Local IV Coil Tuning, Matching, and Signal Preamplification

---

In collaboration with Draper Laboratory we have initiated a project to design miniaturized coil tuning, matching, and pre-amplification circuitry directly at the iv coil to maximize the signal-to-noise ratio (SNR). The functionality includes an ultra low noise transistor amplifier stage, a PIN diode to detune the RF coil and protect the transistor during RF pulses, and a pair of varactor diodes (electrically controllable capacitors) which can be used to tune the coil remotely with DC voltages (see Figure 1). The active components (marked by the white rectangle in Figure 1) occupy a thin strip about 2 mm in width. A miniaturized version of this circuit is currently being fabricated that will fit within a 7F catheter. In addition, an automated tuning circuit is being implemented to allow the tuning and matching of the coil to be automatically adjusted (see Figure 2).

Figure 1: Prototype tuning, matching, and preamplification circuit.

Figure 2: Schematic of the automated tuning circuit. The tuning condition is determined from a measurement of the reflection coefficient of the NMR signal.