Modeling of Blood Perfusion in Dependence of Scanning Angle from

LDPI Data

Jan Kubicek, Iveta Bryjova, Marek Penhaker, Vladimir Kasik, Zbynek Labza, Martin Cerny and

Martin Augustynek

VSB–Technical University of Ostrava, FEECS, K450, 17. Listopadu 15, 708 33, Ostrava-Poruba, Czech Republic

Keywords: Laser, Doppler Effect, Laser Doppler, LDI, LDPI, Microcirculation, Blood Perfusion, Modeling.

Abstract: The paper deals with issue of the modelling and analysis of a scanning angle influence on the blood

perfusion, and consequent proposal for their elimination. The first essential step of analysis is angle

stabilization. In this step, we utilize special artificial arm allowing for a measuring angle adjustment in the

scale of two axes. The modelling allows for simulation of perfusion units (PU) in the form of the quadratic

model, which is consequently recalculated in the form of the linear expression. The second part of the

analysis deals with the PU modelling in the dependence of the distance. In our analysis, we particularly use

a segment of middle finger and forearm. In the last part, we propose theoretical conception of the curvature

correction influence. This theoretical proposal leads to the relationship between measured and real PU

parameter.

1 INTRODUCTION

For tissue activity in a cutaneous plexus, the laser

method is used. The laser beam is absorbed during

tissue passage, changing direction, or wavelength

carrying information to the detector about

erythrocytes velocity in the particular tissue. A

product of the blood elements concentration with the

Doppler shift of a frequency and movement velocity

expresses so called number PD (Perfusion Units).

Interacttion of the laser radiation with the

particular tissue is influenced by the several factors:

type of a tissue, optical tissue properties,

wavelength, performance, power density, exposure

time and in the case of a pulsed laser it is length and

frequency of a pulse. Different refractive indexes in

individual tissue layers and absorption level

(absorption of radiation) cause different

transmittance (passage of radiation), dispersion and

reflection depending on the laser wavelength.

(Augustynek et al., 2010), (Blazek et al., 2015), (Ida

et al., 2016).

The main parameter determining penetration

depth into tissue is tissue absorption calculated for

given wavelength. In the case of interest of surfacing

tissues, we select laser with shorter wavelength

causing higher absorption with high energy

Figure 1: Laser Absorption in the dependence of

wavelength. (Thieme et al., 2016)

concentration. If we do not focuse on deeper

structures, we select laser with wavelength bellow

infrared area (630-750 nm). A level of laser

absorption in UV area and blue spectrum induces a

excitation in biomolecule where in extreme cases

goes to ionization, and contrarily light with greater

wavelengths causes atom oscillation, or molecule

rotation around their axes manifesting in the case of

thermal effects. (Brezinova et al., 2016), (Cerny et

al., 2008), (Thieme et al., 2016).

110

Kubicek J., Bryjova I., Penhaker M., Kasik V., Labza Z., Cerny M. and Augustynek M.

Modeling of Blood Perfusion in Dependence of Scanning Angle from LDPI Data.

DOI: 10.5220/0006142801100117

In Proceedings of the 10th International Joint Conference on Biomedical Engineering Systems and Technologies (BIOSTEC 2017), pages 110-117

ISBN: 978-989-758-216-5

2 MEASUREMENT OF BLOOD

PERFUSION

The blood perfusion imaging by Laser Doppler

Perfusion Imaging (LDPI) is a medical diagnostic

imaging method which is based on the evaluation of

the Doppler shift laser radiation which reflects itself

from a moving blood elements typically erythrocytes

by skin capillaries. This phenomenon creates the

quantitative maps of the blood perfusion. This

diagnostic method is frequently used in the burn

medicine for the objective and non-invasive

assessing of the burn trauma range and depth. By the

clinical evaluation, there is up to 35% errors

especially on the early stages after undergoing

trauma. The correct adjusting of the thermic injuries

depth is key fact for the optimization of the future

diagnosis. The LDPI specificity and the sensitivity

for the burn depth is determined approximately 95

%. (Bevilacqua et al., 2016), (Cerny and Penhaker.,

2009), (Shin et al., 2016).

2.1 Scanning

Although the laser beam movement appears itself as

continuous during the scanning, each measurement

is in the fact created from a set of discrete points.

