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DOI: 10.1148/radiol.2431060310
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(Radiology 2007;243:220-228.)
© RSNA, 2007

Technical Developments

Three-dimensional Black-Blood MR Imaging of Carotid Arteries with Segmented Steady-State Free Precession: Initial Experience1

Ioannis Koktzoglou, PhD, Yiu-Cho Chung, PhD, Timothy J. Carroll, PhD, Orlando P. Simonetti, PhD, Mark D. Morasch, MD and Debiao Li, PhD

1 From the Department of Radiology (I.K., T.J.C., D.L.) and Division of Vascular Surgery, Department of Surgery (M.D.M.), Northwestern University, 448 E Ontario St, Suite 700, Chicago, IL 60611; Department of Biomedical Engineering, Northwestern University, Evanston, Ill (I.K., T.J.C., D.L.); Siemens Medical Solutions, Chicago, Ill (Y.C.C.); and Department of Cardiovascular Medicine and Radiology, College of Medicine and Public Health, the Ohio State University, Columbus, Ohio (O.P.S.). Received February 17, 2006; revision requested April 21; revision received June 5; final version accepted August 1. I.K. supported by the Dr John N. Nicholson Fellowship. Address correspondence to I.K. (e-mail: ioannis.koktzoglou{at}gmail.com).


   ABSTRACT
TOP
 ABSTRACT
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 References
 
This HIPAA-compliant study had institutional review board approval. Informed consent was obtained. The purpose was to prospectively evaluate a segmented three-dimensional (3D) double inversion recovery (DIR)–prepared steady-state free precession (SSFP) magnetic resonance (MR) imaging sequence for fast high-spatial-resolution black-blood carotid arterial wall imaging. Carotid wall–lumen contrast-to-noise ratio (CNR) obtained with this sequence was compared with those obtained with two-dimensional (2D) single- and multisection black-blood fast spin-echo (SE) sequences. MR imaging of both carotid artery bifurcations over 3 cm of transverse coverage was performed in eight volunteers (seven men, one woman; age range, 26–56 years) with no known history of carotid artery disease. Adjusted for section thickness and imaging time per section, higher effective mean CNR was achieved with segmented 3D DIR-prepared SSFP than with single-section 2D DIR-prepared fast SE or multisection 2D saturation-band fast SE (P < .05). Segmented 3D DIR-prepared SSFP enables black-blood carotid arterial wall MR imaging with contiguous thin-section coverage and greater imaging speed and effective CNR than conventional 2D fast SE techniques.

© RSNA, 2007

Magnetic resonance (MR) imaging is a promising modality for noninvasive detection and characterization of carotid atherosclerotic lesions (1–6). The conventional MR imaging sequence used for carotid atherosclerotic plaque imaging is a black-blood–prepared two-dimensional (2D) fast spin-echo (SE) sequence. Two-dimensional MR imaging, however, offers poorer spatial resolution in the section-select direction than does three-dimensional (3D) MR imaging, making 2D MR images more prone to partial volume averaging in the section direction, which can obscure image details. Unfortunately, 3D fast SE is much slower than multisection 2D fast SE for noninvasive MR imaging of the carotid artery wall. To reduce imaging times associated with 3D black-blood MR imaging of a single carotid artery to on the order of 4–12 minutes, others have used reduced field of view imaging (7,8). However, to cover both sides of the carotid arteries, which is necessary because of the bilateral symmetry of carotid atherosclerosis (9), an imaging time longer than what was quoted in these articles will be required.

Steady-state free precession (SSFP) is a fast and signal-to-noise ratio–efficient MR imaging sequence commonly used in the assessment of cardiovascular disease (10). Although SSFP imaging typically results in bright-blood image contrast, segmented SSFP imaging can be combined with magnetization preparations (eg, fat saturation, T2 preparation) to highlight the anatomy of interest. Thus, the purpose of our study was to prospectively evaluate a segmented 3D double inversion recovery (DIR)–prepared SSFP MR imaging sequence for fast high-spatial-resolution black-blood imaging of the carotid artery wall.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 References
 
The authors who are not employees of Siemens Medical Solutions (Chicago, Ill) had control of inclusion of any data and information that might present a conflict of interest for those authors who are employees of Siemens. The Siemens branch in Malvern, Pa, provided the MR imaging unit used in this experiment. This study was approved by the institutional review board of Northwestern University and was compliant with the Health Insurance Portability and Accountability Act. Written informed consent was obtained from all volunteers.

Volunteers
Eight healthy volunteers (seven men, one woman; age range, 26–56 years) underwent carotid artery wall MR imaging. All volunteers who were recruited had no history of carotid artery disease or contraindications to MR imaging.

