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Microvascular Obstruction and Myocardial Function after Acute Myocardial Infarction: Assessment by Using Contrast-enhanced Cine MR Imaging¹

¹ From the Cardiology Division, Department of Internal Medicine (G.L.R., W.W.O., R.E.G., A.D., J.A.G.), and Department of Radiology (K.G.B., A.N.S.), William Beaumont Hospital, 3601 W 13 Mile Rd, Royal Oak, MI 48073-6769. Received March 4, 2005; revision requested April 28; revision received August 11; accepted September 12; final version accepted October 3. Supported in part by a research grant from the Ministrelli Advanced Cardiac Research Imaging Center. Address correspondence to G.L.R. (e-mail: graff{at}beaumont.edu).

	ABSTRACT

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

 
This study was approved by the Human Investigation Committee of William Beaumont Hospital, and all patients gave informed consent. The purpose of this study was to prospectively compare contrast material–enhanced cine magnetic resonance (MR) imaging with more-standard MR imaging for the evaluation of microvascular obstruction and myocardial function in 80 patients (56 men, 24 women; mean age, 57 years; range, 29–80 years) with acute myocardial infarction after reperfusion therapy. Findings at contrast-enhanced cine MR imaging agreed with the global and transmural extent of microvascular obstruction at first-pass perfusion (intraclass correlation coefficient [IC] of 0.96 [P < .001] and 0.88 [P < .001], respectively) and inversion-recovery gradient-echo (IC of 0.90 [P < .001] and 0.93 [P < .001], respectively) MR imaging. There was no significant difference between myocardial function parameters before and after contrast material enhancement. Contrast-enhanced cine MR imaging reduced imaging time by 34% (11 of 32 minutes) and improved spatial resolution.

Supplemental material: radiology.rsnajnls.org/cgi/content/full/240/2/529/DC1

© RSNA, 2006

	INTRODUCTION

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

 
In patients with acute myocardial infarction, successful reperfusion therapy reduces mortality (1,2). Recovery of regional and global myocardial function depends on the adequacy of reperfusion at both the epicardial and microvascular levels (3–5). Coronary "no-reflow," in which there is dissociation between epicardial and microvascular reperfusion because of microvascular obstruction (MO), is a serious cause of therapeutic failure (6–8). The optimal tool for assessment of therapeutic success would therefore delineate MO, as well as myocardial function.

Magnetic resonance (MR) imaging can demonstrate all of these components (9–12) with a single modality by means of the established techniques of first-pass gradient-echo MR imaging for myocardial perfusion (13), balanced steady-state free-precession gradient-echo cine MR imaging for function (14), and inversion-recovery delayed contrast material enhancement MR imaging for infarct sizing (15). The combined protocol begins with cine MR imaging for function, which is followed by first-pass perfusion MR imaging, and, after a 10–15-minute delay, inversion-recovery delayed enhancement MR imaging. This combined protocol generally takes 30–60 minutes and requires substantial patient effort, including multiple breath holds, which are difficult for patients after acute myocardial infarction who have also undergone a reperfusion procedure.

We hypothesized that contrast material–enhanced cine MR imaging could expedite evaluation of reperfusion in patients with acute myocardial infarction by eliminating first-pass perfusion imaging and reducing the delay time. Accordingly, our study was designed to prospectively compare contrast-enhanced cine MR imaging and more-standard MR imaging for evaluation of MO and myocardial function in patients with acute myocardial infarction after reperfusion therapy.

	MATERIALS AND METHODS

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

 
This study was financed in part by a grant from Siemens Medical Solutions (Erlangen, Germany). The authors had full control of the data and information submitted for publication.

Patients
This study was approved by the William Beaumont Hospital Human Investigation Committee and was compliant with the Health Insurance Portability and Accountability Act. All patients were older than 18 years, and all gave informed consent. Between August 2002 and June 2004, we prospectively imaged 80 patients with ST-elevation acute myocardial infarction, which was diagnosed by means of standard electrocardiography and enzymatic criteria, who had been admitted to the hospital within the previous 48 hours. The mean age of the patients was 57 years (age range, 29–80 years), and there were 56 men and 24 women. All patients had undergone coronary angiography and primary percutaneous coronary intervention therapy of the infarct-related artery before MR imaging was performed.

Study Design
The present contrast-enhanced cine MR imaging method is a modification of a standard balanced steady-state free-precession gradient-echo dynamic MR imaging technique (trueFISP; Siemens Medical Solutions) in which gadolinium-based contrast material is administered before image acquisition.

