Magnetic resonance imaging-guided coronary interventions

Using Adaptive Imaging Parameters to Improve PEGylated Ultrasmall Iron Oxide Nanoparticles-Enhanced Magnetic Resonance Angiography

The PEGylated ultrasmall iron oxide nanoparticles (PUSIONPs) exhibit longer blood residence time and better biodegradability than conventional gadolinium-based contrast agents (GBCAs), enabling prolonged acquisitions in contrast-enhanced magnetic resonance angiography (CE-MRA) applications. The image quality of CE-MRA is dependent on the contrast agent concentration and the parameters of the pulse sequences. Here, a closed-form mathematical model is demonstrated and validated to automatically optimize the concentration, echo time (TE), repetition time (TR) and flip angle (FA). The pharmacokinetic studies are performed to estimate the dynamic intravascular concentrations within 12 h postinjection, and the adaptive concentration-dependent sequence parameters are determined to achieve optimal signal enhancement during a prolonged measurement window. The presented model is tested on phantom and in vivo rat images acquired from a 3T scanner. Imaging results demonstrate excellent agreement between experimental measurements and theoretical predictions, and the adaptive sequence parameters obtain better signal enhancement than the fixed ones. The low-dose PUSIONPs (0.03 mmol kg-1 and 0.05 mmol kg-1) give a comparable signal intensity to the high-dose one (0.10 mmol kg-1) within 2 h postinjection. The presented mathematical model provides guidance for the optimization of the concentration and sequence parameters in PUSIONPs-enhanced MRA, and has great potential for further clinical translation.

Catheter-based Arterial Input Function Determination for Myocardial Perfusion Measurements

The quantification of myocardial perfusion with contrast agent (CA) tracers requires the precise knowledge of the arterial input function (AIF). In this study a method for MR-guided vascular interventions is evaluated that determines the AIF via an active tracking catheter during targeted CA injection. A phantom experiment with a dialysis filter was conducted to measure the AIF using an active catheter and a dynamic image series as reference. To compensate for dilution and coil sensitivity effects, correction methods were developed for the catheter-based AIF determination. From the dynamic MR measurements in the perfusion phantom quantitative perfusion maps were calculated by a deconvolution of the measured CA concentration with the AIF, and additional flow measurements were used to normalize the perfusion map. The signal-time-curves of the measured AIF using the catheter-based and imaging-based methods agree while the absolute values differ by a scaling factor of about 9. After normalization to the surrounding flow, both perfusion techniques are in excellent agreement. Catheter-based AIF measurements are feasible but require an additional normalization which can be determined from a flow measurement. The technique might enable faster perfusion measurements during cardiovascular interventions.

Early experience and technical aspects of physician-modified fenestration in thoracic endovascular aortic repair for aortic arch pathologies

Objective

This study was performed to describe the treatment of aortic arch pathologies with a physician-modified fenestration (PMF) technique in thoracic endovascular aortic repair (TEVAR).

Methods

From August 2015 to August 2017, 32 patients with aortic arch pathologies underwent TEVAR with the PMF technique. All patients’ clinical data were analyzed with GraphPad Prism 7.0.

Results

Thirty-four aortic stent-grafts were implanted in 32 patients. The mean proximal diameter of the stent-graft was 32.4 ± 3.4 cm, and the mean length was 170.0 ± 25.2 cm. Twenty-nine PMF procedures were performed to preserve the left subclavian artery (LSA) and three to preserve both the LSA and left common carotid artery. The mean distance between the pathology and LSA was 8.4 ± 4.0 mm. The mean procedure time (from first to last digital subtraction angiography) was 22.8 ± 20.8 min. The mean follow-up time was 8.3 ± 5.3 months. During follow-up, the all-cause survival rate was 83.3% and the patency rate of the branch artery after PMF was 96.0%.

Conclusion

The PMF technique is a relatively safe, feasible, and time-saving method to preserve the branch artery in TEVAR for aortic arch pathologies. The short- to middle-term result of this technique is satisfactory.

A REGRESSION MIXTURE MODEL WITH SPATIAL CONSTRAINTS FOR CLUSTERING SPATIOTEMPORAL DATA

We present a new approach for curve clustering designed for analysis of spatiotemporal data. Such data contains both spatial and temporal patterns that we desire to capture. The proposed methodology is based on regression and Gaussian mixture modeling. The novelty of the herein work is the incorporation of spatial smoothness constraints in the form of a prior for the data labels. This allows to take into account the property of spatiotemporal data according to which spatially adjacent data points have higher probability to belong to the same cluster. The proposed model can be formulated as a Maximum a Posteriori (MAP) problem, where the Expectation Maximization (EM) algorithm is used to estimate the model parameters. Several numerical experiments with both simulated data and real cardiac perfusion MRI data are used for evaluating the methodology. The results are promising and demonstrate the value of the proposed approach.

Intracoronary injection of contrast media maps the territory of the coronary artery: an MRI technique for assessing the effects of locally delivered angiogenic therapies

RATIONALE AND OBJECTIVES

The effects of locally delivered angiogenic factors or stem cells on the coronary artery perfusion territory are not well defined. Therefore, the aim of this study was to determine the ability of the selective injection of magnetic resonance contrast media (MR-CM) to map and quantify the territories of the major coronary arteries.

