Maureen N. Hood

MR angiography using steady-state free precession.

Contrast‐enhanced MR angiography (CE‐MRA) using steady‐state free precession (SSFP) pulse sequences is described. Using SSFP, vascular structures can be visualized with high signal‐to‐noise ratio (SNR) at a substantial (delay) time after the initial arterial pass of contrast media. The peak blood SSFP signal was diminished by <20% 30 min after the initial administration of 0.2 mmol/kg of Gd‐chelate. The proposed method allows a second opportunity to study arterial or venous structures with high image SNR and high spatial resolution. A mask subtraction scheme using spin echo SSFP‐S(−) acquisition is also described to reduce stationary background signal from the delayed SSFP angiography images. Magn Reson Med 48:699–706, 2002.

Flexible cardiac T1 mapping using a modified look–locker acquisition with saturation recovery

A modified Look–Locker acquisition using saturation recovery (MLLSR) for breath‐held myocardial T1 mapping is presented. Despite its reduced dynamic range, saturation recovery enables substantially higher imaging efficiency than conventional inversion recovery T1 mapping because it does not require time for magnetization to relax to equilibrium. Therefore, MLLSR enables segmented readouts, shorter data acquisition windows, and shorter breath holds compared with inversion recovery. T1 measurements in phantoms using MLLSR showed a high correlation with conventional single‐point inversion recovery spin echo. In vivo T1 measurements from normal and infarcted myocardium in 41 volunteers and patients were consistent with previously reported values. Twenty subjects were also scanned with MLLSR using an accelerated sampling scheme that required half the scan time (eight vs. 16 heartbeats) but yielded equivalent results. The flexibility afforded by the improved imaging efficiency of MLLSR allows the acquisition to be tailored to particular clinical needs and to individual patients breath‐holding abilities. Magn Reson Med, 2012.

MRA of the thoracic vessels

Magnetic resonance imaging (MRI) is well suited for the noninvasive evaluation of the thoracic vasculature, and with improvements in scanner technology, the ability of MR to illustrate the thoracic vessels has significantly improved. Dedicated vascular software and pulse sequences have become commercially available, and fast imaging, in particular, has facilitated the time-efficient and comprehensive MR evaluation of most thoracic vascular lesions. Over the years, a host of black and bright blood MRI methods have evolved into practical tools for illustration of the thoracic vessels. As with other MR applications, successful vascular depiction relies significantly on the proper selection and prescription of imaging pulse sequences. In this article, these methods with their specific technical and practical pitfalls for thoracic magnetic resonance angiography (MRA) will be discussed. Current clinical indications for thoracic MRA will also be illustrated.

Preferential arterial imaging using gated thick-slice gadolinium-enhanced phase-contrast acquisition in peripheral MRA

Purpose: To investigate the feasibility of preferential arterial imaging using gadolinium‐enhanced thick‐slice phase‐contrast imaging. Methods: Six healthy volunteers were studied using a peripheral‐gated segmented k‐space CINE phase‐contrast pulse sequence using four views per RR interval with flow encoding in the superior‐inferior direction. Images at the level of the popiteal trifurcation were acquired postcontrast with different section thicknesses (4–8 cm) and VENC values (20–150 cm/sec), and phase‐difference processing. Results: The post‐gadolinium contrast‐enhanced thick‐slice phase‐contrast acquisitions demonstrated the ability to visualize the tibio‐peroneal (trifurcation) arteries, especially in systole. With MR contrast agents, the signal from blood is raised significantly above that of stationary tissue from T1 shortening such that the partial volume artifact is reduced in thick‐slice acquisitions. Furthermore, by selecting the VENC value as a function of the cardiac cycle, the noise floor can be raised to selectively suppress flow values less than that of the noise threshold, allowing better accentuation of arterial structures at systole. Conclusions: Thick‐slice phase‐contrast acquisition with phase‐difference processing has been observed to reduce partial volume artifacts when an MR contrast agent substantially increases signal in the vasculature over that of normal background tissue. Preferential arterial images can be obtained by either increasing the VENC value to selectively suppress signal from slow flow in the veins or by subtracting the diastolic phase image from the peak systolic phase image. J. Magn. Reson. Imaging 2001;13:714–721.

