Maximum Imaging Depth Research Articles

Phantoms for evaluating the impact of skin pigmentation on photoacoustic imaging and oximetry performance.

Recent reports have raised concerns of potential racial disparities in performance of optical oximetry technologies. To investigate how variable epidermal melanin content affects performance of photoacoustic imaging (PAI) devices, we developed plastisol phantoms combining swappable skin-mimicking layers with a breast phantom containing either India ink or blood adjusted to 50-100% SO2 using sodium dithionite. Increasing skin pigmentation decreased maximum imaging depth by up to 25%, enhanced image clutter, and increased root-mean-square error in SO2 from 8.0 to 17.6% due to signal attenuation and spectral coloring effects. This phantom tool can aid in evaluating PAI device robustness to ensure high performance in all patients.

Graphene quantum dot composite with multiphoton excitation as near infrared-II probe in bioimaging

Non-radiative traps and structures are present on the graphene quantum dots doped with nitrogen and functionalized with amino groups (amino-N-GQDs) and multiple crystalline layers because of cross-link-enhanced emission. Secondary and tertiary amines, which are potential fluorophores, have also been observed on the polyethylenimine (PEI) coating of amino-N-GQDs. Cross-linked PEI coating reduced rotation and vibration, thereby enhancing the photoluminescence quantum yield (PL QY). Introduced nitrogen atoms from N dopants, amino-functionalized groups and PEI, as well as sulfur from polystyrene sulfonate (PSS) enhanced the cooperative effect on the properties of heteroatom-doped materials among electrons captured by new surface states. This enhanced radiative recombination and subsequently enhanced PL QY, therefore, surface conjugation improved the amino-N-GQD surfaces by increasing the quantum confinement of their emissive energy, evidenced by the increased PL QY of amino-N-GQD-PSS-PEI (or amino-N-GQD-polymer composites). In some situations, the maximum available power required for delivery to the two-photon imaging plane without damaging tissues limits imaging depth but the additional brightness provided by amino-N-GQD-polymer composites in this study extended the maximum imaging depth to 240 μm. Amino-N-GQD-polymer composites had favorable two-photon properties under two-photon excitation (self-developed femtosecond Ti–sapphire laser optical system; power: 23.93 nJ pixel−1, 160 scans, approximately 1.09 s of total exposure time; excitation wavelength: 980 nm, near-infrared-II region), indicating that cells treated with amino-N-GQD-polymer composites and the anti-epidermal growth factor receptor antibody can achieve two-photon luminescence with 1/81 of the power required for similar-intensity two-photon autofluorescence (1938.33 nJ pixel−1 with 800 scans, total exposure time of ∼5.44 s). The materials can serve as contrast agents for the non-invasive detection of biological specimens and interior tissues using a two-photon excitation wavelength in the near-infrared region.

In vivo deep-brain 2-photon fluorescent microscopy labeled with near-infrared dyes excited at the 1700 nm window

2-Photon fluorescence microscopy (2PFM) is an indispensable imaging technology for neuroscience. However, the imaging depth is usually limited to the cortical layer in mouse brain in vivo. Here, we demonstrate deep brain 2PFM in vivo excited at the 1700 nm window, using IR780 and aza-IR780 as fluorescent labels. Our detailed characterization of the multiphoton excitation and emission properties of IR780 and aza-IR780 show that: (1) IR780 or aza-IR780 generate 2-photon fluorescence excited at the 1700 nm window and are promising for 2PFM; (2) aza-IR780 exhibits a larger ησ2 with better anti-photobleaching property compared to IR780; The 2-photon action cross-sections of IR780 and aza-IR780 in plasma are an order-of-magnitude larger than those in PBS; (3) In vivo 2-photon emission spectra for both dyes show a notable red shift compared to those in vitro. Based on these characterization results, we demonstrate deep brain 2PFM labeled by them. A maximum imaging depth of 1585 μm (labeled by IR780) and 1800 μm (labeled by aza-IR780) into the mouse brain in vivo readily penetrates the subcortical region of hippocampus. Besides, a maximum of 1528 μm hemodynamic imaging depth is realized via 2PFM with aza-IR780 labeling, enabling us to measure blood flow speed in the hippocampus.

In Vivo Deep-Brain 3- and 4-Photon Fluorescence Imaging of Subcortical Structures Labeled by Quantum Dots Excited at the 2200 nm Window.

