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DOI: 10.1148/radiol.2411042201
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(Radiology 2006;241:107-115.)
© RSNA, 2006

Experimental Studies

Characterization of Intimal Changes in Coronary Artery Specimens with MR Microscopy1

Breno S. Pessanha, MD, Kimberlee Potter, PhD, Frank D. Kolodgie, PhD, Andrew Farb, MD, Robert Kutys, PA, Erik K. Mont, MD, Allen P. Burke, MD, Timothy J. O'Leary, MD, PhD and Renu Virmani, MD

1 From the Department of Cardiovascular Pathology (B.S.P., F.D.K., A.F., R.K., E.K.M., A.P.B., R.V.) and Magnetic Resonance Microscopy Facility (K.P.), Armed Forces Institute of Pathology, Washington, DC; Department of Medicine, Cardiovascular Division, George Washington University Medical Center, Washington, DC (B.S.P.); and Biomedical Laboratory Research and Development Service, Veterans Health Administration, 810 Vermont Ave NW, Washington, DC (T.J.O.). Received December 30, 2004; revision requested March 14, 2005; revision received November 2; accepted December 1; final version accepted December 19. R.V. supported by a grant from the Center for Integration of Medicine and Innovative Technology and RO1 HL61799-02. Address correspondence to T.J.O. (e-mail: timothy.oleary{at}va.gov).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 References
 
Purpose: To determine if magnetic resonance (MR) microscopy can yield images sufficient for discriminating early progressive atherosclerotic lesions from nonprogressive atherosclerotic lesions in human coronary arteries.

Materials and Methods: Institutional review board approval and informed consent were not required. Seventeen coronary artery segments (mean diameter, 2.8 mm ± 1.0 [standard deviation]) were collected within 36 hours after death from 11 cadavers (six men, five women; age range at death, 33–65 years). Quantitative T1, T2, intensity-weighted (IW), and magnetization transfer (MT) maps were acquired with a 9.4-T vertical-bore magnet. Coronary artery lesions were classified as adaptive intimal thickening (AIT), pathologic intimal thickening (PIT), or intimal xanthoma (IXA). Internal anatomic fiducial landmarks and stains were applied to proximal and epicardial vessel surfaces and used to register histologic sections with MR images and thus enable comparison of MR images and Movat pentachrome–stained histologic specimens. Unique 0.0012–0.0287-cm2 regions of interest were visually identified on quantitative T1, T2, MT, and IW maps of AIT, IXA, and PIT lesions. Distributions of T1, T2, MT, and IW values were compared with Student t and Wilcoxon two-sample tests.

Results: MR microscopic images of nonprogressive AIT and IXA lesions revealed two intimal layers. The luminal intima had higher T1 and T2 values and lower MT values than did the medial intima; these findings were consistent with compositional differences observed in histologic sections. In the IXA lesion, T2 values of both intimal layers were markedly reduced when compared with T2 values of AIT lesions because of the accumulation of lipid-laden macrophages in both layers. Progressive PIT lesions had a typical multilayered appearance or foci with a short T2 relaxation time and low IW values; these features were not observed in AIT or IXA lesions.

Conclusion: MR microscopy enabled identification of morphologic arterial wall features that enable discrimination of progressive PIT lesions from nonprogressive AIT or IXA lesions.

© RSNA, 2006


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 References
 
Human atherosclerosis is a complex disease process that is not yet fully understood and for which there is no ideal animal model. Our current knowledge of progressive events is based on the findings of highly informative, albeit static, autopsy studies that appear to show that intimal lesions play a key role in the development of symptomatic atherosclerotic disease (1). These studies have been hampered by difficulties in establishing the three-dimensional (3D) anatomic characteristics of individual atherosclerotic plaques on the basis of two-dimensional microscopic sections. Magnetic resonance (MR) microscopy represents an alternative method for 3D visualization of anatomic structures because MR images at or near microscopic resolution may be obtained without slicing and staining tissue specimens. Software that enables 3D visualization may be used to examine MR microscopic images in a way that provides greater appreciation of 3D details.

