Contrast-enhanced multidetector computed tomography viability imaging after myocardial infarction: characterization of myocyte death, microvascular obstruction, and chronic scar

MDCT has the potential to predict percutaneous coronary intervention outcome in swine model: microscopic validation

BACKGROUND

Volumes and sizes of dislodged coronary microemboli vary during PCI so their effects at the left ventricular (LV) and cellular levels cannot be quantified. Furthermore, biopsy for tissue characterization is not an option in PCI patients.

PURPOSE

To characterize and validate microinfarct size, LAD territory where microinfarct were found using multidetector computed tomography (MDCT), histochemical staining and microscopy as a function of microemboli volumes and to scale the effects of microemboli volumes on LV function.

MATERIAL AND METHODS

Under X-ray guidance, a 3F catheter was inserted into LAD coronary artery of 14 pigs for delivering 16 mm(3) or 32 mm(3) of 40-120 μm microemboli. MDCT imaging/histochemical staining/microscopy were performed 3 days later and used to characterize regional and global structural and functional changes in LV by threshold/planimetric methods.

RESULTS

MDCT and ex-vivo methods were able to quantify microinfarct size and LAD territory where microinfarct was found as a function of volumes. However, MDCT and histochemical staining significantly underestimated microinfarct size and territory where microinfarct was found compared with microscopy. MDCT demonstrated the functional changes and showed a moderate correlation between LV ejection fraction and microinfarct size (r = 0.53). Microscopy provided higher spatial resolution for measuring islands of necrotic cells, which explains the difference in measuring structural changes.

CONCLUSION

MDCT showed the difference in microinfarct size and LAD territory as a function of microemboli volumes and scaled the changes in LV function. This experimental study gives clinicians a reference for the effects of defined microemboli volumes on myocardial viability and LV function and the under-estimation of microinfarct on MDCT.

CMR of microvascular obstruction and hemorrhage in myocardial infarction

Microvascular obstruction (MO) or no-reflow phenomenon is an established complication of coronary reperfusion therapy for acute myocardial infarction. It is increasingly recognized as a poor prognostic indicator and marker of subsequent adverse LV remodeling. Although MO can be assessed using various imaging modalities including electrocardiography, myocardial contrast echocardiography, nuclear scintigraphy, and coronary angiography, evaluation by cardiovascular magnetic resonance (CMR) is particularly useful in enhancing its detection, diagnosis, and quantification, as well as following its subsequent effects on infarct evolution and healing. MO assessment has become a routine component of the CMR evaluation of acute myocardial infarction and will increasingly play a role in clinical trials of adjunctive reperfusion agents and strategies. This review will summarize the pathophysiology of MO, current CMR approaches to diagnosis, clinical implications, and future directions needed for improving our understanding of this common clinical problem.

Quantitative three-dimensional evaluation of myocardial perfusion during regadenoson stress using multidetector computed tomography

OBJECTIVE

The ability of multidetector computed tomography (MDCT) to detect stress-induced myocardial perfusion abnormalities is of great clinical interest as a potential tool for the combined evaluation of coronary stenosis and its hemodynamic significance. We tested the hypothesis that quantitative 3-dimensional (3D) analysis of myocardial perfusion from MDCT images obtained during regadenoson stress would more accurately detect the presence of significant coronary artery disease (CAD) than identical analysis when performed on resting MDCT images.

METHODS

We prospectively studied 50 consecutive patients referred for CT coronary angiography (CTCA) who agreed to undergo additional imaging with regadenoson (0.4 mg; Astellas). Images were acquired using prospective gating (256-channel; Philips). Custom analysis software was used to define 3D myocardial segments, and calculate for each segment an index of severity and extent of perfusion abnormality, Qh, which was compared with perfusion defects predicted by the presence and severity of coronary stenosis on CTCA.

RESULTS

Three patients were excluded because of image artifacts. In the remaining 47 patients, CTCA depicted stenosis more than 50% in 23 patients in 37 of 141 coronary arteries. In segments supplied by the obstructed arteries, myocardial attenuation was slightly reduced compared with normally perfused segments at rest (mean [SD], 91 [21] vs 93 [26] Hounsfield units, not significant) and, to a larger extent, at peak stress (102 [21] vs 112 [20] Hounsfield units, P < 0.05). In contrast, index Qh was significantly increased at rest (0.40 [0.48] vs 0.26 [0.41], P < 0.05) and reached a nearly 3-fold difference at peak stress (0.66 [0.74] vs 0.28 [0.51], P < 0.05). The addition of regadenoson improved the diagnosis of CAD, as reflected by an increase in sensitivity (from 0.57 to 0.91) and improvement in accuracy (from 0.65 to 0.77).

CONCLUSIONS

Quantitative 3D analysis of MDCT images allows objective detection of CAD, the accuracy of which is improved by regadenoson stress.

Noise spatial nonuniformity and the impact of statistical image reconstruction in CT myocardial perfusion imaging

PURPOSE

To achieve high temporal resolution in CT myocardial perfusion imaging (MPI), images are often reconstructed using filtered backprojection (FBP) algorithms from data acquired within a short-scan angular range. However, the variation in the central angle from one time frame to the next in gated short scans has been shown to create detrimental partial scan artifacts when performing quantitative MPI measurements. This study has two main purposes. (1) To demonstrate the existence of a distinct detrimental effect in short-scan FBP, i.e., the introduction of a nonuniform spatial image noise distribution; this nonuniformity can lead to unexpectedly high image noise and streaking artifacts, which may affect CT MPI quantification. (2) To demonstrate that statistical image reconstruction (SIR) algorithms can be a potential solution to address the nonuniform spatial noise distribution problem and can also lead to radiation dose reduction in the context of CT MPI.

