3.0-T MR Imaging of the Abdomen: Comparison with 1.5 T

Abstract

Three-tesla magnetic resonance (MR) imaging offers substantially higher signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) than 1.5-T MR imaging does, which can be used to improve image resolution and shorten imaging time. Because of these increases in SNR and CNR, as well as changes in T1 and T2 relaxation times, an increase in magnetic susceptibility, and an increase in chemical shift effect, many abdominal applications can benefit from 3.0-T imaging. Increased CNR obtained with a gadolinium-based contrast agent improves lesion conspicuity, requires less intravenous contrast material, and improves MR angiography by increasing spatial and temporal resolution. Increased SNR improves fluid conspicuity and resolution for applications such as MR cholangiopancreatography. Increased chemical shift effect also improves spectral resolution for MR spectroscopy. Several potential problems remain for abdominal imaging at 3.0 T. Limitations on energy deposition may require compromises in pulse sequence timing and flip angles. These compromises result in prolonged imaging time and altered image contrast. Magnetic susceptibility and chemical shift artifacts are worsened, but they may be counteracted by shortening echo time, performing parallel imaging, and increasing bandwidth. Radiofrequency field inhomogeneity is also a major concern in imaging larger fields of view and often leads to standing wave effects and large local variations in signal intensity. Many issues related to MR device compatibility and safety have yet to be addressed at 3.0 T. A 3.0-T MR imaging system has a higher initial cost and a higher cost of upkeep than a 1.5-T system does.

Interobserver and intraobserver variability of the apparent diffusion coefficient in treated malignant hepatic lesions on a 3.0T machine: Measurements in the whole lesion versus in the area with the most restricted diffusion

“…It might be interesting to see if the difference of resolution and SNR would modify the variability of the measurements (24). Further studies are also required to evaluate other technical parameters, ie, different b-values or slice thickness, to know their potential effects on measurements variability.…”

Comparison of T1‐weighted in‐ and out‐of‐phase single shot magnetization‐prepared gradient‐recalled‐echo with three‐dimensional gradient‐recalled‐echo at 3.0 tesla: Preliminary observations in abdominal studies

“…Precontrast T1-weighted sequences may also suffer from reduced signal intensity (7). T1 relaxation times for most tissues are approximately 20-40% longer at 3.0T than they are at 1.5T (8,9). For comparable pulse sequence parameters, this results in lower soft-tissue contrast and decreased lesion conspicuity on unenhanced T1-weighted images at 3.0T.…”

“…For comparable pulse sequence parameters, this results in lower soft-tissue contrast and decreased lesion conspicuity on unenhanced T1-weighted images at 3.0T. To regain the T1 contrast, longer repetition times (TR) or other sequence modifications are required at 3.0T (9). However, longer TRs increase imaging time, which can degrade clinical workflow or even eliminate the possibility of performing a breath hold acquisition.…”

“…One solution that has been used for unenhanced T1-weighted imaging at higher field strengths is incorporating a magnetization preparation prepulse for gradient-echo imaging, commonly designated as magnetization-prepared (MP)-GRE (7,9). This single-shot technique allows the acquisition of each slice in less than 1 s, and so it is principally used in patients unable to suspend respiration (11)(12)(13)(14)(15).…”

“…At 3.0T, the shortest OP TE is 1.15 ms and the shortest IP TE is 2.3 ms. Many 3.0T MRI systems are not capable of achieving a TE as short as 1.15 ms with good image quality, and therefore sample at the next OP TE, approximately 3.45 ms (9) or at a TE which is not exactly OP. However, the images obtained with the second OP TE suffer from a combination of OP and magnetic susceptibility effects due to prolonged T2* decay (9).…”