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A Tactile Sensor for Minimal Access Surgery Applications
Copyright @ IF AC Mechatronic Systems, Darmstadt, Germany, 2000
A TACTILE SENSOR FOR MINIMAL ACCESS SURGERY APPLICATIONS
M E H Eltaib, J R Hewit
Department of MechanicaL Engineering University of Dundee, UK. Te/: +44 1382344497, Fax: +44 1382345508 Emai/: ).r.hewir@dlllu/ee.ac.llk . [email protected]. uk
Abstract: Touch sensing during new surgical techniques. such as laparoscopy and those involving robotic manipulators. is a challenge . In these techniques . tissue is remotely manipulated using instruments. which do not possess a sense of touch. Important properties such as tissue compliance. which give indications regarding the health of the tissue . can not be accessed. A tactile system for tissue assessment is described. It comprises a tactile sensor attached to the end of a sinusoidally vibrating rod . When the sensor indents the tissue a sinusoidal motion is transmitted to the tissue. The output of the sensor is the contact force between the tissue and the rod tip. This is used to identify the dynamic properties of the tissue. The design and implementation of the tactile sensor are described. Simple experiments involving simulated tissue have been undertaken and the results of these are reported. Copyright©2000 IFAC Keywords: Tactile Sensor. Tissue. Sinusoidal. Minimal Access Surgery. Robotics.
I.
INTRODUCTION
Howe. et al. (1995) have investigated the remote palpation technique for surgical applications: a tactile sensor array in the remote tip of an instrument or probe measures the distribution of pressure across the tissue . The resulting signal is tactually displayed using a tactile feedback device mounted in the finger tip contact area of the surgeon's interface. Omata and Terunuma (1992). used a different approach for stiffness detection. which involves the use of a piezoelectric ceramic as a transducer. This is caused to vibrate at its resonant frequency. When the free end of the probe touches a material the resonant frequency shifts due to acoustic impedance. The shift in resonant frequency depends on the stiffness of the material. Miyaji, et al. (1997). used the same sensor as Omata for measuring the stiffness of the lymph nodes accurately. They concluded that measurement of the stiffness of resected lymph nodes was confirmed as an accurate approach to diagnosing lymph node metastases without knowledge of other factors. such as lymph node size or colour. Brett and Stone (1997). have investigated new methods for obtaining force and tactile information. Their approach is to determine a distribution of contact force using a small number of sensory elements distributed across the surface of a finger of known bending behaviour. The bending of the finger surface is used to assess the contact forces. The output of the sensor elements contacting soft tissue. in conjunction with the behaviour of the finger
Soft tissue can be exami ned and identi fied by palpation to assess its dynamic properties such as compliance. viscosity . lumpiness etc. In laparoscopic surgery. surgeons arc unable to palpate the tissue directly . They manipulate the tissue using instruments without a tactile capability and this makes their job much more difficult. Adding a touch sense to laparoscopic instruments would be immensely advantageous to laparoscopic surgeons and their patients. There are different approaches for dealing with tissue characterisation. The best known are probably those which are based on sensing the static force applied to the tissue and the corresponding tissue deformation or deflection. By this means the stiffness can be quantified. Bicchi . et al. (1996). used this approach to identify elastic properties of different objects . This principle is used in commercial instruments (e.g. laparoscopic pliers) modified to sense force by strain gauges and position by LEDs and optical detectors. Another approach has been proposed by Cohn. et al. (1995) . This involves a capacitive tactile sensor to detect the varying dielectric permittivity of different tissue types. It is suggested that fat, blood vessels and cancerous tissue might all be discriminated by this mean .
505
surface are used to compute surface shape using a special algorithm or using neural networks.
silic on rub b e r d om e
A different approach to tissue condition assessment is described here. This involves the application to the tissue surface of a sinusoidal displacement and measurement of resulting contact force . The sections which follow describe. the tactile sensor, the tissue assessment system and the experimental results.
