Conventional Tracer Research Articles

Investigation of [11C]carfentanil for mu opioid receptor quantification in the rat brain

[11C]Carfentanil ([11C]CFN) is the only selective carbon-11 labeled radiotracer currently available for positron emission tomography (PET) imaging of mu opioid receptors (MORs). Though used extensively in clinical research, [11C]CFN has not been thoroughly characterized as a tool for preclinical PET imaging. As we were occasionally observing severe vital sign instability in rat [11C]CFN studies, we set out to investigate physiological effects of CFN mass and to explore its influence on MOR quantification. In anesthetized rats (n = 15), significant dose-dependent PCO2 increases and heart rate decreases were observed at a conventional tracer dose range (IV, > 100 ng/kg). Next, we conducted baseline and retest [11C]CFN PET scans over a wide range of molar activities. Baseline [11C]CFN PET studies (n = 27) found that nondisplaceable binding potential (BPND) in the thalamus was positively correlated to CFN injected mass, demonstrating increase of MOR availability at higher injected CFN mass. Consistently, when CFN injected mass was constrained < 40 ng/kg (~ 10% MOR occupancy in rats), baseline MOR availability was significantly decreased. For test–retest variability (TRTV), better reproducibility was achieved by controlling CFN injected mass to limit the difference between scans. Taken together, we report significant cardiorespiratory depression and a paradoxical influence on baseline MOR availability at conventional tracer doses in rats. Our findings might reflect changes in cerebral blood flow, changes in receptor affinity, or receptor internalization, and merits further mechanistic investigation. In conclusion, rat [11C]CFN PET requires stringent quality assurance of radiotracer synthesis and mass injected to avoid pharmacological effects and limit potential influences on MOR quantification and reproducibility.

Abstract PO2-23-02: Results of a prospective randomised multicentre study comparing indocyanine green (ICG) fluorescence combined with a standard tracer versus ICG alone for sentinel lymph node biopsy in early breast cancer: The INFLUENCE Trial

Abstract Background: Use of fluorescence mapping for visualization of lymphatic and nodal tissue for sentinel lymph node biopsy (SNB) reveals high rates of identification (&amp;gt;98%). Studies combining ICG with either blue dye or radioisotope (RI) have shown high levels of concordance (&amp;gt;90%) and comparable performance parameters between ICG and standard tracers for SNB localization. ICG combines many advantages of blue dye and RI without the disadvantages of allergic reactions, staining of skin and surgical tissues along with handling and disposal of radioactivity materials. Moreover, magnetic tracers pose challenges of interference relating to surgical instrumentation and magnetic resonance imaging (MRI). The combination of ICG with a conventional tracer may represent a transition phase and this randomized study evaluates ICG as a sole tracer agent for SNB in early-stage breast cancer. Methods: In a prospective randomized study, 100 patients with unilateral clinically node negative tumours scheduled to undergo routine SNB for core-biopsy proven invasive breast cancer (≤5cm) were identified at multidisciplinary meetings [non-invasive tumours excluded]. All patients had pre-operative axillary ultrasound and breast conserving surgery or mastectomy. Patients were recruited in two cohorts (n=50); cohort 1 was assigned to either ICG [2ml 0.5%] alone (n=25) or combined with RI [Technetium99 nanocolloid, 20MBq] (n=25). Cohort 2 received ICG alone (n=25) or combined with blue dye for SNB localization. The number of nodes whether blue, radioactive, fluorescent or a combination thereof were recorded. Lymphatic and nodal tissue was visualized with a fluorescent camera/detection system. Sensitivity of ICG alone and/or in combination with one or another standard tracer was calculated. The main objective was to assess the performance of ICG alone compared with a standard tracer combination in terms of rates of SNB identification along with procedural node positivity rates. Statistical analysis employed Chi-Square test, Fisher’s Exact test, and logistic regression to determine differences between groups. Results: A total of 100 patients were randomized between March and December 2022 with 3 patients excluded from analysis (non-receipt of treatment allocation). Amongst evaluable patients (n=97), the overall SNB identification rate was 96.9% and by tracer category as follows: ICG alone = 97.9% (46/47); ICG + RI = 100% (25/25); ICG + blue dye = 92% (23/25). For cohort 1, the procedural node positivity rates were 17% for ICG alone and 18% for ICG + RI with corresponding figures of 12% for ICG alone and 20% for ICG + blue dye for cohort 2. Mean procedural node retrieval per case was 2.5 in ICG alone Vs ICG + Blue Dye and 2.3 in ICG alone Vs ICG/RI cohorts. There were no significant differences (p&amp;gt;0.05) in performance of ICG alone or combined with a standard tracer, with ICG alone being non-inferior in terms of procedural and nodal detection rates. Similar conclusions were reached from a secondary analysis adjusting for BMI, age and mode of detection (screening/symptomatic). Conclusion: ICG fluorescence imaging permits real-time visualisation of lymphatics and gives an additional dimension to SNB that appears safe versus the competitive alternatives. These results confirm high sensitivity for fluorescence localisation alone for SNB with comparable performance to combined methods with blue dye or RI. The fluorochrome ICG is reliable as a sole tracer and avoids potential drawbacks of blue dye and RI including staining, allergic reactions, availability and costs. Citation Format: Vassilis Pitsinis, Rahul Kanitkar, Alessio Vinci, Emad Elseedawy, Laura Canna, John R Benson. Results of a prospective randomised multicentre study comparing indocyanine green (ICG) fluorescence combined with a standard tracer versus ICG alone for sentinel lymph node biopsy in early breast cancer: The INFLUENCE Trial [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-23-02.

