Myocardial infarction: optimization of inversion times at delayed contrast-enhanced MR imaging

Seventeen patients underwent magnetic resonance (MR) imaging for myocardial viability with a protocol approved by the institutional review board and gave written informed consent. Breath-hold cine inversion-recovery segmented k-space true fast imaging with steady-state precession sequence, referred to as inversion time (TI) mapping, was performed to determine optimal TI for myocardial infarction inversion-recovery imaging. From TI mapping, optimal TI was 180-315 msec 10-15 minutes after administration of 0.15 mmol/kg of gadolinium-based contrast material. At that optimal TI, relative signal intensity of infarcted myocardium compared with uninfarcted myocardium was maximal (mean +/- standard deviation, 297.8% +/- 86.5), whereas signal-to-noise ratio of uninfarcted myocardium was minimal (4.5 +/- 1.2). When applied to conventional myocardial infarction inversion-recovery imaging, optimal TI resulted in nulling of signal intensity of uninfarcted myocardium in all patients and in excellent conspicuity of infarcted myocardium in all nine patients with visible infarction.     

Inversion recovery single-shot TurboFLASH for assessment of myocardial infarction at 3 Tesla

PURPOSE: The aim of the study was to assess the diagnostic accuracy of imaging myocardial infarction with a single-shot inversion recovery turbofast low-angle shot (SS IR turboFLASH) sequence at 3.0 Tesla in comparison with an established segmented inversion recovery turboFLASH sequence at 1.5 Tesla. MATERIALS AND METHODS: Fifteen patients with myocardial infarction were examined at a 1.5 Tesla magnetic resonance (MR) System (Avanto, Siemens, Medical Solutions) and at a 3.0 Tesla MR system (TIM Trio, Siemens, Medical Solutions). Imaging delayed enhancement was started 15 minutes after application of contrast material. A SS IR turboFLASH was performed at 3.0 Tesla and compared with a segmented IR turboFLASH sequence at 1.5 and at 3.0 Tesla. The IR turboFLASH sequence at 1.5 Tesla served as reference method. Infarct volumes, contrast/noise ratio (CNR) of infarcted and normal myocardium were compared with the reference method. RESULTS: The Single-Shot IR turboFLASH technique allows imaging 9 slices during a single breath-hold. The CNR between infarction and normal myocardium of the reference method was 6.4 at 1.5 Tesla. The mean value of CNR of the IR turboFLASH sequence was 7.3 at 3.0 Tesla for the single-shot technique and 14.1 at 3.0 Tesla for the segmented technique. No significant difference was found for the CNR values of the reference technique at 1.5 Tesla and the single-shot technique at 3.0 Tesla, however for the comparison of the segmented technique at 1.5 and at 3 Tesla (P = 0.0001). The correlation coefficients of the infarct volumes, determined with the Single-Shot IR turboFLASH and the segmented IR turboFLASH technique at 3.0 compared with the reference method, were r = 0.95 (P < 0.0001) and r = 0.95 (P < 0.0001). CONCLUSION: The loss of CNR, which is caused by replacement of the segmented technique by the single-shot technique, is completely compensated by the approximately 2-fold CNR increase at the higher field strength. The IR turboFLASH technique at 3.0 Tesla IR can be used as a single-shot technique with acquisition of 9 slices during a single breath-hold without loss of diagnostic accuracy compared with the segmented technique at 1.5 Tesla.     

