Practical tips and tricks in cardiovascular computed tomography: Diagnosis of myocardial infarction

Strengths and weaknesses of alternative noninvasive imaging approaches for microvascular ischemia

Structural and functional abnormalities of coronary microvasculature are highly prevalent in several clinical settings and often associated with worse clinical outcomes. Therefore, there is a growing interest in the detection and treatment of this, often overlooked, disease. Coronary angiography allows the assessment of the Coronary flow reserve (CFR) and the index of microcirculatory resistance (IMR). However, the measurement of these parameters is not always feasible because of limited technical availability and the need for a cardiac catheterization with a small but real risk of potential complications. Recent advances in non-invasive imaging techniques allow the assessment of coronary microvascular function with good accuracy and reproducibility. The objective of this review is to discuss the strengths and weaknesses of alternative non-invasive approaches used in the diagnosis of coronary microvascular dysfunction (CMD), highlighting the most recent advances for each imaging modality.

Technical Considerations for Dynamic Myocardial Computed Tomography Perfusion as Part of a Comprehensive Evaluation of Coronary Artery Disease Using Computed Tomography

Dynamic myocardial computed tomography perfusion (DM-CTP) has good diagnostic accuracy for identifying myocardial ischemia as compared with both invasive and noninvasive reference standards. However, DM-CTP has not yet been implemented in the routine clinical examination of patients with suspected or known coronary artery disease. An important hurdle in the clinical dissemination of the method is the development of the DM-CTP acquisition protocol and image analysis. Therefore, the aim of this article is to provide a review of critical parameters in the design and execution of DM-CTP to optimize each step of the examination and avoid common mistakes. We aim to support potential users in the successful implementation and performance of DM-CTP in daily practice. When performed appropriately, DM-CTP may support clinical decision making. In addition, when combined with coronary computed tomography angiography, it has the potential to shorten the time to diagnosis by providing immediate visualization of both coronary atherosclerosis and its functional relevance using one single modality.

Static CT myocardial perfusion imaging: image quality, artifacts including distribution and diagnostic performance compared to 82Rb PET

Background

Rubidium-82 positron emission tomography (⁸²Rb PET) MPI is considered a noninvasive reference standard for the assessment of myocardial perfusion in coronary artery disease (CAD) patients. Our main goal was to compare the diagnostic performance of static rest/ vasodilator stress CT myocardial perfusion imaging (CT-MPI) to stress/ rest ⁸²Rb PET-MPI for the identification of myocardial ischemia.

Methods

Forty-four patients with suspected or diagnosed CAD underwent both static CT-MPI and ⁸²Rb PET-MPI at rest and during pharmacological stress. The extent and severity of perfusion defects on PET-MPI were assessed to obtain summed stress score, summed rest score, and summed difference score. The extent and severity of perfusion defects on CT-MPI was visually assessed using the same grading scale. CT-MPI was compared with PET-MPI as the gold standard on a per-territory and a per-patient basis.

Results

On a per-patient basis, there was moderate agreement between CT-MPI and PET-MPI with a weighted 0.49 for detection of stress induced perfusion abnormalities. Using PET-MPI as a reference, static CT-MPI had 89% sensitivity (SS), 58% specificity (SP), 71% accuracy (AC), 88% negative predictive value (NPV), and 59% positive predictive value (PPV) to diagnose stress-rest perfusion deficits on a per-patient basis. On a per-territory analysis, CT-MPI had 73% SS, 65% SP, 67% AC, 90.8% NPV, and 34% PPV to diagnose perfusion deficits.

Conclusions

CT-MPI has high sensitivity and good overall accuracy for the diagnosis of functionally significant CAD using ⁸²Rb PET-MPI as the reference standard. CT-MPI may play an important role in assessing the functional significance of CAD especially in combination with CCTA.

Characterization of non-response to cardiac resynchronization therapy by post-procedural computed tomography

INTRODUCTION

Causes of non-response to cardiac resynchronization therapy (CRT) include mechanical dyssynchrony, myocardial scar, and suboptimal left ventricular (LV) lead location. We aimed to assess the utility of Late Iodine Enhancement Computed Tomography (LIE-CT) with image subtraction in characterizing CRT non-response.