Previous researchers have correlated pathologic MO with early hypoenhanced areas that later become partially or completely hyperenhanced on T1-weighted gradient-echo MR images (early hypoenhancement–late hyperenhancement pattern) (16–18). To validate the accuracy of contrast-enhanced cine MR imaging in the measurement of MO, we compared hypoenhancing defect size between this method and both first-pass perfusion and early inversion-recovery gradient-echo methods and additionally investigated the early hypoenhancement–late hyperenhancement pattern. To compare hypoenhancing defect size between contrast-enhanced cine MR imaging and first-pass perfusion MR imaging, in 80 patients a first-pass MR study was obtained in three short-axis sections centered on the mid-papillary muscle. Three contrast-enhanced cine MR sections were acquired in identical section locations immediately thereafter, followed by additional sections to complete left ventricular function studies. To compare contrast-enhanced cine MR imaging with the early inversion-recovery method, in 50 patients an inversion-recovery section was obtained immediately after each contrast-enhanced cine section, following a preliminary inversion-time scout sequence. To define an early hypoenhancement–late hyperenhancement pattern, 18 patients underwent repeat contrast-enhanced cine MR imaging after 10 minutes and after 30 minutes.

Administration of gadolinium-based contrast material before cine MR imaging reduces the signal intensity difference between myocardium and blood pool. Hypothetically, this might reduce the reader's ability to accurately define the endocardial border in assessing myocardial function. Therefore, to validate the accuracy of contrast-enhanced cine MR imaging for evaluation of global and regional myocardial function, in 34 patients we acquired a cine MR study before contrast enhancement and compared the results with those from a second cine MR study acquired after contrast material administration.

First-Pass Perfusion MR Technique
All MR imaging was performed with patients in the supine position. Imaging was performed by using a 1.5-T MR imager (Sonata; Siemens Medical Solutions) with a four-element phased-array cardiac coil, and images were analyzed by using ARGUS software (Siemens Medical Solutions). An intravenous bolus of 0.075 mmol of gadodiamide (Omniscan; GE Healthcare, Chalfont St Giles, United Kingdom) per kilogram of body weight was administered at a rate of 4 mL/sec by means of a mechanical injector (Spectris; Medrad, Indianola, Pa) and was followed by a saline flush. Contrast agent doses between 0.05 mmol/kg and 0.1 mmol/kg have been used for perfusion. The dose of 0.075 mmol/kg was chosen to achieve clarity of the defect while minimizing susceptibility artifacts. Images were obtained in three simultaneous 8-mm-thick short-axis sections centered on the mid-papillary muscle by using a standard electrocardiographically gated saturation-recovery gradient-echo sequence (turboFLASH; Siemens Medical Solutions) (19). Average imaging parameters were as follows: 222/1.14/90 (repetition time msec/echo time msec/inversion time msec) with a nonselective inversion recovery pulse, 15° flip angle, bandwidth of 570 Hz/pixel, field of view of 333 x 400 mm, matrix of 104 x 192 (phase x frequency), in-plane resolution of 3.2 x 2.1 mm, and an average of 60 measurements obtained in 30–50 seconds.

Contrast-enhanced Cine MR Technique
This study consisted of a previously described balanced steady-state free-precession electrocardiographically gated segmented k-space MR imaging pulse sequence (14) beginning immediately after administration of an additional 0.125 mmol/kg of gadolinium-based contrast material (cumulative dose, 0.2 mmol/kg). Three 8-mm short-axis sections were acquired in section locations identical to those for the first-pass perfusion study. Additional short-axis sections (5–9) sufficient to span the ventricle were acquired from apex to base, as were horizontal and vertical long-axis sections. Typical imaging parameters were as follows: 3.0/1.5, flip angle of 55°–80°, bandwidth of 930 Hz/pixel, one signal acquired, field of view of 325 x 400 mm, matrix of 206 x 256 (phase x frequency), interpolated, and in-plane resolution of 1.6 x 1.6 mm, averaging 20 phases and 16–24 segments. By using prospective gating, imaging duration averaged 16 seconds at an R-R cycle length of 800 msec. In the 34 patients undergoing preliminary nonenhanced cine imaging, imaging parameters and section locations were the same for that examination.

Inversion-Recovery Gradient-Echo MR Technique
In 50 patients, early inversion-recovery sections for comparison of hypoenhancement were acquired immediately after each contrast-enhanced cine MR section at identical section locations and thickness, after an initial inversion-time scout sequence was performed. These sections were acquired by using a previously described electrocardiographically gated segmented k-space, T1-weighted inversion-recovery gradient-echo pulse sequence (turboFLASH; Siemens Medical Solutions) (15). Average imaging parameters were as follows: 800/4.3/350–450, flip angle of 30°, bandwidth of 140 Hz/pixel, field of view of 325 x 400 mm, matrix of 160 x 256 (phase x frequency), in-plane resolution of 2.0 x 1.5 mm, and an average of 24 segments.

