Thorough understanding of contrast medium dynamics is essential for the design of effective acquisition and injection protocols. This article provides an overview of the fundamentals affecting contrast enhancement, emphasizing the modifications to contrast material delivery protocols required to optimize cardiothoracic CT angiography.
Cellular behavior is sustained by genetic programs that are progressively disrupted in pathological conditions-notably, cancer. High-throughput gene expression profiling has been used to infer statistical models describing these cellular programs, and development is now needed to guide orientated modulation of these systems. Here we develop a regression-based model to reverseengineer a temporal genetic program, based on relevant patterns of gene expression after cell stimulation. This method integrates the temporal dimension of biological rewiring of genetic programs and enables the prediction of the effect of targeted gene disruption at the system level. We tested the performance accuracy of this model on synthetic data before reverse-engineering the response of primary cancer cells to a proliferative (protumorigenic) stimulation in a multistate leukemia biological model (i.e., chronic lymphocytic leukemia). To validate the ability of our method to predict the effects of gene modulation on the global program, we performed an intervention experiment on a targeted gene. Comparison of the predicted and observed gene expression changes demonstrates the possibility of predicting the effects of a perturbation in a gene regulatory network, a first step toward an orientated intervention in a cancer cell genetic program.temporal gene network | lasso penalty | lymphoproliferative disorder | B-cell antigen receptor | predicted intervention C ellular behavior is conditioned mostly by functional genetic programs in response to various environmental signals, as initially shown in simple organisms (1, 2). External stimuli activate cellular surface receptors that trigger multiple signaling cascades in cells. The ultimate targets of these cascades are transcription factors that initiate sequential transcriptional activations with high temporal coordination. The first activated genes, at early time-points, after cell stimulation, essentially have a fast and transient expression; their gene products activate expression of various target genes downstream of transcriptional regulation cascades. These latter genes have longer-lasting expression, and their products sustain the adapted cellular response to initial environmental stimulation (3). These functional molecular networks are disrupted in various pathologies (e.g., cancer) where genetic aberrations lead to tumoral cellular programs. Since the first application of high-throughput technologies for measuring gene expression, a number of methods have been proposed to reverse-engineer gene regulatory networks; considered to be the underlying structure of these genetic programs (4). These different methods were developed to infer gene potential interactions and to describe these networks at the system level (5). The next important goal was to develop statistical tools to control these systems (6). One of the key challenges is to determine which critical genes whose perturbed expression drive these pathological genetic programs toward targeted states. We propose here a predictive met...
Objective: To assess the impact of piston-based vs peristaltic injection system technology and contrast media viscosity on achievable iodine delivery rates (IDRs) and vascular enhancement in a pre-clinical study. Methods: Four injectors were tested: MEDRAD® Centargo, MEDRAD® Stellant, CT Exprès®, and CT motion™ using five contrast media [iopromide (300 and 370 mgI ml−1), iodixanol 320 mgI ml−1, iohexol 350 mgI ml−1, iomeprol 400 mgI ml−1]. Three experiments were performed evaluating achievable IDR and corresponding enhancement in a circulation phantom. Results: Experiment I: Centargo provided the highest achievable IDRs with all tested contrast media (p < 0.05). Iopromide 370 yielded the highest IDR with an 18G catheter (3.15 gI/s); iopromide 300 yielded the highest IDR with 20G (2.70 gI/s) and 22G (1.65 gI/s) catheters (p < 0.05). Experiment II: with higher achievable IDRs, piston-based injectors provided significantly higher peak vascular enhancement (up to 48% increase) than the peristaltic injectors with programmed IDRs from 1.8 to 2.4 gI/s (p < 0.05). Experiment III: with programmed IDRs (e.g. 1.5 gI/s) achievable by all injection systems, Centargo, with sharper measured bolus shape, provided significant increases in enhancement of 34–73 HU in the pulmonary artery with iopromide 370 (p < 0.05). Conclusion: The tested piston-based injection systems combined with low viscosity contrast media provide higher achievable IDRs and higher peak vascular enhancement than the tested peristaltic-based injectors. With equivalent IDRs, Centargo provides higher peak vascular enhancement due to improved bolus shape. Advances in knowledge: This paper introduces a new parameter to compare expected performance among contrast media: the concentration/viscosity ratio. Additionally, it demonstrates previously unexplored impacts of bolus shape on vascular enhancement.
Venous air embolism as a complication of contrast media administration from power injection systems in CT is found to occur in 7%-55% of patients, impacting patient safety, diagnostic image quality, workflow efficiency, and patient and radiographer satisfaction. This study reviews the challenges associated with reactive air management approaches employed on contemporary systems, proposes a novel air management approach using proactive methods, and compares the impact of reactive and proactive approaches on injected air volumes under simulated clinical use. Methods: Injected air volumes from three power injection systems were measured under simulated clinical use via custom air trap fixture. Two of the systems employed reactive air management approaches, while a new system implemented the proposed proactive air management approach. Results: The proactive system injected significantly less air (average of 0.005mL±0.006mL with a maximum of 0.017mL) when compared to two systems with reactive approaches (averages of 0.130mL±0.082mL and 0.106mL±0.094mL with maximums of 0.259mL and 0.311mL, respectively) (p<0.05). CT images were taken of static and dynamic 0.1mL air bubbles inside of a vascular phantom, both of which were clearly visible. Additionally, the dynamic bubble was shown to introduce image artifacts similar to those observed clinically. Conclusion: Comparison of the injected air volumes show that a system with a proactive air management approach injected significantly less air compared to tested systems employing reactive approaches. Significance: The results indicate that the use of a proactive approach could significantly reduce the prevalence of observable, and potentially artifact-inducing, venous air embolism in contrast-enhanced CT procedures.
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