METHODS

Projection datasets from a numerically simulated perfusion phantom and an in vivo animal myocardial perfusion CT scan were used in this study. In the numerical phantom, multiple realizations of Poisson noise were added to projection data at each time frame to investigate the spatial distribution of noise. Images from all datasets were reconstructed using both FBP and SIR reconstruction algorithms. To quantify the spatial distribution of noise, the mean and standard deviation were measured in several regions of interest (ROIs) and analyzed across time frames. In the in vivo study, two low-dose scans at tube currents of 25 and 50 mA were reconstructed using FBP and SIR. Quantitative perfusion metrics, namely, the normalized upslope (NUS), myocardial blood volume (MBV), and first moment transit time (FMT), were measured for two ROIs and compared to reference values obtained from a high-dose scan performed at 500 mA.

RESULTS

Images reconstructed using FBP showed a highly nonuniform spatial distribution of noise. This spatial nonuniformity led to large fluctuations in the temporal direction. In the numerical phantom study, the level of noise was shown to vary by as much as 87% within a given image, and as much as 110% between different time frames for a ROI far from isocenter. The spatially nonuniform noise pattern was shown to correlate with the source trajectory and the object structure. In contrast, images reconstructed using SIR showed a highly uniform spatial distribution of noise, leading to smaller unexpected noise fluctuations in the temporal direction when a short scan angular range was used. In the numerical phantom study, the noise varied by less than 37% within a given image, and by less than 20% between different time frames. Also, the noise standard deviation in SIR images was on average half of that of FBP images. In the in vivo studies, the deviation observed between quantitative perfusion metrics measured from low-dose scans and high-dose scans was mitigated when SIR was used instead of FBP to reconstruct images.

CONCLUSIONS

(1) Images reconstructed using FBP suffered from nonuniform spatial noise levels. This nonuniformity is another manifestation of the detrimental effects caused by short-scan reconstruction in CT MPI. (2) Images reconstructed using SIR had a much lower and more uniform noise level and thus can be used as a potential solution to address the FBP nonuniformity. (3) Given the improvement in the accuracy of the perfusion metrics when using SIR, it may be desirable to use a statistical reconstruction framework to perform low-dose dynamic CT MPI.

Assessment of coronary heart disease by CT angiography: current and evolving applications

Computed tomography angiography (CTA) of the heart is a rapidly evolving application for comprehensive assessment of coronary arterial anatomy, myocardial function, perfusion, and myocardial viability. Thus, cardiac CTA is capable of retrieving the most critical information for guiding the management of patients with suspected coronary heart disease (CHD). Ongoing technologic advancements have allowed acquiring such information within minutes, at radiation doses that are lower than those from conventional computed tomography imaging or common nuclear imaging techniques. Cardiac CTA has positioned itself as an imaging modality that may be well suited to fulfill central needs of cardiovascular medicine. This article reviews the evidence for the clinical utility of cardiac CTA in patients with suspected CHD.

Spectral CT imaging of myocardial infarction: preliminary animal experience

OBJECTIVES

To evaluate the capability of spectral CT imaging to detect the different stages and angiogenesis of myocardial infarction (MI).

METHODS

MI was surgically induced in 40 rabbits that were evenly divided into four stages of MI: 6 h (6H), 3 days (3D), 7 days (7D) and 14 days (14D). Spectral CT was performed at 10 s, 1 min and 3 min after intravenous contrast medium administration. CD31 immunohistochemistry was used for the microvessel density (MVD) measurement. Iodine concentrations in the myocardium were measured and normalised to the aorta as nIC. The relationships between infarcted myocardial nIC and MVD were analysed.

RESULTS

The nIC of infarct myocardium decreased at 10 s and increased in late-phase CT images. There were significant differences between the 6H and other groups (P ( 6H-3D )  = 0.01, P ( 6H-7D )  = 0.01, P ( 6H-14D )  = 0.00). There was a significant difference in the MVD of infarct myocardium between the two groups except in the 7D and 14D groups (P = 0.08). In the 10-s phase, the nIC of infarct myocardium was negatively correlated with MVD (r = -0.54, P = 0.00), whereas in the late phases, there was a positive correlation between them (r = 0.57, P = 0.00 in the 1-min phase, r = 0.48, P = 0.00 in the 3-min phase).

CONCLUSION

Spectral CT imaging of the myocardium can be used to evaluate the different stages and angiogenesis of MI.

Interstitial myocardial fibrosis assessed as extracellular volume fraction with low-radiation-dose cardiac CT

PURPOSE

To develop a cardiac computed tomographic (CT) method with which to determine extracellular volume (ECV) fraction, with cardiac magnetic resonance (MR) imaging as the reference standard.

MATERIALS AND METHODS

Study participants provided written informed consent to participate in this institutional review board-approved study. ECV was measured in healthy subjects and patients with heart failure by using cardiac CT and cardiac MR imaging. Paired Student t test, linear regression analysis, and Pearson correlation analysis were used to determine the relationship between cardiac CT and MR imaging ECV values and clinical parameters.

RESULTS

Twenty-four subjects were studied. There was good correlation between myocardial ECV measured at cardiac MR imaging and that measured at cardiac CT (r = 0.82, P < .001). As expected, ECV was higher in patients with heart failure than in healthy control subjects for both cardiac CT and cardiac MR imaging (P = .03, respectively). For both cardiac MR imaging and cardiac CT, ECV was positively associated with end diastolic and end systolic volume and inversely related to ejection fraction (P < .05 for all). Mean radiation dose was 1.98 mSv ± 0.16 (standard deviation) for each cardiac CT acquisition.

CONCLUSION

ECV at cardiac CT and that at cardiac MR imaging showed good correlation, suggesting the potential for myocardial tissue characterization with cardiac CT.

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.

Visualizing the complex 3D geometry of the perfusion border zone in isolated rabbit heart

Myocardial infarction, caused by a major blockage of a coronary artery, creates a border zone (BZ) between perfused and nonperfused tissue, which is believed to be the origin of fatal cardiac arrhythmias. We used a combination of optical clearing and polarization-sensitive optical coherence tomography to visualize a three-dimensional organization of the BZ in isolated rabbit hearts (n=5) at the microscopic level with a high spatial resolution. We found that the BZ has a complex three-dimensional structure with nonperfused areas penetrating into perfused tissue with finger-like projections. These "fingers" may play an important role in the initiation and maintenance of ventricular arrhythmias.