~~ onnec;ng re
Fig. 2. The Touch Sensor 2. THE TACTILE SENSOR The tactile sensor used in this work is based on the AML (Applied Microengineering LTD) micromachined capacitive pressure sensor. As shown in Figure I, this sensor consists of a silicon diaphragm of IOOOJlm radius and 57Jlm thickness, mounted above a glass substrate. The silicon is held clear of the glass by a thermall y grown silicon dioxide spacer of I J..lm thickness . The overall dimensions of the chip are 3mmx3mmx I mm . A capacitive cell is formed between the silicon and a gold metallised electrode on the glass. The two electrodes are connected to gold flying wires. Application of positive pressure to the upper surface of the silicon diaphragm causes it to bend downwards. This increases the capacitance up to 60pF before it begins to bottom out. To use this AML pressure sensor as a tactile sensor, some modifications have been made to it. The sensor is supported on a cylindrical base (5mm diameter) containing two conductive paths to connect the gold flying wires . The base also houses a small hole ( I mm diameter) for sensor attachment. A layer of epoxy covers the gold wires and the conductive paths as a protection. A dome of silicon rubber covers the chip. The connecting wires are bonded to the l:o nductive paths using a conductive epoxy. Figure 2, shows the sensor after these modifications.
3. TISSUE ASSESSMENT SYSTEM The modified sensor described above is attached to the end of a sinusoidally driven rod of the tactile probe developed by Eltaib and Hewit, (2000). When the tip of the vibrating rod is pressed lightly onto the surface of the tissue to be examined, the sinusoidal displacement causes a sinusoidal force to be applied to the tactile sensor. The force experienced by the sensor causes a change in capacitance. The capacitance is measured and converted to a voltage using a CSEM2003 chip. The output (a DC voltage) is fed to a computer via a PC-LPM 16 I/O card (National Instruments). Special purpose software has been developed to display the data in graphical form and to perform the assessment of tissue condition from the dynamic behaviour. The sinusoidal displacement is useful in rendering the measurements immune to slower frequency random movements of the probe due to involuntary movements of the users hand (Eltaib and Hewit, 2000). By varying the frequency it is possible to elicit a richer set of dynamic characteristics than could be obtained using a static measurement system . Figure 3. Shows a block diagram of the overall tissue condition assessment.
511 10: :'rj I Cl p h /" 'J.~ll'l
SINU$QIDAU Y
ACruATED MECHANISM
:::.III,,:'\:, n
jjo>(l de
~i~~~'~~~ touch sen r
!
f«()
APPUCATlON
SOfTWARE (V1SUAl BAS IC)
Fig.3 . Overall Tissue Assessment System
::ig. I. AML Micromal:hined Capacitive Pressure Sensor
506
4. EXPERIMENTS AND RESULTS
eru1\
To evaluate the actual tactile sensor performance in tissue condition assessment, some experiments were carried out. The aim of the first experiment was to investigate the sensor performance when used in the assessment of homogeneous tissue. The tactile sensor was made to probe two specImens of rubber of different constitution (Srinivasan and LaMotte. 1995). The specimens were mounted on a table as shown in Figure 4. The table moved in the z direction until the surface of the specimen touched the tactile sensor. The output of the sensor then represents the initial contact force. After this the sensor' s sinusoidal motion (0.5 mm amplitude and 1.9 Hz frequency) was started, indenting the rubber specimen. The output was recorded and displayed and saved for further manipulations. The results of this experiment are presented in Figure 5 and 6 before and after filtering. It is clear that the sensor can discriminate between the two specimens. The large amplitude represents the low compliance and the low amplitude represents the high compliance specimen.
/\"
1I \ \
\j' \
\
/
/
!
\ I
\ I
! \\ ~
I
15
1
Time (sec)
Fig. 6. Output of the Probe Touching Different Specimens (after filtering)
A second experiment was undertaken to simulate the abnormality in otherwise detection of an homogeneous tissue. Here a small metal ball was embedded within the rubber specimen as shown in Figure 7. Two readings were recorded. the first when the sensor touched the soft part of the specimen and the second when the sensor was above the centre of the embedded ball. The result is shown in Figure 8. It is clear that the probe is easily able to detect the presence of the abnormality.
Q
groper\.
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l
---j~WIt
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.'
.......-r--,
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I
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I
steel boil (\l>5mrn',
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Fig. 4. Experimental Set-up
Fig. 7. Specimen Contains Rigid Ball
l00 ,--~-~---_--~-_-
I
80
r
_SO[ §..
40
afler low pass
~~~; low pass
filter
~ soft area
~~
'~o~l--~--~~~~r~~~-~-~lO~--'~ 2 lime (sec)
Fig. 8. Output of the Probe Touching Specimen Contains Rigid Ball
Fig. 5. Output of the Probe Touching Different Specimens (before filtering)
507
CONCLUSIONS A tactile sensor for tissue condition assessment has been described with particular application to minimal access surgery. It uses an existing pressure microsensor modified to register tactile force. It uses a sinusoidal motion of the probe tip to palpate the tissue and this , together with filtering removes problems associated with the involuntary movements of the surgeon's hand. Preliminary results show that the probe can detect differences between soft and hard tissue and can detect the presence of abn ormalities .
