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(Radiology. 2001;219:278-283.)
© RSNA, 2001

Technical Developments

Free-Breathing Black-Blood Coronary MR Angiography: Initial Results1

Matthias Stuber, PhD, René M. Botnar, PhD, Kraig V. Kissinger, RT, MS and Warren J. Manning, MD

1 From the Departments of Medicine, Cardiovascular Division (M.S., R.M.B., K.V.K., W.J.M.) and Radiology (W.J.M.), Beth Israel Deaconess Medical Center and Harvard Medical School, 330 Brookline Ave, Boston, MA 02215; and Philips Medical Systems, Best, the Netherlands (M.S., R.M.B.). Received April 4, 2000; revision requested May 26; revision received July 19; accepted August 15. Address correspondence to M.S. (e-mail: mstuber@caregroup.harvard.edu).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 Materials and Methods
 Results
 Discussion
 REFERENCES
 
The authors developed a free-breathing black-blood coronary magnetic resonance (MR) angiographic technique with a potential for exclusive visualization of the coronary blood pool. Results with the MR angiographic technique were evaluated in eight healthy subjects and four patients with coronary disease identified at conventional angiography. This MR angiographic technique accurately depicted luminal disease in the patients and permitted visualization of extensive continuous segments of the native coronary tree in both the healthy subjects and the patients. Black-blood coronary MR angiography provides an alternative source of contrast enhancement.

Index terms: Coronary angiography, technology, 548.121411, 548.12142, 548.12144 • Coronary vessels, diseases, 548.731, 548.754 • Coronary vessels, stenosis or obstruction, 548.768, 548.754 • Magnetic resonance (MR), vascular studies, 548.12142


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
Materials and Methods
 Results
 Discussion
 REFERENCES
 
During the past decade, coronary magnetic resonance (MR) angiographic techniques have been successfully applied to help visualize proximal and middle portions of the native coronary arteries in healthy or diseased states. Very early attempts to visualize the coronary arteries with black-blood MR angiography included conventional electrocardiographically gated spin-echo MR imaging (1,2). Success was limited, however, and failure to even visualize the coronary ostia was common (2). Subsequently, more rapid breath-hold techniques with use of bright-blood gradient-echo segmented-k-space echo-planar (3,4) or spiral (5) approaches resulted in successful visualization of the native vessels in most subjects. For all those techniques, contrast enhancement between the blood pool and the surrounding tissue is of crucial importance. Nonexogenous contrast enhancement between the coronary arteries and the surrounding tissue has been obtained with use of fat-saturation prepulses (6), magnetization transfer contrast prepulses (7), or more recently T2 preparatory pulses (8) that take advantage of inherent T2 differences between blood and surrounding myocardium. With these latter techniques, the coronary lumen appears bright (high signal intensity) and the surrounding tissue including fat and myocardium appear dark or with reduced signal intensity.

These bright-blood MR angiographic techniques, however, have limitations. These include difficulty in the accurate quantitation of luminal stenosis, especially in the presence of focal turbulence, because turbulent flow may appear as an artifactual darkening (9,10). Residual vessel lumen diameter may therefore be underestimated with respect to conventional x-ray angiography. Metallic implants such as clips or sternal wires, often present in patients after cardiac surgery, are an additional source of image artifacts due to local magnetic field distortion. These artifacts appear accentuated on gradient-echo bright-blood coronary MR angiograms. Furthermore, thrombus may also appear with high signal intensity on bright-blood coronary MR angiograms (11). As a consequence, luminal stenosis may be obscured on bright-blood images (11,12). A spin-echo dark-blood coronary MR angiographic technique that exclusively depicts the coronary blood pool may therefore have advantages for coronary MR angiography, but it remains to be examined.

The purpose of this study was to develop and evaluate a black-blood coronary MR angiographic method for visualization of the coronary blood pool.


