Phase-contrast X-ray tomography resolves the terminal bronchioles in free-breathing mice

Phase-contrast X-ray lung imaging has broken new ground in preclinical respiratory research by improving contrast at air/tissue interfaces. To minimize blur from respiratory motion, intubation and mechanical ventilation is commonly employed for end-inspiration gated imaging at synchrotrons and in the laboratory. Inevitably, the prospect of ventilation induced lung injury (VILI) renders mechanical ventilation a confounding factor in respiratory studies of animal models. Here we demonstrate proof-of-principle 3D imaging of the tracheobronchial tree in free-breathing mice without mechanical ventilation at radiation levels compatible with longitudinal studies. We use a prospective gating approach for end-expiration propagation-based phase-contrast X-ray imaging where the natural breathing of the mouse dictates the acquisition flow. We achieve intrapulmonary spatial resolution in the 30-μm-range, sufficient for resolving terminal bronchioles in the 60-μm-range distinguished from the surrounding lung parenchyma. These results should enable non-invasive longitudinal studies of native state murine airways for translational lung disease research in the laboratory.

Clinical significance of aortic arch plaques simultaneously assessed with coronary atherosclerosis on cardiovascular outcomes in patients undergoing coronary CT angiography

Aims Computed tomography (CT) coronary angiography is a useful diagnostic imaging modality in assessing presence, severity, and extent of coronary artery disease (CAD). Aortic arch plaques have been shown to be an underlying cause of embolic stroke and also related to increased risk of cardiovascular events. Yet, conventional CTCA imaging protocol does not include aortic arch for the reduction of radiation exposure. This study aimed to investigate prevalence of aortic arch plaques simultaneously assessed by CTCA and their clinical significance in combination with the presence of obstructive CAD for prediction of CVD events in patients with suspected CAD. Methods This study consisted of 310 (mean age, 66 years old, 42% female) patients with suspected CAD undergoing CTCA between 2017 and 2019. All CTCA examination was performed with 320-row detector scanner using ECG-triggered prospective gating method. Aortic arch images were simultaneously acquired during CTCA scanning without an increase of contrast media. Using Agatston method, coronary artery calcium score (CACS) was categorized into either of the groups having CACS of 0, 0–99, 100–299, or more than 300. The presence of CAD was reported as non-obstructive or obstructive CAD. High-risk featured aortic plaque was defined as large plaques >4 mm in thickness showing ulceration or protrusion. A composite event of cardiovascular disease, including all-cause mortality, non-fatal myocardial infarction, unplanned hospitalization requiring revascularization or stroke was defined as the primary endpoint. Results Patients having CACS of 0, 0–99, 100–299, and >300 were found in 41%, 24%, 15%, 20%%, respectively, where obstructive CAD was diagnosed in 11%. Aortic HRPs in ascending aorta, aortic arch, and thoracic descending aorta were observed in 1.6%, 6.9%, and 15%, respectively. During a mean follow-up period of 2.2 years, the primary endpoint was observed in 27 patients (8.7%). Cox regression hazard model demonstrated an independent association of aortic arch high-risk plaques (HR; 3.2, 95% CI; 1.20–8.64, p=0.02) and obstructive CAD (HR; 3.3, 95% CI; 1.45–7.92, P=0.005) when adjusted by age, CACS, and chronic kidney disease. Kaplan-Meier curve analysis showed a worse outcome of patients with aortic HRP and obstructive CAD compared to those without aortic plaques and obstructive CAD (p<0.001). Conclusion This study demonstrated an independent association of aortic arch high-risk featured plaques with CVD events. Further study is warranted whether pharmacological interventional therapies can reduce future CVD risks in patients with CAD and aortic arch plaques. FUNDunding Acknowledgement Type of funding sources: None.

Comparison of Prospective and Retrospective Gated 4D Flow Cardiac MR Image Acquisitions in the Carotid Bifurcation

The superior temporal coverage of retrospective versus prospective gating in 4D flow cardiac MRI (cMRI) imaging offers advantages in comprehensively evaluating the hemodynamic environment across the complete cardiac cycle; however, retrospective acquisitions may result in temporal smoothing. Thus, the purpose of this study was to evaluate the agreement of 4D flow cMRI-derived bulk flow features and fluid (blood) velocities in the carotid bifurcation using prospective and retrospective gating techniques. Prospective and retrospective ECG-gated three-dimensional (3D) cine phase-contrast cardiac MRI with three-direction velocity encoding (i.e., 4D flow cMRI) data were acquired in ten carotid bifurcations from men (n = 3) and women (n = 2) that were cardiovascular disease-free. Velocity magnitude data were extracted from the fluid domain within the image volumes and evaluated across the entire volume or at defined anatomic planes (common, internal, external carotid arteries). Vector magnitudes were decomposed into components to quantify flow direction and disturbances, including retrograde flow. Flow streamlines encoded for velocity magnitude and velocity profiles were generated. Qualitative and quantitative agreement was observed in bulk flow features and fluid velocity magnitudes derived from either prospective or retrospective ECG-gated 4D flow cMRI. No significant differences in velocity magnitudes or components (υr, υθ, υz) were observed. Importantly, retrospective acquisitions captured increased retrograde flow in the internal carotid artery (i.e., carotid sinus) compared to prospective acquisitions. Prospective and retrospective ECG-gated 4D flow cMRI acquisitions provide comparable evaluations of the hemodynamic environment in the carotid bifurcation. However, the increased temporal coverage of retrospective acquisitions depicts disturbed blood flow patterns not captured by the prospective gating technique.

