1. Phantom Preparation

1. Determine the implant volume (e.g., by using the water displacement method).
   NOTE: The volume of the CCT-T sample and the Z-T sample measured 0.65 mL and 0.73 mL, respectively.
2. Fix the implant position in the middle of a non-ferromagnetic, plastic, waterproof box by using a thin thread. Use a box that is larger than the expected MRI artifacts.
   NOTE: If no rough estimates of the artifact volumes of the implant and/or pulse sequence of interest are available, perform a test scan by placing the phantom in a box, approximately 10x larger than the phantom, filled with water. The artifact volumes in this study ranged from 7.3 mL (for the CCT-T sample) and 0.09 mL (for the Z-T sample).
3. Carefully melt a mixture of semisynthetic fat (58.8%), water (40%), and macrogol-8-stearate (1.2%), using a water bath at 50 °C.
   NOTE: For the samples in this study, we used a 500 mL mixture for the embedding of each sample.
   1. When the mixture becomes fluid, stop heating and start with slow stirring, and stop heating. Ensure that there is no separation of the fat and water phases.
4. As soon as clotting begins, slowly start embedding the implant with the mixture. For this, pour the embedding mixture slowly into the phantom box with the implant.
   NOTE: Pouring must be performed slowly to avoid air inclusion.
5. Place the phantom box with the embedded implant into the refrigerator at 4 °C overnight for desiccation. The next day, remove any residual fluid parts by decantation.

2. MRI Examination

1. Place the phantom (box with the embedded implant) in the MRI in the same orientation as in the in vivo situation. Position the middle of the phantom in the isocenter of the MRI.
2. For measurements, use a coil which allows for a homogeneous signal distribution within the imaging volume without severe and obvious signal drops (e.g., a head coil).
3. When planning the MRI scans at the MRI console, ensure that the phantom box, including some air at the edges of the box, is within the imaging volume.
4. Next, perform the MRI examination.

3. Image Analysis and Post-processing

1. Export the images without any loss of quality (e.g., by compression) from the MRI console (e.g., using the DICOM format). Import the images in an MRI post-processing software which allows for placing the region of interests (ROI), evaluating ROI signal intensities, a threshold-based segmentation, and a quantification of the segmentation volumes (see Table of Materials).
2. To define the threshold for pile-up artifacts and check for a homogeneous signal distribution within the imaging volume, place lines perpendicular to each other and adjacent to the outer border of the visible artifact on the slice with the maximum artifact size (Figure 1a).
   NOTE: Pile-up artifacts are displacement artifacts, presenting with areas with artificially high signal intensities. They occur in the slice direction and the readout direction.
   1. Place a background ROI (ROI_Background) with 10 mm in diameter outside each of the four intersection points (Figure 1a). Place the lines and the background regions of interests using the segmentation editor.
   2. Measure the mean signal intensity and standard deviation (SD) of all voxels within these 4 ROI_Background values and for each ROI_Background separately. Use the tool Material Statistics in the project view.
   3. Ensure that the mean signal intensity of each ROI­_Background is within the range of ± 1.5 SD of the mean signal of each of the other 3 counterparts to guarantee a homogeneous signal distribution.
   4. Calculate the threshold for pile-up artifacts by adding 3 SD of ROI_Background to the mean signal intensity of all voxels of these 4 ROI_Background values. Perform a semiautomatic threshold-based segmentation of pile-up artifacts by selecting all voxels with the signal intensities larger than the threshold adjacent to the signal loss artifact in every slice. Use the masking tool of the segmentation editor to visualize the predefined signal intensity range and restrict the segmentation to it.
3. To define the threshold for signal loss artifacts, place 4 regions of interests (ROIs) in air-containing regions (ROI_Air; each 10 mm in diameter) at the corners of the phantom box and measure the mean signal intensity and SD of all voxels within these 4 ROI_Air as described in step 3.2, using the segmentation editor and "Material Statistics", respectively.
   NOTE: Signal loss artifacts present with voxels having artificial low signal intensities. They are caused by dephasing and displacement artifacts.
   1. Place an ROI in the core of the signal loss artifact (ROI_Core) defined by the largest connected area of low signal intensities (Figure 1a). Manually increase the size of the ROI_Core until the largest possible size within the signal loss artifact whose mean signal intensity is lower than the mean ROI_Air + 3x of the respective SD is found. Finally, measure the mean signal intensity and SD of the ROI_Core.
   2. Calculate the signal intensity threshold for signal loss artifacts by adding 3 SD of the ROI_Core to the mean of the ROI_Core. Perform a semiautomatic threshold-based segmentation of signal loss artifacts by selecting all voxels connected to the ROI_Core with signal intensities below the threshold.
   3. Use the masking tool of the segmentation editor to visualize the predefined signal intensity range and restrict the segmentation to it. If possible, use the "Fill" function in the tap "Selection" of the segmentation editor to include all voxels within the segmentation that are not yet selected. If applicable, manually add the additional unequivocal signal loss artifacts to the segmentation.
4. Subtract the physical implant volume from the calculated artifact volume to obtain the true artifact volume. Repeat the analysis at least 3x. A time interval of at least two weeks should separate the multiple reads to exclude a learning bias.