Detecting left ventricular myocardial ischemia during intravenous dobutamine with cardiovascular magnetic resonance imaging (MRI).

Advances in computer software, scanner hardware, and hemodynamic monitoring equipment have permitted the development of cardiovascular stress testing protocols for use during intravenous Dobutamine infusions within magnetic resonance imaging (MRI) scanners. Recent studies have documented that the safety profile and clinical utility of Dobutamine/Atropine cardiac stress testing during MRI compares favorably with other noninvasive stress imaging modalities and is particularly useful in patients not well suited for stress echocardiograms.

Cardiac cycle-dependent changes in aortic area and distensibility are reduced in older patients with isolated diastolic heart failure and correlate with exercise intolerance.

OBJECTIVES: The goal of this study was to determine if cardiac cycle-dependent changes in proximal thoracic aortic area and distensibility are associated with exercise intolerance in elderly patients with diastolic heart failure (DHF). BACKGROUND: Aortic compliance declines substantially with age. We hypothesized that a reduction in cardiac cycle-dependent changes in thoracic aortic area and distensibility (above that which occurs with aging) could be associated with the exercise intolerance that is prominent in elderly diastolic heart failure patients. METHODS: Thirty subjects (20 healthy individuals [10 < 30 years of age and 10 > 60 years of age] and 10 individuals > the age of 60 years with DHF) underwent a magnetic resonance imaging (MRI) study of the heart and proximal thoracic aorta followed within 48 h by maximal exercise ergometry with expired gas analysis. RESULTS: The patients with DHF had higher resting brachial pulse and systolic blood pressure, left ventricular mass, aortic wall thickness and mean aortic flow velocity, and, compared with healthy older subjects, they had a significant reduction in MRI-assessed cardiac cycle-dependent change in aortic area and distensibility (p < 0.0001) that correlated with diminished peak exercise oxygen consumption (r = 0.79). After controlling for age and gender in a multivariate analysis, thoracic aortic distensibility was a significant predictor of peak exercise oxygen consumption (p < 0.04). CONCLUSIONS: Older patients with isolated DHF have reduced cardiac cycle-dependent changes in proximal thoracic aortic area and distensibility (beyond that which occurs with normal aging), and this correlates with and may contribute to their severe exercise intolerance.

Metastatic involvement of the heart and pericardium: CT and MR imaging.

Metastases to the heart and pericardium are much more common than primary cardiac tumors and are generally associated with a poor prognosis. Tumors that are most likely to involve the heart and pericardium include cancers of the lung and breast, melanoma, and lymphoma. Tumor may involve the heart and pericardium by one of four pathways: retrograde lymphatic extension, hematogenous spread, direct contiguous extension, or transvenous extension. Metastatic involvement of the heart and pericardium may go unrecognized until autopsy. Impairment of cardiac function occurs in approximately 30% of patients and is usually attributable to pericardial effusion. The clinical presentation includes shortness of breath, which may be out of proportion to radiographic findings in patients with pericardial effusion or may be the result of associated pleural effusion. Patients may also present with cough, anterior thoracic pain, pleuritic chest pain, or peripheral edema. The differential diagnosis of pericardial effusion in a patient with known malignancy includes malignant pericardial effusion, radiation-induced pericarditis, drug-induced pericarditis, and idiopathic pericarditis. Any disease process that causes thickening or nodularity of the pericardium or myocardium or masses within the cardiac chambers can mimic metastatic disease.

Is imaging at intermediate doses necessary during dobutamine stress magnetic resonance imaging?

To determine if visualization of left ventricular contraction throughout the course of a pharmacologic stress test performed with magnetic resonance imaging (MRI) (rather than solely at baseline and peak stress) is necessary, we retrospectively reviewed dobutamine MRI results in 469 consecutively referred patients for diagnosis of inducible ischemia. At each stage of pharmacologic stress, six image planes of the heart were viewed and left ventricular wall motion was scored as normal, hypokinetic, akinetic, or dyskinetic. Inducible ischemia was identified in 102 patients; in 39 patients (38%), evidence of ischemia occurred before receiving high doses of dobutamine. During testing, 103 patients developed chest discomfort consistent with angina, but only 26 of the 103 patients (25%) developed new wall motion abnormalities indicative of ischemia. Continuous image acquisition and review during dobutamine MRI pharmacologic stress testing provides a mechanism to detect ischemia and avoid premature test termination during the early stages of the procedure. Compared with protocols that image only at baseline and at peak stress, continuous acquisition and review may enhance the safety and improve the diagnostic accuracy of pharmacologic stress testing during dobutamine MRI.

