The longitudinal relaxation time constant (T1) of the myocardium is altered in various disease states due to increased water content or other changes to the local molecular environment. Changes in both native T1 and T1 following administration of gadolinium (Gd) based contrast agents are considered important biomarkers and multiple methods have been suggested for quantifying myocardial T1 in vivo. Characterization of the native T1 of myocardial tissue may be used to detect and assess various cardiomyopathies while measurement of T1 with extracellular Gd based contrast agents provides additional information about the extracellular volume (ECV) fraction. The latter is particularly valuable for more diffuse diseases that are more challenging to detect using conventional late gadolinium enhancement (LGE). Both T1 and ECV measures have been shown to have important prognostic significance.T1-mapping has the potential to detect and quantify diffuse fibrosis at an early stage provided that the measurements have adequate reproducibility. Inversion recovery methods such as MOLLI have excellent precision and are highly reproducible when using tightly controlled protocols. The MOLLI method is widely available and is relatively mature. The accuracy of inversion recovery techniques is affected significantly by magnetization transfer (MT). Despite this, the estimate of apparent T1 using inversion recovery is a sensitive measure, which has been demonstrated to be a useful tool in characterizing tissue and discriminating disease. Saturation recovery methods have the potential to provide a more accurate measurement of T1 that is less sensitive to MT as well as other factors. Saturation recovery techniques are, however, noisier and somewhat more artifact prone and have not demonstrated the same level of reproducibility at this point in time.This review article focuses on the technical aspects of key T1-mapping methods and imaging protocols and describes their limitations including the factors that influence their accuracy, precision, and reproducibility.

Background-Diffuse myocardial fibrosis is a final end point in most cardiac diseases. It is missed by the cardiovascular magnetic resonance (CMR) late gadolinium enhancement technique. Currently, quantifying diffuse myocardial fibrosis requires invasive biopsy, with inherent risk and sampling error. We have developed a robust and noninvasive technique, equilibrium contrast CMR (EQ-CMR) to quantify diffuse fibrosis and have validated it against the current gold standard of surgical myocardial biopsy. Methods and Results-The 3 principles of EQ-CMR are a bolus of extracellular gadolinium contrast followed by continuous infusion to achieve equilibrium; a blood sample to measure blood volume of distribution (1Ϫhematocrit); and CMR to measure pre-and postequilibrium T1 (with heart rate correction). The myocardial volume of distribution is calculated, reflecting diffuse myocardial fibrosis. Clinical validation occurred in patients undergoing aortic valve replacement for aortic stenosis or myectomy in hypertrophic cardiomyopathy (nϭ18 and nϭ8, respectively). Surgical biopsies were analyzed for picrosirius red fibrosis quantification on histology. Key Words: magnetic resonance imaging Ⅲ cardiomyopathy Ⅲ imaging Ⅲ endomyocardial fibrosis Ⅲ collagen F ibrosis is a final common end point in virtually all pathological processes in human organs and tissues. In the heart, focal fibrosis (scar) as a result of myocardial infarction is the leading cause of death and heart failure in the world. 1 Cardiovascular magnetic resonance (CMR) using the late gadolinium enhancement (LGE) contrast technique is the gold standard method for its assessment. 2,3 Focal fibrosis also occurs in other diseases, including cardiomyopathy, 4 myocarditis, 5 and infiltrative diseases. 6 Scar leads to an increased volume of distribution for gadolinium and slower contrast kinetics, 7 leading to late enhancement of scar by CMR. Clinical Perspective on p 144Diffuse myocardial fibrosis is a covert process that occurs as a part of normal aging. 8 -10 It is accelerated in diseases such as hypertension, aortic stenosis, and cardiomyopathy, 11Ϫ13 where it contributes to breathlessness, heart failure, and arrhythmia. 14 -16 Unlike scar, however, it may be reversible and is a treatment target. 17,18 Currently, the only method to quantify diffuse fibrosis is invasive biopsy, which carries significant morbidity and is prone to sampling error. 19 The LGE technique cannot be used to visualize diffuse fibrosis because "normal" myocardium with diffuse fibrosis is "nulled" to highlight focal scar, thereby losing all information of any background interstitial expansion. Recently, attempts to quantify diffuse fibrosis with CMR have been made, but they have required complex kinetic modeling and have not definitively excluded confounding factors such as heart rate, body composition, and renal clearance variability. Histological validation, where present, has In this study, we describe a potentially clinically applicable, robust, noninvasive method to quantify diffuse myo...

I n North America most clinical MRI is performed at 1.5 T or 3.0 T, and some research applications have moved to 7.0 T. High field is motivated by higher polarization, promising increased signal-to-noise ratio (SNR), and resolution. However, this causes image distortion, constrained imaging efficiency, increased specific absorption rate, and higher cost. For some applications, low field strength may offer intrinsic advantages (1,2). At low field strength, short T1 and long T2* allow more efficient pulse sequence design; imaging near air-tissue interfaces is improved by virtue of reduced susceptibility gradients; and specific absorption rate is reduced, which can diminish heating of conductive devices and implants, and can eliminate pulse sequence parameter constraints (3). Commercial lower field systems have been largely overlooked as hardware and software have improved over the last 2 decades, and therefore are not well-suited for technically demanding imaging. We developed and evaluated a custom 0.55-T MRI system equipped with contemporary