Tissue phantoms in multicenter clinical trials for diffuse optical technologies

Tissue simulating phantoms are an important part of instrumentation validation, standardization/training and clinical translation. Properly used, phantoms form the backbone of sound quality control procedures. We describe the development and testing of a series of optically turbid phantoms used in a multi-center American College of Radiology Imaging Network (ACRIN) clinical trial of Diffuse Optical Spectroscopic Imaging (DOSI). The ACRIN trial is designed to measure the response of breast tumors to neoadjuvant chemotherapy. Phantom measurements are used to determine absolute instrument response functions during each measurement session and assess both long and short-term operator and instrument reliability

Paxillin Dynamics Measured during Adhesion Assembly and Disassembly by Correlation Spectroscopy

Paxillin is an adaptor molecule involved in the assembly of focal adhesions. Using different fluorescence fluctuation approaches, we established that paxillin-EGFP is dynamic on many timescales within the cell, ranging from milliseconds to seconds. In the cytoplasmic regions, far from adhesions, paxillin is uniformly distributed and freely diffusing as a monomer, as determined by single-point fluctuation correlation spectroscopy and photon-counting histogram analysis. Near adhesions, paxillin dynamics are reduced drastically, presumably due to binding to protein partners within the adhesions. The photon-counting histogram analysis of the fluctuation amplitudes reveals that this binding equilibrium in new or assembling adhesions is due to paxillin monomers binding to quasi-immobile structures, whereas in disassembling adhesions or regions of adhesions, the equilibrium is due to exchange of large aggregates. Scanning fluctuation correlation spectroscopy and raster-scan image correlation spectroscopy analysis of laser confocal images show that the environments within adhesions are heterogeneous. Relatively large adhesions appear to slide transversally due to a treadmilling mechanism through the addition of monomeric paxillin at one side and removal of relatively large aggregates of proteins from the retracting edge. Total internal reflection microscopy performed with a fast acquisition EM-CCD camera completes the overall dynamic picture and adds details of the heterogeneous dynamics across single adhesions and simultaneous bursts of activity at many adhesions across the cell

Paxillin dynamics measured during adhesion assembly and disassembly by correlation spectroscopy.

Paxillin is an adaptor molecule involved in the assembly of focal adhesions. Using different fluorescence fluctuation approaches, we established that paxillin-EGFP is dynamic on many timescales within the cell, ranging from milliseconds to seconds. In the cytoplasmic regions, far from adhesions, paxillin is uniformly distributed and freely diffusing as a monomer, as determined by single-point fluctuation correlation spectroscopy and photon-counting histogram analysis. Near adhesions, paxillin dynamics are reduced drastically, presumably due to binding to protein partners within the adhesions. The photon-counting histogram analysis of the fluctuation amplitudes reveals that this binding equilibrium in new or assembling adhesions is due to paxillin monomers binding to quasi-immobile structures, whereas in disassembling adhesions or regions of adhesions, the equilibrium is due to exchange of large aggregates. Scanning fluctuation correlation spectroscopy and raster-scan image correlation spectroscopy analysis of laser confocal images show that the environments within adhesions are heterogeneous. Relatively large adhesions appear to slide transversally due to a treadmilling mechanism through the addition of monomeric paxillin at one side and removal of relatively large aggregates of proteins from the retracting edge. Total internal reflection microscopy performed with a fast acquisition EM-CCD camera completes the overall dynamic picture and adds details of the heterogeneous dynamics across single adhesions and simultaneous bursts of activity at many adhesions across the cell

Detection of cerebral ischemia in neurovascular surgery using quantitative frequency-domain near-infrared spectroscopy.

ObjectThere is great value in monitoring for signs of ischemia during neurovascular procedures. Current intraoperative monitoring techniques provide real-time feedback with limited accuracy. Quantitative frequency-domain near-infrared spectroscopy (Q-NIRS) allows measurement of tissue oxyhemoglobin (HbO2), deoxyhemoglobin (HHb), and total hemoglobin (tHb) concentrations and brain tissue oxygen saturation (SO2), which could be useful when monitoring for evidence of intraoperative ischemia.MethodsUsing Q-NIRS, the authors monitored 25 neurovascular procedures including aneurysm clip placement, arteriovenous malformation resection, carotid endarterectomy, superficial temporal artery-middle cerebral artery (MCA) bypass surgery, external carotid artery-MCA bypass surgery, encephaloduromyosynangiosis, and balloon occlusion testing. The Q-NIRS technology provides measurable cerebral oxygenation values independent from those of the scalp tissue. Thus, alterations in the variables measured with Q-NIRS quantitatively reflect cerebral tissue perfusion. Bilateral monitoring was performed in all cases. Five of the patients exhibited evidence of clinical ischemic events during the procedures. One patient suffered blood loss with systemic hypotension and developed diffuse brain edema intraoperatively, one patient suffered an ischemic event intraoperatively and developed an occipital stroke postoperatively, and one patient showed slowing on electroencephalography intraoperatively during carotid clamping; in two patients balloon occlusion testing failed. In all cases of ischemic events occurring during the procedure, Q-NIRS monitoring showed a decrease in HbO2, tHb, and SO2, and an increase in HHb.Conclusions. Quantitative frequency-domain near-infrared spectroscopy provides quantifiable and continuous real-time information about brain oxygenation and hemodynamics in a noninvasive manner. This continuous intraoperative oxygenation monitoring is a promising method for detecting ischemic events during neurovascular procedures

