Raymond J. Kim

The use of contrast-enhanced magnetic resonance imaging to identify reversible myocardial dysfunction.

BACKGROUND Recent studies indicate that magnetic resonance imaging (MRI) after the administration of contrast material can be used to distinguish between reversible and irreversible myocardial ischemic injury regardless of the extent of wall motion or the age of the infarct. We hypothesized that the results of contrast-enhanced MRI can be used to predict whether regions of abnormal ventricular contraction will improve after revascularization in patients with coronary artery disease. METHODS Gadolinium-enhanced MRI was performed in 50 patients with ventricular dysfunction before they underwent surgical or percutaneous revascularization. The transmural extent of hyperenhanced regions was postulated to represent the transmural extent of nonviable myocardium. The extent of regional contractility at the same locations was determined by cine MRI before and after revascularization in 41 patients. RESULTS Contrast-enhanced MRI showed hyperenhancement of myocardial tissue in 40 of 50 patients before revascularization. In all patients with hyperenhancement the difference in image intensity between hyperenhanced regions and regions without hyperenhancement was more than 6 SD. Before revascularization, 804 of the 2093 myocardial segments analyzed (38 percent) had abnormal contractility, and 694 segments (33 percent) had some areas of hyperenhancement. In an analysis of all 804 dysfunctional segments, the likelihood of improvement in regional contractility after revascularization decreased progressively as the transmural extent of hyperenhancement before revascularization increased (P<0.001). For instance, contractility increased in 256 of 329 segments (78 percent) with no hyperenhancement before revascularization, but in only 1 of 58 segments with hyperenhancement of more than 75 percent of tissue. The percentage of the left ventricle that was both dysfunctional and not hyperenhanced before revascularization was strongly related to the degree of improvement in the global mean wall-motion score (P<0.001) and the ejection fraction (P<0.001) after revascularization. CONCLUSIONS Reversible myocardial dysfunction can be identified by contrast-enhanced MRI before coronary revascularization.

Relationship of MRI Delayed Contrast Enhancement to Irreversible Injury, Infarct Age, and Contractile Function

BACKGROUND Contrast MRI enhancement patterns in several pathophysiologies resulting from ischemic myocardial injury are controversial or have not been investigated. We compared contrast enhancement in acute infarction (AI), after severe but reversible ischemic injury (RII), and in chronic infarction. METHODS AND RESULTS In dogs, a large coronary artery was occluded to study AI and/or chronic infarction (n = 18), and a second coronary artery was chronically instrumented with a reversible hydraulic occluder and Doppler flowmeter to study RII (n = 8). At 3 days after surgery, cine MRI revealed reduced wall thickening in AI (5+/-6% versus 33+/-6% in normal, P<0.001). In RII, wall thickening before, during, and after inflation of the occluder for 15 minutes was 35+/-5%, 1+/-8%, and 21+/-10% and Doppler flow was 19.8+/-5.3, 0.2+/-0.5, and 56.3+/-17.7 (peak hyperemia) cm/s, respectively, confirming occlusion, transient ischemia, and reperfusion. Gd-DTPA-enhanced MR images acquired 30 minutes after contrast revealed hyperenhancement of AI (294+/-96% of normal, P<0.001) but not of RII (98+/-6% of normal, P = NS). Eight weeks later, the chronically infarcted region again hyperenhanced (253+/-54% of normal, n = 8, P<0.001). High-resolution (0.5 x 0.5 x 0.5 mm) ex vivo MRI demonstrated that the spatial extent of hyperenhancement was the same as the spatial extent of myocyte necrosis with and without reperfusion at 1 day (R = 0.99, P<0.001) and 3 days (R = 0.99, P<0.001) and collagenous scar at 8 weeks (R = 0.97, P<0.001). CONCLUSIONS In the pathophysiologies investigated, contrast MRI distinguishes between reversible and irreversible ischemic injury independent of wall motion and infarct age.

