IEEE TRANSACTIONS ON BIO-MEDICAL ENGINEERING, VOL. BME-17, NO. 2, APRIL 1970

Selective Cerebral Catheterization

JONATHAN MOLCHO, MEMBER, IEEE, H. Z. KARNY, EPHRAIM H. FREI,FELLOW, IEEE, AND HARDEN M. ASKENASY

Abstract-This paper describes a new method for selective cere-

bral catheterization based on the Pod catheter [6], [7], guided andpropelled by means of external magnetic fields. The principles of thePod catheter, and the necessary equipment are described, and con-

clusions are drawn from experiments with a glass model. The middlecerebral artery was catheterized selectively, and cytotoxic materialwas injected into it to treat a malignant tumor of the brain hemi-sphere.

I. INTRODUCTION

_1HE selective catheterization of blood vessels af-fords an approach to certain regions of the bodywhiclh cannot be otherwise reached even by surgi-

cal methods, owing to anatomical difficulties or becauseof the danger of possible functional damage.The human brain is a striking example of these limita-

tions which are well known to neurosurgeons. We con-

centrated our efforts on the development of a selective,endarterial approach to different regions of the brainwith the aim of essaying novel methods which had beenpreviously impractical for the reasons explained above.

Catheters made of stiff materials such as polyethylene,polyurethane, teflon, and dacron have been used forsome time to gain entrance into, and passage through,blood vessels. Their inflexibility facilitates their progress

in the artery; in order to produce a certain measure ofselectivity, their tips are given a form determined by theregion concerned. However, their inflexibility linmitstheir use in tortuous blood vessels. Stiff catheters can

cause serious damage, such as tearing of the intima, theinner lining of the vessels, formation of clots and emboli,reflex elicitation of spasms, and even puncturing of thevessels.The flow-guided catheter [1] makes possible passage

through the convolutions and branches of the mainblood vessels. To our knowledge, it has not been used forthe selective catheterization of cerebral blood vessels.

In order to overcome the limitations resulting from use

of inflexible materials, and to make possible externalcontrol of the catheter, several authors [2 ]- [5 ] havesuggested employment of a catheter guided by externalmagnetic fields, while others [5 ] have exploited the fieldgradient for its propulsion.A very flexible catheter is necessary to make selective

propulsion and direction possible. A propulsion forcemust be given to the leading end of the catheter since it

Manuscript received June 9, 1969; revised October 13, 1969.J. Molcho and E. H. Frei are with the Department of Electronics,

The Weizmann Institute of Science, Rehovot, Israel.H. Karny and H. M. Askenasy are with the Department of

Neurological Surgery, Medical School, Belinson Medical Center,Tel-Aviv University, Petach-Tikva, Israel.

is difficult to push a flexible catheter. These require-ments are satisfied by a magnetically guided and pro-pelled catheter, tlhe Pod catheter, as described in theliterature [6]-[8]. Directivity is achieved by the align-ment of a magnetic dipole in a magnetic field, while thepropulsion force results from the forced vibration of aplastic tail caused by oscillations of a magnetic dipolein an alternating magnetic field. We have attempted toadapt this approach to the selective catheterization ofthe large cerebral blood vessels: the internal carotidartery, the anterior and middle cerebral arteries.

II. PRINCIPLES OF THE POD

A. Guidance

The Pod is directed by means of an external magnet(or electromagnet) producing a torque on the magnetwhich has been magnetized longitudinally. The torqueT is given by the vector product T = vJX H, where v isthe volume of the magnet, J the intensity of magnetiza-tion, and H is the external magnetic field. The Podtends to align its longitudinal axis parallel to the direc-tion of the external field. Selection of the material forthe Pod magnet is guided by two considerations: achiev-ing maximum torque for a given magnet geometry andsafeguarding the magnet from losing its magnetizationdue to external field. The intensity of magnetizationdepends on the characteristic demagnetization curve ofthe material and on the dimensions of the magnet, inthe following way. The relationship between the inten-sity of magnetization and the internal magnetic fieldHd is determined by the geometry of the magnet as ex-pressed by the demagnetizing factor D, such that Hd= - D47rJ. By applying this to the equation B =H+4irJ, where B is the magnetic induction, the equationB = (1- (1/D))Hd is derived. The last equation describesthe shear line whose intersection with the demagnetiza-tion curve determines the magnet working point, Fig. 1[9].The torque increases with the length and the diameter