METHODS

CRT response was defined as a decrease in LV end-systolic volume > 15% at 6 months. LIE-CT was performed after 6 months, and analyzed global and segmental dyssynchrony, myocardial scar, coronary venous anatomy, and position of LV lead relative to scar and segment of latest mechanical contraction.

RESULTS

We evaluated 29 patients (age 71 ± 12 years; 72% men) including 18 (62%) responders. All metrics evaluating residual dyssynchrony such as wall motion index and wall thickness index were worse in non-responders. There was no difference in presence and extent of scar between responders and non-responders. However, in non-responders, the LV lead was more often over an akinetic/dyskinetic area (72% vs. 22%, p = .007), a fibrotic area (64% vs. 8%, p = .0007), an area with myocardial thickness < 6 mm (82% vs. 22%, p = .002), and less often concordant with the region of maximal wall thickness (9% vs. 72%, p = .001). Among the 11 non-responders, eight had at least another coronary venous branch visualized by CT, including three (27%) coursing over a potentially interesting myocardial area (free of scar, with normal wall motion, and with a myocardial thickness ≥6 mm).

CONCLUSION

LIE-CT with image subtraction allows a comprehensive characterization of patients after CRT and may provide clues for management of non-responders.

Acute Myocardial Infarct

This article reviews the imaging manifestations of acute myocardial infarction (MI) on computed tomography (CT) accompanied by case examples and illustrations. This is preceded by a review of the pathophysiology of MI (acute and chronic), a summary of its clinical presentation, and a brief synopsis of the technical aspects of cardiac CT. Several examples of the appearance of acute MI and its complications are shown on routine and cardiac tailored CT, and a sample of the latest advances in imaging technique, including dual-energy CT, are introduced.

Chest pain CT in the emergency department: Watch out for the myocardium

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Hypodense myocardium (HM) can be observed often in chest pain CT examinations of patients presenting to the emergency department with chest pain.

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There is benefit when the myocardium is also analyzed for the presence of HM, even when the heart and coronary arteries were not specifically asked-for.

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Sensitivity, specificity, PPV and NPV for the detection of acute myocardial infarction by assessing HM was 52%, 100%, 100% and 95% respectively.

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Assessment of hypodense myocardium may increase the diagnostic confidence in ambiguous coronary findings in chest pain CT.

Rationale and Objectives

To evaluate the frequency and relevance of hypodense myocardium (HM) encountered in patients undergoing chest-pain CT in the emergency department (ED).

Material and Methods

In this IRB-approved retrospective study, ECG-gated chest-pain CT examinations of 300 consecutive patients (mean age 60 ± 17 years) presenting with acute chest-pain to our ED were evaluated. Once ST-segment elevation infarction was excluded, chest-pain CT including the coronary arteries (rule-out acute coronary syndrome (ACS), pulmonary embolism (PE) and acute aortic syndrome (AAS): chest-pain CT_coronary, n = 121) or not including the coronary arteries was performed (rule-out PE and AAS: chest-pain CT_{w/o coronary}, n = 179). Each myocardial segment was assessed for the presence of HM; attenuation was measured and compared to normal myocardium.

Results

HM was identified in 27/300 patients (9%): 12/179 in chest-pain CT_{w/o coronary} (7%) and 15/121 in chest-pain CT_coronary (12%). Mean attenuation of HM (40 ± 17 HU) was significantly lower than that of healthy myocardium (103 ± 18 HU, p < 0.001), with a mean difference of 61 ± 19 HU. In 15/27 patients (55.6%) with HM, the final diagnosis was acute MI, and in the remaining 12/27 patients (44.4%) previous MI was found in the patients’ history. Chest-pain CT_{w/o coronary} identified HM in 10/15 patients (66.6%) with a final diagnosis of acute MI.

Conclusion

HM indicating acute MI are often encountered in chest pain CT in the ED, also in chest-pain CT_{w/o coronary} when MI is not suspected. This indicates that the myocardium should always be analyzed for hypodense regions even when MI not suspected.

