Cardiac stress MR imaging with dobutamine

Guideline for Cardiovascular Magnetic Resonance Imaging from the Korean Society of Cardiovascular Imaging-Part 1: Standardized Protocol

Cardiac magnetic resonance (CMR) imaging is widely used in many areas of cardiovascular disease assessment. This is a practical, standard CMR protocol for beginners that is designed to be easy to follow and implement. This protocol guideline is based on previously reported CMR guidelines and includes sequence terminology used by vendors, essential MR physics, imaging planes, field strength considerations, MRI-conditional devices, drugs for stress tests, various CMR modules, and disease/symptom-based protocols based on a survey of cardiologists and various appropriate-use criteria. It will be of considerable help in planning and implementing tests. In addressing CMR usage and creating this protocol guideline, we particularly tried to include useful tips to overcome various practical issues and improve CMR imaging. We hope that this document will continue to standardize and simplify a patient-based approach to clinical CMR and contribute to the promotion of public health.

Role of cardiac magnetic resonance in the evaluation of dilated cardiomyopathy: diagnostic contribution and prognostic significance

Dilated cardiomyopathy (DCM) represents the final common morphofunctional pathway of various pathological conditions in which a combination of myocyte injury and necrosis associated with tissue fibrosis results in impaired mechanical function. Recognition of the underlying aetiology of disease and accurate disease monitoring may be crucial to individually optimize therapeutic strategies and stratify patient's prognosis. In this regard, CMR has emerged as a new reference gold standard providing important information for differential diagnosis and new insight about individual risk stratification. The present review article will focus on the role of CMR in the evaluation of present condition, analysing respective strengths and limitations in the light of current literature and technological developments.

[Diagnosis and therapy of chronic myocardial ischemia. Role of cardiac magnetic resonance imaging]

In patients with chronic coronary artery disease different therapeutic strategies, such as optimal medical therapy, revascularization by percutaneous coronary intervention or coronary artery bypass grafting have been shown to improve the prognosis and symptoms and yield proven superiority over other treatment strategies in different patient populations. Thus, individual assessment of cardiac function and structure is of paramount importance to choose the optimal therapeutic strategy and subsequently improve patient prognosis. In this setting cardiac magnetic resonance imaging (CMR) has been shown to provide important diagnostic information. Myocardial ischemia can be detected by either perfusion stress CMR demonstrating perfusion deficits indicative of hemodynamically relevant coronary artery stenosis or dobutamin stress CMR for objectifying wall motion abnormalities during stress. Both techniques are superior to single photon emission computerized tomography and stress echocardiography in specific patient populations. Myocardial viability can be assessed by means of end-diastolic wall thickness or delayed enhancement imaging which allows quantification of the transmural extent of scarring. Furthermore, low-dose dobutamin stress CMR can detect a contractile reserve. Delayed enhancement imaging leads to accurate results due to its high resolution, can be performed at rest requiring no stress within a short time period and is easy to analyze. Thus this technique can be recommended as the favored technique to assess myocardial viability. In the following article the CMR techniques for ischemia and viability testing will be presented and their role in diagnosis and therapy of chronic myocardial ischemia will be discussed.

MRI and CT in the diagnosis of coronary artery disease: indications and applications

In recent years, technical advances and improvements in cardiac computed tomography (CT) and cardiac magnetic resonance imaging (MRI) have provoked increasing interest in the potential clinical role of these techniques in the non-invasive work-up of patients with suspected coronary artery disease (CAD) and correct patient selection for these emerging imaging techniques. In the primary detection or exclusion of significant CAD, e.g. in the patient with unspecific thoracic complaints, and also in patients with known CAD or advanced stages of CAD, both CT and MRI yield specific advantages. In this review, the major aspects of non-invasive MR and CT imaging in the diagnosis of CAD will be discussed. The first part describes the clinical value of contrast-enhanced non-invasive CT coronary angiography (CTCA), including the diagnostic accuracy of CTCA for the exclusion or detection of significant CAD with coronary artery stenoses that may require angioplastic intervention, as well as potentially valuable information on the coronary artery vessel wall. In the second section, the potential of CT for the imaging of myocardial viability and perfusion will be highlighted. In the third and final part, the range of applications of cardiac MRI in CAD patients will be outlined.