Multiphoton microscopy (MPM) is an enabling technology for visualizing deep-brain structures at high spatial resolution in vivo. Within the low tissue absorption window, shifting to longer excitation wavelengths reduces tissue scattering and boosts penetration depth. Recently, the 2200 nm excitation window has emerged as the last and longest window suitable for deep-brain MPM. However, multiphoton fluorescence imaging at this window has not been demonstrated, due to the lack of characterization of multiphoton properties of fluorescent labels. Here we demonstrate technologies for measuring both the multiphoton excitation and emission properties of fluorescent labels at the 2200 nm window, using (1) 3-photon (ησ3) and 4-photon action cross sections (ησ4) and (2) 3-photon and 4-photon emission spectra both ex vivo and in vivo of quantum dots. Our results show that quantum dots have exceptionally large ησ3 and ησ4 for efficient generation of multiphoton fluorescence. Besides, the 3-photon and 4-photon emission spectra of quantum dots are essentially identical to those of one-photon emission, which change negligibly subject to the local environment of circulating blood. Based on these characterization results, we further demonstrate deep-brain vasculature imaging in vivo. Due to the superb multiphoton properties of quantum dots, 3-photon and 4-photon fluorescence imaging reaches a maximum brain imaging depth of 1060 and 940 μm below the surface of a mouse brain, respectively, which enables the imaging of subcortical structures. We thus fill the last gap in multiphoton fluorescence imaging in terms of wavelength selection.

Imaging of simulated muscle based on single chip of AlN piezoelectric micromachined ultrasonic transducer

Most of current portable B-mode medical imaging is based on traditional ultrasonic transducers (UTs) or capacitive micromachined UTs, both of them have defects that impede satisfying performance. Piezoelectric micromachined UTs (pMUTs) is a promising solution for portable/wearable B-mode imaging as alternative. This work demonstrates B-mode imaging of simulated muscle with an aluminum nitride (AlN) pMUT array for application of muscle disorder diagnosis. A 23 × 26 pMUT array with resonant frequency of 5 MHz (in oil) is fabricated based on cavity silicon-on-insulator process. It has transmitting sensitivity of 3.6 kPa V−1 at 10 mm, receiving sensitivity of 1.1 μV Pa−1 and −6 dB bandwidth of 40% (in oil). Feasibility of muscle imaging based on pMUT is demonstrated by using muscle-like phantoms. Imaging results shows clear interfaces among layers, the axial and lateral resolution is 0.20 mm and 1.23 mm respectively. Furthermore, ex-vivo B-mode scans towards porcine tissues based on pMUT are firstly demonstrated. Different tissues including muscle, subcutaneous fat, fascia and hematoma is distinguished. The maximum imaging depth inside the porcine tissue is above 40 mm. These results demonstrate great potential of the pMUT array in muscle imaging.

Synthesis of Holmium-Oxide Nanoparticles for Near-Infrared Imaging and Dye-Photodegradation.

The development of multifunctional nanomaterials has received growing research interest, thanks to its ability to combine multiple properties for severing highly demanding purposes. In this work, holmium oxide nanoparticles are synthesized and characterized by various tools including XRD, XPS, and TEM. These nanoparticles are found to emit near-infrared fluorescence (800–1100 nm) under a 785 nm excitation source. Imaging of the animal tissues was demonstrated, and the maximum imaging depth was found to be 2.2 cm. The synthesized nanoparticles also show the capability of facilitating dye (fluorescein sodium salt and rhodamine 6G) degradation under white light irradiation. The synthesized holmium oxide nanoparticles are envisioned to be useful for near-infrared tissue imaging and dye-degradation.

Visualization of Macrophase Separation and Transformation in Immiscible Polymer Blends

Visualization of Macrophase Separation and Transformation in Immiscible Polymer Blends

A Handheld Microwave Thermoacoustic Imaging System With an Impedance Matching Microwave-Sono Probe for Breast Tumor Screening.

