Calcifications are one of the most important indicators for early breast cancer detection. We explore the feasibility of deep-penetration photoacoustic (PA) imaging of calcifications based on a medical ultrasound array imaging platform. Intralipid and chicken breast phantoms embedded with different-sized hydroxyapatite (HA) particles, which are the major components of calcifications, were imaged to verify the equipment’s capability and penetration depth for the visualization of calcifications. An optimal near-infrared excitation wavelength was selected to maximize PA signals of HAs, resulting in a better HA signal-to-blood ratio. We demonstrated that PA imaging is capable of visualizing 0.5-mm HA particles at a depth of 3 cm in chicken breast phantoms. The noise-equivalent penetration depth of the system for visualizing 0.5-mm HA particles in the human breast was estimated to be about 2.9 to 3.5 cm, which is clinically relevant as calcifications are usually found at a depth of 0.6 to 3.0 cm. Moreover, the feasibility of differentiating HA from blood by the PA spectroscopic technique was presented and the mechanism of the HA signal generation was discussed. The results show that PA imaging is a promising technique for real-time visualization of breast calcifications.
Breast calcification is one of the most important indicators for early breast cancer detection. In this study, based on a
medical ultrasound array imaging platform, we attempt to develop a real-time and high penetration photoacoustic (PA)
array imaging system for visualization of breast calcifications. Phantom studies were used to verify the imaging
capability and penetration depth of the developed PA array system for calcification imaging. Intralipid gelatin phantoms
with different-sized hydroxyapatite (HA) particles - major chemical composition of the breast calcification associated
with malignant breast cancers - embedded were imaged. Laser at 750 nm was used for photoacoustic excitation and a
custom-made 5-MHz photoacoustic array transducer with linear light guides was applied for photoacoustic signal
detection. Experimental results demonstrated that this system is capable of calcification imaging of 0.3-0.5 mm HA
particles. For the 0.5-mm HA particles, the imaging contrast was about 34 dB and the achievable penetration was 20 mm
where the axial, lateral, and elevational resolution of this PA array imaging system is 0.39 mm, 0.38 mm, and 1.25 mm,
respectively. The highest frame rate was 10 frames/sec limited by the laser pulse rate. Overall, our results demonstrate
that it is promising for PA imaging as a real-time diagnosis and biopsy guidance tool of breast micro-calcifications
outside mass lesion. Future work will focus on optimization of the photoacoustic transducer to further improve the
penetration depth and development of photoacoustic and ultrasound dual-modal imaging to enhance the calcification
imaging capability.
Recently, photoacoustic imaging has been intensively studied for blood vessel imaging, and shown its capability
of revealing vascular features suggestive of malignancy of breast cancer. In this study, we explore the feasibility of
visualization of micro-calcifications using photoacoustic imaging. Breast micro-calcification is also known as one of the
most important indicators for early breast cancer detection. The non-ionizing radiation and speckle free nature of
photoacoustic imaging overcomes the drawbacks of current diagnostic tools - X-ray mammography and ultrasound
imaging, respectively. We employed a 10-MHz photoacoustic imaging system to verify our idea. A sliced chicken breast
phantom with granulated calcium hydroxyapatite (HA) - major chemical composition of the breast calcification
associated with malignant breast cancers - embedded was imaged. With the near infared (NIR) laser excitation, it is
shown that the distribution of ~500 μm HAs can be clearly imaged. In addition, photoacoustic signals from HAs rivals
those of blood given an optimal NIR wavelength. In summary, photoacoustic imaging shows its promise for breast
micro-calcification detection. Moreover, fusion of the photoacoustic and ultrasound images can reveal the location and
distribution of micro-calcifications within anatomical landmarks of the breast tissue, which is clinically useful for biopsy
and diagnosis of breast cancer staging.
The rare earth-transition metal (RE-TM) alloys are widely accepted as the most suitable material for magneto-optical (MO) recording. The magnetic and optical properties of the recording media, hence the read-write-erase characteristics of the disk, are crucially dependent on the composition of the RE-TM films. Tailoring the composition of the films to meet the requirements in various magneto-optical recording applications is, therefore, important. In-line sputtering is the most common method for RE-TM film coating in disk production process. There are two common methods for fabricating sputter target; one is powder-sintering, the other is melt-casting. The former method yields a target composed of mixtures of pure element phases and certain percentage of intermetallic compound phases, the latter method yields a target composed of 100% intermetallic compound phases. The sputtering of RE-TM target often gives nonuniform composition distribution on the disk based on past experiences. This problem motivated us to study the sputtered atom distribution of the targets which were fabricated by different methods.
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