In the domain of brain imaging of small animals including rats, ultrasound (US) imaging is an appealing tool because it offers a high frame rate, easy access, and involves no radiation. However, the rat skull causes artifacts that influence brain image quality in terms of contrast and resolution. Therefore, minimizing the skull-induced artifacts in US imaging is a significant challenge. Unfortunately, the amount of literature on rat skull-induced artifacts is limited, and there is a particular lack of studies exploring reducing skull-induced artifacts. Due to the difficulty of experimentally imaging the same rat brain with and without a skull, numerical simulation becomes a reasonable approach to studying skull-induced artifacts. In this work, we investigated the effects of skull-induced artifacts by simulating a grid of point targets inside the skull cavity and quantifying the pattern of skull-induced artifacts. With the capacity to automatically capture the artifact pattern given a large amount of paired training data, deep learning (DL) models can effectively reduce image artifacts in multiple modalities. This work explored the feasibility of using DL-based methods to reduce skull-induced artifacts in US imaging. Simulated data were used to train a U-Net-derived, image-to-image regression network. US channel data with artifact signals served as inputs to the network, and channel data with reduced artifact signals were the regression outcomes. Results suggest the proposed method can reduce skull-induced artifacts and enhance target signals in B-mode images.
KEYWORDS: Calibration, 3D image processing, Photoacoustic spectroscopy, Photoacoustic imaging, Fiber lasers, 3D acquisition, Visualization, Ultrasonography, Data processing, Data acquisition
Two-dimensional and three-dimensional photoacoustic (PA) visualization is an emerging diagnostic procedure for investigation and research in vascular studies. Current manual/mechanized target scanning techniques involve sweeping the target along the elevation to generate 3D visuals. However, since the linear array probes exhibit poor resolution along the direction orthogonal to its focal plane, these techniques are prone to miss out on the organic structures parallel to the lateral direction. This could result in a misrepresentation of the target and is a critical shortfall of the method. We propose a multiview scanning and compounding technique to overcome the directionality bias and obtain more accurate and isotropic imaging performance. Using electromechanical translatory and rotary stages for multiview data acquisition, we generate a unified 3D visualization. A data processing pipeline illustrates an axial implementation of the Hilbert transform followed by spatial integration of the volumetric data to obtain the output. A 6-directional scanning approach improves the completeness of the structural details. We validated the technique using sub-millimeter-sized balls and wire phantoms. We first observed an enhanced resemblance of the outcome with the actual target in the ball phantom. Secondly, we observed imaging quality improvement with isotropic intensity distribution prominently in the wire phantom. A comparative analysis showed around a 50% reduction in the standard deviation of intensity distribution as compared to conventional unidirectional 3D PA imaging.
KEYWORDS: Transducers, Spatial filtering, Ultrasonography, Signal to noise ratio, Image quality, Apodization, Visualization, Design and modelling, Imaging systems, Data acquisition
PurposeCurrent ultrasound (US)-image-guided needle insertions often require an expertized technique for clinicians because the performance of tasks in a three-dimensional space using two-dimensional images requires operators to cognitively maintain the spatial relationships between the US probe, the needle, and the lesion. This work presents forward-viewing US imaging with a ring array configuration to enable needle interventions without requiring the registration between tools and targets.ApproachThe center-open ring array configuration allows the needle to be inserted from the center of the visualized US image, providing simple and intuitive guidance. To establish the feasibility of the ring array configuration, the design parameters causing the image quality, including the radius of the center hole and the number of ring layers and transducer elements, were investigated.ResultsExperimental results showed successful visualization, even with a hole in the transducer elements, and the target visibility was improved by increasing the number of ring layers and the number of transducer elements in each ring layer. Reducing the hole radius improved the region’s image quality at a shallow depth.ConclusionsForward-viewing US imaging with a ring array configuration has the potential to be a viable alternative to conventional US image-guided needle insertion methods.
