Technical Note: Fiducial markers for correlation of whole-specimen histopathology with MR imaging at 7 tesla
Flowchart illustrating workflows for preclinical and clinical studies to correlate in vivo imaging with histology using implanted paint fiducial markers. As the paint markers are not approved for in vivo human use, for clinical studies, the alternative of anatomical landmarks is suggested for the final registration with in vivo imaging.
Experiment 1: MRI example images for IB and ISS and example histology for IB. (a) MRI SE for IB paint in a fresh porcine kidney example slice presenting five visible artifacts from the five injections of paint. (b) Example section of a digitized H&E slide showing an IB marker with a compact appearance. (c) MRI SE for ISS paint in a fresh porcine kidney example slice demonstrating considerable distortion.
Experiment 2: MRI IB porcine liver example slices for SE and GRE pulse sequences and different paint dilutions in fresh and fixed tissue. (a) Fresh SE IB, no dilution. (b) Fresh GRE IB, no dilution. (c) Fresh SE IB, 1:10. (d) Fresh GRE IB, 1:10. (e) Fixed SE IB, no dilution. (f) Fixed GRE IB, no dilution. (g) Fixed SE IB, 1:10. (h) Fixed GRE IB, 1:10. White arrows indicate primary injection tracks and black arrows indicate leakage.
Experiment 3: MRI fresh and fixed slices and corresponding histology. (a)–(c) Prefixation sample MRI slices # 6, 14, and 22, corresponding to the histology section positions. (d)–(f) Postfixation sample MRI slices # 6, 14, and 22. (g)–(i) H&E whole mount histology slides. Colored arrows demarcate the individual paint tracks: Blue for # 1, green for # 2, and black for # 3. Red arrows demarcate apparent susceptibility artifacts possibly caused by trapped air between the tissue and gel [(e) and (f)] or leaked paint (a). Yellow arrows on (b) and (e) indicate intraurethral leakage of paint which was not visible in (h), suggesting its removal during processing. Local paint diffusion is apparent in (b) and (h) for marker 1 (blue arrow), while for other markers, the paint remained constrained in distribution, e.g., marker 2 (green arrow) in (h), which is also displayed at a higher magnification (green box).
Visualization of artifact dimension dependence on MRI receiver bandwidth for fresh and fixed slice examples.
Experiment 3: Canine prostate MRI volumes prefixation and postfixation and corresponding paint-track marker centroid points for tracks 1–3, with 3-D line fits (see legend for color key). The -direction and -direction correspond to the in-plane imaging dimensions, while the -direction corresponds to the imaging slice direction. The -direction was perpendicular to the plane on which the sample rested during fixation.
Experiments 1 and 2: Summary of paint types, dilutions, tissue states, imaging techniques used, and results obtained.
Experiment 3: Angles between fresh and fixed tissue 2-D straight-line fits in the and planes. Gravity contributions to deformation would be predominantly reflected in plane angle differences.
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