Rationale and design of the worldwide prospective multicenter registry on radiation dose estimates of cardiac CT angiography in daily practice in 2017 (PROTECTION VI).

BACKGROUND: Cardiac computed tomography angiography (cardiac CTA) is an increasingly used versatile imaging method to evaluate coronary and cardiac morphology. Owing to improvements in technology, image quality has continuously improved over the last 10-20 years. At the same time, numerous non-randomized and randomized studies have been performed to reduce the associated radiation exposure. Currently, it is unclear if the advances in technology and knowledge about radiation reduction translated into reduced levels of cardiac CTA radiation dose in daily clinical practice as well as a wide utilization of dose-saving strategies. METHODS: The PROTECTION VI study is a multicenter, prospective, worldwide registry designed to evaluate radiation dose exposure, utilization of dose-saving strategies and diagnostic image quality during cardiac CTA in current daily practice. Assessment of image quality will be addressed by the evaluation of diagnostic image quality at the local study site and the calculation of quantitative image quality parameters in an imaging core laboratory. Above 4000 patients will be enrolled from approximately 70 sites in Europe, North America, South America, Asia and Australia. The study will analyze median radiation dose levels, image quality, frequency of use and efficacy of algorithms for dose reduction, and patient and study-related predictors associated with radiation dose. CONCLUSIONS: The PROTECTION VI study is designed to provide a reliable estimate of current radiation dose for cardiac CTA and to assess the potential for additional dose reductions.

Coronary artery disease reporting and data system (CAD-RADSTM): Inter-observer agreement for assessment categories and modifiers.

BACKGROUND: The Coronary Artery Disease Reporting and Data System (CAD-RADS) provides a lexicon and standardized reporting system for coronary CT angiography. OBJECTIVES: To evaluate inter-observer agreement of the CAD-RADS among an panel of early career and expert readers. METHODS: Four early career and four expert cardiac imaging readers prospectively and independently evaluated 50 coronary CT angiography cases using the CAD-RADS lexicon. All readers assessed image quality using a five-point Likert scale, with mean Likert score ≥4 designating high image quality, and <4 designating moderate/low image quality. All readers were blinded to medical history and invasive coronary angiography findings. Inter-observer agreement for CAD-RADS assessment categories and modifiers were assessed using intra-class correlation (ICC) and Fleiss' Kappa (κ).The impact of reader experience and image quality on inter-observer agreement was also examined. RESULTS: Inter-observer agreement for CAD-RADS assessment categories was excellent (ICC 0.958, 95% CI 0.938-0.974, p < 0.0001). Agreement among expert readers (ICC 0.925, 95% CI 0.884-0.954) was marginally stronger than for early career readers (ICC 0.904, 95% CI 0.852-0.941), both p < 0.0001. High image quality was associated with stronger agreement than moderate image quality (ICC 0.944, 95% CI 0.886-0.974 vs. ICC 0.887, 95% CI 0.775-0.95, both p < 0.0001). While excellent inter-observer agreement was observed for modifiers S (stent) and G (bypass graft) (both κ = 1.0), only fair agreement (κ = 0.40) was observed for modifier V (high risk plaque). CONCLUSION: Inter-observer reproducibility of CAD-RADS assessment categories and modifiers is excellent, except for high-risk plaque (modifier V) which demonstrates fair agreement. These results suggest CAD-RADS is feasible for clinical implementation.

Dipyridamole stress and rest transmural myocardial perfusion ratio evaluation by 64 detector-row computed tomography.

BACKGROUND: Myocardial stress CT perfusion (CTP) can detect myocardial ischemia. OBJECTIVE: We evaluated the transmural perfusion ratio (TPR) of dipyridamole stress CTP to detect significant coronary stenosis (>70%) defined by quantitative invasive coronary angiography (ICA). METHODS: Twenty-six patients (61.6 ± 8.0 years old; 14 males), without prior myocardial infarction, with positive single-photon emission computed tomography (SPECT; <2 months) and clinical indication for ICA, underwent a customized multidetector-row CT (MDCT) protocol with rest/stress myocardial perfusion evaluation and coronary CT angiography. TPR was defined as mean subendocardial divided by mean subepicardial attenuation and quantified on rest and stress MDCT images. Abnormal TPR was defined as 2 SDs below the mean rest TPR. RESULTS: All 26 patients completed the CT protocol with no adverse events. Rest TPR was measured in all patients with a mean of 1.06 ± 0.11, and abnormal TPR was considered <0.85. For 6 patients with normal coronary arteries by ICA, the mean TPR of territories with a previous positive perfusion defect in SPECT was 1.02 ± 0.18 (95% CI, 0.86-1.18; n = 6), and mean TPR of territories without perfusion defect in SPECT was 1.03 ± 0.09 (95% CI, -0.95 to 1.11; n = 12; P = 0.83). Mean stress TPR in territories with positive SPECT and significant coronary artery disease by quantitative ICA was 0.71 ± 0.13 (95% CI, -0.64 to 0.77) and in the remote myocardial was 1.01 ± 0.09 (95% CI, -0.96 to 1.06; P < 0001). In these territories, a significant Pearson's correlation was observed (r = -0.74, P < 0.001). CONCLUSION: TPR has a good correlation with SPECT and ICA to detect significant coronary stenosis.

Additional value of dipyridamole stress myocardial perfusion by 64-row computed tomography in patients with coronary stents.