(see Table I). Therefore, the dimensions of the magnetwill be chosen on the basis of the anatomy of the targetarea. For passage through the syphon curvature, it wasdeduced from arteriographs that magnet length islimited to 3 to 5 mm. Experimenting with flow ratesthrough a catheter built using 1-mm-diameter magnetshowed adequate flow of contrast material.The ability of a magnetic material to resist demagne-

tization is measured by the coercive force Hc, Fig. 1. Ina bar magnet operating under internal demagnetization

134

MOLCHO et al.: SELECTIVE CEREBRAL CATHETERIZATION

TABLE ICOMPARISON AMONG MAGNETIC MATERIALS

I [mm 2 4 6

d[71mm Hd-H,[Oel T/H[dyn*ccii Oe-'] Hd-H, T/H Hd-Hc T/HAl V 5 1.2 25 4.5 50 11.2

2 Al IX 60 2.76 300 9.0 780 15PtCo 2670 3.1 3400 6.4 3800 9.6

Al V 25 0.6 110 2.6 320 4.51 Al IX 300 1.1 1050 2.5 1280 3.9

PtCo 3430 0.8 4000 1.6 4140 2.4

Al V 50 0.4 320 1.3 480 2.10.7 Al IX 780 0.6 1280 1.2 1440 1.7

PtCo 3800 0.4 4140 0.7 6450 1.0

Alnico V: Br= 12700 gauss, H=-660 Oe (Thomas & Skinner, Inc.)Alnico IX: Br = 10400 gauss, H, =-1580 Oe (Thomas & Skinner, I nc.)PtCo: B, = 6450 gauss, H, = -4300 Oe (Hamilton Watch Co.)

L,2~~~~~~~~~1<--- > t m -~~~~~~-t-o 0

--H-,4-- s + @-^ 6 2

1000 800 600 400 200 0

DEMAGNETIZING FORCE-H-OERSTEDS

Fig. 1. Demagnetization curve and shear lines.

field Hd, its ability to resist demagnetization is mea-sured by Hd-H,. In Table I, three magnetic materialsare compared as to their torque per unit magnetic fieldand their Hd-H,.The material which is best suited for a Pod magnet of

3 to 5 mm length and 0.7 to 1-mm diameter is Alnico IX.Th-e torque available with this material almost equalsthat of Alnico V whereas it is more resistant to demagne-tization. Platinum cobalt (PtCo) is characterized byvery higlh coercive force but its torque is low. In theexperiment described below, we used Alnico Vimagnetsbecause Alnico IX mlagnets in suitable dimensions werenot available.

B. PropulsionThe propulsion of the Pod in a fluid is attributed to

the transverse nmotion of eaclh cross section of the plastictail caused by the vibration of a magnet fixed at thecatheter tip. This transverse motion causes a flow fieldand pressure distribution resulting in a local lifting forceon each cross section. The resultant propulsion force isobtained by integrating the product of the local lift andslope along the tail. The mechanism of the Pod propul-sion resembles the sw%immiiiing of fish and certain typesof water snakes. The difference is the transverse mnotion.In the case of the Pod, this motion is due to propagation

of elastic waves along the tail, whereas with fish andwater snakes, their tail can perform, at will, a transverseimotion which develops sophisticated forms of propagat-ing waves. These w<aves result in a high efficiency ofswimming.The theory of the "swimming of the Pod" was de-

veloped by Longman and Lavie [10]. The authors as-sumed a mathematical model wvhich considered thechanges in the field of the potential flow. A further de-velopment of the theory suggested by Lavie [1 ] takesinto consideration the fluid viscosity and the influenceof the tube in wlhich the Pod swims.The average Pod propulsion force P is given by