Microwave-induced thermoacoustic imaging (MTAI) is a promising alternative for breast tumor detection due to its deep imaging depth, high resolution, and minimal biological hazards. However, due to the bulky size and complicated system configuration of conventional benchtop MTAI, it is limited to imaging various anatomical sites and its application in different clinical scenarios. In this study, a handheld MTAI system equipped with a compact impedance matching microwave-sono and an ergonomically designed probe was presented and evaluated. The probe integrates a flexible coaxial cable for microwave delivery, a miniaturized microwave antenna, a linear transducer array, and wedge-shaped polystyrene blocks for efficient acoustic coupling, achieving microwave illumination and ultrasonic detection coaxially, and enabling high signal-to-noise ratio (SNR). Phantom experiments demonstrated that the maximum imaging depth is 5 cm (SNR = 8 dB), and the lateral and axial resolutions are 1.5 mm and 0.9 mm, respectively. Finally, three healthy female volunteers of different ages were subjected to breast thermoacoustic tomography and ultrasound imaging. The results showed that the h-MTAI data are correlated with the data of ultrasound imaging, indicating the safety and effectiveness of the system. Thus, the proposed h-MTAI system might contribute to breast tumor screening.

Tissue-mimicking phantoms for performance evaluation of photoacoustic microscopy systems.

Phantom-based performance test methods are critically needed to support development and clinical translation of emerging photoacoustic microscopy (PAM) devices. While phantoms have been recently developed for macroscopic photoacoustic imaging systems, there is an unmet need for well-characterized tissue-mimicking materials (TMMs) and phantoms suitable for evaluating PAM systems. Our objective was to develop and characterize a suitable dermis-mimicking TMM based on polyacrylamide hydrogels and demonstrate its utility for constructing image quality phantoms. TMM formulations were optically characterized over 400-1100 nm using integrating sphere spectrophotometry and acoustically characterized using a pulse through-transmission method over 8-24 MHz with highly confident extrapolation throughout the usable band of the PAM system. This TMM was used to construct a spatial resolution phantom containing gold nanoparticle point targets and a penetration depth phantom containing slanted tungsten filaments and blood-filled tubes. These phantoms were used to characterize performance of a custom-built PAM system. The TMM was found to be broadly tunable and specific formulations were identified to mimic human dermis at an optical wavelength of 570 nm and acoustic frequencies of 10-50 MHz. Imaging results showed that tungsten filaments yielded 1.1-4.2 times greater apparent maximum imaging depth than blood-filled tubes, which may overestimate real-world performance for vascular imaging applications. Nanoparticles were detectable only to depths of 120-200 µm, which may be due to the relatively weaker absorption of single nanoparticles vs. larger targets containing high concentration of hemoglobin. The developed TMMs and phantoms are useful tools to support PAM device characterization and optimization, streamline regulatory decision-making, and accelerate clinical translation.

Oxygen Imaging for Non-Invasive Metastasis Detection.

Sentinel lymph node (SLN) biopsy is an integral part of treatment planning for a variety of cancers as it evaluates whether a tumor has metastasized, an event that significantly reduces survival probability. However, this invasive procedure is associated with patient morbidity, and misses small metastatic deposits, resulting in the removal of additional nodes for tumors with high metastatic probability despite a negative SLN biopsy. To prevent this over-treatment and its associated morbidities for patients that were truly negative, we propose a tissue oxygen imaging method called Photoacoustic Lifetime Imaging (PALI) as an alternative or supplementary tool for SLN biopsy. As the hyper-metabolic state of cancer cells significantly depresses tissue oxygenation compared to normal tissue even for small metastatic deposits, we hypothesize that PALI can sensitively and specifically detect metastases. Before this hypothesis is tested, however, PALI’s maximum imaging depth must be evaluated to determine the cancer types for which it is best suited. To evaluate imaging depth, we developed and simulated a phantom composed of tubing in a tissue-mimicking, optically scattering liquid. Our simulation and experimental results both show that PALI’s maximum imaging depth is 16 mm. As most lymph nodes are deeper than 16 mm, ways to improve imaging depth, such as directly delivering light to the node using penetrating optical fibers, must be explored.

Use of Intertransmission Coherence for Haze Artifact Suppression in Cardiovascular Synthetic Aperture Ultrasound Imaging.

