Stress myocardial CT perfusion: an update and future perspective

Comparison of myocardial transmural perfusion gradient by magnetic resonance imaging to fractional flow reserve in patients with suspected coronary artery disease

The goal of this study was to evaluate the diagnostic accuracy of transmural perfusion gradient (TPG) and transmural perfusion gradient reserve (TPGR) with 3.0 T cardiac magnetic resonance (CMR) against invasively determined fractional flow reserve (FFR) to detect coronary artery stenosis. Quantitative analysis of myocardial perfusion with CMR to diagnosis coronary artery disease (CAD) has been widely accepted. However, traditional transmural myocardial perfusion analysis with CMR neglects that endocardium is more vulnerable to ischemia than epicardium. TPG and TPGR can take the inhomogenous perfusion impairment into account and be more sensitive and specific for diagnosis of CAD. In this study, 71 patients (57 men, age 60.1 ± 6.4 years) with known or suspected CAD referred for invasive angiography study underwent rest and adenosine-induced stress CMR perfusion imaging scan. FFR was attempted to be measured in all major epicardial coronary arteries. FFR ≤0.75 was regarded to indicate a hemodynamic significant coronary lesion. A TPG ≤0.85 predicted significant CAD with sensitivity and specificity of 74.55% and 83.65%, respectively. Sensitivity and specificity of TPGR ≤0.81 were 90.91% and 89.94%, respectively. Area under the receiver-operating curve to detect FFR ≤0.75 was 0.86 for TPG and 0.95 for TPGR. TPGR yielded significantly better sensitivity and specificity for diagnosis of CAD than traditional myocardial blood flow, myocardial perfusion reserve, and TPG (p < 0.0001). In conclusion, TPG and TPGR analyses with MRI are capable of detecting hemodynamic stenosis of coronary artery and superior to traditional myocardial perfusion analysis. Furthermore, TPGR appears to be superior to TPG in the diagnosis of coronary artery stenosis.

Multi-modality imaging for the assessment of myocardial perfusion with emphasis on stress perfusion CT and MR imaging

High-quality and non-invasive diagnostic tools for assessing myocardial ischemia are necessary for therapeutic decisions regarding coronary artery disease. Myocardial perfusion has been studied using myocardial contrast echo perfusion, single-photon emission computed tomography, positron emission tomography, cardiovascular magnetic resonance, and, more recently, computed tomography. The addition of coronary computed tomography angiography to myocardial perfusion imaging improves the specificity and overall diagnostic accuracy of detecting the hemodynamic significance of coronary artery stenosis. This study reviews the benefits, limitations, and imaging findings of various imaging modalities for assessing myocardial perfusion, with particular emphasis on stress perfusion computed tomography and cardiovascular magnetic resonance imaging.

Computed tomography quantification of coronary plaque volume may provide further perspective on intermediate severity stenoses

Coronary computed tomography angiography (CCTA) is an emerging modality for comprehensive non-invasive assessment of coronary artery disease (CAD). CCTA was traditionally used for anatomical assessment of coronary plaque, including luminal narrowing, plaque burden, location, and composition. Preliminary studies have also demonstrated CCTA's capabilities for functional assessment of coronary plaque, including fractional flow reserve (FFR) and myocardial perfusion-albeit they are not routinely available at all centers and are focus of research. Although the identification and development of treatment strategies of severely stenotic lesions has advanced tremendously over the past years, the evaluation, prognostication, and treatment of patients with intermediate severity stenosis in whom there is equipoise between invasive versus medical management is only now receiving attention. Intermediate severity stenosis is the most likely to benefit from additional measures of disease beyond traditional clinical risk profiling and CCTA visual examination. Nakazato et al. studied 58 patients with intermediate severity stenosis and quantified the percent aggregate plaque volume (%APV), a novel measure of total arterial plaque disease. %APV had the highest correlation with ischemic lesions on FFR, outperforming luminal diameter, luminal area, minimal lumen diameter, and minimal lumen area. This study extracts additional information from pre-existing CT data-sets and suggest novel concept that might improve classification of moderate severity coronary stenoses.

