Search

Purpose: The purpose of this study was to evaluate the suitability of two phantoms, one made of capillary plates and the other polyethylene fibers, for assessing the quality of diffusion tensor imaging (DTI). Methods: The first phantom was a stack of glass capillary plates with many parallel micropores (CP). The second phantom was a bundle of polyethylene fiber Dyneema held together with a thermal shrinkage tube (Dy). High resolution multi-shot echo planar imaging (EPI) DTI acquisitions were performed at b-values of 0 and 1000 s/mm2 and diffusion-times (Tdiff) of 37.7 and 97.7 ms on a preclinical 7T MRI scanner. Thirty diffusion-encoding directions were used. The data were used to calculate the fractional anisotropy (FA), mean diffusivity (MD), and angular dispersion (AD). Further acquisitions were performed at b-values from 0 to 8000 s/mm2 in 14 steps with the diffusion gradient applied parallel (axial) and perpendicular (radial) to the Z direction. On the other hand, the data acquired with a 3T MRI scanner were used to confirm that measurements on a clinical machine are consistent with the 7T MRI results. Results: The dependence of FA, MD and AD on Tdiff was smaller for the Dy than for the CPs. The b-value dependent signal attenuations in the axial direction at Tdiff = 37.7 and 97.7 ms were similar for both phantoms. In the radial direction, Dy demonstrated similar b-value attenuation to that of in vivo tissue for both Tdiffs, but the attenuation for the CPs was affected by the change in Tdiff. Parameter estimates were similar for 3T and 7T MRI. Conclusion: The characteristics of the CP indicate that it can be used as a restricted-diffusion dominant phantom, while the characteristics of the Dy suggest that it can be used as a hindered-diffusion dominant phantom. Dy may be more suitable than CP for DTI quality control.

We have been working on the development of a PET insert for existing magnetic resonance imaging (MRI) systems for simultaneous PET/MR imaging, which integrates radiofrequency (RF)-shielded PET detector modules with an RF head coil. In order to avoid interferences between the PET detector circuits and the different MRI-generated electromagnetic fields, PET detector circuits were installed inside eight Cu-shielded fiber-reinforced plastic boxes, and these eight shielded PET modules were integrated in between the eight elements of a 270-mm-diameter and 280-mm-axial-length cylindrical birdcage RF coil, which was designed to be used with a 3-T clinical MRI system. The diameter of the PET scintillators with a 12-mm axial field-of-view became 255 mm, which was very close to the imaging region. In this study, we have investigated the effects of this PET/RF-coil integrated system on the performance of MRI, which include the evaluation of static field (Bo) inhomogeneity, RF field (B1) distribution, local specific absorption rate (SAR) distribution, average SAR, and signal-to-noise ratio (SNR). For the central 170-mm-diameter and 80-mm-axial-length of a homogenous cylindrical phantom (with the total diameter of 200 mm and axial-length of 100 mm), an increase of about a maximum of 3 mT in the Bo inhomogeneity was found, both in the central and 40-mm off-centered transverse planes, and a 5 percentage point increase of B1 field inhomogeneity was observed in the central transverse plane (from 84% without PET to 79% with PET), while B1 homogeneity along the coronal plane was almost unchanged (77%) following the integration of PET with the RF head coil. The average SAR and maximum local SAR were increased by 1.21 and 1.62 times, respectively. However, the SNR study for both spin-echo and gradient-echo sequences showed a reduction of about 70% and 60%, respectively, because of the shielded PET modules. The overall results prove the feasibility of this integrated PET/RF-coil system for using with the existing MRI system.

