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Magnetization transfer magnetic resonance of human atherosclerotic plaques ex vivo detects areas of high protein density.

Qiao Y, Hallock KJ, Hamilton JA - J Cardiovasc Magn Reson (2011)

Bottom Line: MT with appropriate calibration clearly detected regions with high protein density, which showed a higher MTR (thick fibers (collagen type I) (54 ± 8%)) compared to regions with a low amount of protein including lipid (46 ± 8%) (p = 0.05), thin fibers (collagen type III) (11 ± 6%) (p = 0.03), and calcification (6.8 ± 4%) (p = 0.02).Intraplaque hemorrhage (IPH) with different protein density demonstrated different MT effects.Old (rich in protein debris) and recent IPH (rich in fibrin) had a much higher MTR 69 ± 6% and 55 ± 9%, respectively, compared to fresh IPH (rich in intact red blood cells)(9 ± 3%).

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA 02118-2526, USA.

ABSTRACT

Background: Proteins are major plaque components, and their degradation is related to the plaque instability. We sought to assess the feasibility of magnetization transfer (MT) magnetic resonance (MR) for identifying fibrin and collagen in carotid atherosclerotic plaques ex vivo.

Methods: Human carotid artery specimens (n = 34) were obtained after resection from patients undergoing endarterectomy. MR was completed within 12 hr after surgery on an 11.7T MR microscope prior to fixation. Two sets of T1W spoiled gradient echo images were acquired with and without the application of a saturation pulse set to 10 kHz off resonance. The magnetization transfer ratio (MTR) was calculated, and the degree of MT contrast was correlated with histology.

Results: MT with appropriate calibration clearly detected regions with high protein density, which showed a higher MTR (thick fibers (collagen type I) (54 ± 8%)) compared to regions with a low amount of protein including lipid (46 ± 8%) (p = 0.05), thin fibers (collagen type III) (11 ± 6%) (p = 0.03), and calcification (6.8 ± 4%) (p = 0.02). Intraplaque hemorrhage (IPH) with different protein density demonstrated different MT effects. Old (rich in protein debris) and recent IPH (rich in fibrin) had a much higher MTR 69 ± 6% and 55 ± 9%, respectively, compared to fresh IPH (rich in intact red blood cells)(9 ± 3%).

Conclusions: MT MR enhances plaque tissue contrast and identifies the protein-rich regions of carotid artery specimens. The additional information from MTR of IPH may provide important insight into the role of IPH on plaque stability, evolution, and the risk for future ischemic events.

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MTR maps of CEA specimens with different ages of IPH. MTR maps of CEA specimens with different ages of IPH (A-C, arrows). A, fresh stage. IPH is with low MTC. B, recent stage. IPH is intermediate MTC. C, old stage. IPH is with highest MTC.
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Figure 8: MTR maps of CEA specimens with different ages of IPH. MTR maps of CEA specimens with different ages of IPH (A-C, arrows). A, fresh stage. IPH is with low MTC. B, recent stage. IPH is intermediate MTC. C, old stage. IPH is with highest MTC.

Mentions: Finally, to more graphically illustrate both the complexity and utility of applying MTR to advanced plaques with IPH the MTC images of Figure 5 are shown side by side in Figure 8. In a plaque with fresh IPH, as evident by the presence of fresh erythrocytes, the IPH region has very low MTR (Figure 8A) compared to the surrounding fibrous tissue. By comparison, IPH rich in fibrin, which is characteristic of recent IPH, was saturated by MT and had a much higher MTR (Figure 8B). In plaques containing old/organized IPH, which consist of dense proteins, the MT effect was even stronger, creating a very pronounced delineation from the surrounding tissue (Figure 8C). The small MTR observed in fresh IPH with erythrocytes might be due to the strong paramagnetic effects of hemoglobin, which become even more pronounced at high field (11.7 T), and induce a dark signal in T1W gradient echo images. Thick fibers (collagen type I) and fibrin of recent IPH (as established by histology) yielded similar MTR values, suggesting that these two tissue types have the similar organization, concentration and mobilities of their macromolecular pool. The highest MTR associated with old IPH might be due to its highly organized nature and enrichment in cell debris, especially cell membrane proteins, which contribute to the dramatic MT effects [30]. Furthermore, the growth of collagen during the organization of IPH may exert additive MT effects as well [31].