There have been numerous ex vivo and in vivo MR studies of advanced lesions in the aorta and the carotid and coronary arteries; however, these studies have been performed with relatively low spatial resolution. Thus, the spatial organization and composition of plaque components have not been readily discerned, and researchers have been unable to determine the nature of plaque progression on the basis of MR characteristics (2–9). Detection of an early progressive lesion, likely represented by pathologic intimal thickening (PIT) in the modified American Heart Association classification (1), may provide an opportunity to prevent cardiovascular events. Thus, the purpose of our study was to determine if MR microscopy can yield images sufficient for discrimination of early progressive atherosclerotic lesions from nonprogressive atherosclerotic lesions in human coronary arteries.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 References
 
Specimens
Seventeen coronary artery segments (mean diameter, 2.8 mm ± 1.0 [standard deviation]) were collected from 11 cadavers (six men, five women; age range at death, 33–65 years) provided by the Maryland State Medical Examiner's office. All segments were excised within 36 hours after death. The segments were embedded in 1% agarose at 39°–41°C, stored at 4°C, and imaged fresh 2–4 hours after they were removed from the heart. The institutional review board of the Armed Forces Institute of Pathology granted exempt status to this study; thus, informed consent from relatives of the deceased individuals was not required.

MR Microscopy Protocol
Experiments were performed with a Bruker DMX spectrometer (Bruker Instruments, Billerica, Mass) coupled to a vertical-bore magnet operating at 9.4 T (400.1 MHz for proton spectroscopy). Quantitative T1 relaxation maps were calculated from two-dimensional images acquired with a saturation-recovery sequence (repetition time msec/echo time msec, 200–5000/12). The T2 relaxation maps and intensity-weighted (IW) maps were calculated from 16 images acquired with a multi-echo sequence (5000/12–192). IW values were normalized to the IW value of the surrounding agarose gel and reported as a percentage. Magnetization transfer (MT) maps were calculated with the following equation: 1 – Mso/Mo, where Mso divided by Mo is the ratio of image intensities acquired with and without the application of a 5-second 12-µT saturation pulse 6000 Hz off resonance (10).

Quantitative two-dimensional MR images acquired with fat suppression had a section thickness of 1 mm and an in-plane resolution of 78 µm. The 3D fat-suppressed images were acquired for all segments longer than 1 cm with a rapid acquisition with relaxation enhancement (RARE) imaging sequence (2000/8; four signals acquired; RARE factor, eight) (11). The total acquisition time for each segment was 1 hour 40 minutes for T1 data, 42 minutes for T2 data, and 42 minutes for MT data. The 3D RARE images were acquired with a 78-µm3 voxel resolution in 4 hours 40 minutes. Specimen temperature and formalin fixation are known to have profound effects on MR properties of atherosclerotic plaques (12,13); thus, all specimens were imaged unfixed and at 37°C to reproduce the in vivo physical conditions of the plaque components.

Histologic Analysis
After imaging, specimens were fixed in formalin for 4–6 hours for frozen sectioning and for 8–12 hours for paraffin sectioning. All specimens were stained with Movat pentachrome, which is a general connective tissue stain that stains elastic fibers black, collagen fibers yellow, proteoglycans blue or green, and smooth muscle cells red. To analyze more specific tissue components, hematoxylin-eosin, elastic van Gieson, oil red O (applied to frozen specimens only), Alcian blue, and picrosirius red stains were applied to subsequent tissue specimens and were used to characterize cellularity (nuclei stained blue), elastin fibers (stained black), lipids (stained red), proteoglycans (stained blue), and collagen (stained red-green under polarized light), respectively (14,15). Smooth muscle cells were identified with an antibody directed against {alpha}-actin (Clone 1A4 [dilution, 1:1000]; Sigma Chemical, St Louis, Mo). Macrophages were identified with an antibody directed at the CD68 cell surface receptor (KP1 [dilution, 1:200]; Dako, Carpinteria, Calif).

A pathologist with 25 years of experience (R.V.) classified coronary artery lesions. The American Heart Association morphologic criteria used to classify the adaptive intimal thickening (AIT), intimal xanthoma (IXA), and PIT lesions are summarized in Table 1 (1). No MR information was used to classify lesions. The AIT, or normal-appearing, lesion was characterized by intimal thickening. The IXA lesion, otherwise known as a fatty streak, was similar to the AIT lesion except for the presence of lipid-filled macrophages or foam cells, which are positive for CD68 and lipids at tissue staining. The PIT lesion, which is also known as a preatheroma lesion, has a focal absence of smooth muscle cells in regions containing ELPs, with or without cholesterol crystals. Overlaying the ELPs is a layer of lipid-laden macrophages, which are positive for CD68 and lipids at tissue staining.


