We have completed the design and testing of a thermoacoustic computed tomography scanner for whole-breast imaging. We report on the technical changes in this design form our previous TCT scanner, and how these design changes have improved image quality. Improvements to the design include: greater angular coverage of TCT measurements, increased sensitivity of the ultrasound detector array, and improved delivery of radio wave energy. These improvements resulted in higher fidelity 3D reconstructions, reduced scan time, and fewer image artifacts. These improvements were documented by imaging simple, 3D phantoms, formulated from salinated agar spheres. We confirmed improvements in breast image quality by comparing images of patient volunteers taken with our previous TCT scanner and this new TCT scanner.