IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. BME-24, NO. 4, JULY 1977
396
C. W. Fridd, "Localized Tissue Destruction by High-Intensity dard deviation. Thus differences in the absorption coefficients Focused Ultrasound," J. Urology, 107:887-891 (1973). are a partial explanation for the differing thresholds. [6] F. Dunn and F. J. Fry, "Ultrasonic Threshold Dosages for the Baseline temperatures for the tissues under irradiation condiMammalian Central Nervous System," IEEE Trans. Bio.-Med. tions were somewhat lower than body temperature (400C Eng., BME-18:253-256 (1971). measured rectally). In particular, kidney and liver (measured [71 R. Lerner, E. L. Carstensen and F. Dunn, "Frequency Depend0.5 cm below the tissue surface) were 30 and 40C below body ence of Thresholds for Ultrasonic Production of Thermal Lesions temperature, respectively, while testicular temperature was 8° in Tissue," J. Acou st. Soc. Am., 54:504-5 06 (1973). to 9'C below body temperature. The disparity between the ex[8] J. C. Chato, "Heat Transfer in Bioengineering," in B. T. Chao posed organ temperatures and the normal temperatures in situ (Ed) Advanced Heat Transfer, University of Illinois Press, Urbana, Illinois (1969). is probably due to cooling related to exteriorization and con[9] C. A. Linke, A. Elbadawi, V. Netto, A- Roberts and M. Russo, tact of the organs with coupling water during irradiation. The "Effect of Marked Hyperthermia upon the Canine Bladder," testicle seems to have a very uniform temperature profile, J. 107:599-602 (1972). while both liver and kidney exhibit increasing temperature [10] T. Urology, C. Robinson and P. P. Lele, "An Analysis of Lesion Developwith depth from the surface. ment in the Brain and in Plastics by High-Intensity Focused A thermal model [4] for the action of ultrasound on tissue Ultrasound at Low-Megahertz Frequencies," J. Acoust. Soc. Am., was used to calculate intensity thresholds for lesion produc51:1333-1351 (1972). tion on the tissues in this study. A value of 1.0 cal/cm3 0C [11] D. E. Goldman and T. F. Hueter, "Tabular Data of the Velocity and Absorption of High-Frequency Sound in Mammalian Tissues," was assumed for the product pc, and a thermal diffusivity of J Acoust. Soc. Am., 28:35-37 (1956). 0.0014 cm2/s was used [ 10], [ 2]. Thermal sensitivity and an activation energy for thermal damage of 85 k cal/mole were obtained from data on rabbit liver [9]. As discussed above, baseline temperatures and absorption coefficients varied among the tissues and are summarized in Table 1. Integrated Behavior of Artificial Skin In Fig. 5 the 2-MHz intensity thresholds as predicted by the thermal model and the experimentally determined thresholds Z. STOJILJKOVIC AND J. CLOT are plotted. Considering only differences in baseline temperature and absorption coefficients among the tissues, the different thresholds are explained remarkably well. At the longer Abstract-This paper deals with a system of planary distributed transtimes and lower intensities the experimental data for liver are ducers called "Artificial skin." The material used for this purpose is higher than predicted by the thermal model. This might be soft, homogeneous and elastic. The Belgrade hand prosthesis is covered expected if there was movement of the sound beam relative with it. The aim of this paper is to find those properties of the sensor to the tissue. In irradiations of liver, breathing of the animal unit which would enable the optimal integrated behavior of the whole made it particularly difficult to maintain relative position of system to be obtained. Two basic integral properties of artificial skin the transducer and the tissue. Considering experimental errors are implemented: tactile perception and perception proportional to and possible variation in thermal properties and activation pressure on the skin. From this it is possible to have slipping percepenergies, the agreement between predicted and experimentally tion of the grasped objects. determined thresholds is excellent. Related to the slipping perception an automatic grasping force adjustUsing the thermal model it was possible to calculate the ment is implemented. It is shown that it is possible to perceive effect of temperature on the threshold. By this means the hardness. experimentally determined thresholds were corrected to a baseline temperature of 370C. Fig. 6 compares those results INTRODUCTION with brain tissue thresholds of previous investigations. Brain has been reported to have an absorption coefficient of 0.2 Systems with a large number of the same type of units uniNp/cm at 2 MHz [ 10] , [ 1 1]. That would explain the slightly versally appear in nature. The properties of a single unit have lower thresholds observed for brain, if the activation energies no special importance by themselves, but together properties for thermal lesions in brain and the tissues in this study are of a great number of units give a purposeful behavior to the similar. whole. The question is: what properties of the sensor unit