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  		Table 1. Histologic Criteria Used to Classify Early Coronary Artery Lesions

 
Registration of MR Microscopic Images and Histologic Samples
The 1-mm segment of the coronary artery that corresponded to the 1-mm MR section was embedded in paraffin for paraffin sectioning and in OCT (Miles, Elkhart, Ind) for frozen sectioning. Cryosections were approximately 6 µm thick, whereas paraffin sections were approximately 4 µm thick. Internal anatomic fiducial landmarks and stains were applied to the proximal and epicardial surfaces of the vessel and were used to register the histologic samples with MR images. The stains did not affect the MR properties of the vessel.

In several samples, vessels were reconstructed in 3D format from histologic sections with the Bioquant NOVA program (R&M Biometrics, Nashville, Tenn). Four consecutive histologic sections that were 6 µm thick and 306 µm apart were digitally interpolated to produce a vessel that was approximately 950 µm long for comparison with the 1-mm-thick MR image of the vessel.

MR Image Analysis
Unique regions of interest ranging from 0.0012 to 0.0287 cm2 were visually identified (B.S.P.) on quantitative T1, T2, MT, and IW maps of AIT, IXA, and PIT lesions. The T1, T2, MT, and IW values of the regions of interest were averaged for each lesion type and are reported in Table 2.


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  		Table 2. Summary of T1, T2, MT, and IW Values of MR Microscopy Intimal Features for Early Coronary Lesions

 
Statistical Analysis
The Student t test and the Wilcoxon two-sample test were used to compare the distribution of T1, T2, MT, and IW values. Specifically, T1, T2, MT, and IW values were compared between the LI and MI for IXA and AIT lesions. This comparison was not made for PIT lesions because the MI layer could not be visually identified on MR images. Instead, T1, T2, MT, and IW values for PIT lesions were compared between the LI and the regions containing lipid-filled macrophages or ELPs. A two-tailed P value of less than .05 was considered to indicate a significant difference. The Student t test was performed with Statview, version 4.01, software (SAS Institute, Cary, NC), and the Wilcoxon test was performed with a Web-enabled program (www.fon.hum.uva.nl/Service/Statistics.html) from the Institute of Phonetic Sciences at the University of Amsterdam.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 ADVANCES IN KNOWLEDGE
 References
 
Five segments represented AIT, six represented IXA, and six represented PIT, as defined in the modified American Heart Association classification scheme (1).

AIT Lesions
In the Movat pentachrome–stained section (Fig 1), the intima was green, the media was red, and the adventitia was yellow. On the fat-suppressed T2 map, the lipid-rich adventitia was identified as the low-signal-intensity layer on the outside of the vessel and the media was identified as the subjacent intermediate-signal-intensity layer. The intima, however, formed two distinct layers: a high-signal-intensity layer nearest the lumen (the LI) and a low-signal-intensity layer adjacent to the media (the MI). These two layers were observed in all five AIT lesions. When compared with the MI, the LI had higher T1 (2.13 seconds ± 0.30 vs 1.59 seconds ± 0.20; P = .03 and .015 with the t and Wilcoxon tests, respectively), T2 (84 msec ± 14 vs 49 msec ± 12; P = .005 and .008 with the t and Wilcoxon tests, respectively), and IW (97% ± 4 vs 89% ± 13, P values were not significant) values and lower MT ratios (0.54 ± 0.02 vs 0.72 ± 0.02; P < .001 with the t test, P = .04 with the Wilcoxon test) in all cases (Table 2).


Figure 1
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  		Figure 1: A, Representative T2 map of AIT lesion shows low signal intensity in adventitia (Adv). Intima can be divided into high- and low-signal-intensity layers nearest the LI and MI, respectively. B, Movat pentachrome–stained section of corresponding segment shows adventitia, media, and intima (I) stained yellow, red, and green, respectively. In A and B, boxes indicate the area from which C–E were acquired; M = media. C–E, Intimal composition variations are determined with sections stained with Alcian blue (proteoglycans stained blue) (C), picrosirius red (collagen stained red-green under polarized light) (D), and elastic van Gieson (elastin fibers stained black) (E). In D, green line demarcates internal elastic lamina and blue line demarcates luminal surface.

 
The proteoglycan content of the LI was higher than that of the MI in specimens stained with Alcian blue (Fig 1, C). In contrast, specimens stained with picrosirius red and elastic van Gieson revealed the densities of collagen and elastin fibers were greater in the MI than in the LI.