Joint Diagnostic Approach to Pressure and Tracer Responses from Reservoirs: An Experimental and Theoretical Study to Estimate the Accuracy of Reservoir Models

This study presents a novel perspective for improving the understanding of permeable structures at geothermal prospects by jointly diagnosing the responses of conventional pressure transient and tracer testing. The pressure and tracer responses individually yield apparent porosity–thickness products. The difference between them implies the existence of unknown dead-end features involved in a reservoir model. Laboratory experiments and numerical simulations validate this concept. Potential application to hypothetical exploration demonstrates that the logarithmic ratio of the porosity–thickness products, determined based on pressure and tracer responses, indicates the accuracy of the reservoir model to be successively updated with the progress of the exploration. The reservoir model successfully reproduced the synthetic observations regardless of the accuracy of permeable structure if different porosity–thickness products were allowed to be assumed to individually reproduce pressure and tracer responses. These porosity–thickness products coincided only if the reservoir model correctly captured the permeable structure. This novel perspective will provide strategic guides for successful exploration and development at the prospects of geothermal and, potentially, general geofluid resources.

Pathways from the superior colliculus and the nucleus of the optic tract to the posterior parietal cortex in macaque monkeys: Functional frameworks for representation updating and online movement guidance.

The posterior parietal cortex (PPC) integrates multisensory and motor-related information for generating and updating body representations and movement plans. We used retrograde transneuronal transfer of rabies virus combined with a conventional tracer in macaque monkeys to identify direct and disynaptic pathways to the arm-related rostral medial intraparietal area (MIP), the ventral lateral intraparietal area (LIPv), belonging to the parietal eye field, and the pursuit-related lateral subdivision of the medial superior temporal area (MSTl). We found that these areas receive major disynaptic pathways via the thalamus from the nucleus of the optic tract (NOT) and the superior colliculus (SC), mainly ipsilaterally. NOT pathways, targeting MSTl most prominently, serve to process the sensory consequences of slow eye movements for which the NOT is the key sensorimotor interface. They potentially contribute to the directional asymmetry of the pursuit and optokinetic systems. MSTl and LIPv receive feedforward inputs from SC visual layers, which are potential correlates for fast detection of motion, perceptual saccadic suppression and visual spatial attention. MSTl is the target of efference copy pathways from saccade- and head-related compartments of SC motor layers and head-related reticulospinal neurons. They are potential sources of extraretinal signals related to eye and head movement in MSTl visual-tracking neurons. LIPv and rostral MIP receive efference copy pathways from all SC motor layers, providing online estimates of eye, head and arm movements. Our findings have important implications for understanding the role of the PPC in representation updating, internal models for online movement guidance, eye-hand coordination and optic ataxia.

