Detection of Hemodynamically Significant Coronary Artery Stenosis: Incremental Diagnostic Value of Dynamic CT-based Myocardial Perfusion Imaging

Feasibility of dynamic CT-based adenosine stress myocardial perfusion imaging to detect and differentiate ischemic and infarcted myocardium in an large experimental porcine animal model

The purpose of the study is feasibility of dynamic CT perfusion imaging to detect and differentiate ischemic and infarcted myocardium in a large porcine model. 12 Country pigs completed either implantation of a 75 % luminal coronary stenosis in the left anterior descending coronary artery simulating ischemia or balloon-occlusion inducing infarction. Dynamic CT-perfusion imaging (100 kV, 300 mAs), fluorescent microspheres, and histopathology were performed in all models. CT based myocardial blood flow (MBFCT), blood volume (MBVCT) and transit constant (Ktrans), as well as microsphere's based myocardial blood flow (MBFMic) were derived for each myocardial segment. According to histopathology or microsphere measurements, 20 myocardial segments were classified as infarcted and 23 were ischemic (12 and 14 %, respectively). Across all perfusion states, MBFCT strongly predicted MBFMic (β 0.88 ± 0.12, p < 0.0001). MBFCT, MBVCT, and Ktrans were significantly lower in ischemic/infarcted when compared to reference myocardium (all p < 0.01). Relative differences of all CT parameters between affected and non-affected myocardium were higher for infarcted when compared to ischemic segments under rest (48.4 vs. 22.6 % and 46.1 vs. 22.9 % for MBFCT, MBVCT, respectively). Under stress, MBFCT was significantly lower in infarcted than in ischemic myocardium (67.8 ± 26 vs. 88.2 ± 22 ml/100 ml/min, p = 0.002). In a large animal model, CT-derived parameters of myocardial perfusion may enable detection and differentiation of ischemic and infarcted myocardium.

The diagnostic performance of coronary artery angiography with 64-MSCT and post 64-MSCT: systematic review and meta-analysis

PURPOSE

To comprehensively investigate the diagnostic performance of coronary artery angiography with 64-MDCT and post 64-MDCT.

MATERIALS AND METHODS

PubMed was searched for all published studies that evaluated coronary arteries with 64-MDCT and post 64-MDCT. The clinical diagnostic role was evaluated by applying the likelihood ratios (LRs) to calculate the post-test probability based on Bayes' theorem.

RESULTS

91 studies that met our inclusion criteria were ultimately included in the analysis. The pooled positive and negative LRs at patient level were 8.91 (95% CI, 7.53, 10.54) and 0.02 (CI, 0.01, 0.03), respectively. For studies that did not claim that non-evaluable segments were included, the pooled positive and negative LRs were 11.16 (CI, 8.90, 14.00) and 0.01 (CI, 0.01, 0.03), respectively. For studies including uninterruptable results, the diagnostic performance decreased, with the pooled positive LR 7.40 (CI, 6.00, 9.13) and negative LR 0.02 (CI, 0.01, 0.03). The areas under the summary ROC curve were 0.98 (CI, 0.97 to 0.99) for 64-MDCT and 0.96 (CI, 0.94 to 0.98) for post 64-MDCT, respectively. For references explicitly stating that the non-assessable segments were included during analysis, a post-test probability of negative results >95% and a positive post-test probability <95% could be obtained for patients with a pre-test probability of <73% for coronary artery disease (CAD). On the other hand, when the pre-test probability of CAD was >73%, the diagnostic role was reversed, with a positive post-test probability of CAD >95% and a negative post-test probability of CAD <95%.

CONCLUSION

The diagnostic performance of post 64-MDCT does not increase as compared with 64-MDCT. CTA, overall, is a test of exclusion for patients with a pre-test probability of CAD<73%, while for patients with a pre-test probability of CAD>73%, CTA is a test used to confirm the presence of CAD.