IXA Lesions
Findings in the Movat pentachrome–stained section were similar to those in the AIT lesion, with the exception of the eccentric area of intimal thickening and the accumulation of macrophages in the intimal layer, which can be seen with higher magnification of the CD68-stained specimen (Fig 2).


Figure 2
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  		Figure 2: A, T2, and, B, IW maps of an IXA lesion show the intima can be divided into two layers (LI and MI). C, Findings in a Movat pentachrome–stained section were comparable to an AIT lesion except for an eccentric lesion. D, The CD68-stained section contained macrophages (stained red). The box indicates the area from which E was acquired. E, The CD68-stained section is shown at a higher magnification, and foci of macrophages (M{Phi}) are seen in the intima. M = media, L = lumen.

 
Histologically, IXA lesions are similar to AIT lesions except for the presence of lipid-filled macrophages. Accordingly, MR images of IXA lesions (n = 6) were morphologically comparable to MR images of AIT lesions, with the intima divided into two distinct layers. Again, values in the LI were higher than values in the MI for (a) T1 (2.12 seconds ± 0.18 vs 1.63 seconds ± 0.12; P < .001 with the t test, P = .03 with the Wilcoxon test), (b) T2 (78 msec ± 10 vs 41 msec ± 5; P < .001 with the t test, P = .03 with the Wilcoxon test), and (c) IW (98% ± 5 vs 89% ± 10, P values were not significant) maps. Although T2 values of the LI and MI in IXA lesions were notably reduced compared with T2 values for LI and MI in AIT lesions, the differences were not significant.

PIT Lesions
In five of the six PIT lesions, it was possible to identify the more hydrated LI; however, the MI could not be identified reliably. Instead, as observed in the representative T2 map of a PIT lesion (Fig 3, A), there were alternating layers of low and high signal intensity that were juxtaposed to the LI. The low-signal-intensity layer nearest the media was attributed to ELPs that were seen as acellular areas on the Movat pentachrome–stained specimen (Fig 3, B), with a focal absence of smooth muscle cells according to the {alpha}-actin–stained section (Fig 3, C). The low-signal-intensity layer subjacent to the LI was the layer of superficial macrophages and was confirmed by findings in the CD68-stained section seen in Figure 3, D. The appearance of ELPs and macrophages in the Movat pentachrome–stained section was revealed with higher magnification (Fig 3, E). The high T2 value of LI permitted its differentiation from low T2 areas occupied by lipid-filled macrophages (78 msec vs 54 msec) and ELPs (78 msec vs 43 msec), as identified with histologic analysis (for LI vs macrophages and ELPs, P = .05 with the t test; differences were not significant with the Wilcoxon test). However, lipid-laden macrophages could not be differentiated from ELPs on the basis of T2 values.


Figure 3
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  		Figure 3: A, Representative T2 map of PIT lesion shows LI as a high-signal-intensity area. The MI border is not well defined, particularly in areas of lipid accumulation, with lipid-laden macrophages (M{Phi} in E) or ELPs, as determined with histologic analysis. B, Movat pentachrome–stained section shows ELPs in acellular areas with a focal absence of, C, {alpha}-actin staining (smooth muscle cells stained red). D, CD68-stained section confirms the presence of macrophages (stained red) near LI. E, Movat pentachrome–stained section shows characteristic appearance of ELPs and macrophages.

 
3D MR Images
T2-weighted 3D MR images were acquired for 12 of the 17 coronary segments being investigated. In five autopsy cases (corresponding to seven coronary segments), a spatial progression of the atherosclerotic disease process was observed in transverse sections extracted at different distances along the length of the vessel; in the remaining five segments, only one lesion type was observed. Figure 4, A, shows a series of nine images extracted from the 3D data set of one such vessel. The images, which show the vessel in cross section, were approximately 78 µm thick and located approximately 500 µm apart. This particular vessel shows the progression of an AIT lesion to a PIT lesion and, finally, to a fibrocalcific plaque as the vessel is traversed from the proximal to the distal end. The lesion types seen at the locations indicated on Figure 4, A, were verified against histologic sections obtained at approximately the same locations in the vessel. Movat pentachrome–stained sections of the AIT (Fig 4, B) and PIT (Fig 4, C) lesions were similar to those described previously. In sections with more advanced fibrocalcific plaque (Fig 4, D), calcium deposits—which were seen as large low-signal-intensity areas on the corresponding MR image—did not survive histologic processing and were absent in the section shown.


