Small Imaging Probes Research Articles

Contrastive Adversarial Learning for Endomicroscopy Imaging Super-Resolution.

Endomicroscopy is an emerging imaging modality for real-time optical biopsy. One limitation of existing endomicroscopy based on coherent fibre bundles is that the image resolution is intrinsically limited by the number of fibres that can be practically integrated within the small imaging probe. To improve the image resolution, Super-Resolution (SR) techniques combined with image priors can enhance the clinical utility of endomicroscopy whereas existing SR algorithms suffer from the lack of explicit guidance from ground truth high-resolution (HR) images. In this paper, we propose an unsupervised SR pipeline to allow stable offline and kernel-generic learning. Our method takes advantage of both internal statistics and external cross-modality priors. To improve the joint learning process, we present a Sharpness-aware Contrastive Generative Adversarial Network (SCGAN) with two dedicated modules, a sharpness-aware generator and a contrastive-learning discriminator. In the generator, an auxiliary task of sharpness discrimination is formulated to facilitate internal learning by considering the rankings of training instances in various sharpness levels. In the discriminator, we design a contrastive-learning module to mitigate the ill-posed nature of SR tasks via constraints from both positive and negative images. Experiments on multiple datasets demonstrate that SCGAN reduces the performance gap between previous unsupervised approaches and the upper bounds defined in supervised settings by more than 50%, delivering a new state-of-the-art performance score for endomicroscopy super-resolution. Further application on a realistic Voronoi-based pCLE downsampling kernel proves that SCGAN attains PSNR of 35.851dB, improving 5.23dB compared with the traditional Delaunay interpolation.

Device Interventions for Stroke Prevention in Atrial Fibrillation

Atrial fibrillation (AF) is the most common sustained heart rhythm disorder, with an estimated prevalence of 0.4% to 1% in the general population. In addition, AF is responsible for approximately 15% to 20% of ischemic strokes. Device interventions to prevent strokes in patients with AF are nonsurgical procedures to block blood clots (thrombus) from forming and traveling out of the heart. The “quivering” rather than normal contractions of the upper chambers of the heart (atria) from disorganized electric activity (AF) leads to blood stasis and thrombus formation. A small cul-de-sac called the left atrial appendage (LAA) is especially prone to thrombus formation (Figure 1). In AF patients without valvular heart disease, almost all thrombus originates from the LAA. The thrombus travels to and block major vessels in the body. Blocking blood vessels to the brain leads to strokes and transient ischemic attacks (mini-strokes). Figure 1. Transesophageal echocardiogram image of a thrombus in the left atrial appendage (dotted line). Patients with the following risk factors have a higher stroke risk: heart failure, hypertension, age of 75 years or greater, diabetes mellitus, and prior history of strokes or mini-strokes. These are often combined to form the CHADS2 score. The more risk factors you have, the higher your CHADS2 score and risk of stroke are. Blood-thinning medications (anticoagulants) such as warfarin, dabigatran, rivaroxaban, and apixaban are effective stroke prevention therapies. The risks of bleeding associated with long-term anticoagulation led to the development of permanent treatment options like surgery. Closures by sutures (ligation) and removal (amputation) of the LAA …

Probe alignment and design issues of microelectromechanical system based optical coherence tomography endoscopic imaging

Endoscopic optical coherence tomography (OCT) imaging has been demonstrated using microelectromechanical system (MEMS) technology by several research groups. The focus of this work is to study how the OCT imaging performance is affected by the radius of curvature of MEMS mirrors as well as the optical alignment accuracy inside small imaging probes. The goal of this study is to provide guidance for assembly tolerance and design optimization of OCT endoscopic probes. Gaussian beam propagation is used for theoretical analysis which is confirmed by optical simulation and verified experimentally with a time-domain OCT system as well. It has been found that the OCT imaging is very sensitive to the distance from the fiber end to the gradient-index (GRIN) lens, which needs to be controlled within 0.1 mm to achieve working distance (WD) longer than 3.5 mm and lateral resolution around 25 μm. The impact on image quality of the MEMS mirror is negligible if the radius of curvature of the mirror surface is greater than 200 mm. In addition, we studied the astigmatism introduced by cylindrical plastic tubing; the maximum astigmatism ratio is 1.1 when the WD is around 2.5 mm.

Effect of split-focus approach on producing larger coagulation in swine liver

The split-focus approach has the potential to substantially improve the throughput of coagulation high-intensity focused ultrasound (HIFU) treatment. A prototype split-focus transducer with four elements at 4.25 MHz, combined with a small imaging probe at 6.5 MHz, was constructed for transrectal treatment of a prostate. Computer simulation predicted that 1.57 times larger acoustic power than a single-spot focus was required for a split focus to heat the tissue up to the same peak temperature at 4 s from the start of insonation. When the peak temperature was 100°C, the tissue volume above 70°C was predicted to be 2.3 times larger for a split focus. Swine liver lobes were intraoperatively insonated with the split-focus transducer for 4 s. A lesion of coagulation necrosis 3 to 4 times larger in volume than with a single-spot focus was formed with a split focus at the same acoustic power ratio as described above. Furthermore, a lesion about 2 times larger in volume was formed when compared at the same acoustic power. These results show the great advantage of a split-focus approach over a conventional single-spot focus in coagulation treatment. (E-mail: skazuaki@crl.hitachi.co.jp)