Visualization of Myocardial Infarction in Postmortem Multiphase Computed Tomography Angiography: A Feasibility Study

Recent studies have indicated that multiphase postmortem computed tomography angiography (MPMCTA) allows detection of a pathological enhancement of the myocardium in regions that correlate with the localization of the infarction at histology. The aim of this study was to verify this hypothesis by examining MPMCTA images in cases of myocardial infarction. Therefore, we investigated 10 autopsy cases where death was attributed to myocardial infarction or which showed cardiovascular pathology. As a control group, we selected 10 cases of non-natural (namely, not cardiac) death. The MPMCTA was performed in both groups to ascertain whether a pathological enhancement could be observed. We detected a myocardial enhancement in all cardiac death cases, in the same region that showed infarction at histology. No enhancement was observed in control cases. These results have important implications in the routine management of sudden cardiac death cases. In fact, MPMCTA can not only orient about the cause of death before autopsy, but can especially help to identify affected regions for guiding and improving the sampling for microscopic examination.

Myocardial computed tomography perfusion

Despite having excellent diagnostic accuracy to detect anatomical coronary stenosis, coronary CT angiography (CTA) has a limited specificity to detect myocardial ischemia. CT perfusion (CTP) can identify myocardial perfusion defects during vasodilator stress, and when added to coronary CTA, improves the specificity of detecting hemodynamically significant stenosis. A CTP protocol typically involves the acquisition of two separate data sets: (I) a rest scan that can be used as both a coronary CTA and for evaluating rest myocardial perfusion, and (II) a stress CTP scan acquired during vasodilator stress testing. This review summarizes some the techniques, strengths, and limitations of CTP, and provides an overview of the recent evidence supporting the potential use of CTP in clinical practice.

Comprehensive use of cardiac computed tomography to guide left ventricular lead placement in cardiac resynchronization therapy

Background

Optimal lead positioning is an important determinant of cardiac resynchronization therapy (CRT) response.

Objective

The purpose of this study was to evaluate cardiac computed tomography (CT) selection of the optimal epicardial vein for left ventricular (LV) lead placement by targeting regions of late mechanical activation and avoiding myocardial scar.

Methods

Eighteen patients undergoing CRT upgrade with existing pacing systems underwent preimplant electrocardiogram-gated cardiac CT to assess wall thickness, hypoperfusion, late mechanical activation, and regions of myocardial scar by the derivation of the stretch quantifier for endocardial engraved zones (SQUEEZ) algorithm. Cardiac venous anatomy was mapped to individualized American Heart Association (AHA) bull’s-eye plots to identify the optimal venous target and compared with acute hemodynamic response (AHR) in each coronary venous target using an LV pressure wire.

Results

Fifteen data sets were evaluable. CT-SQUEEZ–derived targets produced a similar mean AHR compared with the best achievable AHR (20.4% ± 13.7% vs 24.9% ± 11.1%; P = .36). SQUEEZ-derived guidance produced a positive AHR in 92% of target segments, and pacing in a CT-SQUEEZ target vein produced a greater clinical response rate vs nontarget segments (90% vs 60%).

Conclusion

Preprocedural CT-SQUEEZ–derived target selection may be a valuable tool to predict the optimal venous site for LV lead placement in patients undergoing CRT upgrade.

Infarct characterization using CT

Myocardial infarction (MI) is a major cause of death and disability worldwide. The incidence is not expected to diminish, despite better prevention, diagnosis and treatment, because of the ageing population in industrialized countries and unhealthy lifestyles in developing countries. Nowadays it is highly requested an imaging tool able to evaluate MI and viability. Technology improvements determined an expansion of clinical indications from coronary plaque evaluation to functional applications (perfusion, ischemia and viability after MI) integrating additional phases and information in the mainstream examination. Cardiac computed tomography (CCT) and cardiac MR (CMR) employ different contrast media, but may characterize MI with overlapping imaging findings due to the similar kinetics and tissue distribution of gadolinium and iodinated contrast media. CCT may detect first-pass perfusion defects, dynamic perfusion after pharmacological stress, and delayed enhancement (DE) of non-viable territories.

