Tracking the position and rotational orientation of a catheter using a transmit array system.

A new method for detecting the rotational orientation and tracking the position of an inductively coupled radio frequency (ICRF) coil using a transmit array system is proposed. The method employs a conventional body birdcage coil, but the quadrature hybrid is eliminated so that the two excitation channels can be used separately. The transmit array system provides RF excitations such that the body birdcage coil creates linearly polarized and changing RF pulses instead of a conventional rotational forward-polarized excitation. The receive coils and their operations are not modified. Inductively coupled RF coils are constructed on catheters for detecting rotational orientation and for tracking purposes. Signals from the anatomy and from tissue close to the ICRF coil are different due to the new RF excitation scheme: the ICRF coil can be separated from the anatomy in real time, and after doing so, a color-coded image is reconstructed. More importantly, this novel method enables a real-time calculation of the absolute rotational orientation of an ICRF coil constructed on a catheter. Modified FLASH and TrueFISP sequences are used for the experiments. The acquired images from this technique show the feasibility of different applications, such as catheter tracking. Furthermore, applications where knowledge of the rotational orientation of the catheter is important, such as magnetic resonance-guided endoluminal-focused ultrasound, RF ablation, side-looking optical imaging, and catheters with side ports for needles, become feasible with this method.

Biosensing by densely packed and optically coupled plasmonic particle arrays.

Densely packed plasmonic particle arrays are investigated for biosensing applications. Such particle arrays exhibit interparticle optical coupling creating a strong field between the particles, which is useful for sensing purposes. The sensor properties, such as bulk sensitivity, layer sensitivity, and the depth of sensitivity are investigated with the aid of a multiple multipole program. Sensitivity to the analyte with low concentration is also examined by a dynamic adsorption processes. The detectable concentration limit of streptavidin within 3000 s in the detection system is expected from the signal-to-noise to be less than 150 pM.