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

Detection of myocardial perfusion abnormalities: standard dual-source coronary computed tomography angiography versus rest/stress technetium-99m single-photo emission CT

We compared coronary dual-source computed tomography angiography (corDSCTA) with technetium-99m single-photon emission computed tomography (SPECT) for the detection of myocardial perfusion abnormalities. Fifty-five consecutive patients underwent both gated myocardial perfusion SPECT and corDSCTA, the latter during a single arterial-phase injection of contrast agent. The perfusion defects visualised by corDSCTA correlated with the findings of rest/stress SPECT. Abnormal findings on stress SPECT, which were due to either ischaemia or infarct, were found in 24 patients. In comparison to SPECT at rest, corDSCTA detected perfusion defects with a sensitivity and specificity of 100% and 78%, respectively. Compared to SPECT at stress, the sensitivity and specificity values of corDSCTA were 83.3% and 90.3%, respectively. On corDSCTA , the average attenuation values of perfusion defects that corresponded to chronic infarcts (-8.5+/-22.2 HU) were significantly lower (p = 0.002) than those of non-infarct-related perfusion defects (43.1+/-17.5 HU). Using rest/stress SPECT is the gold standard for the diagnosis of myocardial ischaemia, corDSCTA was able to diagnose ischaemic disease (defined as the presence of high-grade stenotic CAD (>or=50% luminal narrowing)) with a sensitivity and specificity of 59% and 89%, respectively, in patients with no known history of myocardial infarction (n = 4). Thus, corDSCTA may serve as a diagnostic tool for the detection of perfusion abnormalities (first) visualised by SPECT. There appears to be a limited correlation between coronary stenotic disease and SPECT findings.

Myocardial perfusion imaging and infarct characterization using multidetector cardiac computed tomography

Until recently, computed tomography coronary angiography was restricted to the anatomical assessment of coronary stenosis, whereas the functional significance of coronary lesions remained outside of its scope. Nevertheless, the kinetics of iodinated contrast is similar to gadolinium-diethylenetriamine pentaacetic acid used in contrast-enhanced magnetic resonance imaging, allowing assessment of myocardial perfusion and viability by cardiac computed tomography.

Coronary computed tomographic angiography (CCTA) in community hospitals: "current and emerging role"

Coronary computed tomographic angiography (CCTA) is a rapidly evolving test for diagnosis of coronary artery disease. Although invasive coronary angiography is the gold standard for coronary artery disease (CAD), CCTA is an excellent noninvasive tool for evaluation of chest pain. There is ample evidence to support the cost-effective use of CCTA in the early triage process of patients presenting with chest pain in the emergency room. CCTA plays a critical role in the diagnosis of chest pain etiology as one of potentially fatal conditions, aortic dissection, pulmonary embolism, and myocardial infarction. This 'triple rule out' protocol is becoming an increasingly practicable and popular diagnostic tool in ERs across the country. In addition to a quick triage of chest pain patients, it may improve quality of care, decrease cost, and prevent medico-legal risk for missing potentially lethal conditions presenting as chest pain. CCTA is also helpful in the detection of subclinical and vulnerable coronary plaques. The major limitations for wide spread acceptance of this test include radiation exposure, motion artifacts, and its suboptimal imaging with increased body mass index.

Heterogeneous microinfarcts caused by coronary microemboli: evaluation with multidetector CT and MR imaging in a swine model

PURPOSE

To directly compare the sensitivity of 64-section multidetector computed tomography (CT) with that of 1.5-T magnetic resonance (MR) imaging in the depiction and measurement of heterogeneous 7-8-week-old microinfarcts and the quantification of regional left ventricular (LV) function and perfusion in the territory of coronary intervention in a swine model.

MATERIALS AND METHODS

Approval was obtained from the institutional animal committee. An x-ray/MR system was used to catheterize the left anterior descending (LAD) coronary artery with x-ray guidance and to delineate the perfusion territory. The vessel was selectively microembolized in six pigs with small-diameter embolic material (40-120 microm, 250000 count). At 7-8 weeks after microembolization, multidetector CT and MR imaging were used to assess LV function, first-pass perfusion, and delayed contrast enhancement in remote myocardium and microinfarct scars. Histochemical staining with triphenyltetrazolium chloride (TTC) was used to confirm and quantify heterogeneous microinfarct scars. The two-tailed Wilcoxon signed rank test was used to detect differences between modalities and myocardial regions.

RESULTS

The LAD territory was 32.4% +/- 3.8(stadard error of the mean) of the LV mass. Multidetector CT and MR imaging have similar sensitivity in the detection of regional and global LV dysfunction and extent of microinfarct. The mean LV end-diastolic volume, end-systolic volume, and ejection fraction were 93 mL +/- 8, 46 mL +/- 4, and 50% +/- 3, respectively, on multidetector CT images and 92 mL +/- 8, 48 mL +/- 5, and 48% +/- 3, respectively, on MR images (P > or = .05). The extent of heterogeneous microinfarct was not significantly different between multidetector CT (6.3% +/- 0.8 of the LV mass), MR imaging (6.6% +/- 0.5 of the LV mass), and TTC staining (7.0% +/- 0.6 of the LV mass). First-pass multidetector CT and MR imaging demonstrated significant regional differences (P < .05) in time to peak between the heterogeneous microinfarct and remote myocardium (17.0 seconds +/- 0.3 and 12.4 seconds +/- 0.6, respectively, for multidetector CT and 17.2 seconds +/- 0.8 and 12.5 seconds +/- 1.0, respectively, for MR imaging).