Single-shot inversion recovery TrueFISP for assessment of myocardial infarction

OBJECTIVE: The aim of the study was to assess the diagnostic accuracy of imaging the myocardium with a fast multislice inversion recovery 2D single-shot true fast imaging with steady-state precession (trueFISP) sequence during a single breath-hold in comparison with an established segmented inversion recovery turbo fast low-angle shot (turboFLASH) sequence. SUBJECTS AND METHODS: Forty-three patients with myocardial infarction were examined on a 1.5-T MR system 10 min after administration of contrast material (gadodiamide, 0.2 mmol/kg) with a single-shot 2D multislice technique (single-shot inversion recovery trueFISP) that allows one to image the entire short axis during one breath-hold (18 heartbeats) and with a segmented 2D single-slice technique (inversion recovery turboFLASH) that requires one breath-hold per slice (12 heartbeats). Signal intensity was determined in normal myocardium, in infarcted myocardium, and in the left ventricle. The contrast-to-noise ratio (CNR) of normal and infarcted myocardium was determined. The areas of hyperintense infarctions on selected slices and the entire volumes were compared for both sequence techniques. RESULTS: The inversion recovery trueFISP sequence has a lower CNR than the inversion recovery turboFLASH sequence (mean values, 10.0 vs 12.9, respectively; p = 0.005) for differentiation of viable from nonviable myocardium. The CNR of injured myocardium and blood in the left ventricular cavity also has a lower value for the multislice technique compared with the single-slice technique (0.6 vs 1.2, respectively; p = 0.045). Assessment of the area of infarction within one slice (r = 0.97, p < 0.002) and of the volume of the entire infarction (r = 0.96, p < 0.003) is possible with excellent correlation of both techniques. CONCLUSION: Despite having a lower CNR, the inversion recovery 2D single-shot trueFISP sequence allows fast and accurate identification of the area and volume of infarction with high spatial resolution within a single breath-hold.     

Normal and infarcted myocardium: differentiation with cellular uptake of manganese at MR imaging in a rat model

PURPOSE: To assess whether normal myocardium can be distinguished from infarction at magnetic resonance (MR) imaging with low doses of manganese dipyridoxyl diphosphate (Mn-DPDP). MATERIALS AND METHODS: After 1-hour coronary arterial occlusion and 2-hour reperfusion, three groups of eight rats each were injected with 25, 50, or 100 micromol of Mn-DPDP per kilogram of body weight. The longitudinal relaxation rate (R1) in normal myocardium, reperfused infarction, and blood was repeatedly measured at inversion-recovery echo-planar imaging before and for 1 hour after the administration of contrast material. Afterward, several animals from each group were examined at high-spatial-resolution inversion-recovery spin-echo (SE) MR imaging. RESULTS: Manganese accumulated in normal myocardium but was cleared from reperfused infarction and blood. One hour after the administration of Mn-DPDP, R1 in normal myocardium (1.53 sec(-1) +/- 0.03, 1.73 sec(-1) +/- 0.03, and 1.94 sec(-1) +/- 0.02, respectively, for 25, 50, and 100 micromol/kg) was significantly (P <.05) faster than that of reperfused infarction (0.99 sec(-1) +/- 0.03, 1.11 sec(-1) +/- 0.03, and 1.48 sec(-1) +/- 0.06). Normal myocardium appeared hyperintense on T1-weighted inversion-recovery SE MR images and was clearly distinguishable from reperfused infarction. CONCLUSION: Mn-DPDP-enhanced inversion-recovery echo-planar and SE MR images demonstrated retention of manganese in normal myocardium and clearance of manganese from infarction. Mn-DPDP has characteristics similar to those of widely used thallium and may be useful in the assessment of myocardial viability at MR imaging.     

Acute myocardial infarction: MR evaluation in 29 patients

This study evaluated the ability of MR to identify and characterize the region of myocardial infarction in humans. Twenty-nine patients, all with ECG and enzyme rises consistent with an acute myocardial infarction, were studied by MR 3-17 days from the onset of acute chest pain. Four patients were excluded because of inability to acquire adequate MR studies. For comparison, 20 normal subjects were studied who also had gated MR examinations. The site of infarction was visualized in 23 patients as an area of high signal intensity in relation to the normal myocardium, a contrast that increased on the second-echo image. The regions of abnormal signal intensity corresponded to the anatomic site of infarction as defined by the ECG changes. The mean T2 relaxation time of the infarcted myocardium (79 +/- 22 msec) was significantly prolonged in comparison with the mean T2 (43.9 +/- 9 msec) of normal myocardium (p less than .01). The mean percentage of contrast (intensity difference) between normal and infarcted myocardium was much greater on the second-echo images (65.6 +/- 34.0%) than the first-echo images (27.5 +/- 18.7%). In the normal subjects there was no difference in T2 between the anterolateral (40.3 +/- 5.7 msec) and septal (39.5 +/- 7.4 msec) regions, and percentages of contrast between these two regions of myocardium on the first-echo (9.1 +/- 7.4%) and second-echo (15.0 +/- 13.3%) images were similar. Thus, MR can be used to directly visualize acute infarcts. However, it has several pitfalls, including the necessity to differentiate signal from slowly flowing blood in the ventricle, from increased signal from a region of infarction and artifactual variation of signal intensity in the myocardium due to respiratory motion or residual cardiac motion.     