Delayed inversion-recovery sections for infarct size were acquired 10 minutes after administration of the second contrast material dose in all patients, after a second inversion-time scout sequence was performed, with average inversion time of 220–260 msec; other parameters were unchanged.

Imaging Time
The technologist recorded the time of the patient's entrance into the imaging room. The MR imager recorded the time of each image acquisition automatically, and the duration of each phase of the study was calculated.

Scoring of Hypoenhancing Defects
Images were placed in random order and analyzed by two independent observers blinded to all clinical data, patient identities, and other imaging data (G.L.R. and A.D., 5 and 2 years of experience in cardiac MR imaging, respectively). Defect areas and normal areas were measured by means of digital planimetry by using the ARGUS software. Hypoenhancing defects on each type of study were defined as discrete, endocardially based regions of hypointense myocardium (8). By using the ARGUS viewer, the readers drew a region of interest around defects and recorded the area. The final value used was an average of the two readings. The readers also measured the total area of each section. Each section was then divided up into six segments of 60° each, with the anterior segment starting at the junction of the right ventricular free wall and the left ventricle. Hypoenhancing defects within each segment and the area of each segment were then measured.

Global and Transmural Extent of MO
The global extent of abnormality, measured as a percentage of each section, was defined as the area of the defect divided by the total area of the section. The transmural extent of abnormality, measured as a percentage, was defined as the area of the defect within the abnormal segment divided by the total area of the abnormal segment.

Myocardial Function
Cine MR studies were compared before and after contrast enhancement for left ventricular ejection fraction, mass, and regional function by two independent observers blinded to patient identity, clinical data, and other imaging data (G.L.R. and R.E.G., each with 5 years of experience in cardiac MR imaging). For regional function scoring, segmental wall thickening was scored on a five-point scale, as follows: score of 1, normal; 2, mild to moderate hypokinesis; 3, marked hypokinesis; 4, akinesis; and 5, dyskinesis. Wall thickening score index was calculated as the total score divided by the total number of analyzed segments per ventricle.

Statistical Analysis
Summary statistics calculated as mean ± standard deviation were used to describe the performances of the different imaging methods. Relationships between tests' performances were determined by using the Pearson correlation coefficient, and equivalencies (or agreements) between the tests were indicated by the intraclass correlation coefficient (IC). Bland-Altman plots were generated to present graphically the stability and consistency of the agreement between the tests (20,21). For myocardial function studies, paired t tests were employed to determine significant changes before and after contrast material enhancement. All tests were conducted at the 5% (.05) level.

	RESULTS

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

 
MR studies were obtained an average of 44.3 hours ± 8.1 after the onset of chest pain. The infarct-related artery was the left anterior descending artery in 37 (46%) of 80 patients, the left circumflex artery in 13 patients (16%), and the right coronary artery in 24 patients (30%), and was indeterminate in six patients (8%).

MR Imaging Time
Average time for patient positioning, application of electrocardiography leads, and instruction was 7.5 minutes ± 7.3. Average MR imaging time was as follows: for localizers, 4.3 minutes ± 2.7; for first-pass imaging, 4.3 minutes ± 2.9; for contrast-enhanced cine imaging, 6.1 minutes ± 2.8; and for late inversion-recovery delayed-enhancement imaging, 6.2 minutes ± 3.7. Average delay from cine imaging to delayed enhancement imaging was 4.2 minutes ± 2.0. Thus, total imaging time for the standard test sequence would have averaged 32 minutes for all three combined studies if a standard 10 minutes had been added between first-pass and delayed enhancement imaging instead of interpolating the cine study. If, as proposed, contrast-enhanced cine MR imaging was substituted for conventional cine MR imaging, first-pass perfusion, and 60% (6.1 of 10.0 minutes) of the waiting period, imaging time would be reduced by 11 minutes (34%, 11 of 32 minutes).