Figure 4
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  		Figure 4: A, Nine T2-weighted MR images extracted from a 3D rapid acquisition with relaxation enhancement image of a coronary artery embedded in agarose gel show progression of an AIT lesion to a fibrocalcific (FC) lesion. Images corresponding to 78-µm-thick sections with an in-plane spatial resolution were extracted every 500 µm starting approximately 5 mm from the proximal end of the vessel. In all images, the LI had high signal intensity, and calcified deposits (Ca) in the last two images of the series had low signal intensity. Perivascular fat had low signal intensity in all images because images were acquired with fat suppression. B–D, Movat pentachrome–stained sections obtained approximately 1.5 mm apart confirmed progression of normal-appearing AIT lesion (B) to PIT lesion (C) and fibrocalcific lesion (D).

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
ADVANCES IN KNOWLEDGE
 References
 
MR imaging of the aorta and carotid arteries is a well-established technique; however, to our knowledge, neither in vivo nor in vitro techniques have proved capable of providing sufficient spatial resolution to enable characterization of early atherosclerotic lesions (9). In contrast, histologic techniques are capable of enabling a precise description of the extent of atherosclerotic change; however, they cannot be used to follow atherosclerotic progression within one subject over a period of time. In addition, 3D reconstruction is laborious and often impractical. Our study results have shown that high-spatial-resolution ex vivo 9.4-T MR microscopy is capable of providing 3D images that yield insight into the arterial wall changes that occur in three early coronary lesions: AIT, IXA, and PIT.

AIT Lesions
AIT lesions are considered a normal coronary morphologic change in adults since these lesions are reportedly found in the coronary arteries of infants as young as 3 months (16). They are characterized by a thickened intima composed mainly of collagen and proteoglycans (1). High-spatial-resolution MR microscopic images of coronary segments with AIT lesions revealed two distinct intimal layers. In an MR study of carotid, femoral, and aortic arteries at 1.5 T, Martin et al (17) found a similar division in the intima of disease-free arteries. The hypointense rim subjacent to the hyperintense intima was thought to be an imaging artifact because it was associated with only a modest reduction in signal intensity and it was not apparent on images obtained with a higher spatial resolution. In our studies, the two distinct intimal layers were found with MR microscopy in all AIT and IXA lesions. Our histochemical studies correlate with the imaging results; the density of elastic and collagen fibers decreased from the MI to the LI, with a reciprocal increase in the proteoglycan content.

IXA Lesions
The IXA (fatty streak) lesion, which is characterized by intimal thickening with an accumulation of lipid-laden macrophages, is another nonprogressive lesion that is known to regress (1). Again, T2 and IW maps of IXA lesions showed two intimal layers, the LI and the MI; however, T2 values for the LI and MI of IXA lesions were somewhat reduced compared with the T2 value for the MI and LI of AIT lesions. The reduction in T2 values may be attributed to the presence of foam cells with intracellular lipids, such as cholesterol esters, which are motion restricted even at 37°C (18). A larger sample size may be needed to demonstrate a significant difference between AIT and IXA lesions, especially since the reduction in T2 values for IXA lesions might be dependent on the level of macrophage activity.

PIT Lesions
PIT (preatheroma) lesions, which are characterized by a thickened intima with a poorly formed fibrous cap, typically have incompletely coalesced ELPs in acellular areas of the deep intima (1). This stage is thought to represent the link from early to advanced lesions, and some authors (19) have suggested that recognition of the period of life when these lesions begin should lead to the initiation of concentrated preventive measures at that age. All PIT lesions had either (a) the typical multilayered appearance, which was originally described by Stary et al (19), on T2 and IW maps or (b) foci of reduced T2 and IW values near the media.

MR Microscopy Classification of Coronary Lesions
The findings of previous ex vivo studies suggested that low T2 values were associated with motion-restricted cholesterol esters in the cytoplasm of foam cells and deposits of unesterified cholesterol crystals (2,3,18,20). While this has permitted the differentiation of proteoglycan-rich LIs from lipid-laden macrophages and ELPs on T2 relaxation maps, lipid-laden macrophages could not be differentiated from ELPs on the basis of T2 values. By recognizing the characteristic appearance of PIT lesions on MR microscopic images, we were able to differentiate PIT lesions from the nonprogressive lesions described previously. Neither AIT nor IXA lesions had the typical features of PIT lesions on T1, T2, MT, or IW maps. We realize that other plaque characteristics, such as the degree of luminal stenosis, could help with lesion identification; however, they were not used in this study because some overlap may exist between PIT lesions and the more advanced fibrous cap atheromas.