Noninvasive physiologic assessment of coronary stenoses using cardiac CT

Coronary CT angiography (CCTA) has become an important noninvasive imaging modality in the diagnosis of coronary artery disease (CAD). CCTA enables accurate evaluation of coronary artery stenosis. However, CCTA provides limited information on the physiological significance of stenotic lesions. A noninvasive "one-stop-shop" diagnostic test that can provide both anatomical significance and functional significance of stenotic lesions would be beneficial in the diagnosis and management of CAD. Recently, with the introduction of novel techniques, such as myocardial CT perfusion, CT-derived fractional flow reserve (FFRCT), and transluminal attenuation gradient (TAG), CCTA has emerged as a noninvasive method for the assessment of both anatomy of coronary lesions and its physiological consequences during a single study. This review provides an overview of the current status of new CT techniques for the physiologic assessments of CAD.

Multimodality Imaging in Ischemic Cardiomyopathy

Cardiac multimodality (hybrid) imaging can be obtained from a variety of techniques, such as nuclear medicine with single photon emission computed tomography (SPECT) and positron emission tomography (PET), or radiology with multislice computed tomography (CT), magnetic resonance (MR) and echography. They are typically combined in a side-by-side or fusion mode in order to provide functional and morphological data to better characterise coronary artery disease, with more proven efficacy than when used separately. The gained information is then used to guide revascularisation procedures. We present an up-to-date comprehensive overview of multimodality imaging already in clinical use, as well as a combination of techniques with promising or developing applications.

Thoracic dual energy CT: acquisition protocols, current applications and future developments

Thanks to a simultaneous acquisition at high and low kilovoltage, dual energy computed tomography (DECT) can achieve material-based decomposition (iodine, water, calcium, etc.) and reconstruct images at different energy levels (40 to 140keV). Post-processing uses this potential to maximise iodine detection, which elicits demonstrated added value for chest imaging in acute and chronic embolic diseases (increases the quality of the examination and identifies perfusion defects), follow-up of aortic endografts and detection of contrast uptake in oncology. In CT angiography, these unique features are taken advantage of to reduce the iodine load by more than half. This review article aims to set out the physical basis for the technology, the acquisition and post-processing protocols used, its proven advantages in chest pathologies, and to present future developments.

Quantification of myocardial perfusion using cardiac magnetic resonance imaging correlates significantly to rubidium-82 positron emission tomography in patients with severe coronary artery disease: a preliminary study

INTRODUCTION

Aim was to compare absolute myocardial perfusion using cardiac magnetic resonance imaging (CMRI) based on Tikhonov's procedure of deconvolution and rubidium-82 positron emission tomography (Rb-82 PET).

MATERIALS AND METHODS

Fourteen patients with coronary artery stenosis underwent rest and adenosine stress imaging by 1.5-Tesla MR Scanner and a mCT/PET 64-slice Scanner. CMRI were analyzed based on Tikhonov's procedure of deconvolution without specifying an explicit compartment model using our own software. PET images were analyzed using standard clinical software. CMRI and PET data was compared with Spearman's rho and Bland-Altman analysis.

RESULTS

CMRI results were strongly and significantly correlated with PET results for the absolute global myocardial perfusion differences (r=0.805, p=0.001) and for global myocardial perfusion reserve (MPR) (r=0.886, p<0.001). At vessel territorial level, CMRI results were also significantly correlated with absolute PET myocardial perfusion differences (r=0.737, p<0.001) and MPR (r=0.818, p<0.001). Each vessel territory had similar strong correlation for absolute myocardial perfusion differences (right coronary artery (RCA): r=0.787, p=0.001; left anterior descending artery (LAD): r=0.796, p=0.001; left circumflex artery (LCX): r=0.880, p<0.001) and for MPR (RCA: r=0.895, p<0.001; LAD: r=0.886, p<0.001; LCX: r=0.886, p<0.001).

CONCLUSION

On a global and vessel territorial basis, CMRI-measured absolute myocardial perfusion differences and MPR were strongly and significantly correlated with the Rb-82 PET findings.