FUTURE WORK The actuator part of the tactile probe is under investigation taking into account its size relative to the touch sensor. The possibility of varying the frequency to elicit a richer set of dynamic characteristics is also under investigation.
ACKNOWLEDGMENTS The work reported here. was funded by the Egyptian Ministry of Higher Education .
REFERENCES Bicchi. A., G.Canepa, D.De Rossi, P.Iacconi and E.P.Scillingo (1996) . A sensorized minimally invasive surgery tool for detecting tissutal elastic properties. Proc. IEEE Int. Con! on Robotics and Automation. Minneapolis, USA, pp. 884-888. Brett, P. N. and R.S.W.Stone (1997). A technique for measuring contact force distribution in minimally invasive surgical procedures, Proc.lnst. Mech . Engs,Part H. 211,4,309-316. Cohn , M. B., L.S. Crawford,1.M. Wendlant, and S.S. Sas try (1995). Surgical applications of milli robots, loumal of robotic systems. 12,6,401 - 416 Eltaib, M. E. H., and 1. R. Hewit (2000). Tactile probe for use in minimal access surgery , to he presented in t it Mechatronics Forum International Conference, Atlanta. Georgia. USA . Howe, R. D., WJ . Peine, D.A. Kontarinis and 1.S. Son (1995). Remote palpation technology for surgical applications, IEEE Engineering in Medicine and Biology Magazine, 14,3, 318-323. Miyaji , K., A. Furuse , J. Nakajima, Y. Koneko, T. Ohtsuka, K. Yagyu, T. Oka and S.Omata (1997).The stiffness of lymph nodes containing lung carcinoma metastases,Cancer,80,10, 1920-1925.
508
Omata, S. and Y. Terunuma(l992). New tactile sensor like the human hand and its applications, Sensors and Actuators, A-Physics,
35,1,9-15 Srinivasan, M. A., R.H. La Motte (1995) . Tactual discrimination of softness, Journal of Neurophysiology, 73, 1.88-10 I.
A TACTILE SENSOR FOR MINIMAL ACCESS SURGERY APPLICATIONS
M E H Eltaib, J R Hewit
Department of MechanicaL Engineering University of Dundee, UK. Te/: +44 1382344497, Fax: +44 1382345508 Emai/: ).r.hewir@dlllu/ee.ac.llk . [email protected]. uk
Abstract: Touch sensing during new surgical techniques. such as laparoscopy and those involving robotic manipulators. is a challenge . In these techniques . tissue is remotely manipulated using instruments. which do not possess a sense of touch. Important properties such as tissue compliance. which give indications regarding the health of the tissue . can not be accessed. A tactile system for tissue assessment is described. It comprises a tactile sensor attached to the end of a sinusoidally vibrating rod . When the sensor indents the tissue a sinusoidal motion is transmitted to the tissue. The output of the sensor is the contact force between the tissue and the rod tip. This is used to identify the dynamic properties of the tissue. The design and implementation of the tactile sensor are described. Simple experiments involving simulated tissue have been undertaken and the results of these are reported. Copyright©2000 IFAC Keywords: Tactile Sensor. Tissue. Sinusoidal. Minimal Access Surgery. Robotics.
I.
INTRODUCTION
Howe. et al. (1995) have investigated the remote palpation technique for surgical applications: a tactile sensor array in the remote tip of an instrument or probe measures the distribution of pressure across the tissue . The resulting signal is tactually displayed using a tactile feedback device mounted in the finger tip contact area of the surgeon's interface. Omata and Terunuma (1992). used a different approach for stiffness detection. which involves the use of a piezoelectric ceramic as a transducer. This is caused to vibrate at its resonant frequency. When the free end of the probe touches a material the resonant frequency shifts due to acoustic impedance. The shift in resonant frequency depends on the stiffness of the material. Miyaji, et al. (1997). used the same sensor as Omata for measuring the stiffness of the lymph nodes accurately. They concluded that measurement of the stiffness of resected lymph nodes was confirmed as an accurate approach to diagnosing lymph node metastases without knowledge of other factors. such as lymph node size or colour. Brett and Stone (1997). have investigated new methods for obtaining force and tactile information. Their approach is to determine a distribution of contact force using a small number of sensory elements distributed across the surface of a finger of known bending behaviour. The bending of the finger surface is used to assess the contact forces. The output of the sensor elements contacting soft tissue. in conjunction with the behaviour of the finger
Soft tissue can be exami ned and identi fied by palpation to assess its dynamic properties such as compliance. viscosity . lumpiness etc. In laparoscopic surgery. surgeons arc unable to palpate the tissue directly . They manipulate the tissue using instruments without a tactile capability and this makes their job much more difficult. Adding a touch sense to laparoscopic instruments would be immensely advantageous to laparoscopic surgeons and their patients. There are different approaches for dealing with tissue characterisation. The best known are probably those which are based on sensing the static force applied to the tissue and the corresponding tissue deformation or deflection. By this means the stiffness can be quantified. Bicchi . et al. (1996). used this approach to identify elastic properties of different objects . This principle is used in commercial instruments (e.g. laparoscopic pliers) modified to sense force by strain gauges and position by LEDs and optical detectors. Another approach has been proposed by Cohn. et al. (1995) . This involves a capacitive tactile sensor to detect the varying dielectric permittivity of different tissue types. It is suggested that fat, blood vessels and cancerous tissue might all be discriminated by this mean .