Resting cardiac 64-MDCT does not reliably detect myocardial ischemia identified by radionuclide imaging

OBJECTIVE

CT myocardial perfusion imaging is an emerging diagnostic modality that is under intensive study but not yet widely used in clinical practice. The purpose of this study is to evaluate the performance of resting 64-MDCT in revealing ischemia identified on radionuclide myocardial perfusion imaging (MPI).

MATERIALS AND METHODS

We retrospectively identified 35 patients (20 women and 15 men; mean age, 52 years) with myocardial ischemia found on MPI who underwent retrospectively gated CT within 90 days of MPI. Myocardial perfusion on CT was evaluated using both a visual (n = 35) and an automated (n = 34) method. For the visual method, myocardial segments were evaluated qualitatively in systole and diastole. For the automated method, subendocardial perfusion of the standard 17 American Heart Association segments was measured using a commercially available tool in both systole and diastole. Differences between systolic and diastolic perfusion were computed.

RESULTS

Five hundred eighty myocardial segments were evaluated, 152 of which were ischemic on MPI. Visual analysis had a sensitivity of 16% (24/152), specificity of 92% (393/428), positive predictive value of 40% (24/60), and negative predictive value of 75% (392/520) in systole, and a sensitivity of 18% (27/152), specificity of 89% (382/428), positive predictive value of 37% (27/73), and negative predictive value of 75% (382/507) in diastole, as compared with MPI. There was no significant difference in subendocardial perfusion between ischemic and nonischemic segments by the automated method. There was no significant difference in CT perfusion between patients with and without obstructive coronary artery disease on CT angiography using the visual or automated methods.

CONCLUSION

Resting 64-MDCT is unsuitable for clinical use in revealing ischemia seen on MPI.

Assessment of myocardial viability using multidetector computed tomography in patients with reperfused acute myocardial infarction

AIM

To assess the prognostic value of 64-section multidetector computed tomography (MDCT) to predict follow-up myocardial dysfunction and functional recovery after reperfusion therapy in patients with acute myocardial infarction (MI) as defined by echocardiography.

MATERIALS AND METHODS

After reperfusion therapy for acute MI, 71 patients underwent two-phase contrast-enhanced MDCT and follow-up echocardiography. MDCT findings were compared with echocardiographic findings using kappa statistics. The areas under the receiver operating characteristic curves (AUCs) and the odds ratios (ORs) of early perfusion defects (EPD), delayed enhancement (DE), and residual perfusion defects (RPD) for predicting follow-up myocardial dysfunction and functional recovery were calculated on a segmental basis.

RESULTS

The presence of transmural EPD (EPD(TM)) or RPD showed good agreement (k = 0.611 and 0.658, respectively) with follow-up myocardial dysfunction, while subendocardial EPD (EPD(sub)) or subendocardial DE (DE(sub)) showed fair agreement with follow-up myocardial dysfunction (k = 0.235 and 0.234, respectively). The AUC of RPD (0.796) was superior (p < 0.001 and 0.031, respectively) to those of EPD(TM) (0.761) and DE(TM) (0.771). The presence of EPD(TM), DE(TM), and RPD were significant, independent positive predictors of follow-up myocardial dysfunction (OR = 6.4, 1.9, and 9.8, respectively). EPD(TM) was a significant, independent negative predictor of myocardial functional recovery (OR = 0.13).

CONCLUSION

Abnormal myocardial attenuation on two-phase MDCT after reperfusion therapy may provide promising information regarding myocardial viability in patients with acute MI.

Stress CT perfusion: coupling coronary anatomy with physiology

While multiple different imaging tests can be used to evaluate patients with known or suspected coronary artery disease (CAD), each of them is designed to evaluate either coronary anatomy or physiology. Recently, it has been recognized that cardiac CT can be used to evaluate stress and rest myocardial perfusion in addition to its capabilities to image the coronary arteries, thus allowing for the simultaneous evaluation of the anatomical burden and physiological significance of CAD in a single exam. In this review, the strengths and the limitations of imaging coronary anatomy and myocardial perfusion will be discussed. Next, key technical aspects of how to perform and interpret CT perfusion imaging will be summarized while providing an update of the most recent data in this emerging field. Finally, future directions and opportunities for further research will be discussed.

