Improved in-stent lumen visualization using intravascular MRI and a balanced steady-state free-precession sequence

Quantitative assessment of biliary stent artifacts on MR images: Potential implications for target delineation in radiotherapy

PURPOSE

Biliary stents may cause susceptibility artifacts, gradient-induced artifacts, and radio frequency (RF) induced artifacts on magnetic resonance images, which can hinder accurate target volume delineation in radiotherapy. In this study, the authors investigated and quantified the magnitude of these artifacts for stents of different materials.

METHODS

Eight biliary stents made of nitinol, platinum-cored nitinol, stainless steel, or polyethylene from seven vendors, with different lengths (57-98 mm) and diameters (3.0-11.7 mm), were placed in a phantom. To quantify the susceptibility artifacts sequence-independently, ΔB0-maps and T2^∗-maps were acquired at 1.5 and 3 T. To study the effect of the gradient-induced artifacts at 3 T, signal decay in images obtained with maximum readout gradient-induced artifacts was compared to signal decay in reference scans. To quantify the RF induced artifacts at 3 T, B1-maps were acquired. Finally, ΔB0-maps and T2^∗-maps were acquired at 3 T of two pancreatic cancer patients who had received platinum-cored nitinol biliary stents.

RESULTS

Outside the stent, susceptibility artifacts dominated the other artifacts. The stainless steel stent produced the largest susceptibility artifacts. The other stents caused decreased T2^∗ up to 5.1 mm (1.5 T) and 8.5 mm (3 T) from the edge of the stent. For sequences with a higher bandwidth per voxel (1.5 T: BW_vox > 275 Hz/voxel; 3 T: BW_vox > 500 Hz/voxel), the B0-related susceptibility artifacts were negligible (<0.2 voxels). The polyethylene stent showed no artifacts. In vivo, the changes in B0 and T2^∗ induced by the stent were larger than typical variations in B0 and T2^∗ induced by anatomy when the stent was at an angle of 30° with the main magnetic field.

CONCLUSIONS

Susceptibility artifacts were dominating over the other artifacts. The magnitudes of the susceptibility artifacts were determined sequence-independently. This method allows to include additional safety margins that ensure target irradiation.

Two-dimensional visualization of cholesterol and cholesteryl esters within human coronary plaques by near-infrared fluorescence angioscopy

BACKGROUND

Cholesterol (C) and cholesteryl esters (CE) within coronary plaques are minimally visualized directly by any of the available imaging modalities in vivo. If they are rendered visible in vivo, the progression of coronary plaques and the effects of respective therapies on these plaques can be objectively evaluated.

HYPOTHESIS

The C and CE within human coronary plaques can be visualized by near-infrared fluorescence angioscopy (NIRFA).

METHODS

By exciting at 710 ± 25 nm and emitting at 780 nm, near-infrared fluorescence (NIRF) of lipid components was examined by microscopy in vitro. Lipid components in 49 plaques of 32 excised human coronary arteries were examined by NIRFA in vitro. Coronary plaques were examined by NIRFA in 25 patients with coronary artery disease.

RESULTS

C, CE, and calcium (Ca) individually did not exhibit NIRF but did in the presence of β-carotene, which is known to coexist with lipids in the vascular wall. Other substances that are contained in atherosclerotic plaques did not.² The excised human coronary plaques were classified as those with NIRF and those without. The former plaques were classified into homogenous, doughnut-shaped, and spotty types. Histological examinations revealed that these image patterns were determined by the differences in the locations of C, CE, and Ca, and that those deposited within 700 μm in depth from the plaque surface were imaged by NIRFA. Homogenous, doughnut-shaped, or spotty NIRFA images were also observed in patients.

CONCLUSIONS

NIRFA is feasible for 2-dimensional imaging of C and CE deposited in human coronary plaques.