Abbreviated MRI and Ultrafast MRI of the Breast

Detection of breast cancer in MRI requires fast, dynamic contrast enhanced (DCE) imaging covering the immediate post-contrast phase, that is, the first 60 s after contrast injection. This ensures selective depiction of invasive cancer as well as DCIS against an otherwise dark background, that is, before background parenchymal enhancement (BPE) can set in. Thus, breast MRI requires not only high spatial, but also high temporal resolution. Both, abbreviated breast MRI (AB-MRI) as well as ultrafast breast MRI (UF-MRI), exploit the fact that enhancement of cancers versus their non-cancerous background differs most in the immediate post-contrast phase. Beyond this, however, AB-MRI and UF-MRI are unrelated: AB-MRI is a novel MRI paradigm; UF-MRI is a novel MRI pulse sequence that allows time-resolved imaging of the immediate post-contrast phase. AB-MRI is an umbrella term for lean, streamlined MRI protocols designed to answer specific clinical questions. Compared with "all-purpose" full-protocol MRI, AB-MRI allows a substantial reduction of acquisition time. The first proposed use case of AB-MRI was for breast cancer screening, to reduce cost, and thus improve access and tolerability. It had been termed "FAST," short for "first post-contrast subtracted imaging," because it truncated the breast MRI acquisition protocol after one post-contrast scan covering the immediate post-contrast phase. Around the same time, UF-MRI was inaugurated. This may have caused the misunderstanding that both would represent different positions on the same line of development, with "ultrafast" being even faster than "FAST." AB-MRI protocols can be categorized into short and abridged protocols. Short protocols concentrate on the pre- and immediate post-contrast phase, either by regular DCE-MRI, or by UF-MRI. Abridged protocols add carefully selected scans, for example, T2-weighted and/or post-contrast scans. This review aims at clarifying the definitions and respective concepts of AB-MRI and UF-MRI, and to summarize the current evidence regarding the respective utility for breast cancer diagnosis.