Prognostic value of myocardial contrast delayed enhancement with 64-slice multidetector computed tomography after acute myocardial infarction

OBJECTIVES

This study evaluated the clinical value of myocardial contrast delayed enhancement (DE) with multidetector computed tomography (MDCT) for predicting clinical outcome after acute myocardial infarction (AMI).

BACKGROUND

Although some studies have described the use of MDCT for assessment of myocardial viability after AMI, clinical experience remains limited.

METHODS

In 102 patients with first AMI, 64-slice MDCT without iodine reinjection was performed immediately following successful percutaneous coronary intervention (PCI). We measured the size of myocardial contrast DE on MDCT and compared it with clinical outcome. Primary composite cardiac events were cardiac death or hospitalization for worsening heart failure.

RESULTS

Among the 102 patients (24 ± 10 months follow-up), 19 patients experienced primary composite cardiac events (cardiac death, n = 7; heart failure, n = 12). Kaplan-Meier analysis showed higher risk of cardiac events for patients in the third tertile of myocardial contrast DE size (≥ 36 g) than for those in the other 2 tertiles (p < 0.0001). Multivariable Cox proportional hazards regression analysis indicated that myocardial contrast DE size (adjusted hazard ratio [HR] for tertile 3 vs. 1: 16.1, 95% confidence interval [CI]: 1.45 to 72.4, p = 0.022; HR for tertile 3 vs. 2: 5.06, 95% CI: 1.25 to 22.7, p = 0.039) was a significant independent predictor for cardiac events after adjustment for Thrombolysis In Myocardial Infarction risk score, left ventricular ejection fraction, total defect score on single-photon emission CT with technetium tetrofosmin, and transmural extent of myocardial contrast DE on MDCT.

CONCLUSIONS

Myocardial contrast DE size on MDCT immediately after primary PCI may provide promising information for predicting clinical outcome in patients with AMI.

CT for evaluation of myocardial cell therapy in heart failure: a comparison with CMR imaging

OBJECTIVES

The aim of this study was to use multidetector computed tomography (MDCT) to assess therapeutic effects of myocardial regenerative cell therapies.

BACKGROUND

Cell transplantation is being widely investigated as a potential therapy in heart failure. Noninvasive imaging techniques are frequently used to investigate therapeutic effects of cell therapies in the preclinical and clinical settings. Previous studies have shown that cardiac MDCT can accurately quantify myocardial scar tissue and determine left ventricular (LV) volumes and ejection fraction (LVEF).

METHODS

Twenty-two minipigs were randomized to intramyocardial injection of phosphate-buffered saline (placebo, n = 9) or 200 million mesenchymal stem cells (MSC, n = 13) 12 weeks after myocardial infarction (MI). Cardiac magnetic resonance and MDCT acquisitions were performed before randomization (12 weeks after MI induction) and at the study endpoint 24 weeks after MI induction. None of the animals received medication to control the intrinsic heart rate during first-pass acquisitions for assessment of LV volumes and LVEF. Delayed-enhancement MDCT imaging was performed 10 min after contrast delivery. Two blinded observers analyzed MDCT acquisitions.

RESULTS

MDCT demonstrated that MSC therapy resulted in a reduction of infarct size from 14.3 ± 1.2% to 10.3 ± 1.5% of LV mass (p = 0.005), whereas infarct size increased in nontreated animals (from 13.8 ± 1.3% to 16.5 ± 1.5%; p = 0.02) (placebo vs. MSC; p = 0.003). Both observers had excellent agreement for infarct size (r = 0.96; p < 0.001). LVEF increased from 32.6 ± 2.2% to 36.9 ± 2.7% in MSC-treated animals (p = 0.03) and decreased in placebo animals (from 33.3 ± 1.4% to 29.1 ± 1.5%; p = 0.01; at week 24: placebo vs. MSC; p = 0.02). Infarct size, end-diastolic LV volume, and LVEF assessed by MDCT compared favorably with those assessed by cardiac magnetic resonance acquisitions (r = 0.70, r = 0.82, and r = 0.902, respectively; p < 0.001).

CONCLUSIONS

This study demonstrated that cardiac MDCT can be used to evaluate infarct size, LV volumes, and LVEF after intramyocardial-delivered MSC therapy. These findings support the use of cardiac MDCT in preclinical and clinical studies for novel myocardial therapies.

Clinical indications for cardiac computed tomography. From the Working Group of the Cardiac Radiology Section of the Italian Society of Medical Radiology (SIRM)

Cardiac computed tomography (CCT) has grown as a useful means in different clinical contexts. Technological development has progressively extended the indications for CCT while reducing the required radiation dose. Even today there is little documentation from the main international scientific societies describing the proper use and clinical indications of CCT; in particular, there are no complete guidelines. This document reflects the position of the Working Group of the Cardiac Radiology Section of the Italian Society of Radiology concerning the indications for CCT.

Contrast-enhanced C-arm CT evaluation of radiofrequency ablation lesions in the left ventricle

OBJECTIVES

The purpose of this study was to evaluate use of cardiac C-arm computed tomography (CT) in the assessment of the dimensions and temporal characteristics of radiofrequency ablation (RFA) lesions. This imaging modality uses a standard C-arm fluoroscopy system rotating around the patient, providing CT-like images during the RFA procedure.

BACKGROUND

Both cardiac magnetic resonance (CMR) and CT can be used to assess myocardial necrotic tissue. Several studies have reported visualizing cardiac RFA lesions with CMR; however, obtaining CMR images during interventional procedures is not common practice. Direct visualization of RFA lesions using C-arm CT during the procedure may improve outcomes and circumvent complications associated with cardiac ablation procedures.