   Materials and Methods
TOP
 ABSTRACT
 INTRODUCTION
 Materials and Methods
Results
 Discussion
 REFERENCES
 
Black-blood coronary MR angiography was performed in 12 study participants, including eight healthy subjects (five men and three women; age range, 19–50 years; mean age, 22 years ± 2 [SD]) and four patients (two men and two women; age range, 50–65 years; mean age, 56 years ± 6) with coronary artery disease depicted at conventional angiography. Written informed consent was obtained from all participants, and the protocol was approved by the institutional committee on clinical investigation. The hearts of all participants were in sinus rhythm, and there were no contraindications to MR imaging. Consecutive patients and healthy subjects who weighed less than 200 lb (<91 kg) were recruited for this protocol. The healthy subjects were all older than 18 years and had no history of heart disease.

Black-blood coronary MR angiography was performed of the right coronary artery system in two of the four patients and of the left coronary artery system in three. For a preliminary visual comparison, standard free-breathing bright-blood coronary MR angiography with a T2 preparatory pulse was also performed in the left coronary artery system in one patient and of the right system in another (8,13). In the healthy subjects, black-blood coronary MR angiography was performed in both the left and right coronary systems.

Black-blood MR angiography was performed with a 1.5-T whole-body MR imaging system (Gyroscan ACS-NT; Philips Medical Systems, Best, the Netherlands) equipped with cardiac software (CPR6) and a gradient system (PowerTrak 6000; gradient strength, 23 mT/m; rise time, 220 msec). A cardiac synergy coil (two anterior and three posterior elements) was used for signal acquisition with all five elements. All subjects were examined in the supine position, with electrocardiographic leads on the anterior left hemithorax.

Scout Imaging
Two scout images were acquired for coronary artery localization and navigator positioning at the right hemidiaphragm. The first scout image was obtained with an electrocardiographically triggered, free-breathing, multisection, two-dimensional segmented gradient-echo sequence (repetition time msec/echo time msec of 11/2.4, 256 x 128 matrix, 450-mm field of view, 10-mm section thickness, 5-mm intersection gap), with nine transverse, nine coronal, and nine sagittal interleaved acquisitions of the thorax. The total duration of this scout acquisition was less than 1 minute.

From the coronal and transverse sections of the first scout image, the navigator position at the dome of the right hemidiaphragm and the localized transverse three-dimensional volume for the second scout image were planned. For the second scout image, the MR data were acquired in middiastole (14) and at end-expiration by using right-hemidiaphragmatic navigator gating and real-time motion correction around a volume that included the coronary arteries as defined on the first scout image. For this second scout image, a fast interleaved three-dimensional gradient-echo-planar imaging sequence (8.8/5.3) (15) was used (13). A 50-mm-thick transverse three-dimensional volume was imaged with an in-plane resolution of 1.3 x 1.8 mm. Forty overlapping sections with a reconstructed section thickness of 2.5 mm were acquired.

Section Targeting
From the second scout data set, section-targeted double-oblique imaging planes along the major axes of the native left and right coronary artery systems were defined by using a previously described three-point image planning tool (13). A set of overlapping two-dimensional sections was acquired for the left coronary artery or the right coronary artery (RCA). Each section-targeted two-dimensional acquisition was performed with a separate image. For the left coronary artery system, one point on the left main, one on the proximal left circumflex, and one on the middle left anterior descending coronary arteries were identified with an interactive mouse click. The software subsequently prescribed a parallel imaging plane. For the right coronary artery system, points near the ostium, middle RCA, and distal RCA were similarly identified by the user. In one healthy subject, an additional transverse image was acquired to visualize the posterior descending coronary artery.

Imaging Sequence for MR Angiography
High-spatial-resolution black-blood coronary MR angiography was performed (3-mm section thickness, 1.5-mm overlap) by using a two-dimensional fast spin-echo sequence (repetition time, two cardiac cycles or two R-R intervals; echo time, 25 msec) (16) with a linear k-space acquisition scheme, 5.2-msec interecho spacing, repetition time of two cardiac cycles, 25-msec echo time, and echo train length of 23. An initial 90° radio-frequency excitation was followed by repetitive 160° refocusing pulses (17). Half-Fourier sampling was used (18) with 60% of the profiles sampled in the phase-encoding direction. The acquisition window was 120 msec. The field of view was 360 mm with a 512 x 384 matrix (spatial resolution, 0.7 x 0.9 mm). No flow-compensating gradients or fat-suppression prepulses were used.

