Ketones from MCT compensate for the brain glucose deficit in AD in direct proportion to the level of plasma ketones achieved.

Background [ 11 C]-acetate positron emission tomography is used to assess oxidative metabolism in various tissues including the heart, tumor, and brown adipose tissue. For brown adipose tissue, a monoexponential decay model is commonly employed. However, no systematic assessment of kinetic models has been performed to validate this model or others. The monoexponential decay model and various compartmental models were applied to data obtained before and during brown adipose tissue activation by cold exposure in healthy men. Quality of fit was assessed visually and by analysis of residuals, including the Akaike information criterion. Stability and accuracy of compartmental models were further assessed through simulations, along with sensitivity and identifiability of kinetic parameters. Results Differences were noted in the arterial input function between the warm and cold conditions. These differences are not taken into account by the monoexponential decay model. They are accounted for by compartmental models, but most models proved too complex to be stable. Two and three-tissue models with no more than four distinct kinetic parameters, including blood volume fraction, provided the best compromise between fit quality and stability/accuracy. Conclusion For healthy men, a three-tissue model with four kinetic parameters, similar to a heart [ 11 C]-palmitate model seems the most appropriate based on model stability and its ability to describe the main [ 11 C]-acetate pathways in BAT cells. Further studies are required to validate this model in women and people with metabolic disorders. Electronic supplementary material The online version of this article (10.1186/s13550-019-0497-6) contains supplementary material, which is available to authorized users.

The body’s main fuel sources are fats, carbohydrates (glucose), proteins, and ketone bodies. It is well known that an important hallmark of cancer cells is the overconsumption of glucose. Positron emission tomography (PET) imaging using the glucose analog 18F-fluorodeoxyglucose (18F-FDG) has been a powerful cancer diagnostic tool for many decades. Apart from surgery, chemotherapy and radiotherapy represent the two main domains for cancer therapy, targeting tumor proliferation, cell division, and DNA replication—all processes that require a large amount of energy. Currently, in vivo clinical imaging of metabolism is performed almost exclusively using PET radiotracers that assess oxygen consumption and mechanisms of energy substrate consumption. This paper reviews the utility of PET imaging biomarkers for the detection of cancer proliferation, vascularization, metabolism, treatment response, and follow-up after radiation therapy, chemotherapy, and chemotherapy-related side effects.

Brown adipose tissue (BAT) has long been described according to its histological features as a multilocular, lipid-containing tissue, light brown in color, that is also responsive to the cold and found especially in hibernating mammals and human infants. Its presence in both hibernators and human infants, combined with its function as a heat-generating organ, raised many questions about its role in humans. Early characterizations of the tissue in humans focused on its progressive atrophy with age and its apparent importance for cold-exposed workers. However, the use of positron emission tomography (PET) with the glucose tracer [18F]fluorodeoxyglucose ([18F]FDG) made it possible to begin characterizing the possible function of BAT in adult humans, and whether it could play a role in the prevention or treatment of obesity and type 2 diabetes (T2D). This review focuses on the in vivo functional characterization of human BAT, the methodological approaches applied to examine these features and addresses critical gaps that remain in moving the field forward. Specifically, we describe the anatomical and biomolecular features of human BAT, the modalities and applications of non-invasive tools such as PET and magnetic resonance imaging coupled with spectroscopy (MRI/MRS) to study BAT morphology and function in vivo, and finally describe the functional characteristics of human BAT that have only been possible through the development and application of such tools.

O-(2-18 F-fluoroethyl)-L-tyrosine ( 18 F-FET) is a radiolabeled artificial amino acid used in PET for tumor delineation and grading. The present study compares different kinetic models to determine which are more appropriate for 18 F-FET in rats. Methods: Rats were implanted with F98 glioblastoma cells in the right hemisphere and scanned 9-15 d later. PET data were acquired during 50 min after a 1-min bolus of 18 F-FET. Arterial blood samples were drawn for arterial input function determination. Two compartmental pharmacokinetic models were tested: the 2-tissue model and the 1-tissue model. Their performance at fitting concentration curves from regions of interest was evaluated using the Akaike information criterion, F test, and residual plots. Graphical models were assessed qualitatively. Results: Metrics indicated that the 2-tissue model was superior to the 1-tissue model for the current dataset. The 2-tissue model allowed adequate decoupling of 18 F-FET perfusion and internalization by cells in the different regions of interest. Of the 2 graphical models tested, the Patlak plot provided adequate results for the tumor and brain, whereas the Logan plot was appropriate for muscles. Conclusion: The 2-tissue-compartment model is appropriate to quantify the perfusion and internalization of 18 F-FET by cells in various tissues of the rat, whereas graphical models provide a global measure of uptake. Ther adiolabeled artificial amino acid O-(2-18 F-fluoroethyl)-Ltyrosine ( 18 F-FET) has proven useful for the PET assessment of brain tumors in preclinical and clinical settings (1-3). Its high uptake in tumor tissue compared with normal brain and inflamed tissues allows for efficient tumor delineation (4), but the typical SUVs and tumor-to-brain ratios are of limited use for tumor grading (5,6). In contrast, the shape of time-activity curves are indicative of tumor grade and aggressiveness (7). For example, in untreated or recurring gliomas, continuously ascending curves are associated with a better prognosis than curves that reach a maximum a few minutes after injection (6,8), but the underlying mechanisms remain to be clarified (7,9,10). A pharmacokinetic model could help explain these differences and would allow quantitative comparison of cohorts.There have been few reports on 18 F-FET pharmacokinetic modeling (11,12), and a consensus on the most appropriate models has not been proposed. The present study aims at identifying the best models in different tissue types. MATERIALS AND METHODS Animal ModelExperiments were conducted in accordance with the recommendations of the Canadian Council on Animal Care and the local Ethics Committee. F98 glioblastoma cells were implanted in the right hemisphere of 17 male Fischer rats (254.6 6 15.9 g, Charles River Laboratories) according to a previously published protocol (13). The animals underwent dynamic PET scans 9-15 d after implantation. All imaging procedures were performed under isoflurane anesthesia with breathing rate and temperature continuously monitored. An automatic in...

In septic patients, cerebral blood flow was higher than in sedated control subjects and did not vary with mean arterial pressure targets. Further research is required to understand the clinical significance of cerebral hyperperfusion in septic patients on vasopressors and to reassess the neurologic effects of current mean arterial pressure targets in sepsis.

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We report an ultrasonic study of the magneto-elastic coupling of the spin-density wave antiferromagnet CaFe4As3. Longitudinal waves propagating along the a axis reveal anomalies on the acoustic velocity at both the incommensurate (ICM) (TN1 = 89.3 K) and commensurate (CM) (TN2 = 26.3 K) spin-density phases, which are consistent with the magnetic structure established from neutron diffraction experiments. Moreover, at higher temperatures, magnetic fluctuations are likely responsible for a reduced stiffening of the velocity below 150 K. Although the ICM phase appears elastically inhomogeneous below 50 K, a precise magnetic field dependence of the ICM-CM transition at TN2 specifies a preferential orientation of the in-plane easy and hard axes respectively parallel and perpendicular to the vectord (â ·d = cos 30• ). Within the CM phase, a magnetic field aligned along the ribbon b axis reveals a new magnetic transition of the spin-flop type near 16 teslas. For this particular field direction a phase diagram is proposed.