METHODS

RFA lesions were created on the endocardial surface of the left ventricle of 9 swine using a 7-F RFA catheter. An electrocardiographically gated C-arm CT imaging protocol was used to acquire projection images during iodine contrast injection and after the injection every 5 min for up to 30 min, with no additional contrast. Reconstructed images were analyzed offline. The mean and SD of the signal intensity of the lesion and normal myocardium were measured in all images in each time series. Lesion dimensions and area were measured and compared in pathologic specimens and C-arm CT images.

RESULTS

All ablation lesions (n = 29) were visualized and lesion dimensions, as measured on C-arm CT, correlated well with postmortem tissue measurements (linear dimensions: concordance correlation = 0.87; area: concordance correlation = 0.90. Lesions were visualized as a perfusion defect on first-pass C-arm CT images with a signal intensity of 95 HU lower than that of normal myocardium (95% confidence interval: -111 HU to -79 HU). Images acquired at 1 and 5 min exhibited an enhancing ring surrounding the perfusion defect in 24 lesions (83%).

CONCLUSIONS

RFA lesion size, including transmurality, can be assessed using electrocardiographically gated cardiac C-arm CT in the interventional suite. Visualization of RFA lesions using cardiac C-arm CT may facilitate the assessment of adequate lesion delivery and provide valuable feedback during cardiac ablation procedures.

Multidetector computed tomography predictors of late ventricular remodeling and function after acute myocardial infarction

BACKGROUND

Despite advent of rapid arterial revascularization as 1st line treatment for acute myocardial infarction (AMI), incomplete restoral of flow at the microvascular level remains a problem and is associated with adverse prognosis, including pathological ventricular remodeling. We aimed to study the association between multidetector row computed tomography (MDCT) perfusion defects and ventricular remodeling post-AMI.

METHODS

In a prospective study, 20 patients with ST-elevation AMI, treated by primary angioplasty, underwent arterial and late phase MDCT as well as radionuclide scans to study presence, size and severity of myocardial perfusion defects. Contrast echocardiography was performed at baseline and at 4 months follow-up to evaluate changes in myocardial function and remodeling.

RESULTS

Early defects (ED), late defects (LD) and late enhancement (LE) were detected in 15, 7 and 16 patients, respectively and radionuclide defects in 15 patients. The ED area (r=0.74), and LD area (r=0.72), and to a lesser extent LE area (r=0.62) correlated moderately well with SPECT summed rest score. By univariate analysis, follow-up end-systolic volume index and ejection fraction were both significantly related to ED and LD size and severity, but not to LE size or severity. By multivariate analysis, end-systolic volume index was best predicted by LD area (p<0.05) and ejection fraction by LD enhancement ratio.

CONCLUSIONS

LD size and severity on MDCT are most closely associated with pathological ventricular remodeling after AMI and may thus play a role in early identification and treatment of this condition.

Multimodality imaging in the assessment of myocardial viability

The prevalence of heart failure due to coronary artery disease continues to increase, and it portends a worse prognosis than non-ischemic cardiomyopathy. Revascularization improves prognosis in these high-risk patients who have evidence of viability; therefore, optimal assessment of myocardial viability remains essential. Multiple imaging modalities exist for differentiating viable myocardium from scar in territories with contractile dysfunction. Given the multiple modalities available, choosing the best modality for a specific patient can be a daunting task. In this review, the physiology of myocardial hibernation and stunning will be reviewed. All the current methods available for assessing viability including echocardiography, cardiac magnetic resonance imaging, nuclear imaging with single photon emission tomography and positron emission tomography imaging and cardiac computed tomography will be reviewed. The effectiveness of the various techniques will be compared, and the limitations of the current literature 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.

Evaluation of the acute effects of distal coronary microembolization using multidetector computed tomography and magnetic resonance imaging

The purpose of this study was to test the potential of clinical imaging modalities, 64-slice multidetector computed tomography (MDCT) and 1.5T magnetic resonance imaging (MRI) for qualitative and quantitative evaluation of acute microinfarcts and to determine the effects of <120 μm microemboli on left ventricular function, perfusion, cardiac injury biomarkers, arrhythmia, and cellular and vascular structures. Under X-ray fluoroscopy, 40-120 μm (16 mm(3) ) microemboli were delivered to embolize the left anterior descending (LAD) coronary artery of nine pigs. MDCT/MRI were performed at 72 h in a single session. Microinfarcts were visible in six of nine animals on delayed contrast-enhanced MDCT/MR images but measurable in all animals using semiautomated threshold methods. Other MDCT and MRI sequences demonstrated decline in left ventricular ejection fraction, regional strain and perfusion in visible and invisible microinfarcted regions. Microemboli caused significant elevation in cardiac injury enzymes and arrhythmias. Various sizes of microinfarcts appeared microscopically as distinct aggregates of macrophages replacing myocardium. Semiautomated threshold methods are necessary to measure and confirm/deny the presence of myocardial microinfarcts. This study offers support for alternative applications of MDCT/MRI in assessing clinical cases in which microemboli <120 μm escape protective devices during percutaneous coronary interventions. Although microembolization resulted in no mortality, it caused left ventricular dysfunction, perfusion deficit, cellular damage increase in cardiac injury enzymes, and arrhythmias.

Image registration and analysis for quantitative myocardial perfusion: application to dynamic circular cardiac CT

Large area detector computed tomography systems with fast rotating gantries enable volumetric dynamic cardiac perfusion studies. Prospectively, ECG-triggered acquisitions limit the data acquisition to a predefined cardiac phase and thereby reduce x-ray dose and limit motion artefacts. Even in the case of highly accurate prospective triggering and stable heart rate, spatial misalignment of the cardiac volumes acquired and reconstructed per cardiac cycle may occur due to small motion pattern variations from cycle to cycle. These misalignments reduce the accuracy of the quantitative analysis of myocardial perfusion parameters on a per voxel basis. An image-based solution to this problem is elastic 3D image registration of dynamic volume sequences with variable contrast, as it is introduced in this contribution. After circular cone-beam CT reconstruction of cardiac volumes covering large areas of the myocardial tissue, the complete series is aligned with respect to a chosen reference volume. The results of the registration process and the perfusion analysis with and without registration are evaluated quantitatively in this paper. The spatial alignment leads to improved quantification of myocardial perfusion for three different pig data sets.