Global and Transmural Extent of MO
The global extent of hypoenhancing defects with our method showed strong agreement, with similar defects on both first-pass (IC, 0.96; P < .001) and early inversion-recovery (IC, 0.90; P < .001; Fig 1a, 1c) images. The transmural extent of hypoenhancing defects also showed strong agreement with first-pass (IC, 0.88; P < .001) and early inversion-recovery (IC, 0.93; P < .001; Fig 2a, 2c) images. For both global and transmural analysis, Bland-Altman plots indicated that variability of the differences between the two tests for both measures were consistent, and the majority of them were within the 95% confidence intervals (Figs 1b, 1d, 2b, 2d). Figure 3 compares these techniques in a typical patient. An early hypoenhancement–late hyperenhancement pattern was seen in every case in which studies were obtained immediately after contrast material administration (Fig 4a4d) and after 10 minutes (Fig 4b, 4e) and 30 minutes (Fig 4c). Also see the Movie (radiology.rsnajnls.org/cgi/content/full/240/2/529/DC1) for the movie images of Figures 3 and 4.

View larger version (40K): [in this window] [in a new window] [Download PPT slide]   Figure 1a: Graphs of global extent of MO demonstrate strong agreement between contrast-enhanced cine (CE-CINE) MR imaging and first-pass perfusion and delayed enhancement inversion-recovery gradient-echo (IR-DE) MR imaging. Hypoenhancing defects at cine imaging had (a) an IC of 0.96 (P < .001) in comparison with first-pass perfusion imaging and (c) an IC of 0.90 (P < .001) in comparison with early inversion-recovery imaging. (b, d) Corresponding Bland-Altman plots indicate that differences between the tests are consistent, and the majority of them are within the 95% confidence intervals (95% CI).

View larger version (38K): [in this window] [in a new window] [Download PPT slide]   Figure 1b: Graphs of global extent of MO demonstrate strong agreement between contrast-enhanced cine (CE-CINE) MR imaging and first-pass perfusion and delayed enhancement inversion-recovery gradient-echo (IR-DE) MR imaging. Hypoenhancing defects at cine imaging had (a) an IC of 0.96 (P < .001) in comparison with first-pass perfusion imaging and (c) an IC of 0.90 (P < .001) in comparison with early inversion-recovery imaging. (b, d) Corresponding Bland-Altman plots indicate that differences between the tests are consistent, and the majority of them are within the 95% confidence intervals (95% CI).

View larger version (37K): [in this window] [in a new window] [Download PPT slide]   Figure 1c: Graphs of global extent of MO demonstrate strong agreement between contrast-enhanced cine (CE-CINE) MR imaging and first-pass perfusion and delayed enhancement inversion-recovery gradient-echo (IR-DE) MR imaging. Hypoenhancing defects at cine imaging had (a) an IC of 0.96 (P < .001) in comparison with first-pass perfusion imaging and (c) an IC of 0.90 (P < .001) in comparison with early inversion-recovery imaging. (b, d) Corresponding Bland-Altman plots indicate that differences between the tests are consistent, and the majority of them are within the 95% confidence intervals (95% CI).

View larger version (36K): [in this window] [in a new window] [Download PPT slide]   Figure 1d: Graphs of global extent of MO demonstrate strong agreement between contrast-enhanced cine (CE-CINE) MR imaging and first-pass perfusion and delayed enhancement inversion-recovery gradient-echo (IR-DE) MR imaging. Hypoenhancing defects at cine imaging had (a) an IC of 0.96 (P < .001) in comparison with first-pass perfusion imaging and (c) an IC of 0.90 (P < .001) in comparison with early inversion-recovery imaging. (b, d) Corresponding Bland-Altman plots indicate that differences between the tests are consistent, and the majority of them are within the 95% confidence intervals (95% CI).

View larger version (38K): [in this window] [in a new window] [Download PPT slide]   Figure 2a: Graphs of transmural extent of MO demonstrate strong agreement between contrast-enhanced cine (CE-CINE) MR imaging and first-pass perfusion and delayed enhancement inversion-recovery gradient-echo (IR-DE) MR imaging. Hypoenhancing defects at cine imaging had (a) an IC of 0.88 (P < .001) in comparison with first-pass perfusion imaging and (c) an IC of 0.93 (P < .001) in comparison with early inversion-recovery imaging. (b, d) Corresponding Bland-Altman plots indicate that differences between the tests are consistent, and the majority of them are within the 95% confidence intervals (95% CI).

View larger version (47K): [in this window] [in a new window] [Download PPT slide]   Figure 2b: Graphs of transmural extent of MO demonstrate strong agreement between contrast-enhanced cine (CE-CINE) MR imaging and first-pass perfusion and delayed enhancement inversion-recovery gradient-echo (IR-DE) MR imaging. Hypoenhancing defects at cine imaging had (a) an IC of 0.88 (P < .001) in comparison with first-pass perfusion imaging and (c) an IC of 0.93 (P < .001) in comparison with early inversion-recovery imaging. (b, d) Corresponding Bland-Altman plots indicate that differences between the tests are consistent, and the majority of them are within the 95% confidence intervals (95% CI).

