Optical imaging of blood flow in the microcirculation Steve Morgan Electrical Systems and Optics...
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Transcript of Optical imaging of blood flow in the microcirculation Steve Morgan Electrical Systems and Optics...
Optical imaging of blood flow in the microcirculation
Steve MorganElectrical 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• 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
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.
Capillaroscopy (Sub-lingual)
• 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
DA Beach, C Bustamante, KS Wells, and KM Foucar, Biophys. J 53, pp449-456 (1988)Dichroism signal ~3%
In vitro sickled RBCs
SSDF Imaging
Illuminate from the side to ‘back-illuminate’ RBCs
Imaging System
Illumination and Probe Design
Conventional SSDF
CC
D
Focus
Polarization sensitive
CC
D
H V
Focus
Patient Station
Polarization Images (lower lip)
Image alignment
Image alignment
xy
Image segmentation
Segmentation
#%
LD Determination
Capillaroscopy summary
• 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
Full field laser Doppler blood flow imaging
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
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).
Image – GF Clough, MK Church, University of Southampton
Single point blood flow imaging
Originally single point measurement system, measuring doppler shift from moving RBCs (20Hz – 20KHz)
Image - Moor Instruments
Scanning System
Builds up image point by point, slow
Image - Moor Instruments
Field Programmable Gate Array based systems
FPGA implements N-point FFT and frequency weightingParallel processing
64x1 photodiodearray
moorLDLS2
FPGA based systems
• Sampling rate 40KHz/pixel, 1024 point FFT
• Occlusion and release test for a single pixel
• 64 x 64 image (3s/image)
0 5 10 15 20 250
2
4
6
8
10x 10
13 Flux trace
Time [s]
Flu
x [a
.u.]
Occlusion & Release of a Finger
Black ground noise
FPGA based systems(forearm)
In collaboration with Moor Instruments
FPGA based systems(back of hand)
In collaboration with Moor Instruments
Commercial CMOS camera systems, (Serov et al)
• High readout rate CMOS camera • Requires high data rate between sensor and processor
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
• Arrays of photodetectors with on- chip processing• Fabricated using a standard CMOS process • Can be tailored to signals of interest
• Compact, portable design
Smart CMOS sensors
Processing electronics
Off-Chip processing of Doppler signals(single channel)
Low passfilter
Band passfilter
Divider
Frequency weighted filter 0.5
Square andAverage
ConcentrationSquare and
Average
Flow
Optical detection & linear amplification
Beclaro (1994), Laser Doppler, Med-Orion.
• For full field requires each pixel to be sampled at 40KHzand transferred to a processor• High data rate required
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
HDAOptical detection
(normalized)
Frequency weighted filter
Absolute and
Average
ConcentrationAbsolute
andAverage
Flow
ADCBand passfilter
ADC
64x64 array
• pixel size = 55μm x 55μm, 2~3 speckles per pixel• 4 ADCs and on-chip processing
Test configuration, vibrometer
• Provides a reproducible, predictable source of Doppler signals
Test configuration, vibrometer
• can discriminate different frequencies and amplitudes• change in amplitude along length
Frequency:450Hz left, 350Hz right
Amplitude :200mV left, 350mV right
(Hz) (m)
Rotating diffuser tests
Rotating diffuser tests
Concentration Flow
Blood flow tests (64 x 64 pixels)
Unoccluded Occluded
diffuser
Blood flow sensor board
FPGA and USB board
IR and VR combined laser
Mirror
Lens
DC camera Beam splitter
Blood flow video
Actual frame rate: 1 frame/second
before 10 mins
30 mins20 mins
Other techniques
• in vivo flow cytometry• photoacoustic imaging• Doppler OCT• Laser speckle contrast analysis• hyperspectral imaging
In vivo flow cytometry
Georgakoudi et al Cancer Researh 64, 5044–5047, 2004
Line illumination count fluorescent fluctuations of labelled cells
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
Doppler OCT(Makita et al opt express 14:7821 (2006)
• Short coherence length interferometry overcomes scattering• Imaging of retinal vessels
Chick embyro heart(Moor Instruments)
Laser Speckle Contrast Imaging(alternative to laser doppler)
• Full field imaging• Indirect measure of fluctuations• Reduction in spatial resolution, spatial averaging
Hyperspectral imaging
• Imaging oxygen saturation
• Inflammatory response
• retinal imaging
• endoscopy
Summary
Techniques for when cells are superficial and when they are obscured by overlying tissue