Regadenoson-stress myocardial CT perfusion and single-photon emission CT: rationale, design, and acquisition methods of a prospective, multicenter, multivendor comparison

Pharmacologic stress myocardial CT perfusion (CTP) has been reported to be a viable imaging modality for detection of myocardial ischemia compared with single-photon emission CT (SPECT) in several single-center studies. However, regadenoson-stress CTP has not previously been compared with SPECT in a multicenter, multivendor study. The rationale and design of a phase 2, randomized, cross-over study of regadenoson-stress myocardial perfusion imaging by CTP compared with SPECT are described herein. The study will be conducted at approximately 25 sites by using 6 different CT scanner models, including 64-, 128-, 256-, and 320-slice systems. Subjects with known/suspected coronary artery disease will be randomly assigned to 1 of 2 imaging procedure sequences; rest and regadenoson-stress SPECT on day 1, then regadenoson-stress CTP and rest CTP/coronary CT angiography (same acquisition) on day 2; or regadenoson-stress CTP and rest CTP/CT angiography on day 1, then rest and regadenoson-stress SPECT on day 2. The prespecified primary analysis examines the agreement rate between CTP and SPECT for detecting or excluding ischemia (≥2 or 0-1 reversible defects, respectively), as assessed by 3 independent blinded readers for each modality. Non-inferiority will be indicated if the lower boundary of the 95% CI for the agreement rate is within 0.15 of 0.78 (the observed agreement rate in the regadenoson pivotal trials). The protocol described herein will support the first evaluation of regadenoson-stress CTP by using multiple scanner types compared with SPECT.

Advances in stress cardiac MRI and computed tomography

Stress cardiac MRI and stress computed tomography (CT) perfusion are relatively new, noninvasive cardiovascular stress-testing modalities. Both of these tests have undergone rapid technical improvements. Data from randomized controlled trials in stress cardiac MRI are becoming gradually incorporated into cardiovascular clinical practice, not only to assess physiological significance of coronary artery disease, but also to provide prognostic information. As CT perfusion protocols become more uniform with adequate handling of artifacts and decreasing radiation exposure with combined CT coronary angiography/CT perfusion imaging, it has the potential to become a comprehensive diagnostic test.

Personalized assessment of radiation risks from the one-stop-shop myocardial 256-slice CT examination

BACKGROUND

This study provides data on the cumulative life attributable risk (LAR) of radiation-induced cancer from the combination of coronary CT angiography (CCTA), dynamic CT perfusion (CTP) and delayed enhancement (DE) CT scans, required for reliable risk-benefit analysis of the one-stop-shop CCTA + CTP + DECT cardiac examination.

METHODS

Monte Carlo simulation of the dynamic CTP and DECT exposures on 62 adult individuals was employed to determine radiation absorbed dose to exposed radiosensitive organs. Corresponding data for CCTA were derived using patient chest circumference and previously published data. Individual-specific LARs of cancer were estimated using organ/tissue-specific radiogenic cancer risk factors. Total LAR from CCTA + CTP + DECT scans' sequence were estimated and compared to nominal intrinsic risk of cancer.

RESULTS

The main contribution, up to 80%, to cumulative radiation burden from CCTA + CTP + DECT scan-sequence was found to originate from the CTP scan. The total LAR from CCTA + CTP + DECT for females was found 4-6 times higher, compared to males. The mean cumulative risk of radiogenic cancer associated with the complete CCTA + CTP + DECT scan sequence was found to marginally increase the intrinsic risk for cancer induction by less than 0.6% and 0.1% for females and males, respectively.

CONCLUSIONS

The radiation risk from the 256-slice CCTA + CTP + DECT scan sequence may be considered low and should not constitute an obstacle for the clinical endorsement of the one-stop-shop cardiac CT examination, given that its clinical value has been well verified. Nevertheless, every effort should be made towards optimization of the dynamic CTP component which is the main contributor to patient radiation burden.