CONCLUSION

Modern multidetector CT and MR imaging are sensitive modalities with which to depict heterogeneous microinfarcts and determine regional LV dysfunction and decreased perfusion in the territory of intervention. (c) RSNA, 2010.

Impact of tube current in the quantitative assessment of acute reperfused myocardial infarction with 64-slice delayed-enhancement CT: a porcine model

PURPOSE

This study evaluated the impact of tube current (mAs) in delayed-enhancement computed tomography (CT) imaging for assessing acute reperfused myocardial infarction in a porcine model.

MATERIALS AND METHODS

In five domestic pigs (mean weight 24 kg), the circumflex coronary artery was balloon-occluded for 2 h and then reperfused. After 5 days, CT imaging was performed following administration of iodinated contrast material. A 64-slice CT system was used to perform first-pass coronary angiography with a tube current of 15 mAs/kg [Arterial Phase (ART)] followed by two delayed-enhancement (DE) scans 15 min after contrast material administration, with a tube current of 15 mAs/kg and 37.5 mAs/kg, respectively (DE(1) and DE(2)). The mean heart rate decreased to 51±9 beats/min after administration of zatebradine (10 mg/kg IV). The data set was reconstructed during the end-diastolic phase of the cardiac cycle. Areas with DE, no reflow and remote myocardium [remote left ventricular (LV)] were calculated. CT values expressed in Hounsfield units (HU) were measured using five regions of interest (ROI): DE, no reflow, remote LV, LV cavity (LV lumen) and in air, respectively. Differences, correlations, image quality [signal-to-noise ratio (SNR)] and contrast resolution [contrast-to-noise ratio (CNR)] were calculated.

RESULTS

Significant differences were found between attenuation of areas of DE, no reflow and remote LV (p<0.001) within the different scans. There was a fair correlation between DE and no-reflow attenuation (r=0.6; p<0.001). In DE(1) vs. DE(2), areas of DE and no reflow were not significantly different (p>0.05). The SNR and CNR were not significantly different in DE(1) vs. DE(2) (p>0.05).

CONCLUSIONS

Tube current does not significantly affect infarction area, image quality or contrast resolution of DE imaging with CT.

Patient assessment for cardiac resynchronization therapy: Past, present and future of imaging techniques

It has been proposed that dyssynchrony assessment before cardiac resynchronization therapy (CRT) implantation could help predict response to CRT. It is known that up to 40% of patients who receive a CRT device for established indications do not respond to CRT. Great expectations came from the Predictors of Response to Cardiac Resynchronization Therapy (PROSPECT) study, which would finally identify the ultimate echocardiographic dyssynchrony criteria to help select responders. The recently published PROSPECT trial failed to identify an ideal parameter of dyssynchrony. Patient selection for CRT should involve a multimodal approach, and new promising tools are being investigated in that view. The present review integrated new data coming from the exciting field of imaging with currently available evidence to generate a stepwise approach to patient selection.

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.

Prevalence of first-pass myocardial perfusion defects detected by contrast-enhanced dual-source CT in patients with non-ST segment elevation acute coronary syndromes

OBJECTIVE

To investigate the prevalence and diagnostic value of first-pass myocardial perfusion defects (PD) visualised by contrast-enhanced multidetector computed tomography (MDCT) in patients admitted for a first acute coronary syndrome (ACS).

METHODS

Thirty-eight patients with non-ST segment elevation myocardial infarction (NSTEMI) or unstable angina (UA) and scheduled for percutaneous coronary intervention underwent dual-source CT immediately before catheterisation. CT images were analysed for the presence of any PD by using a 17-segment model. Results were compared with peak cardiac troponin-I (cTnI) and angiography findings.

RESULTS

PD were seen in 21 of the 24 patients with NSTEMI (median peak cTnI level 7.07 ng/mL; range 0.72-37.07 ng/mL) and in 2 of 14 patients with UA. PD corresponded with the territory of the infarct-related artery in 20 out of 22 patients. In a patient-based analysis, sensitivity, specificity, negative and positive predictive values of any PD for predicting NSTEMI were 88%, 86%, 80% and 91%. Per culprit artery, the respective values were 86%, 75%, 80% and 83%.

CONCLUSION

In patients with non-ST segment elevation ACS, first-pass myocardial PD in contrast-enhanced MDCT correlate closely with the presence of myocardial necrosis, as determined by increases in cTnI levels.

Reperfusion injury components and manifestations determined by cardiovascular MR and MDCT imaging

Advances in magnetic resonance (MR) and computed tomography (CT) imaging have improved visualization of acute and scar infarct. Over the past decade, there have been and continues to be many significant technical advancements in cardiac MR and multi-detector computed tomography (MDCT) technologies. The strength of MR imaging relies on a variety of pulse sequences and the ability to noninvasively provide information on myocardial structure, function and perfusion in a single imaging session. The recent technical developments may also allow CT technologies to rise to the forefront for evaluating clinical ischemic heart disease. Components of reperfusion injury including myocardial edema, hemorrhage, calcium deposition and microvascular obstruction (MO) have been demonstrated using MR and CT technologies. MR imaging can be used serially and noninvasively in assessing acute and chronic consequences of reperfusion injury because there is no radiation exposure or administration of radioactive materials. MDCT is better suited for assessing coronary artery stenosis and as an alternative technique for assessing viability in patients where MR imaging is contraindicated. Changes in left ventricular (LV) volumes and function measured on cine MR are directly related to infarct size measured on delayed contrast enhanced images. Recent MR studies found that transmural infarct, MO and peri-infarct zone are excellent predictors of poor post-infarct recovery and mortality. Recent MR studies provided ample evidence that growth factor genes and stem cells delivered locally have beneficial effects on myocardial viability, perfusion and function. The significance of deposited calcium in acute infarct detected on MDCT requires further studies. Cardiac MR and MDCT imaging have the potential for assessing reperfusion injury components and manifestations.