View larger version (33K): [in this window] [in a new window] [Download PPT slide]   Figure 2c: Graphs of transmural extent of MO demonstrate strong agreement between contrast-enhanced cine (CE-CINE) MR imaging and first-pass perfusion and delayed enhancement inversion-recovery gradient-echo (IR-DE) MR imaging. Hypoenhancing defects at cine imaging had (a) an IC of 0.88 (P < .001) in comparison with first-pass perfusion imaging and (c) an IC of 0.93 (P < .001) in comparison with early inversion-recovery imaging. (b, d) Corresponding Bland-Altman plots indicate that differences between the tests are consistent, and the majority of them are within the 95% confidence intervals (95% CI).

View larger version (41K): [in this window] [in a new window] [Download PPT slide]   Figure 2d: Graphs of transmural extent of MO demonstrate strong agreement between contrast-enhanced cine (CE-CINE) MR imaging and first-pass perfusion and delayed enhancement inversion-recovery gradient-echo (IR-DE) MR imaging. Hypoenhancing defects at cine imaging had (a) an IC of 0.88 (P < .001) in comparison with first-pass perfusion imaging and (c) an IC of 0.93 (P < .001) in comparison with early inversion-recovery imaging. (b, d) Corresponding Bland-Altman plots indicate that differences between the tests are consistent, and the majority of them are within the 95% confidence intervals (95% CI).

View larger version (147K): [in this window] [in a new window] [Download PPT slide]   Figure 3a: Images in 34-year-old man with chest pain and lateral ST elevation, proximal circumflex occlusion, and "no-reflow" after primary percutaneous stent implantation show comparison between (a) end-diastolic and (b) end-systolic gadolinium-enhanced cine (balanced steady-state free precession), (c) gadolinium-enhanced first-pass perfusion (saturation-recovery gradient-echo), and (d) delayed enhancement (T1-weighted inversion-recovery gradient-echo) MR imaging. In matched areas on a and c, there is evidence of lateral wall hypoperfusion indicated by hypoenhancement (arrow). Cine short-axis frames a and b demonstrate normal thickening of anteroseptal walls (arrowheads) but absence of lateral wall thickening. On b and d, there is hyperenhancement (arrow) indicative of transmural infarction. (e, f) Invasive contrast-enhanced cine angiograms show the responsible left circumflex coronary artery with a proximal subtotal stenosis in e and after percutaneous intervention in f. There was good filling of the left circumflex artery but little myocardial blush downstream.

View larger version (136K): [in this window] [in a new window] [Download PPT slide]   Figure 3b: Images in 34-year-old man with chest pain and lateral ST elevation, proximal circumflex occlusion, and "no-reflow" after primary percutaneous stent implantation show comparison between (a) end-diastolic and (b) end-systolic gadolinium-enhanced cine (balanced steady-state free precession), (c) gadolinium-enhanced first-pass perfusion (saturation-recovery gradient-echo), and (d) delayed enhancement (T1-weighted inversion-recovery gradient-echo) MR imaging. In matched areas on a and c, there is evidence of lateral wall hypoperfusion indicated by hypoenhancement (arrow). Cine short-axis frames a and b demonstrate normal thickening of anteroseptal walls (arrowheads) but absence of lateral wall thickening. On b and d, there is hyperenhancement (arrow) indicative of transmural infarction. (e, f) Invasive contrast-enhanced cine angiograms show the responsible left circumflex coronary artery with a proximal subtotal stenosis in e and after percutaneous intervention in f. There was good filling of the left circumflex artery but little myocardial blush downstream.

View larger version (127K): [in this window] [in a new window] [Download PPT slide]   Figure 3c: Images in 34-year-old man with chest pain and lateral ST elevation, proximal circumflex occlusion, and "no-reflow" after primary percutaneous stent implantation show comparison between (a) end-diastolic and (b) end-systolic gadolinium-enhanced cine (balanced steady-state free precession), (c) gadolinium-enhanced first-pass perfusion (saturation-recovery gradient-echo), and (d) delayed enhancement (T1-weighted inversion-recovery gradient-echo) MR imaging. In matched areas on a and c, there is evidence of lateral wall hypoperfusion indicated by hypoenhancement (arrow). Cine short-axis frames a and b demonstrate normal thickening of anteroseptal walls (arrowheads) but absence of lateral wall thickening. On b and d, there is hyperenhancement (arrow) indicative of transmural infarction. (e, f) Invasive contrast-enhanced cine angiograms show the responsible left circumflex coronary artery with a proximal subtotal stenosis in e and after percutaneous intervention in f. There was good filling of the left circumflex artery but little myocardial blush downstream.