- tdr- PC2u 4(x k! 2 (- PC2 LTZ A (?) - dx

wlhere h(x, t) is the transverse motion of any cross sec-tion, x is the longitudinal axis, t is the time, p is the fluidspecific mass, U is the propulsion velocity, 1 is the Podlength, cl is a coefficient ranging between 1 and 2, c2 is acoefficient depending on fluid viscosity and the angularfrequency of the magnetic field, and A (x) is an equiva-lent area depending on the Pod cross section and thediameter of the vessel. A bar over the derivatives de-notes a time average. The propulsion velocity is de-termined from the equilibrium of the propulsion forceand the drag force, the latter being given by D=2PCDSU2 where CD is the drag coefficient and S is a refer-ence area. Equalizing P and D results in a quadraticequation for U.The transverse motion h(x, t) is given by the differ-

ential equation02/i 02 F 032/i-

m(x) --1+ -[ EJ(x) -F(x, 1) = F(x, 1)

where m(x) is the mass per unit length, E is Young

135

IEEE TRANSACTIONS ON BIO-MEDICAL ENGINEERING, APRIL 1970

12

n

E

0;i

10

8

6

4

2

0 2 4 6 8 10 12

FREQUENCY, in Hz

14

©l

! '-4

16

Fig. 2. Pod velocity versus frequency.

modulus of elasticity, I(x) is the inertial moment of thecross section, F,(x, t) is the local lifting force, and F(x, t)is the force exerted on the Pod magnet by the magneticfield.

In Fig. 2 an analytic solution for U, obtained with theaid of a computer, is presented with experimental data[12]. As can be seen, the analytic solution provides a

good fit for the experimental data until 9Hz. Above thispoint, power supply limitations become apparent. Thecomputation was based uponI an assumed system whichcould supply enough energy to sustain a monotonic in-crease in velocity with frequency. The Pod used in theexperiment consisted of a silastic tail 80 mm in length,4-mm (outside diameter), 3-mm (inside diameter), andan Alnico V bar magnet 3.5 X 14.0 mm. During the ex-

periment the propulsion force was nmeasured and foundto be about 1 gram at a frequency of 11 Hz.

III. MAIATERIALSA. Pod Catheter

The catheter, illustrated in Fig. 3, is manufacturedfrom materials which are sufficiently inert for short-term catheterization. The Pod magnet1 (Q) is of Alnico V,magnetized lengthwise, 4 mm long and 1 nmm in diam-eter. It is inserted in the end of a silicone tube2®( with0.8 mmi ID 1.3 mlnm OD, and lengtlhs of 57, 59, and 61cm. The magnet fits tightIy anid the vibrations will notfree it. About 2 mim beyond the mlagnet, a slit of about7 mm in lengthi (®) was made in the silicone for egress offluids injected into the catheter. A PTFE tube3 (®) 47 cnlong, with 0.58 mmnn ID and 0.88 mim GD is threadedthlrough the otlher end of the silicone tubing. This com-

bination of silicone and PTFE tubing imparts rigidityto the proximal end of the cathieter and enables it to bepushed forward in such a way that the flexible end may

propel withlout pulling after it the whole length of thecatlheter. The length of the free end of the silicone tubingis determineed by the regioin to be approachied. A plastic

1 Permag Co.2 'he Holter Co., i\,ledittide ESTI08R.3 PolypenIc0, #ST'\Vk 24.

Detail A

Fig. 3. The Pod catheter.

fitting (® is attached to the end of the PTFE tube to en-

able injection through the catheter.Before use, the catheter is preloaded into the flexible

joint ( and the Y-joint.4 The flexible joint is of poly-ethylene of internal diameter 2.2 mm, and length of 8,10, or 12 cm according to the length of free siliconetubing in the catheter. The flexible joint allows ma-

nipulation with the end of the catlheter without theapplication of pressure on the point of entry into theartery. The Y-joint prevents the leakage of fluidsaround the catheter while it is passing through.

During the catheterization procedure, heparinizedsaline is passed through the catheter and, occasionally,also through the Y-joint to prevent the formation ofblood clots in the catheter assembly. During radiogra-phy, a contrast substance is injected into the catheter.The catheter is inserted into the carotid artery by means

of a polyethylene cannula (, 9 cm long, 1.8 mm ID and2.4 inm OD, and a suitable trocar (®. The distal end ofthe cannula is ground to an angle of 5°.

B. Directing Magnet

Permanent magnet for guidance is of Alnico IX withdimensions of 20 by 10 by 10 cm and 14.6 kg in weight.It is fixed to a stand to facilitate direction. Fig. 4 showsthe relationship between axial magnetic field5 and dis-tance from the face of the magnet. A field of 100 Oe isrequired for effective deflection of the Pod magnet inthe glass model (See Section IV7), so that the magnetcannot be more than 11 cm from the catheter.

