A rapid 2D time‐resolved variable‐rate k‐space sampling MR technique for passive catheter tracking during endovascular procedures

Abstract

A new, fast, 2D MR imaging technique allowing passive catheter visualization adequate for use as a tool for guiding the movement of a catheter during endovascular procedures is described. This imaging technique samples low spatial frequencies more often than high spatial frequencies; it also uses both k-space view sharing and temporal interpolation. Unlike other techniques for passive visualization that exploit magnetic-susceptibility-induced artifacts, we have adopted a strategy that takes advantage of the T1-shortening effect of paramagnetic contrast agents, such as Gd-DTPA and a projection dephaser. This not only permits visualization of the entire catheter length but also minimizes the risk of intravascular heating. Using this method, a temporal frame rate of up to eight images per second and a tip localization accuracy of +/- 1mm (root mean square difference) can be achieved.

Dynamic coronary MR angiography and first‐pass perfusion with intracoronary administration of contrast agent

“…Furthermore, the SNR and CNR of the coronary arteries in consecutive angiography sessions were essentially unchanged. These capabilities can be instrumental in guiding, for example, a contrast agentfilled catheter (9,11) in order to perform an intervention in the tortuous and moving coronary arteries. Similarly, we demonstrate that first pass studies could be performed with low concentration Gd-based MR contrast injection directly in the coronary artery, allowing identification of the perfusion bed and extraction of SI time curves suitable for quantitative analysis of rMBF.…”

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

“…In this projection MR-DSA mode, which could also be switched on interactively, at otherwise unchanged imaging parameters, a non-selective rf pulse was used for excitation. Through the use of a high flip angle (80°-90°) in combination with an adjustable spoiler gradient in projection direction, the so-called z-dephaser (19), signal from static tissue can be effectively suppressed, whereas the passage of a contrast agent bolus through a vascular segment is visualized similar to X-ray DSA. The z-dephaser in our experiments was adjusted to produce a dephasing of 2 over a geometrical length of 6 cm (gradient duration: 0.2 msec, gradient strength: 2 mT/m).…”

Passive catheter tracking using MRI: Comparison of conventional and magnetization‐prepared FLASH

“…When a T1-weighted sequence is used, these artifacts appear as signal voids and their position can be monitored during a procedure. More recently, Unal et al (7) and Omary et al (8) introduced an alternative passive tracking method where the catheter was filled with diluted MR contrast agent. Diluted contrast agent within the catheter had a short T1, producing greater signal compared to surrounding tissue with a T1-weighted sequence.…”

“…Within a projection image, it is important to reduce background signal to depict catheters because the catheter occupies only a small fraction of the imaging slice. A conventional gradient-echo (GRE) sequence previously was used with a high flip angle (10) or a gradient dephaser (7) to suppress the signal intensity of background tissues. However, a high flip angle GRE sequence does not reliably suppress background when the slice thickness is too large, because in a practical setting the flip angle of the RF pulses applied to spins in the imaging slice tends to drop off toward the edges of the imaging slice.…”