset latencies were located in the granular layer, while largest signal amplitudes were found in the supragranular layers. Evoked cortical activity was sensitive to removal of extracellular Ca(2+) or application of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 microM). Short repetitive stimulation, resembling thalamic burst activity (three pulses at 100 Hz), resulted in an increase of signal amplitude and excited area by approximately 25%, without changing the overall spatiotemporal activity profile. Blockade of N-methyl-D-aspartate receptors by 2-amino-5-phosphonopentanoate (AP5, 50 microM) reduced amplitudes and excited area by approximately 15-30%, irrespective of stimulation frequency. Application of bicuculline (10 microM) greatly increased cortical responses to thalamic stimulation. Under these conditions, evoked activity displayed a pronounced horizontal spread in combination with a 2-3-fold increase in amplitude. In conclusion, afferent thalamic inputs primarily activate supragranular and granular layers in the auditory cortex of adult mice. This activation is predominantly mediated by non-NMDA receptors, while GABA(A) receptor-mediated inhibition limits the horizontal and vertical spread of activity.

Novel technique: staged hybrid surgical and endovascular treatment of acute Type A aortic dissections with aortic arch involvement.

AIM: The standard approach for treating acute Type A aortic dissections (TAD) is replacement of the ascending aorta utilizing hypothermic circulatory arrest (HCA), which is associated with significant morbidity and frequently leaves a residual aortic arch dissection. We describe a staged surgical and endovascular technique of ascending aorta replacement and simultaneous aorto-innominate artery bypass without HCA, followed 4 weeks later by carotid-carotid bypass and endovascular exclusion of the remaining arch dissection with a thoracic endograft. METHODS: From December 2004 to December 2005, 5 consecutive patients (mean age 58 +/- 6.9 years) with TADs underwent the staged procedure. All patients underwent replacement of the ascending aorta and aorto-innominate bypass. Two patients subsequently underwent the second endovascular stage. In one patient the aortic false lumen completely thrombosed following the first surgical stage and two patients are currently awaiting the endovascular stage. RESULTS: There were no major adverse events (death, cerebrovascular accident or paraplegia) following the first surgical stage. One patient suffered a transient minor stroke. The 2 patients who underwent the second endovascular stage showed no immediate adverse events. Postoperative CT scans have demonstrated that the false channel was excluded from the aortic arch down to the distal end of the endograft in the descending aorta in each case, but became patent further downstream. CONCLUSIONS: This procedure appears safe and feasible. It may allow for a more definitive treatment of TADs than the standard surgical approach. It can be adapted by low volume centers, surgeons untrained in aortic arch repair, and in high risk patients.

Great vessel management for endovascular exclusion of aortic arch aneurysms and dissections.

OBJECTIVES: To evaluate a recent approach for the endovascular repair of thoracic aortic aneurysms and dissections involving the aortic arch in high risk patients (HRP). METHODS: Amongst 102 thoracic aortic aneurysms and dissections, we treated 25 patients for aortic arch endovascular exclusion after transposition of the great vessels, of which 14 (56%) had thoracic aortic arch aneurysms and 11 type A and B chronic aortic dissections. Total transpositions were done in 15 cases (60%) and hemi-arch transpositions in 10. We then used Talent, Excluder and Zenith endografts in 12, seven and six cases, respectively. RESULTS: Surgical transpositions were complicated by one minor stroke, which worsened to a major stroke (4%) after endovascular exclusion. After endovascular exclusions, two patients (8%) died from catheterization related complications. One patient had a delayed minor stroke (4%). The successful exclusion rate was 92%. During follow-up (15+/-5.8 months), one patient (4%) developed unilateral limb palsy, successfully treated by CSF drainage. The late exclusion rate remained 92%. No stent-related complications were seen. CONCLUSIONS: Transposition of supra-aortic vessels allows the endovascular exclusion of the aortic arch in HRP. Aortic endografting after surgical transposition proved to be feasible and offers good mid-term results. Specialized surgical centers with both endovascular and surgical expertise are required to treat these patients.

[Transneuronal tracing using neurotropic viruses in the mammals]. / Un usage « sympathique ¼ des virus neurotropes : le traçage transneuronal chez les mammifères.

