Ir4(CO)12-Catalyzed Benzylic C(sp3)-H Silylation of 2-Alkylpyridines with Hydrosilanes Leading to 2-(1-Silylalkyl)pyridines.

The iridium-catalyzed C(sp3)-H silylation of 2-alkylpyridines with hydrosilanes at the benzylic position to afford 2-(1-silylalkyl)pyridines is described. The low product yield was markedly improved by adding 3,5-dimethylpyridine. Norbornene is also an essential additive for the reaction to proceed as a hydrogen scavenger. Carbon monoxide plays an important role in the catalytic cycle as a ligand. Other transition-metal carbonyls such as Rh4(CO)12 and Ru3(CO)12 can also be used as catalysts for this C-H silylation.

Signal contributions to heavily diffusion-weighted functional magnetic resonance imaging investigated with multi-SE-EPI acquisitions.

Diffusion-weighted (DW) functional magnetic resonance imaging (fMRI) signal changes have been noted as a promising marker of neural activity. Although there is no agreement on the signal origin, the blood oxygen level dependent (BOLD) effect has figured as one of the most likely sources. In order to investigate possible BOLD and non-BOLD contributions to the signal, DW fMRI was performed on normal volunteers using a sequence with two echo-planar acquisitions after pulsed-gradient spin-echo. Along with the changes to the signal amplitude (ΔS/S) measured at both echo-times, this sequence allowed changes to the transverse relaxation rate (ΔR2) to be estimated for multiple b-values during hypercapnia (HC) and visual stimulation (VS). ΔS/S and ΔR2 observed during HC were relatively insensitive to increasing b-value. On the other hand, ΔS/S demonstrated a clear dependence on b-value at both echo-times for VS. In addition, ΔR2 during the latter half of VS was significantly more negative at b=1400s/mm(2) than for the time-courses at lower b-value, but ΔR2 during the post-stimulus undershoot was independent of b-value. The results have been discussed in terms of two models: the standard intravascular-extravascular model for fMRI and a three-compartment model (one intra- and two extravascular compartments). Within these interpretations the results suggest that the majority of the response is linked to changes in transverse relaxation, but possible contributions from other sources may not be ruled out.

Comparison of hemodynamics of intracranial aneurysms between MR fluid dynamics using 3D cine phase-contrast MRI and MR-based computational fluid dynamics.

INTRODUCTION: Hemodynamics is thought to play a very important role in the initiation, growth, and rupture of intracranial aneurysms. The purpose of our study was to compare hemodynamics of intracranial aneurysms of MR fluid dynamics (MRFD) using 3D cine PC MR imaging (4D-Flow) at 1.5 T and MR-based computational fluid dynamics (CFD). METHODS: 4D-Flow was performed for five intracranial aneurysms by a 1.5 T MR scanner. 3D TOF MR angiography was performed for geometric information. The blood flow in the aneurysms was modeled using CFD simulation based on the finite element method. We used MR angiographic data as the vascular models and MR flow information as boundary conditions in CFD. 3D velocity vector fields, 3D streamlines, shearing velocity maps, wall shear stress (WSS) distribution maps and oscillatory shear index (OSI) distribution maps were obtained by MRFD and CFD and were compared. RESULTS: There was a moderate to high degree of correlation in 3D velocity vector fields and a low to moderate degree of correlation in WSS of aneurysms between MRFD and CFD using regression analysis. The patterns of 3D streamlines were similar between MRFD and CFD. The small and rotating shearing velocities and higher OSI were observed at the top of the spiral flow in the aneurysms. The pattern and location of shearing velocity in MRFD and CFD were similar. The location of high oscillatory shear index obtained by MRFD was near to that obtained by CFD. CONCLUSION: MRFD and CFD of intracranial aneurysms correlated fairly well.

In vivo hemodynamic analysis of intracranial aneurysms obtained by magnetic resonance fluid dynamics (MRFD) based on time-resolved three-dimensional phase-contrast MRI.