Percutaneous Nephrolithotomy (PCNL), is a minimally invasive surgical procedure for removal of kidney stones typically >1cm. The procedure involves inserting a needle through the patient’s skin into the kidney which is being more commonly performed now using ultrasound (US) guidance. Existing US image-guided needle insertion employed in PCNL faces the challenge in terms of keeping the needle tip visible during the insertion process. We propose a needle insertion mechanism with mirror-integrated US imaging, which provides an intuitive and simple solution to monitor the needle insertion path. This is achieved by using acoustic mirror to change the direction of the US image plane while the needle goes through the spacing in the middle of the acoustic mirror so that the needle path aligns with the US image plane. Both the needle and the acoustic mirror are designed to be rotatable to provide the clinician with the flexibility to search for the optimal needle insertion orientation. According to the law of acoustic wave reflection, the needle should rotate two times the amount of the mirror to keep aligned with the US image plane. A synchronization mechanism consisting of belts and pulleys was designed to achieve this 2:1 rotation ratio. Needle-mirror synchronized rotation is tested using an image-processing-based method. In terms of imaging functionality, US images display point targets inside the gelatin phantom as well as the needle tip clearly. In the needle insertion experiment, a needle is inserted into the gelatin phantom to reach point targets, and results show insertion errors <3mm. Overall, our results demonstrate the potential of using the proposed US image-guided access mechanism in clinical scenarios.
The advancement in bio-engineering technology has enabled tissues to be artificially cultivated from human cells, providing the opportunity to model disease and discover potential treatments 1 . Blood vessel is an important category of human tissues that can be artificially engineered to facilitate the development of treatment plans for vascular diseases. The growth of tissue engineered blood vessels (TEBVs) is a costly procedure, and effective quality control during the growing process could help reduce waste and optimize the cultivation process. Imaging technologies, such as optical coherence tomography5,6 (OCT), have been applied to obtain cross-sectional images of TEBVs, which could be used as a nondestructive method to assess blood vessel during cultivation. Ultrasound (US) imaging has been widely accepted in clinical practice due to its real-time imaging capacity and zero radiation emission; and compared to optics-based imaging modality it is more accessible financially. We implemented an US computer tomography (USCT) based monitoring system on assisting quality control in TEBV growth. In this prototype, a single element transducer is placed in a circular stand that rotates around the TEBV bioreactor to collect A-lines from different angles. Mechatronics systems are used to actuate the transducer for circular motion. A circular back-projection method is used in image reconstruction. Experiments were carried out with point phantom and the bioreactor to validate the imaging functionality of the prototype. Reconstructed images provide validation to the feasibility of using USCT to monitor the growth of TEBV growth.
The needle intervention is required in many clinical procedures such as lumbar puncture and lymph node biopsy. Ultrasound (US) imaging has been applied widely to guide procedures involving needle insertion. However, conventional 2D US image guidance provides a limited field of view (FOV) for the region of interest (ROI), especially toward the outof-plane axis. Also, a high level of hand-eye coordination is required to accurately place the needle to the target in tissue because the needle path and the image plane are not registered to each other. This paper p roposes a needle insertion mechanism that enables 3D US imaging to provide a larger FOV and thus assists clinicians in making better decisions about where to insert the needle. Besides 3D imaging functionality, the image plane and needle path are co-registered in the proposed mechanism to facilitate needle insertion. The proposed mechanism uses actuated acoustic reflectors to redirect acoustic waves to different parts of ROI. 2D image slices are collected along the elevation direction and are then focused on the elevation plane. Elevation focusing is achieved with a synthetic aperture focusing algorithm that considers the acoustic path geometry in the actuated reflector system. Both software simulation and imaging experiments using a prototype are carried out to validate the 3D imaging performance.The simulation and experiment results of point and wire phantoms validate the 3D imaging capa bility and suggest that image quality on the elevation plane after applying elevation focusing improved in terms of both resolution and signal to noise ratio. By providing clinicians with an extended FOV with improved image quality, the proposed mechanism has the potential to enable needle insertion with better efficiency and a higher success rate.
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