Response to Letter to the Editor: “Nomenclature for real‐time magnetic resonance imaging”

Abstract

Figure 1 contains a Venn diagram of current nomenclature and their criteria. The broadest term “dynamic” is used for imaging of dynamic processes (e.g., cardiac function) with adequate temporal resolution to resolve the dynamics. This often involves repetition of a movement with synchronized acquisition, known as gating. The term “real‐time” is used for dynamic imaging without the need for repetition (e.g., dynamic contrast enhanced imaging). The term “real‐time interactive” is used for real‐time imaging with low latency (e.g., interactive localization, or interventional guidance). The term “interactive” was first used in MRI papers 25 to 30 years ago, when substantial engineering was required to accomplish latencies of less than a few seconds.2-4 Many authors since then have used “real‐time” (without “interactive”) even when their methods provided a high degree of interaction. Dietz et al argue that the term real‐time should be reserved for techniques that provide very low latency and that dynamic should be used when this criterion is not met. I disagree for two reasons. First, this would be inconsistent with colloquial nontechnical use of real‐time, which includes live broadcast television that provides ~24 frames per second, latency >2 seconds (sometimes longer to allow for content blocking), and no interaction. Second, this would introduce a new problem of efficiently differentiating methods that do versus those that do not rely on gating (repetitions and synchronization). MRI methods that eliminate the need for gating involve substantial engineering and broaden the scope of MRI applications. Without this capability, it would not be possible to image cardiac function in the setting of arrhythmia, natural speech, or other aperiodic movements. This capability adds substantial value even in the absence of a low‐latency online reconstruction and is worthy of the distinct term.