The MR microscopy–based classification scheme presented in this article was used to establish the lesional state of a vessel on the basis of findings on T2-weighted MR images extracted from 3D MR microscopy data sets. Cross-sectional images were extracted at different longitudinal positions and used to visualize the spatial progression of early lesions to more advanced pathologic lesions within the vessel segment. This approach could potentially be used to study the natural history of disease progression in vivo. With a rapid volumetric imaging technique, it should be possible to determine the plaque burden of tortuous coronary arteries in any arbitrary plane in vivo. This technique has the added advantage of reduced partial volume averaging compared with two-dimensional techniques (5).

Advances in MR imaging of the vessel wall have provided investigators with the requisite tools to study the natural progression of atherosclerosis in humans. In vivo MR imaging of advanced aortic (21,22) and carotid (23–25) atherosclerotic plaques can now be performed with high spatial and temporal resolution. Also, MR imaging of the submillimeter arrangement of plaque components has greatly improved estimates of plaque vulnerability (26) and enabled the longitudinal assessment of the effect of lipid-lowering therapies on plaque composition (21,27).

The application of clinical MR imaging to the characterization of coronary artery plaques, however, is still impaired by the small vessel caliber, the tortuous course of these vessels, and cardiac and respiratory motion (28). Despite these limitations, in vivo studies have demonstrated that these arteries can be imaged (29–31). Worthley et al (30) were able to identify intralesional thrombosis in a swine model, but they did not attempt to characterize other coronary plaque components. With improved MR imaging capabilities, it may be possible to use our proposed MR microscopy classification scheme for in vivo monitoring of the natural progression of atherosclerosis and its subsequent treatment. Further refinements of the MR imaging technique might include the use of contrast agents (7,24,32), intravascular radiofrequency coils (33), faster imaging sequences, and 3-T magnets (34) to improve the signal-to-noise and contrast-to-noise ratios.

Limitations
Our imaging results reflect the application of highly optimized conditions. There were no motion artifacts, the field strength was significantly higher than that of current clinical MR imaging systems, and the spatial resolution was much higher than that used in clinical practice. Acquisition times were much longer than would be clinically acceptable. It is uncertain if technologic improvements will enable similar results to be obtained in vivo.

Practical application: MR microscopy is capable of yielding high-spatial-resolution 3D images of human coronary arteries. The spatial and chemical information obtained thus far is sufficiently robust to enable the discrimination of progressive PIT lesions from nonprogressive AIT and IXA lesions. Thus, MR microscopy may have diagnostic applications as an adjunctive technique for examination of hearts at autopsy. In addition, the nearly histologic image quality obtained with this technique could, if successfully extended to in vivo applications, facilitate accurate characterization of atherosclerotic lesions and effective monitoring of treatments aimed at plaque stabilization.


   ADVANCES IN KNOWLEDGE
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
References
 


   ACKNOWLEDGMENTS
 
We thank Lila Adams, Hedwig Avallone, and Jinky Beyer for the careful preparation of numerous histologic samples.


   FOOTNOTES
 

Abbreviations: AIT = adaptive intimal thickening • ELP = extracellular lipid pool • IW = intensity weighted • IXA = intimal xanthoma • LI = luminal intima • MI = medial intima • MT = magnetization transfer • PIT = pathologic intimal thickening • 3D = three dimensional

The opinions and assertions contained herein are the private views of the authors and are not to be construed as official or reflecting the views of the Department of the Army, the Department of Defense, or the Department of Veterans Affairs.

Authors stated no financial relationship to disclose.

Author contributions: Guarantors of integrity of entire study, B.S.P., K.P.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, B.S.P., K.P., F.D.K., E.K.M., T.J.O.; experimental studies, B.S.P., K.P., F.D.K., A.F., R.K., E.K.M., A.P.B.; statistical analysis, B.S.P., A.P.B.; and manuscript editing, B.S.P., K.P., F.D.K., A.F., A.P.B., T.J.O., R.V.