Assessment of myocardial edema by computed tomography in myocardial infarction

OBJECTIVES

The aim of this study was to analyze whether cardiac computed tomography (CT) permits the assessment of myocardial edema in acute myocardial infarction (MI).

BACKGROUND

Several studies proved the value of detecting myocardial edema from T2-weighted cardiac magnetic resonance (CMR) for differentiating acute from chronic MI. Computed tomography is suited for depicting MI, but there are no data on CT imaging of myocardial edema. We hypothesized that areas of reduced attenuation in acute MI may correspond to edema.

METHODS

In 7 pigs (55.2 +/- 7.3 kg), acute MI was induced using a closed chest model. Animals underwent unenhanced arterial and late-phase dual source computed tomography (DSCT) followed by T2-weighted and delayed contrast-enhanced CMR. Animals were sacrificed, and the excised hearts were stained with 2,3,5-triphenyltetrazolin chloride (TTC). Size of MI, contrast-to-noise ratio, and percent signal difference were compared among the different imaging techniques with concordance-correlation coefficients (rho(c)), Bland-Altman plots, and analysis of variance for repeated measures.

RESULTS

Infarction was transmural on all slices. On unenhanced, arterial, and late-phase DSCT, mean sizes of MI were 27.2 +/- 8.5%, 20.1 +/- 6.9%, and 23.1 +/- 8.2%, respectively. Corresponding values on T2-weighted and delayed enhanced CMR were 28.5 +/- 7.8% and 22.2 +/- 7.7%. Size of MI on TTC staining was 22.6 +/- 7.8%. Best agreement was observed when comparing late-phase CT (rho(c) = 0.9356) and delayed enhanced CMR (rho(c) = 0.9248) with TTC staining. There was substantial agreement between unenhanced DSCT and T2-weighted CMR (rho(c) = 0.8629). Unenhanced DSCT presented with the lowest percent signal difference (46.0 +/- 18.3) and the lowest contrast-to-noise ratio (4.7 +/- 2.0) between infarcted and healthy myocardium.

CONCLUSIONS

Unenhanced DSCT permits the detection of myocardial edema in large acute MI. Further studies including smaller MI in different coronary artery territories and techniques for improving the contrast-to-noise ratio are needed.

Applications of cardiac multidetector CT beyond coronary angiography

Noninvasive imaging of the coronary arteries using multidetector CT (MDCT) represents one of the most promising diagnostic imaging advances in contemporary cardiology. This challenging application has driven a rapid and impressive advancement in CT technology over the past 10 years; leading to increased spatial and temporal resolution, decreased scan times and substantial reductions in radiation dose. Recent technological improvements have not only improved the status of CT coronary angiography but have also enabled new functional myocardial applications that are gaining a foothold in clinical practice as adjuncts or replacements for conventional coronary angiographic studies. Wide-detector CT designs along with prospective ECG-triggered protocols have opened the possibility of performing multiple complementary myocardial measurements during a coronary CT exam with acceptable radiation and contrast exposure. In this Review, we discuss recent technical developments in cardiac MDCT and outline newly enabled noncoronary cardiac applications including viability assessment, myocardial perfusion and molecular imaging.

Chronic myocardial infarction detection and characterization during coronary artery calcium scoring acquisitions

BACKGROUND

Hypoenhanced regions on multidetector CT (MDCT) coronary angiography correlate with myocardial hyperperfusion. In addition to a limited capillary density, chronic myocardial infarction (MI) commonly contains a considerable amount of adipose tissue.

OBJECTIVE

We explored whether regional myocardial hypoenhancement on contrast-enhanced MDCT could be identified with standard coronary artery calcium (CAC) scoring acquisitions with noncontrast CT.

METHODS

Consecutive patients with a history of MI who were referred for contrast-enhanced MDCT from November 2006 until March 2009 were studied. Noncontrast CT for CAC scoring was also performed. The correlation between regional myocardial hypoenhancement on contrast-enhanced CT and regional myocardial hypoattenuated areas on noncontrast CT was defined.

RESULTS

Eighty-three patients (mean age, 61.5+/-12.5 years; n=67; 81% male) with previous MI were studied. A total of 1411 myocardial segments were evaluated. Two hundred thirty-nine segments (17%) showed myocardial hypoenhancement by MDCT and 140 segments (9.6%) by CAC. On a patient level, noncontrast CT showed a sensitivity, specificity, positive predictive value, (PPV) and negative predictive value (NPV) of 66% (95% CI, 0.53-0.77), 100% (95% CI, 0.76-1.00), 100% (95% CI, 0.90-1.00), and 41% (95% CI, 0.26-0.58), respectively, to detect myocardial hypoenhancement. On a per segment level, noncontrast CT showed a sensitivity, specificity, PPV, and NPV of 58% (95% CI, 0.51-0.64), 100% (95% CI, 0.99-1.00), 99% (95% CI, 0.94-1.00), and 92% (95% CI, 0.90-0.93), respectively, to detect myocardial hypoenhancement.