View larger version (151K): [in this window] [in a new window] [Download PPT slide]   Figure 3d: Images in 34-year-old man with chest pain and lateral ST elevation, proximal circumflex occlusion, and "no-reflow" after primary percutaneous stent implantation show comparison between (a) end-diastolic and (b) end-systolic gadolinium-enhanced cine (balanced steady-state free precession), (c) gadolinium-enhanced first-pass perfusion (saturation-recovery gradient-echo), and (d) delayed enhancement (T1-weighted inversion-recovery gradient-echo) MR imaging. In matched areas on a and c, there is evidence of lateral wall hypoperfusion indicated by hypoenhancement (arrow). Cine short-axis frames a and b demonstrate normal thickening of anteroseptal walls (arrowheads) but absence of lateral wall thickening. On b and d, there is hyperenhancement (arrow) indicative of transmural infarction. (e, f) Invasive contrast-enhanced cine angiograms show the responsible left circumflex coronary artery with a proximal subtotal stenosis in e and after percutaneous intervention in f. There was good filling of the left circumflex artery but little myocardial blush downstream.

View larger version (173K): [in this window] [in a new window] [Download PPT slide]   Figure 3e: Images in 34-year-old man with chest pain and lateral ST elevation, proximal circumflex occlusion, and "no-reflow" after primary percutaneous stent implantation show comparison between (a) end-diastolic and (b) end-systolic gadolinium-enhanced cine (balanced steady-state free precession), (c) gadolinium-enhanced first-pass perfusion (saturation-recovery gradient-echo), and (d) delayed enhancement (T1-weighted inversion-recovery gradient-echo) MR imaging. In matched areas on a and c, there is evidence of lateral wall hypoperfusion indicated by hypoenhancement (arrow). Cine short-axis frames a and b demonstrate normal thickening of anteroseptal walls (arrowheads) but absence of lateral wall thickening. On b and d, there is hyperenhancement (arrow) indicative of transmural infarction. (e, f) Invasive contrast-enhanced cine angiograms show the responsible left circumflex coronary artery with a proximal subtotal stenosis in e and after percutaneous intervention in f. There was good filling of the left circumflex artery but little myocardial blush downstream.

View larger version (156K): [in this window] [in a new window] [Download PPT slide]   Figure 3f: Images in 34-year-old man with chest pain and lateral ST elevation, proximal circumflex occlusion, and "no-reflow" after primary percutaneous stent implantation show comparison between (a) end-diastolic and (b) end-systolic gadolinium-enhanced cine (balanced steady-state free precession), (c) gadolinium-enhanced first-pass perfusion (saturation-recovery gradient-echo), and (d) delayed enhancement (T1-weighted inversion-recovery gradient-echo) MR imaging. In matched areas on a and c, there is evidence of lateral wall hypoperfusion indicated by hypoenhancement (arrow). Cine short-axis frames a and b demonstrate normal thickening of anteroseptal walls (arrowheads) but absence of lateral wall thickening. On b and d, there is hyperenhancement (arrow) indicative of transmural infarction. (e, f) Invasive contrast-enhanced cine angiograms show the responsible left circumflex coronary artery with a proximal subtotal stenosis in e and after percutaneous intervention in f. There was good filling of the left circumflex artery but little myocardial blush downstream.

View larger version (136K): [in this window] [in a new window] [Download PPT slide]   Figure 4a: Images demonstrate early hypoenhancement–late hyperenhancement pattern in 57-year-old man with chest pain, anterior ST elevation, and proximal left anterior descending artery occlusion that was treated with primary angioplasty. (a–c) Gadolinium-enhanced balanced steady-state free precession cine MR images and (d–f) T1-weighted inversion-recovery gradient-echo MR images obtained immediately, 10 minutes, and 30 minutes after contrast agent administration, respectively. On images immediately after contrast agent administration (a, d), early endocardial hypoenhancement areas (arrow) are seen with both imaging methods. At 10 minutes (b, e) and 30 minutes (c, f), area of hypoenhancement diminished in size on both sets of images, while hyperenhancement (arrow) became more prominent on f, thus demonstrating the early hypoehancement–late hyperenhancement pattern characteristic of MO.

