[18F]FDG Positron emission tomography with whole body magnetic resonance imaging ([18F]FDG-PET/MRI) as a diagnosis tool in Schwannomatosis.

Schwannomatosis is a rare autosomal dominant genetic syndrome characterized by the presence of multiple schwannomas. The main symptom is neurogenic pain. The diagnosis requires the presence of several schwannomas and whole-body [18F]FDG-PET/MRI might help detect extra schwannomas in patients when the diagnosis is uncertain. Among the 25 patients treated for Schwannomatosis in our tertiary center, three men and two women had had a [18F]FDG-PET/MRI performed, and the number of schwannomas detected by [18F]FDG-PET/MRI outnumbered the number of schwannomas suspected during the clinical examination. The majority of schwannomas exhibited a radiolabeling (median of 66.7%, range 28-93%). Our findings show that [18F]FDG-PET/MRI could prove useful when suspecting schwannomatosis to accelerate diagnosis and offer optimal care to patients.

Prediction of overall survival in patients with hepatocellular carcinoma treated with Y-90 radioembolization by imaging response criteria.

PURPOSE: To evaluate the potential of imaging criteria in predicting overall survival of patients with hepatocellular carcinoma (HCC) after a first transcatheter arterial yttrium-90 radioembolization (TARE) MATERIALS AND METHODS: From October 2013 to July 2017, 37 patients with HCC were retrospectively included. There were 34 men and 3 women with a mean age of 60.5±10.2 (SD) years (range: 32.7-78.9 years). Twenty-five patients (68%) were Barcelona Clinic Liver Cancer (BCLC) C and 12 (32%) were BCLC B. Twenty-four primary index tumors (65%) were>5cm. Three radiologists evaluated tumor response on pre- and 4-7 months post-TARE magnetic resonance imaging or computed tomography examinations, using Response Evaluation Criteria in Solid Tumors (RECIST) 1.1, modified RECIST (mRECIST), European Association for Study of the Liver (EASL), volumetric RECIST (vRECIST), quantitative EASL (qEASL) and the Liver Imaging Reporting and Data System treatment response algorithm. Kaplan-Meier survival curves were used to compare responders and non-responders for each criterion. Univariate and multivariate Cox proportional hazard ratio (HR) analysis were used to identify covariates associated with overall survival. Fleiss kappa test was used to assess interobserver agreement. RESULTS: At multivariate analysis, RECIST 1.1 (HR: 0.26; 95% confidence interval [95% CI]: 0.09-0.75; P=0.01), mRECIST (HR: 0.22; 95% CI: 0.08-0.59; P=0.003), EASL (HR: 0.22; 95% CI: 0.07-0.63; P=0.005), and qEASL (HR: 0.30; 95% CI: 0.12-0.80; P=0.02) showed a significant difference in overall survival between responders and nonresponders. RECIST 1.1 had the highest interobserver reproducibility. CONCLUSION: RECIST and mRECIST seem to be the best compromise between reproducibility and ability to predict overall survival in patients with HCC treated with TARE.

Proteome-wide modulation of S-nitrosylation in Trypanosoma cruzi trypomastigotes upon interaction with the host extracellular matrix.