CONCLUSIONS

Our findings suggest that chronic MI can be detected with standard CAC scoring acquisitions.

Impact of contrast material volume on quantitative assessment of reperfused acute myocardial infarction using delayed-enhancement 64-slice CT: experience in a porcine model

PURPOSE

Our purpose in this study was to compare the impact of contrast material volume in delayed-enhancement computer tomography (CT) imaging for assessing acute reperfused myocardial infarction.

MATERIALS AND METHODS

In five domestic pigs (20-30 kg), the circumflex coronary artery (CX) was balloon-occluded for 2 h followed by reperfusion. After 5 days, CT imaging was performed after intravenous administration of iodinated contrast material (Iomeprol 400 mgI/ml; Bracco, Italy). A 64-slice multidetector CT (MDCT) (Sensation 64, Siemens) scanner was used for imaging, with standard angiography characteristics. Three scans were performed: first, coronary angiography at first pass with 1.25 gI/kg of contrast material (ART); and remaining delayed-enhancement (DE(1)-DE(2)) 15 min after administration of 1.25 (DE(1)) and 15 min after additional administration of 2.50 gI/kg (=total 3.75 gI/kg - DE(2)). Mean heart rate decreased to 51+/-9 bpm after intravenous administration of Zatebradine (10 mg/kg). Data sets were reconstructed during the end-diastolic phase of the cardiac cycle. Areas of infarction-enhanced (DE), no-reflow (no-reflow) and remote myocardial [remote left ventricle (LV)] were manually contoured. CT attenuation values (Hounsfield units) were measured using five regions of interest: DE, no-reflow, remote LV, left ventricular cavity (lumen LV) and in air. Differences, correlations, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated.

RESULTS

We found significant differences between the attenuation of DE, no-reflow and remote LV (p<0.001). DE and no-reflow size were assessed accurately with DEMDCT. In particular, SNR and CNR showed higher values in DE(2) (approximately 6.0 and 3.5, respectively; r(2)=0.90) vs. DE(1) (approximately 4.0 and 2.2, respectively; r(2)=0.85).

CONCLUSIONS

The increase of contrast material volume determines a significant improvement in myocardial infarction image quality with DE-MDCT.

Using multidetector computed tomography in a swine model to assess the effects of sublingual nitroglycerin and intravenous adenosine on epicardial coronary arteries

This study examines the effects of intravenous infusion of adenosine and sublingual nitroglycerin on coronary angiograms obtained by current-generation multidetector computed tomography. We assessed coronary vasodilation at baseline and after intravenous adenosine (140 microg/kg/min) or sublingual nitroglycerin spray (800 microg) in 7 female swine (weight, 40.9 +/- 1.4 kg) by using electrocardiogram-gated coronary angiography with a 64-detector scanner (rotation time, 400 ms; 120kV; 400 mA) and intravenous contrast (300 mg/mL iohexol, 4.5 mL/s, 2 mL/kg). Cross-sectional areas of segments in the left anterior descending, circumflex, and right coronary arteries were evaluated in oblique orthogonal views. Images were acquired at an average heart rate of 73 +/- 11 beats per minute. Changes in aortic pressure were not significant with nitroglycerin but decreased (approximately 10%) with adenosine. Of the 76 segments analyzed (baseline range, 2 to 39 mm2), 1 distal segment could not be assessed after adenosine. Segment cross-sectional area increased by 11.3% with nitroglycerin but decreased by 9.6% during adenosine infusion. The results of the present study are consistent with the practice of using sublingual nitroglycerin to enhance visualization of epicardial vessels and suggest that intravenous adenosine may hinder coronary artery visualization. This study is the first repeated-measures electrocardiogram-gated CT evaluation to use the same imaging technology to assess changes in coronary cross-sectional area before and after treatment with a vasodilator. The nitroglycerin-associated changes in our swine model were modest in comparison with previously reported human studies.

CT of coronary artery disease

Technical innovation is rapidly improving the clinical utility of cardiac computed tomography (CT) and will increasingly address current technical limitations, especially the association of this test with relatively high levels of radiation. Guidelines for appropriate indications are in place and are evolving, with an increasing evidence base to ensure the appropriate use of this modality. New technologies and new applications, such as myocardial perfusion imaging and dual-energy CT, are being explored and are widening the scope of coronary CT angiography from mere coronary artery assessment to the integrative analysis of cardiac morphology, function, perfusion, and viability. The scientific evaluation of coronary CT angiography has left the stage of feasibility testing and increasingly, evidence-based data are accumulating on outcomes, prognosis, and cost-effectiveness. In this review, these developments will be discussed in the context of current pivotal transitions in cardiovascular disease management and their potential influence on the current role and future fate of coronary CT angiography will be examined.

Prospective electrocardiogram-gated delayed enhanced multidetector computed tomography accurately quantifies infarct size and reduces radiation exposure

OBJECTIVES

This study sought to determine whether low-dose, prospective electrocardiogram (ECG)-gated delayed contrast-enhanced multidetector computed tomography (DCE-MDCT) can accurately delineate the extent of myocardial infarction (MI) compared with retrospective ECG-gated DCE-MDCT.

