An important component of the treatment process for many women undergoing breast cancer surgery is reconstruction, wherein surgical procedures are used to rebuild the breast after partial or total mastectomy. Breast reconstruction is integral to improving the cancer survivor’s quality of life, as it can provide psychological benefits related to improvements in body image, self-esteem and depression. The primary aim of reconstruction is to optimize the physical appearance (morphology) of the surgically altered breasts. Breast morphology is described in terms of physical characteristics such as shape, position and appearance, symmetry, and ptosis.1
Standards for breast reconstruction have evolved, and patients and surgeons alike strive to achieve the most optimal cosmetic outcome particularly in terms of symmetry and natural appearance of the breasts. Although, the conventional practice is to qualitatively evaluate breast appearance following reconstructive surgery, there is growing interest in developing new methods for providing an objective quantitative assessment of outcome (i.e., breast morphology in terms of quantitative measures). Reconstructive outcomes can be evaluated using direct anthropometry,2,3
and measurements using three-dimensional (3D) data (or stereophotogrammetry).8–10
Stereophotogrammetry, a practice of determining the geometric properties of an object by measuring defined fiducial (landmark) points on a 3D image of the object, has gained considerable interest in plastic surgery. Because this form of imaging is non-invasive and images can be obtained and processed quickly,11
it has made possible the evaluation of various quantitative measures describing breast shape, symmetry and volume.11–16
Typically, distances between fiducial points, or the ratios of such distances have been proposed as measurements for estimating the structural characteristics of the breast, such as symmetry, projection, proportion and ptosis. Methods of this type have been successfully implemented in the field of breast conservation therapy.6,7,11–16
The ultimate goal of these studies is to objectively quantify the correlation of various patient demographics and treatment parameters with outcome (i.e., the morphology of the reconstructed breast).7
The effectiveness of 3D assessments in terms of the quantitative distances computed depends on the measurement technique. Key methodological factors include the influences of imaging equipment (scanner alignment and calibration, etc.), and subject factors (movement, regaining a certain position, skin properties, etc.). Most equipment manufacturers include stringent calibration and alignment protocols to minimize equipment related artifacts. However, factors influenced due to human interactions need to be addressed both at the user’s (i.e., operator in the clinic), and the subject’s end. Due to the geometry of the breast region, quantitative analyses of characteristics such as symmetry may be of limited usefulness in evaluating factors related to morphological outcome if the measurements are compromised due to human influences. The key subject influence is movement and is typically addressed by requesting the subject to remain still during image acquisition or via simple image based adjustments retrospectively. Furthermore, improved high resolution 3D imaging systems are now available (3dMDTorso™
, 3Q Technologies, Atlanta, GA) that enable high speed (~1.5 ms) image capture which eliminates most artifacts related to subject movement. Similarly, user (operator) related errors are eliminated by the implementation of user-friendly single “click and capture” operation. Thus, the only remaining human influence is related to the differences in breast shape and sizes among women, which imposes a need to establish appropriate acquisition protocols in terms of pose. Previous studies have considered the influence of subject movement on imaging and quantitative measurements, but the impact of pose on quantitative assessment of breast appearance has been less studied and standards for subject positioning have not been defined. In some of the previous studies involving volume measurements,12,16
the arms raised pose is suggested to be preferred; but no data are presented to corroborate the claim.
In this study, we evaluate the influence of subject pose during image acquisition on some objective measures used for quantitative assessment of breast appearance. At present, the most widely used measure for assessing breast symmetry is the Breast Retraction Assessment (BRA) index, introduced by Pezner et al.,17
and refined by Van Limberger et al.,18
as the Percentage Breast Retraction Assessment (pBRA) index. The pBRA measure is normalized to account for images acquired at different magnifications. In this study, we introduce an extension of the pBRA index to three-dimensions; namely the 3D pBRA for stereophotogrammetry and employ it to evaluate the effect of pose on quantification of breast morphology. First, we present data to validate the newly introduced 3D pBRA index, and second, apply 3D pBRA to study the impact of pose on quantitative assessment of symmetry. In order to address these questions, we used both 3D and 2D images of the subject’s torso. Photographs (2D images) were included in this study for calculation of 2D pBRA, which provided the reference for validation of 3D pBRA. Multiple observers annotated fiducial points on both 3D and 2D images to compute: 1) the contoured distance between the fiducial points marked on the surface of the 3D images and 2) the line-of-sight (Euclidean) distance between the fiducial points marked on clinical photographs. The contoured distances were used to compute the 3D pBRA index, whereas the Euclidean distances were used to compute the 2D pBRA index. Statistical analyses were performed to validate the 3D pBRA index and to quantify the influence of pose on the same.