Trypanosoma cruzi trypomastigotes adhere to extracellular matrix (ECM) to invade mammalian host cells regulating intracellular signaling pathways. Herein, resin-assisted enrichment of thiols combined with mass spectrometry were employed to map site-specific S-nitrosylated (SNO) proteins from T. cruzi trypomastigotes incubated (MTy) or not (Ty) with ECM. We confirmed the reduction of S-nitrosylation upon incubation with ECM, associated with a rewiring of the subcellular distribution and intracellular signaling pathways. Forty, 248 and 85 SNO-peptides were identified only in MTy, Ty or in both conditions, respectively. SNO proteins were enriched in ribosome, transport, carbohydrate and lipid metabolisms. Nitrosylation of histones H2B and H3 on Cys64 and Cys126, respectively, is described. Protein-protein interaction networks revealed ribosomal proteins, proteins involved in carbon and fatty acid metabolism to be among the enriched protein complexes. Kinases, phosphatases and enzymes involved in the metabolism of carbohydrates, lipids and amino acids were identified as nitrosylated and phosphorylated, suggesting a post-translational modifications crosstalk. In silico mapping of nitric oxide synthase (NOS) genes, previously uncharacterized, matched to four putative T. cruzi proteins expressing C-terminal NOS domain. Our results provide the first site-specific characterization of S-nitrosylated proteins in T. cruzi and their modulation upon ECM incubation before infection of the mammalian hosts. SIGNIFICANCE: Protein S-nitrosylation represents a major molecular mechanism for signal transduction by nitric oxide. We present for the first time a proteomic profile of S-nitrosylated proteins from infective forms of T. cruzi, showing a decrease in SNO proteins after incubation of the parasite with the extracellular matrix, a necessary step for the parasite invasion of the host mammalian cells. We also show for the first time nitrosylation of H2B (Cys64) and H3 (Cys126) histones, sites not conserved in higher eukaryotic cells, and suggest that some specific histone isoforms are sensitive to NO signaling. S-nitrosylation in H2B and H3 histones are more abundant in MTy. Moreover, proteins involved in translation, glycolytic pathway and fatty acid metabolism are enriched in the present dataset. Comparison of the SNO proteome and the phosphoproteome, obtained previously under the same experimental conditions, show that most of the proteins sharing both modifications are involved in metabolic pathways, transport and ribosome function. The data suggest that both PTMs are involved in reprogramming the metabolism of T. cruzi in response to environmental changes. Although NO synthesis was detected in T. cruzi, the identification of NOS remains elusive. Analysis in silico showed two genes similar in domains to NADPH-dependent cytochrome-P450 reductase and two putative oxidoreductases, but no oxygenase domain of NOS was mapped in the T. cruzi genome. It is tempting to speculate that NO synthase-like from T. cruzi and its early NO-mediated pathways triggered in response to host interaction constitute potential diagnostic and therapeutic targets.

Healthcare-associated Clostridium difficile infection: role of correct hand hygiene in cross-infection control.

INTRODUCTION: Clostridium difficile (CD) is the most common cause of health-care-associated infectious diarrhea with increasing incidence and severity in recent years. The main cause of hospital's acquired cross infections can be attributed to incorrect hand hygiene. We described the epidemiology of CD infection (CDI) in a teaching hospital in Southern Italy during a two years surveillance period and evaluated the health-care workers compliance to hand hygiene. METHODS: CDI Incidence rates were calculated as the number of patients with positive C. difficile toxin assay per 10,000 patient-days. Compliance with hand hygiene was the ratio of the number of performed actions to the number of opportunities observed. Approximately 400 Hand Hygiene (HH) opportunities/year /ward were observed. We finally checked out if any correlation could be found. RESULTS: From January 2015 to December 2016 a total number of 854 CD determinations were performed in patients with clinical symptoms of diarrhea. The search for toxins A and B was positive in 175 cases (21,2%), confirming the diagnosis of CDI. Compliance to hand hygiene was significantly inversely associated with the number of CDIs: the lower the compliance of health-care workers with hand hygiene the higher was the number of cases of CDIs (p = 0.003). CONCLUSIONS: According to our results proper handwashing of health-care workers appears to be a key intervention in interrupting CD cross infections regardless of age and type of department in which the patient is admitted.

Iterative reconstructions in multiphasic CT imaging of the liver: qualitative and task-based analyses of image quality.

AIM: To evaluate the clinical benefits on image quality (IQ) of adaptive statistical iterative reconstruction (ASIR) and model-based iterative reconstruction (MBIR) in multiphasic liver CT compared to filtered back-projection (FBP), in patients and on phantoms using a novel task-based metric. MATERIALS AND METHODS: Image data of 65 patients who underwent a routine multiphasic liver CT during a 1-month period were reconstructed with FBP, ASIR50, ASIR80, and MBIR. IQ was assessed qualitatively by ranking the most distal hepatic artery (HA) and portal vein (PV) visible; and quantitatively by measuring contrast-to-noise ratio (CNR) of the liver parenchyma, HA and PV. IQ was compared between each reconstruction and correlated to CNR and detectability index (d') measurements computed on phantoms scanned with the same CT protocol as for patients. RESULTS: HA and PV were seen more distally on MBIR and ASIR80 compared to FBP (p≤0.001). The CNR correlated weakly between patient and phantom (r=0.76 and 0.80 for HA and PV, respectively), whereas d' correlated strongly with the division order of HA and PV (r=0.96 and 0.95, respectively). CONCLUSION: MBIR and ASIR significantly improve the IQ of multiphasic liver CT, especially through better distal detection of HA and PV, in agreement with the adapted task-based metric d' estimated on phantoms.