MR Imaging System
All examinations were performed with a 1.5-T whole-body MR imaging system (Magnetom Sonata; Siemens Medical Solutions, Erlangen, Germany) with a high-performance gradient system (maximum gradient amplitude, 40 mT/m; maximum slew rate, 200 mT/m/msec). The system's integrated body coil was used for radiofrequency signal transmission, and four-channel phased-array carotid coils (Machnet, Eelde, the Netherlands) with two left and two right channels were used for signal reception (coil size = 6 x 12 cm2).

MR Imaging Procedure
First, the carotid artery bifurcations were localized by two authors (I.K. and Y.C.C., with 4 and 11 years of MR imaging experience, respectively) on transverse segmented SSFP MR imaging sections. Vessel wall MR imaging through the carotid artery bifurcations over a 3-cm transverse distance was subsequently performed, with the following three sequences performed in random order: single-section 2D DIR-prepared fast SE (11), multisection 2D saturation-band fast SE (12,13), and segmented 3D DIR-prepared SSFP. T1-, T2-, and intermediate-weighted imaging were performed with both single-section 2D DIR-prepared fast SE and multisection 2D saturation-band fast SE (Fig 1).


Figure 1
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  		Figure 1: Diagram shows section positions acquired with following imaging sequences: A, segmented 3D DIR-prepared SSFP (acquired section thickness, 1.5 mm); B, segmented 3D DIR-prepared SSFP (reconstructed section thickness after zero-filling interpolation, 1.0 mm); C, multisection 2D saturation-band fast SE (section thickness, 3 mm); and, D, 2D DIR-prepared fast SE (section thickness, 2 mm).

 
Segmented 3D DIR-prepared SSFP MR Imaging
The segmented 3D DIR-prepared SSFP imaging sequence (Fig 2) was designed for (a) time-efficient black-blood imaging and (b) high signal-to-noise ratio carotid wall imaging at in-plane spatial resolutions comparable with those described in previous carotid wall imaging studies (4,5). Collection of 65 SSFP imaging segments every DIR repetition time (TRDIR) enabled measurement of one k-space partition (containing 256 phase-encoding lines) every four TRDIR periods. A TRDIR of 1 second was found empirically to offer a good compromise between MR imaging efficiency and signal-to-noise ratio. Ten sinusoidally ramped SSFP radiofrequency preparation pulses were used before segmented SSFP data acquisition to ensure a smooth signal evolution during data acquisition (14).


Figure 2
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  		Figure 2: Timing diagram for segmented 3D DIR-prepared SSFP sequence. Segmented SSFP imaging is preceded by a sinusoidally ramped radiofrequency series to reduce image artifacts during imaging, a chemically selective fat-saturation radiofrequency pulse to suppress subcutaneous fat signal, and a DIR preparation followed by a delay time (TI) to suppress blood signal. After segmented SSFP acquisition, an {alpha}/2 radiofrequency pulse is applied to flip coherent transverse magnetization to the longitudinal direction. A centric k-space phase-encoding order was used within the segmented SSFP echo train during each heartbeat to maximize effect of fat and blood signal suppression. TRDIR = DIR repetition time.

 
Given the above parameters and an SSFP echo spacing of 5.8 msec—the minimum echo spacing allowed by our MR system with an imaging field of view of 12 x 12 cm and an imaging matrix of 256 x 256—numeric simulations of the segmented SSFP sequence were performed by one author (I.K., with 4 years of MR physics experience) with a software package (MATLAB, version 7.0; Mathworks, Natick, Mass) to determine the appropriate flip angle for imaging the medial layer of the arterial wall (T1 = 860 msec, T2 = 60 msec; T1 and T2 values were adapted from 0.5-T imaging [15] to 1.5-T imaging by using the observations of Bottomley et al [16] and Stanisz et al [17], respectively). By using the matrix formalism proposed by Hargreaves et al (18), medial wall MR signal was simulated over a wide range of flip angles. On the basis of the simulation results (data not shown), a flip angle of 45° was chosen because it yielded high, near-constant signal during the segmented SSFP data acquisition period.

High bandwidth-time product (9.0) hamming-windowed sinc radiofrequency excitation pulses were used during the SSFP ramp-up and acquisition periods to achieve good flip angle uniformity throughout the imaging slab and to mitigate aliasing artifacts in the partition-encoding direction (ie, kz). Black-blood image contrast was achieved through application of a DIR magnetization preparation before data acquisition (19). The thickness of the section-selective inversion radiofrequency pulse within the DIR preparation was set to 1.3 times the thickness of the imaging slab—thick enough to ensure inversion of the entire imaging slab yet thin enough to allow black-blood imaging. In the steady state, the DIR inversion time, TI, used to null blood is given by the following equation:

Formula 1(1)
where T1b is the T1 of blood and TRDIR is the DIR repetition time. When TRDIR is 1 second and T1b is 1250 msec, TI is approximately 400 msec.