CT of coronary heart disease: Part 1, CT of myocardial infarction, ischemia, and viability

OBJECTIVE

This article reviews the CT-based approaches aimed at the assessment of myocardial infarction, ischemia, and viability described in the recent literature.

CONCLUSION

Rapid advances in CT technology not only have improved visualization of coronary arteries but also increasingly enable noncoronary myocardial applications, including analysis of wall motion and the state of the myocardial blood supply. These advancements hold promise for eventually accomplishing the goal of comprehensively evaluating coronary heart disease with a single noninvasive modality.

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.

Infarct detection with a comprehensive cardiac CT protocol

BACKGROUND

Cardiac CT has the potential to offer comprehensive infarct detection by assessing regional wall motion abnormalities (RWMAs), rest perfusion defects (RPDs), and delayed contrast enhancement (DCE). However, the diagnostic accuracy of these techniques for the detection of myocardial infarction (MI) is unknown.

METHODS

Forty-eight patients with intermediate-to-high probability for coronary artery disease after single-photon emitting CT myocardial perfusion imaging were prospectively enrolled for a research comprehensive 64-detector row dual-source cardiac CT protocol that included cine images for RWMA, first-pass images for RPD, and delayed images for DCE. Blinded readers independently assessed each technique. Subsequently, a final combined analysis (cine + rest + DCE) was performed. The universal definition for MI by the 2007 American Heart Association task force was used as the "gold standard."

RESULTS

Twenty-four of 48 patients (50%) had infarct by the universal definition. The combined CT analysis was most accurate (90%) with the highest per-patient sensitivity (88%) and specificity (92%) versus individual assessments (RWMA, 79% and 88%; RPD, 67% and 92%; DCE, 79% and 88%). Similar findings were observed on a per-vessel basis analysis. A combination of DCE and cine showed a good accuracy (85%) and high sensitivity (92%).

CONCLUSIONS

Infarct detection with CT is feasible with overall good diagnostic accuracy compared with the universal definition. A combined evaluation that included all techniques (cine, RPD, and DCE) had the highest diagnostic accuracy. These findings may have implications when designing future clinical and research CT protocols for optimal infarct detection.

A comparison of reconstruction and viewing parameters on image quality and accuracy of stress myocardial CT perfusion

BACKGROUND

Myocardial stress computed tomography perfusion (CTP) has similar diagnostic accuracy for detecting perfusion defects (PDs) versus single-photon emission computed tomography (SPECT). However, the optimal diagnostic viewing and image processing parameters for CTP are unknown.

OBJECTIVE

We sought to compare the diagnostic accuracy of different image processing techniques, cardiac phases, slice thicknesses, and viewing parameters for detection of PDs.

METHODS

A stress and rest dual-source CTP protocol was performed with adenosine. Twelve subjects with severe stenosis proven by quantitative coronary angiography (QCA), with corresponding territorial defects at SPECT, were selected as well as 7 controls (subjects with similar clinical suspicion but negative QCA and SPECT). Short-axis stress images were processed with 3 techniques: minimum intensity projection (MinIP), maximum intensity projection, and average intensity multiplanar reconstruction (MPR), 3 thicknesses (1, 3, 8 mm), and 2 phases (systolic, mid-diastolic). The resulting images (n = 1026) were randomized and interpreted by independent readers.

RESULTS

Diastolic reconstructions (8-mm MPR) showed the highest sensitivity (81%) to detect true PDs. The highest accuracy was achieved with the 8-mm (61%) and 1-mm (61%) MPR diastolic images. The most sensitive and accurate systolic reconstructions were 3-mm MinIP images. These findings related to viewing in relatively narrow window width and window level settings.

CONCLUSION

Viewing parameters for optimal accuracy in detection of perfusion defects on CTP differ for systolic and diastolic images.