Synthetic aperture (SA) beamforming is a principal technology of modern medical ultrasound imaging. In that the use of focused transmission provides superior signal-to-noise ratio (SNR) and is promising for cardiovascular diagnosis at the maximum imaging depth of about 160 mm. But there is a pitfall in increasing the frame rate to more than 80 frames per second (frames/s) without image degradation by the haze artifact produced when the transmit foci (SA virtual sources) placed within the imaging field. We hypothesize that the source of this artifact is a grating lobe caused by coarse (decimated) multiple transmission and manifesting in the low brightness region in the accelerated-frame-rate images. We propose an intertransmission coherence factor (ITCF) method suppressing haze artifacts caused by coarse-pitch multiple transmission. The method is expected to suppress the image blurring because the SA grating lobe signal is less coherent than the main lobe signals. We evaluated an ITCF algorithm for suppressing the grating artifact when the transmission pitch is up to four times larger than the normal pitch (equivalent to 160 frames/s). In in-vitro and in-vivo experiments, we demonstrated the strong relation of haze artifact with the grating lobe due to the coarse-pitch transmission. Then, we confirmed that the ITCF method suppresses the haze artifact of a human heart by 15 dB while preserving the spatial resolution. The ITCF method combined with focused transmission SA beamforming is a valid method for getting cardiovascular ultrasound B-mode images without making a compromise in the trade-off relationship between the frame rate and the SNR.

Extending Imaging Depth in PLD-Based Photoacoustic Imaging: Moving Beyond Averaging.

Pulsed laser diodes (PLDs) promise to be an attractive alternative to solid-state laser sources in photoacoustic tomography (PAT) due to their portability, high-pulse repetition frequency (PRF), and cost effectiveness. However, due to their lower energy per pulse, which, in turn, results in lower fluence required per photoacoustic signal generation, PLD-based photoacoustic systems generally have maximum imaging depth that is lower in comparison to solid-state lasers. Averaging of multiple frames is usually employed as a common practice in high PRF PLD systems to improve the signal-to-noise ratio of the PAT images. In this work, we demonstrate that by combining the recently described approach of subpitch translation on the receive-side ultrasound transducer alongside averaging of multiple frames, it is feasible to increase the depth sensitivity in a PLD-based PAT imaging system. Here, experiments on phantom containing diluted India ink targets were performed at two different laser energy level settings, that is, 21 and [Formula: see text]. Results obtained showed that the imaging depth improves by ~38.5% from 9.1 to 12.6 mm for 21- [Formula: see text] energy level setting and by ~33.3% from 10.8 to 14.4 mm for 27- [Formula: see text] energy level setting by using λ /4-pitch translation and average of 128 frames in comparison to λ -pitch data acquired with the average of 128 frames. However, the achievable frame rate is reduced by a factor of 2 and 4 for λ /2 and λ /4 subpitch translation, respectively.

Characterization of interventional photoacoustic imaging (iPAI) capabilities in biological tissues.

Interventional photoacoustic imaging (iPAI) could improve ultrasound-guided minimally invasive procedures by enabling high precision needle steering, target detection, and molecular and physiologic tissue assessment. However, iPAI capabilities including visualization field, imaging depth, and spatial resolution are not well understood in biological tissues commonly encountered in clinical practice. Therefore, the potential clinical utility of iPAI remains unclear. We aim to experimentally determine iPAI capabilities in a variety of biological tissues, to assess its potential for clinical translation. We constructed an iPAI system capable of simultaneous real-time ultrasound (US) and photoacoustic imaging. This system delivers light directly into tissues using optical fiber integrated into a 16-gauge needle and detects photoacoustic signals with an external linear array ultrasound probe. iPAI's geometric visualization field, maximum imaging depth, and spatial resolution were experimentally determined in fat, muscle, kidney, and liver tissues by processing photoacoustic signal intensities of reference targets placed circumferentially around the fiber tip. The maximum detection depths of blood and indocyanine green (ICG), important common endogenous and exogenous contrast agents, respectively, were estimated in each tissue type by comparing their signal intensities with the reference target signal. iPAI could be performed in real-time concurrently with US and achieved a nearly spherical visualization field centering around the optical fiber tip in all tissues. Maximum imaging depths from the fiber tip were 54.1±1.3, 50.0±1.5, 32.7±1.1, and 16.9±1.3mm in fat, muscle, kidney, and liver tissues, respectively. Calculated maximum detection depths for blood were 41.5±3.0, 39.5±2.1, 24.4±4.0, and 8.6±2.0mm and detection depths for ICG at 0.05mg/mL concentration were 46.6±2.5, 42.6±1.4, 28.2±3.9, and 12.1±1.5mm in fat, muscle, kidney, and liver, respectively. Sub-100μm axial resolution and submillimeter lateral resolution were achieved in all tissues, and resolution did not significantly vary with distance from the fiber tip. Interventional photoacoustic imaging (iPAI) allows real-time visualization of a circumferential volume of tissue around an optical fiber tip, with submillimeter spatial resolution and tissue-dependent imaging depth. Our data strongly support further development of clinical iPAI systems as they could improve needle steering, target detection, and molecular and physiologic tissue assessment during minimally invasive procedures.

