Imaging may be helpful, but I think the answer will lie in molecular or immune signatures that predict response. For instance, in HER2+ breast cancer patients who receive trastuzumab and chemotherapy, activating mutations in PI3K are associated with decreased pathologic responses. These patients may benefit for additional targeted therapies. Myc is another example. We have strong evidence that anti-HER2 CD4+ Th1 immune responses correlate strongly with pathologic responses in these patients also.

Pathological complete response ( PCR)in breast cancer after neoadjuvant treatment is still a big challenge. As we know, there are subtypes of breast cancer that have higher number of PCR, but in the same breast cancer subtypes people do not have the same response. Either in neoadjuvant chemotherapy , hormonal or targeted therapies we do not find the same treatment response. The same happens when multiple blockage, eg, Trastuzumabe and Pertuzumabe are used with or without Docetaxel (Neosphere Protocol). MRI for evaluating patients with clinical complete response is useful if you do not have a good approach in clinical evaluation. In one scenario it’s helpful: when the response is partial and have fragmented islands of residual tumor, but not in routine. It’s mandatory to mark the area of primary tumor prior to the neoadjuvant treatment in order to identifying the site to be excised.

Tumori. 2011 Nov- Dec;97(6):704-10. doi: 10.1700/1018.11085.

Plain answer: not yet. There is no validated tool to predict pCR (pT0 and pN0) after neoadjuvant chemotherapy for breast cancer. Neither MRI, FDG PET-CT, Contrast-enhanced ultrasound, or any omics profile. Its the holy grail in medical oncology. 

Pathological complete response is quite difficult to define, especially clinically. However, try this paper in the attached link, might help you. 

http://www.fda.gov/downloads/drugs/guidancecomplianceregulatoryinformation/guidances/ucm305501.pdf

It is very difficult but in general  some evaluation results were considered like,  major clinical,radiographic, and operative findings including a description or diagram of the original size and location of the tumor, the presence or absence of multifocality, the extent of preoperative lymph node involvement, the number of clips in the breast or nodes, hormone and HER2 receptor status, presence of calcifications if any