Cintilografia de perfusão miocárdica sob baixa dose de dobutamina na identificação do miocárdio viável

OBJETIVO: Verificar se a cintilografia de perfusão miocárdica duoisotópica(99mTc-sestamibi/tálio-201), método de alta sensibilidade para identificação do músculo viável, tem sua especificidade aumentada com a inclusão de informações sobre reserva contrátil miocárdica obtidas simultaneamente através de gated SPECT na vigência de baixas doses de dobutamina de forma semelhante ao ecocardiograma. MATERIAIS E MÉTODOS: Estudaram-se 260 segmentos miocárdicos de 13 pacientes com infarto do miocárdio, encaminhados para pesquisa de viabilidade antes do procedimento de revascularização. Avaliaram-se a integridade celular e a reserva contrátil pela cintilografia de perfusão miocárdica duoisotópica com imagens de repouso e redistribuição do tálio-201 e de estresse (99mTc-sestamibi gated SPECT), em condições basais e na vigência de baixas doses de dobutamina. A melhora do desempenho contrátil em controle cintilográfico pós-revascularização (99mTc-sestamibi gated SPECT) confirmava a presença de viabilidade. Para análise dos resultados quantificaram-se os parâmetros funcionais dos segmentos miocárdicos nas diferentes etapas do estudo, estratificando-os quanto à viabilidade para posterior comparação funcional pós-revascularização. RESULTADOS: No tratamento estatístico a análise do espessamento sistólico se destacou como parâmetro de avaliação da reserva contrátil miocárdica pelo método, mostrando tendência a incremento na especificidade (84%), demonstrando valores superiores aos da literatura. CONCLUSÃO: O método tende a apresentar contribuições efetivas na busca do miocárdio viável.

Comparative analysis of cardiac magnetic resonance viability indexes to predict functional recovery after successful percutaneous coronary intervention in acute myocardial infarction

The aim of this study was to examine the relative value and the influence of the association of 4 cardiac magnetic resonance (CMR) viability indexes for predicting segmental functional recovery after optimal pharmacologic therapies and early percutaneous coronary intervention in acute myocardial infarction (AMI). CMR has been shown to predict functional recovery after AMI. The relative predictive value of CMR viability indexes remains disputed and has not been described in AMI reperfused within the first 12 hours. Sixty-nine patients with a first reperfused (<12 hours) Thrombolysis In Myocardial Infarction grade 3 AMI (61 men, 57.6 +/- 12.6 years) were studied on day 5 +/- 2. Low-dose (10 microg/kg/min) dobutamine response (DOB), microvascular obstruction (MVO), relative delayed enhancement extent (DE), and transmural DE pattern (TMDE) were assessed in each of the 17 left ventricular segments. Segmental functional outcome was assessed by CMR at 3 months. Logistic regression and Bayesian probabilities evaluated the association between viability indexes and functional segmental outcome. At rest, 27% of segments (314 of 1,173) were dysfunctional of which 53% (165 of 314) recovered at follow-up. Odd ratios for dobutamine response, MVO, DE, and TMDE were 15.8, 5.9, 2.6, and 2.5 respectively. The probability of segmental recovery was 0.84 when dobutamine response was positive and increased successively to 0.91 when adding MVO absence, 0.94 when adding TMDE absence, and 0.97 when adding DE absence. In conclusion, contractile response to low-dose dobutamine is the best predictive factor of segmental recovery after Thrombolysis In Myocardial Infarction grade 3 early reperfused AMI. Its value is further increased by other CMR viability indexes.