For fifteen years, the knowledge of the organization of neuronal networks inside the central nervous system of mammals has been considerably enhanced with the use of neurotropic viruses as tracers. Those viruses, pseudorabies, herpes simplex type 1 and rabies propagate in the brain through chains of connected neurons. This means that the transfer from a neuron to another one occurs only at the synaptic level. Each strain of virus has its own specificities which are used to study neuronal networks of different nature. Thus, the Bartha strain of pseudorabies, mostly used for tracing studies in rodents, has been very useful to characterize the networks belonging to the autonomic nervous system following peripheral inoculation. Less employed, rabies virus has been mainly used for the characterization of motor networks and, recently, to map neuronal networks in the cortex of primates after stereotaxic injections. On the other hand, the injection at distinct sites of recombinant pseudorabies viruses expressing different exogenous genes allows the study of interactions between two networks. This revue presents the milestones of the development of the transneuronal tracing using neurotropic viruses and emphasizes what virology and neurosciences bring to each other thanks to this technique.

Great vessels transposition and aortic arch exclusion.

AIM: We describe our experience in endovascular repair of Thoracic Aortic Aneurysms and Dissections (TAAD) involving the aortic arch in high risk patients (HRP). METHODS: Twenty-nine patients presented with TAAD involving the aortic arch and were treated by endovascular exclusion. Pathologies were as follows: atherosclerotic aneurysms of the descending thoracic aorta in 15 cases, acute Stanford type A dissections in 6 cases, Stanford type B dissections in 7 cases (1 acute), and 1 false aneurysm of the ascending aorta. Total-arch transpositions of all supra-aortic vessels (aortic debranching) to the ascending aorta were done in 11 cases throught median sternotomy. We performed carotido-carotid bypass (hemi-arch transposition) in 16 patients by cervicotomy. Secondary to surgical transpositions, we placed endovascular stentgrafts in all but 2 patients for final exclusion, the 2 remaining being planned for later exclusion. The Talent, Excluder, TAG and Zenith endografts were used in 12, 3, 1 and 4 cases respectively. Banding technique was associated in some cases. RESULTS: All surgical transpositions were successful although 1 led to a minor stroke (1/29=3.5%), which worsened to major stroke after endovascular exclusion. Endovascular procedures were performed in all but one case (26/27=96.3%). Two patients (2/26=7.7%) died from catheterization related complications after endovascular exclusion (iliac rupture and left ventricle perforation). One patient had a delayed minor stroke (1/26=3.8%). Recirculation was found in 13.3% (2/15) of aneurysms and 27.3% of thoracic false channels. During a mean follow-up of 15.7 months (13 days to 45.5 months), 1 patient (1/26=3.8%) who had preoperative chronic pulmonary failure died at 6 months from respiratory worsening. We observed one case (3.8%) of unilateral limb palsy unrelated to cerebral ischemia, which we successfully treated by cerebrospinal fluid (CSF) drainage. No stent-related complication was seen. One new type 1 endoleak appeared at 12 months on an aneurysm, which resolved after stentgraft extension. Three thoracic dissection false channels remained patent during follow-up, of which one was retrograde originating distally in the descending aorta. CONCLUSIONS: Secondary endovascular exclusion of thoracic aortic diseases involving the arch in HRP is made feasible thanks to the preliminary aortic debranching. Total-arch transposition may be of greater interest in case of proximal neck length uncertainty and potential embolization from the aortic arch. Mid-term results are good although patients must be followed carefully to detect aortic recirculation and enlargement.

Phox2a gene, A6 neurons, and noradrenaline are essential for development of normal respiratory rhythm in mice.