BACKGROUND

For defining the location and extent of MI, DCE-MDCT compares well with delayed enhanced cardiac magnetic resonance. However, the addition of a delayed scan requires additional radiation exposure to patients. MDCT protocols using prospective ECG gating can substantially reduce effective radiation dose exposure, but these protocols have not yet been applied to infarct imaging.

METHODS

Ten porcine models of acute MI were imaged 10 days after MI using prospective and retrospective ECG-gated DCE-MDCT (64-slice) 10 min after a 90-ml contrast bolus. The MDCT images were analyzed using a semiautomated computed tomography density (CTD) threshold technique. Infarct size, signal-to-noise (SNR) ratios, contrast-to-noise (CNR) ratios, and image quality metrics were compared between the 2 ECG-gating techniques.

RESULTS

Infarct volume measurements obtained by both methods were strongly correlated (R = 0.93, p < 0.001) and in good agreement (mean difference: -0.46 ml +/- 4.00%). Compared with retrospective ECG gating, estimated radiation dosages were markedly reduced with prospective ECG gating (930.1 +/- 62.2 mGy x cm vs. 42.4 +/- 2.3 mGy x cm, p < 0.001). The SNR and CNR of infarcted myocardium were somewhat lower for prospective gated images (22.0 +/- 11.0 vs. 16.3 +/- 7.8 and 8.8 +/- 5.3 vs. 7.0 +/- 3.9, respectively; p < 0.001). However, all examinations using prospective gating protocol achieved sufficient diagnostic image quality for the assessment of MI.

CONCLUSIONS

Prospective ECG-gated DCE-MDCT accurately assesses infarct size compared with retrospective ECG-gated DCE-MDCT imaging. Although infarct SNR and CNR were significantly higher for the retrospective gated protocol, prospective ECG-gated DCE-MDCT provides high-resolution imaging of MI, while substantially lowering the radiation dose.

Myocardial viability and revascularization

Cardiovascular MRI can assess multiple markers of myocardial viability in a single examination. Its accuracy is at least equivalent to, if not superior to, that of other currently available noninvasive imaging techniques, including positron emission tomography. The greater spatial resolution afforded by cardiovascular MRI, especially with the delayed-enhancement MRI (DE-MRI) technique, combined with the breadth and depth of correlative pathologic data, makes cardiovascular MRI a particularly powerful tool for detecting viable and irreversibly damaged myocardium. A wealth of clinical data exist, including data from multicenter efforts, to establish DE-MRI as a new gold standard in myocardial viability assessment. As the high accuracy and broad scope of DE-MRI are recognized, the technique will gain wider clinical use for analysis of dysfunctional myocardium and be integrated into the diagnostic and therapeutic algorithm.

[Technological advances in cardiac CT]

The SFR-SFC presents guidelines dedicated to cardiac and coronary imaging using CT in the area of indications, technological requirement including both hardware and software, patient conditioning, CT protocols and related results concerning radiation dose, image quality and diagnostic value. These guidelines are based either on up-dated medical literature proofs and/or on expert consensus.

Volumetric quantification of myocardial perfusion using analysis of multi-detector computed tomography 3D datasets: comparison with nuclear perfusion imaging

BACKGROUND

Although the ability of multi-detector computed tomography (MDCT) to detect perfusion abnormalities associated with acute and chronic myocardial infarction (MI) has been demonstrated, this methodology is based on visual interpretation of selected 2D slices.

OBJECTIVES

We sought to develop a new technique for quantitative volumetric analysis of myocardial perfusion from 3D datasets and test it against resting nuclear myocardial perfusion imaging (NMPI) reference.

METHODS

We studied 44 patients undergoing CTCA: a control group of 15 patients and a study group of 29 patients. MDCT datasets acquired for CTCA were analyzed using custom software designed to: (1) generate bull's eye display of myocardial perfusion and (2) calculate a quantitative index of extent and severity of perfusion abnormality, Q(H), for 16 volumetric myocardial segments. Visual interpretation of MDCT-derived bull's eyes was compared with rest NMPI scores using kappa statistics of agreement on a coronary territory and patient basis. Quantitative MDCT perfusion data were correlated with rest NMPI summed scores and used for objective detection of perfusion defects.

RESULTS

Visual analysis of MDCT-derived bull's eyes accurately detected perfusion defects in agreement with NMPI (kappa = 0.70 by territory; 0.79 by patient). Quantitative data were in good agreement with NMPI, as reflected by: (1) correlation of 0.87 (territory) and 0.84 (patient) between summed Q(H) and NMPI scores, (2) area under ROC curve 0.87 with sensitivity of 0.79-0.92, specificity 0.83-0.91, and accuracy 0.83-0.89 for objective detection of abnormalities.

CONCLUSIONS

Our new technique for volumetric analysis of 3D MDCT images allows accurate objective detection of perfusion defects. This perfusion information can be obtained without additional radiation or contrast load, and may aid in elucidating the significance of coronary lesions.

Visualization of coronary venous anatomy by cardiovascular magnetic resonance

BACKGROUND

Coronary venous imaging with whole-heart cardiovascular magnetic resonance (CMR) angiography has recently been described using developmental pulse sequences and intravascular contrast agents. However, the practical utility of coronary venous imaging will be for patients with heart failure in whom cardiac resynchronisation therapy (CRT) is being considered. As such complementary information on ventricular function and myocardial viability will be required. The aim of this study was to determine if the coronary venous anatomy could be depicted as part of a comprehensive CMR protocol and using a standard extracellular contrast agent.

