In situ monitoring of lipid droplet release from biopolymer microgels under simulated gastric conditions using magnetic resonance imaging and spectroscopy.

Functional foods are being designed to breakdown in the human gut in a controlled fashion so as to regulate blood nutrient profiles, hormone release, energy intake, and bioavailability. Biopolymer microgels, small spherical beads made from proteins and/or polysaccharides, are a promising tool that can be used to modulate the gastrointestinal behavior of food components. In this study, lipid droplets were loaded into microgels fabricated from either alginate or carrageenan using an injection-gelation method. The lipid-loaded microgels were then incubated in simulated gastric juices and the impact of biopolymer type on the release of the lipid droplets was observed. Optical microscopy and turbidity measurements showed that lipid droplet release occurred more rapidly for the carrageenan microgels, which was attributed to their partial disruption in the gastric fluids. In contrast, lipid droplet release was relatively slow from the alginate microgels because they remained intact. We also showed that magnetic resonance imaging (MRI) could be used for in situ monitoring of carrageenan microgel disruption and lipid droplet release under simulated stomach conditions. This method was based on quantifying the local lipid levels using T1 images and the magnetic resonance spectroscopy. A water-selected VIBE sequence was optimized for obtaining the T1 images and a stimulated echo acquisition mode (STEAM) sequence was selected for obtaining the MR spectra. The MRI method may be particularly useful for in vivo studies of the behavior of filled microgels.

Removal of partial volume averaging with free water in MR diffusion tensor imaging using inversion recovery for b0 image.

PURPOSE: To remove the partial volume averaging effect of free water in MR diffusion imaging of neural tissues by use of the fluid attenuated inversion recovery (FLAIR) without the penalty of an extended scan time. MATERIALS AND METHODS: The magnetic resonance images were obtained from a normal volunteer in a coronal slice orientation at 3T with the 20-channel rf coil. In diffusion imaging only the b0 images were obtained with the FLAIR contrast while the diffusion weighted images were obtained without the FLAIR contrast. A composition of FLAIR b0 and non-FLAIR diffusion weighted images was used in calculating the diffusion tensor and fractional anisotropy after compensating the reduced signal amplitude due to the inversion recovery in the FLAIR b0 images. The fractional anisotropy of the non-FLAIR, FLAIR, and the composite methods were analyzed for the mean and histogram in the corpus callosum, cervical spine, and the fornix tracts. RESULTS: The partial volume averaging effect was observed in the corpus callosum, the cervical spine, and the fornix tracts in the non-FLAIR b0 and diffusion images. The partial volume averaging effect was removed in the FLAIR diffusion images which took more than twice the scan time than the non-FLAIR diffusion imaging. The proposed composite FLAIR diffusion imaging removed the partial volume averaging effect as in the FLAIR diffusion imaging. The distribution of the FA histogram was very different between the non-FLAIR and FLAIR diffusion images, while it was very similar between the FLAIR and the composite FLAIR after correcting the white matter signal in the FLAIR b0 images. CONCLUSIONS: The proposed composite FLAIR diffusion imaging method was equally effective in removing the partial volume averaging effect as the FLAIR diffusion imaging at a limited increase of the scan time since only a small number of b0 images needed to be obtained with the FLAIR contrast.

Parallel imaging with asymmetric acceleration to reduce Gibbs artifacts and to increase signal-to-noise ratio of the gradient echo echo-planar imaging sequence for functional MRI.

Parallel imaging with accelerated acquisition was noted to pronounce Gibbs artifacts which appear as ripples propagated in the phase-encoding (PE) direction near the susceptibility-affected region in echo-planar imaging (EPI). Using the extended EPI sequence, which collected extended readouts outside the regular data sampling time, the pronounced Gibbs artifact was analyzed and found to be caused by an increased echo shift in the pre-echo time (T(E)) of accelerated parallel imaging. This was also confirmed by theoretical derivation of the echo shift caused by the inplane susceptibility gradient in the PE direction (ISG(PE)). A new EPI sequence was developed to reduce the Gibbs artifact and to restore the signal level toward that of nonaccelerated parallel imaging by asymmetrically accelerating only the post-T(E) sampling time and by using the extended EPI in the pre-T(E). The nonaccelerated portion in the pre-T(E) used the delay for the optimum blood oxygen level dependent (BOLD) sensitivity at 3 T, maintaining the same slice coverage as the symmetrical acceleration in both pre-T(E) and post-T(E). The increased data sampling points resulted in an increase of the signal-to-noise ratio (SNR). The restored signal and enhanced SNR of the proposed method were confirmed to deliver a better BOLD functional MRI (fMRI) result in the breath holding experiment.

The anatomy of the callosal and visual-association pathways in high-functioning autism: a DTI tractography study.

