Higher and lower specific activity 131I-MIBG were investigated in normal andreserpinized mice. Biodistribution studies showed a higher uptake of 131I-MIBG in heart with its maXimum of 9.08%ID/g at 4h pi at 3.22TBq/g MIBG
and a lower uptake of 4.8%ID/g at the same take at 18.5GBq/g MIBG. The heart intravesicular uptake is increased with upping specific activity
but the heart extravesicular uptake seems not connect with specific activity. When using MIBG for myocardical imaging
a higher specific activity of 131I-MIBG will be beneficial to diagnosis.