Oversigt Interferens Speckler og deres dynamik Optisk blanding og Dopplerskift Lidt matematik: Campbells teorem og Wiener- Kinchine teoremet Diffusionsmålinger Laser Doppler teknik evt. med OCT Medicinske anvendelser

Speckle/FreePen Surface Incident beam Observation plane A B C Observed field =  j  exp[-iK L j ]  coh  rms rsrs

Speckle/FreePen If spot size is larger than the lateral scale and surface roughnes larger than the wavelength, then the field obeys circular complex Gaussian statistics Re Im A B C A+B+C

Speckle/FreePen This means that the field distribution function is

Speckle/FreePen and the intensity distribution function is

Speckle/FreePen Speckle size given by L

Speckle/FreePen Speckle translation xx pxpx LR Incident beam R is the radius of curvature of the incident beam

Light beating eller optisk blanding Eksempel: en partikel med hastigheden 1 m/sec spredes fra en HeNe-laser. Dopplerskiftet bliver ca. 3 MHz sammenholdt med lysets frekvens på 5*10 14 Hz feltstyrke intensitet

v k in k out Intet Doppler skift!

v k in k out Maksimalt Doppler skift!

v Intet Dopplerskift K sc

v rimeligt Dopplerskift K sc væv blodåre

v rimeligt Dopplerskift K sc væv blodåre detektor Frekvensmoduleret signal

aseropplernemometri LaserDopplerAnemometri

Wiener -Kinchine teoremet: 1

Wiener -Kinchine teoremet: 2

Power spectrum S(t) Filter: w 1,  w Filter: w 0,  w Filter: w 2,  w Filter: w n,  w

Campbells theorem Sum af identiske “bursts”: Korrelationsfunktionen: og dermed spektret:

Hvorfor er spektret interessant? det giver en målelig og let målbar størrelse måling af korrelationsfunktionen er mere kompliceret hastighed er direkte relateret til frekvens

diffusionsmålinger laser detektor K sc

Idet “random walk” betyder at Spektret for strømmen bliver derfor en Lorentz-kurve med en halv- værdi bredde på

 2 flux = k 1  P(  ) d  noise  1 I n = k 2 x Average Speed of blood cells x Number Concentration of Blood Cells

Lisca

The images below show the increase in foot sole tissue perfusion following lumbar sympathetic blockade in a patient with peripheral vascular disease. The Laser Doppler Perfusion Imager has been used successfully for visualization of two-dimensional microvascular flow-maps in a number of clinical settings including investigations of for example peripheral vascular disease, skin irritants, diabetics, burns and organ transplants. Before injection of drug. 2 minutes after injection. 30 minutes after injection. Lisca

Microdialysis guide and probe inserted in forearm skin. Perfusion directly after insertion of probe. The skin at point of insertion is anaesthetized. Perfusion at site of insertion and probe tip 30 min after introduction. Lisca

The moorLDI-VR imager

An example of irritant reaction to two cutting fluids and water control is shown here (courtesy of Mr C Packham, EnvironDerm Services Ltd, UK). Volar forearm 10.6 ´ 4.1 cm 2 Irritancy of metal working fluids 1& 2, compared with water control 3. The moorLDI-VR imager

Two moorLDI laser Doppler images below show plaques of psoriasis that have been treated with coal tar. Clinically treatment was considered to be complete. The active edge on the leg might explain why some plaques recur within a relatively short time of discontinuing treatment whereas others are resolved. In the first case ( a, b ), there is higher blood flow at edge indicating further treatment is required. In the second case ( c, d ), coal tar treatment is complete and blood flow within and outside the plaque are similar Moor Instruments

Two moorLDI laser Doppler images below show plaques of psoriasis that have been treated with coal tar. Clinically treatment was considered to be complete. The active edge on the leg might explain why some plaques recur within a relatively short time of discontinuing treatment whereas others are resolved. In the first case ( a, b ), there is higher blood flow at edge indicating further treatment is required. In the second case ( c, d ), coal tar treatment is complete and blood flow within and outside the plaque are similar

A Laser Doppler Imager (LDI) can be used to show heart tissue blood flow ( b ) during and ( c ) after coronary artery bypass graft (CABG) surgery. The reperfusion is clearly seen and areas of poor perfusion could be identified.

a previously treated 15 mins post treatment 20 mins post treatment b, c not previously treated LDI Applications

Blood flow in the lower limbs improves when the legs are raised to the horizontal. Laser Doppler imager (LDI) images from the moorLDI show improvement in skin bloodmoorLDI flow from ( a ) dependent to ( b ) raised. This type of procedure needs further research to investigate how test responses might be used to select patient treatment and predict its efficacy.

Konklusion Doppler-metoden giver en kvalitativ måling En kvantitativ måling af blod flow er næppe mulig for væv Kombination af CCD-kameraer og speckle metoder giver nye muligheder Kombination af OCT og Doppler metoder kan give dybdeselektiv måling Anvendelse af nære IR-kilder vil give mindre spredning Simultan anvendelse af to bølgelængder vil være interessant