Comparison of sediment biomarker signatures generated using time-integrated and discrete suspended sediment samples

Sediment source fingerprinting using biomarker properties has led to new insights in our understanding of land use contributions to time-integrated suspended sediment samples at catchment scale. A time-integrated mass-flux sampler (TIMS; also known as the ‘Phillips’ sampler), a cost-effective approach for suspended sediment collection in situ. Such samplers are widely being used to collect sediment samples for source fingerprinting purposes, including studies using biomarkers as opposed to more conventional tracer properties. Here, we assessed the performance of TIMS for collecting representative sediment samples for biomarkers during high discharge events in a small lowland grassland-dominated catchment. Concentrations of long odd-chain n-alkanes (> C23) and both saturated free and bound fatty acids (C14-C32), as well as compound-specific 13C were compared between sediment collected by both TIMS and autosamplers (ISCO). The results showed that concentrations of alkanes, free fatty acids, and bound fatty acids are consistently comparable between TIMS and ISCO suspended sediment samples. Similarly, compound-specific 13C signals were not found to be significantly different in the suspended sediment samples collected using the different samplers. However, different magnitudes of resemblance in biomarker concentrations and compositions between the samples collected using the two sediment collection methods were confirmed by overlapping index and symmetric coordinates-based correlation analysis. Here, the difference is attributed to the contrasting temporal basis of TIMS (time-integrated) vs. ISCO (discrete) samples, as well as potential differences in the particle sizes collected by these different sediment sampling methods. Nevertheless, our findings suggest that TIMS can be used to generate representative biomarker data for suspended sediment samples collected during high discharge events.

Expanding Karst Groundwater Tracing Techniques: Incorporating Population Genetic and Isotopic Data to Enhance Flow-Path Characterization

Karst aquifers are unique among groundwater systems because of variable permeability and flow-path organization changes resulting from dissolution processes. Over time, changes in flow-path connectivity complicate interpretations of conduit network evolution in karst hydrogeology. Natural and artificial tracer techniques have long provided critical information for protecting karst aquifers and understanding the potential impacts on ecosystems and human populations. Conventional tracer methods are useful in karst hydrogeologic studies for delineating flow paths and defining recharge, storage, and discharge properties. However, these methods only provide snapshots of the current conditions and do not provide sufficient information to understand the changes in interconnection or larger-scale evolution of flow paths in the aquifer over time. With advances in population genetics, it is possible to assess population connectivity, which may provide greater insights into complex groundwater flow paths. To assess this potential, we combined the more traditional approaches collected in this and associated studies, including artificial (dye) and natural (geochemistry, isotopes, and discharge) tracers, with the population genetic data of a groundwater crustacean to determine whether these data can provide insights into seasonal or longer changes in connections between conduits. The data collected included dye trace, hydrographs, geochemistry, and asellid isopod (Caecidotea bicrenenta) population genetics in Fern Cave, AL, USA, a 25 km-long cave system. Combined, these data show the connections between two separate flow paths during flood events as the downstream populations of isopods belonging to the same subpopulation were measured in both systems. Additionally, the sub-populations found in higher elevations of the cave suggest a highly interconnected unsaturated zone that allows for genetic movement in the vadose zone. Although upstream populations show some similarities in genetics, hydrologic barriers, in the form of large waterfalls, likely separate populations within the same stream.

Review of tracer kinetic models in evaluation of gliomas using dynamic contrast-enhanced imaging.

Glioma is the most common type of primary malignant tumor of the central nervous system (CNS), and is characterized by high malignancy, high recurrence rate and poor survival. Conventional imaging techniques only provide information regarding the anatomical location, morphological characteristics, and enhancement patterns. In contrast, advanced imaging techniques such as dynamic contrast-enhanced (DCE) MRI or DCE CT can reflect tissue microcirculation, including tumor vascular hyperplasia and vessel permeability. Although several studies have used DCE imaging to evaluate gliomas, the results of data analysis using conventional tracer kinetic models (TKMs) such as Tofts or extended-Tofts model (ETM) have been ambiguous. More advanced models such as Brix's conventional two-compartment model (Brix), tissue homogeneity model (TH) and distributed parameter (DP) model have been developed, but their application in clinical trials has been limited. This review attempts to appraise issues on glioma studies using conventional TKMs, such as Tofts or ETM model, highlight advancement of DCE imaging techniques and provides insights on the clinical value of glioma management using more advanced TKMs.

