A mathematical model platform for optimizing a multiprojection breast imaging system

Abstract

Multiprojection imaging is a technique in which a plurality of digital radiographic images of the same patient are acquired within a short interval of time from slightly different angles. Information from each image is combined to determine the final diagnosis. Projection data are either reconstructed into slices as in the case of tomosynthesis or analyzed directly as in the case of multiprojection correlation imaging technique, thereby avoiding reconstruction artifacts. In this study, the authors investigated the optimum geometry of acquisitions of a multiprojection breast correlation imaging system in terms of the number of projections and their total angular span that yield maximum performance in a task that models clinical decision. Twenty-five angular projections of each breast from 82 human subjects in our breast tomosynthesis database were each supplemented with a simulated 3 mm mass. An approach based on Laguerre-Gauss channelized Hotelling observer was developed to assess the detectability of the mass in terms of receiver operating characteristic ͑ROC͒ curves. Two methodologies were developed to integrate results from individual projections into one combined ROC curve as the overall figure of merit. To optimize the acquisition geometry, different components of acquisitions were changed to investigate which one of the many possible configurations maximized the area under the combined ROC curve. Optimization was investigated under two acquisition dose conditions corresponding to a fixed total dose delivered to the patient and a variable dose condition, based on the number of projections used. In either case, the detectability was dependent on the number of projections used, the total angular span of those projections, and the acquisition dose level. In the first case, the detectability approximately followed a bell curve as a function of the number of projections with the maximum between 8 and 16 projections spanning angular arcs of about 23°−45°, respectively. In the second case, the detectability increased with the number of projections approaching an asymptote at 11-17 projections for an angular span of about 45°. These results indicate the inherent information content of the multiprojection image data reflecting the relative role of quantum and anatomical noise in multiprojection breast imaging. The optimization scheme presented here may be applied to any multiprojection imaging modalities and may be extended by including reconstruction in the case of digital breast tomosynthesis and breast computed tomography.

Optimized image acquisition for breast tomosynthesis in projection and reconstruction space

“…This behavior in performance for both imaging modes indicates an interplay of anatomical and quantum noise in the overall detection performance of a multiprojection system: The performance improves as system overcomes anatomical noise by using information from an increasing number of projections; however the influence of anatomical noise diminishes beyond a certain number of projections as the performance becomes quantum noise limited and therefore saturates. 13 While isoimage dose condition illustrates the trend in the performance of projection images and tomosynthesis, it does not delineate the role of the acquisition dose level on the optimization of the acquisition scheme. This is because an increase in the number of projections also increases the total delivered dose; the performance variation seen in Fig.…”

“…The lesion addition routine was based on an algorithm reported earlier. 13 Figure 1 shows example images of a mastectomy specimen acquired at Ϫ22°, 0°͑CC͒, and ϩ23°.…”

“…[19][20][21] The specific observer model-based methodology employed in this study has been reported previously in Ref. 13. Detectability was measured at each of the 25 angular projections, thus resulting in 25 ROC curves.…”

“…This technique used a priori information to fuse binary detection decisions from each of the angular projections. 13,22 The area under the combined ROC curve ͑AUC͒ was employed as an overall figure of merit representative of clinical performance of the projection images at that acquisition configuration.…”

“…As a key step toward that goal, we earlier proposed a mathematical observer-based framework to assess the effect of each of the acquisition parameters on the overall image quality of correlation imaging ͑CI͒ technique, a multiprojection imaging method based on projection images. 13 The framework was based only on projection images and did not incorporate reconstruction in its analysis and thus could not be directly applied to tomosynthesis. Also, the dose levels were limited to the maximum dose level per projection used in our ongoing clinical trial, and thus were significantly lower than a typical clinical dose level.…”