- Email: [email protected]
A radiotelemetrical measuring device, implantable on animals, for long term measurements of radionuclide-tracers
International Journal of Applied Radiation and Isotopes, 1972, Vol. 23, pp. 505--511. Pergamon Press. Printed in Northern Ireland
A Radiotelemetrical Measuring Device, Implantable on Animals, for Long Term Measurements of Radionuclide-Tracers J. B O J S E N and K. W A L L E V I K The Finsen Laboratory, The Finsen Institute, Copenhagen, Denmark
(Received 23 June
1972)
The construction of a radlotelemetrical measuring device implantable on animals as small as rabbits and designed for continuous long term detection of low y-energy radionuclide-tracers is presented. The GM-detector and the FM-trammitter are coated in an araldite shield, the total volume is 140 cm 3 and the weight is 135 g. Reliable continuous measurements can be performed on unrestrained animals in periods up to 5 months. It is possible to measure discontinuously by external switching the measuring device on and off. The implantation technique is described. The detector seems to have its utility in pharmacological tests and in turnover studies. U N I N S T R U M E N T /~ M E S U R E T E L E M E T R I Q U E I M P L A N T A B L E S U R LES A N I M A U X P O U R LES M E S U R E S A L O N G U E T E R M E DES I N D I C A T E U R S A RADIO-NUCLEIDES On pr6sente la construction d'un instrument A mesure radiotdl~m6trique implantable sur des animaux aussi petits que le lapin et destin~ A la d6tection continuelle A longue terme des indicateurs A radionucl~ides de petite ~nergie y. Le d6tecteur Geiger et le transmetteur F M sont enduits d'une couche d'araldite, le volume total est 140 cm 3 et le poids est 135 g. On peut faire des mesures certaines et ininterrompues sur des animaux non contraints pour une p~riode de cinq mois, mais on peut faire des mesures discontinu6es par l'interruption ext~rieure de l'instrument. On d~crit la m~thode d'implantation. Le d6tectenr paralt avolr son utilitd d am les essais pharmacologiques et dans les 6tudes de changement de population. P A ~ H O T E J I E M E T P I f q E C H H F I H P H B O P , HMHJIAHTHPYEMblI?I HA H~HBOTHbIX, ~ J I H ~ O J I F O C P O q H b I X H3MEPEHHI~I PA~(HOAIRTHBHbIX H3OTOIIHbIX HH~HHATOPOB IIpe~cTasJieHa RoncTpy~Ha pa~HoTeaeMeTpHqecKoro I~sMepHTeJIbHOrO ycTpo]~lCTBa, HMHJIaHTHpyeMoI'O Ha H~HBOTHI~IXTaI~HX H~O MaJIeHbHHX HaI~ HpoJIHHax, H paccqI4TaHHOFO RJI~ HeHpepHBHOPO ROJIPOCpOqHOPOReTeKTHpOBaHH~ pa~HOaHTHBHhIX H3OTOIIHMXHHRHKaTopos C MaJIO~ ~Hepr~Ie~ raMMa-~yqel~. I I o ~ p ~ neTeKvop ,GM, ~ nepe~aT~n~ , F M , c 8 a m ~ T O ~ THna , A p a ~ T * , o 6 n ~ z t i 0 5 ~ e M - - 1 4 0 CMs, Bee--135 r. Ha Hec~sepm~saH~X H~I4BOTHMXBO3MOH~HOHpOH3BO~HTI~Ha~e~H~e, HeI~pep~BH~e H3MepeHH~ B TeqeHHH HepHo~a 5 Mecffna, a ~ncHpeTH0e nB~epeHHe n BOBMO~HHOnpH BHeLUHePOBI~IHJIIOqeHHHH BHJnOqeHHH HpHSopa. OHHCaH MeT0~ HMnJIaHTHpOBaHHff. OHash~BaeTcff, tiT0 HoJIe3HOCTI~ ~eTeHTopa HaXO~HTCH B ~apMaHoaorHqecHHx HCII/aITaHHHXH HCCJIe~0BatIIIHXHpyPOBOp0Ta. EINE INDIKATOR-FERNMESSVORRICHTUNG ZUR IMPLANTATION IN TIERE FOR LANGJAHRIGE MESSUNGEN VON RADIONUKLIDENINDIKATOREN Die Konstruktion einer Indikator-Fernmessvorrlchtung, die in so Ideine Tiere wle Kaninchen elnlagef~ihig ist und auf lange J a h r e Radionukliden-Indikatoren niedriger Gammaenergie nachweisen kann, wlrd beschrieben. Der GM-Detektor mad der FM-Sender sind in einem Aralditschlrm eingeschlossen, das Gesamtvolumen betriigt 140 cm ~ und das Gewicht 135 g. 505
J. Bojsenand K. WaUevik
506
Zuverl~issige Dauermessungen k6nnen an unbehinderten Tieren in einem Zeitraum ,con ftinf Monaten untemomrnen werden, doch ist es m6glich, dutch Ein- und Aussehalten der Vorrichtung yon aussen niehfforflaufend zu messen. Das Implantationsverfahren wird beschrieben. Der Detektor scheint eine nutzbare Verwendung ftir pharrnakologische Versuche und in Umsatzstudien zu haben. INTRODUCTION DURING the last decade m a n y biological a n d medical experiments have been performed by radiotelemetry techniques. (6) This technique permits a continuous m e a s u r e m e n t without disturbing the metabolic state of the animal. Initial attempts have been m a d e (2'n) to build instruments for measurement of radioactivity in combination with telemetric transmission of the results, because this would be applicable to m a n y experiments using radionuclide-tracer techniques. However, no implantable telemetry equipment has been developed for experimental or clinical use up to now. This p a p e r describes a telemetry system, which can be implanted on the back of an animal as small as a rabbit. T h e equipment is designed for long t e r m detection of radionuclide-tracers in the blood. io.~o