Fast SE MR Imaging
Two-dimensional fast SE imaging was performed to allow comparison of accepted fast SE carotid wall imaging protocols with the presented segmented 3D DIR-prepared SSFP imaging sequence (Table 1). Multisection 2D saturation-band fast SE imaging was performed for the purpose of comparing the segmented 3D DIR-prepared SSFP sequence with a coverage- and time-matched imaging sequence, while single-section 2D DIR-prepared fast SE imaging was performed for the purpose of comparing segmented 3D DIR-prepared SSFP imaging with the conventional fast SE protocol currently used for black-blood carotid artery wall imaging.


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  		Table 1. Parameters for SSFP and Fast SE MR Imaging Sequences

 
In-plane spatial resolution for all fast SE sequences (Table 1) was 0.47 x 0.47 mm2, equivalent to the in-plane spatial resolution achieved with the segmented 3D DIR-prepared SSFP sequence. Electrocardiographic triggering was used during DIR-prepared fast SE imaging (4), with a repetition time of three R-R intervals for intermediate- and T2-weighted imaging and one R-R interval for T1-weighted imaging. Electrocardiographic triggering was not used during saturation-band fast SE imaging (20). The saturation-band fast SE protocols involved the application of 50-mm-thick saturation bands above and below the imaging sections to suppress blood signal before data were acquired for each section (13). The DIR protocols closely matched those described in the literature (21). The thicknesses of sections acquired with DIR-prepared fast SE and saturation-band fast SE imaging were matched to literature values of 2 mm (4,21) and 3 mm (20), respectively.

Image Evaluation
Images were transferred to an imaging workstation loaded with public-domain image processing software (ImageJ, version 1.34s; National Institutes of Health, Bethesda, Md) for evaluation of contrast-to-noise ratio (CNR) between the carotid artery wall and lumen. CNR measurements were performed by one author (I.K.). Carotid artery wall signal intensity (SW) was measured as the mean signal intensity value within a path (width, 1 pixel) that was manually drawn on the carotid arterial wall. Luminal signal intensity (SL) was measured as the mean signal intensity within a region of interest drawn to contain the carotid arterial lumen. Image noise ({sigma}N) was measured as the standard deviation of air signal intensity within a region of interest that was between 0.25 and 0.50 cm2 in size and was free of artifacts. Hence, the CNR between carotid artery wall and lumen was calculated with the following equation:

Formula 2(2)
In each volunteer, CNR was calculated on all acquired images. CNR values were subsequently averaged to yield one CNR value for each imaging sequence and volunteer.

For each sequence, the imaging time per section (TSECT) was calculated by dividing the total imaging time by the number of imaging sections. Carotid artery wall–lumen CNR efficiency (CNREFF) was defined by the following equation, adapted from previously published work (7,22):

Formula 3(3)
where SLTH is the section thickness (in millimeters), TSECT is the imaging time per section (in minutes), and CNR is as defined in Equation (2). CNREFF was calculated for all imaging sequences. With CNREFF, we sought to normalize CNR by the square root of the imaging time per section and by the section thickness. Note that acquisition of more imaging sections at the expense of fewer MR signal averages (ie, a reduced imaging time per section) does not affect CNREFF as it is defined here.

Multiplanar reconstructions of the segmented 3D DIR-prepared SSFP image sets were performed for in-plane viewing of the arterial wall. All multiplanar reconstructions were created with the 3D viewing tool of an imaging workstation (Leonardo; Siemens Medical Solutions).

Contrast-enhanced MR Angiography
Any volunteers who exhibited possible carotid arterial wall thickening with impingement of the carotid lumen, as assessed visually by a consensus of two authors (I.K. and Y.C.C.) on the 3D DIR-prepared SSFP images (original images and multiplanar reconstructions), were brought back for a second MR imaging session in which contrast material–enhanced MR angiography of the carotid arteries was performed. The presence or absence of carotid arterial lumen impingement on the MR angiographic images was evaluated by two authors (T.J.C. and D.L., with 8 and 18 years of cardiovascular MR imaging experience, respectively) in consensus.

A contrast agent (gadopentate dimeglumine, Magnevist; Berlex Laboratories, Montville, NJ) was administered via an antecubital vein by using an MR-compatible power injector (Spectris; Medrad, Indianola, Pa). The time interval between contrast agent injection and arrival in the carotid arteries was measured with continuous imaging (at 1 frame per second) of a transversely oriented section through the carotid arteries with a 2D inversion-recovery fast low-angle shot (FLASH) sequence after a 2-mL test bolus injection of the contrast agent. Contrast-enhanced MR angiography with a 3D FLASH sequence was performed after a 20-mL injection of contrast agent (flow rate, 2 mL/sec). Before the arrival of the contrast agent in the carotid arteries, a precontrast "mask" 3D FLASH image set was acquired. This set was later subtracted from the postcontrast 3D FLASH image set to eliminate background signals. Parameters for the 3D FLASH sequence were as follows: coronal slab orientation; field of view, 26 x 26 cm; imaging matrix, 256 x 256 (interpolated to 512 x 512); phase-encoding partial Fourier factor, 6/8; flip angle, 25°; radiofrequency repetition time 4.3 msec and echo time 1.4 msec; number of sections, 32; section thickness, 1.5 mm; and bandwidth, 390 Hz/pixel.