Is multidetector computed tomography a suitable alternative to MR imaging for the assessment of myocardial necrosis after alcohol septal ablation?

BACKGROUND

To compare magnetic resonance (MR) imaging and multidetector computed tomography (MDCT) for the assessment of myocardial infarction (MI) after alcohol septal ablation (ASA).

METHODS

Ten patients (mean age, 60 years ± 16) were examined with both MDCT and 1.5-T MR imaging performed 10 minutes after injection, within 3 days after ASA. Half of them had a temporary pacemaker (PM) during MDCT examination. Global image quality (IQ) and localization of MI were noticed on both MDCT and MR images. Volumes of MI, contrast-to-noise ratios (CNR) and signal-to-noise ratios (SNR) were also calculated. ASA effectiveness was evaluated by echocardiography immediately and 3 months after procedure.

RESULTS

Global IQ was considered adequate for both procedures. In 8 patients, MI reached the basal part of the septum on both MDCT and MR images. The 2 remaining patients exhibited sparing of the basal septum on MDCT and MR images. Volumes of MI were within the same range with the 2 techniques (MDCT: 22.1 ± 8.8 mL; MR imaging: 23.8 ± 9.4 mL) and correlated well each other (R(2)=0.85, p<0.002). The 2 patients with sparing of the basal interventricular septum had persistent gradient on echocardiography 3 months after ASA, suggesting failure of the procedure. The volumes of MI didn't correlate with the reduction of pressure gradient on echocardiography 3 months after ASA (R(2)=0.02, p<0.05).

CONCLUSIONS

Evaluation of post ASA MI is feasible with MDCT by comparison with MR imaging. MDCT might serve as an alternative imaging method in case of PM implantation.

Computed tomography imaging in myocardial infarction

Over recent decades, noninvasive imaging has become well established in the diagnostic work-up of patients suffering from myocardial infarction. It provides insights into the individual patient's prognosis and guides therapeutic decisions. MRI has long been considered the standard of reference in the noninvasive imaging of myocardial infarction. Only recently have different multidetector-row spiral computed tomography (MDCT) techniques successfully been evaluated for the visualization of myocardial infarction. This article describes different concepts of cardiac MDCT imaging in acute and chronic myocardial infarction. MDCT assessment of myocardial edema, myocardial perfusion and delayed myocardial contrast enhancement are introduced, with the latter evolving as key concept of viability imaging by means of MDCT. The current status of MDCT in the diagnostic work-up of myocardial infarction is reviewed.

Detection of myocardial perfusion abnormalities using ultra-low radiation dose regadenoson stress multidetector computed tomography

BACKGROUND

The ability of multidetector computed tomography (MDCT) to detect stress-induced myocardial perfusion abnormalities is of great clinical interest as a potential tool for the combined evaluation of coronary stenosis and its significance. However, stress testing requires repeated scanning that is associated with additional radiation exposure and iodine contrast.

OBJECTIVE

Our goal was to determine the effects of reduced tube voltage and contrast dose on the ability to detect perfusion abnormalities.

METHODS

We studied 40 patients referred for coronary CT angiography (CTA) who agreed to undergo additional imaging after administration of an A(2A)-agonist (regadenoson 0.4 mg). Images were acquired at rest and during hyperemia with prospective gating with 120 kV tube voltage with 80-90 mL of contrast in 20 patients (group 1) and 100 kV with 55-70 mL of contrast in the remaining 20 patients (group 2). Custom 3D analysis software was used to define 3D myocardial segments and measure x-ray attenuation in each segment. In each group of patients, myocardial attenuation was averaged for segments supplied by coronary arteries with stenosis causing >50% luminal narrowing on coronary CTA and separately for segments supplied by arteries without significant stenosis.

RESULTS

Coronary CTA detected stenosis >50% in 23 of 120 coronary arteries in 16 of 40 patients. In all patients combined, myocardial attenuation increased from 86 ± 9 at rest to 110 ± 17 HU with stress, reflecting an increase in tissue blood flow, despite the decrease in left ventricular cavity attenuation (347 ± 72 to 281 ± 55 HU), reflecting an increase in cardiac output. Importantly, in both groups, myocardial attenuation was equally reduced in segments supplied by diseased arteries (group 1: 119 ± 19 vs 103 ± 14 HU, P < 0.05; group 2: 108 ± 20 vs 97 ± 16 HU, P < 0.05), despite the 74% reduction in radiation (from 7.4 ± 2.8 to 1.9 ± 0.45 mSv) and the 28% reduction in contrast dose (from 84 ± 7 to 60 ±7 mL) (both P < 0.05).

CONCLUSIONS

Regadenoson stress MDCT imaging can detect hypoperfused myocardium even when imaging settings are optimized to provide a significant reduction in radiation and contrast doses.

Integrative computed tomographic imaging of cardiac structure, function, perfusion, and viability

Recent advances in multidetector-row computed tomography (MDCT) technology have created new opportunities in cardiac imaging and provided new insights into a variety of disease states. Use of 64-slice coronary computed tomography angiography has been validated for the evaluation of clinically relevant coronary artery stenosis with high negative predictive values for ruling out significant obstructive disease. This technology has also advanced the care of patients with acute chest pain by simultaneous assessment of acute coronary syndrome, pulmonary embolism, and acute aortic syndrome ("triple rule out"). Although MDCT has been instrumental in the advancement of cardiac imaging, there are still limitations in patients with high or irregular heart rates. Newer MDCT scanner generations hold promise to improve some of these limitations for noninvasive cardiac imaging. The evaluation of coronary artery stenosis remains the primary clinical indication for cardiac computed tomography angiography. However, the use of MDCT for simultaneous assessment of coronary artery stenosis, atherosclerotic plaque formation, ventricular function, myocardial perfusion, and viability with a single modality is under intense investigation. Recent technical developments hold promise for accomplishing this goal and establishing MDCT as a comprehensive stand-alone test for integrative imaging of coronary heart disease.

