In the absence of any overt task performance, it has been shown that spontaneous, intrinsic brain activity is expressed as systemwide, resting-state networks in the adult brain. However, the route to adult patterns of resting-state activity through neuronal development in the human brain is currently unknown. Therefore, we used functional MRI to map patterns of resting-state activity in infants during sleep. We found five unique resting-states networks in the infant brain that encompassed the primary visual cortex, bilateral sensorimotor areas, bilateral auditory cortex, a network including the precuneus area, lateral parietal cortex, and the cerebellum as well as an anterior network that incorporated the medial and dorsolateral prefrontal cortex. These results suggest that resting-state networks driven by spontaneous signal fluctuations are present already in the infant brain. The potential link between the emergence of behavior and patterns of resting-state activity in the infant brain is discussed.development ͉ functional MRI ͉ spontaneous activity R ecent research on functional connectivity in the brain, in particular during resting-state conditions, has come to focus on low-frequency (Ͻ0.1 Hz), spontaneous fluctuations in the functional MRI (fMRI) signal. Discovered by Biswal et al. (1), it has been shown that systemwide networks in the resting brain are synchronized in time through intrinsic low-frequency signal fluctuations. Whereas early fMRI studies demonstrated synchronicity of intrinsic brain activity across hemispheres in primary sensory cortices (2, 3), succeeding studies have shown temporal synchronization in a resting-state network encompassing higher-order cortices (4). A systematic investigation of resting-state activity in the adult human brain was recently presented by Damoiseaux et al. (5). Using independentcomponent analysis (ICA), a data-driven explorative data analysis approach, they showed that there are numerous networks in the brain that are driven by spontaneous activity. Besides networks that are in part or fully described by the previously reported default mode (6) and task-positive network (7, 8), they found consistent patterns of resting-state activity in the visual cortex, sensorimotor areas, auditory areas, as well as extrastriate brain regions. These findings together with previous investigations on spontaneous activity suggest that the assumption that the brain during rest is idle and waiting to be triggered and respond to changes in the environment is not strictly valid. Rather, in addition to responding to changes in external stimuli or tasks, the brain is characterized by intrinsic dynamics in the form of coherent and spontaneous fluctuations, clustered together in networks that are credible from an anatomical and functional perspective.Interestingly, recent studies have presented evidence that spontaneous activity is relevant for human behavior. Momentary lapses of attention, affecting goal-oriented behavior on a global/ local selective attention task, were related to a fai...

Purpose:To assess the feasibility to use dynamic hepatocyte-specific contrast-enhanced MRI (DHCE-MRI) as an imaging-based liver function test, and to compare two methods for deconvolutional analysis (DA) in healthy human subjects. Materials and Methods:T 1 -weighted DHCE-MRI with the hepatocyte-specific contrast medium Gd-EOB-DTPA was performed in 20 healthy volunteers. DA was performed using truncated singular value decomposition (TSVD) and Fourier analysis with an appended tail (FAϩTail). Hepatic extraction fraction (HEF) and input relative blood flow (irBF) were calculated for each liver segment. A computer simulation comparing the standard deviation (SD) of TSVD and FAϩtail at different levels of signal-to-noise (SNR) ratio was performed. The results obtained were compared using descriptive statistics, the Wilcoxon matched pairs test and the variance ratio test. Results:Median HEF was 0.201 and 0.205 using TSVD and FAϩtail, respectively (P ϭ 0.086). The corresponding results for irBF was 0.240 and 0.239 (P ϭ 0.51). TSVD yielded a smaller SD, although the difference was not significant (P ϭ 0.068 for HEF and P ϭ 0.84 for irBF). The computer simulation showed that TSVD is more stable than FAϩtail at most levels of SNR.Conclusion: DHCE-MRI with Gd-EOB-DTPA enables the calculation of HEF and irBF. We regard these parameters as being markers of hepatic parenchymal function. SCINTIGRAPHIC METHODS ARE currently the only imaging-based liver function tests in clinical use. A radioactive tracer, most commonly from the 99m Tc-IDA family, is injected into the bloodstream and the tracer activity in a region of interest (ROI) placed over the liver is sampled over time, that is, a dynamic study. The activity in the blood pool is registered from a ROI placed over the heart and/or the spleen, and is often used to define the input function (1). Scintigraphic methods are hampered by the low spatial resolution and limited anatomic detail in the images obtained. Regional differences in hepatocyte function may, therefore, be hard or impossible to detect. A method to evaluate segmental liver function with SPECT has been developed, but has not gained a widespread clinical use (2,3).The use of a hepatocyte-specific contrast agent, Gadolinium ethoxybenzyl diethylenetriaminepentaacetic acid (Gd-EOB-DTPA; Primovist , Bayer Schering Pharma AG, Berlin), has been shown to improve detection and characterization of focal liver lesions in T 1 -weighted MRI (4,5). The intrinsic properties of Gd-EOB-DTPA are substantially different from the extracellular gadolinium-based tracers commonly used in dynamic contrast-enhanced MRI (DCE-MRI). The pharmacokinetic properties of Gd-EOB-DTPA are similar to those of the 99m Tc-IDA family with a hepatocellular uptake through the organic anionic transport system (OATS) and subsequent biliary excretion by glutathione-Stransferase (6). Pharmacokinetic studies show that approximately 50% of the administered dose of Gd-EOB-DTPA is extracted by the liver and secreted through the hepatobiliary pathway. The remain...

Despite the lower amount of gadolinium in the standard dose of Gd-EOB-DTPA, the results showed that the arterial enhancement in Gd-EOB-DTPA-enhanced dynamic liver MRI was comparable to Gd-DTPA. This result can be explained mainly by the higher relaxivity. Choosing a lower injection rate additionally supported to compensate for the lower injection volume by stretching the bolus without decreasing the peak. In this respect, an injection rate of 1 mL/s showed better results with regard to the arterial enhancement compared with 2 mL/s.

Dynamic hepatocyte-specific contrast-enhanced MRI (DHCE-MRI) has a potential role as an imaging-based liver function test. The high spatial resolution of MRI enables hepatic function to be assessed on segmental and sub-segmental levels.

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Objectives Conventional MRI at term age has been reported to be superior to cranial ultrasound (cUS) in detecting white matter (WM) abnormalities and predicting outcome in preterm infants. However, in a previous study cUS was performed during the fi rst 6 weeks only and not in parallel to MRI at term age. Therefore, the aim of the present work was to study brain injuries in preterm infants performing concomitant cUS and MRI at full-term age. Methods In a population-based cohort of 72 extremely low gestational age infants paired cUS and conventional MRI were performed at term age. Abnormalities on MRI were graded according to a previously published scoring system. On cUS images the lateral ventricles, the corpus callosum, the interhemispheric fi ssure and the subarachnoidal spaces were measured and the presence of cysts, grey matter abnormalities and gyral folding were scored. Results Moderate or severe WM abnormalities were detected on MRI in 17% of infants and abnormalities of the grey matter in 11% of infants. Among infants with normal ultrasound (n=28, 39%) none had moderate or severe WM abnormalities or abnormal grey matter on MRI. All infants with severe abnormalities (n=3, 4%) were identifi ed as severe on MRI and cUS. Conclusions All severe WM abnormalities identifi ed on MRI at term age were also detected by cUS at term, providing the examinations were performed on the same day. Infants with normal cUS at term age were found to have a normal MRI or only mild WM abnormalities on MRI at term age.

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The study demonstrates a new method to quantify total and segmental liver function using DHCE-MRI in patients with PSC.