505
surface are used to compute surface shape using a special algorithm or using neural networks.
silic on rub b e r d om e
A different approach to tissue condition assessment is described here. This involves the application to the tissue surface of a sinusoidal displacement and measurement of resulting contact force . The sections which follow describe. the tactile sensor, the tissue assessment system and the experimental results.
~~ onnec;ng re
Fig. 2. The Touch Sensor 2. THE TACTILE SENSOR The tactile sensor used in this work is based on the AML (Applied Microengineering LTD) micromachined capacitive pressure sensor. As shown in Figure I, this sensor consists of a silicon diaphragm of IOOOJlm radius and 57Jlm thickness, mounted above a glass substrate. The silicon is held clear of the glass by a thermall y grown silicon dioxide spacer of I J..lm thickness . The overall dimensions of the chip are 3mmx3mmx I mm . A capacitive cell is formed between the silicon and a gold metallised electrode on the glass. The two electrodes are connected to gold flying wires. Application of positive pressure to the upper surface of the silicon diaphragm causes it to bend downwards. This increases the capacitance up to 60pF before it begins to bottom out. To use this AML pressure sensor as a tactile sensor, some modifications have been made to it. The sensor is supported on a cylindrical base (5mm diameter) containing two conductive paths to connect the gold flying wires . The base also houses a small hole ( I mm diameter) for sensor attachment. A layer of epoxy covers the gold wires and the conductive paths as a protection. A dome of silicon rubber covers the chip. The connecting wires are bonded to the l:o nductive paths using a conductive epoxy. Figure 2, shows the sensor after these modifications.
3. TISSUE ASSESSMENT SYSTEM The modified sensor described above is attached to the end of a sinusoidally driven rod of the tactile probe developed by Eltaib and Hewit, (2000). When the tip of the vibrating rod is pressed lightly onto the surface of the tissue to be examined, the sinusoidal displacement causes a sinusoidal force to be applied to the tactile sensor. The force experienced by the sensor causes a change in capacitance. The capacitance is measured and converted to a voltage using a CSEM2003 chip. The output (a DC voltage) is fed to a computer via a PC-LPM 16 I/O card (National Instruments). Special purpose software has been developed to display the data in graphical form and to perform the assessment of tissue condition from the dynamic behaviour. The sinusoidal displacement is useful in rendering the measurements immune to slower frequency random movements of the probe due to involuntary movements of the users hand (Eltaib and Hewit, 2000). By varying the frequency it is possible to elicit a richer set of dynamic characteristics than could be obtained using a static measurement system . Figure 3. Shows a block diagram of the overall tissue condition assessment.
511 10: :'rj I Cl p h /" 'J.~ll'l
SINU$QIDAU Y
ACruATED MECHANISM
:::.III,,:'\:, n
jjo>(l de
~i~~~'~~~ touch sen r
!
f«()
APPUCATlON
SOfTWARE (V1SUAl BAS IC)
Fig.3 . Overall Tissue Assessment System
::ig. I. AML Micromal:hined Capacitive Pressure Sensor
506
4. EXPERIMENTS AND RESULTS
eru1\
To evaluate the actual tactile sensor performance in tissue condition assessment, some experiments were carried out. The aim of the first experiment was to investigate the sensor performance when used in the assessment of homogeneous tissue. The tactile sensor was made to probe two specImens of rubber of different constitution (Srinivasan and LaMotte. 1995). The specimens were mounted on a table as shown in Figure 4. The table moved in the z direction until the surface of the specimen touched the tactile sensor. The output of the sensor then represents the initial contact force. After this the sensor' s sinusoidal motion (0.5 mm amplitude and 1.9 Hz frequency) was started, indenting the rubber specimen. The output was recorded and displayed and saved for further manipulations. The results of this experiment are presented in Figure 5 and 6 before and after filtering. It is clear that the sensor can discriminate between the two specimens. The large amplitude represents the low compliance and the low amplitude represents the high compliance specimen.