Thus it is concluded that thresholds for brain and tissues in must be designed to achieve an optimal integrated behavior of this study are similar. Those differences which have been ob- the artificial skin? This question implies another question. served can be explained on the basis of a thermal model for What is the optimal integrated behavior of artificial skin? the action of ultrasound on the tissues. In our opinion, in the case of hand prostheses to optimize the integrated behavior of artificial skin is to provide it with the following properties: softness, elasticity and mechanical reACKNOWLEDGMENT perception; hardness perception; slipping The authors are indebted to Mrs. Sally Z. Child, Henry Hon, sistance; roughness and perception; perception proportional to pressure. From and Mrs. Linda Emilson for technical assistance. the latter convex and concave patterns could be recognized, and together with a proprioceptive sensor system could be REFERENCES used for pattern recognition of a grasped object [ 1 ] . The construction of the system is first described under the [1] F. J. Fry, G. Kossoff, R. C. Eggleton and F. Dunn, "Threshold" Ultrasonic Dosages for Structural Changes in the Mammalian headings artificial skin, sensor unit, and detection and autoBrain," J. Acoust. Soc. Am., 48:1413-1417 (1970). matic elimination of slippage. The experimental behavior of [2] J. Pond, A Study of the Biological Action of Focussed Mechani- the system is subsequently discussed for two special cases. Fical Waves (Focussed Ultrasound), Ph.D. Thesis, University of nally, the conclusions to be drawn from the work are London (1968). [3] L. Basuri and P. P. Lele, "A Simple Method for Production of presented. Trackless Focal Lesions with Focused Ultrasound: Statistical Evaluation of the Effects of Irradiation on the Central Nervous Manuscript received July 17, 1975; revised May 20, 1976. Z. Stojiljkovic is with the Institute Mihailo Pupin, Belgrade, System of the Cat," J. Physiol., 160:513-534 (1962).
[4] E.
[51
L. Carstensen, M. W. Miller and C. A. Linke, "Biological Effects of Ultrasound," J. Biol. Phys., 2:173-192 (1974). C. A. Linke, E. L. Carstensen, L. A. Frizzell, A. Elbadawi and
Yugoslavia.
J. Clot is with the Laboratoire d'Automatique et d'Analyse des Systemes, Toulouse, France.
COMMUNICATIONS
397
rubber
Fig. 1. Transducer construction.
Fig. 3. Automatic grasping force adjustment.
and,1 its current amplification, then: Uf -
I
e117 Fig. 2. Principal electronic circuit for the sensor unit. I-
--
o
Ucc - uQO
Ube = R .
RI
(1)
and after Ube
396
C. W. Fridd, "Localized Tissue Destruction by High-Intensity dard deviation. Thus differences in the absorption coefficients Focused Ultrasound," J. Urology, 107:887-891 (1973). are a partial explanation for the differing thresholds. [6] F. Dunn and F. J. Fry, "Ultrasonic Threshold Dosages for the Baseline temperatures for the tissues under irradiation condiMammalian Central Nervous System," IEEE Trans. Bio.-Med. tions were somewhat lower than body temperature (400C Eng., BME-18:253-256 (1971). measured rectally). In particular, kidney and liver (measured [71 R. Lerner, E. L. Carstensen and F. Dunn, "Frequency Depend0.5 cm below the tissue surface) were 30 and 40C below body ence of Thresholds for Ultrasonic Production of Thermal Lesions temperature, respectively, while testicular temperature was 8° in Tissue," J. Acou st. Soc. Am., 54:504-5 06 (1973). to 9'C below body temperature. The disparity between the ex[8] J. C. Chato, "Heat Transfer in Bioengineering," in B. T. Chao posed organ temperatures and the normal temperatures in situ (Ed) Advanced Heat Transfer, University of Illinois Press, Urbana, Illinois (1969). is probably due to cooling related to exteriorization and con[9] C. A. Linke, A. Elbadawi, V. Netto, A- Roberts and M. Russo, tact of the organs with coupling water during irradiation. The "Effect of Marked Hyperthermia upon the Canine Bladder," testicle seems to have a very uniform temperature profile, J. 107:599-602 (1972). while both liver and kidney exhibit increasing temperature [10] T. Urology, C. Robinson and P. P. Lele, "An Analysis of Lesion Developwith depth from the surface. ment in the Brain and in Plastics by High-Intensity Focused A thermal model [4] for the action of ultrasound on tissue Ultrasound at Low-Megahertz Frequencies," J. Acoust. Soc. Am., was used to calculate intensity thresholds for lesion produc51:1333-1351 (1972). tion on the tissues in this study. A value of 1.0 cal/cm3 0C [11] D. E. Goldman and T. F. Hueter, "Tabular Data of the Velocity and Absorption of High-Frequency Sound in Mammalian Tissues," was assumed for the product pc, and a thermal diffusivity of J Acoust. Soc. Am., 28:35-37 (1956). 