A REVIEW OF LOCALIZATION SYSTEMS FOR ROBOTIC ENDOSCOPIC CAPSULES

TEC , OYOOR

WIRELESS CAPSULE ENDOSCOPY (WCE) LOCALIZATION METHODS

BASED ON MAGNETIC FIELD STRENGTH

MAGNETIC LOCALIZATION FOR PASSIVE CAPSULE ENDOSCOPE

UTILIZATION OF A PERMANENT MAGNET UTILIZATION OF A SECONDARY COIL UTILIZATION OF A MAGNETO-RESISTIVE SENSOR

MAGNETIC LOCALIZATION FOR ACTIVE ACTUATION SYSTEM

BASED ON HIGH-FREQUENCY ALTERNATING MAGNETIC FIELD LOCALIZATION BASED ON INERTIAL SENSING MEASURING A ROTATIONAL MAGNETIC FIELD

BASED ON ELECTROMAGNETIC WAVES

RADIO WAVES RECEIVED SIGNAL STRENGTH INDICATOR(RSSI) RADIO FREQUENCY IDENTIFICATION(RFID) VISIBLE WAVES X-RAY GAMMA RAY

CONTENTS

• Endoscopy ?

• Conventional techniques

• WCE is an ingestible pill-like device contains a tiny camera and an illuminating system

• WCE offers patient friendly and painless investigation

• A reliable and precise localization system plays an important role in enhancing the benefits of WCE.

• Methods for determining the capsule locations are categorized into two, - magnetic field strength based - electro magnetic wave based

INTRODUCTION

DATA RECORDER

COMPUTER

Data Acquisition & Storage Of Data On Computer

Produces two images per second, approximately 2,600 high quality images.

Movement Of Capsule Through The Digestive System

OPTICAL DOME

LENS HOLDER

LENS ILLUMINATING

LEDCMOS IMAGE SENSOR

BATTERY

ASICTRANSMITTER

ANTENNA

INSIDE A CAPSULE CAMERA

LOCALIZATION METHODS BASED ON MAGNETIC FIELD STRENGTH

• This method is used because of 2 main reasons

* static and low frequency magnetic signals can pass through human tissue without attenuation.

* magnetic tracking is a non line of sight method .

• The negligible interaction between magnetic field and human body

• The problem is the conflict between 2 systems due to interference of 2 applied magnetic fields.

* Magnetic localization for passive capsule endoscope

* Magnetic localization for active actuation system

UTILIZATION OF A PERMANENT MAGNET ENCLOSED INSIDE A CAPSULE

Why a permanent magnet ?

The majority of magnetic tracking systems generate magnetic field through integrating a permanent magnet inside the capsule.

Magnetic flux intensities originating from the magnet vary their magnitudes and direction depending on the magnets location and orientation.

Magnetic sensors are placed outside of a patients body to measure these persistent magnetic signals.

UTILIZATION OF A SECONDARY COIL EMBEDDED IN A CAPSULE

The spatial information of the capsule can be obtained through utilizing a coil enclosed inside a capsule. The field seen by the receiving coil is,

UTILIZATION OF A 3-AXIS MAGNETO-RESISTIVE SENSOR

A 3-axis magneto-resistive sensor used to measure the intensity of the external magnetic field generated by 3 energized coils fixed on the patients body.

The 3 coils are excited in turn by square waves with the same period of 0.03s,and at the end of every cycle, there is a break period of 0.1s when the coils are not activated to estimate earth’s magnetic field magnitudes.

MAGNETIC LOCALIZATION FOR ACTIVE ACTUATION SYSTEM

• These systems were designed to work effectively with their own magnetic actuation mechanisms.

* localization based on high frequency alternating magnetic field * localization method based on inertial sensing * based on measuring a rotational magnetic field by rotating an external permanent magnet.

LOCALIZATION BASED ON HIGH FREQUENCY ALTERNATING MAGNETIC FIELD

• It uses a spiral structure on the surface of a capsule in which a permanent magnet is integrated

• 3 pairs of coils were placed in three perpendicular axial directions to generate an external rotating magnetic field around the patient’s body.

• The spiral structure rotate the capsule by applying this magnetic field on the magnet can propel it forward and backward.

• The frequency of rotating magnetic field should not be higher than 10Hz

LOCALIZATION METHOD BASED ON INERTIAL SENSING

• Magnetic steering , utilized a 6 degree-of-freedom robotic arm to carry a permanent magnet at the end.

