Breast MRI in patients with implantable loop recorder: initial experience

Abstract

Objectives: To investigate the feasibility of breast MRI exams and guided biopsies in patients with an implantable loop recorder (ILR) as well as the impact ILRs may have on image interpretation.

Materials and methods: This retrospective study examined breast MRIs of patients with ILR, from April 2008 to September 2022. Radiological reports and electronic medical records were reviewed for demographic characteristics, safety concerns, and imaging findings. MR images were analyzed and compared statistically for artifact quantification on the various pulse sequences.

Results: Overall, 40/82,778 (0.049%) MRIs during the study period included ILR. All MRIs were completed without early termination. No patient-related or device-related adverse events occurred. ILRs were most commonly located in the left lower-inner quadrant (64.6%). The main artifact was a signal intensity (SI) void in a dipole formation in the ILR bed with or without areas of peripheral high SI. Artifacts appeared greatest in the cranio-caudal axis (p < 0.001), followed by the anterior-posterior axis (p < 0.001), and then the right-left axis. High peripheral rim-like SI artifacts appeared on the post-contrast and subtracted T1-weighted images, mimicking suspicious enhancement. Artifacts were most prominent on diffusion-weighted (p < 0.001), followed by T2-weighted and T1-weighted images. In eight patients, suspicious findings were found on MRI, resulting in four additional malignant lesions. Of six patients with left breast cancer, the tumor was completely visible in five cases and partially obscured in one.

Conclusion: Breast MRI is feasible and safe among patients with ILR and may provide a significant diagnostic value, albeit with localized, characteristic artifacts.

Clinical relevance statement: Indicated breast MRI exams and guided biopsies can be safely performed in patients with implantable loop recorder. Nevertheless, radiologists should be aware of associated limitations including limited assessment of the inner left breast and pseudo-enhancement artifacts.

Key points: • Breast MRI in patients with an implantable loop recorder is an infrequent, feasible, and safe procedure. • Despite limited breast visualization of the implantable loop recorder bed and characteristic artifacts, MRI depicted additional lesions in 8/40 (20%) of cases, half of which were malignant. • Breast MRI in patients with an implantable loop recorder should be performed when indicated, taking into consideration typical associated artifacts.

Keywords: Artifacts; Breast neoplasms; Magnetic resonance imaging.

Figure 1.. Loop recorder artifact appearance on the various MRI sequences.

Images of representative 64-year-old patient with implantable loop recorder. Left breast mammographic medio-lateral oblique (MLO) view reference (a.) highlights the relatively small dimensions of the device and its position at the lower inner breast. Nonfat suppressed pre-contrast T1 weighted image reveals signal void in the device bed (b.). High signal void artifact is demonstrated on fat-suppressed T2-weighted image (b.) and diffusion weighted image (c.), with associated geometrical distortions in the latter. Post-contrast axial (e.), subtracted (f.) and sagittal (g.) T1-weighted images exhibit both central signal void and peripheral non-continuous “ring-like” artifacts. Interestingly, the dipole pattern of inhomogeneity induced by a cylindrical metal object is best visualized on the sagittal plane.

Figure 2.. Dipole artifact pattern on subtracted dynamic contrast-enhanced (DCE) T1-weighted images and artifacts measurements in the three axes.

Sagittal post-contrast T1-weighted image (a.) of a representative 69-year-old patient with implantable loop recorder, exhibiting the typical dipole, four-leaf-clover-like artifact with central signal intensity (SI) void and four round high-SI artifacts, prominent on the cranio-caudal (CC) axis, and representing the interference of the implantable loop recorder with the magnetic field. Plots of box [(median ± interquartile range (IQR)] and whiskers (1.5 IQR) of the artifacts’ measurements in the three orthogonal dimensions, confirming the largest dimension on CC axis, followed by the anterior–posterior (AP) axis, and the right–left (RL) axis (b.).

Figure 3.. “Pseudo enhancement” artifact on subtracted dynamic contrast-enhanced (DCE_T1-weighted images.

MRI of 74-year-old patient with implantable loop recorder, screened due to personal history of breast cancer and extremely dense breasts. Two different slice locations are represented in each row. In the upper row, axial pre- (a.) and post-contrast (b.) T1-weighted images reveal central signal void artifact and additional similar but nonidentical high-signal foci. Subsequently, subtraction image (c.) of the misregistered pre- and post-contrast images may show a “pseudo-enhancing” artifact, which could be misinterpreted as enhancing focus. In the second row, a more typical continuous, peripheral, ring-like high signal is noted on the pre (d.), post (e.) and subtracted (f.) images, facilitating the diagnosis of loop-recorder-induced artifact.

Figure 4.. “Pseudo enhancement” artifact on subtracted dynamic contrast-enhanced (DCE) T1-weighted images.

MRI of 54-year-old patient with implantable loop recorder, screened due to family history of breast cancer. Two different slice locations are represented in each row. In the upper row, axial pre- (a.) and post-contrast (b.) images reveal central signal void artifact and additional similar but nonidentical high-signal foci, which result in a “pseudo-enhancing” artifact on the subtracted respective T1-weighted image (c.). Further inferiorly, the ring-like high signal on the pre (d.), post (e.) and subtracted (f.) images confirms the presence of a characteristic loop-recorder-induced artifact.

Figure 5.. Loop recorder induced artifacts and geometrical distortions on diffusion-weighted images.

Diffusion-weighted (DW) images of four different patients with implantable loop recorder, scanned with either echo planar imaging (EPI)-based (a. and c.) or multiplexed sensitivity-encoding (MUSE)-based (b. and d.) techniques. Interestingly, each features a different artifact appearance: EPI-DW images are characterized by vertical geometrical distortion artifact along the phase encoding axis, whereas MUSE-DWI images exhibit horizontal ghosting artifact in the readout axis.

Figure 6.. MRI-guided breast biopsy in the presence of ipsilateral loop recorder.

MRI of 57-year-old patient with implantable loop recorder and newly diagnosed left breast invasive mucinous carcinoma, for whom MRI-guided biopsy was recommended and successfully performed at two sites. Axial post-contrast T1-weighted image (a.) demonstrates the device artifact in the upper inner breast, as well as the non-mass enhancement in the upper outer breast with susceptibility artifact in its anterior extent, denoting site of biopsy. Sagittal images at medial (b.) and lateral (c.) positions respectively show the typical dipole artifact on the cranio-caudal (CC) plane and the two small susceptibility artifacts, corresponding with biopsies sites (arrows).