Experimental Study On The Effect Of^99mTc-MDP In Vivo Distribution And Bone Scintigraphy After The Application Of Mri Contrast Agent

Objective: To investigate the effects of the MRI contrast agentsOmniscan and Magnevist on in vivo distribution and skeletal imaging of^99mTc-MDP in mice and rabbits; this was done to provide a basis for optimizingthe interval time between MRI contrast agents and bone imaging agents^99mTc-MDP, and provide a approximating circumscription for the time of exertan influence. Methods: The skeletal imaging in rabbits: All rabbits wereadministrated by auricular vein, the dose of Omniscan, Magnevist and normalsaline were all0.2ml/kg, the dose of^99mTc-MDP was18.5MBq/kg.Healthyadult rabbits were randomized into three groups of five, the time intervalbetween experiments was seven days, Group1, treated with Omniscan+^99mTc-MDP; Group2, treated with Magnevist+^99mTc-MDP; Control Group,treated with normal saline+^99mTc-MDP. The interval between injections was30minutes. To observe the distribution and metabolism of imaging agents, wholebody skeletal imaging was performed in the three groups at5min,10min,30min,60min,120min,240min,360min and24h after the^99mTc-MDP injection.Thirty healthy adult rabbits were randomized into six small groups（n=5）by thedifferent interval between injections （30min,60min,120min,240min,360min，24h）, the time interval between experiments was seven days, Group1,treated with Omniscan+^99mTc-MDP; Control Group1, treated with normalsaline+^99mTc-MDP. Whole body skeletal imaging was performed in the two groups at2h after the^99mTc-MDP injection. Twenty healthy adult rabbits wererandomized into four small groups（n=5）by the different interval betweeninjections （30min,60min,120min,240min）,the time interval betweenexperiments was seven days, Group2, treated with Magnevist+^99mTc-MDP;Control Group2, treated with normal saline+^99mTc-MDP. Whole body skeletalimaging was performed in the two groups at30min after the^99mTc-MDPinjection, to observe the distribution and metabolism of imaging agents.Bio-distribution in mice: All mice were administrated by tail vein, the dose ofOmniscan and Magnevist were all0.1mmol/kg. the dose of normal saline was0.2ml, the dose of^99mTc-MDP was0.74MBq.Mice were randomized into threegroups of one hundred and twenty, each group contained forty mice，each groupwere randomized into eight small groups（n=5）by the different time points（5min,10min,30min,60min,120min,240min,360min,24h）, the organs wereharvested in the three groups at above time points after the^99mTc-MDP injection,Group1, treated with Omniscan+^99mTc-MDP; Group2, treated with Magnevist+^99mTc-MDP; Control Group, treated with normal saline+^99mTc-MDP. Theinterval between injections was at30min. And radioactivity was counted. Then,the percentage of tissue radioactivity count per gram to the total injected dose（%ID/g） was calculated to reveal the in vivo distribution of the imaging agentin mice. Mice were randomized into two groups of sixty, each group containedthirty mice, each group were randomized into six small groups（n=5）by thedifferent interval between injections （30min,60min,120min,240min,360 min,24h）. Group1, treated with Omniscan+^99mTc-MDP; Control Group1,treated with normal saline+^99mTc-MDP. The liver, spleen, bone and muscle ofmice were harvested in the two groups at2h after the^99mTc-MDP injection, andradioactivity was counted. Mice were randomized into two groups of forty,each group contained twenty mice, each group were randomized into four smallgroups（n=5）by the different interval between injections （30min,60min,120min,240min）.Group2, treated with Magnevist+^99mTc-MDP; Control Group2,treated with normal saline+^99mTc-MDP. The liver, spleen, bone and muscle ofmice were harvested in the two groups at30min after the^99mTc-MDP injection,and radioactivity was counted. The T/B ratio of the organs and muscle wascalculated. The radiochemical purity change in vitro and in vivo afterinteractions of MRI contrast agents and^99mTc-MDP was investigated by usingthin-layer paper chromatography （TLC）. Results: Omniscan and^99mTc-MDPinjected at an interval of30min,60min,120min,240min was measured in theliver and the spleen. Assay of the in vivo distribution of contrast agents showedthat the T/B ratios of the liver, spleen, and muscle were higher and those of thebone and muscle were lower in the study groups, compared to the control groupat these time points （P <0.05）. The T/B ratios of the liver/spleen and musclewere the highest at the30minute interval （22.37±0.25and18.27±0.56,respectively）. At the30min interval, the imaging agents were still detained inthe liver and spleen at6h after the injection of^99mTc-MDP. In vivo distributionassay showed that at five minutes after the injection of Omniscan+^99mTc-MDP, radioactive distribution was the highest in the kidney （10.34±0.78）%ID/g,followed by the heart （9.07±0.41）%ID/g, and the liver （8.89±0.23）%ID/g, andspleen （5.48±0.16）%ID/g, radioactive distribution was the highest in the bone（8.69±0.32）%ID/g at120min. The uptake ratios of the liver/spleen and musclewere the highest at the120minute （22.58and18.50, respectively）. The uptakeratio of the bone and muscle was the highest at the360minute （86.71）.Magnevist and^99mTc-MDP injected at an interval of30min,60min wasmeasured in the liver and the spleen. Assay of the in vivo distribution ofcontrast agents showed that the T/B ratios of the liver, spleen, and muscle werehigher and those of the bone and muscle were lower in the study groups,compared to the control group at these time points （P <0.05）. The T/B ratios ofthe liver/spleen and muscle were the highest at the30minute interval （16.34±0.33and13.93±0.27, respectively）. At the30min interval, the imaging agentswere only detained in the liver and spleen at5min,10min,30min after theinjection of^99mTc-MDP. In vivo distribution assay showed that at five minutesafter the injection of Magnvesit+^99mTc-MDP, radioactive distribution was thehighest in the kidney （10.94±0.56）%ID/g, followed by the heart（7.93±0.34）%ID/g, and the liver （5.23±0.10）%ID/g, and spleen（4.37±0.18）%ID/g, radioactive distribution was the highest in the bone（9.06±0.23）%ID/g at120min. The uptake ratios of the liver/spleen and musclewere the highest at the30minute （15.92and13.42, respectively）. The uptakeratio of the bone and muscle was the highest at the360minute （92.5）. As shown by the TLC curve, when the MRI contrast agents were first injected, then^99mTc-MDP was injected, a small peak was measured at Rfof0-0.2whennormal saline had been the developing agent, and the radiochemical purity of^99mTc-MDP was decreased. Conclusions: When the injection interval was≤4h,Omniscan and^99mTc-MDP levels were abnormal in the liver and spleen. At the30min interval, the imaging agents were detained in the liver and spleen from5min to6h after the injection of^99mTc-MDP. When the injection interval was≤1h, Magnevist and^99mTc-MDP levels were abnormal in the liver and spleen. Atthe30min interval, the imaging agents were detained in the liver and spleen at5min,10min,30min after the injection of^99mTc-MDP.