We are performing clinical studies on breast cancer examinations at Hokkaido University Hospital with an ultrasound computed tomography (USCT) system. Our studies have revealed that some reflection images exhibit intensity inhomogeneity because ultrasound waves, shot by a 1-D ring array transducer, go non-vertically into the object surface. This trend significantly increases the burden of interpretation. Therefore, we developed a calibration method to remove this heterogeneity based on the distribution of the incident angle of waves that are estimated from the slope of the subject surface morphologically extracted from multi-slice reflection images. Results showed that applying this correction method to clinical images enabled the image contrast and uniformity to be successfully recovered.
Ultrasound Computed Tomography is a very promising medical imaging technology to be used to discover breast cancer early. The conventional ultrasound emission method (fan beam), which utilizes a single element for one emission, might result in a signal-to-noise ratio (SNR) too low for measuring dense breasts. This research proposes a virtual fan emission method that can maintain high accuracy, a large field of view, and a high SNR at the same time, using multiple elements while mimicking the wave field of single element emission. We experimentally proved its effectiveness in improving SNR by imaging a phantom with high attenuation to mimic a dense breast. Imaging of excised human breast tissues also suggested that the proposed virtual fan beam emission is more effective than conventional fan beam emission to screen for breast cancer correctly.