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Background: Several factors may decrease the accuracy of quantitative PET myocardial perfusion imaging (MPI). It is therefore essential to ensure that myocardial blood flow (MBF) values are reproducible and accurate, and to design systematic protocols for assessing this. Until now, no systematic phantom protocols have been available to assess the technical factors affecting measurement accuracy and reproducibility in MPI. Materials and Methods: We implemented a standard measurement protocol, which applies a flow phantom in order to compare image-derived flow values with respect to a ground truth flow value with [15O]H2O MPI performed on both a Discovery MI (DMI-20, GE Healthcare) and a Biograph Vision 600 (Vision-600, Siemens Healthineers) system. Both systems have automatic [15O]H2O radio water generators (Hidex Oy) individually installed, allowing us to also study the differences occurring due to two different bolus delivery systems. To investigate the technical factors contributing to the modelled flow values, we extracted the [15O]H2O bolus profiles, the flow values from the kinetic modeling (Qin and Qout), and finally calculated their differences between test-retest measurements on both systems. Results: The input time activity curves (TAC) showed dependency on the bolus injection curves. The measurements performed on the DMI-20 system produced Qin and Qout values equal to each other as well as to the reference flow value across all test-retest measurements. Also, all DMI-20 repeatability differences were below 15 %. The measurements performed on the Vision-600 system showed more variation between Qin and Qout values across test-retest measurements and exceeded the 15 % difference in half (6/12) of the measurements. Conclusions: This preliminary study proposes a protocol for measuring the accuracy and reproducibility of flow between different injector and PET systems. Our results suggest that flow values can be reproduced on DMI-20 or Vision-600 systems and with two different injector systems, with less than 15 % error. The most significant factor contributing to the variation was the injected bolus, which directly affects the phantom input TAC. In order to extend the protocol to a multi-center setting, a standardized and repeatable bolus injection protocol needs to be designed.

Aflatoxin B1 (AFB1), a common dietary contaminant, is a major risk factor of hepatocellular carcinoma (HCC). Early onset of HCC in some countries in Africa and South-East Asia indicates the importance of early life exposure. Placenta is the primary route for various compounds, both nutrients and toxins, from the mother to the fetal circulation. Furthermore, placenta contains enzymes for xenobiotic metabolism. AFB1, AFB1-metabolites, and AFB1-albumin adducts have been detected in cord blood of babies after maternal exposure during pregnancy. However, the role that the placenta plays in the transfer and metabolism of AFB1 is not clear. In this study, placental transfer and metabolism of AFB1 were investigated in human placental perfusions and in in vitro studies. Eight human placentas were perfused with 0.5 or 5microM AFB1 for 2-4 h. In vitro incubations with placental microsomal and cytosolic proteins from eight additional placentas were also conducted. Our results from placental perfusions provide the first direct evidence of the actual transfer of AFB1 and its metabolism to aflatoxicol (AFL) by human placenta. In vitro incubations with placental cytosolic fraction confirmed the capacity of human placenta to form AFL. AFL was the only metabolite detected in both perfusions and in vitro incubations. Since AFL is less mutagenic, but putatively as carcinogenic as AFB1, the formation of AFL may not protect the fetus from the toxicity of AFB1.

