Dynamic MR-imaging can provide functional and positional information in real-time, which can be conveniently used on-line to control a cancer therapy, e.g. using High Intensity Focused Ultrasound or Radio Therapy. However, a precise real-time correction for motion is fundamental in abdominal organs to ensure an optimal treatment dose associated with a limited toxicity in nearby organs at risk.This paper proposes a real-time direct PCA-based technique which offers a robust approach for motion estimation of abdominal organs and allows correcting motion related artifacts. The PCA was used to detect spatio-temporal coherences of the periodic organ motion in a learning step. During the interventional procedure, physiological contributions were characterized quantitatively using a small set of parameters. A coarse-to-fineresolution scheme is proposed to improve the stability of the algorithm and afford a predictable constant latency of 80 ms.The technique was evaluated on 12 free-breathing volunteers and provided an improved real-time description of motion related to both breathing and cardiac cycles. A reduced learning step of 10 s was sufficient without any need for patient-specific control parameters, rendering the method suitable for clinical use.< Leer menos