C. Excitation in an Alternating Field

The alternating field required is generated in a coilwrith an air core of 40 cm OD, 30 cm ID and 11 cm

heiglht with an inductance of 0.4 henry. Fig. 4 showsthe variation of magnetic field in the space above thecoil5 when a dc current of 4 amperes is flowing throughthe coil. In experiments withl the glass model, it was

fouind that a field of 100 Oe was required for effective

4Becton & Dickinsoni, #3106 (615A).6 Measured with a Bell "110," gauissmeter.

---- Theoretic curve /

Meosured curve //I/_

I_II

.1 1

0 E{s

136

t-&,N.190)

MOLCHO el al.: SELECTIVE CEREBRAL CATHETERIZATION

)of 1I~~~~~

)o

)0

)0

10-

2 4 6 8 10 12 14

DISTANCE, X in cm

LOAD

Fig. 6. Block diagram of the variable frequency power supply.

Fig. 4. Axial magnietic field of Alnico IX directing magnet.

Z 1-I

Ezb==F~~xz-4cm

,1200

DISTANCEX in cm

Fig. 5. Magnetic field above the coil carrying 4 amperes.

movement of the Pod, so that wrhen a current of 10

amperes is applied, the working region of the coil ex-

tends to a radius of 10 cm from the axis at a height of 16

cm above the face. See Fig. 5. The coil is fed from a

variable-frequency square-wave power supply. A cur-

rent of up to 15 amperes can be delivered to a resistive

load in a frequency of 5 to 100 Hz. A block diagram of

the supply is shown in Fig. 6.

The schematic diagram of thle inverter is showrn in

Fig. 7 [13]. The circuit wrorks as follows. The load is

connected to the dc supply by one of two pathways, the

first consisting of L1, SC]?1, D1, D3, SC]?3, and L2; and

the second consisting of L1, SC]?2, D2, D4, SC]?4, and L2.

The current under load changes its direction as the

pathlway followed is changed. After turning on SC]?

and 5CR3, the first pathway conducts; whlen SCR2 and

SC]?4 are turned on, the direction of flowt under load is

reversed. The commutation capacitors C1 and C2 serve

to switch off SCR1 and 5CR3. The diodes D1 to D4 con-

trol dischlarge of the capacitors bzy way to thle requisite

SOR, thuls ensuing comlplete comlnutltation, The chokes

L1 alnd L2 prevent shlort-circuiting the dc sulpply durinlgthe short interval whlen all the SC]?'s are conductinlg.Thle diodes D5 to D8 prevent hlighl-voltage transients

C: 0.1 /iF 600V

C1-2:8,4 F 500VD1-8: MO-60,TAG, 22 A,600V

LI-2:0.5 MH

S.C.R. 1-4: 219k WESTINGHOUSE35A,500V

Fig. 7. Schematic diagram of SCR inverter.

when an inductive load is applied. The series R-C,connected in parallel with all semiconductors, guardsagainst overvoltages.

IV. EXPERIMENTS WITH THE GLASS i\IODEL

To examine the method of catheterization in vitro,three glass models of the internal carotid artery (ICA),the middle cerebral artery (1\ICA), and the anteriorcerebral artery (ACA), with internal diameters of 6, 3,and 3 mm, respectively, were built. The models differedin the convolutions of the siplhon in accordance witlh theexpected anatomical variations. One of the nmodels isshown in Fig. 8; the model is connected to a closed flowcircuit shown in Fig. 9.By means of constriction A and B, the pressure and

the flow rate were adjusted to physiological values, i.e.,a mean pressure of 100 mm Hg and a flow rate of 250cc/min. In the first part of the experiment, water was

passed tlhrough the system, and the following resultswere obtained.

1) In the absence of flow, the catheter may bepushed so that its tip reaches the beginning of thesiplhon.

2) During flow, in the absence of imagnetic flelds, thebeginning of the siphon is reached and even, attimnes, the bifUrcation beyond (flowV-gUided catlh-eter).

l60

140

a 1200

I 100

- 80

F 60

1z

< 40

20

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IEEE TRANSACTIONS ON BIO-MEDICAL ENGINEERING, APRIL 1970

Fig. 8. Glass model of internal carotid artery, middle cerebralartery, and anterior cerebral artery. Fig. 10. Skull X-ray demonstrating selective catheterization of

middle cerebral artery.