Assessment of coronary arterial restenosis with phase-contrast magnetic resonance imaging measurements of coronary flow reserve.

BACKGROUND: After successful percutaneous coronary arterial revascularization, 25% to 60% of subjects have restenosis, a recurrent coronary arterial narrowing at the site of the intervention. At present, restenosis is usually detected invasively with contrast coronary angiography. This study was performed to determine if phase-contrast MRI (PC-MRI) could be used to detect restenosis noninvasively in patients with recurrent chest pain after percutaneous revascularization. METHODS AND RESULTS: Seventeen patients (15 men, 2 women, age 36 to 77 years) with recurrent chest pain >3 months after successful percutaneous intervention underwent PC-MRI measurements of coronary artery flow reserve followed by assessments of stenosis severity with computer-assisted quantitative coronary angiography. The intervention was performed in the left anterior descending coronary artery in 15 patients, one of its diagonal branches in 2 patients, and the right coronary artery in 1 patient. A PC-MRI coronary flow reserve value /=70% and >/=50%, respectively. CONCLUSIONS: Assessments of coronary flow reserve with PC-MRI can be used to identify flow-limiting stenoses (luminal diameter narrowings >70%) in patients with recurrent chest pain in the months after a successful percutaneous intervention.

Utility of fast cine magnetic resonance imaging and display for the detection of myocardial ischemia in patients not well suited for second harmonic stress echocardiography.

BACKGROUND: Some patients referred for pharmacological stress testing with transthoracic echocardiography (TTE) are unable to undergo testing owing to poor acoustic windows. Fast cine MRI can be used to assess left ventricular contraction, but its utility for detection of myocardial ischemia in patients poorly suited for echocardiography is unknown. METHODS AND RESULTS: One hundred fifty-three patients (86 men and 67 women aged 30 to 88 years) with poor acoustic windows that prevented adequate second harmonic TTE imaging were consecutively referred for MRI to diagnose inducible myocardial ischemia during intravenous dobutamine and atropine. Diagnostic studies were completed in an average of 53 minutes. No patients experienced myocardial infarction, ventricular fibrillation, exacerbation of congestive heart failure, or death. In patients who underwent computer-assisted quantitative coronary angiography, the sensitivity and specificity for detecting a >50% luminal diameter narrowing were 83% and 83%, respectively. In the 103 patients with a negative MRI examination, the cardiovascular occurrence-free survival rate was 97%. CONCLUSIONS: Fast cine cardiac MRI provides a mechanism to assess left ventricular contraction and diagnose inducible myocardial ischemia in patients not well suited for stress echocardiography.

Visualization and functional assessment of proximal and middle left anterior descending coronary stenoses in humans with magnetic resonance imaging.

BACKGROUND: Coronary artery bypass grafting improves survival in patients with >70% luminal diameter narrowing of the 3 major epicardial coronary arteries, particularly if there is involvement of the proximal portion of the left anterior descending (LAD) coronary artery. Measurement of coronary flow reserve can be used to identify functionally important luminal narrowing of the LAD artery. Although magnetic resonance imaging (MRI) has been used to visualize coronary arteries and to measure flow reserve noninvasively, the utility of MRI for detecting significant LAD stenoses is unknown. METHODS AND RESULTS: Thirty subjects (23 men, 7 women, age 36 to 77 years) underwent MRI visualization of the left main and LAD coronary arteries as well as measurement of flow in the proximal, middle, or distal LAD both at rest and after intravenous adenosine (140 microgram/kg per minute). Immediately thereafter, contrast coronary angiography and when feasible, intracoronary Doppler assessments of coronary flow reserve, were performed. There was a statistically significant correlation between MRI assessments of coronary flow reserve and (a) assessments of coronary arterial stenosis severity by quantitative coronary angiography and (b) invasive measurements of coronary flow reserve (P<0.0001 for both). In comparison to computer-assisted quantitative coronary angiography, the sensitivity and specificity of MRI for identifying a stenosis >70% in the distal left main or proximal/middle LAD arteries was 100% and 83%, respectively. CONCLUSIONS: Noninvasive MRI measures of coronary flow reserve correlated well with similar measures obtained with the use of intracoronary Doppler flow wires and predicted significant coronary stenoses (>70%) with a high degree of sensitivity and specificity. MRI-based measurement of coronary flow reserve may prove useful for identification of patients likely to obtain a survival benefit from coronary artery bypass grafting.