MATERIALS AND METHODS

Selective coronary catheterization (n = 16 pigs) was performed under x-ray and magnetic resonance imaging (MRI) fluoroscopy in an x-ray and magnetic resonance suite. Catheters were placed in the left anterior descending (LAD), circumflex, or right coronary artery. The coronary perfusion territories were mapped by the intracoronary injection of MR-CM using first-pass perfusion (FPP) and early contrast-enhanced (CE) MRI. Cine MRI was used to quantify left ventricular (LV) mass. In 12 animals, the LAD coronary artery was occluded by microspheres to create infarctions. Infarct size was measured on delayed enhanced (DE) MRI after the intravenous injection of MR-CM.

RESULTS

X-ray and magnetic resonance fluoroscopy were successfully used to catheterize the coronary arteries. The perfusion territories of the coronary arteries were defined as hyperenhanced regions on FPP and CE MRI. The LAD coronary artery territory was 33.7 +/- 2.2% of LV mass on FPP MRI and 33.0 +/- 2.3% on CE MRI (P = .63). Bland-Altman analysis showed close agreement between the two methods (0.7 +/- 5.0%). DE MRI demonstrated the infarcted myocardium as hyperenhanced subregions of the perfusion territory (7.5 +/- 1.2% of LV mass).

CONCLUSIONS

Interventional cardiac x-ray and magnetic resonance fluoroscopy can be used to map and quantify the perfusion territory of each coronary artery. This experimental method can be used before and after the local delivery of angiogenic factors and stem cell therapy to determine their efficacy.

Dynamic imaging of contrast-enhanced coronary vessels with a magnetization prepared rotated stripe keyhole acquisition

PURPOSE

To evaluate dynamic coronary imaging based on a magnetization prepared contrast-enhanced (CE) rotated stripe keyhole acquisition scheme.

MATERIALS AND METHODS

Background suppression of long T(1) tissue was used so that the k-space would be selectively dominated by the contribution of the CE vessel. The phase-encoding axis was then adjusted parallel to the long axis of the vessel to sample the significant power spectrum of the vessel. The performance of this approach was evaluated by means of computer simulations and experimental studies on phantoms and a pig model instrumented with an intracoronary catheter for infusion of contrast media.

RESULTS

Computer simulations and phantom studies demonstrated that by rotating the gradient axes to match the k-space pattern of the frequency spectrum, one can reduce the keyhole band to 20% of the full k-space while preserving the structure's lumen width and sharpness. In vivo studies validated those findings, and dynamic angiograms of the CE coronary arteries were obtained as rapidly as 140 msec per image, with an in-plane spatial resolution of 1.5 mm.

CONCLUSION

With efficient background suppression, a rotated stripes keyhole acquisition can efficiently acquire the significant k-space of a CE vessel, and provide improved vessel definition with a reduced acquisition matrices scheme.

Current Concepts in the Management of Intracranial Atherosclerotic Disease

MEDICALLY REFRACTORY, SYMPTOMATIC intracranial atherosclerotic disease has a poor prognosis. Based on the results of the Warfarin-Aspirin Symptomatic Intracranial Disease study, the risk of ipsilateral stroke at 1.8 years is between 13 and 14% in patients with symptomatic intracranial atherosclerosis. Synergistic advances in intracranial angioplasty and stenting, modern neuroimaging techniques, and periprocedural and postprocedural antithrombotic regimens are creating new models for the diagnosis and successful endovascular treatment of intracranial stenosis. In this article, the most recent clinical developments and concepts for the diagnosis and endovascular treatment of intracranial atherosclerotic disease are discussed.

Fast magnetization-driven preparation for imaging of contrast-enhanced coronary arteries during intra-arterial injection of contrast agent

PURPOSE

To implement a short-duration magnetization preparation sequence, which consists of a saturation followed by multiple inversion pulses, for imaging of short-T1 species and suppression of long-T1 species.

MATERIALS AND METHODS

Computer optimizations were performed to derive preparation schemes that 1) suppress long-T1 background species with T1>or=250 msec, 2) maximize the MZ of contrast-enhanced (CE) structures with T1<or=50 msec, and 3) have a preparation duration in the range of 200 msec. The optimized sequences were tested on a phantom and a pig model instrumented with an intracoronary catheter for infusion of contrast media.

RESULTS

Computer simulations generated preparation schemes with durations of 165-225 msec depending on the number of preparation pulses used, which generated saturation of over 98% for T1>250 msec, and about a 30% reduction for 20 msec<T1<50 msec. The phantom studies validated the performance of the optimized sequences. Coronary artery angiograms (380 msec for preparation and image acquisition) demonstrated signal-to-noise ratios (SNRs) in the range of 13-15.5 and contrast-to-noise ratios (CNRs) in the range of 6.3-7.1 in the CE coronary vessels.

CONCLUSION

This work demonstrates that fast magnetization-driven preparation schemes can be implemented for fast imaging of CE coronary vessels with efficient saturation of background species.