Global economic activity today demands that national measurement standards guaranteeing a high degree of accuracy in measurement be maintained, and that such ultrasonic field measurement standards as ultrasonic power or ultrasonic pressure be included. Ultrasonic power standards and hydrophone sensitivity standards covering conventional medical ultrasound fields have been established in most of the advanced nations. The Consultative Committee for Acoustics, Ultrasound and Vibration (CCAUV) was established in 1998 under the Metre Convention. Only recently, however, have ultrasonic standards been established, and end-users of ultrasound measurement equipment do not appear to have yet acquired sufficient understanding of the metrology for ultrasound. In this paper I describe some historical situations of the metrology for ultrasonic measurement, the role of measurement standards based on the Metre Convention, and the present situation of ultrasonic standards established by the National Metrology Institute of Japan (NMIJ). Ultrasonic standards must apply to an expanded frequency range, and standards for high-intensity ultrasound will be essential. Issues of world-wide concern are increasing discussed at International Electrotechnical Commission (IEC), the Metre Convention, and similar gatherings. To contribute to this trend, I also discuss areas for further study that will enable us to reach the next level of ultrasonic standards at NMIJ.

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The morbidity and the mortality of breast cancer in Japan continue to increase year by year, making early detection very important. It is easy to detect microcalcifications on mammography, but they are more difficult to detect on breast ultrasound, which is said to be a limitation of breast ultrasound. Microcalcifications are found in ductal carcinoma in situ (DCIS), which is the earliest stage of breast cancer. We have developed a new technology, the microcalcification detection filter (firefly), and examined diagnostic and clinical application. It is often difficult to identify the high-intensity echogenic spots of microcalcifications on the monitor because the mammary gland has a very complicated structure on B-mode ultrasound. Using the theory of CFAR (Contrast False Alarm Rate), we have erased the echogenic breast tissue on screen and emphasized punctate high-intensity microcalcifications. The microcalcifications can be identified with this filter, like the glitter of fireflies on a dark night. Two-hundred and eighteen cases were examined, in whom a clear increase in detectability was found. Intervention under stereo (mammography) guide is the mainstay of diagnosis of microcalcifications, but it can be performed only at a limited number of institution. The development of this filter will allow biopsy under guided ultrasound at any hospital, and it will also be possible to observe the microcalcifications on sampling. Furthermore, the extent of the surgical margin needs to be accurately evaluated before surgery. This filter will enable mapping of malignancy at the same position as the operation. Breast cancer screening with ultrasound may become widespread with use of the “firefly” microcalcification detection filter. The significance and utility of “firefly” are great.

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Three-dimensional (3D) US is recently rapidly gaining popularity as it moves out of the research environment and into the clinical setting. Advances in two-dimensional high-frequency US transducer technology in combination with compound imaging and speckle reduction is the basis for high-quality three-dimensional volume US. Four-dimensional US is real-time 3D rendered image information. In addition to conventional 2D sonography, 3D/4D US provides new diagnostic information, allowing us to study a breast mass and the surrounding tissue in three orthogonal planes, or to obtain information about the three-dimensional vessel architecture using glass body rendering. In breast imaging, 3D US has the capacity to demonstrate lesion margins and topography, thereby helping differentiate benign masses from malignant ones. Three-dimensional US can also help determine the need for biopsy and help facilitate needle localization and guidance during biopsy. With recent advances in computer technology and display techniques, 3D US will likely play an increasingly important role in medicine.

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Real-time virtual sonography^® (RVS) is a new mode ultrasound (US) diagnostic system that registers and displays real-time ultrasound images together with corresponding previously acquired CT or MRI images. The clinical advantages of the RVS system for abdominal imaging have are well established and routinely used in the clinic. We extend the RVS system for breast imaging using a high-frequency linear array probe and establish its clinical advantages. Breast CT has been gaining popularity for preoperative evaluation of malignant breast lesions ever since the introduction of multislice CT in Japan. Because high quality three-dimensional reconstruction CT images are acquired in the same supine position as the surgical treatment, it also serves as a valuable simulation tool for breast conservative therapy. However, the correspondence between displayed static CT images and the real field of operation requires visual approximate estimation. Real-time ultrasound would be the modality of choice for overcoming the disadvantage of helical CT in that it provides feedback on which the clinician can base dedcisions. However, ultrasound′s accuracy in detecting and localizing lesions tends to be inferior to that of CT and, in addition, requires an experienced examiner. We attempt to apply RVS to overcome these limitations for breast imaging fusing three dimensional CT data and real-time ultrasound. Our RVS is not limited to CT alone, but can be extended to MRI and other modalities. Although the effect of difference in positioinit varies significantly between MRI and US, our RVS results obtained using the registration algorithm commonly used in CT show promise. We expect that breast RVS combined with MRI data should prove effective as an assistant tool in second-look ultrasound for MR-detected lesions.

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