Delayed enhancement imaging of myocardial viability: low-dose high-pitch CT versus MRI

OBJECTIVES

To evaluate the accuracy of high-pitch delayed enhancement (DE) CT for the assessment of myocardial viability with MRI as the reference standard.

METHODS

Twenty-four patients (mean age 66.9 ± 9.2 years) with coronary artery disease underwent DE imaging with 128-slice dual-source CT (prospective electrocardiography (ECG)-triggering) and MRI at 1.5 T. Two observers assessed DE transmurality per segment, and measured signal intensity (MRI) or attenuation (CT) in infarcted and healthy myocardium and noise in the left ventricular blood pool for calculating contrast-to-noise ratios (CNR).

RESULTS

75/408 (18.4%) segments in 18/24 patients (75.0%) showed DE in MRI, of which 28 segments in 10/24 (41.7%) patients were non-viable (scar tissue transmurality >50%). Sensitivity, specificity and accuracy of CT for diagnosis of non-viability were 60.7%, 96.8% and 94.4% per segment, and 90.0%, 92.9% and 91.7% per patient. CNR was significantly higher in MR (7.4 ± 3.0 vs. 4.6 ± 1.5; p = 0.018), and image noise significantly lower (11.6 ± 5.7 vs.15.0 ± 4.5; p = 0.019). Radiation dose of DECT was 0.89 ± 0.07 mSv.

CONCLUSIONS

CTDE imaging in the high-pitch mode enables myocardial viability assessment at a low radiation dose and good accuracy compared with MR, although associated with a lower CNR and higher noise.

Acute and chronic myocardial infarction in a pig model: utility of multi-slice cardiac computed tomography in assessing myocardial viability and infarct parameters

OBJECTIVES

The aim of this study was to determine the feasibility of multi-slice computed tomography (MSCT) biphasic imaging in assessing myocardial viability and infarct parameters in both acutely and chronically infarcted pig models.

MATERIALS AND METHODS

Seven pigs underwent ligation of the distal left anterior descending artery. Imaging was performed on the day of infarction and 3 months post-infarct, with contrast infusion followed by MSCT scan acquisition at different time-points. Left ventricular ejection fractions (LVEFs) were obtained by left ventriculography (LVG) after 3 months. Infarcted locations found using MSCT were compared with those obtained using SPECT. Infarcted areas were also analysed histopathologically and compared with the findings from MSCT.

RESULTS

Chronic phase images had perfusion defects with lower CT values relative to normal myocardium (43±10HU vs. 156±13HU, p=0.001) on the early images but no residual defects on delayed images. However, we found hyperenhancing regions on delayed images (244±20HU vs. 121±25HU, p=0.001), and good correlation between MSCT- and LVG-derived LVEFs (60.56±7.56%). The areas identified by MSCT corresponded to the location of (201)Tl SPECT-/pathologic staining-derived regions in all models. Infarct size was in good agreement with MSCT and pathological analyses of chronic phase models.

CONCLUSIONS

Necrotic myocardium in different stages after infarction could be qualitatively and quantitatively assessed using MSCT biphasic imaging, as could the status of microcirculation formation. MSCT-measured LVEFs matched well with other modalities, and hence MSCT is a useful tool in assessing post-infarct cardiac function.

Non-contrast cardiac computed tomography can accurately detect chronic myocardial infarction: Validation study

BACKGROUND

This study evaluates whether non-contrast cardiac computed tomography (CCT) can detect chronic myocardial infarction (MI) in patients with irreversible perfusion defects on nuclear myocardial perfusion imaging (MPI).

METHODS

One hundred twenty-two symptomatic patients with irreversible perfusion defect (N = 62) or normal MPI (N = 60) underwent coronary artery calcium (CAC) scanning. MI on these non-contrast CCTs was visually detected based on the hypo-attenuation areas (dark) in the myocardium and corresponding Hounsfield units (HU) were measured.

RESULTS

Non-contrast CCT accurately detected MI in 57 patients with irreversible perfusion defect on MPI, yielding a sensitivity of 92%, specificity of 72%, negative predictive value (NPV) of 90%, and a positive predictive value (PPV) of 77%. On a per myocardial region analysis, non-contrast CT showed a sensitivity of 70%, specificity of 85%, NPV of 91%, and a PPV of 57%. The ROC curve showed that the optimal cutoff value of LV myocardium HU to predict MI on non-contrast CCT was 21.7 with a sensitivity of 97.4% and specificity of 99.7%.

CONCLUSION

Non-contrast CCT has an excellent agreement with MPI in detecting chronic MI. This study highlights a novel clinical utility of non-contrast CCT in addition to assessment of overall burden of atherosclerosis measured by CAC.

MDCT evaluation of cardiac involvement in hypereosinophilic syndrome: differentiating mural thrombus, infarcted, and noninfarcted myocardium by delayed-phase scanning

Hypereosinophilic syndrome is a rare disease that can cause multiple-organ damage. Cardiac involvement, which presents as myocardial necrosis, infarction, or thrombus formation, is the leading cause of morbidity and death. Here, we present the case of a 17-year-old girl who had hypereosinophilic syndrome with cardiac involvement, which was evaluated by multidetector-row computed tomography. By means of arterial-phase and low-dose delayed-phase scanning, multidetector-row computed tomography clearly identified the mural thrombus and the infarcted and noninfarcted myocardium-which surpassed the performance of echocardiography in tissue characterization. Therefore, we propose that multidetector-row computed tomography could be a useful noninvasive tool for evaluating patients with cardiac involvement of hypereosinophilic syndrome.