Contrast-enhanced MRI and routine single photon emission computed tomography (SPECT) perfusion imaging for detection of subendocardial myocardial infarcts: an imaging study

BACKGROUND Myocardial infarcts are routinely detected by nuclear imaging techniques such as single photon emission computed tomography (SPECT) myocardial perfusion imaging. A newly developed technique for infarct detection based on contrast-enhanced cardiovascular magnetic resonance (CMR) has higher spatial resolution than SPECT. We postulated that this technique would detect infarcts missed by SPECT. METHODS We did contrast-enhanced CMR and SPECT examinations in 91 patients with suspected or known coronary artery disease. All CMR and SPECT images were scored, using a 14-segment model, for the presence, location, and spatial extent of infarction. To compare each imaging modality to a gold standard, we also acquired contrast-enhanced CMR and SPECT images in 12 dogs with, and three dogs without, myocardial infarction as defined by histochemical staining. FINDINGS In animals, contrast-enhanced CMR and SPECT detected all segments with nearly transmural infarction (>75% transmural extent of the left-ventricular wall). CMR also identified 100 of the 109 segments (92%) with subendocardial infarction (<50% transmural extent of the left-ventricular wall), whereas SPECT identified only 31 (28%). SPECT and CMR showed high specificity for the detection of infarction (97% and 98%, respectively). In patients, all segments with nearly transmural infarction, as defined by contrast-enhanced CMR, were detected by SPECT. However, of the 181 segments with subendocardial infarction, 85 (47%) were not detected by SPECT. On a per patient basis, six (13%) individuals with subendocardial infarcts visible by CMR had no evidence of infarction by SPECT. INTERPRETATION SPECT and CMR detect transmural myocardial infarcts at similar rates. However, CMR systematically detects subendocardial infarcts that are missed by SPECT.

Visualisation of presence, location, and transmural extent of healed Q-wave and non-Q-wave myocardial infarction

BACKGROUND A technical advance in contrast-enhanced magnetic resonance imaging (MRI) has significantly improved image quality. We investigated whether healed myocardial infarction can be visualised as hyperenhanced regions with this new technique, and whether assessment of the transmural extent of infarction yields new physiological data. METHODS 82 MRI examinations were carried out in three groups: patients with healed myocardial infarction; patients with non-ischaemic cardiomyopathy; and healthy volunteers. Patients with healed myocardial infarction were prospectively enrolled after enyzmatically proven necrosis and imaged 3 months (SD 1) or 14 months (7) later. The MRI procedure used a segmented inversion-recovery gradient-echo sequence after gadolinium administration. Findings were compared with those of coronary angiography, electrocardiography, cine MRI, and creatine kinase measurements. FINDINGS 29 (91%) of 32 patients with infarcts imaged at 3 months (13 non-Q-wave) and all of 19 imaged at 14 months (eight non-Q-wave) showed hyperenhancement. In patients in whom the infarct-related-artery was identified by angiography, 24 of 25 imaged at 3 months and all of 14 imaged at 14 months had hyperenhancement in the appropriate territory. None of the 20 patients with non-ischaemic cardiomyopathy or the 11 healthy volunteers showed hyperenhancement. Irrespective of the presence or absence of Q waves, the majority of patients with hyperenhancement had only non-transmural involvement. Normal left-ventricular contraction was shown in seven patients examined at 3 months and three examined at 14 months, but in these cases hyperenhancement was limited to the subendocardium. INTERPRETATION The presence, location, and transmural extent of healed Q-wave and non-Q-wave myocardial infarction can be accurately determined by contrast-enhanced MRI.

Myocardial Gd-DTPA Kinetics Determine MRI Contrast Enhancement and Reflect the Extent and Severity of Myocardial Injury After Acute Reperfused Infarction

