Seetharaman Aadavan, Thittai Arun K
Biomedical Ultrasound Imaging Laboratory, Department of Applied Mechanics and Biomedical Engineering, Indian Institute of Technology, Madras, Chennai, India.
Ultrason Imaging. 2025 Mar;47(2):68-78. doi: 10.1177/01617346241307637. Epub 2025 Jan 6.
Imaging depth remains a restriction for Synthetic Aperture (SA) approaches, even though SA techniques have been shown to overcome some of the drawbacks of Conventional Focused Beamforming (CFB) technique. This limitation is attributed to lesser energy per transmit in SA techniques compared to that of CFB technique. Therefore, in this paper, a systematic investigation is done to evaluate the improvement in imaging depth and image quality of B-mode ultrasound images in the case of SA technique using PZT transducer by boosting the input voltage to the transducer, while measuring the acoustic exposure parameters recommended in international standards. Note-while acoustic exposure parameters like Mechanical and Thermal index (MI and TI, respectively) are well-studied and reported for CFB techniques, the same is not the case with novel SA techniques. For analysis, the image quality metrics of Contrast Ratio (CR), Contrast to Noise Ratio (CNR) and generalized Contrast to Noise Ratio (gCNR) are employed for the SA techniques of Synthetic Transmit Aperture (STA) and Diverging Beam Synthetic Aperture Technique (DB-SAT). The results show that, when the input voltage is increased from 45 to 70 V in PZT transducer, the following improvements in image quality parameters were observed: CR by 15.6% and 21.25%, CNR by 21.39% and 36.23% and gCNR by 14.1% and 21.5% for STA and DB-SAT techniques, respectively. Results also suggest that the considerable imaging depth improvement is achieved for the incremental input voltage till 60 V, with the highest of 7.5% depth improvement at 60 V, above which the tradeoff between the gain in imaging depth and acoustic safety index becomes critical to consider. Recently, transducers having lead magnesium nitrate lead titanate (PMN-PT) piezoelectric single crystals have shown to produce ultrasound images with higher image quality at greater depths, irrespective of the transmit schemes. The same concept of relatively higher output transmitting energy by cost expensive PMN-PT single crystal transducers for the same applied voltage, compared to the traditional lead zirconate titanate (PZT) transducers, explains the enhanced imaging depth. This study is probably the first one that reports the comparison between PMN-PT and PZT transducer, not only in terms of imaging depth but also reporting them in the context of acoustic exposure safety limits in terms of MI and TI. The findings of this study may help system designers to minimize the trade-off between cost and image quality.
成像深度仍然是合成孔径（SA）方法的一个限制因素，尽管SA技术已被证明能克服传统聚焦波束形成（CFB）技术的一些缺点。这种限制归因于SA技术中每次发射的能量比CFB技术少。因此，在本文中，进行了一项系统研究，以评估在使用PZT换能器的SA技术情况下，通过提高施加到换能器的输入电压来提升B模式超声图像的成像深度和图像质量，同时测量国际标准中推荐的声暴露参数。注意，虽然像机械指数和热指数（分别为MI和TI）这样的声暴露参数在CFB技术中已有充分研究和报道，但在新型SA技术中情况并非如此。为了进行分析，对比度（CR）、对比度噪声比（CNR）和广义对比度噪声比（gCNR）等图像质量指标被用于合成发射孔径（STA）和发散波束合成孔径技术（DB - SAT）的SA技术。结果表明，当PZT换能器的输入电压从45V增加到70V时，观察到图像质量参数有以下改善：对于STA和DB - SAT技术，CR分别提高了15.6%和21.25%，CNR分别提高了21.39%和36.23%，gCNR分别提高了14.1%和21.5%。结果还表明，直到60V的增量输入电压都能实现显著的成像深度改善，在60V时深度改善最高达到7.5%，超过该电压后，成像深度增益与声安全指数之间的权衡就变得至关重要。最近，具有铌镁酸铅钛酸铅（PMN - PT）压电单晶的换能器已被证明，无论发射方案如何，都能在更大深度产生具有更高图像质量的超声图像。与传统的锆钛酸铅（PZT）换能器相比，在相同施加电压下，成本较高的PMN - PT单晶换能器具有相对更高的输出发射能量，这一相同概念解释了成像深度的增强。这项研究可能是第一项不仅在成像深度方面，而且在根据MI和TI的声暴露安全限值背景下报告PMN - PT和PZT换能器之间比较的研究。本研究的结果可能有助于系统设计者将成本与图像质量之间的权衡降至最低。
