Carotid MRI: Tool for Monitoring Individual Response?
Carotid MRI: Tool for Monitoring Individual Response?
Stroke remains a leading cause of morbidity and mortality. While stroke-related mortality has declined over the past four decades, data indicate that the mortality rate has begun to plateau. This change in trend may be attributable to variation in individual response to therapies that were derived from population-based studies. Further reductions in stroke mortality may require individualized care governed by directly monitoring the effects of cardiovascular therapy. In this article, carotid MRI is considered as a tool for monitoring in vivo carotid atherosclerotic disease, a principal etiology of stroke. Carotid MRI has been previously utilized to identify specific plaque features beyond luminal stenosis that are predictive of transient ischemic attack and stroke. To gain perspective on the possibility of monitoring plaque change within the individual, clinical trials and natural history studies that have used serial carotid MRI are considered. Data from these studies indicate that patients with a lipid-rich necrotic core with or without intraplaque hemorrhage may represent the desired phenotype for monitoring treatment effects in the individual. Advances in tissue-specific sequences, acquisition resolution, scan time, and techniques for monitoring inflammation and mechanical forces are expected to enable earlier detection of response to therapy. In so doing, cost-effective multicenter studies can be conducted to confirm the anticipated positive effects on outcomes of using carotid MRI for individualized care in patients with carotid atherosclerosis. In accordance, carotid MRI is poised to emerge as a powerful clinical tool for individualized management of carotid atherosclerotic disease to prevent stroke.
A cornerstone of stroke prevention has been the identification of risk factors. Hypertension, diabetes, smoking and hypercholesterolemia represent the core, noncardiac risk factors for stroke. Therapies directed at specific clinical risk factors have reduced stroke mortality over the past several decades. In the 1970s and 1980s, medical management of hypertension was associated with a sharp decline in incident stroke mortality. Similarly, the widespread use of statin therapy for lowering LDL-cholesterol (LDL-C) was coincident with a continued, albeit slower, decline in stroke-related mortality during the 1990s. Stroke, however, presently remains a leading cause of morbidity and mortality throughout the world. This stark reality has driven a pursuit for novel risk factors, clinical and imaging based, that may improve risk assessment. Unfortunately, additional novel metrics have yielded only incremental increases in risk stratification.
Instead of risk factor expansion, an alternate paradigm for the reduction of stroke is the assessment of therapeutic efficacy against known risk factors. This concept is born from two observations. First, medical therapy directed at an identified risk factor within an individual was derived from multiple large, population-based studies. However, population effects harbor substantial individual variation, which suggests therapies may not work similarly for all individuals. Second, advances in non-invasive imaging technologies have provided a window to the in vivo arterial wall in vessels predisposed to atherosclerotic plaque formation. Atherosclerosis is a principal etiology of stroke. Accordingly, monitoring change in atherosclerotic plaques in response to cardiovascular therapy may be a powerful measure of efficacy and serve to guide individual therapy to further reduce stroke.
Non-invasive imaging of atherosclerotic carotid lesions has been investigated with ultrasound, computed tomography and MRI. For a comparison of the various imaging modalities used to study carotid atherosclerotic disease, we refer the reader to a recent review by U-King-Im et al. The principal advantage that MRI affords compared with other modalities is the acquisition and integration of different contrast weightings to enable soft-tissue characterization of the arterial wall and associated plaques. The utilization of multiple, high spatial resolution contrast weightings for the non-invasive, in vivo assessment of carotid atherosclerotic disease has been termed 'carotid MRI'.
In this article, we consider the use of carotid MRI as a tool to monitor individual response to cardiovascular therapy. First, we briefly describe carotid MRI and the salient identifiable features of atherosclerosis that may prove valuable in risk stratification. Subsequently, we review serial imaging data obtained with carotid MRI for insight regarding the feasibility of detecting individual response to therapy. Finally, we discuss emerging techniques in carotid MRI that promote translation to clinical practice by reducing scan time and simplifying image interpretation.