Combined CT coronary angiography and stress myocardial perfusion imaging for hemodynamically significant stenoses in patients with suspected coronary artery disease: a comparison with fractional flow reserve

OBJECTIVES

We sought to determine the accuracy of combined coronary computed tomography angiography (CTA) and computed tomography stress myocardial perfusion imaging (CTP) in the detection of hemodynamically significant stenoses using fractional flow reserve (FFR) as a reference standard in patients with suspected coronary artery disease.

BACKGROUND

CTP can be qualitatively assessed by visual interpretation or quantified by the transmural perfusion ratio determined as the ratio of subendocardial to subepicardial contrast attenuation. The incremental value of each technique in addition to coronary CTA to detect hemodynamically significant stenoses is not known.

METHODS

Forty symptomatic patients underwent FFR and 320-detector computed tomography assessment including coronary CTA and CTP. Myocardial perfusion was assessed using the transmural perfusion ratio and visual perfusion assessment. Computed tomography images were assessed by consensus of 2 observers. Transmural perfusion ratio <0.99 was used as the threshold for abnormal perfusion. FFR ≤0.8 indicated hemodynamically significant stenoses.

RESULTS

Coronary CTA detected FFR-significant stenoses with 95% sensitivity and 78% specificity. The additional use of visual perfusion assessment and the transmural perfusion ratio both increased the specificity to 95%, with sensitivity of 87% and 71%, respectively. The area under the receiver-operating characteristic curve for coronary CTA + visual perfusion assessment was significantly higher than both coronary CTA (0.93 vs. 0.85, p = 0.0003) and coronary CTA + the transmural perfusion ratio (0.93 vs. 0.79, p = 0.0003). Per-vessel and per-patient accuracy for coronary CTA, coronary CTA + the transmural perfusion ratio, and coronary CTA + visual perfusion assessment was 83% and 83%, 87% and 92%, and 92% and 95%, respectively.

CONCLUSIONS

In suspected coronary artery disease, combined coronary CTA + CTP identifies patients with hemodynamically significant stenoses with >90% accuracy compared with FFR. When interpreted with coronary CTA, visual perfusion assessment provided superior incremental value in the detection of FFR-significant stenoses compared with the quantitative transmural perfusion ratio assessment.

Value of cardiac 320-multidetector computed tomography and cardiac magnetic resonance imaging for assessment of myocardial perfusion defects in patients with known chronic ischemic heart disease

The challenge for therapies targeting perfusion abnormalities is to identify and evaluate the region of interest. The aim of this study was to compare rest and stress myocardial perfusion measured by cardiac multi-detector computed tomography (MDCT) and cardiac magnetic resonance (CMR) imaging in patients with invasive coronary angiography demonstrated occluded vessels. Twenty-four patients with refractory angina due to occluded coronary arteries underwent perfusion imaging obtained by 320-MDCT scanner and 1.5 T MR scanner. Rest and adenosine stress images were obtained and interpreted using the modified 17-segment American Heart Association model. For the qualitative analysis, each segment was graded according to the following scoring system: 0 = no defect, 1 = hypoperfusion transmural extent <1/3, 2 = 1/3-1/2, 3 = >1/2, and 4 = infarct stigmata. In the semiquantitative analysis the perfusion was either scored 0 (normal) or 1 (abnormal). The summed rest and stress scores were calculated. MDCT and CMR had a high probability to identify perfusion defects. An excellent correlation between MDCT and CMR summed rest (r = 0.916) and stress scores (r = 0.915) was found. The interobserver reproducibility was high for MDCT and CMR images. The qualitative and semiquantitative MDCT against CMR analysis of rest and stress images showed high concordance to detect perfusion defects per vascular territory and on a per myocardial segment basis. 320-MDCT and CMR perfusion imaging can be used clinically to identify myocardial perfusion defects and potentially evaluate the effect of therapy targeting perfusion abnormalities.

Adenosine signaling pathways as potential therapeutic targets in respiratory disease

INTRODUCTION

Adenosine receptors (ARs) and their differential pattern of expression modulate a series of pleiotropic activities that are known to contribute to the control of inflammation, remodeling, and tissue repair. Consequently, pharmacological manipulation of adenosine signaling pathway is of great interest and is currently exploited as a therapeutic target for a number of respiratory diseases with several molecules with agonist and antagonist activities against known ARs being developed for the treatment of different conditions of the respiratory system.

