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Optical imaging of blood flow in the microcirculation

Optical imaging of blood flow in the microcirculation. Steve Morgan Electrical Systems and Optics Research Division, University of Nottingham, UK. Imaging the microcirculation. Imaging when superficial tissue is relatively thin eye, mouth, nail fold cells can be visualized

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Optical imaging of blood flow in the microcirculation

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  1. Optical imaging of blood flow in the microcirculation Steve Morgan Electrical Systems and Optics Research Division, University of Nottingham, UK

  2. Imaging the microcirculation Imaging when superficial tissue is relatively thin eye, mouth, nail fold cells can be visualized capillaroscopy for sickle cell anaemia Imaging when superficial tissue is relatively thick skin indication of flow in the microcirculation full field laser doppler blood flowmetry Other techniques

  3. Capillaroscopy Find a site where there is very little scattering ‘Windows’ (eye, nailfold, under tongue, lower lip) x5/x10 microscope objective Polarized light capillaroscope Aim to detect dichroic (sickled) red blood cells in sickle cell anaemia.

  4. Capillaroscopy (Sub-lingual)

  5. Genetic disorder affecting RBCs Haemoglobin polymerizes on de-oxygenation Polymerisation on a cellular and sub-cellular level Effects Painful Crises Organ Damage Currently no in-vivo assessment Sickle Cell Anaemia

  6. DA Beach, C Bustamante, KS Wells, and KM Foucar, Biophys. J53, pp449-456 (1988) Dichroism signal ~3% In vitro sickled RBCs

  7. SSDF Imaging Illuminate from the side to ‘back-illuminate’ RBCs

  8. Imaging System

  9. Illumination and Probe Design

  10. Conventional SSDF Focus CCD

  11. Focus CCD H V Polarization sensitive

  12. Patient Station

  13. Polarization Images (lower lip)

  14. Image alignment

  15. Image alignment Dy Dx

  16. Image segmentation Segmentation LD Determination #%

  17. Camera sensitive to changes in polarization ~0.5% but dichroism not observed in vivo. instrumentation; resolution, dynamic range Clinical reason? Just isn’t present under the tongue or to the extent observed in vitro future – increase magnification, CMOS cameras, single cell oxygenation Capillaroscopy summary

  18. Imaging when superficial tissue is relatively thick skin indication of flow in the microcirculation full field laser doppler blood flowmetry Inflammatory responses, wounds, vein viewing Full field laser Doppler blood flow imaging

  19. vascular response to an intradermal injection of 20 µl of 1 µM histamine into the volar surface of the forearm of a healthy volunteer (33s intervals). Full field laser Doppler blood flow imaging Image – GF Clough, MK Church, University of Southampton

  20. Originally single point measurement system, measuring doppler shift from moving RBCs (20Hz – 20KHz) Single point blood flow imaging Image - Moor Instruments

  21. Scanning System Builds up image point by point, slow Image - Moor Instruments

  22. Field Programmable Gate Array based systems 64x1 photodiode array FPGA implements N-point FFT and frequency weighting Parallel processing moorLDLS2

  23. FPGA based systems • Sampling rate 40KHz/pixel, 1024 point FFT • Occlusion and release test for a single pixel • 64 x 64 image (3s/image)

  24. FPGA based systems (forearm) In collaboration with Moor Instruments

  25. FPGA based systems (back of hand) In collaboration with Moor Instruments

  26. Commercial CMOS camera systems, (Serov et al) • High readout rate CMOS camera • Requires high data rate between sensor and processor

  27. Commercial CMOS camera, Serov et al • Full field imaging • Uses commercial CMOS camera and processing on a PC • Requires high data rate between sensor and processor • Data restricted to 8 bit at 8KHz (ideally ≥ 10bit, 40KHz) • No anti-aliasing filter Proc. SPIE Vol. 6080 608004-1

  28. Processing electronics Smart CMOS sensors Arrays of photodetectors with on- chip processing Fabricated using a standard CMOS process Can be tailored to signals of interest Compact, portable design

  29. Concentration Optical detection & linear amplification Band pass filter Divider Square and Average Flow Low pass filter Frequency weighted filter 0.5 Square and Average Off-Chip processing of Doppler signals (single channel) • For full field requires each pixel to be sampled at 40KHz • and transferred to a processor • High data rate required Beclaro (1994), Laser Doppler, Med-Orion.

  30. Concentration Optical detection (normalized) Band pass filter HDA ADC Absolute and Average Flow Absolute and Average ADC Frequency weighted filter On-Chip Processing of Doppler signals • Design modified for efficient use of silicon on-chip • Only flow and concentration output (low bandwidth) • 16x1, 4x4, 32x32 prototypes developed • tailored to signals e.g. HDA amplifies ac by x40, dc by unity

  31. 64x64 array • pixel size = 55μm x 55μm, 2~3 speckles per pixel • 4 ADCs and on-chip processing

  32. Test configuration, vibrometer • Provides a reproducible, predictable source of Doppler signals

  33. (Hz) (m) Test configuration, vibrometer Frequency: 450Hz left, 350Hz right Amplitude : 200mV left, 350mV right • can discriminate different frequencies and amplitudes • change in amplitude along length

  34. Rotating diffuser tests

  35. Rotating diffuser tests Concentration Flow

  36. Blood flow tests (64 x 64 pixels) Unoccluded Occluded

  37. IR and VR combined laser Mirror FPGA and USB board Blood flow sensor board Beam splitter DC camera Lens diffuser

  38. Blood flow video Actual frame rate: 1 frame/second

  39. before 10 mins 20 mins 30 mins

  40. Other techniques in vivo flow cytometry photoacoustic imaging Doppler OCT Laser speckle contrast analysis hyperspectral imaging

  41. In vivo flow cytometry Georgakoudi et al Cancer Researh 64, 5044–5047, 2004 Line illumination count fluorescent fluctuations of labelled cells

  42. Photoacoustic imaging (wang JBO 15:011101-9 (2010) • Use light to excite u/s in tissue • Used to image vessels but also blood cells • Also Doppler version

  43. Doppler OCT (Makita et al opt express 14:7821 (2006) • Short coherence length interferometry overcomes scattering • Imaging of retinal vessels

  44. Laser Speckle Contrast Imaging (alternative to laser doppler) Chick embyro heart (Moor Instruments) • Full field imaging • Indirect measure of fluctuations • Reduction in spatial resolution, spatial averaging

  45. Imaging oxygen saturation • Inflammatory response • retinal imaging • endoscopy Hyperspectral imaging

  46. Summary Techniques for when cells are superficial and when they are obscured by overlying tissue

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