Arterial input function measurement without blood sampling in the rat using the Beta Microprobe
1
1
UMR 8806 Institut de Physique Nucléaire , Université Paris XI, 91406 Orsay, France; 2
3
F. Pain, 1P. Lanièce,1 R Mastrippolito, 2,3P. Hantraye and 2L. Besret
URA CEA-CNRS 2210, Service Hospitalier Frédéric Joliot, 91401 Orsay, France
Isotopic Imaging Biochemical and Pharmacological Unit (UI2BP), Service Hospitalier Frédéric Joliot, 91401 Orsay, France.
Corresponding author and authors to whom reprints requests should be directed Frédéric Pain Groupe IPB, Institut de Physique Nucléaire d’Orsay Bat 104 91406 Orsay Cedex FRANCE
[email protected] phone 01 69 15 44 89 fax 01 69 15 71 96 This work was supported by the Academic funding program “Imagerie du Petit Animal” CNRS / INSERM / CEA
1
ABSTRACT (345 words) The evaluation of every new radiotracer involves pharmacokinetics studies in small animals to determine the biodistribution and local kinetics of the tracer. To extract relevant biochemical information, time activity curves (TACs) in the regions of interest are mathematically modeled on the basis of compartmental models which require the knowledge of the time course of the tracer concentration in plasma. This TAC, usually named “input function”, is determined in small animals by repeated blood sampling and subsequent counting in a well counter. The aim of the present work was to propose an alternative to blood sampling in small animals, since this procedure requires labor intensive protocols, staff exposition to radiation and lead to an important loss of blood which affect haematological parameters. Methods In a first step, Monte Carlo simulations were carried out to evaluate the feasibility of measuring the arterial input function using a positron sensitive microprobe placed in the femoral artery of a rat. The simulation results showed that in addition to the probe in the femoral artery, a second one inserted in its immediate vicinity was necessary to allow proper subtraction of the background signal arising from tracer accumulation in surrounding tissues. In a second step, this approach was validated in vivo in anaesthetized rats using two 6cm long 250µm diameter probes. Results. The high temporal resolution of the technique allowed accurate determination of the input function peak following
18
F-
Fluorodeoxyglucose (18F-FDG) bolus injection. Quantitative input functions were obtained after normalization of the arterial TAC on a late blood sample activity concentration. In one animal, a third probe was used to determine simultaneously
18
F-FDG accumulation in the
striatum. Compartmental modeling was achieved using either the blood samples or the
2
microprobe data as input function and similar kinetics constants were found in both cases. Conclusion Although direct quantification proved to be difficult, the microprobe allowed accurate arterial input function measurement with a high temporal resolution and no blood loss. The technique offers adequate sensitivity and temporal resolution required to perform kinetic measurements of radiotracers in the blood compartment which should facilitate quantitative modelling for radiotracers studies in small animals.
Keywords: Arterial input function, β -Microprobe, 18F-FDG, rat.
3
TEXT Introduction
Radiotracers studies in living animals require the venous injection of a radioactive tracer. To extract relevant biochemical informations, time activity curves (TACs) in the regions of interest are mathematically modeled on the basis of compartmental models, which describe the transfer steps of the tracer from blood to the target organ and its subsequent incorporation into specific biochemical pathways. For instance, local metabolic rate of glucose can be actually quantified after injection of
18
F-Fluoro deoxyglucose (18F-FDG) a radio labeled
analogue of glucose. Using a classical modeling approach allows the formal identification of each of the kinetics rate constants that govern the passage from one compartment to another (Reivich M et al., 1979). However, such modeling approach requires the accurate determination of the time activity curve of the tracer in plasma- also called “input function”that is used to describe the availability of the tracer to the regions of interest. Usually the input function is obtained by repeated blood sampling and external counting of the radioactive concentration. This involves labor-intensive manual withdrawals which present several drawbacks: the repeated radioactive exposure of staff in charge of blood sampling ; a temporal resolution limited to 5-10s between each sample which affects the accuracy of the input function, and finally the need to collect relatively large amount of blood which in turn could greatly affect the physiological parameters of the animal especially for multiple injections protocols. In that context, the purpose of this study was to evaluate the potential of a beta sensitive microprobe to provide an alternative to blood sampling to measure
18
F-FDG
4
input functions in the rat with a high temporal accuracy. In a first step Monte Carlo simulations were carried out to evaluate the theoretical ability of the technique to deliver an absolute quantification of the tracer concentration in blood. Considering a probe inserted into the femoral artery, we investigated the relative amounts of detected signals arising respectively from radioactivity within the artery and
the surrounding tissues. We also
investigated the influence of the probe positioning relative to the artery walls. The results of these simulations led us to propose an experimental approach using two beta sensitive probes. The first one was inserted into a femoral artery and the second one placed in the vicinity of the artery to allow subtraction of the positron background signal arising from the tracer accumulation in the surrounding tissues. In a second step, this approach was validated in vivo in rats and compared to the gold standard blood sampling method which was performed simultaneously on the other femoral artery. Finally, to illustrate the potential of the technique in the context of compartmental modeling we tested the feasibility of using the input function derived from beta microprobe measurements to evaluate quantitatively the cerebral metabolism of glucose in the rat striatum.