The maximum number of measuring points can

represent matrix with dimension 256 x 256, it means

that in the one image is more than 65 000 tissue

points. Generally, it is appropriate to get average

perfusion value along to many points because the

perfusion value is suffered from noise and the spatial

tissue variation in the every individual point. The

spatial resolution is defined as the smallest object

distance which is possible to recognize. The

resolution is determined by the laser diameter

(PeriScan PIM 3 allows 1 mm) and used scanning

step. The highest scanning effectivity is reached in

the case when the scanning step is equalled to the

laser beam average. The smaller scanning step

improves the visual representation of the scan but

does not contribute any physiological relevant

information.

Besides the perfusion scanning, PeriScan PIM 3

allows for the intensive scanning as well. This mode

is constructed on the base the intensity of the laser

beam back diffused to the photodetector regardless

on the Doppler shift. The pixel dimensions of the

intensive scan are equal as the perfusion scan. The

intensive scan is useful for differentiation of the

scanned object from background. (Kubicek et al.,

2016), (Stetinsky et al., 2015).

The PeriScan PIM 3 also contains the built-in

compensation of the signal noise from lights

supplied from the standard electrical site with the

frequency 50/60 Hz. The other ambient light

fluctuations can also influence the measurement so

that it is appropriate to ensure the stable light

conditions. The light conditions influence on

imaging process is the subject of this analysis.

(PERIMED, 2008).

Figure 2: The arm with the head of PeriScan PIM 3.

(PERIMED, 2008).

2.2 LDPI Software

LDPI software is the analytic tool especially

intended for PeriScan systems. The software allows

for to user the exact numerical overviews of the

measured parameters and the color perfusion maps

as well. Physician can select and highlight the region

of interest (RoI) for detailed the blood perfusion

assessing in the highlighted spot. (Kukucka, 2009)

The LDPI software allows for the following

scanning modes:

• Single mode

• Repeated mode

• Sequential mode

• Duplex mode

The duplex mode allows the fluent measuring of

the blood perfusion only in one discrete point. The

measurement output is the curve of the blood

perfusion dependence within the time. The sample

frequency is adjusted on the 10 kHz and the

sampling period is 10 ms. In the ideal case, the

blood flowing plethysmography curve in the arteries

is clearly observable. This phenomenon is caused by

Modeling of Blood Perfusion in Dependence of Scanning Angle from LDPI Data

111

the change flowing in the arteries which is with the

scattering centers concentration the blood perfusion

expressing. (Elamin et al., 2015), (Klosová et al.,

2013), (Kukucka, 2009), (Machaj et al., 2016).

Figure 3: The measurement output in the duplex mode.

The graph shows the blood perfusion dependence within

the time. The RoI is indicated by blue color. The

quantified blood perfusion and other records are extracted

from RoI. (Elamin et al., 2015)

3 LDPI USING FOR

DIAGNOSTIC PURPOSES

The method LDPI contributes to monitoring of the

dermal plait blood perfusion. A depth of burn

influences a blood perfusion, thus time needed for

burn healing. On the Burn center in the university

hospital in Ostrava, the system PeriScan PIM3 is

used. The output represents 2D color map allowing

for imaging of 256 color scale covering range of

1000 arbitrary perfusion units (PU). If perfusion

rises, the color scale goes from blue to red color.

Increasing blood perfusion reflects increasing skin

metabolism. Patients who have undergone laser-

Doppler measurement, they are classified according

to tissue recovery time which is closely connected

with burn level. (Basak et al., 2016), (Goei et al.,

2016)

• Healing until 14 days (IIa. stage)

• Healing until 21 days (IIb. stage)

• Healing over 21 days (III. stage)

For the reason of edema in an affected area

oppressing of capillaries for 48 hours after injury,

instantaneous values of perfusion are distorting.

(Majernik et al., 2012)

Figure 4: Perfusion change in the dependence of particular

day (selected cases), (A) treatment time < 1 week, (B)

treatment time < 2 weeks, (C) treatment time < 3 weeks,

(D) treatment time > 3 weeks. (Schindler, 2016).

Nevertheless, it is important to start with the

measurement as soon as possible. In the clinical

practice, the measurement is started following day

after injury. Cases when measurement exhibits in 3.-

5. posttraumatic day (PTD) values greater than 147

PU, 6.-7. PTD 191 PU, 8.-9. PTD 273 PU are

classified into second group. Patients with perfusion

value less than 150 PU neither after 9. observed day

are subjected of surgery. (Majernik et al., 2014),

(Simonsen et al., 2016).