For enhanced black-blood characteristics, a dual-inversion prepulse (18–20) was applied immediately after detection of the R wave at electrocardiography. The first nonselective 180° inversion prepulse (INV-NS in Fig 1) was followed by a 7-mm section-selective 180° inversion prepulse (INV-SS in Fig 1) at the anatomic level of interest. Fast spin-echo imaging followed the first inversion pulse with an inversion delay, TI, calculated according to the following equation (21):

where TR is repetition time. A blood T1 of 1,200 msec was assumed for nulling of myocardial blood signal at the time point of the initial 90° pulse of the fast spin-echo sequence.



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  		Figure 1. Schematic of the pulse sequence for free-breathing dual-inversion fast spin-echo black-blood coronary MR angiography. The dual-inversion prepulse consists of a nonselective (INV-NS) and a section-selective (INV-SS) inversion of the magnetization and is followed by a navigator-restore (NAV-RESTORE) section-selective diaphragmatic reinversion of the magnetization for subsequent detection of the navigator interface. The fast spin-echo imaging sequence follows the real-time navigator, and its initial 90° radio-frequency excitation pulse is delayed (for blood signal nulling and diastolic image acquisition) by the inversion time (TI) with respect to the R wave at electrocardiography. 3D = three-dimensional.

 
Navigator
During the developmental phase of the protocol, we frequently observed failure of the standard two-dimensional navigator to detect the lung-liver interface when preceded by the dual-inversion prepulse. We noted that at the time point of the navigator, the magnetization of the lung-liver interface was severely reduced due to the preceding nonselective inversion prepulse, thereby limiting navigator performance. To correct this, we introduced an additional section-selective inversion pulse localized at the dome of the right hemidiaphragm (NAV-RESTORE in Figs 1 and 2), which locally reinverts the magnetization for subsequent navigator lung-liver interface detection. Figure 2b depicts the navigator performance in the presence of the preceding dual-inversion prepulse and the navigator-restore pulse.



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  		Figure 2a. (a) Transverse black-blood coronary MR angiogram acquired with a segmented gradient-echo imaging sequence (11/2.4) demonstrates localization of the navigator at the dome of the right hemidiaphragm. The navigator-restore (NAV-RESTORE) prepulse locally reinverts the magnetization for subsequent detection of the lung-liver interface of the navigator. (b) Free-breathing navigator display as visualized on the console. Time is displayed on the x axis, and the lung-liver interface is displayed on the y axis. High lung-liver contrast is seen.

 


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  		Figure 2b. (a) Transverse black-blood coronary MR angiogram acquired with a segmented gradient-echo imaging sequence (11/2.4) demonstrates localization of the navigator at the dome of the right hemidiaphragm. The navigator-restore (NAV-RESTORE) prepulse locally reinverts the magnetization for subsequent detection of the lung-liver interface of the navigator. (b) Free-breathing navigator display as visualized on the console. Time is displayed on the x axis, and the lung-liver interface is displayed on the y axis. High lung-liver contrast is seen.

 
To suppress bulk cardiac motion related to respiratory motion, a vertical two-dimensional selective (pencil beam) real-time navigator for gating and real-time motion correction (14) in all three spatial coordinates was localized at the dome of the right hemidiaphragm. As previously implemented, a 5-mm gating window with a constant superior-inferior correction factor of 0.6 was used (22). Motion correction was performed in all three spatial coordinates (14). The end-expiratory right-hemidiaphragmatic position was automatically selected as the most superior right-hemidiaphragmatic position (gating level) during the first 16 cardiac cycles (during which no image data were sampled). The diaphragmatic navigator (NAVIGATOR in Fig 1) immediately precedes the imaging portion (Fast Spin Echo in Fig 1) of the sequence.

The duration of each acquisition was automatically written into the logfile of the system. Average imaging duration during free breathing was less than 60 seconds for each two-dimensional section with approximately 50% navigator efficiency.

Visual Assessment
One author (M.S.) performed primary analyses of the images obtained in all study participants. The findings at conventional coronary angiography were subsequently compared qualitatively with those at coronary MR angiography. The visibility and location of pathologic conditions on the coronary MR angiograms were compared with those on the conventional coronary angiograms.