Magnetization transfer magnetic resonance of human atherosclerotic plaques ex vivo detects areas of high protein density.

Qiao Y, Hallock KJ, Hamilton JA - J Cardiovasc Magn Reson (2011)

MTR maps of CEA specimens with different ages of IPH. MTR maps of CEA specimens with different ages of IPH (A-C, arrows). A, fresh stage. IPH is with low MTC. B, recent stage. IPH is intermediate MTC. C, old stage. IPH is with highest MTC.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3278375&req=5

Figure 8: MTR maps of CEA specimens with different ages of IPH. MTR maps of CEA specimens with different ages of IPH (A-C, arrows). A, fresh stage. IPH is with low MTC. B, recent stage. IPH is intermediate MTC. C, old stage. IPH is with highest MTC.
Mentions: Finally, to more graphically illustrate both the complexity and utility of applying MTR to advanced plaques with IPH the MTC images of Figure 5 are shown side by side in Figure 8. In a plaque with fresh IPH, as evident by the presence of fresh erythrocytes, the IPH region has very low MTR (Figure 8A) compared to the surrounding fibrous tissue. By comparison, IPH rich in fibrin, which is characteristic of recent IPH, was saturated by MT and had a much higher MTR (Figure 8B). In plaques containing old/organized IPH, which consist of dense proteins, the MT effect was even stronger, creating a very pronounced delineation from the surrounding tissue (Figure 8C). The small MTR observed in fresh IPH with erythrocytes might be due to the strong paramagnetic effects of hemoglobin, which become even more pronounced at high field (11.7 T), and induce a dark signal in T1W gradient echo images. Thick fibers (collagen type I) and fibrin of recent IPH (as established by histology) yielded similar MTR values, suggesting that these two tissue types have the similar organization, concentration and mobilities of their macromolecular pool. The highest MTR associated with old IPH might be due to its highly organized nature and enrichment in cell debris, especially cell membrane proteins, which contribute to the dramatic MT effects [30]. Furthermore, the growth of collagen during the organization of IPH may exert additive MT effects as well [31].

Bottom Line: MT with appropriate calibration clearly detected regions with high protein density, which showed a higher MTR (thick fibers (collagen type I) (54 ± 8%)) compared to regions with a low amount of protein including lipid (46 ± 8%) (p = 0.05), thin fibers (collagen type III) (11 ± 6%) (p = 0.03), and calcification (6.8 ± 4%) (p = 0.02).Intraplaque hemorrhage (IPH) with different protein density demonstrated different MT effects.Old (rich in protein debris) and recent IPH (rich in fibrin) had a much higher MTR 69 ± 6% and 55 ± 9%, respectively, compared to fresh IPH (rich in intact red blood cells)(9 ± 3%).

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA 02118-2526, USA.

ABSTRACT

Background: Proteins are major plaque components, and their degradation is related to the plaque instability. We sought to assess the feasibility of magnetization transfer (MT) magnetic resonance (MR) for identifying fibrin and collagen in carotid atherosclerotic plaques ex vivo.

Methods: Human carotid artery specimens (n = 34) were obtained after resection from patients undergoing endarterectomy. MR was completed within 12 hr after surgery on an 11.7T MR microscope prior to fixation. Two sets of T1W spoiled gradient echo images were acquired with and without the application of a saturation pulse set to 10 kHz off resonance. The magnetization transfer ratio (MTR) was calculated, and the degree of MT contrast was correlated with histology.

Results: MT with appropriate calibration clearly detected regions with high protein density, which showed a higher MTR (thick fibers (collagen type I) (54 ± 8%)) compared to regions with a low amount of protein including lipid (46 ± 8%) (p = 0.05), thin fibers (collagen type III) (11 ± 6%) (p = 0.03), and calcification (6.8 ± 4%) (p = 0.02). Intraplaque hemorrhage (IPH) with different protein density demonstrated different MT effects. Old (rich in protein debris) and recent IPH (rich in fibrin) had a much higher MTR 69 ± 6% and 55 ± 9%, respectively, compared to fresh IPH (rich in intact red blood cells)(9 ± 3%).

Conclusions: MT MR enhances plaque tissue contrast and identifies the protein-rich regions of carotid artery specimens. The additional information from MTR of IPH may provide important insight into the role of IPH on plaque stability, evolution, and the risk for future ischemic events.

Show MeSH
Related in: MedlinePlus