Assessment of myocardial infarction in humans with (23)Na MR imaging: comparison with cine MR imaging and delayed contrast enhancement

PURPOSE: To demonstrate the feasibility of sodium 23 ((23)Na) magnetic resonance (MR) imaging for assessment of subacute and chronic myocardial infarction and compare with cine, late enhancement, and T2-weighted imaging. MATERIALS AND METHODS: Thirty patients underwent MR imaging 8 days +/- 4 (subacute, n = 15) or more than 6 months (chronic, n = 15) after myocardial infarction by using a (23)Na surface coil with a double angulated electrocardiogram-triggered three-dimensional gradient-echo sequence at 1.5 T. In addition, cine, inversion-recovery gradient-echo, and, in the subacute group, T2-weighted images (n = 9) were obtained. Myocardial infarction mass was depicted as elevated signal intensity or wall motion abnormalities and expressed as a percentage of total left ventricular mass for all modalities. Correlations were tested with correlation coefficients. RESULTS: All patients after subacute infarction and 12 of 15 patients with chronic infarction had an area of elevated (23)Na signal intensity that significantly correlated with wall motion abnormalities (subacute; r = 0.96, P <.001, and chronic; r = 0.9, P <.001); three patients had no wall motion abnormalities or elevated (23)Na signal intensity. Only 10 patients in the subacute and nine in the chronic group revealed late enhancement; significant correlation with (23)Na MR imaging occurred only in subacute group (r = 0.68, P <.05). Myocardial edema in subacute infarction correlated (r = 0.71, P <.05) with areas of elevated (23)Na signal intensity but was extensively larger. CONCLUSION: (23)Na MR imaging demonstrates dysfunctional myocardium caused by subacute and chronic myocardial infarction.     

Enhanced viability imaging: improved contrast in myocardial delayed enhancement using dual inversion time subtraction.

In delayed contrast-enhanced MRI for the assessment of myocardial viability, the TI time in a gated inversion-recovery segmented gradient echo sequence is usually selected to null signal from normal myocardium. Although this TI time generates good contrast between the enhancing infarcted tissue and normal myocardium, there is usually less contrast between the infarct and the blood pool. A subtractive technique utilizing two acquisitions at a long and short TI time is proposed to improve the delineation between infarct-blood and infarct-myocardium. The concept was demonstrated in six mongrel dogs with reperfused myocardial infarction. Infarct-normal myocardium contrast (signal difference) using the proposed enhanced viability imaging (ENVI) technique was 142 +/- 50% (P < 0.001) that of standard magnitude inversion recovery (IR), while at the same TI time for the primary image, infarct-blood contrast, was 247 +/- 136% (P < 0.002) that of magnitude IR. Accounting for increased noise due to the subtraction, signal difference-to-noise ratios (SDNR) did not show a significant change for infarct-myocardium but infarct-blood SDNR for ENVI was 174 +/- 105% that of magnitude-IR (P < 0.03). Thus, marked improvement in the delineation of the infarcted zone was noted over a range of TI times.     

Segmented turboFLASH: method for breath-hold MR imaging of the liver with flexible contrast

A method called segmented turboFLASH imaging allows high-resolution, multisection, short-inversion-time (TI) inversion-recovery (STIR), T1- or T2-weighted magnetic resonance (MR) studies of the liver to be completed within a breath-hold interval. The method was applied in a phantom and in 19 patients with hepatic lesions. Sequence comparisons were performed among segmented turboFLASH, single-shot turboFLASH, T1-weighted gradient-echo with ultrashort echo time, and T2-weighted spin-echo (SE) techniques. Signal from fat and liver could be nulled with the segmented turboFLASH method, with TIs of 10 and 300 msec, respectively; signal from these tissues could not be eliminated with the single-shot approach. Signal-difference-to-noise ratios and contrast for the best segmented sequences were comparable with those of the best T2-weighted SE and T1-weighted gradient-echo techniques. It is concluded that it is feasible to obtain breath-hold images with arbitrary tissue contrast by means of segmented turboFLASH imaging. The method may prove helpful for the detection and characterization of hepatic lesions and will likely have applications to other anatomic regions such as the chest and pelvis.     

