Hyperspectral angular domain imaging for ex-vivo breast tumor detection

ABSTRACT An a ngular domain spectr oscopic imaging system was built and validated using fresh ex vivo breast tissue samp les (~ 2 mm thick). The hyperspectral system consisted of a halogen lamp, collimation optics, scanning stage with controller, a silicon micro -machined micro -channel array, and a pushbroom spectral imager . As a proof of concept, spectral data cubes acquired from tissue samples were input into principal component analysis and M ahalanobis discriminant analysis to differentiate between spectral signatures of breast tumor and normal tissue . It is proposed that the results from training sets can be used to construct a set of classifiers to enable tumor detection in samples representative of the surgical margins. Keywords: Breast cancer; trans -illumination imaging; hyperspectral imaging, prin cipal component analysis 1. INTRODUCTION Breast conserving surgery (i.e. lumpectomy ) followed by radiation is considered the recommended surgical approach over mastectom y for women diagnosed with early breast cancer. A r ecent study of 112,154 women diagnos ed with stage I or II breast cancer compared lumpectomy/radiation (55%) versus mastectomy (45%) procedures and found that the survival rate for women who received lumpectomy/radiation w as more favorable regardless of age or cancer type [1] . Successful breast conserving surgery is directly dependent on complete removal of the tumor mass with clear margins [2] . Should tumor tissue be discovered at or nearby the margins, then a second (or sometimes third) surgery is required to clear the margins of tumor tissue. Recent studies have shown that typically 20 -40% of patients und ergoing lumpectomy require second surgeries because of a close or positive surgical margin diagnosed post -operatively [3] . The current gold standa rd for differentiating between normal and tumor tissue during surgery is by histopathology assessment that includes high -resolut ion microscopy of thin ly sliced and stained tissue. This process is time -consuming with a high chance of under -sampling . Many are as are left micro scopically uninspected since the microscopic field of view is limited. Th erefore, the intra -operative microscopy approach is not ideal for testing the entire three -dimensional volume which would be more desirable [4] as well as effective [5] . Alternatively, ex vivo specimen x-ray based imaging system s used at the point -of -care (e.g. Faxitron BioVision imaging system , Faxitron Bioptics, Tucson, AZ ) may substantially reduce re-excision rate s [8] . However, it is still difficult to identify the tumor margins efficiently in breast carcinomas with non -grossly recognizable abnormalities such as microcalcifications using x -ray based system s [9] . Also , compari son of x -ray procedures to frozen section analysis suggest that it is still not clear whether the x -ray radiography system prov ide s better margin detection accuracy during breast conservation therapy procedure s [10] . Many researchers have studied optical imaging due to its excellent tissue contrast compared to other imaging modalities. In the last decade, methods have been developed for intra -operative tumor margin detection utilizing diffuse reflectance spectroscopy [11] , intrinsic fluorescence spectroscopy [12] , optical coherence tomography [13] , Terahertz pulsed spectroscopy [14] , and Raman spectr oscopy [15] . It is known that a number of cancer types exhibit different spectral signature s compared to the surrounding normal tissue [16] [17] [18] . H yper spectral imaging with subsequent M ahalanobis discriminant analysis has be en applied to ex vivo unstained breast tumor samples from a small animal model [19] .