A Quadricuspid Aortic Valve as Seen by Cardiac Magnetic Resonance Imaging.

We report a case of a 35-year-old active duty male with a rare quadricuspid aortic valve identified via transthoracic echocardiography following the detection of an incidental grade I/VI diastolic murmur. Further characterization of the anatomical findings and aortic valve flow dynamics were evaluated with cardiac magnetic resonance imaging. Accurate assessment of the various valve morphologies is essential, as it guides surgical treatment options to correct the defect. Our case highlights the complimentary role of cardiac magnetic resonance imaging in defining the anatomy and functional consequences of a quadricuspid aortic valve.

Multiacquisition T1-Mapping MRI During Tidal Respiration for Quantification of Myocardial T1 in Swine With Heart Failure

OBJECTIVE The purpose of this article is to evaluate a free-breathing pulse sequence to quantify myocardial T1 changes in a swine model of tachycardia-induced heart failure. MATERIALS AND METHODS Yorkshire swine were implanted with pacemakers and were ventricularly paced at 200 beats/min to induce heart failure. Animals were scanned twice with a 1.5-T MRI scanner, once at baseline and once at heart failure. A T1-mapping sequence was performed during tidal respiration before and 5 minutes after the administration of a gadolinium-chelate contrast agent. T1-mapping values were compared between the baseline and heart failure scans. The percentage of fibrosis of heart failure myocardial tissue was compared with similar left ventricular tissue from control animals using trichrome blue histologic analysis. RESULTS In the study cohort, differences were found between the baseline and heart failure T1-mapping values before the administration of contrast agent (960 ± 96 and 726 ± 94 ms, respectively; p = 0.02) and after contrast agent administration (546 ± 180 and 300 ± 171 ms, respectively; p = 0.005). The animals with heart failure also had a difference histologically in the percentage of myocardial collagen compared with tissue from healthy control animals (control, 5.4% ± 1.0%; heart failure, 9.4% ± 1.6%; p < 0.001). CONCLUSION The proposed T1-mapping technique can quantify diffuse myocardial changes associated with heart failure without the use of a contrast agent and without breath-holding. These T1 changes appear to be associated with increases in the percentage of myocardial collagen that in this study were not detected by traditional myocardial delayed enhancement imaging. T1 mapping may be a useful technique for detecting early but clinically significant myocardial fibrosis.

Heart failure myocardial perfusion swine study with semi-quantitative analysis

Cardiac perfusion imaging is a recognized method for non-invasive evaluation for myocardial ischemia. However, it is unclear how global heart failure affects myocardial perfusion. In this study, we explore semi-quantitative perfusion in a Yorkshire swine heart failure study.

A novel center point trajectory model for cardiac wall motion abnormality assessment compared with echocardiography strain