Application of indocyanine green lymphography combined with methylene blue staining in lymphaticovenular anastomosis of lower limb vessels: A prospective study.

Methylene blue (MB) is a conventional lymphatic tracer. We evaluated the application of indocyanine green (ICG) lymphography combined with MB staining in lower limb lymphaticovenular anastomosis (LVA). A total of 49 patients with lower limb lymphedema were selected as the study subjects and divided into the research (n = 27) and control groups (n = 22). The patients were treated with LVA using ICG lymphography combined with MB staining and simple ICG lymphography as the positioning method, respectively. The number of lymphatic vessels anastomosed and the operating time were compared between the groups. Lower Extremity Lymphedema Index (LEL index) and Lymphoedema Functioning, Disability and Health Questionnaire for Lower Limb Lymphoedema (Lymph-ICF-LL) were used as prognostic indices; 6months after LVA, both groups were evaluated for the symptomatic relief of lymphedema. The number of anastomotic lymphatic vessels in the study group was higher than that in the control group (p < .05), and their procedural time was shorter than that in the control group. The two groups had no significant difference in lymphatic anastomosis time (p > .05). The LEL index and Lymph-ICF-LL of the research and control groups at 6-month follow-up after LVA were lower than those before the operation (p < .05). The circumference of the affected limb is reduced after LVA in patients with lower extremity lymphedema with a favorable prognosis. ICG lymphography combined with MB staining has the advantages of real-time visualization and accurate localization.

Dipole Flow Tracer Test Models for Identifying Skin Properties and Ambient Groundwater Flow Effects.

As a special single-well test with dual-screened configuration, dipole flow test with a tracer (DFTT) has been an efficient tool for aquifer parameter interpretation. The tool is excellent for characterizing the vertical distribution of hydraulic conductivity, dispersivity and in situ reaction rate in aquifers. It is noteworthy that the effects of skin and ambient groundwater flow (AGF) on the solute transport, which have been widely investigated in terms of conventional tracer tests, have not been comprehensively studied with respect to DFTT. Meanwhile, it is important to elucidate the potentials of DFTT in identifying the primary skin properties as well as the methods to avoid the AGF effects on DFTT. Consequently, we developed a mathematical model for DFTT accounting for skin and AGF. The results show that a negative skin acts as a preferential pathway for tracer transport and the AGF effects on breakthrough curves (BTCs) can be easily mistaken for reaction. Through extensive mathematical model-based experiments, the BTCs calculated from the DFTT models with skin effects were categorized into four types, each of which is able to imply a specific kind of skin. Additionally, a new dimensionless parameter , composed of injection/extraction rate, hydraulic conductivity, hydraulic gradient of AGF and screen parameters, was defined to quantitatively indicate the AGF effects on the overestimation degree of the in situ first-order reaction, implying that one can adjust the field parameters of DFTT to keep less than 3.7% to achieve an overestimation error of reaction rate below 50%.

Evolution of a natural dihydropteroate synthase and development of a signal amplified fluorescence method for detection of 44 sulfonamides in milk

In this study, the recognition mechanisms and affinities of a natural dihydropteroate synthase for 44 sulfonamides were studied respectively. Then the key contact amino acid Ser222 was mutated to Arg222 by using site-directed mutagenesis method to produce a mutant. Results showed that the binding energies and affinities for the 44 drugs were generally improved. Then this mutant was used as recognition reagent to develop a direct competitive fluorescence method on 96-well microplate for determination of the 44 drugs in milk. Due to the used signal amplified fluorescent tracer, the limits of detection for the 44 drugs were in the range of 0.025–0.65 ng/mL, and the sensitivities were improved for about 6–86 folds in comparison with the conventional fluorescent tracer. After comprehensive comparison, the present method showed generally better performances than the previously reported immunoassays for sulfonamides. Therefore, this method could be used as an efficient tool for the routine screening of sulfonamides residues in large number of food samples.

