Chitnis Parag V, Aristizábal Orlando, Filoux Erwan, Sampathkumar Ashwin, Mamou Jonathan, Ketterling Jeffrey A
Riverside Research, F.L. Lizzi Center for Biomedical Engineering, New York, NY, USA
Skirball Institute of Biomolecular Medicine, NYU School of Medicine, New York, NY, USA.
Ultrason Imaging. 2016 Jan;38(1):32-43. doi: 10.1177/0161734615583981. Epub 2015 Apr 28.
This paper presents an adaptive synthetic-focusing scheme that, when applied to photoacoustic (PA) data acquired using an annular array, improves focusing across a greater imaging depth and enhances spatial resolution. The imaging system was based on a 40-MHz, 5-element, annular-array transducer with a focal length of 12 mm and an 800-µm diameter hole through its central element to facilitate coaxial delivery of 532-nm laser. The transducer was raster-scanned to facilitate 3D acquisition of co-registered ultrasound and PA image data. Three synthetic-focusing schemes were compared for obtaining PA A-lines for each scan location: delay-and-sum (DAS), DAS weighted with a coherence factor (DAS + CF), and DAS weighted with a sign-coherence factor (DAS + SCF). Bench-top experiments that used an 80-µm hair were performed to assess the enhancement provided by the two coherence-based schemes. Both coherence-based schemes increased the signal-to-noise ratio by approximately 10 dB. When processed using the DAS-only scheme, the lateral dimension of the hair in a PA image with 20 dB dynamic range was between 300 µm and 1 mm for imaging depth ranging from 8 to 20 mm. In comparison, the DAS + CF scheme resulted in a lateral dimension of 200 to 450 µm over the same range. The DAS + SCF synthetic focusing further improved the smallest-resolvable dimension, which was between 150 and 400 µm over the same range of imaging depth. When used on PA data obtained from a 12-day-old mouse embryo, the DAS + SCF processing improved visualization of neurovasculature.
本文提出了一种自适应合成聚焦方案，该方案应用于使用环形阵列采集的光声（PA）数据时，可在更大的成像深度上改善聚焦并提高空间分辨率。成像系统基于一个40 MHz、5阵元的环形阵列换能器，焦距为12 mm，其中心阵元有一个直径800 µm的孔，便于532 nm激光的同轴传输。对换能器进行光栅扫描，以促进共配准超声和PA图像数据的三维采集。比较了三种合成聚焦方案，用于为每个扫描位置获取PA A线：延迟求和（DAS）、用相干因子加权的DAS（DAS + CF）和用符号相干因子加权的DAS（DAS + SCF）。进行了使用80 µm毛发的台式实验，以评估两种基于相干的方案所提供的增强效果。两种基于相干的方案都将信噪比提高了约10 dB。当仅使用DAS方案进行处理时，在8至20 mm的成像深度范围内，具有20 dB动态范围的PA图像中毛发的横向尺寸在300 µm至1 mm之间。相比之下，DAS + CF方案在相同范围内的横向尺寸为200至450 µm。DAS + SCF合成聚焦进一步改善了最小可分辨尺寸，在相同的成像深度范围内为150至400 µm。当应用于从12日龄小鼠胚胎获得的PA数据时，DAS + SCF处理改善了神经血管系统的可视化。