Description of the measuring equipment T h e GM-detector and transmitter are contained in an araldite ® shield (Fig. 1) m a d e waterproof in order to protect the electronic functions, especially the high voltage supply circuit, against humidity from surrounding tissue (1). I n Fig. 2 a block diagram of the transmitter and receiver system is shown. Figure 3 shows a circuit diagram of the implantable electronic transmitter. T h e transmitter circuit can be divided in three parts : the detector, the high voltage supply unit and the frequency modulated transmitter. T h e transducer for detection of the radioactivity is a G M - t u b e (Philips 18515), 26 m m in diameter with end-window (thickness 1.5-2 rag/era2). T h e plateau has been measured to be 400-760 V. T h e high voltage supply is made by a transformer-sinusoid-osciUator (operating
.j
I
FIO. 1. The araldite shield.
Antenna
I
I I I I I I
F.M.
[ F.M,
t'4V Batter y
~
Receiver
Transmitter
I i
,,, H '"'"'
o..,,,.,.. H
Scaler
,0,,.,. ~ °'-'~'", ""'°"" ,
I
I ~,,,,., I 1
'
FIG. 2. T h e block d i a g r a m of the t r a n s m i t t e r a n d receiver system.
24.
C3
12=D1
Et
-
C |
s;, =J
JR, ±c5 l~ '
OsciUator
Voltage Multiplier
Detector
F.M. Transmittef
Fxo. 3. T h e d i a g r a m of the detector a n d t r a n s m k t c r system. C1 Cs Ca C4 Cs C6 C7
Amplifier
= C s ----6-8 pF/6-3 V T a n t a l , Bosch 0678901208 == 0.22 p F / 3 5 V T a n t a l , Bosch 0678901232 ----4.7 nF/125 V d.c. F c r r o p h e r m =- 1 n F / l k V d.c. F e r r o p h e r m =- 100 pF, M i a l polysWrole = 9 pF, M i a l polystyrole = 33 pF, M i n i polystyrole
R I = 0-15 M f ~ R s = I k£~
R3 lOk.Q R4 10 M£~ R s = 100 k ~ R e = 3.3 k£~ T 1 = B C 146 Philips = =
T s = M P S 918 Motorola D 1 = M R 40 Atlantic Semiconductor GM-T = 18515 Philips L I ----HF-coil, 3 turns, prlntcd circuit Tlt -----transformer 10:50:2000 (0.09 ~, 0.05 z Cu) N22 O.L. Sifcrrit Siemens B 6 5 5 4 1 K 0000-R 022 E I = E s = 1.4 V, Mallory R M - I - N - T 2 S I ----S s Logccll, @ m a g n e t switch, Fifth Dimcnsion
Inc. 3000-IC-WLA. I n case o f pulse forming a 1 M ~ c a n b e serialized w i t h C 4. 507
Timer
508
J. Bojsenand K. Wallevik
frequency = 10 kHz) with a voltage multiplier ( × 12) at the transformer output. T h e circuit diagram of the high voltage supply is in principle similar to that of MACKA'¢~), but the low voltage supply is only 1-4V(E1) (Mallory RM1-N1000 mAhr) contrary to 2"8 V, the transformer (Tr) in the oscillator has a different size and winding ratio (Siemens 14 z N220.L.--10:50: 2000) and finally the voltage multiplier (24 X C8, 12 × Dx) is divided into two parallel branches in order to reduce the series reactance of the transformer output circuit. T h e total output charge capacitance is about 1.5 nF, which will secure a high count rate limit. When the low voltage battery has just been renewed the high voltage is 620 V. It will decrease to about 540 V after a period of maxim u m 270 days before the battery leaves the discharge plateau. Implanted at 37°C and at the low level of discharge (150/zA) the life time of the battery will be reduced to about 60 per cent or equal to 160 days of continuous operation. It is obvious that due to the low slope of the plateau for the GM-tube (3 per cent ]100 V) no correction of the count rate is necessary in the measuring period. A fraction of each signal impulse generated by the GM-tube is fed to the basis of the transistor (T,) in the FM-transmitter. ~SJ T h e transmitter is supplied from a separate 1.4 V battery (E,) (Mallory RMI-N) and the supply current is 180 pA, equal to a life time of 140 days. T h e emitter resistor R e can be changed from 3-3 to 2"7 k ~ if a higher output power is necessary, but this increases the power consumption and decreases the life time of the transmitter. T h e operation frequency is about 108 M H z and the range of the transmitter is 1-2 m outside the animal cage wall. $1 and $2 are magnetic bistable switches (Logcell®), which can be externally activated by a magnet. In this way it is possible to save electric power in periods where measurements are of no interest. T h e whole transmitter system is mounted on a printed circuit card (5 cm × 7 cm) (Fig. 4). T h e weight of the total electronics is 60 g of which 40 per cent is the low voltage batteries. The transmitter coil (Lx) radiates the