Anatomical and functional evaluation of the myocardium in patients with acute coronary syndrome (NSTEMI) using MR imaging

PURPOSE

The aim of our study was to evaluate the role of magnetic resonance (MR) imaging in identifying the location and extent of acute ischaemic injury to predict reversibility and distinguish areas of acute from chronic ischaemia in patients with acute coronary syndrome non- ST-elevation myocardial infarction (NSTEMI).

MATERIALS AND METHODS

We evaluated 22 patients with NSTEMI acute coronary syndrome confirmed by coronary angiography (CA). We studied ventricular function indices and segmental changes in wall thickness and kinetics by cine-MR imaging sequences. Subsequently, we evaluated myocardial wall oedema with T2-weighted black-blood short-tau inversion recovery turbo spin echo (T2 BB-STIRTSE) sequences and identified areas of myocardial necrosis using T1-weighted turbo field-echo inversion recovery (T1 TFE-IR) sequences after contrast material administration.

RESULTS

The results obtained with the single sequences were as follows: T2 BB-STIR-TSE: 96.8% sensitivity, 100% specificity, 99.7% negative predictive value, 99.7% positive predictive value; T1 TFE-IR: 45.8% sensitivity, 96.9% specificity, 92.3% negative predictive value, 90.3% positive predictive value; systolic wall thickening: 87.5% sensitivity, 91.8% specificity, 98.7% negative predictive value, 50% positive predictive value, 91.4% accuracy.

CONCLUSIONS

Our study suggests that the sequences used for evaluating oedema and assessing viability allow for precise localisation and differentiation of areas of acute and chronic ischaemia by quantifying the possible mismatch between ischaemia and necrosis.

Dual-energy computed tomography for integrative imaging of coronary artery disease: principles and clinical applications

The introduction of coronary CT angiography (cCTA) has reinvigorated the debate whether management of patients with suspected coronary artery disease (CAD) should be primarily based on physiological, functional versus anatomical testing. Anatomical testing (i.e., cCTA or invasive catheterization) enables direct visualization and grading of coronary artery stenoses but has shortcomings for gauging the hemodynamic significance of lesions for myocardial perfusion. Rest/stress myocardial perfusion imaging (MPI) has been extensively validated for assessing the clinical significance of CAD by demonstrating fixed or reversible perfusion defects but has only limited anatomical information. There is growing evidence that contrast medium enhanced dual-energy cCTA (DECT) has potential for the comprehensive analysis of coronary artery morphology as well as changes in myocardial perfusion. DECT exploits the fact that tissues in the human body and iodine-based contrast media have unique absorption characteristics when penetrated with different X-ray energy levels, which enables mapping the iodine (and thus blood) distribution within the myocardium. The purpose of this communication is to describe the practical application of this technology for the comprehensive diagnosis of ischemic heart disease. We examine recent scientific findings in the context of current pivotal transitions in cardiovascular disease management and demonstrate the potential of cardiac DECT for the integrative assessment of patients with known or suspected CAD within a single CT-based protocol.

Assessment of acute myocardial infarction: current status and recommendations from the North American society for Cardiovascular Imaging and the European Society of Cardiac Radiology

There are a number of imaging tests that are used in the setting of acute myocardial infarction and acute coronary syndrome. Each has their strengths and limitations. Experts from the European Society of Cardiac Radiology and the North American Society for Cardiovascular Imaging together with other prominent imagers reviewed the literature. It is clear that there is a definite role for imaging in these patients. While comparative accuracy, convenience and cost have largely guided test decisions in the past, the introduction of newer tests is being held to a higher standard which compares patient outcomes. Multicenter randomized comparative effectiveness trials with outcome measures are required.

Three-Dimensional Contrast-Enhanced Multidetector CT for Anatomic, Dynamic, and Perfusion Characterization of Abnormal Myocardium To Guide Ventricular Tachycardia Ablations

Background—

Advances in contrast-enhanced multidetector CT enable detailed characterization of the left ventricular myocardium. Myocardial scar and border zone (BZ), as the target of ventricular tachycardia ablations, displays abnormal anatomic, dynamic, and perfusion characteristics during first-pass CT. This study assessed how contrast-enhanced CT can predict voltage-defined scar and BZ and integrate its scar reconstructions into clinical mapping systems to guide ventricular tachycardia ablations.

Methods and Results—

Eleven patients with ischemic cardiomyopathy underwent contrast-enhanced CT before ventricular tachycardia ablation. Segmental anatomic (end-systolic and end-diastolic wall thickness), dynamic (wall thickening, wall motion), and perfusion (hypoenhancement) characteristics were evaluated. Receiver operating characteristic curves assessed the ability of CT to determine voltage-defined scar and BZ segments. Three-dimensional epi- and endocardial surfaces and scar borders were reconstructed, coregistered, and compared to voltages using a 17-segment model. Abnormal anatomic, dynamic, and perfusion data correlated well with abnormal (<1.5 mV) endocardial voltages ( r =0.77). Three-dimensional reconstruction integrated into the clinical mapping system (registration accuracy, 3.31±0.52 mm) allowed prediction of homogenous abnormal voltage (<1.5 mV) in 81.7% of analyzed segments and correctly displayed transmural extent and intramural scar location. CT hypoperfusion correlated best with scar and BZ areas and encompassed curative ablations in 82% cases.

Conclusions—

Anatomic, dynamic, and perfusion imaging using contrast-enhanced CT allows characterization of left ventricular anatomy and 3D scar and BZ substrate. Integration of reconstructed 3D data sets into clinical mapping systems supplements information of voltage mapping and may enable new image approaches for substrate-guided ventricular tachycardia ablation.

Late gadolinium-enhancement cardiac magnetic resonance identifies postinfarction myocardial fibrosis and the border zone at the near cellular level in ex vivo rat heart

BACKGROUND

using a resolution 1000-fold higher than prior studies, we studied (1) the degree to which late gadolinium-enhancement (LGE) cardiac magnetic resonance tracks fibrosis from chronic myocardial infarction and (2) the relationship between intermediate signal intensity and partial volume averaging at distinct "smooth" infarct borders versus disorganized mixtures of fibrosis and viable cardiomyocytes.