/\"
1I \ \
\j' \
\
/
/
!
\ I
\ I
! \\ ~
I
15
1
Time (sec)
Fig. 6. Output of the Probe Touching Different Specimens (after filtering)
A second experiment was undertaken to simulate the abnormality in otherwise detection of an homogeneous tissue. Here a small metal ball was embedded within the rubber specimen as shown in Figure 7. Two readings were recorded. the first when the sensor touched the soft part of the specimen and the second when the sensor was above the centre of the embedded ball. The result is shown in Figure 8. It is clear that the probe is easily able to detect the presence of the abnormality.
Q
groper\.
hI \i,1
\\
05
l
---j~WIt
1I rstond
.'
.......-r--,
touc~/!; probe
11
il
I
>
I ~ _ I !Jrnpl == 1.). "'}rn rl"1
f..---i , -'
I
i:--
7 f=1.9H:
~pec'm~£)b ~Oble~ - , - - - . - ---L.ll.., "'.
__
...
I
steel boil (\l>5mrn',
SDong-= "ubber
'._-- --.-~
Fig. 4. Experimental Set-up
Fig. 7. Specimen Contains Rigid Ball
l00 ,--~-~---_--~-_-
I
80
r
_SO[ §..
40
afler low pass
~~~; low pass
filter
~ soft area
~~
'~o~l--~--~~~~r~~~-~-~lO~--'~ 2 lime (sec)
Fig. 8. Output of the Probe Touching Specimen Contains Rigid Ball
Fig. 5. Output of the Probe Touching Different Specimens (before filtering)
507
CONCLUSIONS A tactile sensor for tissue condition assessment has been described with particular application to minimal access surgery. It uses an existing pressure microsensor modified to register tactile force. It uses a sinusoidal motion of the probe tip to palpate the tissue and this , together with filtering removes problems associated with the involuntary movements of the surgeon's hand. Preliminary results show that the probe can detect differences between soft and hard tissue and can detect the presence of abn ormalities .
FUTURE WORK The actuator part of the tactile probe is under investigation taking into account its size relative to the touch sensor. The possibility of varying the frequency to elicit a richer set of dynamic characteristics is also under investigation.
ACKNOWLEDGMENTS The work reported here. was funded by the Egyptian Ministry of Higher Education .
REFERENCES Bicchi. A., G.Canepa, D.De Rossi, P.Iacconi and E.P.Scillingo (1996) . A sensorized minimally invasive surgery tool for detecting tissutal elastic properties. Proc. IEEE Int. Con! on Robotics and Automation. Minneapolis, USA, pp. 884-888. Brett, P. N. and R.S.W.Stone (1997). A technique for measuring contact force distribution in minimally invasive surgical procedures, Proc.lnst. Mech . Engs,Part H. 211,4,309-316. Cohn , M. B., L.S. Crawford,1.M. Wendlant, and S.S. Sas try (1995). Surgical applications of milli robots, loumal of robotic systems. 12,6,401 - 416 Eltaib, M. E. H., and 1. R. Hewit (2000). Tactile probe for use in minimal access surgery , to he presented in t it Mechatronics Forum International Conference, Atlanta. Georgia. USA . Howe, R. D., WJ . Peine, D.A. Kontarinis and 1.S. Son (1995). Remote palpation technology for surgical applications, IEEE Engineering in Medicine and Biology Magazine, 14,3, 318-323. Miyaji , K., A. Furuse , J. Nakajima, Y. Koneko, T. Ohtsuka, K. Yagyu, T. Oka and S.Omata (1997).The stiffness of lymph nodes containing lung carcinoma metastases,Cancer,80,10, 1920-1925.
508
Omata, S. and Y. Terunuma(l992). New tactile sensor like the human hand and its applications, Sensors and Actuators, A-Physics,
35,1,9-15 Srinivasan, M. A., R.H. La Motte (1995) . Tactual discrimination of softness, Journal of Neurophysiology, 73, 1.88-10 I.