James W. Goldfarb

Partially Parallel Imaging With Localized Sensitivities (PILS)

In this study a novel partially parallel acquisition method is presented, which can be used to accelerate image acquisition using an RF coil array for spatial encoding. In this technique, Parallel Imaging with Localized Sensitivities (PILS), it is assumed that the individual coils in the array have localized sensitivity patterns, in that their sensitivity is restricted to a finite region of space. Within the PILS model, a detailed, highly accurate RF field map is not needed prior to reconstruction. In PILS, each coil in the array is fully characterized by only two parameters: the center of coils sensitive region in the FOV and the width of the sensitive region around this center. In this study, it is demonstrated that the incorporation of these coil parameters into a localized Fourier transform allows reconstruction of full FOV images in each of the component coils from data sets acquired with a reduced number of phase encoding steps compared to conventional imaging techniques. After the introduction of the PILS technique, primary focus is given to issues related to the practical implementation of PILS, including coil parameter determination and the SNR and artifact power in the resulting images. Finally, in vivo PILS images are shown which demonstrate the utility of the technique. Magn Reson Med 44:602–609, 2000.

Myocardial Fat Deposition after Left Ventricular Myocardial Infarction: Assessment by Using MR Water-Fat Separation Imaging

PURPOSEnTo prospectively investigate the prevalence of fat deposition in chronic myocardial infarction (MI) by using magnetic resonance (MR) fat-water separation imaging with sampling of the entire left ventricular (LV) myocardium. A subsidiary aim was to determine the relationship between LV fat deposition and scar characteristics, as well as regional and global cardiac functional parameters.nnnMATERIALS AND METHODSnTwenty-five patients with LV MI were evaluated in this prospective institutional review board-approved, Health Insurance Portability and Accountability Act-compliant study after they provided written informed consent. A 1.5-T MR system was used to perform volumetric cine, fat-sensitive, and late gadolinium-enhanced (LGE) infarct imaging. Water-fat separation was performed by using a three-point Dixon reconstruction from in- and opposed-phase black-blood gradient-echo images. Fat deposition location was compared with LGE infarct imaging by using a 17-segment model. Global and regional functional variables, LGE volumes, and fat deposition were compared by using the Pearson correlation, Student t test, and multiple regression.nnnRESULTSnA fat deposition prevalence of 68% was found in areas of chronic MI. The patients with fat deposition had larger infarctions (30.0 mL +/- 15.1 [standard deviation] vs 14.8 mL +/- 6.1; P = .002), decreased wall thickening (2.3% +/- 20.0 vs 37.8% +/- 34.4; P = .003), and impaired endocardial wall motion (2.9 mm +/- 2.0 vs 5.8 mm +/- 2.6; P = .007). The volume of fat deposition was correlated with infarct volume, LV ejection fraction, LV end-diastolic volume index, and LV end-systolic volume index.nnnCONCLUSIONnThere is a high prevalence of fat deposition in healed MI. It is associated with post-infarction characteristics including infarct volume, LV mass, wall thickness, wall thickening, and wall motion.

Effect of supplemental oxygen on native blood and myocardial MOLLI T1 relaxation times