Length Measurements
The image data sets for all participants were transferred to a workstation (EasyVision 4.0; Philips Medical Systems) for visualization and length measurements of the coronary arteries. The three orthogonal sections of the data set are simultaneously displayed, and the user navigates interactively through the entire data set. The left main and left anterior descending coronary arteries and RCA were visually identified in all three planes. The three-dimensional pathway of the coronary artery then underwent multiplanar reformatting, and the lengths of the individual segments of the native coronary arteries were assessed semiautomatically.

Signal-to-Noise and Contrast-to-Noise Ratios
On images obtained in all study participants, regions of interest were defined in areas of myocardium, the intraventricular blood pool, and the proximal 2 cm of the coronary arteries. A region of interest was also defined in the air anterior to the chest wall; it was 5,000 mm2, and its center was positioned 31/2 cm anterior to the skin of the chest in the horizontal center of the field of view.

The signal-to-noise ratio was defined as the mean signal intensity in a region of interest divided by the SD in the air anterior to the chest wall (23). Regions of interest were 450 mm2 for the intraventricular blood pool and the myocardium, 50–60 mm2 in the proximal 2 cm of the coronary arteries (dependent on the diameter of the individual coronary arteries), and 150 mm2 in regions of epicardial fat. The contrast-to-noise ratio was defined as the difference in the mean signal intensities in two user-specified regions of interest divided by the SD in the air anterior to the chest wall (23).

Statistical Analysis
In all cases, comparisons were made with a two-tailed unpaired Student t test. Differences with a P value of .05 or less were considered statistically significant.


   Results
TOP
 ABSTRACT
 INTRODUCTION
 Materials and Methods
 Results
Discussion
 REFERENCES
 
For all study participants, MR studies were completed without complications and the targeted vessels could be visualized on both the black- and bright-blood coronary MR angiograms.

Coronary Vessel Length
On black-blood coronary MR angiograms obtained in the healthy subjects, the mean length of the combined left main and left anterior descending coronary arteries was 64 mm ± 6, of the left circumflex artery was 26 mm ± 9, and of the RCA was 112 mm ± 22. On black-blood coronary MR angiograms obtained of the left coronary artery systems in patients, the mean length of the combined left main and left anterior descending coronary arteries was 59 mm ± 12 and of the left circumflex artery was 37 mm ± 21. On black-blood coronary MR angiograms obtained of the right coronary artery systems in patients, the mean length of the RCA was 76 mm ± 35.

Coronary MR Angiograms
On black-blood coronary MR angiograms obtained in healthy subjects, a 13.3-cm-long continuous segment of the RCA was depicted with contrast between the bright epicardial fat and the less intense myocardial muscle (Fig 3a). However, there was substantial contrast for both myocardial muscle and fat when compared with the coronary blood pool or the blood in the ventricular cavity. Branch vessels of the left and right coronary artery systems with smaller diameters could also be seen (Fig 3b, 3c). Figure 4 depicts a more distal portion of a right coronary artery system, with the RCA adjacent to the posterior descending coronary artery.



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  		Figure 3a. High-spatial-resolution (0.7 x 0.9 in plane) free-breathing black-blood coronary MR angiograms acquired in three healthy adult subjects depict (a, b) the right coronary artery system and (c) the left coronary artery system. All images were acquired in a double-oblique orientation along the major axes of the coronary arteries (fast spin echo; interecho spacing, 5.2 msec; repetition time, two cardiac cycles; echo time, 25 msec; echo train length, 23). AM = acute marginal branch; Ao = ascending aorta; AV = atrioventricular node branch; DI = first-order diagonal branch vessel; LAD = left anterior descending, LCX = left circumflex, LM = left main coronary arteries; LV = left ventricle; RI = ramus intermedius; RV = right ventricle.

