Biopsies by definition involve contact with tissues and bodily fluids. To protect both technician and electronics, the EnCor was designed as a contaminant-resistant, closed system. The tissue remains in the probe and fluids are removed via vacuum. The driver is splash-resistant and can be cleaned with germicidal wipes. The only elements exposed are the interface gears, which are protected with a plastic dam.

Meeting challenges

Once the tissue is harvested, vacuum pulls it to a removable tissue chamber (left).

EnCor systems are designed to last a minimum of three years. Because of the high duty cycles involved—five or more biopsies per day in some facilities—the SenoRx team put the drivers through stringent lifecycle testing to simulate three years of normal use. “We conduct load and burn-in tests on every motor to ensure that they perform to our stringent specifications,” Shabaz notes. The team also put the units through shock and vibration testing; here a problem cropped up. The units are handheld, and thus subject to being dropped. In shock tests to simulate operating conditions, Shabaz discovered that the interface between the motor and the encoders was being compromised. In some cases, the encoders were merely dislodged so that they generated an error code; in others, they broke off.

To solve the issue, MicroMo’s dedicated machine shop strengthened the encoder-motor interface by lengthening the overlap between the two cases and reinforcing the joint with epoxy. Meanwhile, Shabaz increased the length of the frame holding the motors so that it would encompass the encoders, as well.

To meet safety regulations on startup, the driver goes through a self-test routine for both motors and encoders. Once the probe is attached to the driver, the system goes through a sequence to calibrate the probe. The process doesn’t end when the biopsy starts. Every movement is restricted to a specific window; if the unit attempts motion outside those windows, the microcontroller will generate an appropriate error message and shut down.

Shabaz is looking forward to the next-generation EnCor device, which he says will integrate a MicroMo encoder.