BACKGROUND Contrast medium-enhanced magnetic resonance images of acute, reperfused infarcts have shown hypoenhanced and hyperenhanced regions in areas of injured myocardium. The precise mechanisms that lead to these altered enhancement patterns are unknown. This study was designed to evaluate possible mechanisms and to relate altered enhancement patterns to myocardial perfusion and viability. METHODS AND RESULTS Thirteen rabbits underwent in situ coronary artery occlusion and reperfusion followed by isolated perfusion with cardioplegic solution. T1-weighted spin-echo images were acquired continuously during step changes in perfusate Gd-DTPA concentration. Regional blood flow was also measured by use of radioactive microspheres in all rabbits. There were marked differences in Gd-DTPA wash-in and washout time constants (wash-in, 0.8 +/- 0.1, 2.1 +/- 02, and 16.3 +/- 2.4 minutes, P < .001; washout, 1.6 +/- 0.1, 4.8 +/- 0.5, and 31.1 +/- 3.3 minutes, P < .001) in normal, infarct rim, and infarct core regions, respectively, resulting in differential enhancement of these regions. Microsphere flows in the infarct rim and core were 42.9 +/- 4.0% and 12.0 +/- 1.6% of normal myocardium and correlated well with washout time constants (r = .86, y = 0.77x - 0.002, P < .001), suggesting that these time constants index the severity of microvascular damage. In addition, spatial maps of washout time constants were produced. The extent of regions with abnormal time constants correlated well with triphenyltetrazolium chloride-determined infarct size (r = .94, y = 0.95x + 4.17, P < .001). CONCLUSIONS In contrast-enhanced magnetic resonance images of acute, reperfused rabbit infarcts, differential image intensity is primarily due to regional differences in contrast agent wash-in and washout time constants. These regional differences in time constants also indicate the extent and severity of myocardial injury.

Myocardial scarring in asymptomatic or mildly symptomatic patients with hypertrophic cardiomyopathy

OBJECTIVES We sought to ascertain whether myocardial scarring occurs in living unselected patients with hypertrophic cardiomyopathy (HCM). BACKGROUND Myocardial scarring is known to occur in select HCM patients, who were highly symptomatic prior to death or who died suddenly. The majority of HCM patients, however, are minimally symptomatic and have not suffered sudden death. METHODS Cine and gadolinium-enhanced magnetic resonance imaging was performed in 21 HCM patients who were predominantly asymptomatic. Gadolinium hyperenhancement was assumed to represent myocardial scar, and the extent of scar was compared to left ventricular (LV) morphology and function. RESULTS Scarring was present in 17 patients (81%). Scarring occurred only in hypertrophied regions (> or =10 mm), was patchy with multiple foci, and predominantly involved the middle third of the ventricular wall. All 17 patients had scarring at the junction of the interventricular septum and the right ventricular (RV) free wall. On a regional basis, the extent of scarring correlated positively with wall thickness (r = 0.36, p < 0.0001), and inversely with wall thickening (r = -0.21, p < 0.0001). On a per patient basis, the extent of scarring (mean, 8 +/- 9% of LV mass) was minimally related to maximum wall thickness (r = 0.40, p = 0.07) and LV mass (r = 0.33, p = 0.15), and correlated inversely with ejection fraction (r = -0.46, p = 0.04). CONCLUSIONS Myocardial scarring is common in asymptomatic or mildly symptomatic HCM patients who have not suffered sudden death. When present, scarring occurs in hypertrophied regions, is consistently localized to the junctions of the septum and RV free wall, and correlates positively with regional hypertrophy and inversely with regional contraction.

Contrast-enhanced magnetic resonance imaging of myocardium at risk ☆: Distinction between reversible and irreversible injury throughout infarct healing

OBJECTIVES We sought to determine the relationship of delayed hyperenhancement by contrast magnetic resonance imaging (MRI) to viable and nonviable myocardium within the region at risk throughout infarct healing. BACKGROUND The relationship of delayed MRI contrast enhancement patterns to injured but viable myocardium within the ischemic bed at risk has not been established. METHODS We compared in vivo and ex vivo MRI contrast enhancement to histopathologic tissue sections encompassing the entire left ventricle in dogs (n = 24) subjected to infarction with (n = 12) and without (n = 12) reperfusion at 4 h, 1 day, 3 days, 10 days, 4 weeks and 8 weeks. In vivo MR imaging was performed 30 min after contrast injection. RESULTS The sizes and shapes of in vivo myocardial regions of elevated image intensity (828+/-132% of remote) were the same as those observed ex vivo (241 slices, r = 0.99, bias = 0.05+/-1.6% of left ventricle [LV]). Comparison of ex vivo MRI to triphenyltetrazolim chloride-stained sections demonstrated that the spatial extent of hyperenhancement was the same as the spatial extent ofinfarction at every stage of healing (510 slices, lowest r = 0.95, largest bias = 1.7+/-2.9% of LV). Conversely, hyperenhanced regions were smaller than the ischemic bed at risk defined by fluorescent microparticles at every stage of healing (239 slices, 35+/-24% of risk region, p<0.001). Image intensities of viable myocardium within the risk region were the same as those of remote, normal myocardium (102+/-9% of remote, p = NS). CONCLUSIONS Delayed contrast enhancement by MRI distinguishes between viable and nonviable regions within the myocardium at risk throughout infarct healing.