Coherent Movement of Cell Layers during Wound Healing by Image Correlation Spectroscopy

We have determined the complex sequence of events from the point of injury until reepithelialization in axolotl skin explant model and shown that cell layers move coherently driven by cell swelling after injury. We quantified three-dimensional cell migration using correlation spectroscopy and resolved complex dynamics such as the formation of dislocation points and concerted cell motion. We quantified relative behavior such as velocities and swelling of cells as a function of cell layer during healing. We propose that increased cell volume (∼37% at the basal layer) is the driving impetus for the start of cell migration after injury where the enlarged cells produce a point of dislocation that foreshadows and dictates the initial direction of the migrating cells. Globally, the cells follow a concerted vortex motion that is maintained after wound closure. Our results suggest that cell volume changes the migration of the cells after injury

Coherent movement of cell layers during wound healing by image correlation spectroscopy.

We have determined the complex sequence of events from the point of injury until reepithelialization in axolotl skin explant model and shown that cell layers move coherently driven by cell swelling after injury. We quantified three-dimensional cell migration using correlation spectroscopy and resolved complex dynamics such as the formation of dislocation points and concerted cell motion. We quantified relative behavior such as velocities and swelling of cells as a function of cell layer during healing. We propose that increased cell volume ( approximately 37% at the basal layer) is the driving impetus for the start of cell migration after injury where the enlarged cells produce a point of dislocation that foreshadows and dictates the initial direction of the migrating cells. Globally, the cells follow a concerted vortex motion that is maintained after wound closure. Our results suggest that cell volume changes the migration of the cells after injury

Frequency-domain optical mammography: Edge effect corrections

We have investigated the problem of edge effects in laser-beam transillumination scanning of the human breast. Edge effects arise from tissue thickness variability along the scanned area, and from lateral photon losses through the sides of the breast. Edge effects can be effectively corrected in frequency-domain measurements by employing a two-step procedure: (1) use of the phase information to calculate an effective tissue thickness for each pixel location; (2) application of the knowledge of tissue thickness to calculate an edge-corrected optical image from the ac signal image. The measurements were conducted with a light mammography apparatus (LIMA) designed for feasibility tests in the clinical environment. Operating in the frequency-domain (110 MHz), this instrument performs a transillumination optical scan at two wavelengths (685 and 825 nm). We applied the proposed two-step procedure to data from breast phantoms and from human breasts. The processed images provide higher contrast and detectability in optical mammography with respect to raw data breast images

Age-correlated changes in cerebral hemodynamics assessed by near-infrared spectroscopy.

Cerebral hemodynamic responses due to normal aging may interfere with hormonal changes, drug therapy, diseases, life style, and other factors. Age-correlated alterations in cerebral vasculature and autoregulatory mechanisms are the subject of interest in many studies. Near-infrared spectroscopy (NIRS) is widely used for monitoring cerebral hemodynamics and oxygenation changes at the level of small vessels. We believe that the compensatory ability of cerebral arterioles under hypoxic conditions and the dilatatory ability of cerebral vessels due to vasomotion may decline with normal aging. To test this hypothesis we used frequency-domain NIRS to measure changes in cerebral tissue oxygenation and oxy- and deoxy-hemoglobin concentrations caused by hypoxia during breath holding. We also assessed cerebral vasomotion during profound relaxation. Thirty seven healthy volunteers, 12 females and 25 males, ranging from 22 to 56 years of age (mean age 35 +/- 11 years) participated in the study. We observed age-correlated changes in the cerebral hemodynamics of normal subjects: diminished cerebral hemodynamic response to hypoxia due to breath holding in middle-aged subjects (38-56 years) and reduced amplitude of cerebral hemodynamic changes due to vasomotion during rest. Snoring related changes in cerebral hemodynamics did not allow us to observe the effect of age in a group of snorers. The prolonged supine position influenced measured changes due to hypoxia. In this investigation NIRS methodology allowed detection of age-correlated changes in cerebral oxygenation and hemodynamics. Other variables, such as snoring or posture impacted the observations in our group of healthy volunteers

Frequency-domain techniques enhance optical mammography: Initial clinical results

We present a novel approach to optical mammography and initial clinical results. We have designed and developed a frequency-domain (110-MHz) optical scanner that performs a transillumination raster scan of the female breast in approximately 3 min. The probing light is a dual-wavelength (690 and 810 nm, 10-mW average power), 2-mm-diameter laser beam, and the detection optical fiber is 5 mm in diameter. The ac amplitude and phase data are processed with use of an algorithm that performs edge effect corrections, thereby enhancing image contrast. This contrast enhancement results in a greater tumor detectability compared with simple light intensity images. The optical mammograms are displayed on a computer screen in real time. We present x-ray and optical mammograms from two patients with breast tumors. Our initial clinical results show that the frequency-domain scanner, even at the present stage of development, has the potential to be a useful tool in mammography