Phase-sensitive inversion-recovery MR imaging in the detection of myocardial infarction

PURPOSE: To prospectively determine if phase-sensitive inversion-recovery (IR) magnetic resonance (MR) imaging eliminates the need to find the precise inversion time (TI) to null the signal of normal myocardium to achieve high contrast between infarcted and normal myocardium. MATERIALS AND METHODS: Informed consent was obtained from each patient for this prospective MR imaging research study, which was approved by the institutional review board. Twenty patients (16 men; four women; mean age, 56 years +/- 12.3) who experienced Q-wave myocardial infarction 2 weeks earlier were examined with a 1.5-T MR system 10 minutes after administration of 0.1 mmol per kilogram of body weight gadobenate dimeglumine. To determine the optimal TI, a TI scout sequence was used. A segmented two-dimensional IR turbo fast low-angle shot (FLASH) sequence and a segmented two-dimensional IR true fast imaging with steady-state precession (FISP) sequence that produces both phase-sensitive and magnitude-reconstructed images were used at TI values of 200-600 msec (TI values were varied in 100-msec steps) and at optimal TI (mean value, 330 msec). Contrast-to-noise ratios (CNRs) of normal and infarcted myocardium and the area of infarcted myocardium were determined. Magnitude-reconstructed IR turbo FLASH images were compared with magnitude-reconstructed and phase-sensitive IR true FISP images. Two-tailed unpaired sample Student t test was used to compare CNRs, and two-tailed paired-sample Student t test was used to compare area of infarction. RESULTS: Mean CNR of images acquired with IR turbo FLASH and IR true FISP (phase-sensitive and magnitude-reconstructed images) at optimal TI (mean value, 330 msec) were 6.6, 6.2, and 6.1, respectively. For a TI of 200 msec, CNR values were -4.3, -4.0, and 7.2, respectively; for TI of 600 msec, CNR values were 3.1, 3.3, and 4.3, respectively. Area of infarcted myocardium was underestimated on magnitude-reconstruction images (P = .002-.03) for short TI values (ie, 200 msec) for both sequences and for a TI of 300 msec for IR true FISP but not on phase-sensitive reconstructed IR true FISP images when compared with IR turbo FLASH images obtained at optimal TI. CONCLUSION: Phase-sensitive image reconstruction results in reduced need for precise choice of TI and more consistent image quality.     

T2-prepared steady-state free precession blood oxygen level-dependent MR imaging of myocardial perfusion in a dog stenosis model

PURPOSE: To assess the ability of a T2-prepared steady-state free precession blood oxygen level-dependent (BOLD) magnetic resonance (MR) imaging sequence to depict changes in myocardial perfusion during stress testing in a dog stenosis model. MATERIALS AND METHODS: Study was approved by the institutional Animal Care and Use Committee. A hydraulic occluder was placed in the left circumflex coronary artery (LCX) in 10 dogs. Adenosine was administered intravenously to increase coronary blood flow, and stenosis was achieved in the LCX with the occluder. A T2-prepared two-dimensional steady-state free precession sequence was used for BOLD imaging at a spatial resolution of 1.5 x 1.2 x 5.0 mm3, and first-pass perfusion images were acquired for visual comparison. Microspheres were injected to provide regional perfusion information. Mixed-effect regression analysis was performed to assess normalized MR signal intensity ratios and microsphere-measured perfusion differences. For the same data, 95% prediction intervals were calculated to determine the smallest perfusion change detectable. Means +/- standard deviations were calculated for myocardial regional comparison data. A two-tailed Student t test was used to determine if significant differences (P < .01) existed between different myocardial regions. RESULTS: Under maximal adenosine stress, MR clearly depicted stenotic regions and showed regional signal differences between the left anterior descending coronary artery (LAD)-fed myocardium and the stenosed LCX-fed myocardium. Visual comparisons with first-pass images were also excellent. Regional MR signal intensity differences between LAD and LCX-fed myocardium (1.24 +/- 0.08) were significantly different (P < .01) from differences between LAD and septal-fed myocardium (1.02 +/- 0.07), which was in agreement with microsphere-measured flow differences (LAD/LCX, 3.38 +/- 0.83; LAD/septal, 1.26 +/- 0.49). The linear mixed-effect regression model showed good correlation (R = 0.79) between MR differences and microsphere-measured flow differences. CONCLUSION: On T2-prepared steady-state free precession BOLD MR images in dogs, signal intensity differences were linearly related to flow differences in myocardium, with a high degree of correlation. Supplemental material: radiology.rsnajnls.org/cgi/content/full/236/2/503/DC1     

