Correction of refraction and other angle errors in beam tracking speed of sound estimations using multiple tracking transducers

The beam tracking approach to the estimation of the speed of sound has shown potential for making unbiased estimates in tissues. The speed of sound in a medium can be found from the arrival times of echoes as a function of the position of a tracking transducer. There is a problem in this approach if the angle between the direction of tracked beam and the direction of tracking translation is not zero due to refraction or other effects. An angle error as small as 1 degree would result in an error that is too large for diagnostic applications. A modified technique using three or more tracking transducers is described. This yields a corrected speed of sound estimate, and calculates the angle error. A simulation program has shown that this modified technique could indeed correct for the angle errors.     

Dynamics of magnetization in hyperpolarized gas MRI of the lung

The magnetization in hyperpolarized gas (HP) MRI is generated by laser polarization that is independent of the magnet and imaging process. As a consequence, there is no equilibrium magnetization during the image acquisition. The competing processes of gas inflow and depolarization of the spins lead to large changes in signal as one samples k-space. A model is developed of dynamic changes in polarization of hyperpolarized ³He during infusion and in vivo imaging of the lung and verified experimentally in a live guinea pig. Projection encoding is used to measure the view-to-view variation with temporal resolution <4 ms. Large excitation angles effectively sample the magnetization in the early stages of inflow, highlighting larger airways, while smaller excitation angles produce images of the more distal spaces. The work provides a basis for pulse sequences designed to effectively exploit HP MRI in the lung.     

Single-acquisition chemical-shift imaging of a binary system with use of stimulated echoes

A method for separating binary chemical-shift components with a single image data acquisition by means of stimulated echoes is demonstrated. With a strategy analogous to the modified Dixon method, three stimulated echoes were acquired to form three complex images. In each of the images, the complex pixel intensities were imparted, by design of the pulse sequence, with a phase factor carrying chemical-shift or field inhomogeneity information. With these three images, true fat/water separation can be obtained in biologic tissues. Studies at high field strength (4.7 T) on a toluene phantom, a pseudo-binary chemical-shift system, were used to evaluate the applicability of the method. Its clinical feasibility was demonstrated on a healthy human subject in a 0.6-T whole-body imaging system.     

山莨菪碱和蝙蝠葛碱对白三烯和PAF诱导的牛脑前动脉平滑肌细胞DNA合成的影响(英文)

白三烯和血小板活化因子在低于nmol浓度时就能刺激培养的牛脑前动脉平滑肌细胞的DNA合成,在10~(-7)mol/L时达最大刺激。LTB_4,LTD_4和PAF在10~(-7)mol/L时对上述细胞DNA合成的刺激率分别为32％,29％和77％。山莨菪碱和蝙蝠葛碱在10~(-7)～10~(-4)mol/L范围内呈剂量依赖性地抑制白三烯和血小板活化因子的上述作用。     

Percutaneous extraction of urinary calculi: use of the intercostal approach

The authors achieved successful percutaneous extraction of urinary calculi via an intercostal approach in 24 patients. In one patient, a large hydrothorax developed and thoracentesis was required; 2 patients had moderate and 6 minimal pleural fluid collections which did not require treatment. No patient had pneumothorax. Intercostal puncture provides direct access to the upper and middle poles of the kidney when they lie above the twelfth rib and subcostal angulation is not feasible. Such an approach is advantageous for stones in the ureter, as well as renal stones which are inaccessible from the lower pole. Fluoroscopy should be performed when planning the puncture in order to avoid the lung, and a working sheath is recommended.