InfraScanner Model 2000

All biological tissue is, to differing extent, permeable to electromagnetic (EM) radiation of different frequencies and intensities. This can also be considered permeability to photons of different energy levels. This permeability to EM energy is the basis of all imaging based on transmission/scattering characteristics such as x-ray, Computed Tomography (CT), and Near InfraRed (NIR) imaging. From the principles of spectroscopy, it is also known that different molecules absorb different wavelengths of EM radiation (which is synonymously referred to as light at smaller wavelengths). Similarly, tissue scatters EM radiation to different degrees. The InfraScanner is concerned with NIR imaging of the hemoglobin molecule.


From any light source, photons follow a characteristic path through the target tissue back to a detector on the same approximate plane as the source. While the light is severely attenuated due to the scattering and absorption process, it is nonetheless encoded with the spectroscopic signatures of the molecules encountered en route to the detector.

By carefully choosing the wavelengths that are produced by the source, it is possible to detect the relative concentration of hemoglobin in the target tissue. By comparing these levels to tissue in a “baseline” state, and using some basic knowledge about “interesting” conditions for the tissue, it is possible to draw conclusions from these levels.

Figure 2-1 shows the simulated diffusion path through target tissue from source to detector. This simulation shows the photon path density, not the overall transmission level.

The principle used in identifying intracranial hematomas with the InfraScanner is that extravascular blood absorbs NIR light more than intravascular blood. This is because there is a greater (usually 10-fold) concentration of hemoglobin in an acute hematoma than in normal brain tissue where blood is contained within vessels. The InfraScanner compares left and right side of the brain in four different areas. The absorbance of NIR light is greater (and therefore the reflected light less) on the side of the brain containing a hematoma, than on the uninjured side.The wavelength of 805nm is sensitive only to blood volume, not to oxygen saturation in the blood. The InfraScanner is placed successively in the left and right frontal, temporal, parietal, and occipital areas of the head and the absorbance of light at 805 nm is recorded and compared.

Frontal: Left/Right forehead, above the frontal sinus

Temporal: In the Left/Right temporal fossa in front of the top of the Left/Right ear

Parietal: Above the Left/Right ear, midway between the ear and the midline of the skull

Occipital: Behind the top of the Left/Right ear, midway between the ear and the occipital protuberance

The difference in optical density (ΔOD) in the different areas is calculated from the following formula:








System

            

The system includes two components: the InfraScanner Model 2000 and the Cradle.

The InfraScanner includes a safe Class 1 NIR 808nm diode laser and a silicon detector. The light to and from the laser and detector are optically coupled to the patient’s head through two 19mm long disposable light guides. The light guides are long enough to reach through hair and contact the scalp. The light guides are placed 4 cm apart allowing optimal detection of hematomas. The detector light passes through an optical bandpass filter centered at 808nm in order to minimize background light interference. Electronic circuitry is included to control laser power and the detector signal amplifier gain. The detector signal is digitized and analyzed by a single board computer (SBC) in the InfraScanner. The SBC receives the data from the detector and automatically adjusts the settings of the InfraScanner to ensure good data quality. The data is further processed by the SBC and the results are displayed on the screen.

The InfraScanner is turned on by placing a Fiber Optic Disposable Shield on the InfraScanner and turned off by removing the Fiber Optic Disposable Shield. If after approximately 8 minutes of inactivity the shield is not removed, the InfraScanner starts beeping until the Fiber Optic Disposable Shield is removed. When the InfraScanner is turned on, pressing and releasing one of the Measure Buttons activates a measurement sequence at a given head location. The measurement includes an initial adjustment phase and then the data collection. The adjustment of laser power and detector signal gains is only done at the first head location of a pair. The contra-lateral location uses the same InfraScanner hardware parameters as the ipsi-lateral location. After a measurement pair, the screen will display the differential optical density for that pair. The absolute value of optical density is not relevant, just the relative difference between left and right sides of the head.

Audible signals indicate when the measurement is done. A first short beep indicates when the measurement button is pressed and the measurement begins and a second short beep indicates a completed measurement. Four short beeps indicate a time out message. An elongated beep indicates an error message. The error message must be cleared by pressing the green button. If the data is unacceptable, the measurement pair is to be repeated before proceeding to the next head pair. The InfraScanner can be powered either by a rechargeable NiMH battery pack or by 4 disposable AA batteries. The Cradle is used to charge the rechargeable battery pack, if it is used in the InfraScanner, and to copy the data from the InfraScanner to a Personal Computer (PC).



Easy-To-Use

The InfraScanner is an easy-to-use medical system that provides a simple positive or negative graphic report.


View Training Video








References

C.S. Robertson, E.L. Zager, R.K. Narayan, N. Handly, A. Sharma, D. F. Hanley, H. Garza, E. Maloney-Wilensky, J.M. Plaum, C.H. Koenig, A. Johnson, T. Morgan, “Clinical Evaluation of a Portable Near-Infrared Device for Detection of Traumatic Intracranial Hematomas”, Journal of Neurotrauma. September 2010, Vol. 27, No. 9: 1597-1604.

Zhang Q, Ma H, Nioka S, Chance B., “Study of near infrared technology for intracranial hematoma detection.” J. Biomed. Opt. 5, 206-213 (2000).

C. S. Robertson, S. P. Gopinath, and B. Chance, “Use of near infrared spectroscopy to identify traumatic intracranial hematomas.” J. Biomed. Opt. 2, 31–41 (1997).

S.P. Gopinath, B. Chance, and C.S. Robertson, “Near-infrared spectroscopy in head injury”. Chap. 12 in Neurotrauma, R.K. Narayan, J. Wilberger, and J. Povlishock. Eds., pp. 169-184, McGraw-Hill, New York, NY (1994).

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