Irreversible myocardial injury: assessment with cardiovascular delayed-enhancement MR imaging and comparison of 1.5 and 3.0 T--initial experience

PURPOSE: To prospectively compare visualization and quantification of irreversible myocardial injury in patients with chronic myocardial infarction at 1.5- and 3.0-T magnetic resonance (MR) imaging. MATERIALS AND METHODS: The institutional research ethics committee approved the study. Participants gave written informed consent. Sixteen male patients (mean age, 66 years +/- 13 [standard deviation]) with myocardial infarction were imaged with the same sequence by the same operator at 1.5 and 3.0 T. After cine imaging, a bolus of gadodiamide was administered. Short-axis images of entire left ventricle (LV) were acquired with a breath-hold T1-weighted segmented inversion-recovery turbo fast low-angle shot (FLASH) sequence. Agreement for myocardial hyperenhancement (HE) mass between field strengths was assessed with Bland-Altman method; agreement for detection and transmural extent of HE was assessed with kappa statistics. Intra- and interobserver reproducibility of mass and transmural extent of HE were assessed at 1.5 and 3.0 T. RESULTS: Bland-Altman analysis revealed no systematic bias (mean difference, 0.2 g; 95% confidence interval: -0.7 g, 1.2 g) and acceptable limits of agreement (-3.3 to 3.8 g) between field strengths for HE mass. HE mass measurements were strongly correlated (R(2) = 0.99); there was no significant difference in measurements at 1.5 and 3.0 T (28.1 g +/- 15.7 [22.6% +/- 10.9 of LV mass] vs 27.8 g +/- 15.7 [22.3% +/- 10.7 of LV mass], respectively; P = .599). For all segments, there was a high degree of agreement for HE detection (kappa = 0.90) and transmural grade (kappa = 0.79) between field strengths. Intra- and interobserver variability were low between both field strengths. Initial inversion time selected to null the signal of normal myocardium at 3.0 T was 57 msec +/- 20 longer than at 1.5 T (P < .01). CONCLUSION: By using the same turbo FLASH MR pulse sequence, there was strong agreement in mass and transmural extent of myocardial HE between 1.5 and 3.0 T.     

Phase-sensitive inversion recovery (PSIR) single-shot TrueFISP for assessment of myocardial infarction at 3 tesla

PURPOSE: The aim of the current study was to show if contrast-to-noise ratio (CNR) could be improved without loss of diagnostic accuracy if a phase-sensitive inversion recovery (PSIR) single-shot TrueFISP sequence is used at 3.0 T instead of 1.5 T. MATERIAL AND METHODS: Ten patients with myocardial infarction were examined on a 1.5 T magnetic resonance (MR) system (Avanto, Siemens Medical Systems) and at a 3.0 T MR system. Imaging delayed contrast enhancement was started 10 minutes after application of contrast material. A phase-sensitive inversion recovery (PSIR) single-shot TrueFISP sequence was used at 1.5 and 3.0 T and compared with a segmented IR turboFLASH sequence at 1.5 T, which served as the reference method. Infarct volumes and CNR of infarction and normal myocardium were compared with the reference method. RESULTS: The PSIR Single-Shot TrueFISP technique allows for imaging nine slices during a single breathhold without adaptation of the inversion time. The mean value of CNR between infarction and normal myocardium was 5.9 at 1.5 T and 12.2 at 3.0 T (magnitude images). The CNR mean value of the reference method was 8.4. The CNR mean value at 3.0 T was significantly (P = 0.03) higher than the mean value of the reference method. The correlation coefficients of the infarct volumes, determined with the PSIR single-shot TrueFISP technique at 1.5 T and at 3.0 T and compared with the reference method, were r = 0.96 (P = 0.001) and r = 0.99 (P = 0.0001). CONCLUSION: The use of PSIR single-shot TrueFISP at 3.0 T allows for accurate detection and assessment of myocardial infarction. CNR is significantly higher at 3.0 T compared with 1.5 T. The PSIR single-shot technique at 3.0 T provides a higher CNR than the segmented reference technique at 1.5 T.     

