Generation of anatomically realistic numerical phantoms for photoacoustic and ultrasonic breast imaging

Abstract

Photoacoustic computed tomography (PACT) and ultrasound computed tomography (USCT) are emerging modalities for breast imaging. As in all emerging imaging technologies, computer-simulation studies play a critically important role in developing and optimizing the designs of hardware and image reconstruction methods for PACT and USCT. Using computer-simulations, the parameters of an imaging system can be systematically and comprehensively explored in a way that is generally not possible through experimentation. When conducting such studies, numerical phantoms are employed to represent the physical properties of the patient or object to-be-imaged that influence the measured image data. It is highly desirable to utilize numerical phantoms that are realistic, especially when task-based measures of image quality are to be utilized to guide system design. However, most reported computer-simulation studies of PACT and USCT breast imaging employ simple numerical phantoms that oversimplify the complex anatomical structures in the human female breast. We develop and implement a methodology for generating anatomically realistic numerical breast phantoms from clinical contrast-enhanced magnetic resonance imaging data. The phantoms will depict vascular structures and the volumetric distribution of different tissue types in the breast. By assigning optical and acoustic parameters to different tissue structures, both optical and acoustic breast phantoms will be established for use in PACT and USCT studies.

Fig. 1

Flow chart of the key steps in the breast phantom generation process.

Fig. 2

(a) Illustration of the pooling method on a precontrast MR dataset. (b) The extracted raw contour volume.

Fig. 3

Illustration of skin extraction procedure. (a) Extraction of the raw skin area ${\text{Area}}_{\mathrm{RS}}$, where the white arrow is an example of a voxel “column,” $A$ is the first voxel larger than $T_0$ in this “column,” and the red mask forms ${\text{Area}}_{\mathrm{RS}}$. (b) Extraction of the final skin layer, where the dotted circles indicate a sphere with radius ${\mathrm{R}}_{\max }$, the blue line encloses the true skin region, and the yellow circle represents the adaptively chosen skin thickness ${\mathrm{R}}_{\text{skin}}$. The green masks form ${\mathbf{B}}_{\text{skin}}$. (c) Illustration of skin extraction that avoids superficial vessel structures.

Fig. 4

Extracted blood vessels, skin, fat, and fibroglandular tissues from patient 1, with scattered fibroglandular breasts. Colors in (e): white, vessel; light gray, fibroglandular; dark gray, fat.

Fig. 5

Extracted blood vessels, skin, fat, and fibroglandular tissues from patient 2, with heterogeneously dense breasts. Colors in (e): white, vessel; light gray, fibroglandular; dark gray, fat.

Fig. 6

Extracted blood vessels, skin, fat, and fibroglandular tissues from patient 3, with extremely dense breasts. Colors in (e): white, vessel, light gray, fibroglandular, dark gray, fat.

Fig. 7

From left to right: the $X\text{-}Y$ slice, $X\text{-}Z$ slice, $Y\text{-}Z$ slice, and the 3-D rendered view of the segmented-tissue phantom for patient 1, with scattered fibroglandular breasts.

Fig. 8

From left to right: the $X\text{-}Y$ slice, $X\text{-}Z$ slice, $Y\text{-}Z$ slice, and the 3-D rendered view of the segmented-tissue phantom for patient 2, with heterogeneously dense breasts.

Fig. 9

From left to right: the $X\text{-}Y$ slice, $X\text{-}Z$ slice, $Y\text{-}Z$ slice, and the 3-D rendered view of the segmented-tissue phantom for patient 3, with extremely dense breasts.

Fig. 10

(a) Initial pressure distribution computed from the MC simulation. (b) Speed of sound distribution, with units of m/s. (c) Density distribution, with units of ${\mathrm{kg}/\mathrm{m}}^3$.

Fig. 11

Reconstructed images from the PACT simulation study. (a) Reconstructed image assuming homogeneous acoustic properties. (b) Reconstructed image with true acoustic properties. (c) Profile plot of the phantom and reconstructed images through a vessel structure.