Importance of Ultrawide Bandwidth for Optoacoustic Esophagus Imaging

U-Net enhanced real-time LED-based photoacoustic imaging

Photoacoustic (PA) imaging is hybrid imaging modality with good optical contrast and spatial resolution. Portable, cost-effective, smaller footprint light emitting diodes (LEDs) are rapidly becoming important PA optical sources. However, the key challenge faced by the LED-based systems is the low light fluence that is generally compensated by high frame averaging, consequently reducing acquisition frame-rate. In this study, we present a simple deep learning U-Net framework that enhances the signal-to-noise ratio (SNR) and contrast of PA image obtained by averaging low number of frames. The SNR increased by approximately four-fold for both in-class in vitro phantoms (4.39 ± 2.55) and out-of-class in vivo models (4.27 ± 0.87). We also demonstrate the noise invariancy of the network and discuss the downsides (blurry outcome and failure to reduce the salt & pepper noise). Overall, the developed U-Net framework can provide a real-time image enhancement platform for clinically translatable low-cost and low-energy light source-based PA imaging systems.

Spectroscopic photoacoustic/ultrasound/optical-microscopic multimodal intrarectal endoscopy for detection of centimeter-scale deep lesions

The inadequacy of existing colorectal imaging tools has significantly obstructed the efficient detection of colorectal cancer. To address this issue, this work presents the cross-scale endoscopic imaging of rectal tumors with a combined photoacoustic/ultrasound tomography system and wide-field optical microscopy. This multimodal system combines the merits of centimeter-scale deep penetration, multi-spectral imaging, cross-scale imaging ability, low system cost, and 360° view in a single modality. Results indicated that the proposed system could reliably depict the location of the cancer invasion depth spectroscopically with indocyanine green The tumor angiogenesis can be well identified in the wide-field optical imaging mode, which helps to localize the tumors and guide the following photoacoustic/ultrasound scan. This work may facilitate the accurate characterization of colorectal cancer and promote the clinical translation of photoacoustic-based colorectal endoscopy.

Review of consensus test methods in medical imaging and current practices in photoacoustic image quality assessment

SIGNIFICANCE

Photoacoustic imaging (PAI) is a powerful emerging technology with broad clinical applications, but consensus test methods are needed to standardize performance evaluation and accelerate translation.

AIM

To review consensus image quality test methods for mature imaging modalities [ultrasound, magnetic resonance imaging (MRI), x-ray CT, and x-ray mammography], identify best practices in phantom design and testing procedures, and compare against current practices in PAI phantom testing.

APPROACH

We reviewed scientific papers, international standards, clinical accreditation guidelines, and professional society recommendations describing medical image quality test methods. Observations are organized by image quality characteristics (IQCs), including spatial resolution, geometric accuracy, imaging depth, uniformity, sensitivity, low-contrast detectability, and artifacts.

RESULTS

Consensus documents typically prescribed phantom geometry and material property requirements, as well as specific data acquisition and analysis protocols to optimize test consistency and reproducibility. While these documents considered a wide array of IQCs, reported PAI phantom testing focused heavily on in-plane resolution, depth of visualization, and sensitivity. Understudied IQCs that merit further consideration include out-of-plane resolution, geometric accuracy, uniformity, low-contrast detectability, and co-registration accuracy.

CONCLUSIONS

Available medical image quality standards provide a blueprint for establishing consensus best practices for photoacoustic image quality assessment and thus hastening PAI technology advancement, translation, and clinical adoption.

Ultra-broadband axicon transducer for optoacoustic endoscopy

Image performance in optoacoustic endoscopy depends markedly on the design of the transducer employed. Ideally, high-resolution performance is required over an expanded depth of focus. Current optoacoustic focused transducers achieve lateral resolutions in the range of tens of microns in the mesoscopic regime, but their depth of focus is limited to hundreds of microns by the nature of their spherical geometry. We designed an ultra-broadband axicon detector with a 2 mm central aperture and investigated whether the imaging characteristics exceeded those of a spherical detector of similar size. We show a previously undocumented ability to achieve a broadband elongated pencil-beam optoacoustic sensitivity with an axicon detection geometry, providing approximately 40 μm-lateral resolution maintained over a depth of focus of 950 μm—3.8 times that of the reference spherical detector. This performance could potentially lead to optoacoustic endoscopes that can visualize optical absorption deeper and with higher resolution than any other optical endoscope today.

High-resolution and extended-depth-of-field photoacoustic endomicroscopy by scanning-domain synthesis of optical beams

Photoacoustic endomicroscopy (PAEM) is capable of imaging fine structures in digestive tract. However, conventional PAEM employs a tightly focused laser beam to irradiate the object, which results in a limited depth-of-field (DOF). Here, we propose a scanning-domain synthesis of optical beams (SDSOB) to optimize both transverse resolution and the DOF by synthetic effective focused beams in scanning domain for the PAEM. By utilizing the SDSOB technique, multiple defocused and scattered beams are refocused to synthesize virtual focuses covering a large range of depth. A transverse point spread function that is 5.7-time sharper, and a transverse spatial bandwidth that is 8.5-time broader than those of the conventional PAEM were simulatively obtained through SDSOB-PAEM at the defocus distance of 2.4 mm. We validated the transverse resolution improvement at both in- and out-focus positions via phantom experiments of carbon fibers. In addition, in vivo rabbit experiments were conducted to acquire vascular images over radial depth range of 900 µm. And further morphological analysis revealed that the SDSOB images were acquired with abundant vascular branches and nodes, large total-length and small average-length of blood vessels, which indicated that the SDSOB-PAEM achieved high-resolution imaging in distinct rectal layers. All these results suggest that the SDSOB-PAEM possesses high transverse resolution and extended DOF, which demonstrates the SDSOB-PAEM can provide more accurate information for clinical assessment.