Limited-view Scanning Research Articles

A Deep Learning Method for Limited-View Intravascular Photoacoustic Image Reconstruction

Intravascular photoacoustic tomography (IVPAT) is a newly developed imaging modality in the interventional diagnosis and treatment of coronary artery diseases. Incomplete acoustic measurement caused by limitedview scanning of the detector in the vascular lumen results in under-sampling artifacts and distortion in the images reconstructed by using the standard reconstruction methods. A method for limited-view IVPAT image reconstruction based on deep learning is presented in this paper. A convolutional neural network (CNN) is constructed and trained with computer-simulated image data set. Then, the trained CNN is used to optimize the cross-sectional images of the vessel which are recovered from the incomplete photoacoustic measurements by using the standard time-reversal (TR) algorithm to obtain the images with the improved quality. Results of numerical demonstration indicate that the method can effectively reduce the image distortion and artifacts caused by the limited-view detection. Furthermore, it is superior to the compressed sensing (CS) method in recovering the unmeasured information of the imaging target with the structural similarity around 10% higher than CS reconstruction.

Numerical simulation of endoscopic magnetoacoustic tomography with magnetic induction

Endoscopic magnetoacoustic tomography with magnetic induction (EMAT-MI) provides an interventional tool to detect the electrical conductivity distribution of a tubular structure with high spatial resolution. In this work, a preliminary study on the numerical simulation of EMAT-MI images was conducted. The magnetic excitation, generation and propagation of magnetoacoustic (MA) waves in the multi-layered wall tissues were modeled and numerically simulated. The cross-sectional distribution of the acoustic source and electrical conductivity was recovered from the acoustic pressure series based on time-reversal. The validity has been demonstrated on two computer-generated phantoms. Results suggested that the conductivity boundaries can be clearly distinguished in the images of acoustic-source or conductivity distribution which are highly consistent with the numerical simulation. The resolution of the MA signals excited by the Lorentz force divergence is closely related to the pulse width of the excitation current. Sparse measuring locations and limited-view scanning may reduce the image quality although higher SNR of the MA signals leads to better image reconstruction.

An Efficient Compensation Method for Limited-View Photoacoustic Imaging Reconstruction Based on Gerchberg–Papoulis Extrapolation

The reconstruction for limited-view scanning, though often the case in practice, has remained a difficult issue for photoacoustic imaging (PAI). The incompleteness of sampling data will cause serious artifacts and fuzziness in those missing views and it will heavily affect the quality of the image. To solve the problem of limited-view PAI, a compensation method based on the Gerchberg–Papoulis (GP) extrapolation is applied into PAI. Based on the known data, missing detectors elements are estimated and the image in the missing views is then compensated using the Fast Fourier Transform (FFT). To accelerate the convergence speed of the algorithm, the total variation (TV)-based iterative algorithm is incorporated into the GP extrapolation-based FFT-utilized compensation method (TV-GPEF). The effective variable splitting and Barzilai–Borwein based method is adopted to solve the optimization problem. Simulations and in vitro experiments for both limited-angle circular scanning and straight-line scanning are conducted to validate the proposed algorithm. Results show that the proposed algorithm can greatly suppress the artifacts caused by the missing views and enhance the edges and the details of the image. It can be indicated that the proposed TV-GPEF algorithm is efficient for limited-view PAI.

2-D image reconstruction of photoacoustic endoscopic imaging based on time-reversal

BackgroundsPhotoacoustic endoscopic (PAE) imaging is a rapidly emerging interventional imaging modality for identification and characterization of intraluminal pathological tissues. Since the scanning aperture of PAE is enclosed in the lumen, image reconstruction techniques used in photoacoustic tomography (PAT) can not be directly applied. ObjectiveThe purpose of this work is to design an image reconstruction method based on time-reversal (TR) for a PAE imaging catheter equipped with a single-element NFU transducer with circular scanning. MethodsFirstly, the back-propagation of photoacoustic waves emitted from the tissue absorbers was modeled and simulated. Then, two-dimensional (2-D) grayscale images of the acoustic pressure distribution were obtained displaying the morphological structure of luminal cross-sections. A computer-simulated vessel phantom embedded with atherosclerotic plaques was used to validate and quantitatively evaluate the method. ResultThe structural similarity (SSIM) of the images reconstructed with TR is comparable to algebraic reconstruction technique (ART), which is at least 65% higher than filtered back-projection (FBP). The time cost of TR is about 16 times that of FBP and 1/4 of ART under the same test condition. ConclusionThe reconstructed image quality may degrade when the photoacoustic data are incomplete due to sparse measuring locations and limited-view scanning. The spline interpolation can be used to improve the image quality and eliminate artifacts.

Multi-Source Quantitative Photoacoustic Tomography with Detector Response Function and Limited-View Scanning

Multi-Source Quantitative Photoacoustic Tomography with Detector Response Function and Limited-View Scanning

Investigation of the Scanning Angle and the Orientation of the Absorber Effects on the Photoacoustic Tomography Imaging

In this paper, based on circular scanning configuration of photoacoustic tomography (PAT), we have tested the effects of the stepping angle of scanning and the relationship between the scanning range and the orientation of the absorber on the quality of the reconstructed image. The experiment results have shown that the reconstructed image would be influenced more by artifacts as the increase of the stepping angle of scanning, and for the limited-view scanning, while the relationship of the scanning path and the orientation of the absorber is parallel, compared with vertical, we can use the data got from less detecting position to reconstruct image clearly.

Influence of limited-view scanning on depth imaging of photoacoustic tomography

We study the influence of limited-view scanning on the depth imaging of photoacoustic tomography. The situation, in which absorbers are located at different depths with respect to the limited-view scanning trajectory, is called depth imaging and is investigated in this paper. The results show that limited-view scanning causes the reconstructed intensity of deep absorbers to be weaker than that of shallow ones and that deep absorbers will be invisible if the scanning range is too small. The concept of effective scanning angle is proposed to analyse that phenomenon. We find that an effective scanning angle can well predict the relationship between scanning angle and the intensity ratio of absorbers. In addition, limited-view scanning is employed to improve image quality.

Reconstruction of high quality photoacoustic tomography with a limited-view scanning

The goal of this work is to resolve the limited-view problem of photoacoustic tomography (PAT). We report a two-loop iteration method to inverse the photoacoustic sources from the measured photoacoustic signals. PAT reconstruction with this method does not depend on the detection path. Therefore, the proposed method can provide recognizable image even when the detector only scans a small angle (about 20 degrees approximately 30 degrees). The comparison with the delay-and-sum method shows the advantage of the proposed method in reconstructing image from incomplete data.

Study of the resolution of limited-view photoacoustic tomography

In this study, numerical experiments are carried out to quantitatively investigate the effects of limited-view scanning on the resolution of photoacoustic tomography. An empirical formula is provided to approach our numerical results.The results of the study are helpful for the design of scanning trajectory and the evaluation of reconstruction.