Standardized cardiovascular magnetic resonance imaging (CMR) protocols, society for cardiovascular magnetic resonance: board of trustees task force on standardized protocols

AbstractIndex1. General techniques 1.1. Stress and safety equipment1.2. Left ventricular (LV) structure and function module1.3. Right ventricular (RV) structure and function module1.4. Gadolinium dosing module.1.5. First pass perfusion1.6. Late gadolinium enhancement (LGE) 2. Disease specific protocols2.1. Ischemic heart disease 2.1.1. Acute myocardial infarction (MI)2.1.2. Chronic ischemic heart disease and viability2.1.3. Dobutamine stress2.1.4. Adenosine stress perfusion 2.2. Angiography: 2.2.1. Peripheral magnetic resonance angiography (MRA)2.2.2. Thoracic MRA2.2.3. Anomalous coronary arteries2.2.4. Pulmonary vein evaluation 2.3. Other 2.3.1. Non-ischemic cardiomyopathy2.3.2. Arrhythmogenic right ventricular cardiomyopathy (ARVC)2.3.3. Congenital heart disease2.3.4. Valvular heart disease2.3.5. Pericardial disease2.3.6. Masses

Standardized image interpretation and post processing in cardiovascular magnetic resonance: Society for Cardiovascular Magnetic Resonance (SCMR) Board of Trustees Task Force on Standardized Post Processing

With mounting data on its accuracy and prognostic value, cardiovascular magnetic resonance (CMR) is becoming an increasingly important diagnostic tool with growing utility in clinical routine. Given its versatility and wide range of quantitative parameters, however, agreement on specific standards for the interpretation and post-processing of CMR studies is required to ensure consistent quality and reproducibility of CMR reports. This document addresses this need by providing consensus recommendations developed by the Task Force for Post Processing of the Society for Cardiovascular MR (SCMR). The aim of the task force is to recommend requirements and standards for image interpretation and post processing enabling qualitative and quantitative evaluation of CMR images. Furthermore, pitfalls of CMR image analysis are discussed where appropriate.

Reproducibility of Chronic Infarct Size Measurement by Contrast-Enhanced Magnetic Resonance Imaging

Background—The reproducibility of contrast-enhanced MRI has not been established. We compared MRI reproducibility for infarct size determination with that of 99mTc-sestamibi (MIBI) single photon emission computed tomography (SPECT). Methods and Results—Patients with chronic myocardial infarction defined by enzymes (peak creatine kinase-MB 173±119 U/L) were scanned twice by MRI (MRI I and MRI II, n=20) and twice by SPECT (SPECT I and SPECT II, n=15) on the same day. The MRI contrast agent was injected during MRI I but not MRI II to test the effect of imaging time after contrast. Resting Tc-MIBI SPECT images were acquired and infarct size was determined with commercial software. Infarct size in patients scanned by MRI and SPECT was 14±6% of left ventricular mass (%LV) by MRI (range 4%LV to 27%LV) and 14±7%LV by SPECT (range 4%LV to 26%LV). MRI I and II scans were performed 10±2 and 27±3 minutes after contrast, respectively. For MRI, the difference in infarct size between scans I and II (bias) was −0.1%LV, and the coefficient of repeatability was ±2.4%LV. For SPECT, bias was −1.3%LV, and the coefficient of repeatability was ±4.0%LV. Within individual patients, no systematic differences in infarct size were detected when the 2 MRI scans were compared, the 2 SPECT scans were compared, or MRI was compared to SPECT. Conclusion—The size of healed infarcts measured by contrast-enhanced MRI does not change between 10 and 30 minutes after contrast. The clinical reproducibility of contrast-enhanced MRI for infarct size determination compares favorably with that of routine clinical SPECT.