Quantitative Computed Tomographic Coronary Angiography

Background—

Coronary lesions with a diameter narrowing ≥50% on visual computed tomographic coronary angiography (CTCA) are generally considered for referral to invasive coronary angiography. However, similar to invasive coronary angiography, visual CTCA is often inaccurate in detecting functionally significant coronary lesions. We sought to compare the diagnostic performance of quantitative CTCA with visual CTCA for the detection of functionally significant coronary lesions using fractional flow reserve (FFR) as the reference standard.

Methods and Results—

CTCA and FFR measurements were obtained in 99 symptomatic patients. In total, 144 coronary lesions detected on CTCA were visually graded for stenosis severity. Quantitative CTCA measurements included lesion length, minimal area diameter, % area stenosis, minimal lumen diameter, % diameter stenosis, and plaque burden [(vessel area−lumen area)/vessel area×100]. Optimal cutoff values of CTCA-derived parameters were determined, and their diagnostic accuracy for the detection of flow-limiting coronary lesions (FFR ≤0.80) was compared with visual CTCA. FFR was ≤0.80 in 54 of 144 (38%) coronary lesions. Optimal cutoff values to predict flow-limiting coronary lesion were 10 mm for lesion length, 1.8 mm 2 for minimal area diameter, 73% for % area stenosis, 1.5 mm for minimal lumen diameter, 48% for % diameter stenosis, and 76% for plaque burden. No significant difference in sensitivity was found between visual CTCA and quantitative CTCA parameters ( P >0.05). The specificity of visual CTCA (42%; 95% confidence interval [CI], 31%–54%) was lower than that of minimal area diameter (68%; 95% CI, 57%–77%; P =0.001), % area stenosis (76%; 95% CI, 65%–84%; P <0.001), minimal lumen diameter (67%; 95% CI, 55%–76%; P =0.001), % diameter stenosis (72%; 95% CI, 62%–80%; P <0.001), and plaque burden (63%; 95% CI, 52%–73%; P =0.004). The specificity of lesion length was comparable with that of visual CTCA.

Conclusions—

Quantitative CTCA improves the prediction of functionally significant coronary lesions compared with visual CTCA assessment but remains insufficient. Functional assessment is still required in lesions of moderate stenosis to accurately detect impaired FFR.

Expert consensus for multi-modality imaging evaluation of cardiovascular complications of radiotherapy in adults: a report from the European Association of Cardiovascular Imaging and the American Society of Echocardiography

Cardiac toxicity is one of the most concerning side effects of anti-cancer therapy. The gain in life expectancy obtained with anti-cancer therapy can be compromised by increased morbidity and mortality associated with its cardiac complications. While radiosensitivity of the heart was initially recognized only in the early 1970s, the heart is regarded in the current era as one of the most critical dose-limiting organs in radiotherapy. Several clinical studies have identified adverse clinical consequences of radiation-induced heart disease (RIHD) on the outcome of long-term cancer survivors. A comprehensive review of potential cardiac complications related to radiotherapy is warranted. An evidence-based review of several imaging approaches used to detect, evaluate, and monitor RIHD is discussed. Recommendations for the early identification and monitoring of cardiovascular complications of radiotherapy by cardiac imaging are also proposed.

Accuracy of two-dimensional speckle tracking echocardiography for the detection of significant coronary stenosis

Background

Visual assessment of wall motion abnormalities (WMA) by 2-dimensional echocardiography (2DE) is the most semi-quantitative method used to detect coronary artery disease (CAD), but it carries many limitations. Speckle tracking echocardiography (STE) overcomes these limitations and allows an objective quantification of myocardial deformation. The aim of the study to examine the accuracy of global and segmental longitudinal strain (LS) for the detection of CAD compared with visual assessment of WMA using coronary angiography as a golden standard.

Methods

The study enrolled 25 patients (mean age 51.0 ± 8.7, 64% are male) referred to coronary angiography with clinical suspicion of CAD. 2DE assessment of WMA and evaluation of LS using STE were performed using left ventricular 17-segments models. Significant CAD was defined as ≥ 50% stenosis in one or more major coronary arteries by angiography.