Therapy-induced bone changes in oncology imaging with 18F-sodium fluoride (NaF) PET-CT.

18F-Sodium fluoride (18F-NaF) is a PET tracer that is mostly used in the evaluation of bone metastasis in oncology cases. Recently, 18F-NaF PET/CT is gaining wide popularity owing to its higher sensitivity over the other conventional bone tracer with higher and rapid single-pass extraction, negligible plasma protein binding, rapid blood, and renal clearance. In the era of constant evolution of cancer therapy regimens, considerable bone health impact is seen in the form of avascular necrosis, insufficiency fractures, among others. A significant number of these therapy-induced changes show high bone turnover and thereby 18F-NaF accumulation, mimicking metastatic lesions. This article summarizes and illustrates the pattern and morphological features of 18F-NaF PET/CT findings in these changes in the context of clinical and therapeutic history.

Monitoring Polymer Flooding Performance Using Inflow Tracer Technology in Horizontal Injection and Production Wells

Summary Horizontal wells are frequently used to increase injectivity and for cost-efficient production of mobilized oil in polymer-augmented waterfloods. Usually, only fluid and polymer production data at the wellhead of the production well are available. We used inflow tracer technology to determine changes in hydrocarbon influx owing to polymer injection and to determine the connection from various zones of the horizontal injector to the horizontal producer. Inflow tracer technology was introduced in horizontal polymer injection and production wells. In the production wells, tracers are released when they are contacted by water and oil. Oil and water tracer systems were used in the horizontal production wells. The changes in the observed tracer concentration were used to quantify changes in influx from various sections of the horizontal producers owing to polymer injection. The inflow tracer technology applied in the horizontal injection wells demonstrates connectivity between different sections of the injection wells and two surrounding vertical and horizontal production wells and opens the usage of this technology for interwell water tracer applications. Inflow tracer technology enables one to elucidate the inflow from various sections of the horizontal wells and the changes thereof, even quantifying changes in influx of various fluids (oil and water). The information shows which sections are contributing and the substantial changes in the influx of oil from the various zones due to polymer solution injection. The overall incremental oil could be allocated to the various horizontal well sections based on the tracer results. Even zones that almost exclusively produced water before polymer injection showed a significant increase in oil influx. The inflow tracer technology installed in the injection well allowed us to analyze the connectivity of the injector to producer not only globally but spatially along the horizontal well. These data are used for reservoir characterization, to condition numerical models, and for reservoir management. Conventional interwell tracer technology allows one to determine the connectivity and connected volumes of horizontal well polymer field developments. However, it reveals neither information about influx of the sections nor the connectivity of various sections of the horizontal wells. Inflow tracer technology closes this gap; it allows one to quantify changes in influx of the fluids. Furthermore, the newly developed installed injection well tracer technology gives spatial information about the connectivity of the horizontal well sections.

Microenvironment-triggered multimodal precision diagnostics.

Therapeutic outcomes in oncology may be aided by precision diagnostics that offer early detection, localization and the opportunity to monitor response to therapy. Here, we report a multimodal nanosensor engineered to target tumours through acidosis, respond to proteases in the microenvironment to release urinary reporters and (optionally) carry positron emission tomography probes to enable localization of primary and metastatic cancers in mouse models of colorectal cancer. We present a paradigm wherein this multimodal sensor can be employed longitudinally to assess burden of disease non-invasively, including tumour progression and response to chemotherapy. Specifically, we showed that acidosis-mediated tumour insertion enhanced on-target release of matrix metalloproteinase-responsive reporters in urine. Subsequent on-demand loading of the radiotracer 64Cu allowed pH-dependent tumour visualization, enabling enriched microenvironmental characterization when compared with the conventional metabolic tracer 18F-fluorodeoxyglucose. Through tailored target specificities, this modular platform has the capacity to be engineered as a pan-cancer test that may guide treatment decisions for numerous tumour types.

