Costas Pitris

In vivo ultrahigh-resolution optical coherence tomography

Ultrahigh-resolution optical coherence tomography (OCT) by use of state of the art broad-bandwidth femtosecond laser technology is demonstrated and applied to in vivo subcellular imaging. Imaging is performed with a Kerr-lens mode-locked Ti:sapphire laser with double-chirped mirrors that emits sub-two-cycle pulses with bandwidths of up to 350 nm, centered at 800 nm. Longitudinal resolutions of ~1mum and transverse resolution of 3mum, with a 110-dB dynamic range, are achieved in biological tissue. To overcome depth-of-field limitations we perform zone focusing and image fusion to construct a tomogram with high transverse resolution throughout the image depth. To our knowledge this is the highest longitudinal resolution demonstrated to date for in vivo OCT imaging.

High resolution in vivo intra-arterial imaging with optical coherence tomography

BACKGROUND Optical coherence tomography (OCT) is a new method of catheter based micron scale imaging. OCT is analogous to ultrasound, measuring the intensity of backreflected infrared light rather than sound waves. OBJECTIVE To demonstrate the ability of OCT to perform high resolution imaging of arterial tissue in vivo. METHODS OCT imaging of the abdominal aorta of New Zealand white rabbits was performed using a 2.9 F OCT imaging catheter. Using an ultrashort pulse laser as a light source for imaging, an axial resolution of 10 μm was achieved. RESULTS Imaging was performed at 4 frames/second and data were saved in either super VHS or digital format. Saline injections were required during imaging because of the signal attenuation caused by blood. Microstructure was sharply defined within the arterial wall and correlated with histology. Some motion artefacts were noted at 4 frames/second. CONCLUSIONS In vivo imaging of the rabbit aorta was demonstrated at a source resolution of 10 μm, but required the displacement of blood with saline. The high resolution of OCT allows imaging to be performed near the resolution of histopathology, offering the potential to have an impact both on the identification of high risk plaques and the guidance of interventional procedures.

Imaging needle for optical coherence tomography

We describe a miniature optical coherence tomography (OCT) imaging needle that can be inserted into solid tissues and organs to permit interstitial imaging of their internal microstructures with micrometer scale resolution and minimal trauma. A novel rotational coupler with a glass capillary tube is also presented that couples light from a rotating single-mode fiber to a stationary one. A prototype needle with a 27-gauge (approximately 410-microm) outer diameter has been developed and is demonstrated for in vivo imaging. The OCT needle can be integrated with standard excisional biopsy devices and used for OCT-guided biopsy.

Forward-imaging instruments for optical coherence tomography.

We discuss the design and implementation of forward-imaging instruments for optical coherence tomography (OCT), which require the delivery, scanning, and collection of single-spatial-mode optical radiation. A hand-held surgical probe for use in open surgery can provide cross-sectional images of subsurface tissue before surgical incisions are made. A rigid laparoscope for minimally invasive surgical OCT imaging provides a simultaneous enface view of the area being imaged. OCT imaging is demonstrated on in vitro human specimens.

Feasibility of optical coherence tomography for high-resolution imaging of human gastrointestinal tract malignancies

Abstract: Optical coherence tomography (OCT) is a new imaging technology which can perform high-resolution, cross-sectional imaging of the internal microstructure of biological tissues. OCT is analogous to ultrasound, except that it measures the intensity of back-reflected infrared light rather than sound waves. OCT performs two- and three-dimensional imaging of tissue microstructure in situ and in real time. It can achieve image resolutions approaching the cellular level over approximately the same imaging depths as a conventional biopsy. In this article we examine the feasibility of OCT for high-resolution imaging of gastrointestinal malignancies with ex-vivo imaging of normal and pathologic microstructures. Tissue, both normal and neoplastic, was obtained from patients undergoing surgical resection after an initial diagnosis of a gastrointestinal malignancy. The tissue samples were imaged prior to fixation using a laboratory OCT system. The OCT system consists of a fiber optic-based Michelson interferometer, a commercially available amplified superluminscent light source, and a computer for data acquisition. The images were subsequently compared with histological cross-sections corresponding to the imaged areas. The stratified squamous epithelium of the normal esophagus was clearly visible in the OCT images and contrasted to the disorganized and non-uniform nature of the mucosal layers of Barretts esophagus and squamous carcinoma. The columnar epithelial morphology as well as other mucosal structures in normal colon were distinctly visible using OCT. In contrast, disorganization of the normal mucosal layers and ulcerative lesions were identified in tissues from ulcerative colitis and adenocarcinoma of the colon. The ability of OCT to image tissue microstructure at high resolutions makes it a potentially powerful technology for minimally invasive assessment of the gastrointestinal tract and the evaluation of early neoplastic changes.