Measurement variability of liver metastases from neuroendocrine tumors on different magnetic resonance imaging sequences.

PURPOSE: To assess dimension measurement variability of liver metastases from neuroendocrine tumors (LMNET) on different magnetic resonance imaging (MRI) sequences. MATERIAL AND METHODS: In this institutional review board-approved retrospective study from January 2011 to December 2012, all liver MRI examinations performed at our department in patients with at least one measurable LMNET according to response evaluation criteria in solid tumors (RECIST1.1) were included. Up to two lesions were selected on T2-weighted MR images. Three reviewers independently measured long axes of 135 hepatic metastases in 30 patients (16 men, 14 women, mean age 61±11.4 (SD) years; range 28-78 years), during two separate reading sessions, on T2-weighted, diffusion-weighted MRI (DWI) (b; 50, 400, 800 s/mm2) and arterial, portal and late phases after intravenous administration of a gadolinium chelate. Intraclass-correlation coefficients and Bland-Altman plots were used to assess intra-and interobserver variability. RESULTS: Intra- and interobserver agreements ranged between 0.87-0.98, and 0.88-0.97, respectively. Intersequence agreements ranged between 0.92 [95%CI: 0.82-0.98] and 0.98 [95%CI: 0.93-0.99]. 95% limits of agreement for measurements were -10.2%,+8.9% for DWI (b=50s/mm2) versus -21.9%,+24.2% and -15.8,+17.2% for arterial and portal phases, respectively. CONCLUSION: An increase<9% in measurement and a decrease of -10% on DWI should not be considered as true changes, with 95% confidence, versus 24% and -22% on arterial and 17%, -16% on portal phases, respectively. DWI might thus be the most reliable MR sequence for monitoring size variations of LMNETs.

Applications of dual energy computed tomography in abdominal imaging.

Dual energy computed tomography (CT) is an imaging technique based on data acquisition at two different energy settings. Recent advances in CT have allowed data acquisition and almost simultaneously analysis of two spectra of X-rays at different energy levels resulting in novel developments in the field of abdominal imaging. This technique is widely used in cardiovascular imaging, especially for pulmonary embolism work-up but is now also increasingly developed in the field of abdominal imaging. With dual-energy CT it is possible to obtain virtual unenhanced images from monochromatic reconstructions as well as attenuation maps of different elements, thereby improving detection and characterization of a variety of renal, adrenal, hepatic and pancreatic abnormalities. Also, dual-energy CT can provide information regarding urinary calculi composition. This article reviews and illustrates the different applications of dual-energy CT in routine abdominal imaging.

Imaging of the postoperative liver: review of normal appearances and common complications.

Several benign and malignant liver diseases may require surgical treatment for cure, including anatomical resections based on the segmental anatomy of the liver, non-anatomical (wedge) resections, and surgical management of biliary cysts. The type of surgery depends not only on the location and the nature of the disease, but also on the expertise of the surgeon. Whereas ultrasonography is often the first-line imaging examination in case of suspected postoperative complication, multidetector computed tomography (MDCT) is of greater value for identifying normal findings after surgery, early postoperative pathologic fluid collections and vascular thromboses, and tumor recurrence in patients who have undergone hepatic surgery. Magnetic resonance cholangiopancreatography (MRCP) is the imaging modality of choice for depicting early postoperative bile duct injuries and ischemic cholangitis that may occur in the late postoperative phase. Both MDCT and MRCP can accurately depict tumor recurrence. Radiologists should become familiar with these surgical procedures to better understand postoperative changes, and with the normal imaging appearances of various postoperative complications to better differentiate between complications and normal findings.

Primary rectal cancer local staging.

The treatment of patients with a malignant rectal tumor has evolved over the past few years. The role of medical imaging techniques, notably MRI, has become increasingly important in the preoperative assessment of rectal tumors. Radiologists are finding that their presence is requested more and more frequently at multidisciplinary team meetings for decision-making on the treatment of these tumors and therefore they must have a grounding in the therapeutic issues involved. Locoregional assessment of malignant rectal tumors may be performed prior to initiating treatment or as a re-evaluation following neoadjuvant therapy. We are interested in the assessment of the initial locoregional extension of these rectal tumors and we place much emphasis on the ability to identify MRI criteria which determine the patient's prognosis and treatment. We will also examine the advantages of MRI as well as its limits in this assessment.