View larger version (133K): [in this window] [in a new window] [Download PPT slide]   Figure 4b: Images demonstrate early hypoenhancement–late hyperenhancement pattern in 57-year-old man with chest pain, anterior ST elevation, and proximal left anterior descending artery occlusion that was treated with primary angioplasty. (a–c) Gadolinium-enhanced balanced steady-state free precession cine MR images and (d–f) T1-weighted inversion-recovery gradient-echo MR images obtained immediately, 10 minutes, and 30 minutes after contrast agent administration, respectively. On images immediately after contrast agent administration (a, d), early endocardial hypoenhancement areas (arrow) are seen with both imaging methods. At 10 minutes (b, e) and 30 minutes (c, f), area of hypoenhancement diminished in size on both sets of images, while hyperenhancement (arrow) became more prominent on f, thus demonstrating the early hypoehancement–late hyperenhancement pattern characteristic of MO.

View larger version (129K): [in this window] [in a new window] [Download PPT slide]   Figure 4c: Images demonstrate early hypoenhancement–late hyperenhancement pattern in 57-year-old man with chest pain, anterior ST elevation, and proximal left anterior descending artery occlusion that was treated with primary angioplasty. (a–c) Gadolinium-enhanced balanced steady-state free precession cine MR images and (d–f) T1-weighted inversion-recovery gradient-echo MR images obtained immediately, 10 minutes, and 30 minutes after contrast agent administration, respectively. On images immediately after contrast agent administration (a, d), early endocardial hypoenhancement areas (arrow) are seen with both imaging methods. At 10 minutes (b, e) and 30 minutes (c, f), area of hypoenhancement diminished in size on both sets of images, while hyperenhancement (arrow) became more prominent on f, thus demonstrating the early hypoehancement–late hyperenhancement pattern characteristic of MO.

View larger version (154K): [in this window] [in a new window] [Download PPT slide]   Figure 4d: Images demonstrate early hypoenhancement–late hyperenhancement pattern in 57-year-old man with chest pain, anterior ST elevation, and proximal left anterior descending artery occlusion that was treated with primary angioplasty. (a–c) Gadolinium-enhanced balanced steady-state free precession cine MR images and (d–f) T1-weighted inversion-recovery gradient-echo MR images obtained immediately, 10 minutes, and 30 minutes after contrast agent administration, respectively. On images immediately after contrast agent administration (a, d), early endocardial hypoenhancement areas (arrow) are seen with both imaging methods. At 10 minutes (b, e) and 30 minutes (c, f), area of hypoenhancement diminished in size on both sets of images, while hyperenhancement (arrow) became more prominent on f, thus demonstrating the early hypoehancement–late hyperenhancement pattern characteristic of MO.

View larger version (167K): [in this window] [in a new window] [Download PPT slide]   Figure 4e: Images demonstrate early hypoenhancement–late hyperenhancement pattern in 57-year-old man with chest pain, anterior ST elevation, and proximal left anterior descending artery occlusion that was treated with primary angioplasty. (a–c) Gadolinium-enhanced balanced steady-state free precession cine MR images and (d–f) T1-weighted inversion-recovery gradient-echo MR images obtained immediately, 10 minutes, and 30 minutes after contrast agent administration, respectively. On images immediately after contrast agent administration (a, d), early endocardial hypoenhancement areas (arrow) are seen with both imaging methods. At 10 minutes (b, e) and 30 minutes (c, f), area of hypoenhancement diminished in size on both sets of images, while hyperenhancement (arrow) became more prominent on f, thus demonstrating the early hypoehancement–late hyperenhancement pattern characteristic of MO.

View larger version (169K): [in this window] [in a new window] [Download PPT slide]   Figure 4f: Images demonstrate early hypoenhancement–late hyperenhancement pattern in 57-year-old man with chest pain, anterior ST elevation, and proximal left anterior descending artery occlusion that was treated with primary angioplasty. (a–c) Gadolinium-enhanced balanced steady-state free precession cine MR images and (d–f) T1-weighted inversion-recovery gradient-echo MR images obtained immediately, 10 minutes, and 30 minutes after contrast agent administration, respectively. On images immediately after contrast agent administration (a, d), early endocardial hypoenhancement areas (arrow) are seen with both imaging methods. At 10 minutes (b, e) and 30 minutes (c, f), area of hypoenhancement diminished in size on both sets of images, while hyperenhancement (arrow) became more prominent on f, thus demonstrating the early hypoehancement–late hyperenhancement pattern characteristic of MO.

	DISCUSSION

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

 
These findings demonstrate that the contrast-enhanced cine MR imaging method is rapid and well tolerated by patients early after acute myocardial infarction. This method provides data on MO and myocardial function in a dynamic format with results that compare very closely to those with standard MR imaging techniques.