 


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  		Figure 3b. High-spatial-resolution (0.7 x 0.9 in plane) free-breathing black-blood coronary MR angiograms acquired in three healthy adult subjects depict (a, b) the right coronary artery system and (c) the left coronary artery system. All images were acquired in a double-oblique orientation along the major axes of the coronary arteries (fast spin echo; interecho spacing, 5.2 msec; repetition time, two cardiac cycles; echo time, 25 msec; echo train length, 23). AM = acute marginal branch; Ao = ascending aorta; AV = atrioventricular node branch; DI = first-order diagonal branch vessel; LAD = left anterior descending, LCX = left circumflex, LM = left main coronary arteries; LV = left ventricle; RI = ramus intermedius; RV = right ventricle.

 


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  		Figure 3c. High-spatial-resolution (0.7 x 0.9 in plane) free-breathing black-blood coronary MR angiograms acquired in three healthy adult subjects depict (a, b) the right coronary artery system and (c) the left coronary artery system. All images were acquired in a double-oblique orientation along the major axes of the coronary arteries (fast spin echo; interecho spacing, 5.2 msec; repetition time, two cardiac cycles; echo time, 25 msec; echo train length, 23). AM = acute marginal branch; Ao = ascending aorta; AV = atrioventricular node branch; DI = first-order diagonal branch vessel; LAD = left anterior descending, LCX = left circumflex, LM = left main coronary arteries; LV = left ventricle; RI = ramus intermedius; RV = right ventricle.

 


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  		Figure 4a. Free-breathing black-blood coronary MR angiograms acquired in another healthy adult subject (fast spin echo; interecho spacing, 5.2 msec; repetition time, two cardiac cycles; echo time, 25 msec; echo train length, 23). (a) Double-oblique MR angiogram depicts the RCA and a perpendicular view of the left anterior descending coronary artery (LAD) and the coronary sinus. (b) Transverse MR angiogram depicts the distal RCA and proximal posterior descending coronary artery (PDA).

 


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  		Figure 4b. Free-breathing black-blood coronary MR angiograms acquired in another healthy adult subject (fast spin echo; interecho spacing, 5.2 msec; repetition time, two cardiac cycles; echo time, 25 msec; echo train length, 23). (a) Double-oblique MR angiogram depicts the RCA and a perpendicular view of the left anterior descending coronary artery (LAD) and the coronary sinus. (b) Transverse MR angiogram depicts the distal RCA and proximal posterior descending coronary artery (PDA).

 
A 99% stenosis of the middle RCA was depicted with high signal intensity on a black-blood coronary MR angiogram obtained in a patient (Fig 5). The RCA was depicted as patent distal to the stenosis on both the MR and conventional angiograms. A 100% stenosis in the proximal RCA and an RCA bypass graft were depicted on bright-blood (T2 preparatory pulse [13]) and black-blood coronary MR angiograms obtained in a patient (Fig 6). A local artifactual signal void induced by a metallic clip and another artifact induced by a sternal wire were observed on the bright-blood MR angiogram, and these artifacts were minimized on the black-blood MR angiogram.



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  		Figure 5a. (a) Double-oblique free-breathing black-blood coronary MR angiogram acquired parallel to the RCA (fast spin echo; interecho spacing, 5.2 msec; repetition time, two cardiac cycles; echo time, 25 msec; echo train length, 23) in a 56-year-old man with exertional angina and a 99% stenosis (solid arrow) of the proximal RCA. Distal to the stenosis, the middle RCA (dashed arrow) appears widely patent. (b) Conventional coronary angiogram shows the occluded RCA (solid arrow). As in a, the more distal RCA appears patent (dashed arrow).

 


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  		Figure 5b. (a) Double-oblique free-breathing black-blood coronary MR angiogram acquired parallel to the RCA (fast spin echo; interecho spacing, 5.2 msec; repetition time, two cardiac cycles; echo time, 25 msec; echo train length, 23) in a 56-year-old man with exertional angina and a 99% stenosis (solid arrow) of the proximal RCA. Distal to the stenosis, the middle RCA (dashed arrow) appears widely patent. (b) Conventional coronary angiogram shows the occluded RCA (solid arrow). As in a, the more distal RCA appears patent (dashed arrow).