Computed tomography stress myocardial perfusion imaging in patients considered for revascularization: a comparison with fractional flow reserve

AIMS

Adenosine stress computed tomography myocardial perfusion imaging (CTP) is an emerging non-invasive method for detecting myocardial ischaemia. Its value when compared with fractional flow reserve (FFR), a highly accurate index of ischaemia, is unknown. Our aim was to determine the diagnostic accuracy of CTP and its incremental value when used with computed tomography coronary angiography (CTA) for detecting ischaemia compared with FFR.

METHODS AND RESULTS

Forty-two patients (126 vessel territories), who had at least one ≥50% angiographic stenosis on invasive angiography considered for non-urgent revascularization, were included and underwent FFR and CT assessment, including CTP, delayed contrast enhancement scan and CTA all acquired using 320-detector row CT, and prospective ECG gating. Fractional flow reserve was determined in 86 territories subtended by vessels with ≥50% stenosis upon visual assessment. Fractional flow reserve ≤0.8 was considered to indicate significant ischaemia. Computed tomography myocardial perfusion imaging correctly identified 31/41 (76%) ischaemic territories and 38/45 (84%) non-ischaemic territories. Per-vessel territory sensitivity, specificity, positive, and negative predictive values of CTP were 76, 84, 82, and 79%, respectively. The combination of a ≥50% stenosis on CTA and perfusion defect on CTP was 98% specific for ischaemia, while the presence of <50% stenosis on CTA and normal perfusion on CTP was 100% specific for exclusion of ischaemia. Mean radiation for CTP and combined CT was 5.3 and 11.3 mSv, respectively.

CONCLUSION

Computed tomography myocardial perfusion imaging is moderately accurate in identifying perfusion defects associated with ischaemia as assessed by FFR in patients considered for revascularization. In territories, where CTA and CTP are concordant, CTA/CTP is highly accurate in the detection and exclusion of ischaemia. This is achievable with acceptable radiation exposure using 320-detector row CT and prospective ECG gating.

Indirectly probing Ca(2+) handling alterations following myocardial infarction in a murine model using T(1)-mapping manganese-enhanced magnetic resonance imaging

Prolonged ischemia causes cellular necrosis and myocardial infarction (MI) via intracellular calcium (Ca(2+)) overload. Manganese-enhanced MRI indirectly assesses Ca(2+) influx movement in vivo as manganese (Mn(2+)) is a Ca(2+) analog. To characterize myocardial Mn(2+) efflux properties, T(1)-mapping manganese-enhanced MRI studies were performed on adult male C57Bl/6 mice in which Ca(2+) efflux was altered using pharmacological intervention agents or MI-inducing surgery. Results showed that (1) Mn(2+) efflux rate increased exponentially with increasing Mn(2+) doses; (2) SEA0400 (a sodium-calcium exchanger inhibitor) decreased the rate of Mn(2+) efflux; and (3) dobutamine (a positive inotropic agent) increased the Mn(2+) efflux rate. A novel analysis technique also delineated regional features in the MI mice, which showed an increased Mn(2+) efflux rate in the necrosed and peri-infarcted tissue zones. The T(1)-mapping manganese-enhanced MRI technique characterized alterations in myocardial Mn(2+) efflux rates following both pharmacologic intervention and an acute MI. The Mn(2+) efflux results were consistent with those in ex vivo studies showing an increased Ca(2+) concentration under similar conditions. Thus, T(1)-mapping manganese-enhanced MRI has the potential to indirectly identify and quantify intracellular Ca(2+) handling in the peri-infarcted tissue zones, which may reveal salvageable tissue in the post-MI myocardium.

Comparison of postprocessing techniques for the detection of perfusion defects by cardiac computed tomography in patients presenting with acute ST-segment elevation myocardial infarction

BACKGROUND

Despite rapid advances in cardiac computed tomography (CT), a strategy for optimal visualization of perfusion abnormalities on CT has yet to be validated.

OBJECTIVE

We evaluated the performance of several postprocessing techniques of source data sets to detect and characterize perfusion defects in acute myocardial infarctions with cardiac CT.