An automatic respiratory gating method for the improvement of microcirculation evaluation: application to contrast-enhanced ultrasound studies of focal liver lesions.

Contrast-enhanced ultrasound (CEUS), with the recent development of both contrast-specific imaging modalities and microbubble-based contrast agents, allows noninvasive quantification of microcirculation in vivo. Nevertheless, functional parameters obtained by modeling contrast uptake kinetics could be impaired by respiratory motion. Accordingly, we developed an automatic respiratory gating method and tested it on 35 CEUS hepatic datasets with focal lesions. Each dataset included fundamental mode and cadence contrast pulse sequencing (CPS) mode sequences acquired simultaneously. The developed method consisted in (1) the estimation of the respiratory kinetics as a linear combination of the first components provided by a principal components analysis constrained by a prior knowledge on the respiratory rate in the frequency domain, (2) the automated generation of two respiratory-gated subsequences from the CPS mode sequence by detecting end-of-inspiration and end-of-expiration phases from the respiratory kinetics. The fundamental mode enabled a more reliable estimation of the respiratory kinetics than the CPS mode. The k-means algorithm was applied on both the original CPS mode sequences and the respiratory-gated subsequences resulting in clustering maps and associated mean kinetics. Our respiratory gating process allowed better superimposition of manually drawn lesion contours on k-means clustering maps as well as substantial improvement of the quality of contrast uptake kinetics. While the quality of maps and kinetics was satisfactory in only 11/35 datasets before gating, it was satisfactory in 34/35 datasets after gating. Moreover, noise amplitude estimated within the delineated lesions was reduced from 62 ± 21 to 40 ± 10 (p < 0.01) after gating. These findings were supported by the low residual horizontal (0.44 ± 0.29 mm) and vertical (0.15 ± 0.16 mm) shifts found during manual motion correction of each respiratory-gated subsequence. The developed technique could be used as a basis for accurate quantification of perfusion parameters for the evaluation and follow-up of patients under antiangiogenic therapies.

Renal blood flow quantification in pigs using contrast-enhanced ultrasound: an ex vivo study.

PURPOSE: The aim of the study was to evaluate a new method for the quantification of renal blood flow using contrast-enhanced ultrasound (CEUS) in an ex vivo pig kidney model. MATERIAL AND METHODS: After approval by the animal ethics committee, 4 pig kidneys were explanted and perfused with Celsior liquid (Imtix Sangstat, Lyon, France) at different flow rates (30, 50, 70 and 90 ml/min) in an ex vivo phantom. A 50 % diluted solution of SonoVue (Bracco, Milano, Italy) was infused in the artery at 0.5 ml/min. CEUS was performed with an Aplio system (Toshiba, Nasu, Japan) using a broadband linear transducer and pulse subtraction imaging. A total of 152 destruction-reperfusion sequences were acquired and cine loops were digitally stored for further quantification. Three different ROIs were placed upon the anterior, posterior cortex and segmental artery. Signal intensity measurements were performed in linear units and perfusion parameters were automatically extracted using dedicated software. Curve fitting was performed using a monoexponential model in which a time delay parameter was introduced. This fit allowed the assessment of the local blood flow into the region of interest (called "contrast-enhanced blood flow" (CEBF)). The artery mean signal intensity was averaged from the ten frames prior to the destruction phase. The normalized CEBF (nCEBF) was calculated as the ratio between CEBF and the mean arterial signal intensity. The CEBF and nCEBF were compared to the true blood flow indicated by the pump flow rate. RESULTS: The CEBF was correlated to the true blood flow only for the posterior cortical ROI (R(2) = 0.45, p = 0.05). The normalization using arterial signals improved CEBF correlation to true blood flow: nCEBF became correlated to the true blood flow when considering all ROIs (R(2)= 0.94, p < 0.0001) and correlation was improved for both anterior and posterior cortical ROIs (R(2)= 0, 93, p = 0.0004; R(2)= 0, 90, p = 0.0005, respectively). However, a significant kidney-dependent effect was observed for the anterior cortical ROI (p = 0.017) but not for the posterior cortical ROI (p = 0.89). CONCLUSION: Normalization using arterial signals significantly improved the estimation of blood flow calculated with CEUS.

