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Editorial for “Improved Brain MR Imaging from a Compact, Lightweight 3 Tesla Scanner With High Performance Gradients”

Editorial for “Improved Brain MR Imaging from a Compact, Lightweight 3 Tesla Scanner With High Performance Gradients” Magnetic resonance imaging (MRI) became one of the most versatile and widely used imaging modalities to assess structural and functional information in vivo. Nowadays, 1.5 T and 3 T MRI scanners represent the main working force of clinical practice. Since its approval by the FDA in 2000, 3 T has been increasingly used in clinical practice—yet moving from 1.5 T to 3 T is not trivial, nonetheless clear advantage was reported in early publications regarding brain, vascular, and musculoskeletal imaging. However, due to the inevitable economic advantage (procurement, maintenance, and operational) of 1.5 T systems, along with easier housing, rendered the 1.5 T systems to be the primary choice for highthroughput clinical routine imaging. In this issue of JMRI, Camerucci et al report on a recently developed compact 3 T system (C3T) and compare the clinical performance with a well-developed 3 T whole-body MR scanner (WB3T), which was first introduced in late 2008. The C3T scanner is a small-bore system, which is mainly suitable for head, wrist, ankle, and knee examinations. The magnet uses conventional NbTi superconducting wire at 4 K and a low-volume (12 liters of liquid helium) cryogenic system that requires no emergency helium venting. This approach keeps the manufacturing costs low and increases siting flexibility, especially considering the weight of the system, which is one-third of the WB3T system in comparison. The system is equipped with a highperformance gradient system simultaneously providing 80 mT/m and 700 T/m/s per axis, which will have a dominant effect especially in Echo-planar Imaging (EPI) imaging comparisons. The authors enrolled 30 subjects and conducted clinically indicated brain MR examinations on both systems. Five sequences were used in this comparison: 2D T1 fluid-attenuated inversion recovery (FLAIR), 3D T2 FLAIR, 3D T1 magnetization prepared rapid gradient-echo, 2D fast spinecho T2 (with fat saturation), and diffusion weighted imaging; with identical matrix size, field of view, echo-train length (ETL), number of excitations, flip angle, and slice thickness. Two cohorts were included in the study: a smaller one with nine subjects and the lack of T1 FLAIR sequence and a larger one where all five sequences were applied on 21 subjects. Nonblinded pairs of MR images were independently reviewed by two board-certified neuroradiologists with 22 and 32 years of clinical experience and the following attributes were evaluated on 5-level Likert scales: signal-to noise ratio (SNR), lesion conspicuity, motion artifact, gray/white matter contrast, susceptibility artifacts, cerebellar folia conspicuity, and overall exam quality. Except for T1 FLAIR sequence, the C3T system performed significantly better than the WB3T scanner, while noninferiority was established for T1 FLAIR. Compared to the WB3T, the high slew-rate gradient system on the C3T scanner allows significant echo spacing reduction (25% or for FSE, and up to 40%–50% for EPI) and over 20% decrease of readout duration in case of long ETL measurements (3D T2 FLAIR). The net results are the greater SNR, less image blur, and sharper effective resolution, which explain most of the observed statistical differences. Doing a quick research in open-access online grant databases reveals that multiple groups are developing similar compact, lightweight 3 T MRI systems for head, musculoskeletal, and whole-body neonatal imaging, with significant financial support for good reason. A rationally priced compact 3 T system may represent a viable development direction for imaging centers aiming to increase daily patient throughput economically. The easy siting properties of a C3T system (smaller gross footprint, lack of helium venting, and minimal floor load) make it suitable for both smaller and larger imaging facilities. At our institute, around 60% of the daily examined patients would be eligible for the reported C3T system, based on the examined body part, which probably varies a lot between sites. The applied local transmit/receive coil design may be beneficial in many ways as compared to the receive only head coil and transmit body coil, which is the standard coil arrangement for most of the commercially available whole-body scanners: it keeps the incidence of peripheral nerve stimulation relatively low, despite the high-performance gradient system and may allow the examination of patients with active implants (eg, Vagus nerve stimulator) in a wider range of circumstances.