Abstract and Introduction
Abstract
Stroke remains a leading cause of morbidity and mortality. While stroke-related mortality has declined over the past four decades, data indicate that the mortality rate has begun to plateau. This change in trend may be attributable to variation in individual response to therapies that were derived from population-based studies. Further reductions in stroke mortality may require individualized care governed by directly monitoring the effects of cardiovascular therapy. In this article, carotid MRI is considered as a tool for monitoring in vivo carotid atherosclerotic disease, a principal etiology of stroke. Carotid MRI has been previously utilized to identify specific plaque features beyond luminal stenosis that are predictive of transient ischemic attack and stroke. To gain perspective on the possibility of monitoring plaque change within the individual, clinical trials and natural history studies that have used serial carotid MRI are considered. Data from these studies indicate that patients with a lipid-rich necrotic core with or without intraplaque hemorrhage may represent the desired phenotype for monitoring treatment effects in the individual. Advances in tissue-specific sequences, acquisition resolution, scan time, and techniques for monitoring inflammation and mechanical forces are expected to enable earlier detection of response to therapy. In so doing, cost-effective multicenter studies can be conducted to confirm the anticipated positive effects on outcomes of using carotid MRI for individualized care in patients with carotid atherosclerosis. In accordance, carotid MRI is poised to emerge as a powerful clinical tool for individualized management of carotid atherosclerotic disease to prevent stroke.
Introduction
A cornerstone of stroke prevention has been the identification of risk factors. Hypertension, diabetes, smoking and hypercholesterolemia represent the core, noncardiac risk factors for stroke. Therapies directed at specific clinical risk factors have reduced stroke mortality over the past several decades. In the 1970s and 1980s, medical management of hypertension was associated with a sharp decline in incident stroke mortality. Similarly, the widespread use of statin therapy for lowering LDL-cholesterol (LDL-C) was coincident with a continued, albeit slower, decline in stroke-related mortality during the 1990s. Stroke, however, presently remains a leading cause of morbidity and mortality throughout the world. This stark reality has driven a pursuit for novel risk factors, clinical and imaging based, that may improve risk assessment. Unfortunately, additional novel metrics have yielded only incremental increases in risk stratification.
Instead of risk factor expansion, an alternate paradigm for the reduction of stroke is the assessment of therapeutic efficacy against known risk factors. This concept is born from two observations. First, medical therapy directed at an identified risk factor within an individual was derived from multiple large, population-based studies. However, population effects harbor substantial individual variation, which suggests therapies may not work similarly for all individuals. Second, advances in non-invasive imaging technologies have provided a window to the in vivo arterial wall in vessels predisposed to atherosclerotic plaque formation. Atherosclerosis is a principal etiology of stroke. Accordingly, monitoring change in atherosclerotic plaques in response to cardiovascular therapy may be a powerful measure of efficacy and serve to guide individual therapy to further reduce stroke.
Non-invasive imaging of atherosclerotic carotid lesions has been investigated with ultrasound, computed tomography and MRI. For a comparison of the various imaging modalities used to study carotid atherosclerotic disease, we refer the reader to a recent review by U-King-Im et al. The principal advantage that MRI affords compared with other modalities is the acquisition and integration of different contrast weightings to enable soft-tissue characterization of the arterial wall and associated plaques. The utilization of multiple, high spatial resolution contrast weightings for the non-invasive, in vivo assessment of carotid atherosclerotic disease has been termed 'carotid MRI'.
In this article, we consider the use of carotid MRI as a tool to monitor individual response to cardiovascular therapy. First, we briefly describe carotid MRI and the salient identifiable features of atherosclerosis that may prove valuable in risk stratification. Subsequently, we review serial imaging data obtained with carotid MRI for insight regarding the feasibility of detecting individual response to therapy. Finally, we discuss emerging techniques in carotid MRI that promote translation to clinical practice by reducing scan time and simplifying image interpretation.