An Evaluation of a Self-contained Direct Digital Radiography System for Breast Specimen Imaging

Specimen imaging is an accepted method for evaluating tissue specimens which are obtained either through minimally-invasive breast needle biopsy (MIBB) or breast surgery. Specimen imaging is used to confirm the targeting and sampling adequacy of radiographically apparent breast abnormalities. Specimen images are acquired and then compared to the routine and diagnostic imaging to provide radiographic evidence that the index lesion was adequately targeted and sampled (as in the case of MIBB) or targeted and removed with adequate margins \[as in the case of breast surgical specimens (BSS)\]. Specimen imaging also provides guidance to the histopathologist when evaluating the breast specimen. Near real-time image acquisition, review and feedback is essential for specimen imaging. The patient typically remains in compression on the biopsy table for MIBB or under anesthesia for BSS until the clinician has confirmation that the index abnormality has been adequately sampled (in the case of MIBB) or surgically excised. For this reason, digital techniques are favored over analog (film) counterparts because of the immediacy of image acquisition and transfer and display to the radiologist for review. Image quality and speed are critical factors in specimen imaging. High resolution images are a clinical requirement to delineate the features and extent of mass lesions, and presence and extent of microcalcifications. Conventional full-field digital (FFDM) mammographic equipment located in the mammography department is one accepted approach for specimen imaging. An advantage of this method is that a licensed and skilled mammographic technologist assures the adequate exposure of specimens. However, this method requires that the FFDM system be free at the time the specimen arrives in the mammography department, interfering with mammogram schedules. In the case of BSS, the use of conventional FFDM systems additionally requires the transport of specimens to the mammography department, adding significant time that the patient is under anesthesia. Another mode for specimen radiography is self-contained digital radiography specimen imaging systems that are located in the mammography department or in the Operating Room (intraoperative). The use of self-contained digital systems frees the conventional mammography system for its intended purpose, while providing the clinician all the speed of digital radiography. It has been shown that intraoperative imaging significantly reduces the amount of time that the patient is under anesthesia. Although, self-contained digital radiography specimen imaging systems provide an advantage in speed, resulting images may suffer in image quality and despite the availability of intraoperative self contained systems, many clinicians choose to transfer specimens to the mammography department for imaging on a conventional FFDM system. Current specimen radiography systems employ an indirect digital technique, a two step conversion, where incoming x-ray signal is converted to light and then to digital signal. The intermediate step of converting signal to light, leads to diffusion and scatter over many pixels and this in turn leads to degradation of the very fine features of mass densities and microcalcifications. Direct Digital technique is another method currently used in breast imaging. The direct digital technique has the advantage of converting incoming signal directly to digital signal, avoiding the intermediary light conversion phase of indirect exposure. The direct to digital process results in better use of incoming signal and greater resolution and thus a sharper image, providing high resolution of minute features associated with mass lesions and microcalcifications. Another common characteristic of current self-contained systems is the use of "stitching" many small CMOS chips to create a larger image detector. This type of tiling provides for a more economical system, but shearing effects, gaps between chips and overall concerns with calibration of multiple chips significantly degrades image quality. All digital images, indirect or direct are acquired in a raw state and processed to allow review. While image processing cannot improve or change the raw aspects of the image after acquisition, processing can improve the visibility of features available in the image. Image processing is fundamentally associated with image acquisition technique. If the image is not adequately exposed, image processing will not be optimally applied and in some cases fail, requiring additional imaging.