signal. The receiver antenna, shown in Fig. 2, is a five-turn loop placed horizontally on the outside of the cage wall ~3) in order to measure the near magnetic field from the transmitter. T h e receiver is a commercially available F M tunerset (Larsholt 7250-3000). It has been necessary to increase the signal level 22 dB by means of antenna-preamplifiers. T h e signal to noise ratio for the whole system in operation has been measured to be 32 dB. T h e received impulses are accumulated in the scaler and the printer is controlled by the timer.
Coating of the transmitter T h e shield is made by araldite ® (Ciba: D (CY230)-HY951) (100-0 g: 9"0 g), and the wall of the shield is 2-3 m m thick (Fig. 1). T h e electronic unit is fixed to the lower part of the shield by means of screws. Inside the upper part of the shield the two micro magnet switches are fixed to the surface of the wall by gluing. T h e shield has been moulded in two moulds made by silicone rubber (Wacker Silicon Kautchuk-Abformmasse B). T h e shield is polished before the electronics are mounted, and a small bag of silica gel (2-3 g) is placed inside the shield before it is closed by araldite. Finally a nylon net (Fig. 1) is glued to the shield. T h e total weight of the implantable detector system is 135 g and the volume is 140 cm 3. T h e total thickness of the araldite in front of the GM-tube end-window is about 200 mg/cm 2 and the maximum count rate for the described system is 200 c/s, the background 0.2 c/s. SURGERY
Rabbits (weight 3.5-4.5 kg) were used for tile experiments. T h e implantation was made in nembutal ® anaesthesia (30 mg per kg) under semisterile conditions. T h e shield (Fig. 1) was placed on the back of the rabbit with the front edge just behind and between the shoulder blades. After removal of hair a 10-cm longitudinal incision was made on one side of the rabbit, slightly lower than half way between the back and the abdomen. O n the rabbit the skin is very loosely bound to the underlying facia, and it is possible by hand, to loosen the skin to the same level at the opposite site of the animal. T h e shield was placed in position with the
~/
~
~+/~;:~,:~
~:;;i~:~ ~
~
ii ~
~i~
~ ~;~;;~
~i ....
:
J
• 5t
FIO. 4. The transmitter.
508
A radiotelemetricalmeasuringdevice detector window towards the center of the rabbit, fixed through the nylon net to the underlying muscles by numerous catgut sutures. T h e incision was closed with nylon suture some of them passing through the net. A 5-cm long incision was then made on the opposite flank of the animal down to the nylon net. This wing of the net was then fixed to the muscles and the incision was closed as described. Both wounds were sprayed with nobecutan ®. Postoperatively the rabbit was kept w a r m until it was awake, it started to eat normally 12 hr after the operation. Tetracyclin 20 mg/kg was given for 2 days. T h e skin sutures were removed on the 6th day after operation. After the operation 3--4 weeks have to pass before the shield is sufficiently healed into position in order to permit reliable steady state measurements. I f the shield was removed earlier a strong wound reaction was found in the area with up to 10 ml sterile serous liquid under the foreign body. After a month a considerable amount of strong fibrous connective tissue had developed around the shield-but in front of the window of the G M - t u b e and under the shield--there was no inflammatory reaction and no collection of liquid. After 4 months the shield was richly wrapped in a thin strong fibrous m e m b r a n e without further reaction from the surrounding tissue. T h e fibrous m e m b r a n e was fixed to the skin and to the underlying muscle facia by thin blades of connective tissue. T h e nylon net was part of the muscle facias. Histology of the tissues under the G M - t u b e showed fibrous connective tissue without inflammatory reaction. I n six operations we have had no bacterial infections or expulsion of the shield.