FLOWMETER

PUMP: MANOSTAT Co. VARISTALTIC PUMP

FLOWMETER:FISClER & PORTER.TUBE NO. FP-1/4-20-P-3/37

MANOMETER:ESM M.RON

Fig. 9. Setup for in vitro experinmenit.

3) Application of an alternating field of 7 to 15 Hzunder a power of 8 to 10 amperes enabled facilepassage through the wl\ole of the model with thepossibility of direction to MCA or ACA.

4) The flow barrier in the glass model was measured,and there was a fall of 7.5 percent in the flowrate in MlCA in the presence of the catheter(174 cc/min in its presence and 188 cc/min in itsabsence at a pressure of 120 mm Hg).

5) The length of free silicone tubing depends on theregion to be reached and should be minimal.

6) The magnets employed were 3 to 5 mm long.7) Removal of the catheter is very difficult because

of friction with the inflexible glass walls.8) The optimal location of the coil varies along the

pathway. Free passage of the catheter withoutthe necessity of moving the coil could only beattained by placing the coil witlh its axis per-

pendicular to ICA.

In the second part of the experiment, heparinizedblood was passed througlh the system and the same

results, apart from 7, were obtained.

V. CLINICAL TRAIL

Experiments on the glass model and on cardiovascularcatheterizationi of animinals [7] provided the necessary

experience to completely control the direction of thecatheter. Cerebral catheterization was then employed

on a human subject. The patient was suffering fronm amalignant tumor of the brain, and both surgical andradiation treatment had been unsuccessful. The Podcatheter was used as a means of injecting a cytotoxicmaterial to the site of the tumor. The injection of suchdrugs into the common carotid artery in the neck ofcancer patients has been previously reported [14]. Thesite of the injection of cytotoxic materials is as close aspossible to the tumor, thereby achieving a hiigher localconcentration. The tumor, in this first case, was mainlysupplied by blood from the middle cerebral artery as wasshown by earlier serial angiography.

Penetration by the catheter into this artery wouldenable the injection of a higher concentration of thecytotoxic material into this space-occuping lesion.Under X-ray control with closed-circuit TV, the cath-eter with 11-cm long flexible silicone and 1 by 4 mmmagnet, was inserted into the common carotid artery.The patient's head was stabilized opposite the center ofthe coil which was generating the alternating magneticfleld so that the distance between the coil and the Podin the artery was approximately 13 cm. With a coilcurrent of 10 amperes at a frequency of 10 Hz and withthe catheter intermittently perfused with an anti-coagulant solution,6 the free progression of the Pod tothe required region could be observed. The injection of1.5 cc of urographin 76, afforded a good selectivearteriography of the middle cerebral artery and con-firmed the position of the catheter. The cytotoxic ma-terial7 was then injected and the catheter removed.

It is to be noted that magnetic fields interfere withthe X-ray picture derived from the image intensifier. Aconstant magnetic field causes rotation of the image pro-duced on the monitor but it is still possible to identifythe Pod and distinguish anatomical details. An alter-nating magnetic field causes the picture to be blurred,

6 llepariiized 0.85 percent NaCl solution.7 Methotrexate sodium (4-amino, N'° methyl pteroylglutamic

acid sodium).

138

MOLCHO et al.: SELECTIVE CEREBRAL CATHETERIZATION

and consequently, the alternating field had to be turnedoff during radiography. It is planned to apply magneticshielding to the image intensifier to permit following theadvance of the Pod witlhout interruption.