METHODS AND RESULTS

Thirty-one 3D whole heart CMR studies, performed after intravenous administration of 0.05 mmol/kg gadolinium DTPA, were reviewed. The cardiac venous system was visualized in all patients. The lateral vein of the left ventricle was present in 74%, the anterior interventricular vein in 65%, and the posterior interventricular vein in 74% of patients. The mean maximum distance of demonstrable cardiac vein on the 3D images was 81.5 mm and was dependent on the quality of the 3D data set. Five patients showed evidence of myocardial infarction on late gadolinium enhancement (LGE) images.

CONCLUSION

Coronary venous anatomy can be reliably demonstrated using a comprehensive CMR protocol and a standard extracellular contrast agent. The combination of coronary venous imaging, assessment of ventricular function and LGE may be useful in the management of patients with LV dysfunction being considered for CRT.

Comparison of dual-energy computed tomography of the heart with single photon emission computed tomography for assessment of coronary artery stenosis and of the myocardial blood supply

To evaluate the performance of dual-energy computed tomography (CT) for integrative imaging of the coronary artery morphology and the myocardial blood supply, 36 patients (15 women, mean age 57 +/- 11 years) with equivocal or incongruous single photon emission CT (SPECT) results were investigated by a single-contrast medium-enhanced, retrospectively electrocardiographic-gated dual-energy CT (DECT) scan with simultaneous acquisition of high and low x-ray spectra. Thirteen patients subsequently underwent invasive coronary angiography (ICA). The DECT data were used to reconstruct anatomic coronary CT angiographic images and to map the myocardial iodine distribution within the left ventricular myocardium. Two independent observers analyzed all DECT studies for stenosis and myocardial iodine defects. A segmental comparison was performed between the stress/rest SPECT perfusion defects and DECT iodine defects and between the ICA and coronary CT angiographic findings for stenosis. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were estimated, along with the kappa statistics. Overall, DECT had 92% sensitivity and 93% specificity, with 93% accuracy for detecting any type of myocardial perfusion defect seen on SPECT. Contrast defects at DECT correctly identified 85 (96%) of 89 fixed and 60 (88%) of 68 reversible myocardial perfusion defects. The interobserver agreement was very good (weighted kappa = 0.87). Compared with ICA, coronary CT angiography had 90% sensitivity, 94% specificity, and 93% accuracy for the detection of >50% stenosis. In conclusion, our initial experience suggests that DECT, as a single examination, might be promising for the integrative analysis of the coronary artery morphology and the myocardial blood supply and is in good agreement with ICA and SPECT.

Noninvasive cardiovascular imaging techniques for basic science research: application to cellular therapeutics

Cell therapy continues to be an active area of basic science research with early promise in the treatment of cardiovascular diseases. However, there are many unknowns including the mechanisms by which they work, the most useful cell types, the most efficient delivery strategies, and their safety. Noninvasive imaging provides a wide array of tools to quantitatively address many of these unknowns. This article reviews echocardiography, magnetic resonance imaging, computed tomography, positron emission tomography and single photon emission tomography in the context of imaging cellular therapeutics to demonstrate how these modalities are being used to answer some of these questions.

Cardiac positron emission tomography

Positron emission tomography (PET) is a powerful, quantitative imaging modality that has been used for decades to noninvasively investigate cardiovascular biology and physiology. Due to limited availability, methodologic complexity, and high costs, it has long been seen as a research tool and as a reference method for validation of other diagnostic approaches. This perception, fortunately, has changed significantly within recent years. Increasing diversity of therapeutic options for coronary artery disease, and increasing specificity of novel therapies for certain biologic pathways, has resulted in a clinical need for more accurate and specific diagnostic techniques. At the same time, the number of PET centers continues to grow, stimulated by PET's success in oncology. Methodologic advances as well as improved radiotracer availability have further contributed to more widespread use. Evidence for diagnostic and prognostic usefulness of myocardial perfusion and viability assessment by PET is increasing. Some studies suggest overall cost-effectiveness of the technique despite higher costs of a single study, because unnecessary follow-up procedures can be avoided. The advent of hybrid PET-computed tomography (CT), which enables integration of PET-derived biologic information with multislice CT-derived morphologic information, and the key role of PET in the development and translation of novel molecular-targeted imaging compounds, have further contributed to more widespread acceptance. Today, PET promises to play a leading diagnostic role on the pathway toward a future of high-powered, comprehensive, personalized, cardiovascular medicine. This review summarizes the state-of-the-art in current imaging methodology and clinical application, and outlines novel developments and future directions.

Integration of Infarct Size, Tissue Perfusion, and Metabolism by Hybrid Cardiac Positron Emission Tomography/Computed Tomography

Background— Hybrid positron emission tomography/computed tomography (PET-CT) allows for combination of PET perfusion/metabolism imaging with infarct detection by CT delayed contrast enhancement. We used this technique to obtain biomorphological insights into the interrelation between tissue damage, inflammation, and microvascular obstruction early after myocardial infarction.