Material and Methods The β-Microprobe system. The β-Microprobe is a local beta radioactivity counter, which takes advantage of the limited range of beta particles within biological tissues to define a detection volume in which the radioactivity is counted. For
18
F, the detection volume corresponding to 90% of the detected
positrons is a cylinder of approximately 0.8 mm radius centered on the probe axis. The probes
5
are composed of a β-radiosensitive tip made of scintillating plastic fiber (BICRON Newbury Ohio, USA) fused to an optical fiber light guide. The light pulses generated by β particles crossing the scintillator are guided to a single photon photomultiplier (PMT R7400 Hammamatsu, Hammamatsu city Japan), which delivers a count rate directly proportional to the concentration of tracer in the analyzed volume. A complete description and discussion of the system can be found elsewhere (Pain F et al., 2000; Pain F et al., 2002a). The device has been previously validated for pharmacokinetics studies, some involving coupling with microdialysis (Zimmer L et al., 2002a; Zimmer L et al., 2002b), and quantitative measurements of cerebral metabolism using 18F-FDG (Pain F et al., 2002b).
Monte Carlo simulation To evaluate the ability of the technique to deliver an absolute quantification of the tracer concentration in blood, Monte Carlo simulations were carried out to determine: i)
The influence of the artery dimension on the amount of signal detected within the artery.
ii)
The influence on the detected count rate of the probe positioning in the artery.
These parameters were investigated using a Monte Carlo N- particles Code (MCNP 4C) that allows simulating interactions and trajectories of charged particles and photons in a userdefined geometry (Briefmeister JF, April 2000). The materials used (polystyrene core for the microprobe, blood, soft tissues) were defined in the MCNP input file using their mass percentage per atomic element obtained from the National Institute of Standards and Technology (Berger MJ, Coursey JS and Zucker MA, 1999). The probe was simulated as a
6
plastic cylinder of 250µm diameter and a 6cm sensitive length. We then simulated the immersion of the probe in a 2mm radius cylinder homogenously filled with 18F-FDG to determine the percentage of the signal detected within the artery as a function of the artery diameter. To study the influence of the probe position relative to the artery, the probe was inserted in an artery simulated as a cylinder (800µm diameter, 6,5 cm length). Three positions of the probe relative to the artery were considered. The first concerns the “ideal” case where the probe and artery axis are collinear (position A on figure 2). In the second case, the probe lies on the wall of the artery with its axis parallel to that of the artery (position B on figure 2). In the third case the probe axis is twisted with a 0.8° angle referring to the axis of the artery (position C on figure 2). In all cases, the radioactivity concentrations were assumed to be homogenous in the artery and surrounding tissues.