   References
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 References
 

  1. Virmani R, Kolodgie FD, Burke AP, Farb A, Schwartz SM. Lessons from sudden coronary death: a comprehensive morphological classification scheme for atherosclerotic lesions. Arterioscler Thromb Vasc Biol 2000;20:1262–1275.[Free Full Text]
  2. Shinnar M, Fallon JT, Wehrli S, et al. The diagnostic accuracy of ex vivo MRI for human atherosclerotic plaque characterization. Arterioscler Thromb Vasc Biol 1999;19:2756–2761.[Abstract/Free Full Text]
  3. Serfaty JM, Chaabane L, Tabib A, Chevallier JM, Briguet A, Douek PC. Atherosclerotic plaques: classification and characterization with T2-weighted high-spatial-resolution MR imaging—an in vitro study. Radiology 2001;219:403–410.[Abstract/Free Full Text]
  4. Rogers WJ, Prichard JW, Hu YL, et al. Characterization of signal properties in atherosclerotic plaque components by intravascular MRI. Arterioscler Thromb Vasc Biol 2000;20:1824–1830.[Abstract/Free Full Text]
  5. Coombs BD, Rapp JH, Ursell PC, Reilly LM, Saloner D. Structure of plaque at carotid bifurcation: high-resolution MRI with histological correlation. Stroke 2001;32:2516–2521.[Abstract/Free Full Text]
  6. Yuan C, Beach KW, Smith LH Jr, Hatsukami TS. Measurement of atherosclerotic carotid plaque size in vivo using high resolution magnetic resonance imaging. Circulation 1998;98:2666–2671.[Abstract/Free Full Text]
  7. Yuan C, Kerwin WS, Ferguson MS, et al. Contrast-enhanced high resolution MRI for atherosclerotic carotid artery tissue characterization. J Magn Reson Imaging 2002;15:62–67.[CrossRef][Medline]
  8. Yuan C, Zhang SX, Polissar NL, et al. Identification of fibrous cap rupture with magnetic resonance imaging is highly associated with recent transient ischemic attack or stroke. Circulation 2002;105:181–185.[Abstract/Free Full Text]
  9. Yuan C, Hatsukami TS, Obrien KD. High-resolution magnetic resonance imaging of normal and atherosclerotic human coronary arteries ex vivo: discrimination of plaque tissue components. J Investig Med 2001;49:491–499.[Medline]
  10. Hajnal JV, Baudouin CJ, Oatridge A, Young IR, Bydder GM. Design and implementation of magnetization transfer pulse sequences for clinical use. J Comput Assist Tomogr 1992;16:7–18.[Medline]
  11. Hennig J, Nauerth A, Friedburg H. RARE imaging: a fast imaging method for clinical MR. Magn Reson Med 1986;3:823–833.[Medline]
  12. Dalager-Pedersen S, Falk E, Ringgaard S, Kristensen IB, Pedersen EM. Effects of temperature and histopathologic preparation on the size and morphology of atherosclerotic carotid arteries as imaged by MRI. J Magn Reson Imaging 1999;10:876–885.[CrossRef][Medline]
  13. Yuan C, Petty C, O'Brien KD, Hatsukami TS, Eary JF, Brown BG. In vitro and in situ magnetic resonance imaging signal features of atherosclerotic plaque-associated lipids. Arterioscler Thromb Vasc Biol 1997;17:1496–1503.[Abstract/Free Full Text]
  14. Mikel UV. Advanced laboratory methods in histopathology and pathology. Washington, DC: Armed Forces Institute of Pathology-American Registry of Pathology, 1994; 184–185, 198–199.
  15. Prophet EB, Mills B, Arrington JB, Sobin LH. Laboratory methods in histotechnology. Washington, DC: Armed Forces Institute of Pathology-American Registry of Pathology, 1992; 53–58, 128–130, 134–136, 156–158, 170, 177–178.
  16. Ikari Y, McManus BM, Kenyon J, Schwartz SM. Neonatal intima formation in the human coronary artery. Arterioscler Thromb Vasc Biol 1999;19:2036–2040.[Abstract/Free Full Text]
  17. Martin AJ, Gotlieb AI, Henkelman RM. High-resolution MR imaging of human arteries. J Magn Reson Imaging 1995;5:93–100.[Medline]
  18. Vinitski S, Consigny PM, Shapiro MJ, Janes N, Smullens SN, Rifkin MD. Magnetic resonance chemical shift imaging and spectroscopy of atherosclerotic plaque. Invest Radiol 1991;26:703–714.[CrossRef][Medline]
