Diagnostic Use of T2-Weighted Inversion-Recovery Magnetic Resonance Imaging in Acute Coronary Syndromes Compared With 99mTc-Pyrophosphate, 123I-BMIPP and 201TlCl Single Photon Emission Computed Tomography

Coronary calcification compromises myocardial perfusion irrespective of luminal stenosis

Aim

The aim of this study was to evaluate the relationship between coronary artery calcification (CAC) assessed by multi-detector computed tomography (MDCT) and myocardial perfusion assessed by cardiac magnetic resonance imaging (CMR) in a group of symptomatic patients.

Method

Retrospective analysis of 120 patients (age 65.1 ± 8.9 years, 88 males) who presented with atypical chest pain to Bethanien Hospital, Frankfurt, Germany, between 2007 and 2010 and who underwent CAC scoring using MDCT, CMR, and conventional coronary angiography. Patients were divided into those with high-grade (HG) stenosis (n = 67, age 65.1 ± 9.4 years) and those with no-HG stenosis (n = 53, age 65.1 ± 8.6 years).

Results

There were more males with HG stenosis (82.1% vs. 62.3%, p = 0.015), in whom the percentage and number of abnormal perfusion segments were higher at rest (37.3% vs. 17%, p = 0.014) but not different with stress (p = 0.83) from those with no-HG stenosis. Thirty-four patients had myocardial perfusion abnormalities at rest and 26 patients developed perfusion defects with stress. Stress-induced myocardial perfusion defects were 22.4% sensitive and 79.2% specific for detecting HG stenosis. The CAC score was lower in patients with no-HG stenosis compared to those with HG stenosis (p < 0.0001). On the ROC curve, a CAC score of 293 had a sensitivity of 71.6% and specificity of 83% in predicting HG stenosis [(AUC 0.80 (p < 0.0001)]. A CAC score of 293 or the presence of at least 1 segment myocardial perfusion abnormality was 74.6% sensitive and 71.7% specific in detecting HG stenosis, the respective values for the 2 abnormalities combined being 19.4% and 90.6%. The severity of CAC correlated with the extent of myocardial perfusion in the patient group as a whole with stress (r = 0.22, p = 0.015), particularly in those with no-HG stenosis (r = 0.31, p = 0.022). A CAC score of 293 was 31.6% sensitive and 87.3% specific in detecting myocardial perfusion abnormalities.

Conclusion

In a group of patients with exertional angina, coronary calcification is more accurate in detecting high-grade luminal stenosis than myocardial perfusion defects. In addition, in patients with no stenosis, the incremental relationship between coronary calcium score and the extent of myocardial perfusion suggests coronary wall hardening as an additional mechanism for stress-induced angina other than luminal narrowing. These preliminary findings might have a clinical impact on management strategies of these patients other than conventional therapy.

T2-weighted cardiac MR assessment of the myocardial area-at-risk and salvage area in acute reperfused myocardial infarction: comparison of state-of-the-art dark blood and bright blood T2-weighted sequences

PURPOSE

To compare different state-of-the-art T2-weighted (T2w) imaging sequences combined with late gadolinium enhancement (LGE) for myocardial salvage area (MSA) assessment by cardiac magnetic resonance (CMR). T2w imaging has been used to assess the myocardial area at risk (AAR) in acute myocardial infarction (AMI) patients, but its clinical application is challenging due to technical and physical limitations.

MATERIALS AND METHODS

Thirty patients with reperfused AMI underwent complete CMR imaging 2-5 days after hospital admission. Myocardial AAR and MSA were quantified on four different T2w sequences: (a) free-breathing T2-prepared single-shot balanced steady-state free precession (T2p_ssbSSFP); (b) breathhold T2-weighted acquisition for cardiac unified T2 edema (ACUTE); (c) breathhold T2w dark-blood inversion recovery turbo-spin echo (IR-TSE) (short-term inversion recovery: STIR); and (d) free-breathing high-resolution T2 dark-blood navigated BLADE. The diagnostic performance of each technique was also assessed.