Selection of the isotope I n serum albumin (SA) turnover studies the isotopes z31I or z~sI can be used to label the SA. T h e isotope z25I was chosen in our experiment because it only emits 7-rays, and the low 7-energy (35 keV) would reduce the probability of interference from already catabolised iodine in the bladder. O t h e r low 7-energy isotopes are of course suitable in different experiments. T h e ]~SI-sensitivity of the counter is 1 c/s per 1 nCi/ml measured on a 2-1. water-phantom. T h e sensitivity of a z25I2
509
pointsource in water is about 10 per cent of the m a x i m u m count rate 40 m m below the counter window.
The measuring room During the experiment the rabbit was kept in a plastic cage (100 × 50 × 50 cm) installed in a room with controlled 12 hr light (L) and 12 hr darkness (D). RESULTS AND DISGUSSION T o illustrate the potential of the method we present a few experimental curves obtained with x~sI- (Figs. 5 and 6) and rabbit serum albumin labelled with z25I (Fig. 7). These results could by no means have been obtained by conventional techniques. T h e extensive blood sampling necessary to obtain the main shape of the curves would have displaced the steady state of the rabbits severely. Whole body counting (WBC) would disturb the physiological conditions of the animal, besides W B C measurements within short intervals would be disturbed by the discontinuous emptying of the bladder. Counts 400 sec 2.104
10,~
5~103
2xlO 3
103
5~I0 2
2N102
102
Light
FIG. 5. T h e u r e d on a
t
Dark
i
z~sI c o u n t rate p e r 4 0 0 sec m e a s -
rabbit by the shield in a period of 27 hr.
d. Bojsen and K. Wallevik
5 lO tO0
g E ® E
2O
tO
i 1251
0-5
0"2 Light ,
Dork
6
12
& 18
24
-30
36
42
48 hr
FIo. 6. T h e xs"I count rate per hour in per cent of first measurement. O is the activity retention in the rabbit calculated on basis of urine samples; [] is the result measured by the shield; and A is the plasma activity concentration curve calculated on basis of plasma samples. COUntS hr 10 s
2x 10/'
104
Dose
:
• ~o0c~:~,::bdb:ubSt;rum
. . Atbum,n '2Sl
.=U" -~ Tt 5 3 d o y s
5~10 3
2x10 3
10 3
D L tOz
l~ t
, t.._-a 2
l~ 3
i t,..--,l 4
i ~,,--i 5
i ~.-,. • s ~ 6 7
i L--.J 8
l l---J 9
i ~ 10
i L--..-I I L i . J 11 12
aL-,,m.~ ! 13 16 d a y s
FIG. 7. Long term measurement of rabbit serum albumin-t25I.
A radiotelemetrical measuring d~vlce
As mentioned in the introduction the advantage of the radiotelemetrical techniques is the possibility to measure the p a r a m e t e r of interest continuously over a long period of time under the most physiological, unrestrained condition of the anlmal.* T o obtain better information than could have been gained by the conventional techniques it must furthermore be required that it is possible to determine small fluctuations in the rate constants for the elimination of the actual compounds, and of course that observed fluctuations are not caused by the measuring system. T h e shield is by the described implantation technique completely fixed to the underlying muscles on the back and is not displaced by movements of the rabbit. T h e variations on the count rate curve shown in Fig. 7 can only be due to small physiological fluctuations because the variations in the light and dark period are of the same magnitude. This together with the good reproducibility of the experiments establish that the geometry is sufficiently well defined. I t has to be pointed out that the detector will measure an unknown mixture of the different compartments of the body (inter* T h e d a t a presented was collected from the animal in 83 days.
same
511
vascular, extracellular space etc.), hence it follows that this measuring device cannot be used to distinguish the distribution and metabolism in the different compartments. I n conditions of steady state of the animal the implanted detector system will measure the overall rate of elimination of the labelled compound. This means that in pharmacological tests and in determining the overall rate constants of metabolism of physiological compounds the method should be of utility. Acknowledgement--The
authors wish to thank Or.E
JENSEN and K_~UD J~ROENSEN for their excellent technical assistance.
1. 2. 3. 4. 5. 6. 7. 8.
REFERENCES BOJSEN J., MOLLER U. and FABER M. Pfl~gers Arch. 328, 176 (1971). BOJSENJ., WALLEVXKK. and MeLL~R U. Proc. Int. Symposium on Biotelemetry 1971, p. 337 (1972), FRYEg T. B., DEBoo G. J. and WINOETC. M. J. appl. Physiol. 21, 295 (1956). FRYEI~ T.B. Implantable telemetry systems NASA SP-5094. National Aeronautics and Space Administration, Washington D.C. (1970). ~ X C H H. P. and Vos J. A. Biotelemetry, InternationalSymposium 1971. Meander, N. V. Leiden. The Netherlands (1972). MACKAY R. S. Bio-Medical Telemetry, pp. 212, 119. Wiley, New York (1970). Me_~FARt.Ar~ A. S. Biochem. J. 62, 135 (1956). MCFARL~¢E A. S. Nature, Lond. 182, 53 (1958).
