Current Medical Imaging - Volume 8, Issue 3, 2012

Diffuse optical imaging (DOI) of the brain has emerged as a new neuroimaging technique that is seeing growing applications in brain research. The technique's simplicity, lower cost and applicability to children have contributed to its popularity. However, the translation of DOI to clinically relevant scenarios has lagged. Poor quantification of local hemodynamic changes based on optical signals remains a major hurdle and significant efforts are still being pursued to better understand how to recover accurate images of functional activation and generate statistical maps, and to identify the limitations of DOI. This paper reviews the underlying principles of brain DOI and applications that may find a niche in the clinic.

Optical coherence tomography (OCT) can perform high-speed, micron-level high resolution imaging of tissue microstructures in vivo and in real time and can function as a type of optical biopsy to visualize the structural and functional alterations associated with various diseases. The advances in endoscopic OCT and optical coherence microscopy (OCM) provide an exciting avenue for many promising clinical applications with the potential of enhancing diagnostic capabilities and treatment efficacies. In this review paper, we first review the basic principles for time- and Fourierdomain OCT. We then survey the various endoscopic OCT technologies followed by the review of several representative clinical applications using endoscopic OCT. Lastly, we discuss endoscopic-OCT-based, multi-modality imaging approaches and their translational potentials.

The development and clinical application of a novel near-infrared diffuse correlation spectroscopy (DCS) have been reviewed in this paper. DCS measures speckle fluctuations of near-infrared diffuse light in tissue, which are sensitive to the motions of red blood cells. DCS offers several new features which make it appealing for blood flow measurement such as noninvasiveness, high temporal resolution (up to 100 Hz), portability, and relatively large penetration depth (up to ~1.5 centimeters). DCS technology can be utilized for bedside monitoring of tissue blood flow as exemplified by applications involving tumors, brains, and skeletal muscles. In these investigations, DCS measurements show promise for quantification of tissue hemodynamic status, for diagnosis of vascular-related diseases (e.g., cancers, stroke, peripheral arterial disease), and for continuous monitoring and evaluation of therapeutic effects (e.g., chemotherapy, radiation therapy, photodynamic therapy, arterial revascularization).

The use of fluorescence detection for surgical applications has grown significantly over the last two decades through advances in fluorescent markers, instrumentation and data processing methods. Synergistic combinations of these developments have produced optical methods that provide biochemical, structural and functional information during surgical procedures. In this review, we focus on the surgical methods used clinically for in vivo fluorescence detection. An introduction to basic principles, including the characteristics of fluorescent molecules and intrinsic tissue optical properties, is provided along with an overview of the instrumentation being deployed in the operating room (OR). The intraoperative fluorescent contrast mechanisms currently available in the OR are presented. Discussion is followed by a detailed organ-system summary of clinical research involving in vivo fluorescence detection during surgery. While the emphasis is on clinical applications, a growing body of pre-clinical studies is leading to the discovery of more sensitive and specific molecular fluorescent makers of disease as well as the development of cutting-edge optical technology poised to make its way into the clinical setting.

Progress with technology and regulatory approvals has recently allowed the successful clinical translation of fluorescence molecular imaging to intra-operative applications. Initial studies have demonstrated a promising outlook for imaging cancer micro-foci, margins and lymph-nodes. However, not all surgeries will benefit equally from fluorescence guidance. This review paper outlines the clinical necessity for improving surgical procedures in the most prevalent solid tumors worldwide, demarcates major challenges currently encountered intra-operatively and outlines the role of imaging fluorescent agents during the operation.

Diffuse optical imaging (DOI) techniques provide a non-invasive, low cost and sensitive method for assessing the functional state of the human breast. Several studies undertaken in recent years with the objective of investigating the clinical applications of diffuse optical methods, demonstrate the potential of the technique for screening for breast cancer, associated risk factors and for monitoring the efficacy of therapeutic regimen post-diagnosis. In this review, the different diffuse optical methods and instrumentation used in the functional imaging of the breast are described and the results of the clinical studies of the healthy and diseased breast are provided. Moreover, the application of optical imaging in monitoring neo-adjuvant chemotherapy is summarized, the role of alternate contrast mechanisms in optical imaging is outlined and lastly, the role of optical imaging in multimodal imaging – wherein optical imaging is combined with existing clinical imaging modalities providing complementary diagnostic information – is discussed.