Statistical Analysis
Statistical analysis was performed with two statistical software programs (SYSTAT, version 10.2, Systat Software, Point Richmond, Calif; SPSS, version 11.0, SPSS, Chicago, Ill). One-way analysis of variance with a Bonferroni posttest was used to compare CNR and CNREFF values obtained with the 3D DIR-prepared SSFP sequence with those obtained with the T1-, T2-, and intermediate-weighted 2D saturation-band fast SE and 2D DIR-prepared fast SE sequences. A one-way analysis of variance with a Games-Howell posttest (unequal variance assumption) was used to compare TSECT values among sequences.

For all tests, statistical significance was defined at the P < .05 level. Power analysis at a level of significance of .05 was performed to verify the acceptability of the statistical results. Any power of .8 or greater was considered acceptable.


   RESULTS
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 ADVANCES IN KNOWLEDGE
 References
 
CNR
Mean carotid wall–lumen CNR and CNREFF values were significantly different among the fast SE and segmented SSFP imaging sequences (P < .05, one-way analysis of variance) (Table 2). CNR values for intermediate-weighted 2D saturation-band fast SE imaging and intermediate-weighted 2D DIR-prepared fast SE imaging were larger than the CNR value attained with segmented 3D DIR-prepared SSFP imaging (P < .05, one-way analysis of variance with Bonferroni posttest). Figure 3 shows the image contrast obtained with 3D DIR-prepared SSFP and 2D DIR-prepared fast SE imaging. Differences in CNREFF were found between the segmented 3D DIR-prepared SSFP sequence and all fast SE imaging sequences (P < .05, one-way analysis of variance with Bonferroni posttest), with segmented 3D DIR-prepared SSFP producing the largest CNREFF value. The many sections obtained with the 3D DIR-prepared SSFP sequence (Fig 4) partially contributed to its high CNREFF.


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  		Table 2. CNR and CNR Efficiency Values for SSFP and Fast SE MR Imaging Sequences

 

Figure 3A
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  		Figure 3a: Transverse MR images in 50-year-old man show image contrast and CNR obtained with the following sequences: (a) segmented 3D DIR-prepared SSFP (section thickness, 1.5 mm interpolated to 1.0 mm; TSECT, 9.6 seconds), (b) 2D DIR-prepared intermediate-weighted fast SE (section thickness, 2 mm; TSECT, 111 seconds), (c) 2D DIR-prepared T2-weighted fast SE (section thickness, 2 mm; TSECT, 111 seconds), and (d) 2D DIR-prepared T1-weighted fast SE (section thickness, 2 mm; TSECT, 76 seconds). Images were acquired with 0.47 x 0.47 mm2 in-plane spatial resolution. Magnified insets of regions enclosed with dashed boxes in a depict carotid arterial wall (arrowheads). Note appearance of both carotid arteries on the images.

 

Figure 3B
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  		Figure 3b: Transverse MR images in 50-year-old man show image contrast and CNR obtained with the following sequences: (a) segmented 3D DIR-prepared SSFP (section thickness, 1.5 mm interpolated to 1.0 mm; TSECT, 9.6 seconds), (b) 2D DIR-prepared intermediate-weighted fast SE (section thickness, 2 mm; TSECT, 111 seconds), (c) 2D DIR-prepared T2-weighted fast SE (section thickness, 2 mm; TSECT, 111 seconds), and (d) 2D DIR-prepared T1-weighted fast SE (section thickness, 2 mm; TSECT, 76 seconds). Images were acquired with 0.47 x 0.47 mm2 in-plane spatial resolution. Magnified insets of regions enclosed with dashed boxes in a depict carotid arterial wall (arrowheads). Note appearance of both carotid arteries on the images.

 

Figure 3C
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  		Figure 3c: Transverse MR images in 50-year-old man show image contrast and CNR obtained with the following sequences: (a) segmented 3D DIR-prepared SSFP (section thickness, 1.5 mm interpolated to 1.0 mm; TSECT, 9.6 seconds), (b) 2D DIR-prepared intermediate-weighted fast SE (section thickness, 2 mm; TSECT, 111 seconds), (c) 2D DIR-prepared T2-weighted fast SE (section thickness, 2 mm; TSECT, 111 seconds), and (d) 2D DIR-prepared T1-weighted fast SE (section thickness, 2 mm; TSECT, 76 seconds). Images were acquired with 0.47 x 0.47 mm2 in-plane spatial resolution. Magnified insets of regions enclosed with dashed boxes in a depict carotid arterial wall (arrowheads). Note appearance of both carotid arteries on the images.