Nitrosodimethylamine (NDMA) is a carcinogenic compound present in tobacco smoke and food such as cured meat, smoked fish and beer. The O(6)-methylguanine formed in human cord blood in mothers highly exposed to such products implicates NDMA exposure of the fetus. Dual recirculating human placental perfusion was used to get direct evidence of the transplacental transfer of NDMA and DNA adduct formation in perfused human placenta. Eleven placentas from normal full-term pregnancies were collected immediately after delivery and an isolated lobule was perfused with 1 or 5 microM of (14)C-NDMA with a reference substance, antipyrine (0.1mg/ml) added to the maternal circulation. Perfusate samples were collected from both maternal and fetal circulations every half an hour for the first two hours and once per hour from thereon. NDMA was analyzed by scintillation counting and antipyrine by high performance liquid chromatography. The transfer of NDMA was comparable to that of antipyrine and probably occurred through passive diffusion, with the concentrations in maternal and fetal sides equilibrating in 2-3h. No indication of any effect by efflux transporters on NDMA kinetics was noticed in the experiments utilizing Caco-2 or MDCK- MDCKII-MDR1 cell culture monolayer in a transwell system, either. Furthermore, no NDMA-DNA-adducts were found after the perfusions and no DNA-binding of NDMA was seen in in vitro incubations with human placental microsomes from 8 additional placentas. Thus, our study demonstrates that the human fetus can be exposed to NDMA from the maternal circulation. According to this study and the literature, NDMA is not metabolized in full-term human placenta from healthy non-smoking, non-drinking mothers. It remains to be studied whether NDMA concentrations high enough to evoke fetal toxicity can be obtained from dietary sources. We appreciate the collaboration with all members in Dan Segerbäck's group, partner of the Network of Excellence ECNIS. Finally, the authors thank Dr. Ewen MacDonald for his comments on English language in the paper. The project was financially supported by EU network NewGeneris (FOOD-CT-2005 016320).

In the E.U. integrated project NewGeneris, we studied placental transport of thirteen immunotoxic and genotoxic agents in three ex vivo placental perfusion laboratories. In the present publication, all placental perfusion data have been re-analyzed and normalized to make them directly comparable and rankable. Antipyrine transfer data differed significantly between the studies and laboratories, and therefore normalization of data was necessary. An antipyrine normalization factor was introduced making the variance significantly smaller within and between the studies using the same compound but performed in different laboratories. Non-normalized (regular) and normalized data showed a good correlation. The compounds were ranked according to their transplacental transfer rate using either antipyrine normalized AUC120 or transfer index (TI120(%)). Normalization generated a division of compounds in slow, medium and high transfer rate groups. The transfer rate differed slightly depending on the parameter used. However, compounds with passage similar to antipyrine which goes through the placenta by passive diffusion, and good recovery in media (no accumulation in the tissue or adherence to equipment) were highly ranked no matter which parameter was used. Antipyrine normalization resulted in the following ranking order of compounds according to AUC(120NORM) values: NDMA ≥ EtOH ≥ BPA ≥ IQ ≥AA ≥ GA ≥ PCB180 ≥ PhIP ≥ AFB1DON ≥ BP ≥ PCB52 ≥ TCDD. As the variance in all parameters within a study decreased after antipyrine normalization, we conclude that this normalization approach at least partially corrects the bias caused by the small methodological differences between studies.

The placenta has an important role in transporting nutrients and oxygen to the fetus. Transplacental transport is, however, not restricted to physiological exchange of agents, but includes the majority, if not all, of xenobiotics in maternal blood. Although passive diffusion is the most common transfer mechanism, transporter proteins play a significant role in transplacental transfer. The largest superfamily of transporters and one of the most interesting groups regarding xenobiotics is the ATP-binding cassette (ABC) transporters. The efflux ABC transporters from families ABCB, ABCC and ABCG play a role in transporting xenobiotics and their conjugates in addition to endogenous compounds. Many of them probably play a role in the protection of the fetus, as is implicated in animal studies. Both genetic polymorphisms, endogenous regulation, e.g. by hormones, and xenobiotics can modify the expression and function of transporters. Interference in the function of transporters (e.g., inhibition) may significantly increase the fetal exposure to xenobiotics or drugs. Many different models can be used to study human placental ABC transporters. These include human placental perfusion, tissue preparations, tissue explants, primary cell cultures, immortalized cell lines, cancer cell lines, placental membrane vesicles and cloning. When estimating the contribution of an ABC transporter for fetal exposure localization has to be taken into account in addition to the level of expression, functional status and substrate specificity.