Although respiration is vital to the survival of all mammals from the moment of birth, little is known about the genetic factors controlling the prenatal maturation of this physiological process. Here we investigated the role of the Phox2a gene that encodes for a homeodomain protein involved in the generation of noradrenergic A6 neurons in the maturation of the respiratory network. First, comparisons of the respiratory activity of fetuses delivered surgically from heterozygous Phox2a pregnant mice on gestational day 18 showed that the mutants had impaired in vivo ventilation, in vitro respiratory-like activity, and in vitro respiratory responses to central hypoxia and noradrenaline. Second, pharmacological studies on wild-type neonates showed that endogenous noradrenaline released from pontine A6 neurons potentiates rhythmic respiratory activity via alpha1 medullary adrenoceptors. Third, transynaptic tracing experiments in which rabies virus was injected into the diaphragm confirmed that A6 neurons were connected to the neonatal respiratory network. Fourth, blocking the alpha1 adrenoceptors in wild-type dams during late gestation with daily injections of the alpha1 adrenoceptor antagonist prazosin induced in vivo and in vitro neonatal respiratory deficits similar to those observed in Phox2a mutants. These results suggest that noradrenaline, A6 neurons, and the Phox2a gene, which is crucial for the generation of A6 neurons, are essential for development of normal respiratory rhythm in neonatal mice. Metabolic noradrenaline disorders occurring during gestation therefore may induce neonatal respiratory deficits, in agreement with the catecholamine anomalies reported in victims of sudden infant death syndrome.

Altered respiratory activity and respiratory regulations in adult monoamine oxidase A-deficient mice.

The abnormal metabolism of serotonin during the perinatal period alters respiratory network maturation at birth as revealed by comparing the monoamine oxidase A-deficient transgenic (Tg8) with the control (C3H) mice (Bou-Flores et al., 2000). To know whether these alterations occur only transiently or induce persistent respiratory dysfunction during adulthood, we studied the respiratory activity and regulations in adult C3H and Tg8 mice. First, plethysmographic and pneumotachographic analyses of breathing patterns revealed weaker tidal volumes and shorter inspiratory durations in Tg8 than in C3H mice. Second, electrophysiological studies showed that the firing activity of inspiratory medullary neurons and phrenic motoneurons is higher in Tg8 mice and that of the intercostal motoneurons in C3H mice. Third, histological studies indicated abnormally large cell bodies of Tg8 intercostal but not phrenic motoneurons. Finally, respiratory responses to hypoxia and lung inflation are weaker in Tg8 than in C3H mice. dl-p-chlorophenyl-alanine treatments applied to Tg8 mice depress the high serotonin level present during adulthood; the treated mice recover normal respiratory responses to both hypoxia and lung inflation, but their breathing parameters are not significantly affected. Therefore in Tg8 mice the high serotonin level occurring during the perinatal period alters respiratory network maturation and produces a permanent respiratory dysfunction, whereas the high serotonin level present in adults alters the respiratory regulatory processes. In conclusion, the metabolism of serotonin plays a crucial role in the maturation of the respiratory network and in both the respiratory activity and the respiratory regulations.

Optimization of a new scintillation gas detector used to localize electrons emitted by 99mTc.

UNLABELLED: We have developed a scintillation gas detector to localize electrons emitted by 99mTc. This type of detector allows direct quantification of images and so provides a clear advantage over autoradiographic film. We have optimized the device to give an image spatial resolution that closely approximates that of typical autoradiographic film. To improve this resolution, it was necessary to select only low-energy electrons (2 and 15 keV) and to devise novel detection and localization techniques for the ionizing particles. METHODS: A parallel-plate proportional avalanche chamber is subject to a uniform electrical field and amplifies the number of released electrons through collisions of ionizing particles in the gas mixture. Light emitted by the gas scintillator during the avalanche process is collected by a highly intensified charge coupled device camera. The centroid of each resulting light distribution is calculated, resulting in a quantitative mapping of the sample's activity. Insertion of the sample within the gas volume improves the efficiency and so provides a method that is both very sensitive and linear. RESULTS: We have shown that in a parallel-plate structure, the application of a high electrical field to the surface of the sample and the selection of appropriate light spots, according to their morphology, can overcome localization errors due to the particles' trajectories. We have obtained a resolution of the order of 30 microm, using electrons from 99mTc. CONCLUSION: This detection technique allows considerable improvement in image resolution. This "electron camera" is a serious rival to existing autoradiographic techniques, because it provides certain other advantages, including direct quantification, linearity, high dynamic range and low noise levels. Thus, new perspectives are made available in quantitative double tracer autoradiography, because electrons can be selected for imaging as a function of their energy.