False aneurysm of the pulmonary artery induced by a Swan-Ganz catheter: clinical presentation and radiologic management.

OBJECTIVE: This study evaluates retrospectively the clinical presentation, radiographic findings, and angiographic management of false aneurysm of the pulmonary artery resulting from Swan-Ganz catheter placement. MATERIALS AND METHODS: Over a 4-year period, seven false aneurysms of the pulmonary artery were diagnosed in five patients (four women, one man) who were 67-81 years old. All five patients underwent Swan-Ganz catheter placement to monitor cardiac surgery--coronary artery bypass grafting in four and mitral valve replacement in one. All patients were anticoagulated. For five patients, we reviewed the medical records and the results of chest radiography, digital subtraction pulmonary angiography, and pulmonary artery embolization. For two patients, we reviewed the results of CT scanning. RESULTS: Non-life-threatening hemoptysis was noted in all cases and occurred in three patients after the Swan-Ganz catheter had been removed (elapsed time of 1-19 days). Chest radiographs revealed a pulmonary infiltrate in one patient and a pulmonary mass in two patients. The results were unremarkable in the other two patients. CT depicted two false aneurysms of the pulmonary artery as round masses with eccentrically enhanced lumina circumscribed by thrombosis. Pulmonary angiography revealed a single false aneurysm in three patients and two false aneurysms in two patients. All false aneurysms were localized in segmental or subsegmental branches of the right middle pulmonary artery (n = 4) or the right lower pulmonary artery (n = 3). All patients were successfully treated with transcatheter steel-coil embolization. CONCLUSION: Even when the chest radiograph appears unremarkable, patients clinically suspected of developing a false aneurysm of the pulmonary artery after Swan-Ganz catheter placement require enhanced CT or pulmonary angiography to establish the diagnosis. False aneurysms of the pulmonary artery can be treated at the time of pulmonary angiography by steel-coil embolization.

Three-dimensional MRI of the glenoid labrum.

The objective of this study was to assess the accuracy of three-dimensional (3D) magnetic resonance imaging (MRI) reformation in the evaluation of tears of the glenoid labrum complex (GLC). Fifty-five shoulders were evaluated by MRI using standard spin-echo sequences. Gradient-refocused-echo axial projections were used to assess the GLC on the two-dimensional (2D) studies. Three-dimensional Fourier transform multiplanar gradient-recalled imaging with a resolution of 0.7 mm was also performed in all patients. Independent analyses of the anterior and posterior labra were performed in a blinded manner for both the 2D and 3D studies by three experienced musculoskeletal radiologists. Observations of the imaging studies were compared with the videoarthroscopic findings. The appearance of the GLC was rated on a scale of 0 to 4 (0-2 = normal, 3, 4 = abnormal or torn). The diagnostic confidence was averaged from the three reader's scores. Anterior labral tears were effectively detected with sensitivities of 89% and 96% and specificities of 96% and 100% (P < 0.0001) for the 2D and 3D studies, respectively. For posterior labral tears, the sensitivity and specificity of the 2D method were 47% and 98%, respectively. The sensitivity and specificity of the 3D volume sequence were 53% and 98%, respectively. The lower sensitivity of both imaging methods for detecting posterior labral tears may be influenced by the smaller number (n = 5) of arthroscopically confirmed cases in our study and reflects the difficulty of visualizing the posteroinferior borders of the GLC with present MRI techniques.

MR evaluation of cardiac/juxtacardiac masses.