• 4 cylindrical magnets were mounted uniformly on the body of a capsule in order to create a magnetic link between body and the external permanent magnet.

• By this design , the capsule can be dragged and steered effectively with the assistance of the magnetic interaction.

• For the localization function , a 3-axis accelerometer was inserted into the capsule.

.

LOCALIZATION BASED ON MEASURING A ROTATIONAL MAGNETIC FIELD GENERATED BY ROTATING AN EXTERNAL PERMANENT MAGNET

• It uses an endoscopic capsule with a helical architecture , created an external rotational magnetic field to rotate 2 permanent magnets embedded in the endoscopic device.

• instead of utilizing 6 bulky coils around the patients body , here rotates a big parallel piped permanent magnet made by 7 smaller rectangular magnets to generate a rotational mag.field.

• The magnetic field generator was driven by an electrical motor mounted on a manipulator , so that it could spin and its position can be changed during the control process of capsule.

• When the external permanent magnet is spinning , field strength changes periodically and its highest or lowest value occurs at XZ/XY plane.

LOCALIZATION METHODS BASED ON ELECTROMAGNETIC WAVES

• These methods are not influenced by magnetic field generated for the actuation purpose.

• Radio frequency has been widely used for locating an object in both outdoor and indoor environments.

- Received Signal Strength Indicator(RSSI)

- Radio Frequency Identification(RFID)

1. RECEIVED SIGNAL STRENGTH INDICATOR(RSSI)

The transmitter built inside the capsule wirelessly sends endoscopic images ,which are captured during its travel along the inner parts ,to 8 receivers placed uniformly on the exterior of the patient abdomen.

The low accuracy achieved by this localization system can make it impossible to provide feedback for actuation systems.

2. RADIO FREQUENCY IDENTIFICATION(RFID)

RFID is also investigated in radio frequency based localization systems for WCE.

A cubic antenna array is built surrounding a patient’s body to track a RFID tag integrated inside a capsule.

VISIBLE WAVES

Visible waves cannot penetrate human body , it has still been exploited for the aim of capsule localization through computer vision.

Inside the WCE ,white light emitting diodes(LED) illumination sources are used in conjunction with a miniature camera for capturing images . X-RAY

Beside the application of medical imaging , X-rays can also be exploited to track an object

Fluoroscopy GAMMA RAY

A gamma ray has not been employed in the localization approaches for WCE , was exploited in gamma scintigraphy technique .

OTHER LOCALIZATION METHODS

1) MRI (MAGNETIC RESONANCE IMAGING) Diagnostic imaging technique used widely in medical

clinics.

2) ULTRA SOUND

A potential method for localization in soft tissue.

Localization methods extra extra accuracy interference real health space power time effectspassive permanent magnet Yes No High Yes Yes No WCE secondary coil Yes Yes Mdm Yes -- No magneto-resistive sensor Yes Yes Mdm Yes No No

Active HF alternating m.f Yes No High No Yes --WCE Inertial sensing Yes Yes Low No -- No Rotating external permanent magnet Yes Yes Mdm No -- No

EM Visible No No Low No --Waves X-ray No No -- No Yes Yes Gamma Yes No -- No Yes Yes

Others MRI Yes Yes High -- Yes Little Ultra sound Yes Yes -- No Yes Little

COMPARISON OF LOCALIZATION METHODS

ADVANTAGES

Painless, no side effects or complications

Miniature size , so can move easily through digestive tract.

Accurate , precise and effective

Images taken are of high quality which are sent almost instantaneously to the data recorder for storage.

Made of bio-compatible material , doesn’t cause any harm to the body.

DRAWBACKS

Patients with gastrointestinal structures or narrowing are not good candidates for this procedure.

The pill will get stucked , if there is a partial obstruction in the small intestine.

Impossible to control camera behavior.

CONCLUSION

WCE with the capability of moving automatically in the digestive tract under an external control will be introduced in the near future.

Such an active system requires a sufficiently accurate localization system

None of the existing methods could offer a complete solution to address the challenging capsule localization problem.

A future WCE is expected to have fully robotic capabilities such that it will be able to accomplish both diagnosis and disease treatment

In order to achieve such an autonomous WCE , building a complete localization system which is , - acceptably accurate in real-time

- minimally invasive

- work with different actuation mechanisms

- easily implementable

A FUTURE CAPSULE

THANQ

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