Results

Patients were classified into 2 groups: group I included 15 patients with significant CAD and group II included 10 patients with insignificant and/or absence of CAD. WM score was strongly correlated with the global LS in group I and II (R = 0.80, p < 0.0001 and R = 0.88, p < 0.0001 respectively). In all patients, 425 segments were analyzed. WMA was detected in 163 segments of 425 (38.3%) while abnormal LS was detected in 214 segments (50.3%). Compared with coronary angiography, the total sensitivity, specificity and accuracy for visual analysis and STE were (56%, 88.2%, and 60% vs. 68.6%, 77%, and 81.8% respectively).

Conclusion

Segmental LS is more accurate for the detection of ischemic myocardial segment corresponding to functionally relevant coronary anatomy than visual assessment of WM.

Dose reduction in dynamic CT stress myocardial perfusion imaging: comparison of 80-kV/370-mAs and 100-kV/300-mAs protocols

OBJECTIVES

To determine the effect of reduced 80-kV tube voltage with increased 370-mAs tube current on radiation dose, image quality and estimated myocardial blood flow (MBF) of dynamic CT stress myocardial perfusion imaging (CTP) in patients with a normal body mass index (BMI) compared with a 100-kV and 300-mAs protocol.

METHODS

Thirty patients with a normal BMI (<25 kg/m(2)) with known or suspected coronary artery disease underwent adenosine-stress dual-source dynamic CTP. Patients were randomised to 80-kV/370-mAs (n = 15) or 100-kV/300-mAs (n = 15) imaging. Maximal enhancement and noise of the left ventricular (LV) cavity, contrast-to-noise ratio (CNR) and MBF of the two groups were compared.

RESULTS

Imaging with 80-kV/370-mAs instead of 100-kV/300-mAs was associated with 40% lower radiation dose (mean dose-length product, 359 ± 66 vs 628 ± 112 mGy[Symbol: see text]cm; P < 0.001 ) with no significant difference in CNR (34.5 ± 13.4 vs 33.5 ± 10.4; P = 0.81) or MBF in non-ischaemic myocardium (0.95 ± 0.20 vs 0.99 ± 0.25 ml/min/g; P = 0.66). Studies obtained using 80-kV/370-mAs were associated with 30.9% higher maximal enhancement (804 ± 204 vs 614 ± 115 HU; P < 0.005), and 31.2% greater noise (22.7 ± 3.5 vs 17.4 ± 2.6; P < 0.001).

CONCLUSIONS

Dynamic CTP using 80-kV/370-mA instead of 100-kV/300-mAs allowed 40% dose reduction without compromising image quality or MBF. Tube voltage of 80-kV should be considered for individuals with a normal BMI.

KEY POINTS

• CT stress perfusion imaging (CTP) is increasingly used to assess myocardial function. • Dynamic CTP is feasible at 80-kV in patients with normal BMI. • An 80-kV/370-mAs protocol allows 40% dose reduction compared with 100-kV/300-mAs. • Contrast-to-noise ratio and myocardial blood flow of the two protocols were comparable.

320-row CT coronary angiography predicts freedom from revascularisation and acts as a gatekeeper to defer invasive angiography in stable coronary artery disease: a fractional flow reserve-correlated study

OBJECTIVES

To determine the accuracy of 320-row multidetector coronary computed tomography angiography (M320-CCTA) to detect functional stenoses using fractional flow reserve (FFR) as the reference standard and to predict revascularisation in stable coronary artery disease.

METHODS

One hundred and fifteen patients (230 vessels) underwent M320-CCTA and FFR assessment and were followed for 18 months. Diameter stenosis on invasive angiography (ICA) and M320-CCTA were assessed by consensus by two observers and significant stenosis was defined as ≥50%. FFR ≤0.8 indicated functionally significant stenoses.

RESULTS

M320-CCTA had 94% sensitivity and 94% negative predictive value (NPV) for FFR ≤0.8. Overall accuracy was 70%, specificity 54% and positive predictive value 65%. On receiver operating characteristic (ROC) curve analysis, the area under the curve (AUC) for CCTA to predict FFR ≤0.8 was 0.74 which was comparable with ICA. The absence of a significant stenosis on M320-CCTA was associated with a 6% revascularisation rate. M320-CCTA predicted revascularisation with an AUC of 0.71 which was comparable with ICA.