Advances in radiological imaging of gastrointestinal tumors.

This article summarizes the recent advances in radiological imaging in the hepatogastrointestinal field in terms of detection, characterization and staging of tumors. Introduction of multidetector row computed tomography technology has helped computed tomography to excel in its already established indications, and has expanded its capabilities by adding new clinical applications, such as computed tomography angiography, liver perfusion, computed tomography enterography or enteroclysis, and virtual colonoscopy. Contrast-enhanced ultrasound has dramatically changed the role of ultrasound in liver tumor characterization, detection, and other applications. Combining the advantages of unsurpassed soft tissue contrast and lack of ionizing radiation, magnetic resonance imaging of the gastrointestinal tract has become increasingly used clinically. Moreover, substantial progress in molecular and cellular magnetic resonance imaging has been achieved in the past few years. Particularly, the increasing number of available specific contrast agents dedicated to the evaluation of the liver and lymph nodes shows promises in the area of oncologic abdominal imaging.

Preparation, microstructure and hydrogen sorption properties of nanoporous carbon aerogels under ambient drying.

Organic aerogels are prepared by the sol-gel method from polymerization of resorcinol with furfural. These aerogels are further carbonized in nitrogen in order to obtain their corresponding carbon aerogels (CA); a sample which was carbonized at 900 °C was also activated in a carbon dioxide atmosphere at 900 °C. The chemical reaction mechanism and optimum synthesis conditions are investigated by means of Fourier transform infrared spectroscopy and thermoanalyses (thermogravimetric/differential thermal analyses) with a focus on the sol-gel process. The carbon aerogels were investigated with respect to their microstructures, using small angle x-ray scattering (SAXS), transmission electron microscopy (TEM) and nitrogen adsorption measurements at 77 K. SAXS studies showed that micropores with a radius of gyration of <0.35 ± 0.07 to 0.55 ± 0.05 nm were present, and TEM measurements and nitrogen adsorption showed that larger mesopores were also present. Hydrogen storage properties of the CA were also investigated. An activated sample with a Brunauer-Emmett-Teller surface area of 1539 ± 20 m(2) g(-1) displayed a reasonably high hydrogen uptake at 77 K with a maximum hydrogen sorption of 3.6 wt% at 2.5 MPa. These results suggest that CA are promising candidate hydrogen storage materials.

[Tissue attenuation in small animals on contrast enhanced ultrasound]. / Prise en compte de l'atténuation ultrasonore en présence d'agents de contraste chez le petit animal.

Despite recent advances in contrast-enhanced ultrasound imaging, evaluation of tissue perfusion with contrast-enhanced ultrasound is still impaired by shadowing effects. These effects are particularly relevant in small animal studies due to high frequency imaging. Current methods of tissue attenuation correction are not suited for contrast-enhanced ultrasound examinations, because microbubble acoustic response to ultrasound waves is far more complex than that of tissues. A method allowing in vivo tissue attenuation correction in the presence of contrast agents is presented.

Cytokeratin expression in primary epithelial cell culture from bovine conjunctiva.

Aim of the present study is to extend our previous observations on a model of primary epithelial cell culture obtained from bovine conjunctiva, and analyse the maintenance of the conjunctival phenotype, relative to cytokeratin (CK) expression, through extended periods of cultivation under different conditions. Conjunctival epithelial cells were grown in transwell filters, and cultured either under liquid covered (LC), or air-interface (AI) conditions. The physiological state of the cells was monitored daily by measurement of the trans-epithelial electrical resistance (TEER). Analysis of cytokeratin expression was then carried out at different time points (up until 14 days), and compared to the original profile of the conjunctival tissue in order to assess deviations from the primitive phenotype. Immunodetection studies, carried out by both western immunoblot and immunofluorescence analyses, revealed constant expression of the pan-epithelial marker AE3 (recognizing basic type cytokeratins), confirming the epithelial nature of the culture. Other cytokeratins characteristic of non-keratinized stratified epithelia (CK4 and CK13) were absent in corneal tissue, while in conjunctival epithelial cells were more expressed under AI than under LC culture conditions. Expression of CK12, a specific marker of corneal tissue, revealed by the antibody AE5, was never observed in conjunctival epithelial cells. These results indicate that the conjunctival phenotype is conserved during extended periods of culturing, making this system a reliable substitute of conjunctival tissue for pharmaceutical analyses.