Technical principles of cardiovascular CT

This chapter covers the technical mechanisms by which CT scanners work. X-ray tube voltage is explained, and the effects of changing voltage on radiation exposure and the resultant CT image are defined. Scan pitch for both single- and multi-slice CT have their formulae given, and the effects of changing pitch are described. Both spatial and temporal resolution are discussed, and multi-segment reconstruction concepts are explained. ECG gating, including retrospective and prospective gating are covered. Finally, axial and helical scanning acquisition modes are described.

A Computational Framework for Data Fusion in MEMS-Based Cardiac and Respiratory Gating

Dual cardiac and respiratory gating is a well-known technique for motion compensation in nuclear medicine imaging. In this study, we present a new data fusion framework for dual cardiac and respiratory gating based on multidimensional microelectromechanical (MEMS) motion sensors. Our approach aims at robust estimation of the chest vibrations, that is, high-frequency precordial vibrations and low-frequency respiratory movements for prospective gating in positron emission tomography (PET), computed tomography (CT), and radiotherapy. Our sensing modality in the context of this paper is a single dual sensor unit, including accelerometer and gyroscope sensors to measure chest movements in three different orientations. Since accelerometer- and gyroscope-derived respiration signals represent the inclination of the chest, they are similar in morphology and have the same units. Therefore, we use principal component analysis (PCA) to combine them into a single signal. In contrast to this, the accelerometer- and gyroscope-derived cardiac signals correspond to the translational and rotational motions of the chest, and have different waveform characteristics and units. To combine these signals, we use independent component analysis (ICA) in order to obtain the underlying cardiac motion. From this cardiac motion signal, we obtain the systolic and diastolic phases of cardiac cycles by using an adaptive multi-scale peak detector and a short-time autocorrelation function. Three groups of subjects, including healthy controls (n = 7), healthy volunteers (n = 12), and patients with a history of coronary artery disease (n = 19) were studied to establish a quantitative framework for assessing the performance of the presented work in prospective imaging applications. The results of this investigation showed a fairly strong positive correlation (average r = 0.73 to 0.87) between the MEMS-derived (including corresponding PCA fusion) respiration curves and the reference optical camera and respiration belt sensors. Additionally, the mean time offset of MEMS-driven triggers from camera-driven triggers was 0.23 to 0.3 ± 0.15 to 0.17 s. For each cardiac cycle, the feature of the MEMS signals indicating a systolic time interval was identified, and its relation to the total cardiac cycle length was also reported. The findings of this study suggest that the combination of chest angular velocity and accelerations using ICA and PCA can help to develop a robust dual cardiac and respiratory gating solution using only MEMS sensors. Therefore, the methods presented in this paper should help improve predictions of the cardiac and respiratory quiescent phases, particularly with the clinical patients. This study lays the groundwork for future research into clinical PET/CT imaging based on dual inertial sensors.

Prognostic Performance of Prospective versus Retrospective Electrocardiographic Gating in Coronary Computed Tomographic Angiography

Coronary computed tomographic angiography (CCTA) with prospective electrocardiographic gating reduces radiation exposure, but its prognostic power for predicting cardiovascular risk in patients with suspected CAD has not been fully validated. To determine whether prospective gating performs as well as retrospective gating in this population, we compared these scan modes in patients undergoing 64-slice CCTA. From January 2009 through September 2011, 1,407 patients underwent CCTA; of these, 915 (mean age, 57.8 ± 13.5 yr; 54% male) had suspected coronary artery disease at the time of CCTA and were included in the study. Prospective gating was used in 195 (21%) and retrospective gating in 720 (79%). The mean follow-up duration was 2.4 ± 0.9 years. Overall, 390 patients (42.6%) had normal results on CCTA, 382 (41.7%) had nonobstructive coronary artery disease, and 143 (15.6%) had obstructive disease. Major adverse cardiac events occurred in 32 patients (3.5%): 11 cardiac deaths, 15 late revascularizations, and 6 nonfatal myocardial infarctions. Total event occurrences were similar in both groups (retrospective, 3.8%; prospective, 2.6%; P=0.42), as were the occurrences of each type of event. On adjusted multivariate analysis, nonobstructive (P=0.015) and obstructive (P <0.001) coronary artery disease were independently associated with major adverse cardiac events. Scan mode was not a predictor of outcome. The mean effective radiation dose was 4 ± 2 mSv for prospective compared with 12 ± 4 mSv for retrospective gating (P <0.01). The prognostic value of CCTA with prospective electrocardiographic gating compares favorably with that of retrospective gating, and it involves significantly less radiation exposure.