METHODS AND RESULTS

sprague-Dawley rats underwent myocardial infarction by coronary ligation. Two months later, rats were euthanized 10 minutes after administration of 0.3 mmol/kg intravenous gadolinium. LGE images ex vivo at 7 T with a 3D gradient echo sequence with 50×50×50 μm voxels were compared with histological sections (Masson trichrome). Planimetered histological and LGE regions of fibrosis correlated well (y=1.01x-0.01; R(2)=0.96; P<0.001). In addition, LGE images routinely detected clefts of viable cardiomyocytes 2 to 4 cells thick that separated bands of fibrous tissue. Although LGE clearly detected disorganized mixtures of fibrosis and viable cardiomyocytes characterized by intermediate signal intensity voxels, the percentage of apparent intermediate signal intensity myocardium increased significantly (P<0.01) when image resolution was degraded to resemble clinical resolution consistent with significant partial volume averaging.

CONCLUSIONS

these data provide important validation of LGE at nearly the cellular level for detection of fibrosis after myocardial infarction. Although LGE can detect heterogeneous patches of fibrosis and viable cardiomyocytes as patches of intermediate signal intensity, the percentage of intermediate signal intensity voxels is resolution dependent. Thus, at clinical resolutions, distinguishing the peri-infarct border zone from partial volume averaging with LGE is challenging.

Dual source dual-energy computed tomography of acute myocardial infarction: correlation with histopathologic findings in a canine model

PURPOSE

To evaluate the feasibility and value of dual-energy computed tomography myocardial iodine maps in the diagnosis of acute myocardial infarction.

MATERIALS AND METHODS

In 6 dogs, arterial-phase myocardial dual-energy computed tomography imaging were performed 1 day prior to and 3 hours after the surgical ligation of the left anterior descending artery to generate 100 kVp, 140 kVp, average weighted images, and dual energy myocardial iodine maps. For each of the 17 segments of the left ventricle (LV, 102 total segments), the presence or absence myocardial infarction was determined by histopathology and correlated to blinded reader determination of infarcted and noninfarcted myocardium at computed tomography (CT). Statistical analysis for diagnostic accuracy of aforementioned techniques and inter-reader agreement was performed.

RESULTS

The LV myocardial contrast enhancement at the average weighted images and iodine maps were uniform in all 6 dogs before surgery. Following anterior descending artery ligation, histopathology showed 40 infarcted left ventricular segments and 62 noninfarcted segments. For the postligation CT scans, 100 kVp, 140 kVp, average weighted images, and myocardial iodine maps showed 33, 28, 33, 34 infarcted segments and 53, 56, 56, 52 noninfarcted segments for both readers; corresponding to per-segment sensitivities of 83%, 70%, 80%, 92% and specificities of 85%, 90%, 92%, 80% for detecting myocardial infarction. No statistical difference was found for diagnostic accuracy of 100 kV, 140 kV, weighted average images, and iodine maps to detect myocardial infarct segments (all P > 0.05 for both readers). Good inter-reader agreement was seen for myocardial infarct detection using iodine maps (kappa = 0.80).

CONCLUSIONS

Myocardial single- and dual-energy CT imaging shows high per-segment sensitivity and moderate specificity for detecting acute myocardial infarction in a canine model with histopathology as the standard of reference.

Evaluation of reperfused myocardial infarction by low-dose multidetector computed tomography using prospective electrocardiography (ECG)-triggering: comparison with magnetic resonance imaging

PURPOSE

To evaluate the potential of prospective electrocardiography (ECG)- gated 64-slice multidetector computed tomography (MDCT) for evaluation of myocardial enhancement, infarct size, and stent patency after percutaneous coronary intervention (PCI) with stenting in patients with myocardial infarction.

MATERIALS AND METHODS

Seventeen patients who were admitted with acute myocardial infarction were examined with prospective ECG-gated 64-slice cardiac MDCT and magnetic resonance (MR) imaging after reperfusion using PCI with stenting. Cardiac MDCT was performed with two different phases: arterial and delayed phases. We evaluated the stent patency on the arterial phase, and nonviable myocardium on the delayed phase of computed tomography (CT) image, and they were compared with the results from the delayed MR images.

RESULTS

Total mean radiation dose was 7.7 +/- 0.5 mSv on the two phases of CT images. All patients except one showed good patency of the stent at the culprit lesion on the arterial phase CT images. All patients had hyperenhanced area on the delayed phase CT images, which correlated well with those on the delayed phase MR images, with a mean difference of 1.6% (20 +/- 10% vs. 22 +/- 10%, r = 0.935, p = 0.10). Delayed MR images had a better contrast-to-noise ratio (CNR) than delayed CT images (27.1 +/- 17.8% vs. 4.3 +/- 2.1%, p < 0.001).

CONCLUSION

Prospective ECG-gated 64-slice MDCT provides the potential to evaluate myocardial viability on delayed phase as well as for stent patency on arterial phase with an acceptable radiation dose after PCI with stenting in patients with myocardial infarction.

Cardiac computed tomography and magnetic resonance imaging: the clinical use from a cardiologist's perspective

The introduction and continued evolution of cardiac computed tomography and magnetic resonance imaging have added considerable noninvasive diagnostic insight into a wide range of frequently encountered clinical cardiology scenarios. With an increasing range of imaging modalities, and multiple methods of image acquisition in each, a detailed understanding of the clinical question at hand is often necessary to select the proper study and make optimal use of imaging data. We review common cardiac issues from a clinician's perspective, along with the unique role to be played by computed tomography and magnetic resonance imaging in each condition. This review will hopefully facilitate a strong dialogue between imagers and managing clinicians, creating a shared knowledge of both the capabilities of imaging and the management challenges that treating clinicians face.