Background Magnetic resonance (MR) T1 relaxation time measurements are increasingly used for myocardial tissue characterization. Significant differences in native and gadolinium-enhanced measurements have been associated with ischemic and non-ischemic cardiomyopathies, myocardial fat deposition, fibrosis and edema as well as regional and global ventricular functional parameters. Supplemental oxygen is often given to cardiac MR patients for improved breatholding. High flow supplemental oxygen with a non-rebreather mask is reported to reduce both myocardial and blood T1 relaxation times and has been studied with HASTE and FLASH T1 relaxation measurements for the optimization of MR ventilation scanning. The primary mechanism is dissolved oxygen acting as a paramagetic contrast agent. Conversely other reports show an increase of blood T1 times with increasing oxygen saturation. We studied the effect of supplemental oxygen on myocardial and blood T1 relaxation times using a well-documented T1 MOdified Look-Locker Imaging (MOLLI) protocol. Methods Twelve healthy subject without respiratory or cardiac disease (age: 47.4±5.3 years; 6 male) were studied at 1.5T using MOLLI T1 mapping (TE/TE= 2.8/1.2 ms; 3(3)-5; 2 inversions, 3 heartbeat rest period; TI start=120 ms; TI increment=120ms; 3 parameter curve fitting). Images were acquired in the four chamber view. Five measurements spaced by 10 minutes were performed with supplemental oxygen supplied by nasal cannula and a non-reberather mask alternating with room air (M1: Room air, M2: nasal oxygen (2 l/m), M3: Room air, M4: non-rebreather mask (15 l/m), M5: room air). Regions-of-interest were drawn for T1 measurements in the boodpool of each ventricle and atria as well as septal myocardium. The effects of supplemental oxygen were investigated statistically using a mixed model analysis of variance.

Cardiovascular magnetic resonance TE-averaged susceptibility weighted imaging of reperfused intramyocardial hemorrhage.

Background In the setting of acute myocardial infarction (AMI), therapeutic and spontaneous reperfusion of ischemic myocardium can lead to interstitial intramyocardial hemorrhage (IMH) which is associated with microvascular obstruction (MVO) and subsequent adverse clinical outcomes. Imaging without contrast agents (native imaging) can be used in AMI patients for additional myocardial tissue characterization. Native T1 and T2 weighted imaging and quantitative measurements have been reported to detect myocardial edema and depict the myocardial area at risk. IMH affects T1, T2 and T2* relaxation as well as susceptibility and the feasibility of several MR image contrasts (T1, T2, T2* and gradientecho phase) has been demonstrated for the depiction of IMH. Susceptibility weighted imaging (SWI) uses a type of image contrast different from traditional spin density, T1 or T2 weighted MR imaging. In the present work, we report our experience with myocardial SWI imaging (combined gradient-echo magnitude and phase imaging) for the detection of IMH. We propose TE image averaging and gray-scale inversion as a means of providing a single image with good image SNR and excellent contrast for the detection of IMH.

Three-compartment modeling of chronic myocardial infarction gadolinium kinetics

Introduction The mechanism behind late gadolinium-enhanced (LGE) chronic myocardial infarct (MI) imaging is widely thought to be an increased gadolinium (Gd) concentration due to fibrotic tissue. Several groups have employed T1 measurements to measure the partition coefficient (ratio of tissue-to-blood Gd-concentrations) using a twocompartment model. A three-compartment model yields not only information about flow of Gd from the capillaries to the intracellular space, but in the case of chronic MI to fibrotic tissue and in the case of acute MI in the myocytes themselves. With model inputs of the LV bloodpool and tissue Gd-concentrations, the model yields transfer constants (K) between the compartments, compartment fractional volumes (v) and Gd-concentrations curves for tissue blood plasma, the extravascular extracellular space (EES) and fibrotic tissue. A detailed model may not only be useful to detect and characterize MI, but non-ischemic cardiomyopathies with global or diffuse fibrosis.

Association between left ventricular myocardial resting perfusion and intramyocardial fat deposition in patients with chronic myocardial infarction

Introduction Ischemic evaluation of the left ventricle (LV) by MR imaging can be performed using a combination of rest and stress images during a bolus contrast injection. Additionally, late-gadolinium-enhanced images are used determine the presence and extent of infarction. Myocardial tissue composition and vascular status may be determinants of myocardial blood flow in the resting and stress states. The effects of fibrosis as well as fat deposition on MR first-pass perfusion images have not been well studied. LV fat deposition is easily detected with MR imaging and is associated with chronic LV myocardial infarction, with a prevalence of approximately 60%. Assessment of perfusion in myocardial segments with fibrosis is clinically relevant for the determination of peri-infarct ischemia.