A Radiotelemetrical Measuring Device, Implantable on Animals, for Long Term Measurements of Radionuclide-Tracers J. B O J S E N and K. W A L L E V I K The Finsen Laboratory, The Finsen Institute, Copenhagen, Denmark
(Received 23 June
1972)
The construction of a radlotelemetrical measuring device implantable on animals as small as rabbits and designed for continuous long term detection of low y-energy radionuclide-tracers is presented. The GM-detector and the FM-trammitter are coated in an araldite shield, the total volume is 140 cm 3 and the weight is 135 g. Reliable continuous measurements can be performed on unrestrained animals in periods up to 5 months. It is possible to measure discontinuously by external switching the measuring device on and off. The implantation technique is described. The detector seems to have its utility in pharmacological tests and in turnover studies. U N I N S T R U M E N T /~ M E S U R E T E L E M E T R I Q U E I M P L A N T A B L E S U R LES A N I M A U X P O U R LES M E S U R E S A L O N G U E T E R M E DES I N D I C A T E U R S A RADIO-NUCLEIDES On pr6sente la construction d'un instrument A mesure radiotdl~m6trique implantable sur des animaux aussi petits que le lapin et destin~ A la d6tection continuelle A longue terme des indicateurs A radionucl~ides de petite ~nergie y. Le d6tecteur Geiger et le transmetteur F M sont enduits d'une couche d'araldite, le volume total est 140 cm 3 et le poids est 135 g. On peut faire des mesures certaines et ininterrompues sur des animaux non contraints pour une p~riode de cinq mois, mais on peut faire des mesures discontinu6es par l'interruption ext~rieure de l'instrument. On d~crit la m~thode d'implantation. Le d6tectenr paralt avolr son utilitd d am les essais pharmacologiques et dans les 6tudes de changement de population. P A ~ H O T E J I E M E T P I f q E C H H F I H P H B O P , HMHJIAHTHPYEMblI?I HA H~HBOTHbIX, ~ J I H ~ O J I F O C P O q H b I X H3MEPEHHI~I PA~(HOAIRTHBHbIX H3OTOIIHbIX HH~HHATOPOB IIpe~cTasJieHa RoncTpy~Ha pa~HoTeaeMeTpHqecKoro I~sMepHTeJIbHOrO ycTpo]~lCTBa, HMHJIaHTHpyeMoI'O Ha H~HBOTHI~IXTaI~HX H~O MaJIeHbHHX HaI~ HpoJIHHax, H paccqI4TaHHOFO RJI~ HeHpepHBHOPO ROJIPOCpOqHOPOReTeKTHpOBaHH~ pa~HOaHTHBHhIX H3OTOIIHMXHHRHKaTopos C MaJIO~ ~Hepr~Ie~ raMMa-~yqel~. I I o ~ p ~ neTeKvop ,GM, ~ nepe~aT~n~ , F M , c 8 a m ~ T O ~ THna , A p a ~ T * , o 6 n ~ z t i 0 5 ~ e M - - 1 4 0 CMs, Bee--135 r. Ha Hec~sepm~saH~X H~I4BOTHMXBO3MOH~HOHpOH3BO~HTI~Ha~e~H~e, HeI~pep~BH~e H3MepeHH~ B TeqeHHH HepHo~a 5 Mecffna, a ~ncHpeTH0e nB~epeHHe n BOBMO~HHOnpH BHeLUHePOBI~IHJIIOqeHHHH BHJnOqeHHH HpHSopa. OHHCaH MeT0~ HMnJIaHTHpOBaHHff. OHash~BaeTcff, tiT0 HoJIe3HOCTI~ ~eTeHTopa HaXO~HTCH B ~apMaHoaorHqecHHx HCII/aITaHHHXH HCCJIe~0BatIIIHXHpyPOBOp0Ta. EINE INDIKATOR-FERNMESSVORRICHTUNG ZUR IMPLANTATION IN TIERE FOR LANGJAHRIGE MESSUNGEN VON RADIONUKLIDENINDIKATOREN Die Konstruktion einer Indikator-Fernmessvorrlchtung, die in so Ideine Tiere wle Kaninchen elnlagef~ihig ist und auf lange J a h r e Radionukliden-Indikatoren niedriger Gammaenergie nachweisen kann, wlrd beschrieben. Der GM-Detektor mad der FM-Sender sind in einem Aralditschlrm eingeschlossen, das Gesamtvolumen betriigt 140 cm ~ und das Gewicht 135 g. 505
J. Bojsenand K. WaUevik
506
Zuverl~issige Dauermessungen k6nnen an unbehinderten Tieren in einem Zeitraum ,con ftinf Monaten untemomrnen werden, doch ist es m6glich, dutch Ein- und Aussehalten der Vorrichtung yon aussen niehfforflaufend zu messen. Das Implantationsverfahren wird beschrieben. Der Detektor scheint eine nutzbare Verwendung ftir pharrnakologische Versuche und in Umsatzstudien zu haben. INTRODUCTION DURING the last decade m a n y biological a n d medical experiments have been performed by radiotelemetry techniques. (6) This technique permits a continuous m e a s u r e m e n t without disturbing the metabolic state of the animal. Initial attempts have been m a d e (2'n) to build instruments for measurement of radioactivity in combination with telemetric transmission of the results, because this would be applicable to m a n y experiments using radionuclide-tracer techniques. However, no implantable telemetry equipment has been developed for experimental or clinical use up to now. This p a p e r describes a telemetry system, which can be implanted on the back of an animal as small as a rabbit. T h e equipment is designed for long t e r m detection of radionuclide-tracers in the blood. io.~o
