Subtraction imaging is a technique whereby an unenhanced T1-weighted sequence is digitally subtracted from the identical sequence performed after gadolinium administration. By performing this operation, any native T1 signal is removed and the remaining signal on the subtracted images is due solely to enhancement
Subtraction MRI is an excellent technique for evaluating hemorrhagic masses or lesions with high signal intensity on unenhanced T1-weighted sequences, such as complicated cysts or hepatic nodules. Moreover, there are additional clinical scenarios in which it is essential to determine the presence or absence of enhancement within a mass. These include postablation therapy and evaluation for residual tumor versus postsurgical change. In these situations, the body imager should consider subtraction MRI as a useful problem-solving technique that can aid in arriving at a confident diagnosis.
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