  19. Stary HC, Chandler AB, Glagov S, et al. A definition of initial, fatty streak, and intermediate lesions of atherosclerosis: a report from the committee on vascular lesions of the council on arteriosclerosis, American Heart Association. Circulation 1994;89:2462–2478.[Abstract/Free Full Text]
  20. Maynor CH, Charles HC, Herfkens RJ, Suddarth SA, Johnson GA. Chemical shift imaging of atherosclerosis at 7.0 Tesla. Invest Radiol 1989;24:52–60.[CrossRef][Medline]
  21. Corti R, Fayad ZA, Fuster V, et al. Effects of lipid-lowering by simvastatin on human atherosclerotic lesions: a longitudinal study by high-resolution, noninvasive magnetic resonance imaging. Circulation 2001;104:249–252.[Abstract/Free Full Text]
  22. Fayad ZA, Nahar T, Fallon JT, et al. In vivo magnetic resonance evaluation of atherosclerotic plaques in the human thoracic aorta: a comparison with transesophageal echocardiography. Circulation 2000;101:2503–2509.[Abstract/Free Full Text]
  23. Yuan C, Mitsumori LM, Ferguson MS, et al. In vivo accuracy of multispectral magnetic resonance imaging for identifying lipid-rich necrotic cores and intraplaque hemorrhage in advanced human carotid plaques. Circulation 2001;104:2051–2056.[Abstract/Free Full Text]
  24. Wasserman BA, Smith WI, Trout HH 3rd, Cannon RO 3rd, Balaban RS, Arai AE. Carotid artery atherosclerosis: in vivo morphologic characterization with gadolinium-enhanced double-oblique MR imaging—initial results. Radiology 2002;223:566–573.[Abstract/Free Full Text]
  25. Toussaint JF, LaMuraglia GM, Southern JF, Fuster V, Kantor HL. Magnetic resonance images lipid, fibrous, calcified, hemorrhagic, and thrombotic components of human atherosclerosis in vivo. Circulation 1996;94:932–938.[Abstract/Free Full Text]
  26. Hatsukami TS, Ross R, Polissar NL, Yuan C. Visualization of fibrous cap thickness and rupture in human atherosclerotic carotid plaque in vivo with high-resolution magnetic resonance imaging. Circulation 2000;102:959–964.[Abstract/Free Full Text]
  27. Zhao XQ, Yuan C, Hatsukami TS, et al. Effects of prolonged intensive lipid-lowering therapy on the characteristics of carotid atherosclerotic plaques in vivo by MRI: a case-control study. Arterioscler Thromb Vasc Biol 2001;21:1623–1629.[Abstract/Free Full Text]
  28. Fayad ZA, Fuster V. Clinical imaging of the high-risk or vulnerable atherosclerotic plaque. Circ Res 2001;89:305–316.[Abstract/Free Full Text]
  29. Botnar RM, Stuber M, Kissinger KV, Kim WY, Spuentrup E, Manning WJ. Noninvasive coronary vessel wall and plaque imaging with magnetic resonance imaging. Circulation 2000;102:2582–2587.[Abstract/Free Full Text]
  30. Worthley SG, Helft G, Fuster V, et al. Noninvasive in vivo magnetic resonance imaging of experimental coronary artery lesions in a porcine model. Circulation 2000;101:2956–2961.[Abstract/Free Full Text]
  31. Worthley SG, Helft G, Fayad ZA, et al. Cardiac gated breath-hold black blood MRI of the coronary artery wall: an in vivo and ex vivo comparison. Int J Cardiovasc Imaging 2001;17:195–201.[CrossRef][Medline]
  32. Schmitz SA, Coupland SE, Gust R, et al. Superparamagnetic iron oxide-enhanced MRI of atherosclerotic plaques in Watanabe hereditable hyperlipidemic rabbits. Invest Radiol 2000;35:460–471.[CrossRef][Medline]
  33. Correia LC, Atalar E, Kelemen MD, et al. Intravascular magnetic resonance imaging of aortic atherosclerotic plaque composition. Arterioscler Thromb Vasc Biol 1997;17:3626–3632.[Abstract/Free Full Text]
  34. Botnar RM, Stuber M, Lamerichs R, Smink J, Fischer S, Manning WJ. Initial experience with coronary vessel wall imaging on a 3T whole body system [abstract]. In: Proceedings of the 10th Meeting of the International Society for Magnetic Resonance in Medicine. Berkeley, Calif: International Society for Magnetic Resonance in Medicine, 2002; 63.



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