Accelerated two- and three-dimensional cine MR imaging of the heart by using a 32-channel coil

PURPOSE

To compare accelerated real-time two-dimensional (2D) and segmented three-dimensional (3D) cine steady-state free precession magnetic resonance (MR) imaging techniques by using a 32-channel coil with a conventional 2D cine imaging approach for imaging the heart and to evaluate any difference caused by free breathing and breath holding for real-time imaging.

MATERIALS AND METHODS

In this institutional review board-approved HIPAA-compliant study, 10 healthy volunteers and 22 consecutive patients who were suspected of having or were known to have heart disease underwent cardiac MR imaging by using a 32-channel coil. A conventional multisection 2D real-time cine sequence was used as the reference standard, and three additional accelerated cine sequences were implemented. Volumetric parameters, including ejection fraction (EF), end-diastolic volume (EDV), end-systolic volume (ESV), stroke volume(SV), and myocardial mass, were derived. Wall motion and image quality were assessed by two radiologists. In addition, image time was registered. An additional set of images was acquired by using real-time sequences with free breathing, and quantitative measurements were compared with measurements on images obtained with breath holding. For quantitative analysis, repeated-measures analysis of variance, paired t test, and Bland-Altman analysis were used; for qualitative analysis, nonparametric Wilcoxon signed-rank test was used.

RESULTS

All volumetric measurements were significantly correlated with those of the standard sequence (r > 0.80, P < .01). No significant difference among protocols was observed in terms of mean levels for EF or ESV (P > .05). However, a significant difference was indicated for EDV and SV (P < .01).The accelerated protocols had significantly shorter image times (P < .001). Wall motion scores were concordant with the standard sequence in 43-44 (93%-96%) segments for the accelerated protocols, with a strong interreader agreement (intraclass correlation coefficient, > or =0.93). No significant difference was identified between real-time protocols with free breathing and those with breath holding for measurement of volumetric parameters.

CONCLUSION

Accelerated real-time 2D and segmented 3D cine techniques are comparable to the standard clinical protocol in assessment of left ventricular global and regional parameters in substantially shorter image times.

Accelerated CMR using zonal, parallel and prior knowledge driven imaging methods

Accelerated imaging is highly relevant for many CMR applications as competing constraints with respect to spatiotemporal resolution and tolerable scan times are frequently posed. Three approaches, all involving data undersampling to increase scan efficiencies, are discussed in this review. Zonal imaging can be considered a niche but nevertheless has found application in coronary imaging and CMR flow measurements. Current work on parallel-transmit systems is expected to revive the interest in zonal imaging techniques. The second and main approach to speeding up CMR sequences has been parallel imaging. A wide range of CMR applications has benefited from parallel imaging with reduction factors of two to three routinely applied for functional assessment, perfusion, viability and coronary imaging. Large coil arrays, as are becoming increasingly available, are expected to support reduction factors greater than three to four in particular in combination with 3D imaging protocols. Despite these prospects, theoretical work has indicated fundamental limits of coil encoding at clinically available magnetic field strengths. In that respect, alternative approaches exploiting prior knowledge about the object being imaged as such or jointly with parallel imaging have attracted considerable attention. Five to eight-fold scan accelerations in cine and dynamic CMR applications have been reported and image quality has been found to be favorable relative to using parallel imaging alone.With all acceleration techniques, careful consideration of the limits and the trade-off between acceleration and occurrence of artifacts that may arise if these limits are breached is required. In parallel imaging the spatially varying noise has to be considered when measuring contrast- and signal-to-noise ratios. Also, temporal fidelity in images reconstructed with prior knowledge driven methods has to be studied carefully.