Beta Microprobe experimental setup for input function measurements
The diameter of the probe, which was originally 1mm, was reduced down to 0.25mm to minimize the invasiveness of the technique. This diameter is close to that of commonly used microdialysis probes and allows easy insertion of the probe into the femoral artery of a rat. However, this smaller diameter leads to a reduced sensitivity of the probe due to a smaller sensitive volume and a higher fragility of the fusion point at the interface between the clear and scintillating fiber. In the particular case of input function measurement, it was possible to overcome simply these drawbacks, using probes entirely made of scintillating fiber directly
7
coupled to a PMT. We used two identical probes with a 6cm long scintillating tip inserted for one probe, in the left femoral artery, and for the other one, in the muscle just above the artery. Since the diameter of a rat femoral artery (between 0.2 and 1mm) is smaller than the maximum range of
18
F beta particles in tissues (about 2,3mm), the activity detected in the
artery is the sum of two contributions: the beta radioactivity in blood and the radioactivity accumulated in surrounding tissues. To subtract this background contribution, a second probe was inserted in tissues above the artery. Each detection channel (probe, photodetector and associated electronics) was calibrated using a beaker (with dimensions larger than the detection volume associated to 18F), filled with an homogenous solution of 18F-FDG of known radioactivity concentration. The detected count rates were recorded with the probes entirely dived in the solution. Sensitivities of 1.80cps/kBq/ml and 1.55cps/KBq/ml were determined respectively for the “signal” and “background” channels. For one experiment a 0.5mm diameter probe with a 1mm long sensitive tip was implanted in the left striatum to measure the 18F-FDG TAC in the striatum simultaneously to the input function. The “striatum” probe was calibrated similarly and presented a 0.78cps/KBq/ml sensitivity. The high voltage was applied to the photomultipliers about 15 minutes before the start of the experiments to evaluate photodetectors dark count rates after stabilization. For the two PMTs the dark count ranged between 1 and 6 counts per second. For each channel, it was averaged and subtracted to the experimental count rates measured after tracer injection. Animal preparation All experiments were conducted on male Wistar rats (IFFA CREDO, France, mean weight of 463 +/-55g). Anaesthesia was induced with 5% isoflurane in a gas mixture of O2/N2O
8
(30%/70%) and maintained with 1.5% to 2.5% isoflurane during the entire experiment. Catheters were placed in the right femoral vein and artery for radiotracer injection and blood samples collection, respectively. First a Beta-sensitive probe was then inserted into the left artery and a second one at the surface of the same vessel. The diameter of these two probes were 250 µm, i.e. small enough to avoid any occlusion of the vessel. Moreover their flexibility as well as their smooth tips preserve the artery from perforation. However, before securing the probe within the artery, it is safer to check the location of the probe in order to make sure that the vessel was not occluded or perforated. For the experiment dedicated to illustrate the potential of the technique for compartmental modeling, a third beta sensitive probe (500µm diameter, 7mm long, sensitive tip 1mm long) was used. The animal was mounted in a stereotaxic frame and a craniotomy was performed for the insertion of a microprobe into the left striatum (anterior -0.5 mm bregma, lateral +/-3 mm, ventral –5 mm from dura matter). Isoflurane was discontinued 30 min following αchloralose bolus injection (60 mg/kg, i.p.) and maintenance (40 mg/kg.h-1, i.p. as a cyclodextrin complex). For all experiments the injected activities ranged from 17.4MBq to 31.8MBq of FDG in a 1ml saline solution. Timed arterial blood samples were collected continuously for the first 3 min following the FDG administration and then at increasing intervals up to 60 min. Then radioactivity was counted on 10 µl of whole blood using a Beckman counting system Mathematical modeling A classical
18
F-FDG compartmental model with three compartments was used for the
determination of the FDG kinetics rate constants in the striatum (Reivich M et al., 1979).
