Melanie Suzanne Kotys

Necrotic core thickness and positive arterial remodeling index: Emergent biomechanical factors for evaluating the risk of plaque rupture

Fibrous cap thickness is often considered as diagnostic of the degree of plaque instability. Necrotic core area (Core(area)) and the arterial remodeling index (Remod(index)), on the other hand, are difficult to use as clinical morphological indexes: literature data show a wide dispersion of Core(area) thresholds above which plaque becomes unstable. Although histopathology shows a strong correlation between Core(area) and Remod(index), it remains unclear how these interact and affect peak cap stress (Cap(stress)), a known predictor of rupture. The aim of this study was to investigate the change in plaque vulnerability as a function of necrotic core size and plaque morphology. Cap(stress) value was calculated on 5,500 idealized atherosclerotic vessel models that had the original feature of mimicking the positive arterial remodeling process described by Glagov. Twenty-four nonruptured plaques acquired by intravascular ultrasound on patients were used to test the performance of the associated idealized morphological models. Taking advantage of the extensive simulations, we investigated the effects of anatomical plaque features on Cap(stress). It was found that: 1) at the early stages of positive remodeling, lesions were more prone to rupture, which could explain the progression and growth of clinically silent plaques and 2) in addition to cap thickness, necrotic core thickness, rather than area, was critical in determining plaque stability. This study demonstrates that plaque instability is to be viewed not as a consequence of fibrous cap thickness alone but rather as a combination of cap thickness, necrotic core thickness, and the arterial remodeling index.

Measurement of coronary flow response to cold pressor stress in asymptomatic women with cardiovascular risk factors using spiral velocity-encoded cine MRI at 3 tesla

Background: Coronary sinus (CS) flow in response to a provocative stress has been used as a surrogate measure of coronary flow reserve, and velocity-encoded cine (VEC) magnetic resonance imaging (MRI) is an established technique for measuring CS flow. In this study, the cold pressor test (CPT) was used to measure CS flow response because it elicits an endothelium-dependent coronary vasodilation that may afford greater sensitivity for detecting early changes in coronary endothelial function. Purpose: To investigate the feasibility and reproducibility of CS flow reactivity (CSFR) to CPT using spiral VEC MRI at 3 Tesla in a sample of asymptomatic women with cardiovascular risk factors. Material and Methods: Fourteen asymptomatic women (age 38 years ± 10) with cardiovascular risk factors were studied using 3D spiral VEC MRI of the CS at 3 T. The CPT was utilized as a provocative stress to measure changes in CS flow. CSFR to CPT was calculated from the ratio of CS flow during peak stress to baseline CS flow. Results: CPT induced a significant hemodynamic response as measured by a 45% increase in rate-pressure product (P<0.01). A significant increase in CS volume flow was also observed (baseline, 116 ± 26 ml/min; peak stress, 152 ± 34 ml/min, P=0.01). CSFR to CPT was 1.31 ± 0.20. Test-retest variability of CS volume flow was 5% at baseline and 6% during peak stress. Conclusion: Spiral CS VEC MRI at 3 T is a feasible and reproducible technique for measuring CS flow in asymptomatic women at risk for cardiovascular disease. Significant changes in CSFR to CPT are detectable, without demanding pharmacologic stress.

Profile order and time-dependent artifacts in contrast-enhanced coronary MR angiography at 3T: Origin and prevention†

To enhance the clinical value of coronary magnetic resonance angiography (MRA), high‐relaxivity contrast agents have recently been used at 3T. Here we examine a uniform bilateral shadowing artifact observed along the coronary arteries in MRA images collected using such a contrast agent. Simulations were performed to characterize this artifact, including its origin, to determine how best to mitigate this effect, and to optimize a data acquisition/injection scheme. An intraluminal contrast agent concentration model was used to simulate various acquisition strategies with two profile orders for a slow‐infusion of a high‐relaxivity contrast agent. Filtering effects from temporally variable weighting in k‐space are prominent when a centric, radial (CR) profile order is applied during contrast infusion, resulting in decreased signal enhancement and underestimation of vessel width, while both pre‐ and postinfusion steady‐state acquisitions result in overestimation of the vessel width. Acquisition during the brief postinfusion steady‐state produces the greatest signal enhancement and minimizes k‐space filtering artifacts. Magn Reson Med, 2009.

Rapid flow quantification in iliac arteries with spiral phase-contrast MRI

Phase contrast MRI is a powerful tool for blood flow quantification. Conventional cartesian phase contrast sequences require lengthy acquisition on the order of several minutes. Spiral acquisition phase-contrast (PC) MRI is capable of reducing the TR and TE in order to minimize flow dependent artifacts and total imaging time. Despite this, in general, spiral phase contrast sequences suffer from off-resonance artifacts and inconsistent data artifacts. In this work, we show that short interleaved spiral readout trajectories have the capability to obtain high spatio-temporal resolution flow images in the common iliac artery distal to the aortoiliac bifurcation with little or no artifacts and with significant savings in image acquisition time over the Cartesian trajectory. To verify the accuracy, we compare our results with a Conventional cartesian trajectory.