 

Figure 3D
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  		Figure 3d: Transverse MR images in 50-year-old man show image contrast and CNR obtained with the following sequences: (a) segmented 3D DIR-prepared SSFP (section thickness, 1.5 mm interpolated to 1.0 mm; TSECT, 9.6 seconds), (b) 2D DIR-prepared intermediate-weighted fast SE (section thickness, 2 mm; TSECT, 111 seconds), (c) 2D DIR-prepared T2-weighted fast SE (section thickness, 2 mm; TSECT, 111 seconds), and (d) 2D DIR-prepared T1-weighted fast SE (section thickness, 2 mm; TSECT, 76 seconds). Images were acquired with 0.47 x 0.47 mm2 in-plane spatial resolution. Magnified insets of regions enclosed with dashed boxes in a depict carotid arterial wall (arrowheads). Note appearance of both carotid arteries on the images.

 

Figure 4A
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  		Figure 4a: Images in 53-year-old man. (a) Thirty consecutive transverse MR images of right carotid bifurcation acquired with segmented 3D DIR-prepared SSFP show right common carotid (cc), internal carotid (ic), and external carotid (ec) arteries. Note suppression of blood signal in carotid lumen (arrows) and delineation of carotid artery wall. (b) Magnified transverse 2D DIR-prepared fast SE (FSE) images acquired with intermediate weighting (IW), T2 weighting (T2W), and T1 weighting (T1W). Segmented 3D DIR-prepared SSFP images at same positions are shown above for purposes of comparison. Arrow in internal carotid artery points to what may be either residual lumen signal or minor arterial wall thickening. Note appearance of arterial lumen boundaries as depicted in the four data sets. Numbers in bottom right corners indicate section positions (see Fig 1).

 

Figure 4B
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  		Figure 4b: Images in 53-year-old man. (a) Thirty consecutive transverse MR images of right carotid bifurcation acquired with segmented 3D DIR-prepared SSFP show right common carotid (cc), internal carotid (ic), and external carotid (ec) arteries. Note suppression of blood signal in carotid lumen (arrows) and delineation of carotid artery wall. (b) Magnified transverse 2D DIR-prepared fast SE (FSE) images acquired with intermediate weighting (IW), T2 weighting (T2W), and T1 weighting (T1W). Segmented 3D DIR-prepared SSFP images at same positions are shown above for purposes of comparison. Arrow in internal carotid artery points to what may be either residual lumen signal or minor arterial wall thickening. Note appearance of arterial lumen boundaries as depicted in the four data sets. Numbers in bottom right corners indicate section positions (see Fig 1).

 
Imaging Time
Mean imaging times for the five-section electrocardiographically triggered intermediate-, T2-, and T1-weighted 2D DIR-prepared fast SE sequences were 578 seconds ± 71, 559 seconds ± 77, and 402 seconds ± 72, respectively. MR imaging times for the segmented 3D DIR-prepared SSFP and intermediate-, T2-, and T1-weighted 2D saturation-band fast SE sequences were 192, 188, 188, and 187 seconds, respectively. Imaging time per section (TSECT) values are listed in Table 2. Among the sequences performed in this study, substantial differences in TSECT values were observed (P < .05, one-way analysis of variance). Notably, the TSECT value obtained with the 3D DIR-prepared SSFP sequence (9.6 seconds per section) was significantly smaller than the TSECT values obtained with all remaining 2D DIR-prepared and saturation-band fast SE imaging sequences (range, 20.8–115.6 seconds per section) (P < .05, one-way analysis of variance with Games-Howell posttest).

MR Angiography
Apparent carotid arterial wall thickening with impingement on the carotid artery lumen was observed in one volunteer with the segmented 3D DIR-prepared SSFP sequence during MR imaging. In this volunteer (Fig 5), heterogeneous signal intensity on the 3D DIR-prepared SSFP images was observed within the arterial wall. A multiplanar reconstruction through the segmented 3D DIR-prepared SSFP image data set conveniently displayed the location and severity of the wall thickening. The impingement of the apparently thickened arterial wall on the carotid arterial lumen was confirmed on a contrast-enhanced MR angiogram.


