Optimization of the UWB Radar System in Medical Imaging

doi:10.4236/jsip.2011.23031

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Journal of Signal and Information Processing, 2011, 2, 227-231

doi:10.4236/jsip.2011.23031 Published Online August 2011 (http://www.SciRP.org/journal/jsip)

227

Optimization of the UWB Radar System in

Medical Imaging

Taoufik Elmissaoui, Nabila Soudani, Ridha Bouallegue

6’Tel Research Unit Higher School of Communications of Tunis, Sup’Com University of Carthage, Tunis, Tunisia.

Email: {elmissaoui.enit, ridha.bouallegue}@gmail.com, [email protected]

Received December 18th, 2010; revised May 20th, 2011; accepted May 30th, 2011.

ABSTRACT

During the last decades, we have witnessed a widespread deployment of the ultra wide band (UWB) radar systems.

Considering a medical field, an algorithm optimizing these systems is pointed out in this contribution. Beginning with

the description of the UWB radar system, this algorithm has proved to be not only able to take a medical image of the

human body but also capable of diverting the human tissue. Moreover, we insist on the fact that this algorithm can

easily optimize different radar parameters. So, the human body layer width, the incident angle and the frequency maxi-

mizing reflection coefficient are estimated in this paper.

Keywords: UWB, Radar, Medical Image, Human Body Model

1. Introduction

The ultra wide band (UWB) technology presents many

advantages. This technology is used in many fields such

as the transmission system and the radar application. In

the literature, many studies recommend the deployment

the UWB radar in medical imaging [1-4]. In fact, these

systems consist of sending ultra short electromagnetic

pulses and analyzing the echo reflected by the human

body which is exposed to this radiation. Each human

body layer makes its proper signature in the reflected

signal. Because the human body structure has a variety of

composition and electric properties.

The UWB radar has several key advantages such as

[5]:

 The pulse has a wide frequency spectrum that can

easily cross obstacles,

 The pulse length is very short but has a very elevated

resolution,

 The short pulse leads to a little energy consumption,

 It has a good resistance to the multi-path interference,

 It allows not only the detection of a human being, but

also its positioning.

In this paper, we introduce an algorithm that optimizes

the radar system in the imaging application. In fact, the

human body characteristics vary with several parameters

like age, sex and organ composition. For this goal, we

define our proposed algorithm in the first position.

Moreover, we present the different stages of this algo-

rithm in the second position. Indeed, our radar system is

capable of estimating these parameters automatically in

an attempt to optimize the capture of the medical image.

For this reason, the UWB radar system starts by com-

puting the layer width. After that, she calculates the fre-

quency that enables us to maximize the echo strength of

each layer. Similarly, we take into consideration the spe-

cific absorption rate in order to minimize the effect of the

radar radiation. Finally, we discuss the results in the con-

clusion.

2. The UWB Radar System for a Medical

Application

The UWB radar is a system that uses an ultra wide elec-

tromagnetic pulse. The band of this device must be

greater than 25% [6]. The purpose of our system is to

capture the human body layer image. This system en-

ables doctors to diagnose the human body structure. In-

deed, it can also be used in cancer detection because it

presents electric properties different form the normal

human tissue. Similarly, UWB radar enables doctors to

control the human heart movement because the human

dilated tissue has electric properties different from the

non dilated tissue.

The bases of our radar system is sending an electro-

magnetic pulse and exploiting the several echoes re-

flected by each human body structure.

Figure 1 presents the radar system architecture that is

Optimization of the UWB Radar System in Medical Imaging

228

Receiver

Tr ansce iv er

Human body layer

Skin Fat

Figure 1. The radar architecture.

used for a medical application. We propose to use multi-

static radar in an attempt to have several copies of the

echo reflected by each human body layer on one hand,

and to assure the coverage of all the human body struc-

ture on the second hand.

Moreover, Figure 2 illustrates an algorithm that en-

ables us to optimize our radar system. The later is capa-

ble of changing its parameters automatically according to

the electric characteristics of the patient. In fact, the

width and the electric properties of each layer vary with

the age, the sex and the human body region of the patient.

