Cardiac SSFP imaging at 3 Tesla

Abstract

Balanced steady-state free precession (SSFP) techniques provide excellent contrast between myocardium and blood at a high signal-to-noise ratio (SNR). Hence, SSFP imaging has become the method of choice for assessing cardiac function at 1.5T. The expected improvement in SNR at higher field strength prompted us to implement SSFP at 3.0T. In this work, an optimized sequence protocol for cardiac SSFP imaging at 3.0T is derived, taking into account several partly adverse effects at higher field, such as increased field inhomogeneities, longer T 1 , and power deposition limitations. SSFP contrast is established by optimizing the maximum amplitude of the radiofrequency (RF) field strength for shortest TR, as well as by localized linear or second-order shimming and local optimization of the resonance frequency. Given the increased SNR, sensitivity encoding (SENSE) can be employed to shorten breath-hold times. Shortaxis, long-axis, and four-chamber cine views obtained in healthy adult subjects are presented, and three different types of artifacts are discussed along with potential methods for reducing them.Magn The benefits of high-field (Ն3.0T) MR systems have been thoroughly explored for neuroimaging (1), functional imaging based on blood oxygenation level-dependent (BOLD) contrast (2), intracranial and cervical MRA (3), and spectroscopy of the head (4). Recently, work on cardiac imaging at 3.0T has demonstrated increased signal-to-noise ratio (SNR) with respect to imaging at 1.5T, in accordance with theory (5-7). Based on the initial data, it is expected that many cardiac imaging applications may benefit considerably from higher SNR. With the increasing availability of clinical 3.0T whole-body MR systems, cardiac imaging at 3.0T may become an important application in the near future.Standard cardiac imaging procedures for assesssing wall motion and ventricular function at 1.5T are based mainly on balanced steady-state free precession (SSFP) techniques (8) (also known as balanced fast field echo (bFFE), fast imaging employing steady-state acquisition (FIESTA), and fast imaging with steady precession (true FISP)). These sequences offer a high contrast-to-noise ratio (CNR) between myocardial muscle and oxygenated blood at a high SNR. The excellent CNR between myocardium and blood has been shown to greatly improve the reliability and robustness of imaging segmentation methods (9 -11).Concurrently with the success of SSFP imaging, parallel imaging techniques such as sensitivity encoding (SENSE) (12,13) have emerged as major tools for speeding up data acquisition. With respect to cardiac examinations, SENSE allows the use of shorter breath-holds; this in turn reduces the RF energy deposition in the subjects, which is a concern when imaging at higher field strength. With SENSE, the gain in speed is traded for a reduced SNR according to (12):where R denotes the reduction or acceleration factor, and g reflects the coil sensitivities, receiver noise correlation, and degree of reduction. The SNR loss with SENSE might be compens...

Initial results on in vivo human coronary MR angiography at 7 T

“…Although initial studies comparing 1.5 T coronary MRA with 3 T coronary MRA and the gold standard x-ray coronary angiography showed little advantage of 3 T for the identification of significant luminal coronary artery disease, a more recent report (4) appears much more promising, and other studies that take advantage of new high-field specific improvements are ongoing. Notably, the increase in magnetic field strength between 1.5 and 3 T produces a series of challenges, including adequate electrocardiograph (ECG) triggering (7), sophisticated higherorder shimming (8) to account for increased magnetic field susceptibility, and spatially homogeneous magnetization preparation for contrast generation (9).…”

Cortical phase changes in Alzheimer's disease at 7T MRI: A novel imaging marker

“…A navigator echo was included to correct for these artifacts [34]. Shimming up to third order was performed using an imagebased shimming approach [35]. The phase images were subsequently unwrapped by high-pass filtering with a 92 !…”

Klinischer Stellenwert und Indikationen zur Magnetresonanztomografie des Herzens 2013: Ein interdisziplinäres Expertenstatement

“…Die zunehmende Magnetfeldstärke bringt aber auch Effekte wie einen stärkeren magnetohydrodynamischen Effekt im EKG, geänderte magnetische Relaxationszeiten, geänderten "Chemical Shift", vermehrte Inhomogenitäten des anregenden Hochfrequenzfelds, höhere spezifische Absorptionsraten (SAR) bei gleichen Sequenzparametern und schlussendlich größere Magnetfeldinhomogenitäten mit sich [77,78]. Besonders drastisch ist diese Situation bei der Steady-State-Free-Precession-Sequenz (SSFP), für deren Anwendung bei 3 T verbesserte Shim-Prozeduren [79,80] und/oder eine über Scouting zu bestimmende Optimierung der Resonanzfrequenz [81] verwendet werden müssen, um Banding-Artefakte zu vermeiden. Die Datenlage bzgl.…”