A high duty-cycle,multi-channel,power amplifier for high-resolution radiofrequency encoded magnetic resonance imaging

Magnetic Resonance Materials in Physics, Biology and Medicine - A radiofrequency (RF) power amplifier is an essential component of any magnetic resonance imaging (MRI) system. Unfortunately, no...     

Cerebral blood flow response to a hypoxic-ischemic insult differs in neonatal and juvenile rats

To compare the cerebral blood flow (CBF) response to a transient episode of hypoxia–ischemia producing damage in neonatal and juvenile rats. One- and four-week-old rats were subjected to unilateral carotid artery occlusion plus hypoxia (8% oxygen). Perfusion MR images were acquired either in sham controls or in hypoxic–ischemic rats before, during, 1 h and 24 h after hypoxia–ischemia. At 24 h post hypoxia–ischemia, T₂ maps and histology were used to assess damage. In sham controls, CBF increased twofold between the age of one and four weeks. Reductions in CBF ipsilateral to the occlusion occurred during hypoxia–ischemia followed by a substantial recovery at 1 h post in both age groups. However, contralaterally, hyperemia occurred during hypoxia–ischemia in four-week but not one-week-old rats. Similarly, hyperemia occurred ipsilaterally at 24 h post hypoxia–ischemia in four-week but not one-week-olds, corresponding to the distribution of elevations in T_2. Despite CBF differences, extensive cell death occurred ipsilaterally in both age groups. The CBF responses to hypoxia–ischemia and reperfusion differ depending on postnatal age, with hyperemia occurring in juvenile but not neonatal rats. The results suggest a greater CBF responsiveness and differential relationship between post-ischemic vascular perfusion and tissue injury in older compared with immature animals.     

MRI-based assessment of liver perfusion and hepatocyte injury in the murine model of acute hepatitis

Objective

To assess alterations in perfusion and liver function in the concanavalin A (ConA)-induced mouse model of acute liver failure (ALF) using two magnetic resonance imaging (MRI)-based methods: dynamic contrast-enhanced MRI (DCE-MRI) with Gd-EOB-DTPA contrast agent and arterial spin labelling (ASL).

Materials and methods

BALB/c mice were studied using a 9.4 T MRI system. The IntraGateFLASH^TM and FAIR-EPI pulse sequences were used for optimum mouse abdomen imaging.

Results

The average perfusion values for the liver of the control and ConA group were equal to 245 ± 20 and 200 ± 32 ml/min/100 g (p = 0.008, respectively). DCE-MRI showed that the time to the peak of the image enhancement was 6.14 ± 1.07 min and 9.72 ± 1.69 min in the control and ConA group (p < 0.001, respectively), while the rate of the contrast wash-out in the control and ConA group was 0.037 ± 0.008 and 0.021 ± 0.008 min^?1 (p = 0.004, respectively). These results were consistent with hepatocyte injury in the ConA-treated mice as confirmed by histopathological staining.

Conclusions

Both the ASL and DCE-MRI techniques represent a reliable methodology to assess alterations in liver perfusion and hepatocyte integrity in murine hepatitis.

     

Fate of Polybrominated Diphenyl Ethers, Nonylphenol, and Estrogenic Activity during Managed Infiltration of Wastewater Effluent

About a billion cubic meters of wastewater effluent are artificially recharged annually in the United States for maintenance of groundwater levels and prevention of seawater intrusion. There is concern that trace contaminants, including various endocrine disrupting compounds (EDCs), are not completely removed during infiltration, leading to deterioration of groundwater quality. In this work, we investigate the mechanisms and efficiency of EDC removal at the Sweetwater Recharge Facility, which is used to recharge secondary effluent from the Roger Road Wastewater Treatment Plant in Tucson, Ariz. Material was collected from the top meter of sediments in two infiltration basins and analyzed for extractable nonylphenol (NP), polybrominated diphenyl ethers (PBDE) and total estrogenic activity. The basins differed significantly in length of service (7 versus 15 years). Nevertheless, profiles of extractable contaminants and estrogenic activity were similar in the two basins. Results suggest that hydrophobic determinants of estrogenic activity are efficiently retained in surface sediments during soil-aquifer treatment. However, measurable levels of PBDEs, NP, and estrogenic activity are present in infiltrate that reaches the local unconfined aquifer at ～ 40?m below land surface.     

Analysis for vinyl chloride in PVC powders by head-space gas chromatography

At a temperature above the glass transition point of poly(vinyl chloride) (PVC), the solubility of vinyl chloride monomer (VCM) in PVC accurately follows Henry's law behavior for VCM contents up to 4000 ppm. This observation has lead to a rapid, simple gas-chromatographic method for the determination of VCM in PVC from the analysis of the vapor phase (head-space) over PVC powder samples in a sealed container. The basic experimental techniques, calculations, and examples of experimental data are given. The method can be used with any commercial gas chromatograph equipped with a flame ionization detector without instrument modification.     

High-resolution imaging at 3T and 7T with multiring local volume coils

Magnetic resonance (MR) microimaging of the human is becoming increasingly common for studies of tissue microstructure and microfunction. In this study, we consider the constraints that such experiments place on the design of radio-frequency (rf) coils, and describe the advantages of multiring coils, which offer a locally uniform B₁ field. We show that these coils are particularly suitable for high-field imaging of a restricted region of larger experimental animals or humans, offering the same simplicity and efficient use of rf power as a simple surface coil but without requiring sequence modifications such as adiabatic pulses. Imaging results are shown from human brain and from the abdominal aorta of an experimental animal.Acknowledgements. We thank Dr. S. King for his helpful assistance.