VI. DISCUSSION

In the light of the limitations of access to variousregions of the body, the approach by way of the bloodvessels (arteries or veins) affords a possible solution tosome of the problems. Since the approach to manyareas of the brain is hindered by their location and bythe sensitivity of neiglhboring vital structures, theauthors were able to gain access to the brain by guidedcatheterization. To overcome the obvious limitations ofrigid catlheters, a catheter composed of a rigid proximalportion and a flexible distal portion terminated by anelongated magnet was employed with success. Applica-tion of an alternating magnetic field perpendicular tothe axis of this magnet caused it to oscillate and gave apropulsion force to the distal end of the catheter. Theprogression was helped by manipulation of the rigidportion of th-e catheter which protruded from the neck.The catlheter was inserted into the common carotid

artery and led to the internal carotid artery. After pass-ing througlh the arterial siphon, it reached the bifurca-tion of the middle cerebral artery and the anteriorcerebral artery and was thence directed into its targetin the middle cerebral artery. The success of the pro-cedure illustrates the reliability of the method whichdepends on the direction and propulsion of a catheterby means of magnetic fields.

It must also be pointed out that the advance of thecatheter was greatly facilitated by the blood flow whichpulls along the catlheter and lessens the friction in thearterial walls. It is concluded that the catheter affordsan acceptable means of selective catheterization inarterial blood vessels.No useful information of a humiian catheterization

can be gained through experiments involving cerebralcatlheterization of animals. The reason is the differencesin the cerebral vascular circulations.

Experiments Tith the glass model and human cath-eterization have shown that with an appropriate sizecatheter there is no danger due to reduced blood flow.Such work has been done by our group and has alsobeen announced recently by personnel of the AMas-sachusetts General Hospital in the third internationalBiophysics Congress and by otlhers at the ColumbiaUniversity M\Iedical Center [15 ]. Up to the present date,we have performed tlhree catheterizations successfully.

Development of this method will provide the neuro-surgeon with a new operative technique enabling en-darterial approach townards cerebral aneurysms, ar-terio-venous malformations, and tumors. These pa-thologies carry a high operative risk using present-daysurgical techniques. Direct injection of highly concen-trated cytotoxic materials may be more efficient than

systemic injection in treatment of malignant tumors ofthe brain.The behavior of the Pod catheter and its propulsion

in venous blood vessels are being currently investigated,and the results will be published shortly, together with adescription of additional possibilities of use of th-e Podin endarterial routes.

Potential damage due to direct magnetic interactionwith substances of the living body should be considered.According to Becker [16], who summarizes earlierworks on this subject, we concluded that no damage canbe expected by the magnetic field strengths, gradients,and frequencies that we used. Prof. H. P. Schzwan [17 ],from University of Philadelphia, pointed out the pos-sibility of eddy current induced in the brain tissue dueto alternating fields. This has been considered and foundto be far below possible damage.

ACKNOWLEDGMENT

The authors wish to thank Dr. A. 1\I. Lavie for hiscontribution to the portion dealing with the propulsionof the Pod, A. Kedem and J. Leibowitz for their helpin building the catheter, Z. Friedman for his technicalassistance during catheterization, and Dr. S. K. Hilal,Eng. J. Driller, and their group for their cooperationand free exchange of information.

REFERENCES[1] C. T. Dotter and K. R. Straube, "Flow guided cardiac cathe-

terization," Am. J. Reontg., vol. 88, pp. 27-30, July 1962.[2] J. W. Devine and J. W. Devine, Jr., "Duodenal intubation,"

Surgery, vol. 33, pp. 513-515, April 1953.[31 H. Tillander, "Selective angiography of the abdominal aorta

with a guided catheter," Acta Radiol., vol. 45, pp., 21-26,January 1956.

[4] H. F. McCarthy, H. P. Hovnanian, T. A. Brennan, P. Brand,and T. J. Cummings, Proc. 4th Inst. Conf. Med. Elect. (NewYork, N. Y.), p. 134, 1961.

[5] S. B. Yodh, N. T. Pierce, R. J. Weggel, and D. B. Mont-gomery, "A new magnet system for intravascular navigation,"Med. and Biol. Engrg., vol. 6, pp. 143-147, March 1968.

[6] E. H. Frei, S. Leibinzohn, H. N. Neufeld, and H. M. Askenasy,Proc. 16th Conf. on Engrg. in AMedicine and Biology, (BaltimoreMd.), p. 156, 1963.

[7] E. H. Frei, J. Diller, H. N. Neufeld, 1. Barr, L. Bleiden, andH. M. Askenasy, "The Pod and its applications," AMed. Res.Engrg., vol. 5, pp. 11-18, 1966.

[8] S. K. Hilal, WV. J. Michelsen, and J. Driller, "The Pod catheter,A means for small vessel exploration," 14th Annual Conf. Mag.and Magnetic MIaterials (New York, N. Y.) November 1968.