CONCLUSIONS

M320-CCTA has excellent sensitivity and NPV for functional stenoses and therefore may act as an effective gatekeeper to defer ICA and revascularisation. Like ICA, M320-CCTA lacks specificity for functional stenoses and only has moderate accuracy to predict the need for revascularisation.

KEY POINTS

• Important information about the heart is provided by 320-row multidetector CT coronary angiography (M320-CCTA). • M320-CCTA accurately detects and excludes functional stenoses determined by fractional flow reserve (FFR). • Non-significant stenoses on M320-CCTA associated with fewer cardiac events and less revascularisation. • M320-CCTA may act as a gatekeeper for invasive angiography and inappropriate revascularisation. • Like ICA, M320-CCTA only has moderate accuracy to predict vessels requiring revascularisation.

Myocardial CT perfusion imaging in a large animal model: comparison of dynamic versus single-phase acquisitions

OBJECTIVES

This study sought to compare dynamic versus single-phase high-pitch computed tomography (CT) acquisitions for the assessment of myocardial perfusion in a porcine model with adjustable degrees of coronary stenosis.

BACKGROUND

The incremental value of the 2 different approaches to CT-based myocardial perfusion imaging remains unclear.

METHODS

Country pigs received stent implantation in the left anterior descending coronary artery, in which an adjustable narrowing (50% and 75% stenoses) was created using a balloon catheter. All animals underwent CT-based rest and adenosine-stress myocardial perfusion imaging using dynamic and single-phase high-pitch acquisitions at both degrees of stenosis. Fluorescent microspheres served as a reference standard for myocardial blood flow. Segmental CT-based myocardial blood flow (MBFCT) was derived from dynamic acquisitions. Segmental single-phase enhancement (SPE) was recorded from high-pitch, single-phase examinations. MBFCT and SPE were compared between post-stenotic and reference segments, and receiver-operating characteristic curve analysis was performed.

RESULTS

Among 6 animals (28 ± 2 kg), there were significant differences of MBFCT and SPE between post-stenotic and reference segments for all acquisitions at 75% stenosis. By contrast, although for 50% stenosis at rest, MBFCT was lower in post-stenotic than in reference segments (0.65 ± 0.10 ml/g/min vs. 0.75 ± 0.16 ml/g/min, p < 0.05), there was no difference for SPE (128 ± 27 Hounsfield units vs. 137 ± 35 Hounsfield units, p = 0.17), which also did not significantly change under adenosine stress. In receiver-operating characteristic curve analyses, segmental MBFCT showed significantly better performance for ischemia prediction at 75% stenosis and stress (area under the curve: 0.99 vs. 0.89, p < 0.05) as well as for 50% stenosis, regardless of adenosine administration (area under the curve: 0.74 vs. 0.57 and 0.88 vs. 0.61, respectively, both p < 0.05).

CONCLUSIONS

At higher degrees of coronary stenosis, both MBFCT and SPE permit an accurate prediction of segmental myocardial hypoperfusion. However, accuracy of MBFCT is higher than that of SPE at 50% stenosis and can be increased by adenosine stress at both degrees of stenosis.

Diagnostic performance of dual-source CT coronary angiography with and without heart rate control: systematic review and meta-analysis

AIM

To investigate the diagnostic accuracy of dual-source computed tomography (DSCT) coronary angiography with and without the application of a β-blocker.

MATERIALS AND METHODS

An exact binomial rendition of the bivariate mixed-effects regression model was used to synthesize diagnostic test data.

RESULTS

The pooled sensitivity at the patient level was 0.98 [95% confidence intervals (CI): 0.97-0.99], and specificity 0.88 (95% CI: 0.84-0.91). The results showed that without heart rate control, the sensitivity and specificity at the patient level did not decrease (p = 0.27 and 0.56, respectively). At the artery level, no significant differences in sensitivity and specificity for studies with and without heart rate control were detected (p = 0.04 and 0.05, respectively). At the segment level, the specificity decreased without heart rate control (p = 0.03), whereas the sensitivity was not influenced (p = 0.63). The median radiation exposure was 2.6 mSv, with 1.6 mSv and 8 mSv for heart rate-controlled studies and uncontrolled studies, respectively.

