Thrombus-mimicking artifacts in two-point Dixon MRI: Prevalence, appearance, and severity

Abstract

Purpose To evaluate the incidence and severity of potentially thrombus mimicking, flow-induced misallocation artifacts in a clinical setting. Two-point “Dixon” fat–water separation methods, with bipolar readout gradients, may suffer from flow-induced fat–water misallocation artifacts. If these artifacts occur within blood vessels, they may mimic thrombus. Materials and Methods Two-point Dixon coronal and axial images acquired in 102 consecutive patients were retrospectively evaluated for the presence of flow-induced artifacts in arteries and veins. Artifacts were graded on a 3-point scale (none, mild, severe) by two independent readers. Interreader agreement was evaluated with kappa statistics. Results Reader 1 reported 63 artifacts in 46 (45%) of the cases (severe in 19 cases, 18.6%). Reader 2 reported 51 artifacts in 43 (42.2%) of the cases (severe in 18 cases, 17.6%). Misallocation of fat and water was apparent in all datasets with severe artifacts, whereas variable signal intensity changes in water and fat images were observed in mild artifacts. Interreader agreement was good for artifacts appearing in coronal images (κ = 0.7) and fair for artifact appearance in axial images (κ = 0.24). Conclusion Our study shows a high incidence of flow-induced mild and severe artifacts in a two-point Dixon method with bipolar readout gradients. This artifact should not be misinterpreted as intravascular thrombus.

Time‐resolved contrast‐enhanced MR angiography with single‐echo Dixon fat suppression

“…Changes in flow between the calibration scan and the time‐resolved series may lead to artifacts similar to those seen in Refs. and . However, the inherent velocity encoding that results from a bi‐polar dual‐echo readout gradient is prone to produce artifacts when flow is along the readout direction, while the proposed technique would only produce artifacts in the less‐likely event of large changes in flow between the calibration and the time‐resolved series.…”

“…In this work, image update times as short as 4.5 seconds were attained in the brain with SENSE undersampling factors of R = 4 and a relatively low readout bandwidth of BW = ±62.5 kHz at 3.0T. Direct comparison to dual‐echo studies in the literature is difficult due to differences in protocol choices and hardware capabilities; however, in general, higher readout bandwidths are used in dual‐echo studies to keep TE and TR values short . This strategy can keep image update times short but at the cost of SNR.…”

“…Direct comparison to dualecho studies in the literature is difficult due to differences in protocol choices and hardware capabilities; however, in general, higher readout bandwidths are used in dual-echo studies to keep TE and TR values short. 9,10,14,21 This strategy can keep image update times short but at the cost of SNR. Dual-echo Dixon imaging with bipolar readout has also been shown to be susceptible to flow-induced artifacts that mimic thrombus 19,21 due to the mismatched gradient moments at the center of each readout.…”

“…First, these techniques can be limited by diminished temporal resolution from the need to acquire a second image at a different echo time (TE), either due to prolongation of the repetition time (TR) to accommodate multiple images in a single repetition, or due to acquisition of additional echoes in separate repetitions. Second, flow‐induced misallocation artifacts have been observed due to the additional phase induced by the flow of blood . If, however, the system nonidealities are known a priori (e.g., from a dual‐echo calibration scan) a single image is sufficient to reconstruct fat and water images and avoids the above limitations, provided an appropriate TE is used .…”

“…Second, flow-induced misallocation artifacts have been observed due to the additional phase induced by the flow of blood. [18][19][20][21] If, however, the system nonidealities are known a priori (e.g., from a dual-echo calibration scan) a single image is sufficient to reconstruct fat and water images and avoids the above limitations, provided an appropriate TE is used. 12,15 Therefore, single-echo Dixon CE-MRA can avoid the limitations of dual-echo Dixon CE-MRA while providing some of the benefits.…”