MR‐guided intravascular procedures: Real‐time parameter control and automated slice positioning with active tracking coils

Abstract

Purpose: To implement and optimize a real-time pulse sequence and user interface to perform intravascular interventions using active catheter tracking. Materials and Methods:In magnetic resonance (MR)-guided interventions, small radio-frequency coils can be used to rapidly determine the device position (active tracking). In this work, active catheter tracking was combined with a dedicated real-time pulse sequence and user interface. The pulse sequence offered the imaging contrasts fast low angle shot (FLASH), true Fast imaging with steady state precession (TrueFISP), and projection MR digital subtraction angiography (MR-DSA), which could be selected by the radiologist from within the scanner room at any time during the intervention. Automatic slice positioning was added to the real-time pulse sequence so that the location of the tracking coils defined the image slice position and orientation. The technique was assessed in phantoms and animal experiments.Results: At a reaction time of 24 msec and a frame rate of three images per second, the movement of an active intravascular catheter could be monitored in the aorta and the renal arteries of a pig. With interactive contrast and orientation changes, the renal vasculature could be assessed by a fully MR-guided catheterization in less than 10 minutes. Conclusion:With carefully designed active catheters, a dedicated user interface, and an optimized pulse sequence intravascular interventions can successfully be performed by a single operator from within the MR scanner room.

Automatic slice positioning (ASP) for passive real‐time tracking of interventional devices using projection‐reconstruction imaging with echo‐dephasing (PRIDE)

“…In order to reduce such false positives, intelligent postprocessing may be introduced such as that provided in Ref. 24 or by restricting peak detection within the close vicinity of the vessel anatomy (for example; from previously acquired angiograms). Recently, a similar tracking approach has been presented (25) that is based solely on an off-resonance tissue excitation and may lead to confounding results in the presence of fat tissues.…”

“…The systematic deviations due to gradient nonlinearity are known to be approximately Ϯ5 mm at a distance of around 100 mm from the isocenter for the used gradient system. Thus, the error variation was related to the nonlinearity of the gradient system (24). As a result, with PRIDE, an absolute constant positional error of (4 -4.5) mm was observed.…”

Dynamic coil selection for real‐time imaging in interventional MRI

“…The DCS algorithm was integrated into a real-time interactive pulse sequence for active catheter tracking (16,17). The pulse sequence allows for interactive contrast changes (e.g., as in FLASH and trueFISP), automatic slice alignment with the catheter coil, and real-time parallel image acquisition.…”

MR‐guided intravascular interventions: Techniques and applications

“…The operator does not need to manually realign the image position (or with multiple coils, the image orientation), but controls the imaging process and even selected imaging parameters through the catheter motion (9,10). If the position measurement is combined with a fast imaging pulse sequence (eg, balanced SSFP, TrueFISP) (45-47), the position of the catheter is detected between the acqui- sition of two real-time images, and the information can be used to reposition the imaging slice.…”