INTRODUCTION: Hemodynamics is thought to play a very important role in the initiation, growth, and rupture of intracranial aneurysms. The purpose of our study was to perform in vivo hemodynamic analysis of unruptured intracranial aneurysms of magnetic resonance fluid dynamics using time-resolved three-dimensional phase-contrast MRI (4D-Flow) at 1.5 T and to analyze relationships between hemodynamics and wall shear stress (WSS) and oscillatory shear index (OSI). METHODS: This study included nine subjects with 14 unruptured aneurysms. 4D-Flow was performed by a 1.5-T magnetic resonance scanner with a head coil. We calculated in vivo streamlines, WSS, and OSI of intracranial aneurysms based on 4D-Flow with our software. We evaluated the number of spiral flows in the aneurysms and compared the differences in WSS or OSI between the vessel and aneurysm and between whole aneurysm and the apex of the spiral flow. RESULTS: 3D streamlines, WSS, and OSI distribution maps in arbitrary direction during the cardiac phase were obtained for all intracranial aneurysms. Twelve aneurysms had one spiral flow each, and two aneurysms had two spiral flows each. The WSS was lower and the OSI was higher in the aneurysm compared to the vessel. The apex of the spiral flow had a lower WSS and higher OSI relative to the whole aneurysm. CONCLUSION: Each intracranial aneurysm in this study had at least one spiral flow. The WSS was lower and OSI was higher at the apex of the spiral flow than the whole aneurysmal wall.

A multi-compartmental SE-BOLD interpretation for stimulus-related signal changes in diffusion-weighted functional MRI.

A new interpretation is proposed for stimulus-induced signal changes in diffusion-weighted functional MRI. T(2)-weighted spin-echo echo-planar images were acquired at different diffusion-weightings while visual stimulation was presented to human volunteers. The amplitudes of the positive stimulus-correlated response and post-stimulus undershoot (PSU) in the functional time-courses were found to follow different trends as a function of b-value. Data were analysed using a three-compartment signal model, with one compartment being purely vascular and the other two dominated by fast- and slow-diffusing molecules in the brain tissue. The diffusion coefficients of the tissue were assumed to be constant throughout the experiments. It is shown that the stimulus-induced signal changes can be decomposed into independent contributions originating from each of the three compartments. After decomposition, the fast-diffusion phase displays a substantial PSU, while the slow-diffusion phase demonstrates a highly reproducible and stimulus-correlated time-course with minimal undershoot. The decomposed responses are interpreted in terms of the spin-echo blood oxygenation level dependent (SE-BOLD) effect, and it is proposed that the signal produced by fast- and slow-diffusing molecules reflect a sensitivity to susceptibility changes in arteriole/venule- and capillary-sized vessels, respectively. This interpretation suggests that diffusion-weighted SE-BOLD imaging may provide subtle information about the haemodynamic and neuronal responses.

Double hepatic arterial phase MRI of the liver with switching of reversed centric and centric K-space reordering.

OBJECTIVE: The purpose of our study was to evaluate the clinical feasibility and usefulness of a 2D spoiled gradient-recalled echo MR sequence with serial switching of reversed centric and centric k-space reordering for high-spatial-resolution gadolinium-enhanced double hepatic arterial phase (HAP) MRI of the liver. SUBJECTS AND METHODS: MR images (frequency, 512; phase encoding without interpolation, 224; 6-mm thickness with 1-mm gap; 30 slices per 18 seconds) were obtained with multiphase imaging in which central k-space line data were filled 10, 21, 49, and 181 seconds after arrival of contrast medium in the abdominal aorta for the early HAP (reversed centric reordering, center of k-space lines acquired at end of acquisition), late HAP (centric reordering, center of k-space lines at beginning of acquisition), portal venous phase (centric reordering), and equilibrium phase (centric reordering), respectively, in 102 consecutive patients with suspected liver disease, including 48 untreated hepatocellular carcinomas (HCCs) in 35 patients. Images were quantitatively assessed for degree of contrast enhancement in the abdominal aorta, spleen, portal trunk, liver parenchyma, hepatic veins, and HCCs. Images were qualitatively assessed for the effectiveness of contrast enhancement in each phase and for degree of image degradation due to artifacts. RESULTS: Enhancement of the abdominal aorta peaked in the early HAP, of the portal trunk in the late HAP, and of the hepatic parenchyma and veins in the portal venous phase. Mean HCC-to-liver contrast peaked in the early HAP and turned to a negative value in the portal venous and equilibrium phases. Sufficient image quality was achieved in 99 (97%) of the patients. One of the other three patients had motion artifacts due to body motion, and the other two had unsatisfactory respiratory suspension. Scan timing for early and late HAP was optimal in 74 (73%) of the patients, for late HAP lagged in 20 (20%), for early HAP was premature in six (6%), and for early HAP lagged in five (5%) of the patients. CONCLUSION: We confirmed the feasibility and usefulness of a 2D gadolinium-enhanced double HAP spoiled gradient-recalled echo sequence incorporating serial switching of reversed centric and centric k-space reordering. This method has the potential for use in high-spatial-resolution double HAP MRI for the diagnosis of hypervascular HCC.