Multiscale high-speed photoacoustic microscopy based on free-space light transmission and a MEMS scanning mirror.

The conventional photoacoustic microscopy (PAM) system allows trade-offs between lateral resolution and imaging depth, limiting its applications in biological imaging in vivo. Here we present an integrated optical-resolution (OR) and acoustic-resolution (AR) multiscale PAM based on free-space light transmission and fast microelectromechanical systems (MEMS) scanning. The lateral resolution for OR is 4.9 µm, and the lateral resolution for AR is 114.5 µm. The maximum imaging depth for OR is 0.7 mm, and the maximum imaging depth for AR is 4.1 mm. The imaging speed can reach 50 k Alines per second. The high signal-to-noise ratios and wavelength throughput are achieved by delivering light via free-space, and the high speed is achieved by a MEMS scanning mirror. The blood vasculature from superficial skin to the deep tissue of a mouse leg was imaged in vivo using two different resolutions to demonstrate the multiscale imaging capability.

Conical ring array detector for large depth of field photoacoustic macroscopy.

Photoacoustic microscopy and macroscopy (PAM) using focused detector scanning are emerging imaging methods for biological tissue, providing high resolution and high sensitivity for structures with optical absorption contrast. However, achieving a constant lateral resolution over a large depth of field for deeply penetrating photoacoustic macroscopy is still a challenge. In this work, a detector design for scanning photoacoustic macroscopy is presented. Based on simulation results, a sensor array geometry is developed and fabricated that consists of concentric ring elements made of polyvinylidene fluoride (PVDF) film in a geometry that combines a centered planar ring with several inclined outer ring elements. The reconstruction algorithm, which uses dynamic focusing and coherence weighting, is explained and its capability to reduce artefacts occurring for single element conical sensors is demonstrated. Several phantoms are manufactured to evaluate the performance of the array in experimental measurements. The sensor array provides a constant axial and lateral resolution of 95 µm and 285 µm, respectively, over a depth of field of 20 mm. The depth of field corresponds approximately to the maximum imaging depth in biological tissue, estimated from the sensitivity of the array. With its ability to achieve the maximum resolution even with a very small scanning range, the array is believed to have applications in the imaging of limited regions of interest buried in biological tissue.

Synthesis of praseodymium-and molybdenum- sulfide nanoparticles for dye-photodegradation and near-infrared deep-tissue imaging

Development of nanoparticles with multi-functionalities is of great importance. In this study, praseodymium sulfide (Pr2S3) and molybdenum sulfide (MoS2) nanoparticles were synthesized. The structural, morphological and optical properties of the as-obtained products were investigated by XRD, XPS, TEM, UV–vis-NIR spectroscopy, and photoluminescence spectroscopy. Pr2S3 is found to be used in selective photodegradation of fluorescein sodium salt. MoS2 can be utilized for selective photodegradation of rhodamine B. In the mixture of rhodamine B, fluorescein sodium salt and rhodamine 6 G, most of rhodamine B and part of fluorescein sodium salt are optically degraded by Pr2S3. In the mixture of rhodamine B, fluorescein sodium salt and rhodamine 6 G, part of fluorescein sodium salt and most of rhodamine B is degraded by MoS2. Moreover, they emit near-infrared fluorescence (800–1100 nm) when excited by the 785 nm light. Deep tissues imaging with high-contrast is shown, utilizing a nanoparticle-filled centrifuge tube covered with animal tissues (pig Bacon meat). Maximum imaging depth below the tissue surface of 1 cm is achieved. Our work provides a rapid yet efficient procedure to make nanoparticles for dual-application-potential in dye-photodegradation and near-infrared deep tissue imaging.