[9] Thomas and Skinner, Inc., "Permanent magnet design,"Bulletin no. 303, p. 9.

[10] I. M. Longman and A. M. Lavie, "On the swimming of a Pod,"J. Inst. Math. Appl., vol. 2, pp. 273-282, September 1966.

[11] A. M. Lavie, "Analysis of the swimming of a slender flexiblecylinder in the presence of viscosity," to be published.

[12 ] A. M. Lavie and J. Molcho, "Further investigation of theswimming of a Pod," to be published.

[13] A. Hoffman and K. Stocker, Thyristor Hadbuch. Berlin:Siemens Schuckertweske, 1966.

[14] E. A. Bering, Jr., C. B. Wilson, and H. A. Norrell, "The Ken-tucky conference on brain tumor chemotherapy," J. Neuro-surgery, vol. 27, No. 1, pp. 1-10. 1967.

[151 J. Driller, S. K. Hilal, W. J. Michelsen, B. Sollish, L. Katz, andW. Konig, Jr., "Development and use of the Pod catheter in thecerebral vascular system," MIed. Res. Engrg., vol. 8, pp. 11-16,August-September 1969.

[16] R. 0. Becker, "The biological effects of magnetic fields-Asurvey," Med. Electron. Biol. Engrg., vol. 1, pp. 293-303, 1963.

[17] H. P. Schwan, private communication.

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IEEE TRANSACTIONS ON BIO-MEDICAL ENGINEERING, APRIL 1970

Jonathan Moicho (M'66) was born in Petach-Tikva, Israel, on July 1, 1942. Hereceived the B.Sc. and M.Sc degrees in electrical engineering from the Technion-Israel Institute of Technology, Haifa, in 1964 and 1968, respectively.From 1964 to 1966 he was a Research Assistant in control engineering at the

Technion. Since 1966 he has been working in medical engineering at the WeizmannInstitute of Science, Rehovoth, Israel, and at the Technion. His main fields of in-terest are vascular catheterization and vascular pulsations.

Mr. Molcho is a member of the Israel Society of Biomedical Engineering.

H. Z. Karny was born in Tel-Aviv, Israel, on December 27, 1936. He received theM.D. degree from Hebrew University, Jerusalem, in 1965.

Since 1965 he has been working in the Department of Neurological Surgery,Belinson Medical Center, Petach-Tikva, Israel, and at the Tel-Aviv University, underthe supervision of Prof. H. M. Askenasy. In addition, since 1968 he has been workingin the field of neurophysiology, doing research and teaching in the Department ofPhysiology, Hebrew University, Tel-Aviv.

Ephraim H. Frei (M'51-SM'62-F'67) was born in Vienna, Austria, on March 2, 1912.He received the Dr. Phil. degree from the University of Vienna in 1936.With the exception of the years 1950 through 1952, which were spent with the

Computer Project of the Institute for Advanced Study, Princeton, N. J., he has beenwith the Department of Electronics, Weizmann Institute of Science, Rehovot, Israel,since 1948. He was appointed Professor in 1960, and Head of Department in 1961.During the year 1959-1960 he was on sabbatical leave at the Stanford Research In-stitute, Menlo Park, Calif., where he worked on magnetic computer devices andmeasurements. During the summer of 1968 he was on sabbatical leave at the MedicalSchool of Stanford University where he worked on magnetic devices for medical ap-plications.

Dr. Frei is Chairman of the Israel Society for Biomedical Engineering. He is amember of the Israel Physical Society and the American Physical Society.

Harden M. Askenasy was born in Bucharest, Romania, on July 31, 1908. He re-ceived the M.D. degree from the Medical Faculty of the University of Paris in 1934.He has worked in Europe and the United States and, since 1948, has been Chief of

Neurosurgery at the Belinson Medical Center, Petach-Tikva, Israel. Since 1965 hehas been Professor and Chairman of the Department of Neurological Surgery at theUniversity of Tel-Aviv Medical School.

Dr. Askenasy is an honorary member of the French Society of Neurosurgery and amember of the American Association of Neurological Surgeons (The Harvey CushingSociety). He is the President of the Israel Society of Neurological Surgery.

140