Isotropic diffusion-weighted MR imaging with tetrahedral gradients in the upper abdomen.

A tetrahedral gradient diffusion sequence for body imaging for a 1.5T scanner was implemented, and we compared the quality of images acquired with the new technique and with the conventional orthogonal technique. Image quality was better using the tetrahedral technique in terms of signal homogeneity in the right liver lobe and signal loss artifact in the left lobe, and the technique was considered useful for magnetic resonance imaging in the upper abdomen.

Efficacy of multislice computed tomography for gastroenteric and hepatic surgeries.

AIM: To determine the efficacy of multislice CT for gastroenteric and hepatic surgery. METHODS: Dual-phase helical computed tomography was performed in 50 of 51 patients who underwent gastroenteric and hepatic surgeries. Twenty-eight, eighteen and four patients suffering from colorectal cancer, gastric cancer, and liver cancer respectively underwent colorectal surgery (laparoscopic surgery: 6 cases), gastrectomy, and hepatectomy. Three-dimensional computed tomography imaging of the inferior mesenteric artery, celiac artery and hepatic artery was performed. And in the follow-up examination of postoperative patients, multiplanar reconstruction image was made in case of need. RESULTS: Scans in 50 patients were technically satisfactory and included in the analysis. Depiction of major visceral arteries, which were important for surgery and other treatments, could be done in all patients. Preoperative visualization of the left colic artery and sigmoidal arteries, the celiac artery and its branches, and hepatic artery was very useful to lymph node dissection, the planning of a reservoir and hepatectomy. And multiplanar reconstruction image was helpful to diagnosis for the postoperative follow-up of patients. CONCLUSION: Three-dimensional volume rendering or multiplanar reconstruction imaging performed by multislice computed tomography was very useful for gastroenteric and hepatic surgeries.

Acoustic noise transfer function in clinical MRI a multicenter analysis.

RATIONALE AND OBJECTIVES: Acoustic noise both in terms of its magnitude and frequency during magnetic resonance imaging (MRI) scan is influenced by imaging parameters and pulse sequences. It varies because of many different factors such as structure, materials, and magnetic field strength. The purpose of our study is to evaluate the characteristics of acoustic noise independent of MRI scan protocol by measuring a gradient-pulse-to-acoustic-noise transfer function (GPAN-TF) at various MRI scanners. MATERIALS AND METHODS: We measured sound pressure levels in the frequency domain in a 0.4-T, seven 1.5-T, and three 3.0-T clinical MRI systems when applying a simple narrower trapezoidal gradient pulse. We calculated a GPAN-TF [µPa/(mT/m)] in each gradient coil (ie, X, Y, and Z-axis) by the deconvolution process. RESULTS: GPAN-TF at a high-frequency range (1000-10,000 Hz) was larger than that at low frequency for all MRI (P<0.01) scanners except for a low static field machine. For high frequency (>1000 Hz), the 3.0-T MRI scanner had a larger GPAN-TF than that of 0.4-T and 1.5-T (P < .01). MR scanner with a vacuum chamber reduced GPAN-TF at a lower frequency (P < .01), but this effect decreased at higher frequency. CONCLUSION: GPAN-TF analysis makes it possible to obtain more detailed information on acoustic noise properties among MRI scanners.

Calibrated magnetic resonance hydrometry to quantify pancreatic juice: a preliminary study.