The potential for colour to provide a robust alternative to high-cost sediment source fingerprinting: Assessment using eight catchments in England

Excess diffuse fine sediment losses from agriculture are associated with a reduction in the ecological status of lakes and rivers. Agri-environment initiatives aim to help reduce these excessive losses through targeted on-farm advice and capital grants. However, to deliver optimum cost-benefit such initiatives must target the most important sediment sources. Sediment source fingerprinting provides an approach by which sediment provenance data can be generated; however, conventional tracers are expensive and state-of-the-art data processing for source discrimination and apportionment requires significant expertise. In consequence, sediment fingerprinting is not routinely used for catchment management. Against this context, sediment colour measured using an ordinary document scanner is trialled as an inexpensive and accessible tracer in eight catchments classed as high priority for an agri-environment initiative in England. Colour is interpreted using simple scatter bi-plots of source and sediment samples and compared to the results produced by a conventional composite tracer sediment source fingerprinting methodology. It was found that in two study catchments, sediment colour was as effective as conventional sediment fingerprinting. In four catchments, sediment colour provided less source discrimination or minor differences in results but still identified the most important targets for sediment mitigation. In two catchments, colour was un-successful; however, significant challenges were also encountered with more conventional tracers due to specific local conditions. The findings suggest that use of low-cost colour tracers by non-experts has the potential to significantly increase the uptake of sediment source tracing to improve the cost-benefit of agri-environment initiatives combating the degradation of water quality and aquatic ecology by accelerated sediment losses.

Nebulised Gadolinium-Based Nanoparticles for a Multimodal Approach: Quantitative and Qualitative Lung Distribution Using Magnetic Resonance and Scintigraphy Imaging in Isolated Ventilated Porcine Lungs.

PurposeThis study aims at determining lung distribution of gadolinium-based polysiloxane nanoparticles, AGuIX® (small rigid platform – SRP), as a potential theranostic approach by the pulmonary route.MethodsFirst, the aerodynamic size distribution and the aerosol output rate were thoroughly characterized. Then, a multimodal approach using magnetic resonance (MR) and gamma-camera (GC) imaging allows to assess the deposition of the aerosolised nanoparticles in the respiratory tract using isolated ventilated porcine lungs.ResultsThe SRP has proven to be radiolabelled by radioisotope with a good yield. Crude SRP or radiolabelled ones showed the same aerodynamic size distribution and output as a conventional molecular tracer, as sodium fluoride. With MR and GC imaging approaches, the nebulised dose represented about 50% of the initial dose of nanoparticles placed in the nebuliser. Results expressed as proportions of the deposited aerosol showed approximately a regional aerosol deposition of 50% of the deposited dose in the lungs and 50% in the upper airways. Each technique assessed a homogeneous pattern of deposited nanoparticles in Lungs. MR observed a strong signal enhancement with the SRP, similar to the one obtained with a commonly used MRI contrast agent, gadoterate meglumine.ConclusionAs a known theranostic approach by intravenous administration, SRP appeared to be easily aerosolised with a conventional nebuliser. The present work proves that pulmonary administration of SRP is feasible in a human-like model and allows multimodal imaging with MR and GC imaging. This work presents the proof of concept of SRP nebulisation and aims to generate preclinical data for the potential clinical transfer of SRP for pulmonary delivery.

Probabilistic delineation of hyporheic zone depth using heat transfer analysis

Delineating the hyporheic zone, where groundwater and surface water mix, is of great importance for managing groundwater contamination introduced through surface water. A prior study proposed a method for estimating the hyporheic zone’s depth using heat transfer analysis; this approach’s high sensitivity compared with conventional tracer tests made it more appropriate for delineate the hyporheic zone depth. However, that method treated all related parameters as deterministic values, while real-world parameters are not fixed but vary widely around their means. In this study, we improved on this approach by converting it into a probabilistic method, in which the principal parameters in the governing equation were considered random values and were sampled using Monte-Carlo simulation. We conducted repeated heat transfer analyses for each case and collected the resulting hyporheic zone depths as probabilistic distributions. This allowed us to calculate the distribution of the hyporheic zone and its mean value more accurately and time-efficiently.

Descending forebrain projections targeting respiratory control areas in the midbrain and brainstem of rats.

