1. A Cost Effective System For Optical Imaging
Nam H. Kim1, A. Chaibi1, C. Ketonis, J. Semmlow, & S. Dunn
Biomedical Engineering, Rutgers University, New Jersey
Vascular endothelial cells are exposed to shear stress which can affect the morphology and signaling of a cell. Cell-cell and cell-material interactions can have a strong influence on the adhesion strength and viability of a cell. Shear stress can induce detachment of the cells from their ECM and potentially cause cellular apoptosis. Previous studies have studied a serum starvation model where shear stress supposedly rescues the cells from an apoptotic state. We hypothesize that shear stress triggers apoptosis and can lead to a cell’s detachment from a biomaterial.
Cells were seeded on PET membranes at a density of 105 cells. Control groups were fed either GF+ medium or GF- medium. Experimental groups were exposed to 1 dyne/cm2 or 10 dynes/cm2 over a period of 6 hours or 24 hours. Fixed membranes were stained with EtBr and observed under a fluorescent microscope for nuclear condensation.
Apoptotic cells demonstrated condensed chromatin visible by a stronger fluorescence. For both time periods,10 dynes/cm2 was significant compared to the GF+ controls. We can conclude from this data that increasing shear stress does have an affect on the percent apoptosis of PET adherent HAEC. This study indicates that the serum starvation model used to show apoptotic cell rescue may not be physiologically accurate.
I. Abstract
An optical imaging system using pulsed NIR to monitor brain activity of the frontal lobe has been developed. This system utilizes the transducers and the computer-based controller/analyzer to obtain data from the brain, and presents the results in a two-dimensional display. As contrasted to MRI or PET, this portable device can be used to detect brain dysfunction in children who cannot be easily immobilized.
Keywords –optical, imaging, NIR, brain dysfunction
III. Methodology : System Configuration
The optical tomography system consists of three primary components, the transducers, the computer-based controller/analyzer, and the main circuit board. (Fig.2)
  The first includes an array of light sources, which generate light at two wavelengths, and a set of detectors, which receive the reflected light from the head. The computer-based controller/analyzer is composed of two C-language programs; the interface program, which switches the diodes, acquires the data from the photodetector amplifier, and sends the data to the analyzer program. The analysis program evaluates the optical signal to estimate regional blood flow and displays the results.
Photodetector circuit with headband
Main circuit board
Fig.4 : Actual photos of the system
I/O Bus
x x x x x
o o o o
X : LED (multi wavelength) |
2.5cm
O : Photodetector (ultra-low noise) with amplifier
LED driver with intensity control
Multiplexer (4 channel) for photodetector signals
Analog to Digital converter
LED sequencing
Data acquisition
Data processing (determination of O2 signal)
Image processing to improve resolution
I/O Bus
C Language
Fig . 2 : Three components of the system.
Headpiece (transducer) Interface Board Computer
II. Introduction
Recently it has been shown that optical methods can be used to assess brain activity through the intact skull in human subjects (Chance et al. 1998). The pioneering work of B. Chance utilizes the better penetration of near infrared light to measure changes in blood hemoglobin concentrations in the brain, associated with neural activity. In this approach, weak near infrared light illuminates the head from LEDs attached to the scalp. This light passes through the skull and reaches the cerebral cortex. It penetrates to a depth of only few centimeters, and is scattered by the hemoglobin in the blood. The light is partially reflected back through the scalp.
The reflected light contains information about the cortical blood flow. The light will be substantially attenuated before it reaches the detectors: the reflected light level can be as low as a hundred millionth of the irradiated light. This reflected light is detected using sensitive photodiode detectors. (Fig.1)
IV. Results
SNR Calculation
Signal
LED on, signal difference on the palm raised / lowered : ~ 2 (Volts)
Noise
LED off : ~ 400 (mV)
SNR = 20 log (S/N) = (dB)
Preliminary results show good differentiation between oxygenated and non-oxygenated tissue. Currently, modifications in signal processing algorithm are under development to improve effective localization of blood flow changes. Figure 5 is showing the baseline readings of each photodetector-photodiode pair at the bottom, and the actual readings on top section.