PURPOSE: To investigate the effectiveness of the calibrated MR hydrometry (CMRH) method for accurately measuring pancreatic secretion. MATERIALS AND METHODS: All studies were performed on a 1.5-T MR system using a fat-suppressed, single-shot half-Fourier fast spin-echo sequence with a standard body coil. A certain volume (20 mL) of saline solution was employed as an extrabody calibrator. The validity of the CMRH method was tested both in vitro and in vivo, and actual and calculated volumes were compared. RESULTS: The in vitro study yielded a high correlation (r = 0.99; P < 0.0001) between the actual volume of saline solution in the imaging field and the calculated volume. In the in vivo study, for all volunteers, there was a very strong and significant positive correlation between the measured signal intensities or calculated volumes and actual volumes (correlation coefficient range: 0.94-0.99; P < 0.0001). CONCLUSION: This preliminary study shows that CMRH is an effective tool to measure the amount of pancreatic fluid secretion.

Magnetic resonance elastography to observe deep areas: comparison of external vibration systems.

MRE methods deform the sample using an external vibration system. We have been using a transverse driver, which generates shear waves at the object surface. One of the problems is that shear waves rapidly attenuate at the surface of tissue and do not propagate into the body. In this study, we compared the shear waves generated by transverse and longitudinal drivers. The longitudinal driver was found to induce shear waves deep inside a porcine liver phantom. These results suggest that the longitudinal driver will allow measurement of the shear modulus deep inside the body.

Visualization of hemodynamics in intracranial arteries using time-resolved three-dimensional phase-contrast MRI.

PURPOSE: To visualize the hemodynamics of the intracranial arteries using time-resolved three-dimensional phase-contrast (PC)-MRI (4D-Flow). MATERIALS AND METHODS: MR examinations were performed with a 1.5T MR unit on six healthy volunteers (22-50 years old, average = 30 years). 4D-Flow was based on a radiofrequency (RF)-spoiled gradient-echo sequence, and velocity encoding (VENC) was performed along all three spatial directions. Measurements were retrospectively gated to the electrocardiogram (ECG), and cine series of three-dimensional (3D) data sets were generated. The voxel size was 1 x 1 x 1 mm, and acquisition time was 30-40 minutes. 4D data sets were calculated into time-resolved images of 3D streamlines, 3D particle traces, and 2D velocity vector fields by means of flow visualization software. RESULTS: We were able to see the 3D streamlines from the circle of Willis to the bilateral M2 segment of the middle cerebral arteries (MCAs). Time-resolved images of 3D particle traces also clearly demonstrated intracranial arterial flow dynamics. 2D velocity vector fields on the planes traversing the carotid siphon or the basilar tip were clearly visualized. These results were obtained in all six volunteers. CONCLUSION: 4D-Flow helped to elucidate the in vivo 3D hemodynamics of human intracranial arteries. This method may be a useful noninvasive means of analyzing the hemodynamics of intracranial arteries in vivo.

Inhibition of tumor-promoting effects by poricoic acids G and H and other lanostane-type triterpenes and cytotoxic activity of poricoic acids A and G from Poria cocos.

The structures of two novel 3,4-seco-lanostane-type triterpenes isolated from the sclerotium of Poria cocos were established to be 16alpha-hydroxy-3,4-seco-lanosta-4(28),8,24-triene-3,21-dioic acid (1; poricoic acid G) and 16alpha-hydroxy-3,4-seco-24-methyllanosta-4(28),8,24(24(1))-triene-3,21-dioic acid (2; poricoic acid H) on the basis of spectroscopic methods. These two, and eight other known compounds isolated from the sclerotium, poricoic acid B (3), poricoic acid A (4), tumulosic acid (5), dehydrotumulosic acid (6), 3-epidehydrotumulosic acid (7), polyporenic acid C (8), 25-hydroxy-3-epidehydrotumulosic acid (9), and dehydroabietic acid methyl ester (10), showed potent inhibitory effects on Epstein-Barr virus early antigen (EBV-EA) activation induced by the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). Evaluation of the cytotoxicity of compounds 1 and 4 against human cancer cell lines revealed that 1 was significantly cytotoxic to leukemia HL-60 cells [GI(50) (concentration that yields 50% growth) value 39.3 nM], although it showed only moderate cytotoxicity to the other cells. Compound 4 exhibited moderate cytotoxicity to all of the cancer cell lines tested.