9
These compartments correspond respectively to the concentrations of FDG in plasma, tissues and FDG-6P in tissues. Since these experiments were carried out for 45 minutes after a single injection of
18
F-FDG the activity of the glucose phosphatase enzyme (reverse of glucose
phosphorylation by hexokinase) was considered to be negligible. The three kinetics rate constants are identified as K1, k2, k3. A 4% vascular fraction was considered. The parameters were fitted using Comkat (Muzic RF and Cornelius S, 2001) an open source compartmental modeling software dedicated to nuclear medicine applications. This software uses minimization of a weighted least squares function and a Levenberg Marquardt algorithm. Results Monte Carlo Simulations According to literature the femoral artery mean diameter of rats with a mean weight of 312+/-15g is about 741+/-22µm(Porret, Stergiopulos and Meister, 1998; Faber, Porret, Meister and Stergiopulos, 2001). However it may vary in normal conditions from 0.50mm to 1mm. Assuming that the density of blood, artery walls, and surrounding tissues are very similar, we simulated a 6cm long 250µm diameter probe inside an homogenous 2mm diameter 65 mm long cylindrical volume filled homogeneously
with
18
F activity. We
evaluated the percentage of detected beta particles as a function of the distance of their origin point to the axis of the fiber. As can be seen on figure 1, under such conditions, about 90% of the detected signal arises from within a 800µm radius cylinder. However, the artery to background signal decreases as a function of the diameter of the artery. For an 400µm radius artery, 59% of the total signal arises from the artery, the rest being positron background signal arising from the artery walls and surrounding tissues. For a 200µm radius artery only 30% of
10
the total signal corresponds to effective blood activity. This led us to propose the use of two probes : one inserted in a femoral artery and the other one placed in the vicinal tissues to allow positron background suppression. The second aim of the Monte Carlo simulation was to examine the influence of the artery/probe geometry on the amount of signal detected within the artery. Three cases have been particularly investigated regarding the position of the probe relative to the artery (Figure 2). We considered an 800µm diameter artery with the 250µm diameter 4cm long probe centered on the axis, laid on the artery wall or slightly twisted. The detection efficiencies were respectively 14,5% 10,0% and 11,8% of the β+ emitted within the artery corresponding to calculated apparent sensibilities of 2,07cps/KBq/ml 1,4cps/KBq/ml and 1,6cps/KBq/ml. These simulations demonstrated that the dimension of the artery and the relative position of the probe inside the artery, which are uncontrolled parameters, can significantly influence the amount of detected signal. Thus it may be difficult to obtain direct quantitative input function measurements from the probes sensitivities, which were determined in an homogenous
18
F
solution. To overcome this difficulty we normalized the input functions determined by the microprobe to the activity of a late blood sample (t=40min) which is also required at the end of the experiment to monitor the physiological parameters of the animal ( PaO2, PaCo2, oxygen saturation, pH). Input function measurements in anesthetized rats Preliminary experiments were necessary to optimize the probes positioning and consequently the background rejection. The relative placement of the background suppression probe relative to the artery is crucial since the accuracy of background suppression depends on it.
11
This probe was placed in the immediate vicinity of the artery in order to measure the fraction of
18
F-FDG accumulating within surrounding tissues. Both signals (artery and background
probes) were corrected first for the dark count of each detection channel and were then normalized to detection sensitivities of each channel. The background signal was then subtracted from the artery signal. Finally the result was corrected for radioactive decay of 18F (T1/2=1.829hr). Figure 3 shows the raw data from the two probes for a representative experiment. After the first 90 s, data have been averaged every 10 seconds for the sake of clarity. The resulting input function normalized on a late blood sample compared well with the whole blood input function simultaneously measured by blood sampling as can be seen on figure 4 and in table 1 that summarize the area under curves for both techniques on 5 animals. Furthermore the high temporal resolution (data points were acquired every seconds) of the microprobe allows much more accurate determination of the peak of activity concentration in blood in comparison to manual samplings. Since tracer adsorption to plastic materials has been reported (Ranicar A et al., 1991), eventual tracer contamination that might have accumulated on the plastic cladding of the fiber was checked at the end of the experiment. Just after the probe was removed from the artery it did not present any traces of blood and the count rate measured was not much than the dark count rate of the photodetectors. Compartmental modeling using the input function generated by the β-microprobe measurements To illustrate the potential of the technique in the context of compartmental modeling, an additional experiment was carried out to determine quantitatively the local cerebral glucose metabolic rate in the rat brain. In addition to the two probes required to determine the tracer
12
arterial input function as described above, a third probe was stereotaxicaly implanted in the rat striatum to record the local 18F-FDG accumulation. Figure 5 shows the time activity curves for
18
F-FDG in the striatum and the blood input function determined either in situ or with
blood withdrawals. As shown on figure 6,we used successively the blood time activity curves measured either by blood sampling or the microprobe technique as input functions to the compartmental model of 18F-FDG metabolism. Table 2 summarizes the kinetic rate constants K1, k2, k3 determined using both methods. Discussion In studies using radiolabeled molecules, the knowledge of the tracer arterial input function is requested when compartmental modeling is to be carried out unless a tissue model is used (Lammertsma AA and Hume SP, 1996). The most currently used technique to measure this input function is blood sampling usually performed in rats from the catheterized femoral artery.