Optical Coherence Tomography for Neurosurgical Imaging of Human Intracortical Melanoma

OBJECTIVE Intraoperative identification of brain tumors and tumor margins has been limited by either the resolution of the in vivo imaging technique or the time required to obtain histological specimens. Our objective was to evaluate the feasibility of using optical coherence tomography (OCT) as a high-resolution, real-time intraoperative imaging technique to identify an intracortical melanoma. INSTRUMENTATION OCT is a new, noncontact, high-speed imaging technology capable of resolutions on the micrometer scale. OCT is analogous to ultrasound B-mode imaging, except that reflections of infrared light, rather than sound, are detected. OCT uses inherent tissue contrast, rather than enhancement with dyes, to differentiate tissue types. The compact, fiberoptic-based design is readily integrated with surgical instruments. METHODS A portable handheld OCT surgical imaging probe has been constructed for imaging within the surgical field. Cadaveric human cortex with metastatic melanoma was harvested and imaged in two and three dimensions. Changes in optical backscatter intensity were used to identify regions of tumor and to locate tumor margins. Structures within the optical coherence tomographic images were compared with the histological slides. RESULTS Two-dimensional images showed increased optical backscatter from regions of tumor, which was quantitatively used to determine the tumor margin. The images correlated well with the histological findings. Three-dimensional reconstructions revealed regions of tumor penetrating normal cortex and could be resectioned at arbitrary planes. Subsurface cerebral vascular structures could be identified and were therefore avoided. CONCLUSION OCT can effectively differentiate normal cortex from intracortical melanoma based on variations in optical backscatter. The high-resolution, high-speed imaging capabilities of OCT may permit the intraoperative identification of tumor and the more precise localization of tumor margins.

High-resolution imaging of gynecologic neoplasms using optical coherence tomography

BACKGROUND A modality capable of imaging the female reproductive tract, at or near the cellular level, could lead to the detection of diseases at earlier stages than currently possible. Optical coherence tomography achieves high resolutions in the cellular range (4-20 microm) and could accomplish that level of detection. METHOD Optical coherence tomography imaging of gynecologic tissue was studied in vitro on normal and neoplastic human cervical and uterine tissue. EXPERIENCE The structures of the normal ectocervix and endocervix, including epithelium, basal membrane, and glands, were identified clearly. These findings were compared with changes associated with carcinoma in situ and invasive carcinoma. The optical coherence tomography images of the uterus also showed changes between microstructural features of normal tissue and endometrial adenocarcinoma. CONCLUSION Optical coherence tomography of tissue microstructures showed potential for powerful, minimally invasive assessment of the female reproductive tract at a resolution greater than any current clinical imaging method.

Ultrahigh resolution in vivo versus ex vivo OCT imaging and tissue preservation

Summary form only given. Many previous studies have compared ex vivo OCT imaging to histopathology. While some tissues, such are arterial pathology or cartilage, are relatively stable post mortem, others, such as epithelial tissues, exhibit rapid degradation. It is therefore important to preserve these tissues with minimal changes in morphology. The goal of this study is to investigate the difference between in vivo and ex vivo OCT imaging and the effect of different preservation solutions on image quality using the hamster cheek pouch. The hamster cheek pouch was chosen because of its easy access and because it is a well established model for carcinogenesis and cancer progression. The advent of the ultrahigh resolution OCT imaging technology is important for this study because it enables changes in tissue morphology to be dearly visualized which may have been difficult to resolve with standard resolution OCT imaging.

Fluorescence spectroscopy of the cervix: influence of acetic acid, cervical mucus, and vaginal medications.

Fluorescence spectroscopy has been shown to provide information useful in the detection of cervical dysplasia. The goal of this study was to determine if substances found on the cervix such as acetic acid, mucus, and vaginal medications can influence the fluorescence in the spectral region useful for discriminating normal cervical tissue from abnormal tissue.

High resolution imaging of endometriosis and ovarian carcinoma with optical coherence tomography: feasibility for laparoscopic-based imaging

High resolution imaging of gynaecological tissue offers the potential for identifying pathological changes at early stages when interventions are more effective. Optical coherence tomography (OCT) is a high resolution high speed optical imaging technology which is analogous to ultrasound B–mode imaging except reflections of light are detected rather than sound. The OCT technology is capable of being integrated with laparoscopy for real–time subsurface imaging. In this report, the feasibility of OCT for differentiating normal and pathologic laparoscopically–accessible gynaecologic tissue is demonstrated. Differentiation is based on architectural changes of in vitro tissue morphology. OCT has the potential to improve conventional laparoscopy by enabling subsurface imaging near the level of histopathology.