5/20/2023 0 Comments New quick note macThis wider dynamic range of effect leads to a higher contrast to noise ratio (CNR) with increasing field strength (Figures 3 and 4). In addition, the use of parallel imaging can greatly shorten imaging time.Īlthough T1 relaxation times of soft tissues generally increase with a higher magnetic field strength, the relative T1 shortening effects of contrast agents, such as gadolinium, remain unchanged leading to more pronounced contrast enhancement of gadolinium-based contrast agents (GBCA) upon a background of tissues with longer T1 relaxation time. 3,4 Short echo time (TE) gradient echo techniques have been successfully utilized as well. Magnetization preparation pulses,as have been used in MR angiography (MRA), can also aid in generating T1 contrast. Another possible solution is the use of an inversion recovery preparatory pulse to accentuateT1 contrast. While decreased, unenhanced soft-tissue contrast may be compensated with a longer TR, this change leads to longer imaging time and is limited by the length of a single breath-hold. A longer pulse repetition time (TR) may be required to generate a similar degree of soft tissue contrast (Figures 1 and 2). 1 When comparing signal intensities of soft tissues at 3T and 1.5T, use of similar imaging parameters may lead to a significant decrease in relative soft-tissue contrast at 3T. Nevertheless, the benefit of a higher SNR can be used to increase spatial and temporal resolution, orsome combination of both.Īn increase in field strength leads to a prolongation of T1 relaxation time. However, the actual realized gain is less than this due to several factors including physiological noise, FDA-imposed specific absorption rate (SAR) limits (discussed below), inadequate scanner hardware, software optimization for 3T, radiofrequency (RF) field inhomogeneity, and increased susceptibility effects. When 3T is compared with 1.5T, the SNR should theoretically double. The central promise of imaging at higher field strengths lies in an increased number of protons aligned with the stronger static magnetic field,contributing to greater signal and a higher signal-to-noise ratio (SNR). This article also discusses challenges related to imaging at 3T and various strategies that may be employed to solve them. This article will discuss the theoretical advantages of imaging at higher field strength as compared with 1.5T systems and the current imaging standards for body MRI. However, growth in the use of 3T in body imaging has been hampered due to problems related to more prominent artifacts occurring within the larger field of view of abdominal andpelvic studies. The theoretical advantages and promises of higher field imaging have greatly benefited many neurologic and musculoskeletal applications and potentially can improve imaging in the abdomen and pelvis as well. Since the first 3 Tesla (3T) magnetic resonance imaging (MRI) scanners were approved for clinical use by the U.S Food and Drug Administration (FDA) in 2002, the use of 3T imaging has shown a gradual increase, especially for neuroradiologic and musculoskeletal studies. Kamel is Associate Professor and Section Chief of Body and Cardiovascular MRI, Department of Radiology and Radiological Sciences, The Johns Hopkins University School of Medicine. Chang is Assistant Professor, Department of Diagnostic Imaging, Warren Alpert Medical School of Brown University and Rhode Island Hospital, Providence, RI and Dr.
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