For this reason, we propose to use of adaptable radar

parameters for each kind of patients. Nevertheless, the

receiver antenna positions vary only with the incident

angle and the human body layer thickness.

Our radar system must start to compute each human

body layer width in the first position. In fact, the radar

system sends an oblique incident electromagnetic wave

that will be divided into two parts: a transmitted and a

reflected part. The transmitted part crosses the first hu-

man layer and reaches the second layer and undergoes

the same division. The reflected part by the second layer

crosses the first layer and arrives at the antenna. At this

stage, our radar can compute the first layer thickness by

exploiting the antenna position.

Then, the radar system computes the incident angle

that maximizes the radar resolution in the second posi-

tion. Indeed, our system changes the incident angle and

computes the strength of the echo reflected by the human

body layer.

At this stage, our system is capable of selecting an an-

tenna that enables us to capture the echo of each layer.

After that, the radar computes the frequency that

maximizes the reflection coefficient of each layer by

changing the frequency of the incident pulse. Because the

human body electric characteristics vary with the fre-

quency of the incident electromagnetic pulse.

Subsequently, the radar compares the echo reflected

by each layer with another reference echo in an attempt

to create an image of the layer source of the reflected

electromagnetic pulse.

3. The Electric Properties of the Human

Body Layer

The UWB radar in medicine exploits the echo reflected

by each human body layer to create an image. For this

reason, we must study the interaction between the human

body layer and the incident electromagnetic pulse. Many

studies in literature model the human body layer by a

good dielectric that has a dependent electric characteris-

tic frequency [7-10]. Indeed, the propagation of the elec-

tromagnetic wave in the human body structure is deter-

mined by their electrical parameters. The permittivity of

the human body tissue is given by its molecular structure.

Moreover, the permittivity of each human body layer is a

complex quantity and it can be expressed by [7-10]:









 (1)

where ε′ is the relative permittivity of the biological tis-

sue and ε" is the out-of-phase loss factor associated with

Pulse generation

Comparator

Layer Image

User layer

selected

Layers frequency

computer

Layers width

calculation

Pulse generation

(refrence)

Echo

layer

,, n

ff

Figure 2. Radar algorithm.

Optimization of the UWB Radar System in Medical Imaging229

it. As such:







  (2)

As before, the skin depth of the electromagnetic pulse

in each human body layer can be written as follows [11]:

 





























1

(3)

where:



: the wave angular frequency



: the free space permittivity.



: the free space electromagnetic permeability.



: the relative conductivity.



: the relative permittivity.

The conductivity of the human body layer tissue has

different values depending on their compositions and

physiological functions.

Figure 3 shows the human body us the biological

structure used in this paper.

4. Thickness Estimate of Each Layer

The first step of our radar system is the computing each

layer width. For this purpose, we use an electromagnetic

pulse with an oblique incident. According to [2], we can

estimate the antenna position that enables us to capture

the echo of each human body layer.

In our case, we place many receiver antennas that en-

able us to capture each echo reflected by the human

structure. In fact, the nearest layer of the transmission

antenna has the antenna position closest to the trans-

ceiver antenna.

Let us start by the first layer in a free space. In this

section, we presume a transmitter antenna placed in a

position P that radiates electromagnetic with an incident

angle in



equal to 45˚. We start by computing the dis-

tance that separates the radar antenna transmitter and the

skin layer. In fact, the distance can be expressed as:



02tan in





 (4)

where, P1 is the antenna position that captures the echo

reflected by layer 1.

Moreover, the skin width can be expressed as:

Figure 3. Layered at a tissue model.



2tan

SKin







 (5)

Here, P2 is the antenna position that captures the echo

reflected by layer 2.

Similarly, the thickness of the muscle layer can be

written as:



312

2tan

Muscl e

Pll





 (6)

Here, P3 is the antenna position that captures the echo

reflected by layer 3.

At this stage, we can generalize this result. The width

of each layer that composes the human body structure

can be formulated as:







12 1

2tan

th ii

ll l









(7)

where, Pi is the antenna position that captures the echo

reflected by the layer.