This work is labor intensive and the subsequent loss of blood may lead to
haemodynamic instability. Several alternative techniques have been developed to avoid this procedure. Some of these techniques rely on automatic sampling and radioactivity counting of small blood volumes (Eriksson L et al, 1988 ; Ranicar A et al., 1991; Eriksson L et al., 1995; Wollenweber SD et al, 1997 ; Lapointe D et al, 1998 ; Seki C et al., 1998). Although these techniques present the advantages that they can be standardized process and that they minimize staff exposure to radioactivity they all require blood withdrawal unless a shunt system is used (Weber B et al, 2002). Furthermore two difficulties are inherent to the use of rather long catheters to drive the blood from the artery to the detection system. First, it is necessary to take into account the dispersion function of the blood sampling system and
13
second, the possible adsorption of the tracer on the catheter walls may lead to incorrect evaluations of radiotracers concentrations. As an alternative, input function derived from PET images has been proposed in rats and mice. Attempts to determine the input function from PET images in mice were not entirely convincible (Green LA et al., 1996) but 18F-FDG blood input functions have been successfully derived from left ventricles images of the rat heart . However this required the use of a small animal PET dedicated to cardiac studies (with ECG gated acquisition) and careful analysis of the signal to deal with motion artifacts and spill over. The aim of the present study was to establish a simple and sensitive approach for in situ blood input function measurement which would overcome these limitations. The method presents an adequate sensitivity and therefore a high temporal resolution, which allows an accurate determination of the whole blood TAC including the first minutes after bolus injection. This high temporal resolution may also be very useful for tracers labeled with short period isotopes especially flow studies with H2015 (T1/2 =2min). Since the technique does not require blood sampling there is no staff repeated exposition to high activity levels and minimal blood loss. This last point makes the method convenient for multi injections experiments which have proven to be powerful experiments to determine complex pharmacokinetics parameters and which require the successive measurements of at least two input functions. The in situ measurements presents however its inherent problems. As evaluated by Monte Carlo simulations, the probe position relative to the artery and the artery diameter are a priori uncontrolled parameters and prevent from direct quantification of the whole blood time
14
activity curve. To obtain a quantitative input function in µCi/ml it is thus necessary to renormalize the measured TAC to a late point sample. Nevertheless this does not interfere with the experimental scheme since at least one or two blood samples are necessary to control the physiological parameters of the animal throughout the experiment. Another difficulty is, that the measured input function is the whole blood TAC whereas quantification often requires the plasma TAC. For
18
F-FDG, if a standardized injection protocol is used, a simple correction
based on the time course of the plasma to blood ratio is achievable (Weber B, Burger C, Biro P and A, 2002). The weakest point in our technique is the necessity to subtract background signal from the 18F-FDG accumulation in surrounding tissues. However after a few attempts, it was possible to position correctly the background probe close to the femoral artery to ensure proper background subtraction. This point should be less critical for others tracers which do not accumulate as much as FDG in the femoral artery surrounding tissues. Conclusion The use of two positron sensitive probes allowed to determine accurately the input function following
18
F-FDG bolus injection provided accurate background suppression is achieved.
The high temporal resolution allowed not to miss the peak as sometimes observed with sampling. The technique is not associated to blood collection, which reduces staff exposure to radioactivity and the blood loss. This latter point should be of great interest for multi injections experiments, which require the measurements of successive input functions. The technique offers the adequate sensitivity and temporal resolution required to perform accurate kinetic measurements of radiotracers in the blood compartment. Therefore the beta
15
microprobe system allows simultaneous measurements of the blood and cerebral tissues TACs to be performed at the same time following a single injection in the animal.
