Imagery has long been considered an important part of music practice, yet its use in professional musicians' practice and teaching has not yet received a great amount of research attention. A participant observation study of a five-day masterclass for 11 expert pianists, given by the pianist and Alexander Technique teacher Nelly Ben-Or (NBO), examined deliberate multimodal musical imagery techniques in a real-world setting. The study aimed to generate an interpretive description of NBO's pedagogy, to investigate how pianists experienced and implemented her techniques, and to explore the possible mechanisms by which teaching according to these principles might work. Data collection incorporated observation, video documentation, interviews, notes, questionnaires and email correspondence. Thematic analysis was used across the corpus. NBO's pedagogy focuses on creating a clear image of the piece to be performed via multimodal imagery techniques and chunking strategies, which can be used during memorisation as well as to improve problematic aspects of performance. Imagery rehearsal may thus provide a means of managing complex tasks in discrete stages and lead to an enhanced sense of integration between intention and action, by diverting attention from the process of playing to the goal outcome, internalised as a multimodal representation. Deliberate imagery strategies were associated with positive outcomes but were also often experienced as challenging. The findings imply that these strategies can be taught and improved over time, their efficacy modulated by skill level and motivation. Overall, participants reported that imagery rehearsal led to improvements in technical facility, musical quality and memory security. Issues for further investigation and application in other domains are discussed.