Apparent transverse relaxation rates in systems with coupled carbon-13 spins.

In systems with homonuclear scalar couplings, the envelopes of spin echoes obtained with simple refocusing pulses or trains of such pulses are normally modulated so that it is difficult to extract transverse relaxation rates. It has been shown recently that echo modulations can be quenched by cumulative pulse errors that arise after applying a large number of refocusing pulses with moderate rf amplitudes. The resulting unmodulated decays allow one to extract apparent transverse relaxation rates. Early work on systems comprising only two nitrogen-15 nuclei or two carbon-13 spins has recently been extended to systems with coupled protons. This work focuses on systems with three coupled carbon-13 spins, which in turn are coupled to several neighbouring protons. Unmodulated echo trains can be obtained by optimizing the pulse interval, the carrier frequency and the rf amplitude of the refocusing pulses.

Area under the real-time contact force curve (force-time integral) predicts radiofrequency lesion size in an in vitro contractile model.

INTRODUCTION: Electrode tissue contact, radiofrequency (RF) power and duration are major determinants of RF lesion size. Since contact forces (CF) vary in the beating heart, we evaluated contact force-time integral (FTI) as a predictor of lesion size at constant RF power in a contractile bench model simulating the beating heart. METHODS AND RESULTS: An open-tip irrigated catheter was attached to a movable mount incorporating a dynamic force sensor allowing closed loop control to achieve desired force variations between the catheter tip and bovine skeletal muscle placed on a ground plate. RF energy (20 and 40 W for 60 seconds, 17 cc/min irrigation) was delivered during (1) constant contact (C) at 20 g, (2) variable contact (V) with a 20 g peak and 10 g nadir, and (3) intermittent contact (I) with a 20 g peak and 0 g nadir with loss of contact. V and I protocols were performed at 50 and 100 catheter movements/min and 2 systole:diastole time ratios (50:50 and 30:70). The area under the CF curve was calculated as the FTI. Measured FTI was highest in C, intermediate during V and lowest during I and correlated linearly with lesion volume (P < 0.0001 for 20 and 40 W). Lesion volume was highest in group C, intermediate in V and lowest in group I (P < 0.05 for C vs V, V vs I, and C vs I). CONCLUSIONS: Lesion size correlates linearly with measured contact FTI. Constant contact produces the largest and intermittent contact the smallest lesions despite constant RF power and identical peak contact forces.

Novel contact force sensor incorporated in irrigated radiofrequency ablation catheter predicts lesion size and incidence of steam pop and thrombus.

BACKGROUND: An open-irrigated radiofrequency (RF) ablation catheter was developed to measure contact force (CF). Three optical fibers measure microdeformation of the catheter tip. The purpose of this study was to (1) validate the accuracy of CF sensor (CFS) (bench test); and (2) determine the relationship between CF and tissue temperatures, lesion size, steam pop, and thrombus during RF ablation using a canine thigh muscle preparation. METHODS AND RESULTS: CFS measurements (total 1409) from 2 catheters in 3 angles (perpendicular, parallel, and 45 degrees ) were compared with a certified balance (range, 0 to 50 g). CFS measurements correlated highly (R(2) > or =0.988; mean error, < or =1.0 g). In 10 anesthetized dogs, a skin cradle over the thigh muscle was superfused with heparinized blood at 37 degrees C. A 7F catheter with 3.5-mm saline-irrigated electrode and CFS (Endosense) was held perpendicular to the muscle at CF of 2, 10, 20, 30, and 40 g. RF was delivered (n=100) for 60 seconds at 30 or 50 W (irrigation 17 or 30 mL/min). Tissue temperature (3 and 7 mm depths), lesion size, thrombus, and steam pop increased significantly with increasing CF at each RF power. Lesion size was greater with applications of lower power (30 W) and greater CF (30 to 40 g) than at high power (50 W) with lower CF (2 to 10 g). CONCLUSIONS: This novel ablation catheter, which accurately measures CF, confirmed CF is a major determinant of RF lesion size. Steam pop and thrombus incidence also increases with CF. CFS in an open-irrigated ablation catheter that may optimize the selection of RF power and application time to maximize lesion formation and reduce the risk of steam pop and thrombus.