BACKGROUND: Coronary computed tomography angiography (CTA) is a well-established diagnostic tool for coronary artery disease (CAD). However, coronary segments with prior stent implantation visualized with CTA may have limited evaluation and reduced accuracy. OBJECTIVE: We assessed the incremental value of stress myocardial CT perfusion (CTP) over anatomical assessment by coronary CTA alone in patients with stents, using quantitative invasive coronary angiography (≥50%) as reference. METHODS: Forty-six patients (56.9 ± 7.2 years; 28 men) referred to invasive coronary angiography were evaluated, combining coronary CTA and dipyridamole stress myocardial CTP with 64 detector-row CT. Coronary CTA was evaluated for ≥50% coronary stenosis, and myocardial CTP was used to potentially reclassify coronary territories, including those with stents and poorly evaluated stents because of artifacts. RESULTS: We evaluated 138 coronary territories, 62 with ≥1 stent. From these, 21 (34%) territories had adequately evaluated stents, 28 (45%) had limitedly evaluated stents still allowing diagnosis, and 13 (21%) had inadequately evaluated stents (no luminal assessment possible). Sensitivity, specificity, positive predictive value, negative predictive value and accuracy for coronary CTA in stent territories were, respectively, 85%, 77%, 87%, 74%, and 81%, and the combined use of coronary CTA and myocardial CTP were 88%, 95%, 97%, 81%, and 91% (P = 0.0292). In territories with impaired stent evaluation (limited or inadequate), the diagnostic performance of coronary CTA alone was 83%, 72%, 79%, 76% and 77%, and combined with myocardial CTP were 87%, 94%, 95%, 85%, and 91% (P = 0.036). CONCLUSION: The combined evaluation of coronary CTA and stress myocardial CTP improved the diagnostic accuracy for the detection of significant obstructive CAD in patients with stents.

Tomografia de coronárias: indicações clínicas e perspectivas futuras / Coronary CT: clinical indications and future directions

A tomografia computadorizada de multidetectores (TCMD) iniciou sua aplicação dentro da cardiologia com a quantificação de cálcio das placas coronarianas, no estudo sem contraste, por meio do escore de cálcio, mostrando um importante preditor independente de futuros eventos cardíacos. O exame com contraste endovenoso, a angiotomografia de coronárias, surgiu posteriormente como um método não invasivo para avaliação da anatomia e da doença obstrutiva coronariana, caracterizando o grau de estenose e também a presença da placa aterosclerótica não calcificada, avaliando não somente o lúmen, mas também a parede do vaso. Com o advento de novos aparelhos com mais detectores e maior resolução temporal, tem ocorrido uma redução da dose de radiação e a possibilidade de novas aplicações.

Dipyridamole stress and rest myocardial perfusion by 64-detector row computed tomography in patients with suspected coronary artery disease.

Recently, stress myocardial computed tomographic perfusion (CTP) was shown to detect myocardial ischemia. Our main objective was to evaluate the feasibility of dipyridamole stress CTP and compare it to single-photon emission computed tomography (SPECT) to detect significant coronary stenosis using invasive conventional coronary angiography (CCA; stenosis >70%) as the reference method. Thirty-six patients (62 +/- 8 years old, 20 men) with previous positive results with SPECT (<2 months) as the primary inclusion criterion and suspected coronary artery disease underwent a customized multidetector-row CT protocol with myocardial perfusion evaluation at rest and during stress and coronary CT angiography (CTA). Multidetector-row computed tomography was performed in a 64-slice scanner with dipyridamole stress perfusion acquisition before a second perfusion/CT angiographic acquisition at rest. Independent blinded observers performed analysis of images from CTP, CTA, and CCA. All 36 patients completed the CT protocol with no adverse events (mean radiation dose 14.7 +/- 3.0 mSv) and with interpretable scans. CTP results were positive in 27 of 36 patients (75%). From the 9 (25%) disagreements, 6 patients had normal coronary arteries and 2 had no significant stenosis (8 false-positive results with SPECT, 22%). The remaining patient had an occluded artery with collateral flow confirmed by conventional coronary angiogram. Good agreement was demonstrated between CTP and SPECT on a per-patient analysis (kappa 0.53). In 26 patients using CCA as reference, sensitivity, specificity, and positive and negative predictive values were 88.0%, 79.3%, 66.7%, and 93.3% for CTP and 68.8, 76.1%, 66.7%, and 77.8%, for SPECT, respectively (p = NS). In conclusion, dipyridamole CT myocardial perfusion at rest and during stress is feasible and results are similar to single-photon emission CT scintigraphy. The anatomical-perfusion information provided by this combined CT protocol may allow identification of false-positive results by SPECT.

Comprehensive cardiac CT study: evaluation of coronary arteries, left ventricular function, and myocardial perfusion--is it possible?

With advances in multidetector computed tomography (MDCT) technology, the new generation of 64-slice MDCT scanners with submillimeter collimation and a faster gantry rotation allows imaging of the entire heart in a single breath-hold with excellent temporal and spatial resolution. This potentially permits a comprehensive assessment of coronary anatomy, left ventricular function, and myocardial perfusion. As will be seen in this review of the current literature regarding 16- and 64-slice MDCT, there is great promise for a comprehensive cardiac computed tomography (CT) study. The available data support the notion that CT coronary angiography may be an alternative to invasive coronary angiography in symptomatic patients with a low to intermediate likelihood of having coronary artery disease. By use of the same data acquired for CT coronary angiography, evaluation of global and regional left ventricular function and myocardial perfusion can be added to the MDCT evaluation without additional exposure to contrast medium or radiation and may provide a more conclusive cardiac workup in these patients. The potential applications and limitations of coronary stenosis detection, global and regional left ventricular function, and myocardial perfusion assessment by MDCT will be reviewed. The full potential of cardiac MDCT is just beginning to be realized.