This finding enables us to compute the travel echo of

each human layer. In addition with [2] the travel time for

the layer can be expressed as:

ttv



 (8)

Here, di is the distance crossed by the ith echo layer

and presented by:



2sin





 (9)

When we examine the result given by the last equation,

we conclude that it is possible to distinguish the echo

layer by its arrival time to the receiver.

5. The Frequency of Each Layer

Our radar system exploits the echo reflected by the hu-

man body structure. On this basis, we must optimize the

reflection coefficient of each human body layer. In this

section, we try to set the frequency that enables our sys-

tem to maximize the power of the signal reflected by the

human body structure.

The reflection of each layer is dealt with [1], we out-

line briefly the results in this section. Indeed, this value is

presented by:

232 31

TTTTTT 

 







(10)

where, i and i



present respectively the total field

transmission and the reflection by the ith layer for an in-

cident wave on the left side. They can be expressed as:

1,, 1

(1)(1) exp(2)

1exp(2)

ii iii

iiii i

Trr









 



(11)

Optimization of the UWB Radar System in Medical Imaging

230



1,, 1

exp 2

1exp2

ii iii











  (12)

i, is the reflection coefficient of the i layer of a com-

ing pulse from the right.

T



1,, 1

(1)(1) exp2

1exp2

ii iii

iiii i

Trr









 



(13)

,1ii

r, is the coefficient between two successive layers.





 (14)

Zi represents the i layer impedance



 (15)

where, Z0 is the impedance of the free space.

6. The Specific Absorption Rate

The electromagnetic wave is able to penetrate in a bio-

logical structure. The interaction between the human

body layer and the incident pulse result in a complex

distribution of the local fields. This interaction is related

to the dielectric properties of the human layer and the

wave frequency. The distribution of the electromagnetic

wave in the human body is known by SAR (Specific

Absorption Rate). SAR can be expressed by [12]:

SAR E





 (16)

where,



is the conductivity of the tissue in Siemens/

Meter



is the mass density in kg/m3 and E is the

strength of the electric field in volts/meter.

Our goal in this section is to minimize SAR value of

each layer that composes the human body.

According to Figure 4, the SAR decreases according

to the frequency of the incident pulse. The maximum

SAR was, in all the cases, located in the muscle and lung

layer.

The density of each layer is indicated in the Table 1.

7. The Thickness Measurement of Each

Human Body Layer

To illustrate the given results in this section, we will try

to compute the human body section. In fact, we used

multi-static radar that sends an electromagnetic pulse

with an oblique incident. This signal reaches the human

body layer and comes to the radar antennas. Each echo

layer has its own way, direction and an antenna receiver.

Finally, each layer triggers its own antenna. For this rea-

son, we consider the excited antenna positions and we

compute the thickness of that layer sources of the echo

Figure 4. The SAR of each human body layer versus fre-

quency.

Table 1. Density ρ in kg/m3 of the body tissues [13].

Layer ρ in Kg/m3

Skin 1100

Fat 1100

Muscle 1041

Bone 1990

Lung 655

Table 2. Estimated antenna position and the measured

thickness of each echo layer.

Layer Skin FAT Muscle Bone Lung

Estimated

antenna

position (mm)

100 100.3572 108.3314 111.1587113.6691

Permittivity

(S/m) 35.7745.0291 49.54 16.05 44.859

Measured

thickness (mm)1.5 12 14 7 6

reflected. The permittivity of each layer used in this sec-

tion, is measured by Gabriel at a frequency equal to 5

GHz. The results are summed up in the Table 2.

8. Conclusions

The UWB and radar systems have several advantages.

This encourages us to use these inventions in several

fields including medical applications. To enhance these

advantages we propose to use the UWB radar systems in

the medical imaging field. In fact, we put the emphasis

on this manuscript on an algorithm that optimizes our

radar system. This technique makes the radar system

capable of adapting its parameters depending on the

Optimization of the UWB Radar System in Medical Imaging

231

characteristics of the tissue of the patient.

Furthermore, our UWB radar system estimates the

width of each layer and computes the frequency enabling

us to maximize the echo reflected by the human body as

exposed in the radar radiation. For example we deploy a

frequency 5 GHz and 6 GHz respectively in an attempt to

detect the echo reflected by the skin and muscle layer.

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