CONCLUSIONS

DSCT coronary angiography without heart rate control has a similar excellent diagnostic performance at the patient level as that of heart rate control groups. However, controlling for heart rate to decrease radiation and to provide effective information for selecting the therapeutic strategy and risk stratification is recommended.

Dynamic CT perfusion imaging of the myocardium: a technical note on improvement of image quality

Objective

To improve image and diagnostic quality in dynamic CT myocardial perfusion imaging (MPI) by using motion compensation and a spatio-temporal filter.

Methods

Dynamic CT MPI was performed using a 256-slice multidetector computed tomography scanner (MDCT). Data from two different patients–with and without myocardial perfusion defects–were evaluated to illustrate potential improvements for MPI (institutional review board approved). Three datasets for each patient were generated: (i) original data (ii) motion compensated data and (iii) motion compensated data with spatio-temporal filtering performed. In addition to the visual assessment of the tomographic slices, noise and contrast-to-noise-ratio (CNR) were measured for all data. Perfusion analysis was performed using time-density curves with regions-of-interest (ROI) placed in normal and hypoperfused myocardium. Precision in definition of normal and hypoperfused areas was determined in corresponding coloured perfusion maps.

Results

The use of motion compensation followed by spatio-temporal filtering resulted in better alignment of the cardiac volumes over time leading to a more consistent perfusion quantification and improved detection of the extend of perfusion defects. Additionally image noise was reduced by 78.5%, with CNR improvements by a factor of 4.7. The average effective radiation dose estimate was 7.1±1.1 mSv.

Conclusion

The use of motion compensation and spatio-temporal smoothing will result in improved quantification of dynamic CT MPI using a latest generation CT scanner.

Detection of ischaemic myocardial lesions with coronary CT angiography and adenosine-stress dynamic perfusion imaging using a 128-slice dual-source CT: diagnostic performance in comparison with cardiac MRI

OBJECTIVE

We assessed the diagnostic performance of adenosine-stress dynamic CT perfusion (ASDCTP) imaging and coronary CT angiography (CCTA) for the detection of ischaemic myocardial lesions using 128-slice dual-source CT compared with that of 1.5 T cardiac MRI.

METHODS

This prospective study included 33 patients (61±8 years, 82% male) with suspected coronary artery diseases who underwent ASDCTP imaging and adenosine-stress cardiac MRI. Two investigators independently evaluated ASDCTP images in correlation with significant coronary stenosis on CCTA using two different thresholds of 50% and 70% diameter stenosis. Hypoattenuated myocardial lesions on ASDCTP associated with significant coronary stenoses on CCTA were regarded as true perfusion defects. All estimates of diagnostic performance were calculated and compared with those of cardiac MRI.

RESULTS

With use of a threshold of 50% diameter stenosis on CCTA, the diagnostic estimates per-myocardial segment were as follows: sensitivity, 81% [95% confidence interval (CI): 70-92%]; specificity, 94% (95% CI: 92-96%); and accuracy 93% (95% CI: 91-95%). With use of a threshold of 70%, the diagnostic estimates were as follows: sensitivity, 48% (95% CI: 34-62%); specificity, 99% (95% CI: 98-100%); and accuracy, 94% (95% CI: 92-96%).

CONCLUSION

Dynamic CTP using 128-slice dual-source CT enables the assessment of the physiological significance of coronary artery lesions with high diagnostic accuracy in patients with clinically suspected coronary artery disease.

ADVANCES IN KNOWLEDGE

Combined CCTA and ASDCTP yielded high accuracy in the detection of perfusion defects regardless of the threshold of significant coronary stenosis.

Reduction of image noise in low tube current dynamic CT myocardial perfusion imaging using HYPR processing: a time-attenuation curve analysis

PURPOSE

This study describes a HighlY constrained backPRojection (HYPR) image processing method for the reduction of image noise in low tube current time-resolved CT myocardial perfusion scans. The effect of this method on myocardial time-attenuation curve noise and fidelity is evaluated in an animal model, using varying levels of tube current.