Breathing can be voluntarily modulated via descending inputs from the forebrain to evoke respiratory‐related behaviours, such as vocalization, sniffing, swallowing or breath‐holding. Such behaviors require controlled laryngeal adduction and thus, are conducted during the post‐inspiratory phase of respiratory cycle. However, descending pathways that connect forebrain regions with primary post‐inspiratory control areas such as the pontine Kölliker‐Fuse nucleus (KF) and the medullary Bötzinger complex (BötC) remain to be identified. Here, we investigated the topography of forebrain descending projection neurons to a variety of bulbar respiratory nuclei.We locally microinjected the conventional retrograde tracer cholera toxin subunit B (CT‐B, 100–150nL) into the BötC, KF, the pre‐Bötzinger complex (pre‐BötC), the midline raphé nuclei and the midbrain periaqueductal gray (PAG). Twelve days after unilateral CT‐B injections, brains were sectioned (40μm) and immunohistochemically stained with an anti‐CT‐B antibody. The strength of descending projections was qualitatively assessed: as strong (+++), moderate (++) or weak (+) numbers of CT‐B labeled cell bodies.Retrogradely labelled neurons after unilateral injections into the lateral PAG confirmed the predominantly ipsilateral location of strong and moderate descending projection neurons in the cingulate (+++), pre‐limbic (+++), ectorhinal (++), motor (+++) and insular (++) cortices, the lateral septum (++), amygdala (+++) and hypothalamus (+++). In comparison, retrogradely labeled neurons after unilateral KF injection were also found ipsilaterally in the motor (++), prelimbic (++) and insular cortices (+++), the amygdala (++) and hypothalamus (+++). However, amongst all analysed descending target areas, only the KF receives substantial inputs from the ectorhinal (+++) and endopiriform (++) cortices. In addition, the medullary BötC receives weaker inputs from prelimbic (+) and insular (+) cortices and receives moderate inputs from the amygdala and hypothalamus. Descending projection neurons to the pre‐BötC were in accordance with the literature: motor (+) and insular (+) cortices, amygdala (+++) and hypothalamus (++). Finally, descending inputs to the medullary raphé obscurus and raphé magnus nuclei also arose from motor, prelimbic and insular cortices, amygdala and hypothalamus. However, these projections were significantly weaker compared to KF or PAG.The results suggest that descending forebrain projections into respiratory control areas are organized in general pathways that originate from motor, prelimbic and insular cortices as well as the amygdala and hypothalamus. However, only the KF, a key area for the gating of post‐inspiratory activity and respiratory plasticity, receives projections arising from the endopiriform and ectorhinal cortex. The functional implications of these descending control pathways need to be explored in future studies.Support or Funding InformationMelbourne Research Scholarship (University of Melbourne) [181858] to PT‐B.

Efficacy comparison between minimally invasive fixation and routine fixation of tracer in robot-assisted pedicle screw placement

Objective To investigate the clinical efficacy of modified tracer minimally invasive fixation in robot-assisted pedicle screw placement. Methods A prospective randomized controlled study was conducted to analyze the clinical data of 41 patients with thoracolumbar fresh fracture at the orthopaedics department of Karamay Central Hospital from July 2017 to December 2017. There were 20 males and 21 females, aged 25-55 years, with an average of 40.6 years. According to AO fracture typing, there were 28 patients with type A and 13 patients with type B. The patients underwent robot-assisted pedicle screw placement. Random number table method was used to divide the patients into the conventional group (20 patients) and modified group (21 patients). The conventional group was treated with conventional tracer fixation, and the modified group modified tracer minimally invasive fixation. A total of 92 pedicle screws were implanted in the conventional group and 96 pedicle screws were implanted in the modified group. The size of wound, wound bleeding, time of fixing the tracer, complications (spinal cord injury and nerve root injury when fixing the tracer), development of the tracer fixator and artifacts were recorded. The accuracy of nail placement was evaluated by 320-slice CT scan and Gertzbein-Robbins criteria. Results There was no significant difference in age, sex, diagnosis, transverse diameter of pedicle and e angle between the two groups (P>0.05). The wound size, wound bleeding, and time of fixing the tracer in the modified group were (6.00±1.26)mm, (1.38±0.22)ml and (1.42±0.17)minutes, respectively, while those of the conventional group were (40.16±5.71)mm, (11.61±1.15)ml, and (5.12±0.64)minutes respectively (P 0.05). Conclusion In the robot-assisted pedicle screw placement, the modified tracer minimally invasive fixation method is safe and less traumatic, with no side effect on the accuracy of pedicle screw placement. Key words: Robotics; Spinal fractures; Surgical procedures, minimally invasive; Tracer fixation

Influx rate of 18F-fluoroaminosuberic acid reflects cystine/glutamate antiporter expression in tumour xenografts.