Quenching and recoupling of echo modulations in NMR spectroscopy.

Trains of spin echoes are normally modulated by homonuclear scalar couplings. It has long been known that echo modulations are quenched when the pulse-repetition rates are much larger than the offsets of the coupling partners, because the spin systems behave as if they consisted of magnetically equivalent spins when the offsets are suppressed. This type of quenching of the echo modulations can occur when the radio-frequency (RF) pulses are ideal, that is, when they are perfectly homogeneous, properly calibrated to induce rotations through an angle, pi, and have an RF amplitude, omega(1)=-gammaB(1), that is strong compared to the largest offset, Omega(S)=omega(0S)-omega(RF), with respect to the carrier frequency. Recently, it was discovered that echo modulations can also be quenched when the RF pulses are nonideal, that is, when they are too weak to bring about an ideal rotation of the magnetization of the coupling partners, so that the effective fields associated with the RF pulses are tilted in the rotating frame. This phenomenon typically occurs when the pulse-repetition rates are much slower than the offset of the coupling partner. Under such conditions, it turns out, however, that for certain offsets, when the phase, Phi(S) (which arises from a free precession of the magnetization of the coupling partner, S, in the pulse interval, 2tau, and the pulse length, tau(pi)), approaches a multiple of 2pi, the echo modulations are restored. However, the frequencies of these echo modulations are not simply determined by the homonuclear scalar coupling, J(IS). The Fourier transforms of the echo trains (the so-called "J spectra") reveal surprising multiplet patterns, and the amplitudes of the echo modulations depend on the offsets of the coupling partners. Herein, we present a unified theory, based on an average-Hamiltonian approach, to describe these effects for two-spin systems. Experimental evidence of echo modulations in a system of two spins is presented. Experiments with three and more spins, backed up by extensive numerical simulations, will be presented elsewhere.

Feasibility and safety of intra-coronary Beta irradiation with 144Ce/Pr for prevention of restenosis after percutaneous transluminal coronary angioplasty of in-stent restenotic lesions.

BACKGROUND: Endovascular brachytherapy is a proven and efficacious treatment of coronary in-stent restenosis with established long-term benefit. Owing to its complexity and logistic inconveniences, brachytherapy did not find wide acceptance, especially in the current drug-eluting stents era. We conducted a single center, non-randomized pilot trial with 144Ce/Pr, utilizing a new high-energy Beta emitting source, for prevention of restenosis after percutaneous treatment of in-stent restenotic lesions. METHODS AND RESULTS: Thirty consecutive patients presenting in-stent restenosis were enrolled in the study. After conventional balloon angioplasty, 144Ce/Pr was applied to the dilated coronary segment at a dose of 21Gy. Technical feasibility, safety and efficacy of 144Ce/Pr at 9 months clinical and angiographic follow-up were tested. Thirty-seven arterial segments were irradiated with 100% technical success and no in-hospital major adverse cardiac events (MACE). Five MACE were observed (13.5% of the treated segments) during 9 months follow-up, including four target lesion revascularizations and one episode of acute coronary syndrome secondary to sudden late thrombotic occlusion of the irradiated segment. CONCLUSIONS: The study confirmed the safety and the feasibility of the intra-coronary Beta irradiation utilizing the 144Ce/Pr source. It also shows some practical advantages compared to traditional Gamma or other Beta sources. Considering the high-risk restenosis profile of the selected patients (i.e. diffuse in-stent restenosis, bifurcation lesions, small vessels) these results are encouraging in terms of restenosis prevention. Late acute thrombosis remains a problem requiring further improvement.