ACKNOWLEDGEMENTS
The authors would like to thank Dr Ray Muzic for help with Comkat use, societies Luxeri (Gometz le Chatel, France) and Biospace (Paris, France) for helpful discussions. This work was funded by the “Imagerie du Petit Animal” CNRS/INSERM/CEA program.
16
Figure 1: Monte Carlo evaluation of the fraction of the detected signal corresponding to radioactivity in the femoral artery as a function of the artery radius.
Figure 2: Probe positioning considered for the Monte Carlo simulation
Figure 3 : Raw time activity curves recorded by the artery and background probes after bolus injection of 18F-FDG Figure 4 :Comparison of normalised arterial input functions determined with blood sampling or the β-Microprobe
Figure 5 : Simultaneous determination of the arterial input function and striatum time activity curve after 18F-FDG bolus injection
Figure 6 : Compartmental modelling fit of the striatum 18F-FDG accumulation using either the blood sampling or the microprobe arterial input function.
Table 1: Ratio between the area under curve (AUC) input functions for derived from the microprobe measurements in comparison to input functions derived from blood samples.
Table 2 : Kinetics rate constants for 18F-FDG uptake in striatum determined using the input function determined
either by blood sampling or using the β-Microprobe (fit
parameters k4=0; vascular fraction = 4%)
17
120
% of detected β +
100
80
60 femoral artery
40
R β-sensitive microprobe
20
0 0
0,2
0,4
0,6
0,8
1
1,2
1,4
1,6
1,8
2
R=Orthogonal distance from the β + emission point to the fiber axis (mm)
Figure 1: Monte Carlo evaluation of the fraction of the detected signal corresponding to radioactivity in the femoral artery as a function of the artery radius.
18
60mm
0,8mm
A
B
C
Figure 2: Probe positioning considered for the Monte Carlo simulation
19
Count rate (cps)
600 500
Artery probe
400
Background probe
300 200 100 0 0
10
20
30
40
50
60
Time ( min) Figure 3 : Raw time activity curves recorded by the artery and background probes after bolus injection of 18F-FDG
20
20000 18000 16000
nCi/ml
14000 12000
blood samples microprobe
10000 8000 6000 4000 2000 0
0
10
20
30
40
50
60
Time ( min) Figure 4 :Comparison of normalised arterial input functions determined with blood sampling or the β-Microprobe
21
200
striatum
180
unnormalized input function
Count rate (cps)
160 140 120 100 80 60 40 20 0 0
5
10
15
20
25
30
35
40
45
50
55
60
Time (min.)
Figure 5 : Simultaneous determination of the arterial input function and striatum time activity curve after 18F-FDG bolus injection
22
5
µCi/ml
4 3 Fit input function from blood sampling
2
Fit input function form the Microprobe
1
Experimental data in striatum
0 0
5
10
15
20
25
30
35
40
45
Time( min) Figure 6 : Compartmental modelling fit of the striatum 18F-FDG accumulation using either the blood sampling or the microprobe arterial input function.
23
Animal
1
2
3
4
5
AUC relative to plasma
0,96
0,85
1,07
0,87
1,54
Table 1: Ratio between the area under curve (AUC) input functions for derived from the microprobe measurements in comparison to input functions derived from blood samples.
kinetics rate constants (min-1) Microprobe Blood sampling
k1 0,1043 0,1015
k2 0,1195 0,1195
k3 0,054 0,056
Table 2 : Kinetics rate constants for 18F-FDG in striatum determined using either the blood sampling or the β-Microprobe derived input function (fit parameters k4=0, vascular fraction =4%).
