The present invention relates to a new intravascular imaging device based on a Shape Memory Alloy actuator mechanism embedded inside an elongate member such as a guide wire or catheter. Vacuum fluctuations may be detected based on a detected beam current andor may be compensated for without measuring pressure in an implantation chamber. When a desired output force is in the crossover region, the two drive signals are alternated to cause the output force to quickly switch directions. A pump spacer structure 10 surrounds at least a portion of the fuel pump and positions the fuel pump within the pocket The pump spacer structure 10 has a portion 18 that engages the internal wall 20 of the filter 19. The frequency doubler circuit, using the reference current, operates to compensate for process variation of capacitance of the frequency doubler circuit and uses the reference current to maintain a known duty cycle.