The additional value of first pass myocardial perfusion imaging during peak dose of dobutamine stress cardiac MRI for the detection of myocardial ischemia

Purpose of this study was to assess the additional value of first pass myocardial perfusion imaging during peak dose of dobutamine stress Cardiac-MR (CMR). Dobutamine Stress CMR was performed in 115 patients with an inconclusive diagnosis of myocardial ischemia on a 1.5 T system (Magnetom Avanto, Siemens Medical Systems). Three short-axis cine and grid series were acquired during rest and at increasing doses of dobutamine (maximum 40 μg/kg/min). On peak dose dobutamine followed immediately by a first pass myocardial perfusion imaging sequence. Images were graded according to the sixteen-segment model, on a four point scale. Ninety-seven patients showed no New (Induced) Wall Motion Abnormalities (NWMA). Perfusion imaging showed absence of perfusion deficits in 67 of these patients (69%). Perfusion deficits attributable to known previous myocardial infarction were found in 30 patients (31%). Eighteen patients had NWMA, indicative for myocardial ischemia, of which 14 (78%) could be confirmed by a corresponding perfusion deficit. Four patients (22%) with NWMA did not have perfusion deficits. In these four patients NWMA were caused by a Left Bundle Branch Block (LBBB). They were free from cardiac events during the follow-up period (median 13.5 months; range 6–20). Addition of first-pass myocardial perfusion imaging during peak-dose dobutamine stress CMR can help to decide whether a NWMA is caused by myocardial ischemia or is due to an (inducible) LBBB, hereby preventing a false positive wall motion interpretation.

Myocardial tagging with steady state free precession techniques and semi-automatic postprocessing--impact on diagnostic value

Our aim was to determine the diagnostic value of myocardial tagging sequences with regard to the evaluable share of the cardiac cycle. Thirty-three patients were examined at 1.5 T using tagging sequences with gradient-echo (GRE) readout, 18 patients at 1.5 T with steady-state free precession (SSFP), and 11 patients at 3 T using GRE. Two observers graded image quality and determined the share of the cardiac cycle for which postprocessing could be performed (1, optimal; 2, little interaction; 3, whole cycle assessable; 4, diastole non-assessable; 5, systole incomplete; 6, non-diagnostic). With GRE at 1.5 T, median image quality was 4.0 (95% CI 4.0-5.0), while it was significantly better with 2.0 (2.0-3.0) using the SSFP technique and similar at 3 T with 2.9 (1.7-3.5). With GRE at 1.5 T, systole could be assessed in 69% of patients, and an evaluation of the whole cardiac cycle was not possible. With the SSFP sequence at 1.5 T and GRE at 3 T, an evaluation of the whole cardiac cycle was possible in 71% and 70% of the patients, respectively, and systole was assessable in all patients. Tagging sequences with SSFP readout at 1.5 T make a semi-automatic evaluation of the whole cardiac cycle feasible in a large share of patients.

High-resolution myocardial perfusion imaging at 3 T: comparison to 1.5 T in healthy volunteers

The purpose of this study was to evaluate high-resolution (HR) myocardial first-pass perfusion in healthy volunteers at 3 T compared to a typical clinical imaging protocol at 1.5 T, with respect to overall image quality and the presence of subendocardial dark rim artifacts. Myocardial first-pass rest perfusion studies were performed at both field strengths using a T1-weighted saturation-recovery segmented k-space gradient-echo sequence combined with parallel imaging (Gd-DTPA 0.05 mmol/kg). Twenty-six healthy volunteers underwent (1) a HR perfusion scan at 3 T(pixel size 3.78 mm(2)) and (2) a standard perfusion approach at 1.5 T(pixel size 9.86 mm(2)). The contrast enhancement ratio (CER) and overall image quality (4-point grading scale: 4: excellent; 1: non-diagnostic) were assessed, and a semiquantitative analysis of dark rim artifacts was performed for all studies. CER was slightly higher (1.31 +/- 0.32 vs. 1.14 +/- 0.34; p<0.01), overall image quality was significantly improved (3.03 +/- 0.43 vs. 2.37 +/- 0.39; p<0.01), and the number of dark rim artifacts (139 +/- 2.09 vs. 243 +/- 2.33; p<0.01) was significantly reduced for HR perfusion imaging at 3 T compared to the standard approach at 1.5 T. HR myocardial rest perfusion at 3 T is superior to the typical clinical perfusion protocol performed at 1.5 T with respect to the overall image quality and presence of subendocardial dark rim artifacts.