Quantitation and confirmation of the diazolo- and triazolobenzodiazepines in human urine by gas chromatography/mass spectrometry.

We report a reliable, rapid, sensitive, and quantitative method for the N- and O-trimethylsilyl (TMS) derivatives of the diazolo- and triazolobenzodiazepines after enzymatic incubation (2 h) and liquid-liquid extraction of 0.5-mL urine volumes. Each analyte was identified by gas chromatography/mass spectrometry through the retention time for the total ion current (TIC) and selected ion monitoring (SIM) of four ion currents. Quantitation of the diazolobenzodiazepines was obtained by the ratio of the base peak ion of the TMS analyte to that of the internal standard bromazepam in the concentration range 50-500 ng/mL (1-10 ng injected into the GC/MS). The limit of detection (LOD) at p less than 0.01 was 50 ng/mL for all the diazolobenzodiazepines. The assay was not quite as sensitive for triazolobenzodiazepines (5-20 ng injected in the GC/MS). The extraction efficiency of the assay ranged from 75 to 92% for all the analytes. The coefficient of variation (CV) for the diazolobenzodiazepines ranged from 5.4 to 9.4% for within-day runs and from 11.1 to 13.9% for between-day runs. For the triazolobenzodiazepines the values were 3.8 to 18.9% for a single day and 3.4 to 19.9% between days. The selected ion current ratio for each analyte was determined for a single day and over a one-week period. There was no statistical difference in the ratios during this time. The confirmation of diazolobenzodiazepines in urine by this method was relatively easy after screening by the immunoassay technique. Identification of triazolobenzodiazepines appeared to be more difficult by both the screening technique and the GC/EI/MS analysis.

Confirmation and quantitation of barbiturates in human urine by gas chromatography/mass spectrometry.

A sensitive, reliable, rapid quantitative method was developed for the N,N'-dimethyl derivatives of the 5,5'-disubstituted barbiturates (NNDM-barbiturates) after liquid-liquid extraction of 0.5-mL urine volumes. Each barbiturate was identified by GC/MS through the retention time for the total ion current and selected ion monitoring of four ion currents for each analyte. Quantitation was achieved through the base peak ion ratios for each NNDM-barbiturate/tolylbarbiturate (IS) over the concentration range 20-250 ng/mL (0.4 to 5 ng injected into the GC/MS). The limit of detection for all the barbiturates (p less than 0.01) was 20 ng/mL (0.4 ng total). The extraction efficiency ranged from 75 to 84% for all the barbiturates. The coefficient of variation of the barbiturates for the within-day run was 2.5 to 4.8% and between days was 6.7 to 8.6%. The percentage abundances of the ion current ratios for each NNDM-barbiturate was determined and found to be fully stable over a one-week period. This method is currently in routine use in our laboratory for the GC/MS confirmation of presumably positive barbiturate urine samples.

Rendering the "poppy-seed defense" defenseless: identification of 6-monoacetylmorphine in urine by gas chromatography/mass spectroscopy.

We report a sensitive, rapid, quantitative gas chromatographic/mass spectroscopic method for measuring the 6-monoacetylmorphine (6-MAM) metabolite of heroin in 0.5 mL of human urine. After a simple liquid-liquid extraction and derivatization, the trimethylsilyl derivative of 6-MAM is identified from its retention time (total ion current) and by selected ion monitoring. The limit of detection was 10 micrograms/L, corresponding to 0.2 ng of trimethylsilyl-6-MAM injected into the gas chromatograph/mass spectrometer. The presence of 6-MAM in urine is indicative of heroin. 6-MAM is not present in poppy seeds or in urine after the ingestion of products containing poppy seed.

Active and realistic passive marijuana exposure tested by three immunoassays and GC/MS in urine.

Human urine samples obtained before and after active and passive exposure to marijuana were analyzed by immune kits (Roche, Amersham, and Syva) and gas chromatography/mass spectrometry (GC/MS). Seven of eight subjects were positive for the entire five-day test period with one immune kit. The latter correlated with GC/MS in 98% of the samples. Passive inhalation experiments under conditions likely to reflect realistic exposure resulted consistently in less than 10 ng/mL of cannabinoids. The 10-100-ng/mL cannabinoid concentration range essential for detection of occasional and moderate marijuana users is thus unaffected by realistic passive inhalation.