Description of the measuring equipment T h e GM-detector and transmitter are contained in an araldite ® shield (Fig. 1) m a d e waterproof in order to protect the electronic functions, especially the high voltage supply circuit, against humidity from surrounding tissue (1). I n Fig. 2 a block diagram of the transmitter and receiver system is shown. Figure 3 shows a circuit diagram of the implantable electronic transmitter. T h e transmitter circuit can be divided in three parts : the detector, the high voltage supply unit and the frequency modulated transmitter. T h e transducer for detection of the radioactivity is a G M - t u b e (Philips 18515), 26 m m in diameter with end-window (thickness 1.5-2 rag/era2). T h e plateau has been measured to be 400-760 V. T h e high voltage supply is made by a transformer-sinusoid-osciUator (operating
.j
I
FIO. 1. The araldite shield.
Antenna
I
I I I I I I
F.M.
[ F.M,
t'4V Batter y
~
Receiver
Transmitter
I i
,,, H '"'"'
o..,,,.,.. H
Scaler
,0,,.,. ~ °'-'~'", ""'°"" ,
I
I ~,,,,., I 1
'
FIG. 2. T h e block d i a g r a m of the t r a n s m i t t e r a n d receiver system.
24.
C3
12=D1
Et
-
C |
s;, =J
JR, ±c5 l~ '
OsciUator
Voltage Multiplier
Detector
F.M. Transmittef
Fxo. 3. T h e d i a g r a m of the detector a n d t r a n s m k t c r system. C1 Cs Ca C4 Cs C6 C7
Amplifier
= C s ----6-8 pF/6-3 V T a n t a l , Bosch 0678901208 == 0.22 p F / 3 5 V T a n t a l , Bosch 0678901232 ----4.7 nF/125 V d.c. F c r r o p h e r m =- 1 n F / l k V d.c. F e r r o p h e r m =- 100 pF, M i a l polysWrole = 9 pF, M i a l polystyrole = 33 pF, M i n i polystyrole
R I = 0-15 M f ~ R s = I k£~
R3 lOk.Q R4 10 M£~ R s = 100 k ~ R e = 3.3 k£~ T 1 = B C 146 Philips = =
T s = M P S 918 Motorola D 1 = M R 40 Atlantic Semiconductor GM-T = 18515 Philips L I ----HF-coil, 3 turns, prlntcd circuit Tlt -----transformer 10:50:2000 (0.09 ~, 0.05 z Cu) N22 O.L. Sifcrrit Siemens B 6 5 5 4 1 K 0000-R 022 E I = E s = 1.4 V, Mallory R M - I - N - T 2 S I ----S s Logccll, @ m a g n e t switch, Fifth Dimcnsion
Inc. 3000-IC-WLA. I n case o f pulse forming a 1 M ~ c a n b e serialized w i t h C 4. 507
Timer
508
J. Bojsenand K. Wallevik
frequency = 10 kHz) with a voltage multiplier ( × 12) at the transformer output. T h e circuit diagram of the high voltage supply is in principle similar to that of MACKA'¢~), but the low voltage supply is only 1-4V(E1) (Mallory RM1-N1000 mAhr) contrary to 2"8 V, the transformer (Tr) in the oscillator has a different size and winding ratio (Siemens 14 z N220.L.--10:50: 2000) and finally the voltage multiplier (24 X C8, 12 × Dx) is divided into two parallel branches in order to reduce the series reactance of the transformer output circuit. T h e total output charge capacitance is about 1.5 nF, which will secure a high count rate limit. When the low voltage battery has just been renewed the high voltage is 620 V. It will decrease to about 540 V after a period of maxim u m 270 days before the battery leaves the discharge plateau. Implanted at 37°C and at the low level of discharge (150/zA) the life time of the battery will be reduced to about 60 per cent or equal to 160 days of continuous operation. It is obvious that due to the low slope of the plateau for the GM-tube (3 per cent ]100 V) no correction of the count rate is necessary in the measuring period. A fraction of each signal impulse generated by the GM-tube is fed to the basis of the transistor (T,) in the FM-transmitter. ~SJ T h e transmitter is supplied from a separate 1.4 V battery (E,) (Mallory RMI-N) and the supply current is 180 pA, equal to a life time of 140 days. T h e emitter resistor R e can be changed from 3-3 to 2"7 k ~ if a higher output power is necessary, but this increases the power consumption and decreases the life time of the transmitter. T h e operation frequency is about 108 M H z and the range of the transmitter is 1-2 m outside the animal cage wall. $1 and $2 are magnetic bistable switches (Logcell®), which can be externally activated by a magnet. In this way it is possible to save electric power in periods where measurements are of no interest. T h e whole transmitter system is mounted on a printed circuit card (5 cm × 7 cm) (Fig. 4). T h e weight of the total electronics is 60 g of which 40 per cent is the low voltage batteries. The transmitter coil (Lx) radiates the
signal. The receiver antenna, shown in Fig. 2, is a five-turn loop placed horizontally on the outside of the cage wall ~3) in order to measure the near magnetic field from the transmitter. T h e receiver is a commercially available F M tunerset (Larsholt 7250-3000). It has been necessary to increase the signal level 22 dB by means of antenna-preamplifiers. T h e signal to noise ratio for the whole system in operation has been measured to be 32 dB. T h e received impulses are accumulated in the scaler and the printer is controlled by the timer.
