Biomedical Engineering Reference
In-Depth Information
field, while the main OCT instrument can be remotely located in the surgi-
cal suite. The use of OCT in image-guided surgical procedures represents a
paradigm shift for the surgical oncology community. While the surgical on-
cologist typically resects macroscopic solid tumors, consideration must still
be given to the microscopic, cellular extent of the disease. To address this,
surgeons typically resect with large margins in an effort to remove any occult
cells or nests of tumor. Resected tissue is sent to the surgical pathology lab
where margins are examined following histological processing to ensure that
they are clean. During this time, a fully staffed operating room and anes-
thetized patient must often wait for the decision on these margins. Therefore,
moving the high-resolution microscopic imaging of tumor margins from the
surgical pathology lab into the operating room would represent a substantial
reduction in costs, including time, costs, and patient health. The use of OCT
for examining tumor margins has many advantages, as well as introducing
new challenges. Large surface areas (and three-dimensional volumes) of tissue
must be examined in real-time at micron resolutions. Improvements in data
management, acquisition rates, automated tissue identification, and zooming
capabilities all must be addressed.
An example of the use of OCT for identifying tumors at varying stages is
shown in Fig. 8.11. Using a well-characterized carcinogen-induced rat mam-
mary tumor model that mimics the progression and histological findings of
human ductal carcinoma of the breast, OCT images were acquired at varying
time-points and compared to corresponding histology [67]. In good agreement,
the OCT images identify not only late-stage morphological changes and the
clear tumor margin, but also early ductal changes and evidence of abnormal
cells located away from the primary tumor.
A portable OCT system has been constructed for intraoperative imaging of
surgical margins following lumpectomy procedures for the surgical treatment
of breast cancer (Fig. 8.12). Different OCT biopsy needles have also been con-
structed for imaging into solid tumors or for guiding needle-biopsy procedures
in breast cancer [28] (Fig. 8.12). Ongoing intraoperative and image-guided
procedure studies are underway to determine the sensitivity and specificity of
OCT compared with the gold-standard histopathological analysis.
8.8 Optical Coherence Tomography Contrast Agents
When imaging biological tissues, it is often desirable to enhance the signals
measured from specific structures. Contrast agents that produce a specific
image signature have been utilized in virtually every imaging modalities, in-
cluding ultrasound, computed tomography, magnetic resonance imaging, and
optical microscopy, among many others. There are multiple optical properties
that are amenable for generating contrast in optical images, including OCT
images (Fig. 8.13). Recently, new engineered contrast agents and molecular
contrast techniques specifically designed for OCT have been developed and
