Photoacoustic imaging of breast microcalcifications : a preliminary study with 8-gauge core-biopsied breast specimens

Abstract

Purpose: To present the photoacoustic imaging (PAI) tool and to evaluate whether microcalcifications in breast tissue can be detected on PA images.

Materials and methods: We collected 21 cores containing microcalcifications (n=11, microcalcification group) and none (n=10, control group) in stereotactic or ultrasound (US) guided 8-gauge vacuum-assisted biopsies. Photoacoustic (PA) images were acquired through ex vivo experiments by transmitting laser pulses with two different wavelengths (700nm and 800nm). The presence of microcalcifications in PA images were blindly assessed and compared with specimen mammography. A ratio of the signal amplitude occurring at 700nm to that occurring at 800nm was calculated for each PA focus and was called the PAI ratio.

Results: Each PA focus of the cores in the microcalcification group was matched against existing microcalcifications on specimen mammography. Based on the spectral change of PA signal amplitude between 700 nm and 800 nm, 10 out of 11 specimens containing microcalcifications and 8 out of 10 specimens without calcifications

were identified correctly by two blinded radiologists; the sensitivity, specificity, accuracy, positive predictive and negative predictive values of our blind review were 90.91%, 80.0%, 85.71%, 83.33% and 88.89%. The PAI ratio in the microcalcification group was significantly higher than that in the control group (the median PAI ratio, 2.46 versus 1.11, respectively, P= .001).

Conclusion: Breast microcalcifications generated distinguishable PA signals unlike breast tissue without calcifications. So, PAI, a non-ionizing and non-invasive hybrid imaging technique, can be an alternative in overcoming the limitations of conventional US imaging.