With its superb contrast resolution, multiplanar imaging capability, and large field of view, magnetic resonance imaging is the gold standard in the imaging evaluation of cardiac and juxtacardiac masses. Spin echo images graphically display the pathoanatomy of intracavitary, valvular, myocardial, pericardial, and juxtacardial masses. Dynamic imaging techniques are used to identify their pathophysiologic consequences on myocardial contraction dynamics, valvular function, or blood flow mechanics. Echocardiography is a good modality to evaluate the heart and in most institutions, remains the initial test in the workup of cardiac masses. However, equivocal echocardiographic studies are common and, in fact, are the leading indication for the use of MR in the workup of cardiac/juxtacardiac masses.

Thoracic aortic disease: evaluation using a single MRA volume series.

OBJECTIVE: Use of MRA for thoracic aortic disease (TAD) evaluation has been limited. This report describes an initial experience with TAD evaluation using a single MRA volume series. MATERIALS AND METHODS: A single volume series, based on sequential 2D TOF MRA, was acquired in 30 cases (28 with suspected TAD and 2 normals). Each series was processed using multiplanar reconstruction (MPR) and maximum intensity projection (MIP); resulting tomographic (one base and two MPR) and MIP sets were blindly interpreted by four reviewers to detect TAD and, if present, to diagnose its specific form. For cases incorrectly interpreted, the standard MR images were subsequently interpreted. RESULTS: The TAD categories included aneurysm (n = 13), dissection (n = 9), and arch anomalies (n = 5). Sensitivities were high for TAD overall (89-100%) and TAD in ascending and descending portions; sensitivities were lower for TAD of the arch (two of four reviewers > or = 90% for TAD overall and descending TAD). Specificities for TAD overall had a wider range (67-100%), but were high for ascending, arch, and descending portions (three to four of four reviewers > or = 90% for each). Sensitivities for aneurysms (69-92%) and dissections overall (67-100%) were comparable, as they were in ascending and arch portions; descending dissection was better detected than descending aneurysm (two of four reviewers > or = 90% for ascending or arch aneurysm and for descending dissection); overall specificities (88-100 vs. 81-95%) and specificities in ascending, arch, and descending portions were also comparable (three to four of four reviewers > or = 90% for both in each portion; two of four reviewers > or = 90% for dissection overall). Each reviewer achieved > or = 70% diagnostic accuracy for TAD (one of four reviewers = 85%); accuracies for each category were comparable. Interpretation of standard MR images corrected all detection and most diagnostic (> or = 63%) errors. CONCLUSION: This initial experience with conventional TOF MRA for TAD evaluation is encouraging, but it indicates the potential for advancements in data acquisition and/or postprocessing.

Patient screening prior to MR imaging: a practical approach synthesized from protocols at 15 U. S. medical centers.

The article by Boutin et al. [1] in this issue of the AJR documents a surprinsingly great variation in the MR screening procedures used at different academic centers throughout the United States. Although considerable literature now exists concerning the MR imaging of patients with ferromagnetic implants, devices, and foreign bodies [2-4], no uniform screening protocol to identify such patients has yet been adopted. The Safety Committee of the Society for Magnetic Resonance Imaging (SMRI) has recommended that "each imaging site should develop a standardized policy for screening patients with suspected metallic foreign bodies" [5]. To date, however, the SMRI has neither proposed nor endorsed a specific screening protocol for general use.

Magnetic resonance imaging of the thoracic aorta.

Magnetic resonance imaging (MRI) is steadily becoming recognized as a premier imaging modality for evaluating the thoracic aorta. Its noninvasive, nonimaging approach and refined resolution capabilities effectively combine the advantages of echocardiography, angiography, and computed tomography (CT) under the auspices of a single imaging device. On static spin-echo MRI, blood flow appears dark, allowing superb depiction of both intra- and extra vascular anatomy. With dynamic MR studies, gradient echo (cine) and phase velocity mapping techniques have proven effective in assessing the physiological consequences of anatomic vascular abnormalities in a qualitative and quantitative manner, respectively. Magnetic resonance angiography (MRA) is fast becoming a prominent vascular imaging method. Although still evolving, MRA bolsters the vascular imaging capabilities of MRI by enhancing the imaging resolution of the major branch vessels and collateral vessels. With continued advances in this area, MRI may adopt the role as the primary imaging method for assessing the thoracic aorta.