There is increasing recognition that many of the core behavioral impairments that characterize autism potentially emerge from poor neural synchronization across nodes comprising dispersed cortical networks. A likely candidate for the source of this atypical functional connectivity in autism is an alteration in the structural integrity of intra- and inter-hemispheric white matter (WM) tracts that form large-scale cortical networks. To test this hypothesis, in a group of adults with high-functioning autism (HFA) and matched control participants, we used diffusion tensor tractography to compare the structural integrity of three intra-hemispheric visual-association WM tracts, the inferior longitudinal fasciculus (ILF), the inferior fronto-occipito fasciculus (IFOF) and the uncinate fasciculus (UF), with the integrity of three sub-portions of the major inter-hemispheric fiber tract, the corpus callosum. Compared with the control group, the HFA group evinced an increase in the volume of the intra-hemispheric fibers, particularly in the left hemisphere, and a reduction in the volume of the forceps minor (F-Mi) and body of the corpus callosum. The reduction in the volume of the F-Mi also correlated with an increase in repetitive and stereotypical behavior as measured by the Autism Diagnostic Interview. These findings suggest that the abnormalities in the integrity of key inter- and intra-hemispheric WM tracts may underlie the atypical information processing observed in these individuals.

Recovery of signal loss due to an in-plane susceptibility gradient in the gradient echo EPI through acquisition of extended phase-encoding lines.

In gradient echo imaging the in-plane susceptibility gradient causes an echo shift which results in signal loss. The loss of signal becomes more severe in gradient echo EPI, due to the low amplitude of the gradient which is applied in the phase-encoding direction during a long echo train. As the readout gradient amplitude is set to be very high in gradient echo EPI, the echo shift in the readout direction is negligible compared to that in the phase-encoding direction. Traditionally, a z-shimming technique has been applied to the phase-encoding direction of gradient echo EPI to restore the lost signal. This technique, however, requires a significant increase of scan time, as is also the case with the through-plane z-shimming technique. A new approach that allows one to restore the lost signal is to acquire additional phase-encoding lines beyond the regular phase-encoding range. The extension of the phase-encoding lines prior to the regular phase-encoding range exploits the delay time for optimum echo time of the BOLD sensitivity. Therefore, scan time is increased only for the extended phase-encoding lines posterior to the regular phase-encoding range. This technique has been confirmed experimentally by imaging human subject's heads at 3T.

Synthesis methods of multiple phase-cycled SSFP images to reduce the band artifact and noise more reliably.

The band artifact in steady-state free precession can be reduced by synthesizing the multiple images obtained through different phase increments of successive radiofrequency pulses. Even though the complex summation method was reported to be effective in reducing the band artifact, it has the pitfalls of intensity abnormality and sensitivity to the phase abnormality. Two new methods have been developed for more reliable reduction of the band artifact than the complex summation method. One method is to sum the complex images partially and to take the maximum intensity of the partially summed images. The other method is to sum the free induction decay (FID) and primary echo components of the Fourier series that are obtained through Fourier analysis of the complex base images. Both proposed methods were compared with other magnitude (maximum intensity projection, spectrally decomposed synthesis, sum-of-squares, nonlinear averaging) and complex-based (complex summation, magnitude-weighted complex summation) methods experimentally at 3 T for the phantom and volunteer's head imaging. Both proposed methods were confirmed to maintain the advantage of the complex summation in reducing both the dark and bright band artifacts while reducing the intensity abnormality and sensitivity to the phase abnormality from that of the complex summation method over a wide range of flip angles and relaxation times.

Lateral inferior prefrontal cortex and anterior cingulate cortex are engaged at different stages in the solution of insight problems.

Two studies used puzzles that required participants to find a word that satisfied a set of constraints. The first study used a remote-association task, where participants had to find a word that would form compound words with 3 other words. The second study required participants to complete a word fragment with an associate of another word. Both studies produced distinct patterns of activity in the lateral inferior prefrontal cortex (LIPFC) and the anterior cingulate cortex (ACC). Activation in the LIPFC rose only as long as the participants were trying to retrieve the solution and dropped off as soon as the solution was obtained. However, activation in the ACC increased upon the retrieval of a solution, reflecting the need to process that solution. The data of the second experiment are fit by an information-processing model that interprets the activity in the LIPFC as reflecting retrieval operations and the activity in the ACC as reflecting subgoal setting.

A nonlinear BOLD model accounting for refractory effect by applying the longitudinal relaxation in NMR to the linear BOLD model.

A mathematical model to regress the nonlinear blood oxygen level-dependent (BOLD) fMRI signal has been developed by incorporating the refractory effect into the linear BOLD model of the biphasic gamma variate function. The refractory effect was modeled as a relaxation of two separate BOLD capacities corresponding to the biphasic components of the BOLD signal in analogy with longitudinal relaxation of magnetization in NMR. When tested with the published fMRI data of finger tapping, the nonlinear BOLD model with the refractory effect reproduced the nonlinear BOLD effects such as reduced poststimulus undershoot and saddle pattern in a prolonged stimulation as well as the reduced BOLD signal for repetitive stimulation.