METHODS

Twenty-one subjects (18 men; 60 +/- 13 years) that were successfully treated with percutaneous coronary intervention for ST-segment myocardial infarction underwent 64-slice cardiac CT and 1.5 Tesla cardiac magnetic resonance imaging (MRI) scans after revascularization. Delayed enhancement MR images were analyzed to identify the location of infarcted myocardium. Contiguous short-axis images of the left ventricular myocardium were created from the CT source images with 0.75-mm multiplanar reconstruction (MPR), 5-mm MPR, 5-mm maximal intensity projection (MIP), and 5-mm minimum intensity projection (MinIP) techniques. Segments already confirmed to contain infarction by MRI were then evaluated qualitatively and quantitatively with CT.

RESULTS

Overall, 143 myocardial segments were analyzed. On qualitative analysis, the MinIP and thick MPR techniques had greater visibility and definition than the thin MPR and MIP techniques (P < 0.001). On quantitative analysis, the absolute difference in Hounsfield unit attenuation between normal and infarcted segments was significantly greater for the MinIP (65.4 Hounsfield unit [HU]) and thin MPR (61.2 HU) techniques. However, the relative difference in Hounsfield unit attenuation was significantly greatest for the MinIP technique alone (95%; P < 0.001). Contrast to noise was greatest for the MinIP (4.2) and thick MPR (4.1) techniques (P < 0.001).

CONCLUSION

The results of our current investigation found that MinIP and thick MPR detected infarcted myocardium with greater visibility and definition than MIP and thin MPR.

Integration of coronary anatomy and myocardial perfusion imaging

Advances in cardiovascular imaging have resulted in the development of multiple noninvasive techniques to evaluate myocardial perfusion and coronary anatomy, each of which has unique strengths and limitations. For example, CT angiography can directly visualize the presence of atherosclerosis, but the hemodynamic effect of many lesions identified by this technique is unknown. Alternatively, myocardial perfusion imaging enables a physiological assessment, but it may underestimate the extent of atherosclerosis in patients with multivessel disease. Dual-modality simultaneous imaging or multimodal sequential imaging techniques facilitate integration of information on both myocardial perfusion and coronary anatomy, and thus have the potential to improve diagnostic and prognostic evaluation, which could translate into improved care of patients. This Review discusses the strengths and limitations of the currently available individual noninvasive techniques for imaging coronary anatomy and myocardial perfusion. Approaches to integration of these imaging modalities are described, followed by an exploration of the clinical utility and future directions of hybrid imaging.

Incremental value of adenosine-induced stress myocardial perfusion imaging with dual-source CT at cardiac CT angiography

PURPOSE

First, to assess the feasibility of a protocol involving stress-induced perfusion evaluated at computed tomography (CT) combined with cardiac CT angiography in a single examination and second, to assess the incremental value of perfusion imaging over cardiac CT angiography in a dual-source technique for the detection of obstructive coronary artery disease (CAD) in a high-risk population.

MATERIALS AND METHODS

Institutional review board approval and informed patient consent were obtained before patient enrollment in the study. The study was HIPAA compliant. Thirty-five patients at high risk for CAD were prospectively enrolled for evaluation of the feasibility of CT perfusion imaging. All patients underwent retrospectively electrocardiographically gated (helical) adenosine stress CT perfusion imaging followed by prospectively electrocardiographically gated (axial) rest myocardial CT perfusion imaging. Analysis was performed in three steps: (a)Coronary arterial stenoses were scored for severity and reader confidence at cardiac CT angiography, (b)myocardial perfusion defects were identified and scored for severity and reversibility at CT perfusion imaging, and (c)coronary stenosis severity was reclassified according to perfusion findings at combined cardiac CT angiography and CT perfusion imaging. The sensitivity, specificity, negative predictive value (NPV), and positive predictive value (PPV) of cardiac CT angiography before and after CT perfusion analysis were calculated.