 


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  		Figure 6a. Proximal RCA occlusion (long solid arrow) and an RCA bypass graft (short solid arrow) in a 65-year-old man are depicted on (a) conventional bright-blood (segmented-k-space gradient-echo [7.2/2.2]) and (b) black-blood (fast spin echo; interecho spacing, 5.2 msec; repetition time, two cardiac cycles; echo time, 25 msec; echo train length, 23) coronary MR angiograms. Both images were acquired in the same double-oblique view, parallel to the RCA bypass graft. Local artifacts induced by a vascular clip (dotted arrow) and a sternal wire (dashed arrow) obscure a but are minimized in b, which depicts a long continuous segment of the RCA bypass graft.

 


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  		Figure 6b. Proximal RCA occlusion (long solid arrow) and an RCA bypass graft (short solid arrow) in a 65-year-old man are depicted on (a) conventional bright-blood (segmented-k-space gradient-echo [7.2/2.2]) and (b) black-blood (fast spin echo; interecho spacing, 5.2 msec; repetition time, two cardiac cycles; echo time, 25 msec; echo train length, 23) coronary MR angiograms. Both images were acquired in the same double-oblique view, parallel to the RCA bypass graft. Local artifacts induced by a vascular clip (dotted arrow) and a sternal wire (dashed arrow) obscure a but are minimized in b, which depicts a long continuous segment of the RCA bypass graft.

 
In a patient with an obtuse marginal aneurysm depicted at conventional angiography, the left main, left anterior descending, and left circumflex coronary arteries and the obtuse marginal aneurysm were depicted on both the black-blood and bright-blood coronary MR angiograms. The left main and left anterior descending coronary arteries were depicted as normal on both MR angiograms. On the black-blood coronary MR angiogram, the aneurysm was hypointense when compared with the surrounding tissue.

Black-blood coronary MR angiograms obtained in a patient with isolated left circumflex arterial disease depicted normal left main and left anterior descending coronary arteries as well as luminal irregularities.

Signal-to-Noise and Contrast-to-Noise Ratios
In the healthy subjects, the signal-to-noise ratio of epicardial fat was increased when compared with that of the myocardium (40 ± 12 vs 18 ± 6, P < .001). Consistent with the desired suppression of blood signal, the signal-to-noise ratios of the ventricular cavity and the proximal 2 cm of the coronary arteries were very low (3 ± 1 vs 5 ± 2, P < .05). In the four patients, a trend was seen for an increased signal-to-noise ratio of fat when compared with that of myocardial muscle (45 ± 17 vs 24 ± 14, P = .14). Consistent with the results in the healthy subjects, the signal-to-noise ratios in the ventricular cavities and the proximal coronary arteries were low (2 ± 1 vs 6 ± 2, P < .05).

In the healthy subjects, the contrast-to-noise ratio between epicardial fat and the coronary blood pool was increased with respect to myocardium and the coronary blood pool (37 ± 12 vs 15 ± 6, P < .005). In the patients, we found a trend for an increased contrast-to-noise ratio (37 ± 16 vs 18 ± 13, P = .17). When comparing the ventricular cavity blood pool with the blood in the proximal coronary arteries, the contrast-to-noise ratio was minimal in the healthy subjects (2 ± 1) and patients (3 ± 2).

The contrast-to-noise ratios between the myocardium and ventricular cavity and between the myocardium and coronary blood pool were similar in the healthy subjects (16 ± 5 vs 15 ± 6 [difference not significant]). This was also observed in patients (18 ± 13 vs 18 ± 2 [difference not significant]).


   Discussion
TOP
 ABSTRACT
 INTRODUCTION
 Materials and Methods
 Results
 Discussion
REFERENCES
 
Black-blood coronary MR angiography was successfully implemented in all study participants.

Coronary Images
Extensive segments of the major left and right coronary arteries were consistently visualized on black-blood coronary MR angiograms obtained in all participants, as were coronary branch vessels with smaller diameters and distal coronary structures such as the posterior descending coronary artery.

