3 Optical Imaging in Interventional Procedures
Beyond diagnostic procedures, optical imaging technologies are of increasing
importance in current and future interventional medical techniques. For example,
in oncology, surgery is the primary treatment modality for most solid tumors.
Although optical imaging plays an essential role in cancer diagnosis and preoperative planning, during the surgery, the operating surgeon often depends on visual
appearance and manual palpation to differentiate between tumor and normal tissue
and to establish a sufficient tumor-free margin. Reliance on white light limits the
visual contrast apparent to the surgeon to a narrow dynamic range in the colorimetric
spectrum. Thus, limitations in specificity and sensitivity are a critical aspect of
oncologic surgeries, and real-time image guidance is highly desirable in the operating room [27–29].
In this review, we explain the concept of optical image-guided surgery in surgical
oncology. Image-guided surgery enables surgeons to perform surgery under the
guidance of live intraoperative images, wherein surgeons are able to track the
resection area on a monitor with reliable real-time feedback on any remaining
tumor tissues or other diseased areas, such as ischemia. Because of the delicate
nature and time sensitivity of surgery, the imaging time must be short, and image
processing must be rapid – essentially in real time, at high temporal resolution and
with minimal latency [30]. As a result, surgical procedures are easier to undertake
with greater certainty that the critical landmarks are secured. Tumor cells left behind
at the edge of the surgical resection area, defined as positive margins, result in
increased recurrence and poor prognosis for patients with head and neck cancer,
brain cancer, breast cancer, non-small cell lung cancer, colorectal cancer, and
urogenital tract cancer [31–38]. Image guidance allows careful identification of
primary and microscopic tumors and the complete removal of cancerous tissue [39].
Elevated cellular metabolism, increased expression of growth factor signaling
receptors, hypoxia, and increased tumor angiogenesis are common traits that sustain
the hyperproliferative potential of tumor cells. These biomarkers specific to cancer
cells or the tumor microenvironment potentially allow cancer to be distinguished
from normal tissue and could be exploited as potential targets to direct imaging
agents [28]. An approach to incorporate biomarker-targeted molecular imaging
agents in the imaging procedure improves the tumor-to-background signal ratio
needed for fast assessment of lesions [30, 40]. Ease of image acquisition, relatively
low-cost imaging devices, high resolution, and real-time applicability of imaging
agents for use in optical imaging methods are highly desirable for use in real-time
image-guided surgery [30]. However, there are substantial technical issues such as
specific tumor labeling, imaging system portability, and patient-like animal models
in which to develop the technology, which need to be addressed for image-guided
surgery going forward toward clinical use [41].
Image-Guided Surgery Fluorescence-guided surgery emerged as a technique
using fluorescence to visualize cancer cells to guide intraoperative procedures.
Classical fluorescent techniques primarily use probes in the visible light spectrum
The Present and Future of Optical Imaging Technologies in the Clinic:. . .
211
Beyond diagnostic procedures, optical imaging technologies are of increasing
importance in current and future interventional medical techniques. For example,
in oncology, surgery is the primary treatment modality for most solid tumors.
Although optical imaging plays an essential role in cancer diagnosis and preoperative planning, during the surgery, the operating surgeon often depends on visual
appearance and manual palpation to differentiate between tumor and normal tissue
and to establish a sufficient tumor-free margin. Reliance on white light limits the
visual contrast apparent to the surgeon to a narrow dynamic range in the colorimetric
spectrum. Thus, limitations in specificity and sensitivity are a critical aspect of
oncologic surgeries, and real-time image guidance is highly desirable in the operating room [27–29].
In this review, we explain the concept of optical image-guided surgery in surgical
oncology. Image-guided surgery enables surgeons to perform surgery under the
guidance of live intraoperative images, wherein surgeons are able to track the
resection area on a monitor with reliable real-time feedback on any remaining
tumor tissues or other diseased areas, such as ischemia. Because of the delicate
nature and time sensitivity of surgery, the imaging time must be short, and image
processing must be rapid – essentially in real time, at high temporal resolution and
with minimal latency [30]. As a result, surgical procedures are easier to undertake
with greater certainty that the critical landmarks are secured. Tumor cells left behind
at the edge of the surgical resection area, defined as positive margins, result in
increased recurrence and poor prognosis for patients with head and neck cancer,
brain cancer, breast cancer, non-small cell lung cancer, colorectal cancer, and
urogenital tract cancer [31–38]. Image guidance allows careful identification of
primary and microscopic tumors and the complete removal of cancerous tissue [39].
Elevated cellular metabolism, increased expression of growth factor signaling
receptors, hypoxia, and increased tumor angiogenesis are common traits that sustain
the hyperproliferative potential of tumor cells. These biomarkers specific to cancer
cells or the tumor microenvironment potentially allow cancer to be distinguished
from normal tissue and could be exploited as potential targets to direct imaging
agents [28]. An approach to incorporate biomarker-targeted molecular imaging
agents in the imaging procedure improves the tumor-to-background signal ratio
needed for fast assessment of lesions [30, 40]. Ease of image acquisition, relatively
low-cost imaging devices, high resolution, and real-time applicability of imaging
agents for use in optical imaging methods are highly desirable for use in real-time
image-guided surgery [30]. However, there are substantial technical issues such as
specific tumor labeling, imaging system portability, and patient-like animal models
in which to develop the technology, which need to be addressed for image-guided
surgery going forward toward clinical use [41].
Image-Guided Surgery Fluorescence-guided surgery emerged as a technique
using fluorescence to visualize cancer cells to guide intraoperative procedures.
Classical fluorescent techniques primarily use probes in the visible light spectrum
The Present and Future of Optical Imaging Technologies in the Clinic:. . .
211