Imaging near metal: The impact of extreme static local field gradients on frequency encoding processes

Abstract

3D-MSI techniques can enable substantially enhanced magnetic resonance imaging capabilities near metallic implants. However, strong local static field gradients generate residual artifacts whose direct mitigation are ultimately limited by frequency encoding processes. Applications of 3D encoding strategies or additional post processing may be required to further reduce residual artifacts in multispectral images near metal implants.

Metallic implant geometry and susceptibility estimation using multispectral B0field maps

“…In Figures e,f, for both implant models, the simulated MAVRIC‐SL composite images had artifacts including signal loss and ripple‐like signal oscillations near metal, as seen in 3D‐MSI experiments of previous studies . The artificial signal voids corresponded well with the region where the susceptibility‐induced field shift (Figs.…”

Stereotactic ultrasound for target volume definition in a patient with prostate cancer and bilateral total hip replacement

“…Multimodal imaging offers the possibility for target definition in this situation. Pelvic MRI has been shown to be helpful 2 ; however, metal-induced image distortion [6][7][8][9] and different rectal and vesical filling caused by spatial and temporal distances from the planning CT may result in matching difficulties. This report demonstrates that fusing planning CT and 3D US data sets can successfully define prostate and seminal vesicle contours and thus the PTV for radiation therapy offering a noninvasive therapy option instead of prostatectomy also for patients with bilateral THRs.…”

“…Image distortion resulting from metal artifacts also occurs in MRI images and further complicates matching. [6][7][8][9] Matching MRI and CT is usually based on a visually fitted best-match procedure 2 without direct referencing to the treatment isocenter.…”

2D multi‐spectral imaging for fast MRI near metal

“…The relative scanning efficiencies of 2D MSI and 3D selective MSI techniques depend on the application—primarily the range of resonance offsets and the spatial range of desired slices. Although prior work has shown that areas of extreme frequency gradients or very large frequency offsets may be not recoverable due to additional effects , we will ignore these effects for simplicity in this discussion. Assuming an excitation bandwidth (or increment) B , number of slices of interest N , and frequency range , 2D MSI would require times as many excitations as standard spin‐echo imaging, regardless of the number of slices of interest.…”