RESULTS

With use of a reference standard of greater than 50% stenosis at invasive angiography, all parameters of diagnostic accuracy increased after CT perfusion analysis: Sensitivity increased from 83% to 91%; specificity, from 71% to 91%; PPV, from 66% to 86%; and NPV, from 87% to 93%. The area under the receiver operating characteristic curve increased significantly, from 0.77 to 0.90 (P < .005).

CONCLUSION

A combination protocol involving adenosine perfusion CT imaging and cardiac CT angiography in a dual-source technique is feasible, and CT perfusion adds incremental value to cardiac CT angiography in the detection of significant CAD.

Viability imaging by cardiac computed tomography

First-pass perfusion and delayed enhancement cardiac imaging have been shown to be feasible by cardiac CT. However, questions remain about its reliability, and ideal scanning parameters have yet to be fully established. In general, scar imaging with cardiac CT typically requires 2 scans, with first-pass perfusion information derived from the same data set used to visualize the coronary arteries. Reduced contrast enhancement on first-pass cardiac CT images represents reduced perfusion. Higher doses of contrast are required to perform viability imaging by cardiac CT. Approximately 10 minutes after contrast administration, viability information is obtained by performing a second (noncontrast) scan. In addition to the concepts of perfusion and viability imaging by cardiac CT, we review parameters such as scan timing, tube settings, contrast delivery, reconstruction, and postprocessing techniques, as well as the associated pitfalls and technical limitations in perfusion and viability imaging by cardiac CT.

Adenosine-induced stress myocardial perfusion imaging using dual-source cardiac computed tomography

OBJECTIVES

This study sought to determine the feasibility of performing a comprehensive cardiac computed tomographic (CT) examination incorporating stress and rest myocardial perfusion imaging together with coronary computed tomography angiography (CTA).

BACKGROUND

Although cardiac CT can identify coronary stenosis, very little data exist on the ability to detect stress-induced myocardial perfusion defects in humans.

METHODS

Thirty-four patients who had a nuclear stress test and invasive angiography were included in the study. Dual-source computed tomography (DSCT) was performed as follows: 1) stress CT: contrast-enhanced scan during adenosine infusion; 2) rest CT: contrast-enhanced scan using prospective triggering; and 3) delayed scan: acquired 7 min after rest CT. Images for CTA, computed tomography perfusion (CTP), and single-photon emission computed tomography (SPECT) were each read by 2 independent blinded readers.

RESULTS

The DSCT protocol was successfully completed for 33 of 34 subjects (average age 61.4 +/- 10.7 years; 82% male; body mass index 30.4 +/- 5 kg/m(2)) with an average radiation dose of 12.7 mSv. On a per-vessel basis, CTP alone had a sensitivity of 79% and a specificity of 80% for the detection of stenosis > or =50%, whereas SPECT myocardial perfusion imaging had a sensitivity of 67% and a specificity of 83%. For the detection of vessels with > or =50% stenosis with a corresponding SPECT perfusion abnormality, CTP had a sensitivity of 93% and a specificity of 74%. The CTA during adenosine infusion had a per-vessel sensitivity of 96%, specificity of 73%, and negative predictive value of 98% for the detection of stenosis > or =70%.

CONCLUSIONS

Adenosine stress CT can identify stress-induced myocardial perfusion defects with diagnostic accuracy comparable to SPECT, with similar radiation dose and with the advantage of providing information on coronary stenosis.

One scan for all: extended role of cardiac CT angiography in acute myocardial infarction

BACKGROUND

Cardiac computed-tomographic angiography (CTA) has gained widespread acceptance as a useful non-invasive technique in the assessment of coronary artery disease. Although most interest has focused on coronary vessels, analysis of myocardial perfusion, left ventricular wall motion, ejection fraction and left ventricular structure can easily be performed at the same time allowing comprehensive assessment of anatomy and function in a single examination. We present a case of acute ST elevation myocardial infarction where cardiac catheterization was deferred, but assessment by CTA permitted a management plan to be constructed using rest perfusion and blood pool inversion analyses of the dataset obtained during the coronary artery study.

CONCLUSION

Coronary CT angiography can provide a comprehensive assessment of coronary arteries, myocardial perfusion and structural features in those not suitable for coronary angiography after myocardial infarction.