RESULTS

Quantitative analysis showed significant differences in myocardial AAR extent as quantified by the four T2w sequences (P < 0.05). There were also significant differences in sensitivity, specificity and overall diagnostic performance.

CONCLUSION

Detection and quantification of AAR, and thus of MSA, by T2wCMR in reperfused AMI patients varied significantly between different T2w sequences in the same clinical setting.

Myocardium at risk after acute infarction in humans on cardiac magnetic resonance: quantitative assessment during follow-up and validation with single-photon emission computed tomography

OBJECTIVES

Our goal was to validate myocardium at risk on T2-weighted short tau inversion recovery (T2-STIR) cardiac magnetic resonance (CMR) over time, compared with that seen with perfusion single-photon emission computed tomography (SPECT) in patients with ST-segment elevation myocardial infarction, and to assess the amount of salvaged myocardium after 1 week.

BACKGROUND

To assess reperfusion therapy, it is necessary to determine how much myocardium is salvaged by measuring the final infarct size in relation to the initial myocardium at risk of the left ventricle (LV).

METHODS

Sixteen patients with first-time ST-segment elevation myocardial infarction received (99m)Tc tetrofosmin before primary percutaneous coronary intervention. SPECT was performed within 4 h and T2-STIR CMR within 1 day, 1 week, 6 weeks, and 6 months. At 1 week, patients were injected with a gadolinium-based contrast agent for quantification of infarct size.

RESULTS

Myocardium at risk at occlusion on SPECT was 33 +/- 10% of the LV. Myocardium at risk on T2-STIR did not differ from SPECT, at day 1 (29 +/- 7%, p = 0.49) or week 1 (31 +/- 6%, p = 0.16) but declined at week 6 (10 +/- 12%, p = 0.0096 vs. 1 week) and month 6 (4 +/- 11%, p = 0.0013 vs. 1 week). There was a correlation between myocardium at risk demonstrated by T2-STIR at week 1 and myocardium at risk by SPECT (r(2) = 0.70, p < 0.001), and the difference between the methods on Bland-Altman analysis was not significant (-2.3 +/- 5.7%, p = 0.16). Both modalities identified myocardium at risk in the same perfusion territory and in concordance with angiography. Final infarct size was 8 +/- 7%, and salvage was 75 +/- 19% of myocardium at risk.

CONCLUSIONS

This study demonstrates that T2-STIR performed up to 1 week after reperfusion can accurately determine myocardium at risk as it was before opening of the occluded artery. CMR can also quantify salvaged myocardium as myocardium at risk minus final infarct size.

Acute oedema in the evaluation of microvascular reperfusion and myocardial salvage in reperfused myocardial infarction with cardiac magnetic resonance imaging

The accurate measurement of myocardial salvage is critical to the ongoing refinement of reperfusion strategies in acute myocardial infarction (AMI). Cardiac magnetic resonance imaging (CMR) can define the area at risk in AMI by the presence of myocardial oedema, identified by high signal intensity on T(2)-weighted imaging with a short inversion time inversion-recovery (STIR) sequence. In addition, myocardial necrosis can be identified with CMR delayed contrast enhanced imaging. In this prospective study we examined the relationship of acute oedema and necrosis with impaired microvascular reperfusion. We also evaluated acute oedema as a marker of the area at risk in AMI, for the purposes of documenting myocardial salvage. CMR was performed on 15 patients with (AMI), within 24h of successful percutaneous coronary intervention (PCI). Left ventricular (LV) systolic dysfunction was defined by a systolic thickening <40% (severe <20%). Microvascular reperfusion was evaluated during the acute phase of contrast wash-in. CMR was repeated 3 months post-PCI to evaluate recovery of LV function and final infarct size. Myocardial salvage was defined as the percentage of the area at risk that was not infarcted on follow up CMR. There was a significant correlation between impaired microvascular reperfusion and the extent of segmental oedema (R=0.363, P<0.01), but not myocardial necrosis (R=0.110, P>0.5). The extent of myocardial salvage correlated with recovery of systolic function (R=0.241, P<0.05), which was strongest in LV segments with severely reduced systolic function (R=0.422, P<0.01).

