Freehand three-dimensional ultrasound is a technique for acquiring ultrasonic data of a 3D volume by recording the trajectory of the ultrasound probe using a position sensor. In planning and registration, a freehand ultrasound systems is used to track a two-dimensional probe. Probe calibration is necessary to find the rigid body transformation from the coordinate system of the B-scan to that of the mobile part of the position sensor. Numerous techniques for this have been developed over the past decade. In this review, we give a comprehensive description of existing calibration techniques and classify them according to the mathematical principles on which they are based. We give a thorough analysis of these approaches based on their accuracy, ease of use, reliability, and speed of calibration. To ensure consistency, these comparisons are done by the authors based on experimental results and not on figures quoted in previous papers.

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Z-fiducial phantoms allow three-dimensional ultrasound probe calibration with a single B-scan. One of the main difficulties in using this phantom is the need for reliable segmentation of the wires in the ultrasound images, which necessitates manual intervention. In this article, we have shown how we can solve this problem by mounting a thin rubber membrane on top of the phantom. The membrane is segmented automatically and the wires can be easily located as they are at known positions relative to the membrane. This enables us to segment the wires automatically at the full PAL frame rate of 25 Hz, to produce calibrations in real-time, while achieving accuracies similar to those reported in the literature. We have also devised a technique to improve the estimation of the elevational offset (calibration parameter) by capturing a few images of the planar membrane. If spatial calibration is known, fully automatic wire segmentation allows the fiducials to be tracked in real-time. This also enables temporal calibration to be performed in real-time as the probe is moved away from the phantom. We have evaluated the performance of our phantom by calibrating a probe at 8 cm and 15 cm depth. The precision of the calibrations are 0.7 mm and 1.2 mm, respectively. The point reconstruction accuracies of fiducial points provided by the same Z-phantom are slightly below 1.5 mm. The point reconstruction accuracies obtained by scanning the end of a wire tip are 2.5 mm and 3.0 mm. These results match the accuracies achieved in the literature. It takes approximately 2 min to set up the experiment, submerge the phantom in the water bath, locate the phantom in space with a pointer and capture six images of the planar membrane. After this, spatial calibration can be performed in less than a second. Temporal calibration can be completed in approximately 3 s.

This paper presents improvements to the plane-based technique for calibrating freehand 3D ultrasound systems. The improvements are designed to make it easier for inexperienced users to perform plane-based calibration and to know that they have got a reliable result. In particular, we enable the calibration to be performed using water at room temperature while producing a result that is valid for average soft tissue, and we show how it is possible to provide feedback on the reliability of the calibration using a metric based on the curvature of the calibration criterion function. We present comprehensive results showing that these innovations improve the precision of the calibration and offer useful feedback to the user.

Z-fiducial phantoms allow 3D ultrasound probe calibration with a single B-scan. One of the main hindrances of using this phantom is the necessity of segmenting the wires reliably, which requires human intervention. In this paper, we have shown how we can solve this problem by mounting a thin rubber membrane on top of the phantom. The membrane is segmented automatically and the wires can be easily located as they are at known positions relative to the membrane. This enables us to segment the wires automatically at the full PAL frame rate of 25Hz, to produce calibrations in real-time, while achieving accuracies similar to those reported in the literature. We also devise a technique to improve the estimation of the elevational offset by capturing a few images of the planar membrane. If spatial calibration is known, fully automatic wire segmentation allows the fiducials to be tracked in real-time. This also enables temporal calibration to be performed in real-time as the probe is moved away from the phantom.

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The supply chain of the semiconductor industry is experiencing painful growth and advancement in chip development with the help of recently passed U.S legislation and funding to address a chip shortage. However, it is not without some drawbacks, one of which is the challenge of maintaining control over the manufacturing quality throughout the entire process. As a result of this, physical inspection for hardware security is a necessity to assure the semiconductor devices. In this paper, various physical inspection methods are reviewed and scanning acoustic microscopy (SAM) is proved to be the ideal physical inspection method to minimize the possibility of counterfeits which might be the feasible solution in detecting counterfeits on a large scale.