Figure 1.
Canine left ventricular wedge and experimental setup with optical mapping, ultrasound imaging, and HIFU ablation.
(A) Photograph of a canine heart immersed in cardioplegia before wedge preparation. Black box indicates the tissue region used. Dash lines highlight marginal coronary arteries. (B) Photograph of the transmural surface of a wedge with HIFU transducer at the left and ultrasound imaging in the same plane from the top. In thirteen dog experiments, HIFU was applied from either endocardial (n = 8) or epicardial (n = 5) side. (C) Schematic experimental setup. The HIFU transducer was mounted on a high precision XYZ motor stage. Imaging and ablation were synchronized via a custom programmed FPGA circuit.
Figure 2.
Demonstration of image registration.
(A) Ultrasound B-mode image of a wedge preparation acquired after HIFU ablation with endocardium (ENDO) on the left and epicardium on the right (EPI). Sharp corners (red asterisk) of a “V” shape carving marker on the acoustic transparent screen show hyperechoic signals, making it a suitable fiducial marker for image registration. Green box indicates the field-of-view (FOV) of M2D mode imaging. (B) Photograph of a canine wedge preparation after HIFU ablation. Purple asterisk labeled the lesion centroid. (C) Background optical mapping image of the same wedge preparation. M2D mode image, gross image, and optical images were registered based on the FOV and fiducial marker. (D) Masson's trichrome (MT) stained microscopic slide of the same transmural plane. E – J, Registered FOV of M2D-mode image, gross photograph, lesion mask from gross photograph, background optical image, MT slide, and lesion mask from MT image.
Figure 3.
Electrophysiology and optical action potentials (OAPs) of a canine left ventricular wedge preparation.
(A) Activation map superimposed on the photograph of the transmural surface of the wedge. Black box is the region of interest. The color asterisks indicate representative locations across ventricular wall. Pacing (cycle length = 1000 ms) was applied from the epicardium. (B) APD80 map superimposed on the same gross photograph of the transmural surface. (C) Representative OAPs at subepicardium (EPI), midmyocardium (MID), and subendocardium (ENDO) indicated by the colored asterisks in (A – B).
Figure 4.
Spatiotemporal changes of transmural AP surrounding HIFU lesion.
(A) Photograph of a left ventricle wedge with a HIFU lesion. (B) Masson's trichrome (MT) stained slide corresponding to the same tissue plane in A. Black dash line encircles lesion boundary. Black asterisks labeled representative locations at inside lesion, border, and normal tissue. (C) Microscopically magnified (40X) MT images at labeled locations in B: lesion (a1), border (b1), and normal tissue (c1). Corresponding normalized OAPs (a2, b2, c2) before (blue) and after (pink) HIFU ablation. (D) Amplitude of fractional fluorescence intensity (ΔF) before and 24 s after HIFU ablation, and change of action potential amplitude (ΔAPA) with dashed line highlighting the same lesion in B. (E) APD50 before and after HIFU ablation and ΔAPD50. (F) APD80 before and after HIFU ablation, and ΔAPD80.
Figure 5.
Spatiotemporal AP triangulation, excitability, and activation pattern for HIFU ablation.
(A) Ratio of APD50 and APD80 before and after HIFU ablation, and ΔAPD50/APD80. (B) Upstroke rising rate (dΔF/dt)max before and after HIFU, and their difference. (C) Activation time before and after HIFU, and their difference. (D) Conduction velocities (CVs) before and after HIFU ablation in the white boxed ROI in the activation maps in (C). Directions of electrical wave propagation and magnitude of CVs are indicated by the directions of the red arrows and their lengths. Same lesion area as in Figure 4 is indicated by black dash lines.
Figure 6.
Acute changes of AP prior, during, and after HIFU ablation.
(A) Changes of OAPs amplitude (ΔAPA) at t = 32 s (colored) superimposed on background optical mapping image (gray scale). Black box represents the ROI (6mm×5.6 mm) within the field-of-view of M2D ultrasound imaging. Colored asterisks labeled representative locations inside lesion, border, and normal tissue. (B) Normalized OAPs at the representing locations in (A) with each “spikes” corresponding to single cardiac cycle. Cyan shaded area indicates HIFU duration. Single cycle OAPs at t = 1.8, 8.8, 17.8, and 31.8 s indicated by a, b, c, and d. (C) Normalized OAPs at the representative locations in (A) superimposed at representative times (arrows a – d in B). (D) Spatiotemporal changes of ΔAPA. Blue labeled frames were during HIFU ablation. (E) Spatiotemporal changes of ΔAPD50. (F) Normalized ΔAPA at representative locations (asterisks in D and E). (G) Normalized ΔAPD50 at the same representative locations.
Figure 7.
OAPs changes within and outside a HIFU lesion.
(A) Photograph and masson's trichrome (MT) stained slide of a wedge preparation after HIFU ablation (top panels) along with the corresponding binary lesion mask (lesion as white and non-lesion as black) (bottom left panel), ΔAPA obtained at t = 32 s. Black dash lines highlight lesion edges. (B) ΔAPA (n = 13) within lesion and outside lesion (non-lesion) determined by lesion mask. A black dash line indicates a threshold (−0.43±0.01) of ΔAPA used to predict irreversible lesions determined from receiver-operating characteristic (ROC) analysis. (C) ROC curves for ΔAPA detection of lesion for all cases (individual and overall curve are marked gray and red respectively) with an area under ROC curve (AUC) of 0.961. Inset: ΔAPA predicted lesion (red) for the representative example in (A) is overlaid on the real binary lesion mask.
Figure 8.
Lesion detection using parametric ultrasound imaging and optical mapping.
(A) Selected ΔAPA maps prior, during, and after HIFU ablation. HIFU ablation was applied from t = 4.55 to 8.55 s. (B) Selected grayscale ultrasound images (from t = 4 to 8.64 s) corresponding to the ΔAPA maps in (A). Frames during HIFU ablation are labeled with blue time indices. (C) Temporal change of the ROC area-under-curves (AUCs) for |ΔGS|max (black), |Δα|max (blue), and |Δσ|max (red), with maximum at t = 8.03±0.19 s (black dash box). (D) Temporal changes of detection accuracy, sensitivity (true positive rate), and specificity (true negative rate) using |Δσ|max. (E) M2D-mode images color-coded by lesion map determined by ΔAPA threshold (cyan). (F) M2D images color-coded by lesion region determined by cumulative extrema of log-normal parameter |Δσ|max (red). (G) Stacked temporal M2D images superimposed with lesion mask detected by |Δσ|max.
Table 1.
The area under the receiver-operating characteristic curve (ROC AUC) for detection of lesion from various ultrasound parameters on all canine wedges (n = 13).
Figure 9.
Spatiotemporal correlation of APA with parametric ultrasound imaging.
(A) Temporal changes of the ROC area-under-curves (AUCs) using |Δσ|max for detecting lesion and ΔAPA below lesion threshold (non-lesion). (B) Temporal changes of detection accuracy, sensitivity (true positive rate), and specificity (true negative rate) using cumulative extrema of log-normal parameter (|Δσ|max) for detection of lesion and peripheral ΔAPA regions. (C) M2D images color coded by true lesion region (ΔAPA<–0.43, blue) and non-lesion ΔAPA (–0.43<ΔAPA<–0.19, green) determined from ΔAPA maps. (D) Gray-scale M2D images color coded with lesion (red) and non-lesion ΔAPA (yellow) regions determined from |Δσ|max images. Blue time indices indicate frames during HIFU application. (E) Stacked temporal M2D images coded with lesion and non-lesion ΔAPA masks detected by |Δσ|max.