PET insert for the existing MRI systems can be a potential affordable alternative of body PET/MRI system. To avoid mutual interference between PET front-end electronics and the MRI system, PET front-end (F/E) electronics are enclosed in RF shielded Faraday cage that is connected to the RF ground for shielding purpose. On the other hand, strip transmission line RF coil requires a grounded plane in parallel with a strip conductor as coil that are connected by shunt capacitors. In this study, we proposed a strip transmission line coil that replaced the ground one layer conductor with the shielded PET detector module. The combined system shows promise for a compact PET/RF coil modality as insert for simultaneous PET/MR imaging with existing MRI systems, suitable even at ultrahigh field MRI., ISMRM 2018 Annual Meeting

Glutamatergic neurotransmission in the brain is coupled with cerebral and possibly with systemic glucose metabolism, which could be affected by food intake. The current study aimed to investigate effects of food intake on metabotropic glutamate receptor 5 (mGluR5) binding and glutamate levels in the brains of living subjects. Eleven healthy males underwent two clinical PET scans 3 hours apart using (E)-[11C]ABP688, a radioligand for mGluR5. Imaging sessions were performed with (n=5) or without (n=6) food intake between the two scans. Two MRS scans were also conducted, one before the first and the other after the second PET scan. Arterial blood was sampled during the PET scans to estimate mGluR5 binding as total distribution volume (VT). Glutamate concentrations in the right anterior and posterior insulae were measured using MRS data. To support the clinical PET findings, four awake rats underwent two PET scans on different days, one under control condition and the other under glucose-load (2g/kg p.o.) condition. In assays of human subjects with food intake, VT increased in the whole brain by 29% on average (p = 0.01) and glutamate concentrations in the right posterior insula increased by 10% (p = 0.02) between the first and second scans. By contrast, VT decreased by 20% on average (p = 0.02) and glutamate concentrations decreased by 8% (p = 0.01) in the corresponding areas of subjects without food intake. Cerebral VT was significantly and positively correlated with the blood glucose level (Pearson’s r = 0.87, p = 0.001). In the rat experiment, intake of glucose alone was sufficient to increase mGluR5 binding by 18%. These results indicate that plasma glucose levels are intimately involved in the dynamic activities of glutamate neurons represented by the mGluR5 status and glutamate metabolism in the brain, as cerebral glutamate neurotransmitter cycling is concurrent with aerobic glycolysis., The 31st CINP World Congress

Subject-specific head models of which their geometry is based on structural magnetic resonance images are essential to accurately estimate the spatial sensitivity profiles for image reconstruction in diffuse optical tomography. T1-weighted magnetic resonance images, which are commonly used for structural imaging, are not sufficient for the thresholdbased segmentation of the superficial tissues. Two types of pulse sequences, which provide a high contrast among the superficial tissues, are introduced to complement the segmentation to construct the subject-specific head models. The magnetic resonance images acquired by the proposed pulse sequences are robust to the threshold level and adequate for the thresholdbased segmentation of the superficial tissues compared to the T1- and T2- weighted images. The total scan time of the proposed pulse sequences is less than one-fourth of that for the T2-weighted pulse sequence.

We have investigated degeneration of the nerve fibers in chronic cerebral hypoperfusion model mice using DTI. Simple t-tests indicated that there are significant differences in CBF between the control and occluded sides of the brain, but there was no significant difference for MD. However, analysis of covariance showed that MD was strongly correlated with CBF, and that there were significant differences in MD between the contra- and ipsilateral sides. The result suggests degeneration of the nerve fibers due to chronic hypoperfusion. It is also suggested that CBF-related signal changes might be important for pathological diagnosis with DTI., ISMRM 25th Annual Meeting

The purpose of this study was to investigate how image preprocessing might help overcome two problems for deep-neural-network (DNN) based image diagnosis: the need for a large training database to achieve high accuracy and the difficulty humans have in understanding the internal decision process. Five DNNs were trained with a brain image series (preprocessed in five different ways), to judge the age-range of a volunteer. The performance of the DNNs was then compared statistically. The results suggested that image preprocessing may facilitate higher accuracy, and also make it easier to understand how and why a judgement was made., ISMRM 2016 2016 Annual Meeting

To evaluate the effect of the static magnetic field of magnetic resonance (MR) scanners on keepers (ie, ferromagnetic stainless steel plate adhered to the abutment tooth of dental magnetic attachments).