Methods and Results— A porcine model of left anterior descending coronary artery occlusion/reperfusion was studied. Seven animals underwent PET-CT within 3 days of infarction, and a control group of 3 animals was scanned at >4 weeks. Perfusion and glucose uptake were assessed by [ 13 N]-ammonia/[ 18 F]-deoxyglucose (FDG), and 64-slice CT delayed contrast enhancement was measured. In the acute infarct model, CT revealed a no-reflow phenomenon suggesting microvascular obstruction in 80% of all infarct segments. PET showed increased FDG uptake in 68% of the CT-defined infarct segments. Ex vivo staining and histology showed active inflammation in the acute infarct area as an explanation for increased glucose uptake. In chronic infarction, CT showed no microvascular obstruction and agreed well with matched perfusion/metabolism defects on PET.

Conclusions— Perfusion/metabolism PET and delayed enhancement CT can be combined within a single hybrid PET-CT session. Increased regional FDG uptake in the acute infarct area is frequently observed. In contrast to the chronic infarct setting, this indicates tissue inflammation that is commonly associated with microvascular obstruction as identified by no reflow on CT. The consequences of these pathophysiological findings for subsequent ventricular remodeling should be explored in further studies.

Coronary computed tomography and magnetic resonance imaging

Cardiac computed tomography and magnetic resonance are relatively new imaging modalities that can exceed the ability of established imaging modalities to detect present pathology or predict patient outcomes. Coronary calcium scoring may be useful in asymptomatic patients at intermediate risk. Computed tomographic coronary angiography is a first-line indication to evaluate congenitally abnormal coronary arteries and, along with stress magnetic resonance myocardial perfusion imaging, is useful in symptomatic patients with nondiagnostic conventional stress tests. Cardiac magnetic resonance is indicated for visualizing cardiac structure and function, and delayed enhancement magnetic resonance is a first-line indication for assessing myocardial viability. Imaging plaque and molecular mechanisms related to plaque rupture holds great promise for the presymptomatic detection of patients at risk for coronary events but is not yet suitable for routine clinical use.

Characterization of peri-infarct zone heterogeneity by contrast-enhanced multidetector computed tomography: a comparison with magnetic resonance imaging

OBJECTIVES

This study examined whether multidetector computed tomography (MDCT) improves the ability to define peri-infarct zone (PIZ) heterogeneity relative to magnetic resonance imaging (MRI).

BACKGROUND

The PIZ as characterized by delayed contrast-enhancement (DE)-MRI identifies patients susceptible to ventricular arrhythmias and predicts outcome after myocardial infarction (MI).

METHODS

Fifteen mini-pigs underwent coronary artery occlusion followed by reperfusion. Both MDCT and MRI were performed on the same day approximately 6 months after MI induction, followed by animal euthanization and ex vivo MRI (n = 5). Signal density threshold algorithms were applied to MRI and MDCT datasets reconstructed at various slice thicknesses (1 to 8 mm) to define the PIZ and to quantify partial volume effects.

RESULTS

The DE-MDCT reconstructed at 8-mm slice thickness showed excellent correlation of infarct size with post-mortem pathology (r2 = 0.97; p < 0.0001) and MRI (r2 = 0.92; p < 0.0001). The DE-MDCT and -MRI were able to detect a PIZ in all animals, which correlates to a mixture of viable and nonviable myocytes at the PIZ by histology. The ex vivo DE-MRI PIZ volume decreased with slice thickness from 0.9 +/- 0.2 ml at 8 mm to 0.2 +/- 0.1 ml at 1 mm (p = 0.01). The PIZ volume/mass by DE-MDCT increased with decreasing slice thickness because of declining partial volume averaging in the PIZ, but was susceptible to increased image noise.

CONCLUSIONS

A DE-MDCT provides a more detailed assessment of the PIZ in chronic MI and is less susceptible to partial volume effects than MRI. This increased resolution best reflects the extent of tissue mixture by histopathology and has the potential to further enhance the ability to define the substrate of malignant arrhythmia in ischemic heart disease noninvasively.

Combined assessment of coronary anatomy and myocardial perfusion using multidetector computed tomography for the evaluation of coronary artery disease

Multidetector computed tomography (MDCT) is increasingly used as an alternative to invasive coronary angiography. Although computed tomographic coronary angiography (CTCA) has been validated against invasive coronary angiography and nuclear myocardial perfusion imaging, the potential of MDCT to evaluate perfusion has not been fully explored. We sought to (1) develop a new technique for quantitative assessment of myocardial enhancement based on analysis of MDCT images acquired for CTCA, (2) identify the underlying causes of myocardial hypoenhancement detected by MDCT, and (3) determine the added diagnostic value of the MDCT perfusion index when combined with CTCA. We studied 84 patients undergoing clinical CTCA (64 patients with invasive coronary angiogram and a control group of 20 patients). MDCT perfusion index was calculated from x-ray attenuation measured in 16 myocardial segments. Hypoenhancement was automatically detected using comparisons with the normal range obtained in the control group, and its added value was determined against invasive coronary angiographic findings combined with known previous myocardial infarction. Myocardial hypoenhancement was detected in 29 of 64 patients in 47 vascular territories, of which 36 (77%) were abnormal by the reference technique. Of these 36 abnormalities, 10 (28%) were associated with previous myocardial infarction, whereas 26 (72%) corresponded to significant coronary stenosis. The addition of MDCT perfusion index to CTCA improved its diagnostic accuracy (sensitivity 0.87 to 0.96, accuracy 0.84 to 0.88, despite a decrease in specificity 0.79 to 0.68). In conclusion, myocardial hypoenhancement is a potentially valuable addition to MDCT evaluation of coronary artery disease without additional cost in radiation dose or contrast load.