Myocardial viability: assessment with three-dimensional MR imaging in pigs and patients

PURPOSE: To prospectively evaluate the correlation between a three-dimensional (3D) delayed enhancement magnetic resonance (MR) imaging sequence and a two-dimensional (2D) delayed enhancement MR imaging sequence for noninvasive assessment of myocardial viability in pigs and patients. MATERIALS AND METHODS: The pig and patient studies were approved by the responsible authorities, and patients gave written informed consent. MR imaging was performed by using a rapid 3D inversion-recovery balanced steady-state free precession sequence and a 2D segmented inversion-recovery fast low-angle shot sequence as the reference standard. Fourteen pigs with reperfused (n=7) or nonreperfused (n=7) myocardial infarction and 17 patients (13 men, four women; mean age, 64.9 years+/-8.6 [standard deviation]) suspected of having myocardial infarction were included. Linear regression analysis and Bland-Altman analysis were used to compare the infarction volumes. RESULTS: In 10 of the 14 pigs the induction of myocardial infarction was successful. In these pigs, altogether 81 segments with myocardial infarction were demonstrated by both MR sequences, and agreement between the two sequences for classification of transmural extent of myocardial infarction was 99.7%. The infarction volume determined by using 3D MR imaging (4.64 cm3+/-2.48) in the pigs highly correlated with that of 2D MR imaging (4.65 cm3+/-2.39, r=0.989, P<.001) and that of staining by using triphenyltetrazolium chloride (4.67 cm3+/-2.44, r=0.996, P<.001). Thirteen of the 17 patients examined showed myocardial infarction in 34 myocardial segments with both sequences, and agreement between the two sequences for classification of transmural extent of myocardial infarction was 98.6%. In the patients, the infarction volume determined with both sequences highly correlated (9.71 cm3+/-7.47 for the 3D sequence vs 10.01 cm3+/-8.04 for the 2D sequence, r=0.982, P<.001). The breath-hold time necessary for the 3D MR imaging (21.0+/-2.3 seconds) was significantly shorter than that for 2D MR imaging (188.3+/-20.2 seconds, P<.001). CONCLUSION: Myocardial infarction volumes obtained with the 3D MR imaging sequence are highly correlated and in good agreement with volumes obtained with the 2D MR imaging standard approach and reduced the acquisition time by a factor of nine.     

Early-phase myocardial infarction: evaluation by MR imaging

In vivo gated magnetic resonance (MR) imaging was performed in 12 dogs immediately after occlusion of the left anterior descending coronary artery and serially up to 5 hours and again between 4 and 14 days. This was done to evaluate the appearance of acute myocardial infarcts and to determine how soon after coronary artery occlusion MR imaging can demonstrate the site of acute myocardial ischemia. In nine dogs with postmortem evidence of myocardial infarction, regional increase of signal intensity of the myocardium was present by 3 hours after coronary artery occlusion and conformed to the site of myocardial infarct found at autopsy. The signal intensity on T2-weighted images of the infarcted myocardium was significantly greater than that of normal myocardium at 3, 4, and 5 hours after occlusion. The T2 (spin-spin) relaxation time was significantly prolonged in the region of myocardial infarct at 3, 4, and 5 hours postocclusion compared with normal myocardium. Myocardial wall thinning and increased intracavitary flow signal were found in six dogs with comparable pre- and postocclusion images in late systole.     

Stunned,infarcted, and normal myocardium in dogs: simultaneous differentiation by using gadolinium-enhanced cine MR imaging with magnetization transfer contrast