These observations are consistent with and extend those of prior studies demonstrating the value of contrast-enhanced MR imaging in acute myocardial infarction. Steady-state free-precession cine cardiac MR imaging has become the reference standard for the assessment of cardiac morphologic characteristics and function because of its high spatial resolution and favorable signal-to-noise characteristics (14). The contrast-enhanced cine MR imaging method represents a simple modification of this technique in which a cine image is acquired after contrast enhancement during the 10 minutes normally used for waiting to begin delayed enhancement imaging for viability. Our results show that this method helps determine regional and global left ventricular function with no significant differences in left ventricular ejection fraction, mass, or regional wall motion score index when compared with standard cine cardiac MR imaging.

In our study, contrast-enhanced cine MR imaging also showed close correspondence with standard methods for identification and quantification of MO. Early hypoenhancing regions during the first 2 minutes after contrast agent injection have been correlated with histopathologic evidence of MO in experimental animal studies (16,18) and with adverse clinical outcomes in patient studies (7,8,21). Signal intensity in these hypointense zones rises slowly in the first 5–10 minutes after contrast agent administration, with conversion to partial or complete hyperenhancement over the course of 15–30 minutes (early hypoehancement–late hyperenhancement pattern). Our data show that the size of hypoenhancing regions on contrast-enhanced cine MR images strongly agrees with the global and transmural size of hypoenhancing regions on both first-pass perfusion and early inversion-recovery studies, and the early hypoenhancement–late hyper pattern was seen on images in every patient tested.

By performing MR imaging during the normal 10-minute waiting period between contrast enhancement and delayed enhancement studies, contrast-enhanced cine MR imaging reduces imaging time. In our study, the imaging time would have been reduced from 32 to 21 minutes (34%) if we had not added additional research imaging.

Contrast-enhanced cine MR imaging makes MO easier to measure because of the high spatial resolution and signal-to-noise characteristics of steady-state free-precession pulse sequences. First-pass perfusion sequences must be optimized for acquisition speed because each image must be acquired during one heartbeat, while cine MR imaging uses segmented k-space and phase sharing over an average of 20 heartbeats. In our study, in-plane resolution of first-pass perfusion MR images averaged 3.2 x 2.1 mm compared with 1.6 x 1.6 mm on contrast-enhanced cine MR images.

Myocardial function studies acquired by means of this method also display MO throughout the entire volume of the left ventricle, whereas three short-axis sections are usually acquired during first-pass studies. In addition, long-axis planes that include horizontal, vertical, and three-chamber long-axis views are frequently obtained during cine sequences, and these can also show MO with contrast enhancement.

In summary, compared with more-standard MR imaging, contrast-enhanced cine MR imaging reduces study duration, improves spatial resolution and extent of coverage of MO, and displays MO in a dynamic format in patients with acute myocardial infarction. This method may assist in rapid triage to novel drug and device interventions designed to treat ischemic but viable myocardium.

It is important to consider the limitations pertinent to the methods of this study. This study was performed in patients with acute myocardial infarction and the results cannot be extrapolated to other clinical conditions, including chronic infarctions. The mechanism of hypoenhancement due to MO is not the same as those of stress-induced perfusion defects, and contrast-enhanced cine MR imaging is not effective for the latter. The patients in our study demonstrated a high frequency and relatively large extent of MO in comparison with findings in some prior studies. Since our patient group consisted of those with ST elevation who were undergoing percutaneous interventional therapy, they may represent a group with more extensive necrosis.

This study was performed prior to recently developed rapid parallel imaging techniques that can further reduce imaging time. Similarly, the present research did not use novel contrast-enhanced cine MR imaging pulse sequences that may offer additional improvements, such as high contrast-to-noise display of nonviable muscle (22,23). However, the advantage of the present method is that it represents a simple modification of a robust, widely used cine pulse sequence, yet it can expedite acquisition and display important additional information.

	ADVANCE IN KNOWLEDGE

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

 

• Compared with more-standard MR imaging, contrast-enhanced cine MR imaging reduces study duration, improves spatial resolution and extent of coverage of microvascular obstruction, and displays this finding in a dynamic format in patients with acute myocardial infarction.
  

	FOOTNOTES

 

Abbreviations: IC = intraclass correlation coefficient • MO = microvascular obstruction

See Materials and Methods for pertinent disclosures.

Author contributions: Guarantors of integrity of entire study, G.L.R., J.A.G.; 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, G.L.R., J.A.G.; clinical studies, G.L.R., W.W.O., R.E.G., A.D., K.G.B., J.A.G.; statistical analysis, G.L.R.; and manuscript editing, all authors

	References

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

 

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