Figure 5A
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  		Figure 5a: Images in 43-year-old man. (a) Consecutive (from left to right and top to bottom) transverse MR images obtained with segmented 3D DIR-prepared SSFP depict apparent thickening of left internal carotid artery wall, producing luminal impingement opposite the flow divider (arrows). (b) In-plane view of carotid bifurcation obtained through multiplanar reconstruction of 3D DIR-prepared SSFP image set. Carotid lumen (*), normal carotid wall (solid arrows), and thickened wall (dashed arrow) are well depicted. (c) Thin maximum intensity projection of contrast-enhanced FLASH MR angiogram corroborates presence of thickened arterial wall (dashed arrow) and its impingement on the lumen (*). Solid arrows point to normal carotid wall. Note morphologic similarity of the arterial lumen boundaries as depicted in b and c. Dashed lines in b and c indicate position of image in center of bottom row in a.

 

Figure 5B
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  		Figure 5b: Images in 43-year-old man. (a) Consecutive (from left to right and top to bottom) transverse MR images obtained with segmented 3D DIR-prepared SSFP depict apparent thickening of left internal carotid artery wall, producing luminal impingement opposite the flow divider (arrows). (b) In-plane view of carotid bifurcation obtained through multiplanar reconstruction of 3D DIR-prepared SSFP image set. Carotid lumen (*), normal carotid wall (solid arrows), and thickened wall (dashed arrow) are well depicted. (c) Thin maximum intensity projection of contrast-enhanced FLASH MR angiogram corroborates presence of thickened arterial wall (dashed arrow) and its impingement on the lumen (*). Solid arrows point to normal carotid wall. Note morphologic similarity of the arterial lumen boundaries as depicted in b and c. Dashed lines in b and c indicate position of image in center of bottom row in a.

 

Figure 5C
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  		Figure 5c: Images in 43-year-old man. (a) Consecutive (from left to right and top to bottom) transverse MR images obtained with segmented 3D DIR-prepared SSFP depict apparent thickening of left internal carotid artery wall, producing luminal impingement opposite the flow divider (arrows). (b) In-plane view of carotid bifurcation obtained through multiplanar reconstruction of 3D DIR-prepared SSFP image set. Carotid lumen (*), normal carotid wall (solid arrows), and thickened wall (dashed arrow) are well depicted. (c) Thin maximum intensity projection of contrast-enhanced FLASH MR angiogram corroborates presence of thickened arterial wall (dashed arrow) and its impingement on the lumen (*). Solid arrows point to normal carotid wall. Note morphologic similarity of the arterial lumen boundaries as depicted in b and c. Dashed lines in b and c indicate position of image in center of bottom row in a.

 

   DISCUSSION
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
ADVANCES IN KNOWLEDGE
 References
 
In our study, the 3D DIR-prepared SSFP sequence depicted the carotid arterial wall in a way similar to that achieved with the single-section 2D DIR-prepared fast SE sequence, the sequence for black-blood carotid artery wall imaging conventionally used for patient studies. The 3D DIR-prepared SSFP sequence allowed imaging at a faster speed (shorter time per section) than did the 2D saturation-band fast SE sequence, the latter being a time-efficient method that enables multisection carotid artery wall imaging. The carotid wall–lumen CNR attained with 3D DIR-prepared SSFP imaging was comparable with that attained with T1-weighted single-section DIR-prepared fast SE imaging, while the imaging speed (1/TSECT) and CNR efficiency of 3D DIR-prepared SSFP imaging were substantially higher than those of both single-section and multisection fast SE protocols.

The use of 3D rather than 2D imaging can provide improved spatial resolution in the section-select direction. In our study, 3D DIR-prepared SSFP imaging allowed acquisition of contiguous 1.5-mm-thick sections. On the other hand, single-section fast SE imaging involved the acquisition of 2-mm-thick sections, consistent with protocols described in literature (4). A gap between sections was necessary to reduce the total imaging time required to cover the region of interest. Acquisition of contiguous thin sections with 3D imaging should reduce partial-volume averaging and hence may improve depiction of fine plaque structures and be useful for identifying thinning of the fibrous cap overlying the thrombogenic lipid core, an event that appears to be related to the risk of clinical ischemic events (23). The contiguous and thin sections provided by 3D DIR-prepared SSFP imaging also facilitated display of the carotid bifurcation through multiplanar reconstruction.

The 3D DIR-prepared SSFP technique has certain advantages over 3D fast SE sequences previously proposed for artery wall imaging (7,8). With fast SE imaging, relatively short echo trains are necessary to limit signal decay caused by transverse relaxation during data acquisition (24,25), resulting in relatively long imaging times. For 3D DIR-prepared SSFP imaging, our simulations show that with a flip angle of 45° and sinusoidally ramped preparation radiofrequency pulses, vessel wall signal is near-constant during data acquisition while approaching steady state; this enables more lines to be acquired after each black-blood preparation, which reduces imaging time.