PURPOSE: To simultaneously differentiate stunned, infarcted, and normal myocardial regions by using gadolinium-enhanced cine magnetic resonance (MR) imaging with magnetization transfer contrast. MATERIALS AND METHODS: Twelve dogs were imaged on days 1 and 8 after transient 90-minute coronary artery occlusion. A magnetization transfer contrast with echo-train readout (MTET) MR sequence was performed before and 30 minutes after gadolinium contrast enhancement. Ex vivo analysis consisted of MR imaging, microsphere blood flow analysis, and triphenyltetrazolium chloride (TTC) staining. A paired two-tailed t test was used to compare wall thickening from day 1 to day 8. Linear regression and Bland-Altman analyses were used to compare infarct size depicted with MTET imaging with that seen on TTC-stained tissue. RESULTS: Severe wall motion abnormalities were detected in all dogs. At TTC analysis, seven dogs had evidence of myocardial infarction and five had evidence of stunned myocardium. The mean percentages of left ventricular wall thickening in infarcted, stunned, and remote myocardial regions were 2% +/- 4 (SD), 4% +/- 8, and 33% +/- 5, respectively. Wall thickening did not improve in the infarcted zones, but it improved to nearly normal levels in the stunned region 1 week after induced occlusion (mean, 40% +/- 8; P <.02). MTET images clearly depicted infarcted myocardium as brighter than both the normal and stunned myocardial regions but darker than the blood pool. In vivo MTET infarct volume correlated with ex vivo TTC analysis data (y = 1.01x + 0.00, R = 0.98, standard error of the estimate = 0.019). CONCLUSION: One day after myocardial ischemia, MTET during one MR imaging examination enabled simultaneous differentiation of infarcted, stunned, and normal myocardial regions on the basis of gadolinium enhancement and regional function.     

Recent myocardial infarction: assessment with unenhanced T1-weighted MR imaging

The purpose of the study was to prospectively evaluate a T1-weighted technique for detection of myocardial edema resulting from recent myocardial infarction (MI) or intervention. This study was HIPAA compliant and institutional review board approved. Fifteen men and one woman (mean age, 57.8 years+/-11.5 [standard deviation]) were examined with T1-weighted magnetic resonance (MR) imaging and inversion-recovery cine pulse sequence in two groups, recent MI and chronic MI, and gave informed consent. T1 relaxation times of MI and adjacent myocardium were compared (Student t test and correlation analysis). In patients with recent MI, areas of myocardial edema were well depicted with T1-weighted MR imaging. T1 relaxation times of recent infarcts were longer than those of older MIs (925 msec+/-169 vs 551 msec+/-107, P<.001). From local edema, T1 relaxation time of infarcted myocardium is increased, may remain elevated for 2 months, and enables imaging with T1-weighted techniques.     

Occlusive myocardial infarction: investigation of bis-gadolinium mesoporphyrins-enhanced T1-weighted MR imaging in a cat model

PURPOSE: To test whether bis-gadolinium mesoporphyrins-enhanced magnetic resonance (MR) imaging can accurately depict irreversibly damaged myocardium in occlusive myocardial infarction. MATERIALS AND METHODS: Ten cats were subjected to 90 minutes of occlusion of the left anterior descending coronary artery. Bis-gadolinium mesoporphyrins-enhanced T1-weighted MR imaging was performed in the cats for 6 hours. Histopathologic examinations with 2'3'5-triphenyl tetrazolium chloride (TTC) staining and electron microscopy were performed on the resected specimens. The time course and pattern of signal intensity enhancement were evaluated. The size of the infarcted myocardium was estimated on the MR images by measuring the size of the signal intensity-enhanced area. RESULTS: In eight of 10 cats, it was impossible to distinguish infarcted myocardium from normal myocardium at visual inspection of T1-weighted MR images. The contrast ratio between infarcted and normal myocardium did not increase significantly over time. In one of the two remaining cats, a doughnut pattern of signal intensity enhancement was noted. The other cat showed intensely homogeneous enhancement of infarcted myocardium at MR imaging. The size of the area of signal intensity enhancement at MR imaging in these two cats was accurately mapped to that of the infarction on the TTC-stained specimens. CONCLUSION: Occlusive myocardial infarction cannot be accurately detected at bis-gadolinium mesoporphyrins-enhanced MR imaging.     

Inversion-recovery-prepared SSFP for cardiac-phase-resolved delayed-enhancement MRI.