0.0014 cm2/s was used [ 10], [ 2]. Thermal sensitivity and an activation energy for thermal damage of 85 k cal/mole were obtained from data on rabbit liver [9]. As discussed above, baseline temperatures and absorption coefficients varied among the tissues and are summarized in Table 1. Integrated Behavior of Artificial Skin In Fig. 5 the 2-MHz intensity thresholds as predicted by the thermal model and the experimentally determined thresholds Z. STOJILJKOVIC AND J. CLOT are plotted. Considering only differences in baseline temperature and absorption coefficients among the tissues, the different thresholds are explained remarkably well. At the longer Abstract-This paper deals with a system of planary distributed transtimes and lower intensities the experimental data for liver are ducers called "Artificial skin." The material used for this purpose is higher than predicted by the thermal model. This might be soft, homogeneous and elastic. The Belgrade hand prosthesis is covered expected if there was movement of the sound beam relative with it. The aim of this paper is to find those properties of the sensor to the tissue. In irradiations of liver, breathing of the animal unit which would enable the optimal integrated behavior of the whole made it particularly difficult to maintain relative position of system to be obtained. Two basic integral properties of artificial skin the transducer and the tissue. Considering experimental errors are implemented: tactile perception and perception proportional to and possible variation in thermal properties and activation pressure on the skin. From this it is possible to have slipping percepenergies, the agreement between predicted and experimentally tion of the grasped objects. determined thresholds is excellent. Related to the slipping perception an automatic grasping force adjustUsing the thermal model it was possible to calculate the ment is implemented. It is shown that it is possible to perceive effect of temperature on the threshold. By this means the hardness. experimentally determined thresholds were corrected to a baseline temperature of 370C. Fig. 6 compares those results INTRODUCTION with brain tissue thresholds of previous investigations. Brain has been reported to have an absorption coefficient of 0.2 Systems with a large number of the same type of units uniNp/cm at 2 MHz [ 10] , [ 1 1]. That would explain the slightly versally appear in nature. The properties of a single unit have lower thresholds observed for brain, if the activation energies no special importance by themselves, but together properties for thermal lesions in brain and the tissues in this study are of a great number of units give a purposeful behavior to the similar. whole. The question is: what properties of the sensor unit Thus it is concluded that thresholds for brain and tissues in must be designed to achieve an optimal integrated behavior of this study are similar. Those differences which have been ob- the artificial skin? This question implies another question. served can be explained on the basis of a thermal model for What is the optimal integrated behavior of artificial skin? the action of ultrasound on the tissues. In our opinion, in the case of hand prostheses to optimize the integrated behavior of artificial skin is to provide it with the following properties: softness, elasticity and mechanical reACKNOWLEDGMENT perception; hardness perception; slipping The authors are indebted to Mrs. Sally Z. Child, Henry Hon, sistance; roughness and perception; perception proportional to pressure. From and Mrs. Linda Emilson for technical assistance. the latter convex and concave patterns could be recognized, and together with a proprioceptive sensor system could be REFERENCES used for pattern recognition of a grasped object [ 1 ] . The construction of the system is first described under the [1] F. J. Fry, G. Kossoff, R. C. Eggleton and F. Dunn, "Threshold" Ultrasonic Dosages for Structural Changes in the Mammalian headings artificial skin, sensor unit, and detection and autoBrain," J. Acoust. Soc. Am., 48:1413-1417 (1970). matic elimination of slippage. The experimental behavior of [2] J. Pond, A Study of the Biological Action of Focussed Mechani- the system is subsequently discussed for two special cases. Fical Waves (Focussed Ultrasound), Ph.D. Thesis, University of nally, the conclusions to be drawn from the work are London (1968). [3] L. Basuri and P. P. Lele, "A Simple Method for Production of presented. Trackless Focal Lesions with Focused Ultrasound: Statistical Evaluation of the Effects of Irradiation on the Central Nervous Manuscript received July 17, 1975; revised May 20, 1976. Z. Stojiljkovic is with the Institute Mihailo Pupin, Belgrade, System of the Cat," J. Physiol., 160:513-534 (1962).
[4] E.
[51
L. Carstensen, M. W. Miller and C. A. Linke, "Biological Effects of Ultrasound," J. Biol. Phys., 2:173-192 (1974). C. A. Linke, E. L. Carstensen, L. A. Frizzell, A. Elbadawi and
Yugoslavia.
J. Clot is with the Laboratoire d'Automatique et d'Analyse des Systemes, Toulouse, France.
COMMUNICATIONS
397
rubber
Fig. 1. Transducer construction.
Fig. 3. Automatic grasping force adjustment.
and,1 its current amplification, then: Uf -
I
e117 Fig. 2. Principal electronic circuit for the sensor unit. I-
--
o
Ucc - uQO
Ube = R .
RI
(1)
and after Ube