Blood signal was effectively suppressed throughout the 3-cm slab with 3D imaging in our study. Because blood signal suppression relies on blood inflow into the imaging slab during the 400-msec delay period, the slab thickness is limited by the blood velocity in the carotid arteries. As measured with Doppler ultrasonography, the mean blood flow velocity in the common carotid arteries of healthy subjects is approximately 20 cm/sec (26). Thus, a slab up to 8 cm in thickness could be imaged, in principle. Taking into account the 20% oversampling in the section-select direction and the 1.3 thickness ratio of the selective inversion radiofrequency pulse within the DIR preparation, a slab of up to 5 cm in thickness could be imaged with effective blood signal suppression.

The DIR-prepared fast SE sequence involved the acquisition of one section within the repetition time. Although the single-section 2D DIR-prepared fast SE sequence is accepted as the conventional sequence for black-blood carotid artery wall MR imaging, it requires long imaging times to cover the region of interest with multiple measurements, resulting in relatively low CNR efficiency. Song et al (27) and Parker et al (28) proposed time-efficient 2D DIR-prepared fast SE sequences that allow data acquisition of multiple sections (up to four) within the repetition time. These sequences were not available with our MR imaging system at the time our study was performed and therefore were not evaluated in our work. With these multisection 2D DIR-prepared fast SE sequences, a doubling of CNREFF could theoretically be expected. Nevertheless, on the basis of our measurements, this doubled CNREFF would still be lower than that achieved with 3D DIR-prepared SSFP imaging. More important, these methods are still 2D techniques with less ideal section profiles than 3D imaging and noncontiguous sections and hence result in greater partial-volume signal averaging than 3D imaging. We emphasize that transient SSFP imaging rather than true, noninterrupted steady-state imaging was used in our study to provide suppression of blood and fat signal. The capability of the segmented 3D DIR-prepared SSFP technique for characterizing arterial wall composition needs further investigation.

Our study had several limitations. First, it would have been useful to compare the 3D DIR-prepared SSFP sequence with previously proposed 3D fast SE sequences (7,8). Unfortunately, this comparison was not possible because these sequences were not available with our MR imaging system at the time our study was performed. Second, the 3D slab thickness was 3 cm in the superior-inferior direction. The effectiveness of DIR black-blood suppression with thicker slabs or an oblique orientation needs to be further validated. We point out, however, that positioning of the 3-cm-thick 3D DIR-prepared SSFP imaging slab so as to cover both proximal carotid bifurcations was possible in all volunteers imaged in our study. Third, our study was performed in healthy volunteers. Blood flow dynamics in patients with carotid artery stenoses are different from those in healthy subjects. In such patients, the effectiveness of DIR blood signal suppression with 3D imaging needs to be further investigated.

In conclusion, segmented 3D DIR-prepared SSFP is a fast MR imaging sequence that enables black-blood carotid arterial wall imaging with contiguous thin-section coverage and greater imaging speed and CNR efficiency than conventional 2D techniques. Studies in patients with carotid artery disease are necessary to evaluate the capability of 3D DIR-prepared SSFP imaging in the quantification of plaque burden and, potentially, the characterization of atherosclerosis.


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


   FOOTNOTES
 

Abbreviations: CNR = contrast-to-noise ratio • DIR = double inversion recovery • FLASH = fast low-angle shot • SE = spin echo • SSFP = steady-state free precession • 3D = three-dimensional • 2D = two-dimensional

See Materials and Methods for pertinent disclosures.

Author contributions:Guarantors of integrity of entire study, I.K., D.L.; 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, I.K.; clinical studies, I.K., Y.C.C., T.J.C., D.L.; statistical analysis, I.K.; and manuscript editing, I.K., Y.C.C., T.J.C., O.P.S., D.L.


