Cardiorespiratory motion‐tracking via self‐refocused rosette navigators

Abstract

Purpose: To develop a flexible method for tracking respiratory and cardiac motions throughout MR and PET-MR body examinations that requires no additional hardware and minimal sequence modification. Methods: The incorporation of a contrast-neutral rosette navigator module following the RF excitation allows for robust cardiorespiratory motion tracking with minimal impact on the host sequence. Spatial encoding gradients are applied to the FID signal and the desired motion signals are extracted with a blind source separation technique. This approach is validated with an anthropomorphic, PET-MR-compatible motion phantom as well as in 13 human subjects. Results: Both respiratory and cardiac motions were reliably extracted from the proposed rosette navigator in phantom and patient studies. In the phantom study, the MR-derived motion signals were additionally validated against the ground truth measurement of diaphragm displacement and left ventricle model triggering pulse. Conclusion: The proposed method yields accurate respiratory and cardiac motion-state tracking, requiring only a short (1.76 ms) additional navigator module, which is self-refocusing and imposes minimal constraints on sequence design.

Estimation of Physiological Motion Using Highly Accelerated Continuous 2D MRI

“…At the moment, the sequence is implemented as a separate scan in the imaging workflow. However, due to the low acquisition time of around 30 ms per image, it is easily conceivable that it can be implemented as a 2D navigator-sequence interlaced between the excitations of the clinical sequences, similar to the approach in [31]. However, one limiting factor could be that clinical sequences have to be modified to incorporate this navigator acquisition.…”

Free‐breathing radial imaging using a pilot‐tone radiofrequency transmitter for detection of respiratory motion

“…Another type of navigator involves dedicated gradient events introduced within the MR pulse sequence. For example, a “butterfly” navigator 16 provides motion‐tracking information during data acquisition that is well suited to Cartesian sampling, whereas “rosette” navigators 17 sample the motion information prior to acquisition of imaging data and can be incorporated into almost any sampling scheme. Even though these navigators do not significantly impact the scan efficiency, they still require specific pulse sequence modifications.…”

Scattering matrix imaging pulse design for real‐time respiration and cardiac motion monitoring

“…Alternative methods estimate cardiac and respiratory motion from surrogate signals that are derived from the continuous acquisition of the k‐space centre, from a region‐of‐interest in the image domain, or from navigator echoes that are added to the imaging sequence. Some of these methods have sequence design constraints; others are limited to a specific k‐space sampling trajectory.…”

“…Other external devices that are independent to the electrical activity of the heart are based on finger plethysmography, Doppler ultrasound, 7 or on heart tones (phonocardiograms). 8 Alternative methods estimate cardiac and respiratory motion from surrogate signals that are derived from the continuous acquisition of the k-space centre, [9][10][11][12][13][14][15][16][17] from a region-of-interest in the image domain, 18,19 or from navigator echoes [20][21][22][23] that are added to the imaging sequence. Some of these methods have sequence design constraints; others are limited to a specific k-space sampling trajectory.…”