Coating of the transmitter T h e shield is made by araldite ® (Ciba: D (CY230)-HY951) (100-0 g: 9"0 g), and the wall of the shield is 2-3 m m thick (Fig. 1). T h e electronic unit is fixed to the lower part of the shield by means of screws. Inside the upper part of the shield the two micro magnet switches are fixed to the surface of the wall by gluing. T h e shield has been moulded in two moulds made by silicone rubber (Wacker Silicon Kautchuk-Abformmasse B). T h e shield is polished before the electronics are mounted, and a small bag of silica gel (2-3 g) is placed inside the shield before it is closed by araldite. Finally a nylon net (Fig. 1) is glued to the shield. T h e total weight of the implantable detector system is 135 g and the volume is 140 cm 3. T h e total thickness of the araldite in front of the GM-tube end-window is about 200 mg/cm 2 and the maximum count rate for the described system is 200 c/s, the background 0.2 c/s. SURGERY
Rabbits (weight 3.5-4.5 kg) were used for tile experiments. T h e implantation was made in nembutal ® anaesthesia (30 mg per kg) under semisterile conditions. T h e shield (Fig. 1) was placed on the back of the rabbit with the front edge just behind and between the shoulder blades. After removal of hair a 10-cm longitudinal incision was made on one side of the rabbit, slightly lower than half way between the back and the abdomen. O n the rabbit the skin is very loosely bound to the underlying facia, and it is possible by hand, to loosen the skin to the same level at the opposite site of the animal. T h e shield was placed in position with the
~/
~
~+/~;:~,:~
~:;;i~:~ ~
~
ii ~
~i~
~ ~;~;;~
~i ....
:
J
• 5t
FIO. 4. The transmitter.
508
A radiotelemetricalmeasuringdevice detector window towards the center of the rabbit, fixed through the nylon net to the underlying muscles by numerous catgut sutures. T h e incision was closed with nylon suture some of them passing through the net. A 5-cm long incision was then made on the opposite flank of the animal down to the nylon net. This wing of the net was then fixed to the muscles and the incision was closed as described. Both wounds were sprayed with nobecutan ®. Postoperatively the rabbit was kept w a r m until it was awake, it started to eat normally 12 hr after the operation. Tetracyclin 20 mg/kg was given for 2 days. T h e skin sutures were removed on the 6th day after operation. After the operation 3--4 weeks have to pass before the shield is sufficiently healed into position in order to permit reliable steady state measurements. I f the shield was removed earlier a strong wound reaction was found in the area with up to 10 ml sterile serous liquid under the foreign body. After a month a considerable amount of strong fibrous connective tissue had developed around the shield-but in front of the window of the G M - t u b e and under the shield--there was no inflammatory reaction and no collection of liquid. After 4 months the shield was richly wrapped in a thin strong fibrous m e m b r a n e without further reaction from the surrounding tissue. T h e fibrous m e m b r a n e was fixed to the skin and to the underlying muscle facia by thin blades of connective tissue. T h e nylon net was part of the muscle facias. Histology of the tissues under the G M - t u b e showed fibrous connective tissue without inflammatory reaction. I n six operations we have had no bacterial infections or expulsion of the shield.