Reduced structural connectivity in ventral visual cortex in congenital prosopagnosia.

Using diffusion tensor imaging and tractography, we found that a disruption in structural connectivity in ventral occipito-temporal cortex may be the neurobiological basis for the lifelong impairment in face recognition that is experienced by individuals who suffer from congenital prosopagnosia. Our findings suggest that white-matter fibers in ventral occipito-temporal cortex support the integrated function of a distributed cortical network that subserves normal face processing.

Reduction in white matter connectivity, revealed by diffusion tensor imaging, may account for age-related changes in face perception.

An age-related decline in face processing, even under conditions in which learning and memory are not implicated, has been well documented, but the mechanism underlying this perceptual alteration remains unknown. Here, we examine whether this behavioral change may be accounted for by a reduction in white matter connectivity with age. To this end, we acquired diffusion tensor imaging data from 28 individuals aged 18 to 86 years and quantified the number of fibers, voxels, and fractional anisotropy of the two major tracts that pass through the fusiform gyrus, the pre-eminent face processing region in the ventral temporal cortex. We also measured the ability of a subset of these individuals to make fine-grained discriminations between pairs of faces and between pairs of cars. There was a significant reduction in the structural integrity of the inferior fronto-occipital fasciculus (IFOF) in the right hemisphere as a function of age on all dependent measures and there were also some changes in the left hemisphere, albeit to a lesser extent. There was also a clear age-related decrement in accuracy of perceptual discrimination, especially for more challenging perceptual discriminations, and this held to a greater degree for faces than for cars. Of greatest relevance, there was a robust association between the reduction of IFOF integrity in the right hemisphere and the decline in face perception, suggesting that the alteration in structural connectivity between the right ventral temporal and frontal cortices may account for the age-related difficulties in face processing.

Information-processing modules and their relative modality specificity.

This research uses fMRI to understand the role of eight cortical regions in a relatively complex information-processing task. Modality of input (visual versus auditory) and modality of output (manual versus vocal) are manipulated. Two perceptual regions (auditory cortex and fusiform gyrus) only reflected perceptual encoding. Two motor regions were involved in information rehearsal as well as programming of overt actions. Two cortical regions (parietal and prefrontal) performed processing (retrieval and representational change) independent of input and output modality. The final two regions (anterior cingulate and caudate) were involved in control of cognition independent of modality of input or output and content of the material. An information-processing model, based on the ACT-R theory, is described that predicts the BOLD response in these regions. Different modules in the theory vary in the degree to which they are modality-specific and the degree to which they are involved in central versus peripheral cognitive processes.

An information-processing model of three cortical regions: evidence in episodic memory retrieval.

ACT-R (Anderson, J.R., et al., 2003. An information-processing model of the BOLD response in symbol manipulation tasks. Psychon. Bull. Rev. 10, 241-261) relates the inferior dorso-lateral prefrontal cortex to a retrieval buffer that holds information retrieved from memory and the posterior parietal cortex to an imaginal buffer that holds problem representations. Because the number of changes in a problem representation is not necessarily correlated with retrieval difficulties, it is possible to dissociate prefrontal-parietal activations. In two fMRI experiments, we examined this dissociation using the fan effect paradigm. Experiment 1 compared a recognition task, in which representation requirement remains the same regardless of retrieval difficulty, with a recall task, in which both representation and retrieval loads increase with retrieval difficulty. In the recognition task, the prefrontal activation revealed a fan effect but not the parietal activation. In the recall task, both regions revealed fan effects. In Experiment 2, we compared visually presented stimuli and aurally presented stimuli using the recognition task. While only the prefrontal region revealed the fan effect, the activation patterns in the prefrontal and the parietal region did not differ by stimulus presentation modality. In general, these results provide support for the prefrontal-parietal dissociation in terms of retrieval and representation and the modality-independent nature of the information processed by these regions. Using ACT-R, we also provide computational models that explain patterns of fMRI responses in these two areas during recognition and recall.

Extraction of overt verbal response from the acoustic noise in a functional magnetic resonance imaging scan by use of segmented active noise cancellation.

A method to extract the subject's overt verbal response from the obscuring acoustic noise in an fMRI scan is developed by applying active noise cancellation with a conventional MRI microphone. Since the EPI scanning and its accompanying acoustic noise in fMRI are repetitive, the acoustic noise in one time segment was used as a reference noise in suppressing the acoustic noise in subsequent segments. However, the acoustic noise from the scanner was affected by the subject's movements, so the reference noise was adaptively adjusted as the scanner's acoustic properties varied in time. This method was successfully applied to a cognitive fMRI experiment with overt verbal responses.