45–47 Similar stability of Paclitaxel imaging characteristics were reported from 30 minutes to 12 hours following ablation, though the lesion check details contrast by T1-weighted imaging appears to be less than for T2-weighted imaging.46
Gadolinium delayed enhancement CMR (DECMR) can provide better visualization of RF ablation lesions compared with non-contrast imaging techniques (Figure 6). The time to achieve full enhancement of RF ablation lesions, 1 to 2 hours, is considerably longer than Inhibitors,research,lifescience,medical for DECMR of myocardial infarct scar.48 However, good correlation with pathologic lesion size was noted for intermediate enhancement patterns from 1 minute to 2 hours after contrast injection, allowing lesion extent to be assessed without waiting for full enhancement.48 The 1 to 2 hour interval Inhibitors,research,lifescience,medical required for renal clearance between repeated dosing of gadolinium and the ceiling on total allowable gadolinium dose limit the use of this technique for serial lesion assessment during a procedure.45 Still, gadolinium-enhanced imaging may be useful for evaluating gaps in ablation
lines after completion of a procedure to assess the need to place additional lesions. Figure 6 Example of gadolinium-enhanced T1-weighted MR imaging of right ventricular epicardial RF ablation lesions with pathologic correlation. Inhibitors,research,lifescience,medical Different lesion enhancement patterns are seen from 1 minute to 2 hours after contrast injection. Figure included with … Other methods for monitoring ablation lesion formation during RF energy application are also being investigated. Proton resonance shift thermography is an MRI technique that takes advantage of the decrease in the proton resonance frequency with increasing temperature.49 This technique Inhibitors,research,lifescience,medical has been used to follow tumor ablation in the uterus, liver, prostate, and brain using diverse energy sources including RF, high-frequency ultrasound, laser, and microwave.50–55 Its use for following RF ablation in the beating heart is being investigated. Current-vector mapping
Inhibitors,research,lifescience,medical has also been described for monitoring the extent of tissue power deposition during RF ablation.56 While most cardiac ablation lesion MRI studies have been performed in roughly 10 mm thick ventricle, imaging the less than 3 mm thick human atria is of particular clinical interest given the difficulty of achieving long-term pulmonary GSK-3 vein isolation following atrial fibrillation ablation. Peters et al. demonstrated 3-D DECMR of left atrial ablation lesions 10 to 15 minutes after contrast injection using image-based respiratory gating.24 This gating technique, also known as respiratory navigator imaging, allowed higher-resolution 3-D imaging to be performed without the need for prolonged breath-holding by tracking diaphragm position on fast 1-D images and collecting 3-D image data within a narrow range of diaphragm positions. Current applications have used a roughly 100 ms mid-diastolic acquisition window timed to precede atrial systole to reduce atrial motion during imaging. Image resolutions of 1.25 × 1.25 × 2.