Delayed-enhancement magnetic resonance imaging (DE-MRI) can be used to visualize myocardial infarction (MI). DE-MRI is conventionally acquired with an inversion-recovery gradient-echo (IR-GRE) pulse sequence that yields a single bright-blood image. IR-GRE imaging requires an accurate estimate of the inversion time (TI) to null the signal from the myocardium, and a separate cine acquisition is required to visualize myocardial wall motion. Simulations were performed to examine the effects of a steady-state free precession (SSFP) readout after an inversion pulse in the setting of DE-MRI. Using these simulations, a segmented IR-SSFP sequence was optimized for infarct visualization. This sequence yields both viability and wall motion images over the cardiac cycle in a single breath-hold. Viability images at multiple effective TIs are produced, providing a range of image contrasts. In a study of 11 patients, IR-SSFP yielded infarct sizes and left ventricular ejection fractions (LVEFs) similar to those obtained by IR-GRE and standard SSFP, respectively. IR-SSFP images yielded improved visualization of the infarct-blood border because of the simultaneous nulling of healthy myocardium and blood. T(1) (*) recovery curves were extracted from IR-SSFP images and showed excellent qualitative agreement with theoretical simulations.     

Delayed contrast enhancement on MR images of myocardium: past, present, future

Differential enhancement of myocardial infarction was first recognized on computed tomographic (CT) images obtained with iodinated contrast material in the late 1970s. Gadolinium enhancement of myocardial infarction was initially reported for T1-weighted magnetic resonance (MR) imaging in 1984. The introduction of an inversion-recovery gradient-echo MR sequence for accentuation of the contrast between normal and necrotic myocardium was the impetus for widespread clinical use for demonstrating the extent of myocardial infarction. This sequence has been called delayed-enhancement MR and MR viability imaging. The physiologic basis for differential enhancement of myocardial necrosis is the greater distribution volume of injured myocardium compared with that of normal myocardium. It is now recognized that delayed enhancement occurs in both acute and chronic (scar) infarctions and in an array of other myocardial processes that cause myocardial necrosis, infiltration, or fibrosis. These include myocarditis, hypertrophic cardiomyopathy, amyloidosis, sarcoidosis, and other myocardial conditions. In several of these diseases, the presence and extent of delayed enhancement has prognostic implications. Future applications of delayed enhancement with development of MR imaging and CT techniques will be discussed.     

Combined first-pass perfusion and viability study at MR imaging in patients with non-ST segment-elevation acute coronary syndromes: feasibility study

PURPOSE: To assess the feasibility of combined perfusion and viability testing by using magnetic resonance (MR) imaging in one setting in patients with non-ST segment-elevation acute coronary syndromes. MATERIALS AND METHODS: The data of 13 patients (mean age, 68 years; range, 40-85 years) at high risk for myocardial infarction who underwent MR imaging at 1.5 T were reviewed. Risk factors were increased troponin T levels in seven, reversible ST depression on an electrocardiogram in four, history of myocardial infarction in two, and presence of heart failure in four. Cine imaging of the left ventricle was performed with a true-fast imaging with steady-state precession (FISP) sequence to assess the regional myocardial contraction and ejection fraction. After injection of 0.1 mmol per kilogram of body weight of gadopentetate dimeglumine, first-pass MR images were obtained by using an inversion-recovery true-FISP sequence at rest and during infusion of adenosine (140 microg/kg/min). Resting and stress images were assessed qualitatively for abnormal regional perfusion (hypoenhancement). The myocardium was divided into three radial segments corresponding to the three coronary artery territories. Delayed (after 15 minutes) contrast material-enhanced images were acquired with use of a segmented inversion-recovery fast low-angle shot sequence. Conventional coronary angiograms were compared with the first-pass images. A more than 50% stenosis in diameter in any coronary artery was considered substantial. Mann-Whitney test was used to assess any significant difference between the left ventricular ejection fraction (LVEF) in patients with and those without myocardial infarct. RESULTS: Mean LVEF was 51.5% (range, 30%-77%). First-pass stress perfusion studies depicted 25 segments of hypoenhancement in 11 patients. Comparison of first-pass perfusion defects with findings on coronary angiograms indicated an overall sensitivity of 92% (24 of 26) and specificity of 92% (12 of 13) in detection of substantial coronary artery disease. Infarcts detected from hyperenhancement on delayed contrast-enhanced images were present in eight segments (four were transmural) in five patients. No significant difference was noted in the LVEF between patients with and those without infarct (P =.724). CONCLUSION: Combined stress perfusion and viability MR imaging was feasible in patients with acute coronary syndromes. First-pass MR perfusion defects compare well with the presence of substantial coronary artery stenosis on conventional angiograms.