The Study Of Imaging Efficacy By Using Minimal Quantity Of Exogenous Contrast Agents In High-field MRI

Magnetization can be regarded as an intrinsic property of matter,which reflects the degree of magnetization of a substance in an external magnetic field.It is generally measured by the magnetic susceptibility.For the human tissue,the magnetic susceptibility is different because of the difference between the tissue composition and the microstructure.The effectively use of the difference of magnetic susceptibility between different organizations can provide additional information for the tissue structure and functions.Magnetic susceptibility contrast agent is such a magnetic substance that utilizes its unique magnetization to enhance the contrast of MR signals and the images resolution of the tissue.The emergence of the contrast agents break the limitation of traditional magnetic resonance imaging which can only rely on the original biophysical characteristics of tissues and enhance the contrast between the target and the surrounding tissue.The contrast agent is an important complement of the MR imaging.Nowadays,the contrast agents we used most commonly are synthetic chemical reagents mostly.Such as the gadopentetate dimeglumine(Gd-DTPA)and superparamagnetic iron oxide particles(SPIO)coated with polymers,etc.Although some contrast agents have undergone a large number of clinical trials and safety tests strictly,these contrast agents are exogenous substances for human body.The natural state of the tissue might have a certain impact after the CAs injection.On the other hand,the widespread use of contrast agents brings not only a huge breakthrough in medical diagnosis and treatment,but also the potential safety issues.The related studies had confirmed that contrast agents would deposits and residues in the human body and some contrast agents might have potential adverse biological effects on human tissues.Therefore,the amount of exogenous contrast agent should be minimized under the satisfactory image contrast.It was important to study the imaging efficacy by using minimal quantity of exogenous contrast agents in MRI.But there were still a lack of systematic research in the field.In this thesis,we investigate the imaging efficacy by using minimal quantity of exogenous contrast agents in high-field magnetic resonance imaging with two representative exogenous contrast agents,Gd-DTPA and SPIO.Firstly,we studied the effect of magnetic imaging blooming systematically.We established the quantitative relationship between each parameters and this effect by measuring the number of pixels and calculating the blooming factor.Secondly,we study the different contrast of the SPIO and Gd-DTPA under different imaging parameters.And then we explored the minimal quantity of exogenous contrast agents that causes image changes.In the study of the effect of magnetic imaging blooming,the difference of magnetic susceptibility and the inhomogeneity of magnetic field would affect a minimal magnetic substances.We utilizes those effect to study the blooming of different magnetic substances under the different parameters and established the quantitative relationship between each parameters and this effect.The results shows that the magnetic blooming imaging is significant in the pixel or sub-pixel model,and the blooming factor is up to 51 in the SWI image.In the study of imaging contrast by minimal quantity of exogenous contrast agents in multi parameters,we use Gd-DTPA and SPIO as representative to investigate the CNR changing with each parameters.We established the quantitative relationship between the amount of substance of the exogenous contrast agent and the CNR under the different resolution,echo times,flip angle.Moreover,we explored the minimal quantity of exogenous contrast agents that causes image changes.The result showed that,the amount of SPIO in the 3 T magnetic field that satisfies the minimum contrast requirement is more than 0.64?mol,while the Gd-DTPA is 0.02?mol(resolution is 1.2 mm,res 1),under our experimental conditions.At 7T,the minimum amount of SPIO inducing image change in the T2 sequence was 0.16?mol while the minimum amount in the SWI was 0.08 ?mol(the echo time was 30 ms).In summary,this thesis comprehensively evaluates the imaging efficacy changes of the minimal quantity of exogenous contrast agents under different conditions.It had important reference value and significance for the rational use of clinical exogenous contrast agents and imaging of small changes.The study had made an important contribution for achieving an accurate MR image with minimal quantity contrast agents.