Purpose : Recent development of diffusion tensor imaging enables the evaluation of the microstructural characteristics of the brain white matter. However, optimal imaging parameters for diffusion tensor imaging, particularly concerning the number of diffusion gradient direction, have not been studied thoroughly yet. The purpose of this study was to evaluate the influence of the number of diffusion gradient direction on the fiber tracking of the white matter. Materials and methods : 13 healthy volunteers (ten men and three women, mean age 30 years, age range 23-37 years) were included in this study. Diffusion tensor imaging was performed with different numbers of diffusion gradient direction as 6, 15, and 32, keeping the other imaging parameters constant. The imaging field ranged from 1 cm below the pons to 2-3 cm above the lateral ventricle, parallel to the anterior commissure-posterior commissure line. FA (fractional anisotropy) maps were created via image postprocessing, and then FA and its standard deviation were calculated in the genu and the splenium of the corpus callosum on each of FA maps. Fiber tracking of the corticospinal tract in the brain was performed and the number of the reconstructed fibers of the tract was measured. FA, standard deviation of FA and the number of the reconstructed fibers were compared statistically between the different diffusion gradient directions. Results : FA is not statistically significantly different between the different diffusion gradient directions. By increasing the number of diffusion gradient direction, standard deviation of FA decreased significantly, and the number of the reconstructed fibers increased significantly. Conclusion : The higher number of diffusion gradient direction provided better quality of fiber tracking.

The dissolution behavior of tin from pure tin and Sn–Fe alloys in sodium hydroxide solutions has been investigated using a rotating disc. The effects of the composition of the alloys, disc rotation speed, sodium hydroxide concentration, oxygen potential and temperature on the dissolution kinetics of tin have been studied. The dissolution rate of tin from a 50 wt.% Sn–50 wt.% FeSn2 mixture in sodium hydroxide solutions was found to be higher than that from pure tin. This is attributed to the fact that polarity reversal occurred between tin and iron from Sn–FeSn2 in sodium hydroxide media and therefore, tin of the FeSn2 acted as an anodic. The dissolution rate of tin from pure tin in sodium hydroxide solutions was found to be controlled by mass transfer of oxygen through the diffusion boundary layer. The dissolution of tin from Fe–Sn alloys, however, involved a mixed-control mechanism of diffusion and chemical reaction.

PURPOSE:To characterize the appearance and determine the importance of the "flow-void" sign on magnetic resonance (MR) images of patients with osseous metastasis from renal cell carcinoma. MATERIALS AND METHODS:Three musculoskeletal radiologists retrospectively and independently reviewed the medical records of 16 patients who had undergone MR imaging and in whom 20 osseous metastatic lesions from renal cell carcinoma had been diagnosed on the basis of clinical and radiologic findings. They assessed the MR images for the presence and frequency of the flow-void sign--multiple dot-like or tubular structures with low signal intensity. They then compared these findings on MR images with the corresponding areas on available images obtained with radiography (n = 16), computed tomography (CT) (n = 6), and digital subtraction angiography (n = 3) and with the results of histopathologic analysis for the same patient group. They noted the location, diameter, and appearance of the lesion and the flow-void sign, as well as variations in signal intensity within the lesion and among lesions. Statistical analysis was performed to determine the level of interobserver agreement. RESULTS:Radiographic findings and the level of signal intensity on MR images were nonspecific for diagnosis of osseous metastasis from renal cell carcinoma. The flow-void sign was identified at the lesion core or margin with a mean frequency of 76.7% by the three observers (in 15, 16, and 15 of 20 lesions, by observers 1, 2, and 3, respectively). Most of these areas of low signal intensity were tubular structures of less than 3 mm in diameter; in three lesions, they measured 5-8 mm in diameter. In 14 lesions, these structures corresponded to dilated blood vessels or veins identifiable on CT images (six lesions) or digital subtraction angiographic images (four lesions) or at histopathologic analysis (four lesions). The flow-void sign on MR images corresponded to vessels depicted on the CT scans available for six lesions and on the angiographic images available for four lesions. CONCLUSION:Observation of the flow-void sign in lesions depicted on musculoskeletal MR images may prove helpful for diagnosing osseous metastasis from renal cell carcinoma and for treatment planning, especially in patients with occult or forgotten primary renal tumor.

RATIONALE AND OBJECTIVES:To document a simple algorithm that quantifies power Doppler signals by computer-based statistical image analysis. METHODS:Personal computer-based software was developed. Color pixels representing power Doppler signals were separated from the background gray pixels in power Doppler images converted in BMP format. To avoid misregistration during this segmentation, a threshold value is required to adequately distinguish between gray and color pixels. Equating the intensity of each color pixel to a Power Value (PV), a histogram of Power Values in power Doppler images was obtained. RESULTS:The software was designed to allow users to adjust two thresholds (Difference Threshold and Intensity Threshold) by observing the segmentation results in real time. The software calculates the following indexes within any region of interest as defined by the operator: mean PV, peak PV, standard deviation of PV, percentage power Doppler area, and integrated PV per unit area. CONCLUSIONS:Power Doppler signals can be objectively quantified using this straightforward algorithm. This simple and practical method can be applied to comparative or longitudinal studies upon vascularity or blood flow.