IMPAIRED CORONARY VASCULAR REACTIVITY IN CARDIAC SYNDROME X MEASURED NON-INVASIVELY BY 3T MRI

Background: Cardiac syndrome X (CSX) describes women with chest pain, abnormal stress tests but no significant coronary stenoses by angiography. Impaired coronary vascular reactivity (CVR) predicts cardiovascular events in CSX. Non-invasive detection of impaired CVR could facilitate early diagnosis and risk stratification in CSX. We previously demonstrated significant increases in coronary flow (CF) in healthy women using 3T magnetic resonance imaging (MRI) and the cold pressor test (CPT). We sought to determine if women with CSX had impaired CVR compared to matched controls using MRI.

High resolution imaging of the right ventricle using ZOOM MRI

Introduction ZOOM is a spin echo based technique with high spatial resolution [1]. ZOOM differs from traditional spin echo imaging in that the 180° refocusing radiofrequency pulse is applied perpendicular to the 90° excitation pulse, limiting the field of view to the intersection of these pulses. Turbo spin echo (TSE) black blood images are acquired routinely during MRI assessment of patients with arrhythomogenic right ventricular dysplasia (ARVD). High spatial resolution is necessary for characterizing the thin RV wall in suspected ARVD patients, which is typically only 23.5 mm thick.

Orthogonal CSPAMM (OCSPAMM) MR tagging for imaging ventricular wall motion

Tagged magnetic resonance imaging (MRI) has the ability to directly and non-invasively alter tissue magnetization and produce tags on the deforming tissue [1], [2]. Since its development, the Spatial Modulation of Magnetization (SPAMM) [2] tagging pulse sequence has been widely available and is the most commonly used technique for producing sinusoidal tag patterns. However, SPAMM suffers from tag fading which occurs in the later phases of the cardiac cycle. Complementary SPAMM (CSPAMM) was introduced to solve this problem by acquiring and subtracting two SPAMM images [3]. The drawback of CSPAMM is that it results in doubling of the acquisition time. In this paper, we propose a novel pulse sequence, termed Orthogonal CSPAMM (OCSAPMM), which results in the same acquisition time as SPAMM for 2D deformation estimation while keeping the advantages of CSPAMM. Different from CSPAMM, in OCSPAMM the second tagging pulse orientation is rotated 90 degrees relative to the first one so that motion information can be obtained simultaneously in two directions. A cardiac motion phantom, which independently models cardiac wall thickening and rotation in the human heart was used to show the effectiveness of the proposed pulse sequence.

An improved real-time cine Late Gadolinium Enhancement (LGE) imaging method at 3T

A real-time Late Gadolinium Enhancement (LGE) MRI technique (free breathing and non-gated) is presented for detection of myocardial scars. Conventional LGE imaging methods currently in use are applied in conjunction with breath-hold and, thus, are difficult to use in patients with cardiac disease and may lead to motion artifacts. Additionally, conventional techniques involve ECG gating, which is problematic in patients with arrhythmias requiring multiple breath holds and use of arrhythmia rejection techniques. Finally, conventional LGE techniques require accurate estimates for the inversion time in order to null the normal myocardium, revealing the location of the scar with high contrast. Real-time LGE imaging obviates these difficulties and can, in principle, acquire cine images to assess wall motion over several heart phases as part of the same scan. To date, the main limitation of real-time LGE imaging has been long acquisition window and low temporal resolution. These limitations lead to temporal blurring of wall motion and possible overestimation of infarct size. The goal of this study was to increase the temporal resolution of real-time, cine LGE imaging, providing the possibility for better visualization of the wall motion and more accurate assessment of myocardial viability.

MR-guided catheter-based excitation emission optical spectroscopy for in vivo tissue characterization

Excitation emission spectroscopy (EES) has been used in the past to characterize many different types of tissue. This technique uses multiple excitation wavelengths and samples a complete optical spectrum for each, yielding an excitation-emission matrix (EEM). Upon study of the EEM, it is possible to determine the presence of multiple optical contrast agents since these dyes can have characteristic spectra that can be separated. Here, we demonstrate EES specifically designed for use in conjunction with MR. This EES is applied with an in-suite control setup that permits real-time navigation, utilizing active MR tracking catheters, and providing a platform for MR-guided tissue characterization. The EES system is used in a demonstration experiment to highlight MR imaging, MR guidance in conjunction with a catheter-based optical measurement.

236 Quantitative T2 Signal intensity in patients undergoing stress perfusion imaging

Myocardial T2-weighted imaging has been used to detect edema associated with acute ischemia and injury. The images are often evaluated visually for the presence of increased signal. MR stress perfusion imaging is used to detect significant coronary stenosis in patients with suspected CAD. The purpose of this study is to compare quantitative intensity maps of T2-weighted images with the presence and severity of stress perfusion defects.