Switchable optical and acoustic resolution photoacoustic dermoscope dedicated into in vivo biopsy-like of human skin

As a promising branch of optical absorption-based photoacoustic microscopy, photoacoustic dermoscopy (PAD) can provide manifold morphologic and functional information in clinical diagnosis and the assessment of dermatological conditions. However, most PAD setups are insufficient for clinical dermatology, given their single optical resolution (OR) or acoustic resolution (AR) mode, which results in poor spatiotemporal resolution or imaging depth for visualizing the internal texture of skin. Here, a switchable optical and acoustic resolution photoacoustic dermoscope (S-OR-ARPAD) system is developed, which provides a smooth transition from OR mode in microscopic imaging of superficial skin layers to AR mode when imaging at greater depths within intensely scattering deep skin layers. The lateral resolution can be seamlessly switched between 4.4 and 47 μm as the maximum imaging depth is switched between 1.2 and 1.8 mm for skin imaging. Using the S-OR-ARPAD, we identified the two distinct resolution modes responsible for resolving features of different skin layers and demonstrated the fine structures with strong contrast in the stratum corneum, dermal papillae, and microvascular structures in the horizontal plexus by imaging the healthy human skin at different locations.

Tissue imaging depth limit of stimulated Raman scattering microscopy.

Stimulated Raman scattering (SRS) microscopy is a promising technique for studying tissue structure, physiology, and function. Similar to other nonlinear optical imaging techniques, SRS is severely limited in imaging depth due to the turbidity and heterogeneity of tissue, regardless of whether imaging in the transmissive or epi mode. While this challenge is well known, important imaging parameters (namely maximum imaging depth and imaging signal to noise ratio) have rarely been reported in the literature. It is also important to compare epi mode and transmissive mode imaging to determine the best geometry for many tissue imaging applications. In this manuscript we report the achievable signal sizes and imaging depths using a simultaneous epi/transmissive imaging approach in four different murine tissues; brain, lung, kidney, and liver. For all four cases we report maximum signal sizes, scattering lengths, and achievable imaging depths as a function of tissue type and sample thickness. We report that for murine brain samples thinner than 2 mm transmissive imaging provides better results, while samples 2 mm and thicker are best imaged with epi imaging. We also demonstrate the use of a CNN-based denoising algorithm to yield a 40 µm (24%) increase in achievable imaging depth.

Absolute linear-in-k spectrometer designs enabled by freeform optics.

Linear-in-wavenumber, k, spectrometers have the merits of saving signal processing time and improving the sensitivity of spectral-domain optical coherence tomography (SD-OCT) by avoiding post-k-interpolation. We report on an approach leveraging freeform optics to linearize spectrometers in k to achieve an extremely low residual k-nonlinearity in design. A freeform lens reduced the k-nonlinearity from 2.47% for a benchmark spectrometer to 2.79 × 10-5% and 3.36 × 10-9% using the Fringe Zernike coefficients up to the 16th term and 37th term, respectively. A simulation model was developed to evaluate the performance of SD-OCT with the designed spectrometers. Without the k-interpolation in software, results show that the two freeform spectrometers achieve a roll-off gain of 5.24 dB over the imaging depth from 0.5 to 5.5 mm, while the maximum imaging depth is 5.8 mm. Finally, a 4.2-µm-FWHM axial PSF was maintained throughout the imaging depth in air.

Imaging of subendocardial adipose tissue and fiber orientation distributions in the human left atrium using optical coherence tomography.

BackgroundOptical coherence tomography (OCT) has the potential to provide real‐time imaging guidance for atrial fibrillation ablation, with promising results for lesion monitoring. OCT can also offer high‐resolution imaging of tissue composition, but there is insufficient cardiac OCT data to inform the use of OCT to reveal important tissue architecture of the human left atrium. Thus, the objective of this study was to define OCT imaging data throughout the human left atrium, focusing on the distribution of adipose tissue and fiber orientation as seen from the endocardium.Methods and ResultsHuman hearts (n = 7) were acquired for imaging the left atrium with OCT. A spectral‐domain OCT system with 1325 nm center wavelength, 6.5 μm axial resolution, 15 μm lateral resolution, and a maximum imaging depth of 2.51 mm in the air was used. Large‐scale OCT image maps of human left atrial tissue were developed, with adipose thickness and fiber orientation extracted from the imaging data. OCT imaging showed scattered distributions of adipose tissue around the septal and pulmonary vein regions, up to a depth of about 0.43 mm from the endocardial surface. The total volume of adipose tissue detected by OCT over one left atrium ranged from 1.42 to 28.74 mm3. Limited fiber orientation information primarily around the pulmonary veins and the septum could be identified.ConclusionOCT imaging could provide adjunctive information on the distribution of subendocardial adipose tissue, particularly around thin areas around the pulmonary veins and septal regions. Variations in OCT‐detected tissue composition could potentially assist ablation guidance.