4 EXPERIMENTAL PART

There are two factors going to the process of

measurement. The factors are divided into affected

and unaffected. Each of these factors can be

differentiated as examples:

• Large burn areas

• Local burn areas

In the case of large burn areas (back or stomach)

– in this case of middle distance there is only

affected factor of measurement. By retaining of

imaginary parallelism plane of measuring head with,

we bring the least possible error of the method to the

measurement procedure, and measured values are

slightly different from real (values are depended on

distance and selected mode Low, Medium, High and

Very High). It is not needed to perform a scan

correction. If we change a measuring head position

where laser beam is not perpendicular on surface, we

bring a measurement error causing in the result

unreliable perfusion values. (Penhaker et al., 2013)

Case of curved surface large burns of long bones

(limbs) belongs to partially influenced case, only

when burn is led in longitudinal direction with bone,

and we are not focused on real values in the

neighbourhood of curved surfaces. All burn areas

which we cannot achieve the situation that all

measured points of burned area are perpendicular to

measured head are classified into unaffected cases.

Our analysis is primarily aimed to purposes of

unaffected measurements, but also deals with

infraction of main condition of measure head

parallelism in the case of affected measurement.

(Marek and Krejcar, 2015), (Penhaker et al., 2011).

4.1 Angle Stabilization

Before approaching to the measurement, it is needed

to perform of measured place angle stabilization. For

this purpose, we use artificial arm (fig. 5.) allowing

for an angle adjustment in two directions where it is

necessary to adjust the angle scale. In the one case, it

BIODEVICES 2017 - 10th International Conference on Biomedical Electronics and Devices

112

is angle led along of edge joint (fig. 6.A), with

radius 20mm (distance 90°-90° is 62.8 mm). In two

cases, they are angles in the circle (fig. 6.B), with

inner radius 15.5 mm and external radius 34.5 mm.

Figure 5: Detail view on the stabilizing arm with

measurement angles (left), whole stabilizing arm (right).

Figure 6: Used angle configuration for given radius, (B)

circle configuration with inner radius 15.5 mm and

external radius 34.5 mm, (A) angle led along of edge joint.

Since some of human parts do not have

completely flat surface for measurement, it is needed

to establish approach for placing of measured area

into plane. For this purpose, we use protractor for tilt

measurement. In this phase, we can approach to

device calibration. Calibration is done by using of

reference etalon using Brownian move.

4.2 Procedure of Measurement

Measurement in the single mode is carried out by the

conditions summarized in (Table.1.). Single mode

generates static image record, user sets scan

resolution and intensity threshold. After process of

measurement, software allows for intensive and

perfusion scan together with color image.

Table 1: Controlled conditions in single mode.

Atmospheric pressure 101.2 kPa

Light conditions 57 lx

Surrounding temperature 24.5 °C

Tissue temperature 36.2 °C

Humidity 32.2 °C

The output values from single mode will be used

for area comparison measured under angle 50°C,

and in the second case under 60°C.

Measurement in the duplex mode is carried out

by the conditions summarized in (Table.2.). Duplex

mode is different in the sense of scanning way. This

mode performs continual measurement of blood

perfusion in one point with sample frequency 100

Hz (step 10 ms). After selecting this mode, it is

possible to control of head distance to tissue, sample

frequency and change of intensity threshold.

Table 2: Controlled conditions in duplex mode.

Atmospheric pressure 101.4 kPa

Light conditions 95.5 lx

Surrounding temperature 28.5 °C

Tissue temperature 36.4 °C

Humidity 22.6 °C

Record length 9 s

For processing of results we use perfusion values

and intensity from duplex mode. The measured

values are related on one skin point (back of the

hand), they have inclination angle 0° to 70° from

parallel surface of measuring head (Fig. 7.). The fig.

8. shows graphical representation of the correction

curve of perfusion change in the dependence of

incidence angle. Perfusion units (PU) are

approximated by quadratic model:

 =     



(1)

Parameter 



is approximated by the confidence

interval: {-0.0136312; 0.036515} containing zero

point, and p-value: 0.293605 which is greater than

0.05. On the base of the results, for this case the

parameter 



is negligible against rest of the values.

After recalculation of values for the linear equation:

 =    (2)

We obtain the linear dependence (fig. 9.). The

resulting linear equation is expressed by the

following way:

Modeling of Blood Perfusion in Dependence of Scanning Angle from LDPI Data

113

 = 348.74 − 3.31619 (3)

This formulation consist the main part of the

final perfusion recalculation 



to 



The white line led by the center of the correction

graph determines the linear correction curve. The

dark gray band around the correction curve consists

of 95% probability of value occurrence in the

measured point.

Figure 7: 9 second perfusion records in the dependence of

angle.

Figure 8: Perfusion change within angle change for

quadratic model.

Figure 9: Perfusion change within angle change for linear

model.

