THERE HAS BEEN controversy regarding the appropriate use of magnetic resonance (MR) contrast agents in the evaluation of central nervous system (CNS) tumors. When MR imaging was first available in clinical practice in the early 1980s. contrast agents were thought to be unnecessary because of the excellent tissue contrast provided by nonenhanced MR images.
After the introduction of the first MR contrast agent, gadopentetate dimeglumine (Magnevist; Berlex Laboratories, Wayne, N J ) (standard dose, 0.1 mmoV kg), contrast material-enhanced MR imaging provided improved lesion detection, delineation, and specificity. Recently, several investigators have suggested that examinations with doses of contrast material greater than the standard dose further improve detection of small or early metastases and improve delineation of gliomas ( 1 4 ) . Higher doses are often avoided because of concern over increased examination cost, potential side effects, and loss of potency of the contrast material due to the T2 shortening effect. In fact, doses less than the standard dose have been used in the evaluation of brain tumors. Some believe that, in addition to saving money, lower doses are just as effective in the detection of CNS lesions.
No single dose of MR contrast agent is optimal or adequate for the evaluation of all types of brain tumors. An understanding of a l l the factors influencing lesion conspicuity is of paramount importance in deciding on the optimal dose of contrast material for a specific MR imaging examination. The major factors influencing lesion detection include lesion contrast, size, location, and type. This review addresses the theories behind the importance of lesion contrast-specif-Index terms: Brain neoplasms. dlagnosls. 10.12143 -Brain neoplasms. MR. 10.12143 * Contrast enhancement * Nervous system. MR. 10.12143 -Nervous system. neoplasms. 10.12143 JMRl 1994. 4:243-249 Abbrevhtions: lntenslty ratlo. MTC = magnetlzatlon transfer contrast. CNS = central nervous system. L/B = lesion-to-background signal I From the Department of Radiology. Unlverslty of Iowa College of Mediclne, 200 Hawklns Dr. Iowa Clty. IA 52242.