18F-fluoroaminosuberic acid (18F-FASu) is a recently developed amino acid tracer for positron emission tomography (PET) of oxidative stress that may offer improved tumour assessment over the conventional tracer 18F-fluorodeoxyglucose (18F-FDG). Our aim was to evaluate and relate dynamic 18F-FASu and 18F-FDG uptake with pharmacokinetic modelling to transporter protein expression levels in a panel of diverse tumour xenograft lines. Four different tumour xenograft lines were implanted in female athymic nude mice: MAS98.12 and HBCx3 (breast), TPMX (osteosarcoma) and A549 (lung). Dynamic PET over 60min was performed on a small animal unit. The time-activity curves (TACs) for 18F-FASu and 18F-FDG in individual tumours were used to extract early (SUVE; 2min p.i.) and late (SUVL; 55min p.i.) standardised uptake values. Pharmacokinetic two-tissue compartment models were applied to the TACs to estimate rate constants K1-k4 and blood volume fraction vB. Relative levels of cystine/glutamate antiporter subunit xCT were assessed by western blotting, and expression of GLUT1 and CD31 by immunohistochemistry. 18F-FASu showed higher SUVE, whilst 18F-FDG exhibited higher SUVL. Influx rate K1 for 18F-FASu was significantly correlated with xCT levels (p = 0.001) and was significantly higher than K1 for 18F-FDG (p < 0.001). K1 for 18F-FDG was significantly correlated with GLUT1 levels (p = 0.002). vB estimated from 18F-FASu and 18F-FDG TACs was highly consistent and significantly correlated (r = 0.85, p < 0.001). Two qualitatively different 18F-FASu uptake profiles were identified: type α with low xCT expression and low K1 (A549 and HBCx3), and type β with high xCT expression and high K1 (MAS98.12 and TPMX). The influx rate of 18F-FASu reflects xCT activity in tumour xenografts. Dynamic PET with pharmacokinetic modelling is needed to fully appraise 18F-FASu distribution routes.

Ascending vestibular pathways to parietal areas MIP and LIPv and efference copy inputs from the medial reticular formation: Functional frameworks for body representations updating and online movement guidance.

The posterior parietal cortex (PPC) serves as a sensorimotor interface by integrating multisensory signals with motor related information for generating and updating body representations and movement plans. Using retrograde transneuronal transfer of rabies virus combined with a conventional tracer, we identified direct and polysynaptic pathways to two PPC areas, the rostral medial intraparietal area (MIP) and the ventral part of the lateral intraparietal area (LIPv) in macaque monkeys. We found that rostral MIP and LIPv receive ascending vestibular pathways, and putative efference copy inputs disynaptically from the medullary medial reticular formation (MRF) where reticulospinal pathways to neck and arm motoneurons originate. LIPv receives minor disynaptic vestibular inputs, and substantial projections from the head movement-related rostral MRF, consistent with head gain modulation of LIPv activity and a role in planning gaze shifts. Rostral MIP is the target of prominent disynaptic pathways from reaching- and head movement-related MRF domains, and major ascending vestibular pathways trisynaptically from both labyrinths, explaining prominent vestibular responses and discrimination between active and passive movements demonstrated in rostral MIP and in the neighboring ventral intraparietal area, which are heavily interconnected. The findings that rostral MIP (belonging to the 'parietal reach region'), receives vestibular inputs as directly as classical vestibular areas, via a parallel channel, and efference copy signals pathways from MRF reticulospinal domains that belong to reach and head movement networks have important implications for the understanding of the role of the PPC in updating body representations and internal models for online guidance of movement.