METHODS

CT perfusion scans of four healthy pigs (42-59 kg) were acquired at 500, 250, 100, 50, 25, and 10 mA on a 64-slice scanner (4 cm axial coverage, 120 kV, 0.4 s∕rotation, 50 s scan duration). For each scan a sequence of ECG-gated images centered on 75% R-R was reconstructed using short-scan filtered back projection (FBP). HYPR processing was applied to the scans acquired at less than 500 mA using parameters designed to maintain the voxel noise level in the 500-mA FBP images. The processing method generates a series of composite images by averaging over a sliding time window and then multiplies the composite images by weighting images to restore temporal fidelity to the image sequence. HYPR voxel noise relative to FBP noise was measured in AHA myocardial segment numbers 1, 5, 6, and 7 at each mA. To quantify the agreement between HYPR and FBP time-attenuation curves (TACs), Bland-Altman analysis was performed on TACs measured in full myocardial segments. The relative degree of TAC fluctuation in smaller subvolumes was quantified by calculating the root mean square deviation of a TAC about the gamma variate curve fit to the TAC data.

RESULTS

HYPR image sequences were produced using 2, 7, and 20 beat composite windows for the 250, 100, and 50 mA scans, respectively. At 25 and 10 mA, all available beats were used in the composite (41-60; average 50). A 7-voxel-wide 3D cubic filter kernel was used to form weighting images. The average ratio of HYPR voxel noise to 500-mA FBP voxel noise was 1.06, 1.10, 0.97, 1.11, and 2.15 for HYPR scans at 250, 100, 50, 25, and 10 mA. The average limits-of-agreement between HYPR and FBP TAC values measured 0.02+∕-0.91, 0.04+∕-1.92, 0.19+∕-1.59, 1.13+∕-4.22, and 1.07+∕-6.37 HU (mean difference +∕-1.96 SD). The HYPR image subvolume that yielded a fixed level of TAC fluctuations was smaller, on average, than the FBP subvolume determined at the same mA.

CONCLUSIONS

HYPR processing is a feasible method for generating low noise myocardial perfusion data from a low-mA time-resolved CT myocardial perfusion scan. The method is applicable to current clinical scanners and uses conventional image reconstructions as input data.

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.

Myocardial perfusion imaging with cardiac computed tomography: state of the art

Cardiac computed tomography (CCT) has become an important tool for the anatomic assessment of patients with suspected coronary disease. Its diagnostic accuracy for detecting the presence of underlying coronary artery disease and ability to risk stratify patients are well documented. However, the role of CCT for the physiologic assessment of myocardial perfusion during resting and stress conditions is only now emerging. With the addition of myocardial perfusion imaging to coronary imaging, CCT has the potential to assess both coronary anatomy and its functional significance with a single non-invasive test. In this review, we discuss the current state of CCT myocardial perfusion imaging for the detection of myocardial ischemia and myocardial infarction and examine its complementary role to CCT coronary imaging.

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.

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.

Current status of cardiac CT for the detection of myocardial ischemia

Stress and rest myocardial perfusion imaging using computed tomography (CT) can be accurately and safely performed. CT angiography allows for the anatomic visualization of coronary lesions and the components of atherosclerotic plaque, whereas according to currently available data, CT perfusion imaging improves the diagnostic accuracy for detecting ischemic lesions. However, the radiation exposure and contrast load that are involved cannot be neglected. Owing to the limited number of trials that have been published so far, and the fact that they used a wide variety of image acquisition and stress protocols, a standard acquisition protocol for CT perfusion imaging still needs to be found and evaluated in larger multicenter trials. Therefore, CT perfusion imaging, as opposed to other modalities such as magnetic resonance perfusion, SPECT, or positron emission tomography, cannot yet be regarded as clinical routine, but may be considered in patients with contraindications for other imaging modalities.

