Strategic decisions have to be made when long-lasting architectures for software-intensive systems are developed. It is a good idea to consider various changes in the business environment before the final system architecture is proposed. Since the future cannot be predicted accurately, strategic scenarios are a useful way of guiding the strategic decision-making process. Strategic scenarios can be defined as stories that describe plausible futures; they are particularly useful for guiding one's perception of the future. This paper presents our approach to the use of strategic scenarios for directing the strategic and tactical decision-making process when developing long-lasting system architectures. This approach was applied in a case study carried out in the medical imaging domain.