As expected, minimal contrast was found between the ventricular blood pool and the blood in the proximal portions of the coronary arteries. Fat signal was maximized, and substantial contrast was obtained between myocardium and the coronary blood pool. Therefore, the coronary lumina consistently appeared as regions of low signal intensity with surrounding high signal intensity from epicardial fat and myocardium. The signal-to-noise and contrast-to-noise ratios were similar among healthy subjects and patients, which suggests excellent image quality and a substantial contrast between the coronary blood pool and the surrounding tissue with black-blood coronary MR angiography. The signal-to-noise and contrast-to-noise ratios we obtained compare favorably with those obtained with bright-blood methods with a T2 preparatory pulse (8). Black-blood coronary MR angiography allows thin-slab (3 mm) two-dimensional acquisitions with high in-plane spatial resolution.

In the patient with an RCA bypass graft and metallic implants (Fig 6), the local artifacts from the clip and the sternal wire obscured the region of interest on the conventional bright-blood coronary MR angiogram. However, these artifacts were minimized on the black-blood coronary MR angiogram. This finding highlights an advantage of fast spin-echo black-blood techniques when compared with conventional gradient-echo bright-blood coronary MR angiographic methods.

Black-Blood Capabilities
Although gradient-echo bright-blood coronary MR angiographic approaches have received greater attention, black-blood coronary MR angiographic methods have several advantages. We found excellent suppression of the blood signal in both the ventricular cavities and the coronary lumen. As previously mentioned (11,17), fast spin-echo sequences yield a substantial signal attenuation in small-diameter vessels. This has been reported to occur preferentially and most consistently with flow parallel to the imaging plane (17), a situation promoted by our use of the three-point image planning tool.

In theory, the relatively short time between the dual-inversion prepulse and the imaging part of the sequence (<600 msec) may lead to a reduced blood exchange in the volume of interest and thus to potentially less accentuated black-blood characteristics. However, the present image data suggest that this apparently does not preclude the visualization of smaller diameter vessels with potentially reduced coronary blood flow.

Navigator
With the use of the navigator-restore pulse, the dual-inversion prepulse did not preclude the use of real-time navigator technology. As a consequence, free-breathing data acquisition is enabled for dual-inversion black-blood coronary MR angiography, which is most important for patients who are unable to sustain prolonged breath holds.

Limitations
Only a limited number of patients were included in the present study. Pathologic conditions were visualized, but larger clinical studies are required to fully explore the clinical role of black-blood coronary MR angiography. The RCA proximal to the stenosis on the black-blood coronary MR angiogram in Figure 5a may appear ambiguous and inconsistent with findings on the conventional coronary angiogram in Figure 5b. This may be explained by local calcifications, which would also appear dark on black-blood coronary MR angiograms. Combination with a bright-blood approach therefore remains to be evaluated.

Nonisotropic image resolution with 0.7 x 0.9 x 3.0-mm voxels may also be a limitation (24). In addition, recent studies have shown that shortening of the MR angiographic data acquisition window is crucial (8,25,26). In the present study, we used a relatively long acquisition window of 120 msec. Shortening of this acquisition interval may further improve image quality.

In conclusion, the combination of a dual-inversion technique together with a fast spin-echo imaging sequence provides a source of endogenous contrast enhancement in coronary MR angiography. Combined with use of a prospective adaptive navigator, this approach allows high-spatial-resolution free-breathing black-blood coronary MR angiography in which the coronary lumen appears black and the surrounding tissue appears bright. Extensive portions of the native coronary arteries, including small-diameter branch coronary vessels, were successfully and consistently visualized with high contrast in both healthy subjects and patients with coronary disease.

Larger studies including direct comparisons with conventional coronary angiography and bright-blood coronary MR angiography are required to confirm these observations.


   FOOTNOTES
 
Abbreviation: RCA = right coronary artery

Author contributions: Guarantors of integrity of entire study, M.S., W.J.M.; study concepts and design, M.S.; definition of intellectual content, M.S., R.M.B.; literature research, M.S., R.M.B.; clinical studies, M.S.; data acquisition, M.S., K.V.K.; data analysis, M.S.; statistical analysis, M.S.; manuscript preparation, M.S.; manuscript editing, M.S., W.J.M.; manuscript review, M.S., K.V.K; manuscript final version approval, M.S., W.J.M.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 Materials and Methods
 Results
 Discussion
 REFERENCES
 

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