Abstract |
Recently, [I-123]IPT SPECT has been used for early
diagnosis of Parkinson's patients(PP) by imaging
dopamine transporters. The dynamic time activity curves
in basal ganglia(BG) and occipital cortex(OCC) without
blood samples were obtained for 2 hours. These data
were then used to measure dopamine transporters by
operationally defined ratio methods of (BG-OCC)/OCC at
2 hrs, binding potential Rv=k3/k4 using graphic method
or RA= (ABBG-ABOCC)/ABOCC for 2 hrs, where ABBG
represents accumulated binding activity in basal
ganglia(∫0 120minBG(t)dt) and ABOCC represents
accumulated binding activity in occipital cortex(∫0
120minBG(t)dt). The purpose of this study was to
examine the IPT pharmacokinetics and investigate the
usefulness of simplified methods of (BG-OCC)/OCC, RA,
and RA which are often assumed that these values
reflect the true values of k3/k4. The rate constants
K1, k2, k3 and k4 to be used for simulations were
derived using [I-123]IPT SPECT and aterialized blood
data with a standard three compartmental model. The
sensitivities and time activity curves in BG and OCC
were computed by changing K1 and k3(only BG) for every
5min over 2 hours. The values (BG-OCC)/OCC, RA, and Rv
were then computed from the time activity curves and
the linear regression analysis was used to measure the
accuracies of these methods. The rate constants K1, k2,
k3, k4 at BG and OCC were 1.26±5.41%, 0.044±19.58%,
0.031±24.36%, 0.008±22.78% and 1.36±4.76%,
0.170±6.89%, 0.007±23.89%, 0.007±45.09%,
respectively. The Sensitivities for ((△S/S)/(△k3/k3))
and ((△S/△S)/(△K1/K1)) at 30min and 120min were
measured as (0.19, 0.50) and (0.61, 0.23),
respectively. The correlation coefficients and slopes
of ((BG-OCC)/OCC, RA, and Rv) with k3/k4 were (0.98,
1.00, 0.99) and (1.76, 0.47, 1.25), respectively. These
simulation results indicate that a late [1-123]IPT
SPECT image may represent the distribution of the
dopamine transporters. Good correlations were shown
between (BG-OCC)/OCC, RA or Rv and true k3/k4,,
although the slopes between them were not unity.
Pharmacokinetic computer simulations may be very useful
technique in studying dopamine transpoter systems. |