Tracer-kinetic modeling of dynamic contrast-enhanced MRI and CT: a primer

Dynamic contrast-enhanced computed tomography (DCE-CT) and magnetic resonance imaging (DCE-MRI) are functional imaging techniques. They aim to characterise the microcirculation by applying the principles of tracer-kinetic analysis to concentration-time curves measured in individual image pixels. In this paper, we review the basic principles of DCE-MRI and DCE-CT, with a specific emphasis on the use of tracer-kinetic modeling. The aim is to provide an introduction to the field for a broader audience of pharmacokinetic modelers. In a first part, we first review the key aspects of data acquisition in DCE-CT and DCE-MRI, including a review of basic measurement strategies, a discussion on the relation between signal and concentration, and the problem of measuring reference data in arterial blood. In a second part, we define the four main parameters that can be measured with these techniques and review the most common tracer-kinetic models that are used in this field. We first discuss the models for the capillary bed and then define the most general four-parameter models used today: the two-compartment exchange model, the tissue-homogeneity model, the "adiabatic approximation to the tissue-homogeneity model" and the distributed-parameter model. In simpler tissue types or when the data quality is inadequate to resolve all the features of the more complex models, it is often necessary to resort to simpler models, which are special cases of the general models and hence have less parameters. We discuss the most common of these special cases, i.e. the uptake models, the extended Tofts model, and the one-compartment model. Models for two specific tissue types, liver and kidney, are discussed separately. We conclude with a review of practical aspects of DCE-CT and DCE-MRI data analysis, including the problem of identifying a suitable model for any given data set, and a brief discussion of the application of tracer-kinetic modeling in the context of drug development. Here, an important application of DCE techniques is the derivation of quantitative imaging biomarkers for the assessment of effects of targeted therapeutics on tumors.

CT imaging of myocardial perfusion: possibilities and perspectives

Functional imaging in patients with suspected or known coronary artery disease (CAD) is crucial for the identification of patients who could benefit from coronary revascularization. Several studies demonstrated the high diagnostic accuracy of Single-photon-emission computed tomography myocardial perfusion imaging, stress perfusion magnetic resonance imaging, and of invasive FFR measurements for the detection of hemodynamic relevant stenosis. Cardiac computed tomography (CT) used to be limited to coronary angiography (CTA); current guidelines recommend CTA only for the exclusion of CAD. Technological advances now offer the possibility to assess myocardial perfusion by computed tomography (CT-MPI). Though different acquisition protocols and post-processing algorithms still have to be evaluated, initial clinical studies could already show a diagnostic accuracy comparable to the established imaging modalities. Thus, cardiac CT may offer a combined approach of anatomical and functional imaging. Beside the need for further studies, especially on the prognostic value of CT-MPI to stratify future cardiovascular events, the comparatively high radiation exposure and additional administration of contrast agent has to be taken in account.

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.

Adenosine-stress dynamic myocardial perfusion imaging using 128-slice dual-source CT: optimization of the CT protocol to reduce the radiation dose

The aim of this study was to compare the radiation dose and image quality of different adenosine-stress dynamic myocardial perfusion CT protocols using a 128-slice dual-source computed tomography (DSCT) scanner. We included 330 consecutive patients with suspected coronary artery disease. Protocols employed the following dynamic scan parameters: protocol I, a 30-s scan with a fixed tube current (FTC, n = 172); protocol II, a 30-s scan using an automatic tube current modulation (ATCM) technique (n = 108); protocol III, a 14-s scan using an ATCM (n = 50). To determine the scan interval for protocol III, we analyzed time-attenuation curves of 26 patients with myocardial perfusion who had been scanned using protocol I or II. The maximum attenuation difference between normal and abnormal myocardium occurred at 18.0 s to 30.3 s after initiation of contrast injection. Myocardial perfusion images of FTC and ATCM were of diagnostic image quality based on visual analysis. The mean radiation dose associated with protocols I, II, and III was 12.1 ± 1.6 mSv, 7.7 ± 2.5 mSv, and 3.8 ± 1.3 mSv, respectively (p < 0.01). Use of a dose-modulation technique and a 14-s scan duration for adenosine-stress CT enables significant dose reduction while maintaining diagnostic image quality.

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.

Stress CT perfusion: coupling coronary anatomy with physiology

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