CONCLUSIONS

In acutely reperfused AMI, oedema can be used to identify the area at risk for the purpose of calculating myocardial salvage. The correlation between myocardial oedema and reperfusion status suggests a pathological role of acute oedema in the impairment of microvascular reperfusion.

A new imaging modality in detection of caustic oesophageal injury: Technetium-99m pyrophosphate scintigraphy

OBJECTIVES

Early oesophagoscopy is usually recommended in children after caustic ingestion to assess the severity of the initial digestive lesions. An oesophagoscopic procedure in children always demands to be performed under sedation and bears a certain risk of iatrogenic injury. The purpose of the study is to determine the value and sensitivity of Tc-99m pyrophosphate (99mTc-PYP) scintigraphy for the detection of caustic oesophageal injury.

METHODS

The caustic oesophageal burns were created with 25% NaOH in an experimental rat model. Seventeen rats were divided into two groups. The BURN group (n=9) included caustic oesophageal burning rats. Non-BURN group (n=8) included sham-operated rats. All animals underwent 99mTc-PYP scintigraphy 72 h after the burning experiment. Anterior static and single-photon emission computed tomography images were obtained using a low-energy all-purpose collimator, 2.55 zoom factor, 3h after intravenous injection of 10 mCi 99mTc-PYP. After the imaging, all the oesophagi were explored for external determination of the injury sites and macroautoradiographic scintigraphy as well. Rectangular region of interest were placed in the visually determined lesion of oesophagus (O) as well as non-lesion area (N), and an ON ratio was created. The severity and extension of oesophageal burn were assessed 3 days after burning by histopathologic evaluation. The injuries were graded according to the ulcer depth, ulcer width, thrombus formation, and the development of perivascular fibrinoid necrosis.

RESULTS

The oesophageal burning areas were demonstrated by visual evaluation of the Tc-99m PYP scintigraphy on all animals. The mean ON ratio of 99mTc-PYP was 21.61+/-7.01 in the BURN group and in the non-BURN group, was 2.25+/-0.24 (p<0.001). The best cut-off point of the ON ratio for caustic oesophageal injury was 5.45, with sensitivity and specificity of 100%. PYP scan findings were also confirmed by histological evidence of ulcer depth, ulcer width, thrombus formation, and perivascular fibrinoid necrosis in the same areas.

CONCLUSIONS

The caustic oesophageal injuries have been demonstrated by 99mTc-PYP scintigraphy in burning experiment. 99mTc-PYP scintigraphy is sensitive for detection of caustic oesophageal injury. This new imaging tool is found to be sensitive and specific for the detection of caustic oesophageal injury in the rats.

Delayed enhancement morphology on cardiac magnetic resonance imaging is correlated with signal-averaged electrocardiogram and QT dispersion in myocardial infarction

BACKGROUND

In patients with myocardial infarction, ventricular tachycardia is related with nonconductive ventricular scar. Cardiac magnetic resonance imaging is an excellent modality to evaluate myocardial scars in myocardial infarction. Furthermore, late potential obtained from signal-averaged electrocardiogram and QT dispersion are both well-known parameters for predicting lethal arrhythmias.

METHODS AND RESULTS

To investigate whether the pattern of necrotic scar tissue visualized by delayed enhancement on cardiac magnetic resonance imaging is associated with late potential and QT dispersion, we measured late potential and QT dispersion in 27 patients (68 +/- 8 years old) with a prior myocardial infarction. Cardiac magnetic resonance imaging was also obtained using a 1.5-tesla cardiac magnetic resonance scanner, and delayed enhancement was analyzed in the short axis of the left ventricle. By conducting this, we tried to determine whether the pattern of necrotic scar tissue predicts lethal ventricular arrhythmias. Semiquantitative patchy scores were identified as the mean patchy score and the maximum patchy score in each patient. There were 9 patients with a positive late potential and 18 patients with a negative late potential. Patients with positive late potentials had significantly larger mean (1.7 +/- 0.3) and maximum (2.2 +/- 0.6) patchy scores than patients with negative late potentials (mean, 1.3 +/- 0.2, P < .05; maximum, 1.7 +/- 0.4, P < .05). QT dispersion was significantly correlated with the number of slices showing delayed enhancement, which reflects the size of necrotic scar tissue (r = .59, P < .05).