Methods The method entails the tracking of the left ventricular center point of the left ventricle on 2D SSFP images over time. A polar coordinate map indicating amplitude and angle parameters provides a quantitative way to describe systolic (red) and diastolic (blue) wall motion. Transthoracic echocardiography using 2D strain maps were used to validate the findings from CMR and CPT analysis. Three patients with myocardial infarction (3 Male, 67 ± 4 y/o, EF 54% ± 14%) and one healthy volunteer (1 Female, 51 y/ o, EF 63%) were enrolled in this IRB approved study. On the echocardiography peak systolic strain map, the smaller the magnitude absolute value, the less the echocardiographic strain measurement. Results CPT analysis demonstrates significant movement of the center in the first column Figures 1, 2, 3 (a). The second column (b) represents the corresponding short axis T2 weighted or delayed enhancement positive images. The third column (c) represents the long axis echocardiographic strain maps. Figures 1 and 2 are patients with myocardial infarction of the anteroseptal wall of the left ventricle. The CPT plot provides amplitude and angle of center point progression, which reflects the degree of abnormal wall motion during both systolic contraction, and diastolic filling of the left ventricle. In these two cases, the center point trajectory points toward the hypokinetic anteroseptal wall [arrow on the T2 weighted and myocardial delayed enhancement images (1b and 2b) and echocardiographic strain maps (1c and 2c)]. Figure 3 shows a patient with myocardial infarction of the anterior and anterior lateral wall (3b, arrow) with corresponding hypokinesis and an abnormal strain map clearly visualized on echocardiography. Figure 4 shows a normal volunteer without significant center point movement on CPT and corresponding normal echocardiographic strain maps. Strain analysis from echocardiography confirms the hypothesis of the center point trajectory model from cardiac MR. from 13th Annual SCMR Scientific Sessions Phoenix, AZ, USA. 21-24 January 2010

A Novel Cardiac MR Chamber Volume Model for Mechanical Dyssynchrony Assessment

A novel cardiac chamber volume model is proposed for the assessment of left ventricular mechanical dyssynchrony. The tool is potentially useful for assessment of regional cardiac function and identification of mechanical dyssynchrony on MRI. Dyssynchrony results typically from a contraction delay between one or more individual left ventricular segments, which in turn leads to inefficient ventricular function and ultimately heart failure. Cardiac resynchronization therapy has emerged as an electrical treatment of choice for heart failure patients with dyssynchrony. Prior MRI techniques have relied on assessments of actual cardiac wall changes either using standard cine MR images or specialized pulse sequences. In this abstract, we detail a semi-automated method that evaluates dyssynchrony based on segmental volumetric analysis of the left ventricular (LV) chamber as illustrated on standard cine MR images. Twelve sectors each were chosen for the basal and mid-ventricular slices and 8 sectors were chosen for apical slices for a total of 32 sectors. For each slice (i.e. basal, mid and apical), a systolic dyssynchrony index (SDI) was measured. SDI, a parameter used for 3D echocardiographic analysis of dyssynchrony, was defined as the corrected standard deviation of the time at which minimal volume is reached in each sector. The SDI measurement of a healthy volunteer was 3.54%. In a patient with acute myocardial infarction, the SDI measurements 10.98%, 16.57% and 1.41% for basal, mid-ventricular and apical LV slices, respectively. Based on published 3D echocardiogram reference threshold values, the patients SDI corresponds to moderate basal dysfunction, severe mid-ventricular dysfunction, and normal apical LV function, which were confirmed on echocardiography. The LV chamber segmental volume analysis model and SDI is feasible using standard cine MR data and may provide more reliable assessment of patients with dyssynchrony especially if the LV myocardium is thin or if the MR images have spatial resolution insufficient for proper resolution of wall thickness-features problematic for dyssynchrony assessment using existing MR techniques.

2118 Contrast Inflow Dynamics MRA (CIDA) with automatic triggering:novel approach for ECG-gated dynamic contrast enhanced MRA

Purpose ECG-gated 3D contrast enhanced MRA (ceMRA) provides high spatial resolution and minimal pulsation artifacts in the visualization of cardiac and pulmonary vasculatures [1,2]. Dynamically-resolved ceMRA techniques can improve workflow by eliminating the needs for timing bolus acquisition, and enables better separation of arterial and venous vasculatures [3]. However, applications of dynamically-resolved gated ceMRA have been limited due to the increase in scan time associated with ECG-gating. Spatial and temporal resolution, or alternatively anatomic coverage, are often compromised to meet the breathhold limitation. We propose a novel multi-dynamic-phase ECG-gated 3D MRA approach to obtain high-spatial resolution and temporally-selective contrast-enhanced images within a single breathhold. Automatic triggerring is also incorporated to robustly capture the desire dynamic phases.