Reducing and continuously varying the flip angle of the refocusing RF pulses in a rapid acquisition with relaxation enhancement (RARE; fast/turbo spin echo) sequence is a useful means of addressing high RF power deposition and modulation transfer function (MTF) distortion due to relaxation. This work presents a streamlined technique to generate a sequence of refocusing flip angles on a per-prescription basis that produces relatively high SNR and limits blurring in a wide range of materials encountered in vivo. Since the "effective TE" (traditionally defined as the time at which the center of k-space is sampled) no longer corresponds to the expected amount of spin-echo T 2 contrast due to the mixing of stimulated and spin echoes, a "contrast-equivalent" TE is defined and experimentally demonstrated that allows annotation of a more accurate effective TE that matches the contrast produced by 180°refocusing. Furthermore, contrast is shown to be manipulable by the addition of magnetization preparation pulse sequence segments, such as

No abstract

For T 1 quantification, a three-dimensional (3D) acquisition is desired to obtain high-resolution images. Current 3D methods that use steady-state spoiled gradient-echo (SPGR) imaging suffer from high SAR, low signal-to-noise ratio (SNR), and the need for retrospective correction of contaminating T 1 effects. In this study, a novel 3D acquisition scheme-magnetization-prepared angle-modulated partitioned-k-space SPGR snapshots (3D MAPSS)-was developed and used to obtain in vivo T 1 maps. Transient signal evolving towards the steady-state were acquired in an interleaved segmented elliptical centric phase encoding order immediately after a T 1 magnetization preparation sequence. Noninvasive early detection of cartilage degeneration in osteoarthritis (OA) is of increasing clinical importance. Magnetic resonance imaging (MRI) has been widely used for detecting and monitoring cartilage injuries (1). Recent developments in high field MR (such as the availability of clinical systems with a field strength of 3 T) have further enhanced image spatial resolution and signal-to-noise ratio (SNR) (2). However, conventional MRI is limited to providing primarily morphologic changes of cartilage. Since damage to the collagen-proteoglycan (PG) matrix in cartilage occur early in the course of OA, imaging markers that can probe biochemical changes are essential for early detection of cartilage degeneration. Recent developments in this active field include delayed gadolinium enhanced MRI of cartilage (dGEMRIC) (3-5), T 2 (6 -10), and T 1 (11-16) relaxation time quantification.The T 1 parameter describes the spin-lattice relaxation in the rotating frame (17). It reflects the slow motion interactions between motion-restricted water molecules and their local macromolecular environment. The extracellular matrix (ECM) in articular cartilage provides a motionrestricted environment for water molecules. Changes to the ECM therefore may be reflected in measurements of T 1 . T 1 relaxation rate (1/T 1 ) has been shown to decrease linearly with decreasing PG content in ex vivo bovine patellae (11) and in trypsinized cartilage (18). In vivo studies have also shown increased cartilage T 1 values for patients with OA (19,20).Current T 1 quantification techniques are based on either two dimensional (2D) fast spin echo (FSE) (21), spiral imaging (16), echo planar imaging (EPI) (22), or 3D gradient echo sequences (20,23). Compared with 2D methods, 3D imaging is free from artifacts caused by slice cross-talk. Therefore 3D sequences can generally have a thinner slice thickness, and consequently may provide a more accurate assessment of cartilage degeneration. High-resolution MRI is particularly attractive in the context of OA, in which cartilage becomes very thin-on the order of or less than 1 mm. Furthermore, a 3D acquisition is desired due to the non-slice-selective nature of the T 1 preparation pulses (spin-lock pulses). A 3D T 1 mapping technique has been developed based on a steady-state spoiled gradient echo (SPGR) imaging sequence (23) and has s...

FSE-Cube has similar diagnostic performance as a routine MR imaging protocol for detecting cartilage lesions, cruciate ligament tears, collateral ligament tears, meniscal tears, and bone marrow edema lesions within the knee joint at 3.0 T.

Three-dimensional FSE XETA acquires high-resolution (approximately 0.7 mm) isotropic data with intermediate and T2-weighting that may be reformatted in arbitrary planes. Three-dimensional FSE XETA is a promising technique for MRI of the knee.