Four-dimensional ultrasound imaging of complex biological systems such as the brain is technically challenging because of the spatiotemporal sampling requirements. We present computational ultrasound imaging (cUSi), an imaging method that uses complex ultrasound fields that can be generated with simple hardware and a physical wave prediction model to alleviate the sampling constraints. cUSi allows for high-resolution four-dimensional imaging of brain hemodynamics in awake and anesthetized mice.

In this study, we demonstrate a 12x36 mm motorized capsule for OCT imaging of the esophagus. The capsule produces unobstructed images by using a distal reflector design, thus avoiding shadow caused by the motor wires. The motor synchronous control enables three working modes: circumferential imaging, angular sector imaging and accurate beam positioning. Distortion artifacts shown in the sector imaging were found to be induced by velocity changes of the motor. We specifically characterized the motor speed and found a symmetric and repeatable behavior during sector scanning. Resampling of the sector images A-lines was carried out to achieve uniform angular spacing according to the measured speed profile. Also, distortion between consecutive sector frames was corrected using image registration to achieve stable imaging.

In interventional electrophysiology, catheter-based radiofrequency (RF) ablation procedures restore cardiac heart rhythm by interrupting aberrant conduction paths. Real-time feedback on lesion formation and post-treatment lesion assessment could overcome procedural challenges related to ablation of underlying structures and lesion gaps. This study aims to evaluate real-time visualization of lesion progression and continuity during intra-atrial ablation with photoacoustic (PA) imaging, using clinically deployable technology. A PA-enabled RF ablation catheter was used to ablate and illuminate porcine left atrium, both excised and intact in a passive beating heart ex-vivo, for photoacoustic signal generation. PA signals were received with an intracardiac echography catheter. Using the ratio of PA images acquired with excitation wavelengths of 790 nm and 930 nm, ablation lesions were successfully imaged through circulating saline and/or blood, and lesion gaps were identified in real-time. PA-based assessment of RF-ablation lesions was successful in a realistic preclinical model of atrial intervention.

Prospective identification of lipid-rich vulnerable plaque has remained an elusive goal. Intravascular photoacoustics, a hybrid optical and ultrasonic technology, was developed as a tool for lipid-rich plaque imaging. Here, we present the first in vivo images of lipid-rich coronary atherosclerosis acquired with this new technology in a large animal model, and relate them to independent catheter-based imaging and histology.

We demonstrate a tethered motorized capsule for unobstructed optical coherence tomography (OCT) imaging of the esophagus. By using a distal reflector design, we avoided the common shadow artifact induced by the motor wires. A synchronous driving technique features three types of beam-scanning modes of the capsule, i.e., circumferential beam scanning, localized beam scanning, and accurate beam positioning. We characterized these three modes and carried out ex vivo imaging experiments using the capsule. The results show that the capsule can potentially be a useful tool for diagnostic OCT imaging and OCT-guided biopsy and therapy of the esophagus.

Atrial fibrillation is a cardiac arrhythmia stemming from abnormal electrical conduction/impulse formation in the atria. To restore cardiac rhythm an RF ablation (RFA) procedure, interrupting aberrant electrical patterns, is commonly performed. One way of improving the procedure (current success rate 60%) is to enable visual feedback on lesion progression, thereby reducing complications linked to over-ablation and mitigating recurrent conductivity due to under-ablation. To visualize the ablation process, we propose photoacoustic (PA) imaging using an ablation catheter for light delivery and an ICE (Intracardiac Echo) catheter for signal reception In this work, we demonstrate two PA-enabled ablation catheters which provide sufficient optical intensity to image fresh and ablated porcine tissue ex vivo.

Intravascular photoacoustic/ultrasound imaging (IVPA/US) can image the structure and composition of atherosclerotic lesions identifying lipid-rich plaques ex vivo and in vivo. In the literature, multiple IVPA/US catheter designs were presented and validated both in ex-vivo models and preclinical in-vivo situations. Since the catheter is a critical component of the imaging system, we discuss here a catheter design oriented to imaging plaque in a realistic and translatable setting. We present a catheter optimized for light delivery, manageable flush parameters and robustness with reduced mechanical damage risks at the laser/catheter joint interface. We also show capability of imaging within sheath and in water medium.

We present a form of acoustic microscopy, called Structured Ultrasound Microscopy (SUM). It creates a volumetric image by recording reflected echoes of ultrasound waves with a structured phase front using a moving single-element transducer and computational reconstruction. A priori knowledge of the acoustic field produced by the single element allows us to relate the received echoes to a 3D scatter map within the acoustic beam itself, leading to an isotropic resolution at all depths. An aberration mask in front of the acoustic element imposes the phase structure, broadening the beam and breaking the spatial coherence between different voxels at equal acoustic propagation delay, increasing the uniqueness of the reconstruction. By translating the transducer across the 3D volume, we synthetically enlarge the imaging aperture by using multiple overlapping and spatially sparsely sampled measurements to solve for the entire image. In this paper, we explain the SUM technique and demonstrate microscopic imaging at 20 MHz of a 2.3 × 2.3 × 1.2 mm object in water, with an isotropic resolution below 100 μm. The proposed approach allows for wide-field 3D imaging at isotropic microscopic resolution using a small unfocused ultrasound sensor and multiple spatially sparsely sampled measurements. This technique may find applications in many other fields where space is constrained, device simplicity is desired, and wide-field isotropic high-resolution imaging is required.

Lipid deposition can be assessed with combined intravascular photoacoustic/ultrasound (IVPA/US) imaging. To date, the clinical translation of IVPA/US imaging has been stalled by a low imaging speed and catheter complexity. In this paper, we demonstrate imaging of lipid targets in swine coronary arteries in vivo, at a clinically useful frame rate of 20 s⁻¹. We confirmed image contrast for atherosclerotic plaque in human samples ex vivo. The system is on a mobile platform and provides real-time data visualization during acquisition. We achieved an IVPA signal-to-noise ratio of 20 dB. These data show that clinical translation of IVPA is possible in principle.

Photoacoustic imaging couples the chemical specificity of optical absorption with the viewing depth of ultrasound. Systems based on linear array transducers have the versatility to be applied in various (pre-) clinical scenarios but face a trade-off between viewing depth and image resolution depending on transducer frequency and aperture. We propose here a method to disentangle, with precision, small, closely spaced targets with optical spectral contrast, without impairing the imaging depth. Photoacoustic data sets were recorded at two different optical wavelengths. We accurately recovered object separation distances (mean error = 2.3% ô 6%) from the phase difference between signals across the array, down to a spacing of 1/20th of the system's beam-formed lateral resolution. The proposed method may enable the translation of super-resolution microscopy to deep tissue imaging.