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

  1. Yuan C, Murakami JW, Hayes CE, et al. Phased-array magnetic resonance imaging of the carotid artery bifurcation: preliminary results in healthy volunteers and a patient with atherosclerotic disease. J Magn Reson Imaging 1995;5:561–565.[Medline]
  2. 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]
  3. von Ingersleben G, Schmiedl UP, Hatsukami TS, et al. Characterization of atherosclerotic plaques at the carotid bifurcation: correlation of high-resolution MR imaging with histologic analysis—preliminary study. RadioGraphics 1997;17:1417–1423.[Abstract]
  4. 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]
  5. Cai JM, Hatsukami TS, Ferguson MS, Small R, Polissar NL, Yuan C. Classification of human carotid atherosclerotic lesions with in vivo multicontrast magnetic resonance imaging. Circulation 2002;106:1368–1373.[Abstract/Free Full Text]
  6. Mitsumori LM, Hatsukami TS, Ferguson MS, Kerwin WS, Cai J, Yuan C. In vivo accuracy of multisequence MR imaging for identifying unstable fibrous caps in advanced human carotid plaques. J Magn Reson Imaging 2003;17:410–420.[CrossRef][Medline]
  7. Luk-Pat GT, Gold GE, Olcott EW, Hu BS, Nishimura DG. High-resolution three-dimensional in vivo imaging of atherosclerotic plaque. Magn Reson Med 1999;42:762–771.[CrossRef][Medline]
  8. Crowe LA, Gatehouse P, Yang GZ, et al. Volume-selective 3D turbo spin echo imaging for vascular wall imaging and distensibility measurement. J Magn Reson Imaging 2003;17:572–580.[CrossRef][Medline]
  9. Adams GJ, Simoni DM, Bordelon CB Jr, et al. Bilateral symmetry of human carotid artery atherosclerosis. Stroke 2002;33:2575–2580.[Abstract/Free Full Text]
  10. Fuchs F, Laub G, Othomo K. TrueFISP: technical considerations and cardiovascular applications. Eur J Radiol 2003;46:28–32.[CrossRef][Medline]
  11. Zhang S, Hatsukami TS, Polissar NL, Han C, Yuan C. Comparison of carotid vessel wall area measurements using three different contrast-weighted black blood MR imaging techniques. Magn Reson Imaging 2001;19:795–802.[CrossRef][Medline]
  12. Felmlee JP, Ehman RL. Spatial presaturation: a method for suppressing flow artifacts and improving depiction of vascular anatomy in MR imaging. Radiology 1987;164:559–564.[Abstract/Free Full Text]
  13. Steinman DA, Rutt BK. On the nature and reduction of plaque-mimicking flow artifacts in black blood MRI of the carotid bifurcation. Magn Reson Med 1998;39:635–641.[Medline]
  14. Paul D, Hennig J. Comparison of different flip angle variation functions for improved signal behavior in SSFP sequences [abstr]. In: Proceedings of the Twelfth Meeting of the International Society for Magnetic Resonance in Medicine. Berkeley, Calif: International Society for Magnetic Resonance in Medicine, 2004; 2663.
  15. 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]
  16. Bottomley PA, Hardy CJ, Argersinger RE, Allen-Moore G. A review of 1H nuclear magnetic resonance relaxation in pathology: are T1 and T2 diagnostic? Med Phys 1987;14:1–37.[CrossRef][Medline]
  17. Stanisz GJ, Odrobina EE, Pun J, et al. T1, T2 relaxation and magnetization transfer in tissue at 3T. Magn Reson Med 2005;54:507–512.[CrossRef][Medline]
  18. Hargreaves BA, Vasanawala SS, Pauly JM, Nishimura DG. Characterization and reduction of the transient response in steady-state MR imaging. Magn Reson Med 2001;46:149–158.[CrossRef][Medline]
  19. Edelman RR, Chien D, Kim D. Fast selective black blood MR imaging. Radiology 1991;181:655–660.[Abstract/Free Full Text]
  20. Mani V, Itskovich VV, Aguiar SH, et al. Comparison of gated and non-gated fast multislice black-blood carotid imaging using rapid extended coverage and inflow/outflow saturation techniques. J Magn Reson Imaging 2005;22:628–633.[CrossRef][Medline]
  21. Yarnykh VL, Yuan C. Multislice double inversion-recovery black-blood imaging with simultaneous slice reinversion. J Magn Reson Imaging 2003;17:478–483.[CrossRef][Medline]
  22. Mani V, Itskovich VV, Szimtenings M, et al. Rapid extended coverage simultaneous multisection black-blood vessel wall MR imaging. Radiology 2004;232:281–288.[Abstract/Free Full Text]
  23. Bassiouny HS, Sakaguchi Y, Mikucki SA, et al. Juxtalumenal location of plaque necrosis and neoformation in symptomatic carotid stenosis. J Vasc Surg 1997;26:585–594.[CrossRef][Medline]
  24. Constable RT, Gore JC. The loss of small objects in variable TE imaging: implications for FSE, RARE, and EPI. Magn Reson Med 1992;28:9–24.[Medline]
  25. Listerud J, Einstein S, Outwater E, Kressel HY. First principles of fast spin echo. Magn Reson Q 1992;8:199–244.[Medline]
  26. Holdsworth DW, Norley CJ, Frayne R, Steinman DA, Rutt BK. Characterization of common carotid artery blood-flow waveforms in normal human subjects. Physiol Meas 1999;20:219–240.[CrossRef][Medline]
  27. Song HK, Wright AC, Wolf RL, Wehrli FW. Multislice double inversion pulse sequence for efficient black-blood MRI. Magn Reson Med 2002;47:616–620.[CrossRef][Medline]
  28. Parker DL, Goodrich KC, Masiker M, Tsuruda JS, Katzman GL. Improved efficiency in double-inversion fast spin-echo imaging. Magn Reson Med 2002;47:1017–1021.[CrossRef][Medline]



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