Equally as for imaging of the quadratic and

linear model, it is approached to building of

quadratic (Fig. 10.) and linear (Fig. 11.) intensity

model.

Figure 10: Intensity change within angle change for

quadratic model.

Figure 11: Intensity change within angle change for linear

model.

BIODEVICES 2017 - 10th International Conference on Biomedical Electronics and Devices

114

The last effect of measured parameters is

dependence of PU in the dependence of the distance.

A selected location of measurement is focused on 1.

A Segment of middle finger (digitus medius)

measured from side of back of the hand (Fig. 12.).

Consequently, we are focused on forearm (Fig. 13.).

On the base of statistical values of the linear models,

it is obvious that in the distance from 10.5 to 35.5

cm effect of distance change is statistically

negligible. We must state that the values of this

graph are obtained from person suffering from

Reynolds syndrome.

Figure 12: Intensity change within angle change for linear

model.

Figure 13: Perfusion change within distance change for

linear model „Forearm“.

Figure 14: Intensity change within distance change for

linear model „ middle finger “and their inverse quadrat.

Figure 15: Intensity change within distance change for

linear model „ forearm “and their inverse quadrat.

4.3 Theoretical Proposal of Curvature

Correction Influence

The reference plane is placed perpendicularly to

axes of measuring head in distance 



from the

reference point of head H. Particularly for PeriScan

PIM3 it is 



=25. A laser beam comes from

deeper place of head – point S, whose distance from

reference plane is 



>



. It comes from the

calibration curve (rather from calibration line).

The Cartesian coordinates system is fitted by z

axis to axis of head, where orientation of z axis is

equal with outgoing laser beam direction. The x and

y axes are oriented in parallel with lines connecting

of laser beam intersection with reference plane (in

the scanning positions). The beginning of the

coordinate system is denoted by 0, intersection of

head axis with measured area is denoted by Q. A

laser beam outgoing from (virtual) point S is swept

by the way that in the moment of measurement in

reference plane it pass through points with

coordinates (u,v,0), one such point is denoted as R

(Fig. 16.). These points consist the regular grid with

sides 



and 



Modeling of Blood Perfusion in Dependence of Scanning Angle from LDPI Data

115

If we have perfusion calibration curve for incidence angle

correction, we have:





=





() (4)

, respectively directly for cos function we have:





=



.() (5)

Figure 16: Proposed situation of measurement correction.

On the base of the perfusion map





[, ] and the incidence angle map [, ]

(respectively [, ]) we can determine perfusion

map corrected on incidence angle 



[, ] on the

base of the equation 5.

5 CONCLUSIONS

Before performing practical measurement, it was

necessary to add markers of tentative angles to

stabilizing arm. The arm performs stabilization only

of arm area of interest. Before performing of each

measurement, the surrounding conditions of

experiment were recorded in which experiment can

be repeated.

The results from single mode exhibit differences

in imagined areas. In the fact the imagined tissue in

dermis layer has same microcirculation of blood

elements, but measurement under different angle

showed that the device is affected by personally

unaffected influences distorting measurement

results. Consequences of this angle change were

observable on Duplex mode. Under perpendicular

angle of laser beam to tissue, laser beam goes

through the thinnest thickness of epidermis layer,

and direction of major number of blood elements is

predominantly forward and reverse. Any scanning of

skin under different angle than perpendicular cause

greater absorption of laser beam, because trajectory

of laser beam intersection is extended. Furthermore,

blood element movement is detected under certain

angle α. The correction curve created in the Duplex

mode shows the particular dependence of PU change

on angle change. For using of correction curve

(linear characteristic) to any measured area, it was

necessary to put measured curve values to ratio with

stable part of linear characteristic.

Within making of the theoretical procedure, it

was found out that PeriScan PIM3 together with

software do not have sufficient equipment which

would be able to measure of each perfusion matrix

discrete point. There are three reasons why it was

not possible to make experiments with the device. It

is only one device utilized for acute burn states, for

determining of proper diagnosis uses non-invasive

diagnostic method, and it does not belongs to

commonly used devices and the device must have

been acquired from own budget of University

hospital in Ostrava. Nevertheless, the theoretical

model conception is relatively strongly depended on

this feature. All other acquired records are sufficient

to correction of discretely values 



transformation on real values 



ACKNOWLEDGEMENTS

This article has been supported by financial support of TA

ČR ,PRE SEED Fund of VSB-Technical univerzity of

Ostrava/TG01010137. The work and the contributions

were supported by the project SV4506631/2101

'Biomedicínské inženýrské systémy XII'.

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