24
References Berger MJ, Coursey JS, Zucker MA ESTAR, PSTAR and ASTAR : Computer Programs for Calculating Stopping Power and Range Tables for Electrons, Protons and Helium Ions. [ Online ] : http://physicsnistgov/Star 1999. Briefmeister JF (April 2000) MCNP - A general Monte Carlo N Particle Transport Code, Version 4C. In.: Los Alamos National Laboratory LA-13709 M. Eriksson L, S. Holte, C. Bohm, M. Kesselberg, B. Hovander Automated Blood Sampling Systems for Positron Emission Tomography. IEEE TNS 1988; 35:703-707. Eriksson L, M. Ingvar, G. Rosenqvist, S. Stone-Elander, T. Ekdahl, P. Kappel Characteristics of a New Automated Blood Sampling System for Positron Emission Tomography. IEEE 1995;:1383-1388. Faber LL, Porret C-A, Meister J-J, Stergiopulos N In vitro diameter response of rat femoral artery to flow in the presence and absence of endothelium. Journal of Biomechanics 2001; 34:1023-1030. Green LA, Gambhir SS, Srinivasan A, Namavari M, Hoh C, SR C, et al. Non-invasive methods for quantitating input functions from FDG PET Images. J Nucl Med Proceedings of the 43rd Annual Meeting Poster N°649 1996; 37:147P. Lammertsma AA, Hume SP simplified Reference Tissue Model for PET Receptor Studies. Neuroimage 1996; 4:153-158. Lapointe D, Cadorette J, Rodrigue S, Rouleau D, Lecomte R a Microvolumetric Blood counter/Sampler for Metabolic PET Studies in Small Animals. IEEE TNS 1998; 45:2195-2199.
25
Muzic RF, Cornelius S COMKAT : Compartment Model Kinetic Analysis Tool. J Nucl Med 2001; 42:636-645. Pain F, Lanièce P, Mastrippolito R, Charon Y, Comar D, Leviel V, et al.
SIC, an
intracerebral rdiosensitive probe for in vivo neuropharmacology investigations in small laboratory animals : theoretical considerations and physical characteristics. IEEE TNS 2000; 47:25-32. Pain F, Lanièce P, Mastrippolito R, Charon Y, Comar D, Leviel V, et al.
SIC, an
intracerebral rdiosensitive probe for in vivo neuropharmacology investigations in small laboratory animals : first prototype design characterisation and in vivo evaluation. IEEE TNS 2002a; 46:822-826. Pain F, Besret L, Vaufrey F, Grégoire MC, Pinot L, Gervais P, et al. In vivo quantification of localized neuronal activation and inhibition in the rat brain using a dedicated high temporal resolution Beta-sensitive MICROPROBE. PNAS 2002b; 99:10807-10812. Porret CA, Stergiopulos N, Meister JJ Flow-driven diameter response in rat femoral arteries perfused in vitro. Ann Biomed Eng 1998; 26:526-533. Ranicar A, Williams CW, Schnorr L, Clark JC, Rhodes CG, Blommfield PM Jones T The on-line monitoring of conyinuously withdrawn arterial blood during PET studies using a single BGP/photomultiplier assembly and non-stick tubing. Medical Progress through Technology 1991; 17:259-264. Reivich M, Kuhl D, Wolf A, Greenberg J, Phelps M, Ido T, et al.
The
[18F]Fluorodeoxyglucose Method for the Measurement of Local Cerebral Glucose Utilization in Man. Circ Res 1979; 44:127-137.
26
Seki C, Okada H, Mori S, Kakiuchi T, Yoshikawa E, Nishiyama S, et al. Application of a beta microprobe for quantification of regional cerebral blood flow with 15O-water and PET in rhesus monkeys. Annals of Nuclear Medicine 1998; 12:7-14. Weber B, Burger C, Biro P, A B A femoral arteriovenous shunt facilitates arterial whole blood sampling in animals. Eur J Nucl Med 2002; 29:319-323. Wollenweber SD, Hichwa RD, Ponto LLB A Simple On-Line Arterial Time -Activity Curve Detector for [O-15]Water PET Studies. IEEE TNS 1997; 44:1613-1617. Zimmer L, Hassoun W, Pain F, Bonnefoi F, Lanièce P, Mastrippolito R, et al. SIC, an intracerebral Beta range sensitive probe for radiopharmacology investigations in small laboratory animals : binding studies with [11C]-Raclopride. J Nucl Med 2002a; 43:227-233. Zimmer L, Pain F, Mauger G, Plenevaux A, Le Bars D, Mastrippolito R, et al. The potential of the Beta-MICROPROBE, an intracerebral radiosensitive probe, to monitor the [18F]-MPPF binding in the rat dorsal raphe nucleus. Eur J Nucl Med 2002b; 29:12371247.
27
