Dynamic contrast in scanning microscopic OCT.

While optical coherence tomography (OCT) provides a resolution down to 1 µm, it has difficulties in visualizing cellular structures due to a lack of scattering contrast. By evaluating signal fluctuations, a significant contrast enhancement was demonstrated using time-domain full-field OCT (FF-OCT), which makes cellular and subcellular structures visible. The putative cause of the dynamic OCT signal is the site-dependent active motion of cellular structures in a sub-micrometer range, which provides histology-like contrast. Here we demonstrate dynamic contrast with a scanning frequency-domain OCT (FD-OCT), which we believe has crucial advantages. Given the inherent sectional imaging geometry, scanning FD-OCT provides depth-resolved images across tissue layers, a perspective known from histopathology, much faster and more efficiently than FF-OCT. Both shorter acquisition times and tomographic depth-sectioning reduce the sensitivity of dynamic contrast for bulk tissue motion artifacts and simplify their correction in post-processing. Dynamic contrast makes microscopic FD-OCT a promising tool for the histological analysis of unstained tissues.

Dynamic microscopic optical coherence tomography to visualize the morphological and functional micro-anatomy of the airways.

In the imaging of airway tissue, optical coherence tomography (OCT) provides cross-sectional images of tissue structures, shows cilia movement and mucus secretion, but does not provide sufficient contrast to differentiate individual cells. By using fast sequences of microscopic resolution OCT (mOCT) images, OCT can use small signal fluctuations to overcome lack in contrast and speckle noise. In this way, OCT visualizes airway morphology on a cellular level and allows the tracking of the dynamic behavior of immune cells, as well as mucus transport and secretion. Here, we demonstrate that mOCT, by using temporal tissue fluctuation as contrast (dynamic mOCT), provides the possibility to study physiological and pathological tissue processes in vivo.

Microscopic optical coherence tomography (mOCT) at 600 kHz for 4D volumetric imaging and dynamic contrast.

Volumetric imaging of dynamic processes with microscopic resolution holds a huge potential in biomedical research and clinical diagnosis. Using supercontinuum light sources and high numerical aperture (NA) objectives, optical coherence tomography (OCT) achieves microscopic resolution and is well suited for imaging cellular and subcellular structures of biological tissues. Currently, the imaging speed of microscopic OCT (mOCT) is limited by the line-scan rate of the spectrometer camera and ranges from 30 to 250 kHz. This is not fast enough for volumetric imaging of dynamic processes in vivo and limits endoscopic application. Using a novel CMOS camera, we demonstrate fast 3-dimensional OCT imaging with 600,000 A-scans/s at 1.8 µm axial and 1.1 µm lateral resolution. The improved speed is used for imaging of ciliary motion and particle transport in ex vivo mouse trachea. Furthermore, we demonstrate dynamic contrast OCT by evaluating the recorded volumes rather than en face planes or B-scans. High-speed volumetric mOCT will enable the correction of global tissue motion and is a prerequisite for applying dynamic contrast mOCT in vivo. With further increase in imaging speed and integration in flexible endoscopes, volumetric mOCT may be used to complement or partly replace biopsies.

Totally laparoscopic creation of a novel stapled orthotopic neobladder in the porcine model.

PURPOSE: Laparoscopic urinary diversion remains difficult and time consuming even when performed by experienced laparoscopists. Here we describe a novel procedure that quickly creates an ileal orthotopic neobladder with an afferent tubular segment using a laparoscopic stapling device. MATERIALS AND METHODS: Laparoscopic cystectomy and stapled ileal neobladder were performed in five domestic juvenile pigs. Following cystectomy, 30 to 40 cm of terminal ileum was harvested, and ileal continuity restored. The harvested ileum was made into a J configuration, and three to seven laparoscopic staple firings were used to create a spherical pouch with an afferent limb modeled after the Studer-type neobladder. An aperture was created in the dependent portion of the neobladder, and urethral anastomosis was performed using six interrupted absorbable sutures. Ureterointestinal anastomosis was performed using a Wallace technique. Postoperative cystography and intravenous pyelography were performed. A 1-month survival study was completed in one pig. RESULTS: All five procedures were completed successfully without conversion to open surgery. The majority of the steps of the procedures were performed by second- and third-year urology residents (PGY 3-4). Neobladder stapling, ureterointestinal anastomosis, and the first three urethral sutures were performed by an endourology fellow. Average time for neobladder creation and entire procedure was 78 and 355 minutes, respectively. Postoperative cystography revealed spherical orthotopic neobladder with minimal or no leakage in all animals. Average neobladder capacity was 100 mL, and no obstruction was visualized on intravenous pyelography immediately after the procedures. One pig successfully survived the 1-month study period. There was excellent neobladder storage, no clinically apparent renal obstruction, and no postoperative complications. CONCLUSIONS: Total laparoscopic urinary diversion and specifically orthotopic neobladder remains one of the frontiers of minimally invasive urologic surgery. Our technique for stapled ileal neobladder provides substantial advantages in terms of the operative time required for orthotopic neobladder reconstruction. This may offer an avenue to foster the development of more feasible techniques for laparoscopic urinary tract reconstructive surgery.

Noncontact holographic detection for photoacoustic tomography.

A holographic method for high-speed, noncontact photoacoustic tomography is introduced and evaluated. Relative changes of the object's topography, induced by the impact of thermoelastic pressure waves, were determined at nanometer sensitivity without physical contact. The object's surface was illuminated with nanosecond laser pulses and imaged with a high-speed CMOS camera. From two interferograms measured before and after excitation of the acoustic wave, surface displacement was calculated and then used as the basis for a tomographic reconstruction of the initial pressure caused by optical absorption. The holographic detection scheme enables variable sampling rates of the photoacoustic signal of up to 50 MHz. The total acquisition times for complete volumes with 230 MVoxel is far below 1 s. Measurements of silicone and porcine skin tissue phantoms with embedded artificial absorbers, which served as a model for human subcutaneous vascular networks, were possible. Three-dimensional reconstructions of the absorbing structures show details with a diameter of 310 µm up to a depth of 2.5 mm. Theoretical limitations and the experimental sensitivity, as well as the potential for in vivo imaging depending on the detection repetition rate, are analyzed and discussed.

Full-field speckle interferometry for non-contact photoacoustic tomography.

A full-field speckle interferometry method for non-contact and prospectively high speed Photoacoustic Tomography is introduced and evaluated as proof of concept. Thermoelastic pressure induced changes of the objects topography are acquired in a repetitive mode without any physical contact to the object. In order to obtain high acquisition speed, the object surface is illuminated by laser pulses and imaged onto a high speed camera chip. In a repetitive triple pulse mode, surface displacements can be acquired with nanometre sensitivity and an adjustable sampling rate of e.g. 20 MHz with a total acquisition time far below one second using kHz repetition rate lasers. Due to recurring interferometric referencing, the method is insensitive to thermal drift of the object due to previous pulses or other motion. The size of the investigated area and the spatial and temporal resolution of the detection are scalable. In this study, the approach is validated by measuring a silicone phantom and a porcine skin phantom with embedded silicone absorbers. The reconstruction of the absorbers is presented in 2D and 3D. The sensitivity of the measurement with respect to the photoacoustic detection is discussed. Potentially, Photoacoustic Imaging can be brought a step closer towards non-anaesthetized in vivo imaging and new medical applications not allowing acoustic contact, such as neurosurgical monitoring or burnt skin investigation.