An important aspect of localization in optical studies arises from transducer placement. A single ("point") measurement with optical techniques is more complicated than, for example, an EEG electrode placement, because an optical measurement involves two transducers (a source and detector); an EEG point measurement requires only a single electrode location. It is assumed that the sensitivity to changes in brain tissue will be maximal below and between the source and detector. As an approximate rule of thumb––for frequency domain and continuous wave measurements––the depth of maximum brain sensitivity is approximately half the source-detector separation distance. (Erel et al., 2001) Thus, for a source-detector separation of 2.5cm region of maximum brain sensitivity will be found between the source and detector transducer locations, and roughly 1.5 cm below the surface of the scalp, though banana-shaped region of sensitivity extends both above and below this depth. It is typically assumed that the scalp and skull produce little or no change in hemoglobin concentrations, which implies that observed changes localize to brain tissue (Firbank et al 1998). The sensitivity pattern for time domain measurements, on the other hand, is variable, affording deeper sensitivities by selectively rejecting light that travels exclusively through these superficial tissue layers.
Fig.5 : An example of the mapped result displayed
V. Conclusion
Future design improvements
Software
improve resolution using advanced signal processing
enhance display
Hardware
improve headband design
upgrade signal detection
Advantages
Non-invasive O2 content monitoring
Less constraints, Compact, Easy to apply
Good for children or infants
Enables continuous, real-time measurement for extended time
Low cost
Disadvantages
Much lower resolution than fMRI
Cannot detect deeper area
VI. Primary Application
Identifying neural correlation with behavior in children of drug using parents.
They have behavioral problems caused by,
Environment (nurture) or Brain damage (nature)
Once identified we can cure them more efficiently.
Transducers and Associated components:
The transducer hardware consists of two diodes at different wavelengths (ex. 780nm and 830nm) to identify hemoglobin concentration. Fig.3 shows that the absorption of oxy- and deoxy-hemoglobin is quite different of those two frequencies. The reflected light is measured every milliseconds, and the reflected light of one frequency is subtracted from the reflected light of the other frequency to determine the change in concentration of hemoglobin. It is necessary for the spectral line width of the light to be narrow enough to determine precisely the two results. Thus, light-emitting diodes are used. 
IV. Discussion
The system measures the change of hemoglobin concentration in the cerebral cortex of the brain with oxy-hemoglobin and deoxy-hemoglobin separately. The result is given real-time in continuous mode or immediately after measurement in analysis mode. Since the system utilizes the safe, low intensity near infrared light, it enables long time continuous measurement over extended time periods with fewer restraints on examinee. The flexible cables connecting the examinee and the main unit make it easy to test an examinee who is difficult to be at rest during measurement such as an infant or a child. This system is compact and is easy to move. Since this system does not have the cross interference effect with the other modalities such as EEG or MRI in principle, there is no hindrance to the usage in combination with them.
The system under development in the Optical Imaging Laboratory of Rutgers University uses near infrared light to measure the changes in oxy- and deoxy-hemoglobin, as well as in total blood volume, in the cerebral cortex. When a specific area of the brain is activated, the localized blood volume in that area changes quickly. Optical imaging can determine the location and activity of specific regions of the brain, by continuously monitoring blood hemoglobin levels. The system under development will take less than few tenths of a second to perform one measurement cycle, so this system can provide a "real-time" measurement of brain activity. Moreover, the system is non-invasive, and can be used under a variety of conditions with minimal restriction on the examinee.
Controller / Analyzer:
The controller subcomponents provide the interface between all the other components. It switches the light emitting diodes, acquires the data from the detectors, and provides the appropriate data to the analysis subcomponents that subtracts the signals acquired at two different wavelengths and displays the results (Fig.2).
Acknowledgement
This work is supported by a grant from the New Jersey Commision on Science and Technology.