AREAS COVERED

Herein, we will review the rational basis leading to the development of novel therapies for asthma, chronic obstructive pulmonary disease (COPD), interstitial lung disease (ILD), pulmonary arterial hypertension (PAH), and cystic fibrosis. Their most recent clinical development will be also discussed.

EXPERT OPINION

Advances in our understanding of the pathogenetic role of adenosine in respiratory diseases may be soon translated into effective treatment options. In consideration of the complex interplay driven by the different pattern of receptor distribution and/or affinity of the four known AR subtypes in specific cell types at different stages of the disease, it is likely that combination of selective antagonist/agonists for different AR subtypes will be required to obtain reasonable clinical efficacy. Alternatively, controlling the factors involved in driving adenosine concentrations in the tissue may be also of great significance.

Adenosine-stress low-dose single-scan CT myocardial perfusion imaging using a 128-slice dual-source CT: a comparison with fractional flow reserve

BACKGROUND

Coronary CT angiography (CCTA) allows accurate evaluation of coronary artery stenosis but has limitations in information on hemodynamic significance of stenotic lesions.

PURPOSE

To determine the feasibility of adenosine-stress low-dose single-scan CT myocardial perfusion imaging (MPI) using a 128-slice dual-source CT scanner for the diagnosis of hemodynamically significant coronary artery stenosis as defined by fractional flow reserve (FFR).

MATERIAL AND METHODS

This study was proved by the Institutional Review Board and informed consent was obtained from the patients before enrollment in the study. Ninety-seven patients with chest pain and low-to-intermediate pretest probability of coronary artery disease were prospectively enrolled. Adenosine-stress CCTA using ECG-correlated maximum tube current modulation (Mindose(®)) with 128-slice dual-source CT was performed in all 97 patients. In 37 patients (38.1%; 28 men, nine women; mean age, 61.7 ± 20.5 years; mean heart rate, 74.6 ± 2.8 bpm) with significant stenosis at CCTA (lumen diameter reduction >50%), FFR was performed after CCTA, as a reference standard for the evaluation of myocardial perfusion. FFR value ≤0.75 was considered as positive. CTMPI and CCTA were read by two experienced radiologists with consensus, respectively.

RESULTS

The effective radiation dose of adenosine-stress single-scan CTMPI was 4.63 ± 2.57 mSv. Compared with FFR, sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for identifying significant coronary stenoses were 93.1%, 82.7%, 75.0%, and 95.6%, respectively, on CCTA and 93.1%, 90.3%, 84.4%, and 95.9%, respectively, on CTMPI. On combined CCTA and CTMPI, sensitivity, specificity, PPV, and NPV were 93.1%, 94.2%, 90.0%, and 96.0%, respectively.

CONCLUSION

Adenosine-stress low-dose single scan CTMPI using a 128-slice dual-source CT can provide complementary information on the hemodynamical significance of coronary artery stenosis as well as anatomical information of coronary arteries.

CT fractional flow reserve: the next level in non-invasive cardiac imaging

The haemodynamic effect of a coronary artery stenosis is a better predictor of prognosis than anatomical lumen obstruction. Until recently, no individual non-invasive test could provide both accurate coronary anatomy and lesion-specific myocardial ischaemia. However, computer tomography (CT) fractional flow reserve, which can be calculated from a standard CT coronary angiogram, was recently demonstrated to accurately detect and rule out the haemodynamic significance of individual coronary artery stenoses.

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.

Non-invasive imaging in acute chest pain syndromes

This review has the purpose of informing the reader about the current use of imaging techniques in patients presenting with acute chest pain to the emergency department. We will focus on three aspects of managing the patient with acute chest pain: Imaging to increase the number of correct diagnoses in the acute situation; Imaging to rule out other than coronary causes of chest pain; Use of imaging for risk stratification once myocardial infarction has been ruled out in the CPU. Special emphasis is given to how these management aspects are discussed in current guidelines on the management of patients with acute chest pain or acute coronary syndrome.