Theory and experiment of Fourier-Bessel field calculation and tuning of a pulsed wave annular array

A one-dimensional (1D) Fourier–Bessel series method for computing and tuning (beamforming) the linear lossless field of flat pulsed wave annular arrays is developed and supported with both numerical simulation and experimental verification. The technique represents a new method for modeling and tuning the propagated field by linking the quantized surface pressure profile to a known set of limited diffraction Bessel beams propagating into the medium. This enables derivation of an analytic expression for the field at any point in space and time in terms of the transducer surface pressure profile. Tuning of the field then also follows by formulating a least-squares design for the transducer surface pressure with respect to a given desired field in space and time. Simulated and experimental results for both field computation and tuning are presented in the context of a 10-ring annular array operating at a central frequency of 2.5 MHz in water

Study of rare earth encapsulated carbon nanomolecules for biomedical uses

Gd@C82(OH)40 has been proposed to be as a new generation of the magnetic resonance imaging (MRI) contrast agent, but water-soluble fullerenols Gd@C82(OH)n with n > 36 can easily lead to open-caged structures of a high instability. This restricts the practical bio-uses of Gd-metallofullerenols with a large number of hydroxyl groups. To explore how the imaging efficiency varies with decreasing hydroxyl number in Gd@C82(OH)n of a good stability in vivo, Gd@C82(OH)22 was prepared, characterized and its imaging efficiency in mice was studied. This work aims at searching a chemical form of water-soluble Gd-metallofullerenols that satisfy both requirements of the good stability and high imaging efficiency in vivo. The results indicate that the proton relaxivity of Gd@C82(OH)22 is lower than that of Gd@C82(OH)40, but still higher than the commercial Gd-DTPA MRI contrast agent. © 2005 Elsevier B.V. All rights reserved.link_to_subscribed_fulltex