A thermoacoustic imaging device is provided having a transmitter configured to provide an electromagnetic transmit signal to an object being imaged. The backpack frame includes a plurality of stays having flexible joints therebetween. A disclosed test involves electronically setting a defined charge in a selected pixel of the CMOS imager; reading the output of the selected pixel; and comparing the output of the selected pixel to an expected value based upon the defined charge set in the selected pixels. The longitudinal member extends longitudinally within the axial bore of the percussion bit from an upper end portion, mounted within the upper portion of the axial bore, to a lower end portion disposed in the lower portion of the axial bore.