Selection of the isotope I n serum albumin (SA) turnover studies the isotopes z31I or z~sI can be used to label the SA. T h e isotope z25I was chosen in our experiment because it only emits 7-rays, and the low 7-energy (35 keV) would reduce the probability of interference from already catabolised iodine in the bladder. O t h e r low 7-energy isotopes are of course suitable in different experiments. T h e ]~SI-sensitivity of the counter is 1 c/s per 1 nCi/ml measured on a 2-1. water-phantom. T h e sensitivity of a z25I2
509
pointsource in water is about 10 per cent of the m a x i m u m count rate 40 m m below the counter window.
The measuring room During the experiment the rabbit was kept in a plastic cage (100 × 50 × 50 cm) installed in a room with controlled 12 hr light (L) and 12 hr darkness (D). RESULTS AND DISGUSSION T o illustrate the potential of the method we present a few experimental curves obtained with x~sI- (Figs. 5 and 6) and rabbit serum albumin labelled with z25I (Fig. 7). These results could by no means have been obtained by conventional techniques. T h e extensive blood sampling necessary to obtain the main shape of the curves would have displaced the steady state of the rabbits severely. Whole body counting (WBC) would disturb the physiological conditions of the animal, besides W B C measurements within short intervals would be disturbed by the discontinuous emptying of the bladder. Counts 400 sec 2.104
10,~
5~103
2xlO 3
103
5~I0 2
2N102
102
Light
FIG. 5. T h e u r e d on a
t
Dark
i
z~sI c o u n t rate p e r 4 0 0 sec m e a s -
rabbit by the shield in a period of 27 hr.
d. Bojsen and K. Wallevik
5 lO tO0
g E ® E
2O
tO
i 1251
0-5
0"2 Light ,
Dork
6
12
& 18
24
-30
36
42
48 hr
FIo. 6. T h e xs"I count rate per hour in per cent of first measurement. O is the activity retention in the rabbit calculated on basis of urine samples; [] is the result measured by the shield; and A is the plasma activity concentration curve calculated on basis of plasma samples. COUntS hr 10 s
2x 10/'
104
Dose
:
• ~o0c~:~,::bdb:ubSt;rum
. . Atbum,n '2Sl
.=U" -~ Tt 5 3 d o y s
5~10 3
2x10 3
10 3
D L tOz
l~ t
, t.._-a 2
l~ 3
i t,..--,l 4
i ~,,--i 5
i ~.-,. • s ~ 6 7
i L--.J 8
l l---J 9
i ~ 10
i L--..-I I L i . J 11 12
aL-,,m.~ ! 13 16 d a y s
FIG. 7. Long term measurement of rabbit serum albumin-t25I.
A radiotelemetrical measuring d~vlce
As mentioned in the introduction the advantage of the radiotelemetrical techniques is the possibility to measure the p a r a m e t e r of interest continuously over a long period of time under the most physiological, unrestrained condition of the anlmal.* T o obtain better information than could have been gained by the conventional techniques it must furthermore be required that it is possible to determine small fluctuations in the rate constants for the elimination of the actual compounds, and of course that observed fluctuations are not caused by the measuring system. T h e shield is by the described implantation technique completely fixed to the underlying muscles on the back and is not displaced by movements of the rabbit. T h e variations on the count rate curve shown in Fig. 7 can only be due to small physiological fluctuations because the variations in the light and dark period are of the same magnitude. This together with the good reproducibility of the experiments establish that the geometry is sufficiently well defined. I t has to be pointed out that the detector will measure an unknown mixture of the different compartments of the body (inter* T h e d a t a presented was collected from the animal in 83 days.
same
511
vascular, extracellular space etc.), hence it follows that this measuring device cannot be used to distinguish the distribution and metabolism in the different compartments. I n conditions of steady state of the animal the implanted detector system will measure the overall rate of elimination of the labelled compound. This means that in pharmacological tests and in determining the overall rate constants of metabolism of physiological compounds the method should be of utility. Acknowledgement--The
authors wish to thank Or.E
JENSEN and K_~UD J~ROENSEN for their excellent technical assistance.
1. 2. 3. 4. 5. 6. 7. 8.
REFERENCES BOJSEN J., MOLLER U. and FABER M. Pfl~gers Arch. 328, 176 (1971). BOJSENJ., WALLEVXKK. and MeLL~R U. Proc. Int. Symposium on Biotelemetry 1971, p. 337 (1972), FRYEg T. B., DEBoo G. J. and WINOETC. M. J. appl. Physiol. 21, 295 (1956). FRYEI~ T.B. Implantable telemetry systems NASA SP-5094. National Aeronautics and Space Administration, Washington D.C. (1970). ~ X C H H. P. and Vos J. A. Biotelemetry, InternationalSymposium 1971. Meander, N. V. Leiden. The Netherlands (1972). MACKAY R. S. Bio-Medical Telemetry, pp. 212, 119. Wiley, New York (1970). Me_~FARt.Ar~ A. S. Biochem. J. 62, 135 (1956). MCFARL~¢E A. S. Nature, Lond. 182, 53 (1958).