Saturday Physics Honors presents. Professor Enrico Gratton, Looking Into the Brain with Lasers. (With some demonstrations)

Transcription

1 Saturday Physics Honors presents Professor Enrico Gratton, Looking Into the Brain with Lasers (With some demonstrations)

2 Can we see through the body using light? What we expect to see?

3 Startrek Movie clip Captain James T. Kirk Leonard H. McCoy Montgomery Scott What is happening in the scene? Is this science fiction? (of course it is!! But )

4 Light can pass through tissues Demonstration using a laser pointer Two physical processes Scattering Absorption

5 What is scattering? Light is refracted by the particle Amount of light refracted depends on the difference of the index of refraction between the particle and the medium n air =1 n water =1.33 n oil =1.42

6 Multiple scattering in tissues Due to multiple scattering, Instead of a sharp point, we have a diffuse image

7 Why we cannot see through the tissue? Demonstration using milk

8 What is absorption? Light is absorbed by the particle Amount of light that passes through depends on how dark is the substance. Some substances are colored. That means that some wavelengths of light are more absorbed than others

9 In human tissues, light is absorbed by blood (hemoglobin) and scattered by cells and other microscopic structures

10 The capillary bed

11 Hemoglobin changes color when it binds molecular oxygen Brownish RED

12 Basic physiology during brain activity When we use a part of the brain, cellular (neuronal) activity uses energy This energy must be replenished fast CO 2 is also produced by cellular metabolism and it need to be washed out Blood vessels dilate, more oxygen is brought in and the CO 2 is washed out

13 The BOLD effect (Blood Oxygen Level Dependent effect)

14

15 Schematic of light propagation in the brain Detector fiber Laser diode Reflected Collected Absorbed Light

16 Hemodynamic response to motor cortex activation [O 2 Hb] (µm) Subject A Subject B Subject C Subject D Time (s ) HHb (µm)

17 Optical detection of brain activation Axial Coronal Axial Coronal Saggital Saggital A typical map for the regression of BOLD signal by P(t) and R(t). The letters A, P, R, and L show the image orientation according to the radiological convention, and denote anterior, posterior, right, and left, respectively. Each experiment included ten 1-s stimulation epochs, which were separated by ten 17-s control epochs. During stimulation epochs subjects performed light palm squeezing with the right hand. The synchronization of the exercise sequence with the MRI and NIRS recordings was provided by a computer program, which generated the commands for the subject and the scanner operator based on preset command timing. The total length of one data record was about 5 minutes. (measurements performed by Dr. Toronov)

18 Visual cortex activation measurement locations µmol/l stimulation O 2 Hb 1.5 HHb time (s) µmol/l stimulation O 2 Hb 1.5 HHb time (s) µmol/l stimulation O 2 Hb 1.5 HHb time (s) µmol/l stimulation O 2 Hb 1.5 HHb time (s) µmol/l stimulation O 2 Hb.5 HHb time (s) µmol/l stimulation HHb O 2 Hb time (s) µmol/l stimulation O 2 Hb.5 HHb time (s) µmol/l stimulation O 2 Hb HHb time (s)

19 Real-time brain activation due to hand movement Movie obtained at UIUC, Physics by Maria Angela Franceschini

20 Applications Application to neonatal care Premature babies brain oxygen monitor

21 Applications Brain vasoreactivity (what it is?) Age dependent effect Clinical reasons for lack of vasoreactivity How brain vasoreactivity affects brain function? Why it is important? How to measure it? What can we do?

22 Sensors: multi-distance approach. Dual sensor probe for lengthy recordings, attached on the forehead by means of a medical adhesive (Hollister #773). It is used for simultaneous measurements of the oxygenation and hemodynamics of the frontal lobes.

23 Oxiplex, Tissue Oximeter, ISS Inc, Champaign.

24 Measurement of vasoreactivity Breath holding Durnal nap Diurnal nap [O2Hb], [HHb], µmol/l Control non-snorer Respiratory signal, AU [O2Hb] [HHb] Time period during breath holding, s [O2Hb], [HHb], µmol/l Respiratory signal, AU [HHb] Control non-snorer [O2Hb] Time period during daytime napping, s [O2Hb], [HHb], µmol/l OSA subject Respiratory signal, AU [HHb] [O2Hb] [O2Hb], [HHb], µmol/l [HHb] Respiratory signal, AU OSA subject [O2Hb] Time period during breath holding, s Time period during daytime napping, s

25 Summary of this lecture Physics of light propagation in tissues, scattering and absorption Basic physiological response to different stimuli Measurement of the quantity of oxygen in the tissue using hemoglobin spectrum

26 Summary of this lecture (cont) During the past 1 years we made enormous progress in understanding how to use light to see inside the human body Light is safe Light provides signals about the physiology of tissues Many optical devices have now been produced and they are used in research and in the clinic UIUC is at the frontier in this novel field of research

27 Acknowledgements UIUC, Laboratory for Fluorescence Dynamics NIH, for providing funds for this research

28 The research group at UIUC Enrico D amico Raj Gupta Schwayta Kukreti Natalia Machado Bill Mantulin Antonios Michalos Chiara Polzonetti Molly Rossow Paul Simonson Kandice Tanner Neonatal care, neurosurgery Sleep apnea disorders Breast cancer Swallowing disorders Neurosurgery, ADH Sleep apnea disorders ADH in kids Blood flow measurements Breast cancer Brain activation in animals