Noncoronary applications of cardiac multidetector row computed tomography

Multidetector row computed tomography (MDCT) has a high diagnostic accuracy to evaluate coronary artery stenoses. Additionally, the 4-dimensional aspect of cardiac MDCT allows a comprehensive evaluation of cardiac structure and function. Left ventricular volumes and systolic function can be accurately assessed with MDCT, and imaging of myocardial infarction is a promising application of cardiac MDCT. In addition, MDCT may provide anatomical visualization of heart valves. Also, evaluation of anatomy of the pulmonary veins and cardiac venous system render MDCT a valuable tool for the cardiologist performing electrophysiological procedures. In this article, the role of MDCT in the noninvasive evaluation of cardiac structure and function is discussed. An overview of the wide range of noncoronary applications of cardiac MDCT is provided, focusing on the assessment of left ventricular function, valvular heart disease, and cardiac venous anatomy.

Value of multidetector computed tomography evaluation of myocardial perfusion in the assessment of ischemic heart disease: comparison with nuclear perfusion imaging

MDCT-derived myocardial perfusion has not yet been validated against accepted standards. We developed a technique for quantification of myocardial perfusion from MDCT images and studied its diagnostic value against SPECT myocardial perfusion imaging (MPI). Ninety-eight patients were studied. Abnormal perfusion was detected by comparing normalized segmental x-ray attenuation against values obtained in 20 control subjects. Disagreement with resting MPI was investigated in relationship to MDCT image quality, severity of MPI abnormalities, and stress MPI findings. Resting MPI detected mild or worse abnormalities in 20/78 patients. MDCT detected abnormalities in 15/20 patients (sensitivity of 0.75). Most abnormalities missed by MDCT analysis were graded as mild on MPI. Additional abnormalities found in 16/78 patients were not confirmed on resting MPI (specificity of 0.72). However, 8 of these 16 apparently false positive MDCT perfusion tests had abnormal stress MPI; of these 8 patients, 7 had optimal MDCT image quality, while in 6/8 remaining patients, image quality was suboptimal. When compared with resting MPI, MDCT detected perfusion abnormalities with high accuracy. Moreover, half of MDCT perfusion abnormalities not confirmed by resting MPI were associated with abnormal stress MPI. Importantly, this information can be obtained without additional radiation dose or contrast agent.

Recent developments in wide-detector cardiac computed tomography

Multidetector computed tomography (MDCT) using 64 detectors is widely used for cardiac imaging in the clinical setting. Despite promising results, 64-slice MDCT has important limitations for cardiac applications related to detector coverage, which leads to longer scan times, image artifacts, increased radiation and the need for higher contrast doses. The advent of wide or full cardiac coverage with 256- or 320-slice MDCT provides important advantages that can potentially improve the status of these limitations and expand the utility of cardiac MDCT imaging beyond coronary imaging. Additionally, the combination of wide-detectors and multi-energy acquisitions offer interesting possibilities of improved coverage and temporal resolution that may improve plaque characterization as well as viability and perfusion imaging. In this review we will discuss the current status of wide-detector MDCT scanners and their advantages for clinical coronary and ventricular imaging. We will also review examples of wide detector coronary angiography imaging and discuss emerging complementary non-coronary applications that have been enabled by wide-detector MDCT imaging.

Quantitative measurement of iodine concentration in the liver using abdominal C-arm computed tomography

RATIONALE AND OBJECTIVES

C-arm computed tomography is an option on a C-arm angiographic system capable of acquiring projections while rotating the C-arm around the patient and reconstructing cross-sectional images with improved contrast resolution of 5 to 10 Hounsfield units. Typical abdominal C-arm computed tomographic (CCT) images, however, exhibit artifacts with spatially varying and drifting pixel values. Considering liver tumor oncologic procedures, the aim of this study was to evaluate the accuracy of liver iodine concentration (IC) estimated from CCT images under such challenging conditions.

MATERIALS AND METHODS

The proposed method estimates the IC in a region of interest (ROI) using pixel values of CCT images measured at the ROI and a nonenhanced background. Two approaches to measure the background value were tested: one approach, L-BG, measured a corresponding local background value near each ROI, and the other, G-BG, used one global background value for the entire object. The accuracy of estimations using CCT and computed tomographic scanners was evaluated; an elliptical cylinder water phantom with iodine solution inserts and seven patient data sets with transcatheter arterial chemoembolization were used.

RESULTS

With the least "truncation" (the edge of the object being outside the field of view) of 27 mm, the IC was accurately estimated with CCT images (n = 9; root-mean-square error [RMSE], 1.60-1.63 mg/mL; normalized RMSE, 11.8%; r(2) = 0.97; P < .001), with the true concentration ranging from 2.32 to 31.82 mg/mL. With truncations of up to 100 mm (n = 88), the estimation by L-BG remained accurate independent of the amount of truncation (RMSE, 1.58 mg/mL; normalized RMSE, 12.5%; r(2) = 0.06; P = .02), whereas the estimation by G-BG reduced the accuracy (RMSE, 4.61 mg/mL; normalized RMSE, 34.3%; r(2) = 0.10; P = .003). Clinical data (n = 37) showed that the estimation from CCT images using the L-BG method agreed well with that from computed tomographic images (RMSE, 2.86 mg/mL; normalized RMSE, 38.7%; r(2) = 0.76; P < .001).

CONCLUSION

The liver IC can be accurately estimated with abdominal CCT images.