CONCLUSIONS

These findings suggest that the pattern of necrotic scar tissue visualized by delayed enhancement with cardiac magnetic resonance imaging was correlated to the predictive indices of lethal ventricular arrhythmias.

[Comparsion with myocardial perfusion MRI and myocardial perfusion SPECT in the diagnostic performance of coronary artery disease: a meta-analysis]

We compared the diagnostic abilities of stress myocardial perfusion MRI (myocardial perfusion MRI) and myocardial perfusion SPECT, using a meta-analysis method. We investigated the diagnostic abilities of MRI and SPECT in similar subject groups in reports written in English or Japanese. The reports to be used for analysis were selected according to a "screening standard," which was established in advance. After consolidating the data from the selected reports, we compared (1) the integrated odds ratio, (2) the point estimation values of sensibility/specificity, and (3) the summary ROC curve. For the analysis, six reports were selected (subjects: 153, coronary-artery target sites: 447). Meta-analysis revealed that the diagnostic ability of myocardial perfusion MRI was superior to that of myocardial perfusion SPECT regarding each of the parameters (1)-(3). This is considered to be supportive evidence of the usefulness of myocardial perfusion MRI.

Emergency cardiac imaging: state of the art

Multiple strategies and testing modalities are available to evaluate patients presenting to the emergency department with cardiac complaints. Many provide anatomic and prognostic information about coronary stenosis and long-term out-comes. Although nuclear and stress echo imaging have the ability to predict outcomes in patients in the emergency department population, the newer modalities of cardiac imaging (EBCT, MDCT,and CMR) continue to show promising results and may soon be incorporated into emergency department chest pain centers. Protocols can be developed within an institution to meet the needs of the patient population while minimizing risk and improving outcomes for all patients.

Usefulness of cardiac magnetic resonance imaging for detecting acute myocardial infarction in patients with no significant electrocardiogram changes

A 73-year-old man presented with suspected acute myocardial infarction at the outpatient clinic. However, the clinical symptoms and the laboratory findings were not diagnostic. Only emergency cardiac magnetic resonance imaging (MRI) was helpful in making a definitive diagnosis of acute myocardial infarction. Cardiac MRI is a useful diagnostic tool for suspected acute coronary syndrome in emergency room settings when conventional modalities do not provide a definitive diagnosis.

Usefulness of Delayed Enhancement Magnetic Resonance Imaging for Detecting Cardiac Rupture Caused by Small Myocardial Infarction in a Case of Cardiac Tamponade

Delayed enhancement magnetic resonance imaging (DE-MRI) has excellent spatial resolution and compared with other cardiac imaging techniques it can detect a small myocardial infarction (MI) or a subendocardial infarction. A 76-year-old man was admitted for loss of consciousness because of cardiac tamponade. The cause of tamponade was unknown, but electrocardiography and blood test suggested a recent MI. The removal of 100 ml bloody fluid by immediate pericardiocentesis normalized his hemodynamics, and he regained consciousness. Neither echocardiography nor scintigraphy could determine the location of the MI or rupture, but DE-MRI clearly demonstrated a transmural enhancement in a very narrow range of the lateral wall of the left ventricle. Coronary angiography revealed a severely stenotic lesion in the obtuse marginal branch of the left circumflex artery. DE-MRI is a powerful tool for diagnosing small MI that are undetectable with other imaging. Therefore, DE-MRI should be applied in cases with cardiac tamponade by unknown causes.