Fast Imaging With Steady Precession Research Articles

Acceleration of 2D-MR fingerprinting by reducing the number of echoes with increased in-plane resolution: a volunteer study

ObjectiveTo compare the absolute values and repeatability of magnetic resonance fingerprinting (MRF) with 3000 and 1500 echoes/slice acquired in 41 s and 20 s (MRF3k and MRF1.5k, respectively).Materials and methodsMRF3k and MRF1.5k scans based on fast imaging with steady precession (FISP) were conducted using a 3 T scanner. Inter-scan agreement and intra-scan repeatability were investigated in 41 and 28 subjects, respectively. Region-of-interest (ROI) analysis was conducted on T1 values of MRF3k by two raters, and their agreement was evaluated using intraclass correlation coefficients (ICCs). Between MRF3k and MRF1.5k, differences in T1 and T2 values and inter-measurement correlation coefficients (CCs) were investigated. Intra-measurement repeatability was evaluated using coefficients of variation (CVs). A p value < 0.05 was considered statistically significant.ResultsThe ICCs of ROI measurements were 0.77–0.96. Differences were observed between the two MRF scans, but the CCs of the overall ROIs were 0.99 and 0.97 for the T1 and T2 values, respectively. The mean and median CVs of repeatability were equal to or less than 1.58% and 3.13% in each of the ROIs for T1 and T2, respectively; there were some significant differences between MRF3k and MRF1.5k, but they were small, measuring less than 1%.DiscussionBoth MRF3k and MRF1.5k had high repeatability, and a strong to very strong correlation was observed, with a trend toward slightly higher values in MRF1.5k.

M.P.5.04 Evaluation of in-phase and out-of-phase and FISP MRI to quantify muscle fat content in OPMD

Purpose: The long-term goal of our research is the development of non-invasive MRI techniques for monitoring muscular dystrophy progression that could be suitable as outcome measures for clinical trials. Here, we evaluated in-phase and out-of-phase and fast imaging with steady precession (FISP) MRI sequences in the estimation of muscle fat content in patients with oculopharyngeal muscular dystrophy (OPMD). Materials and methods: Informed consent was obtained in written from all included patients.

Real-time MR fluoroscopy-navigated lumbar facet joint injections: feasibility and technical properties

We prospectively evaluated the feasibility and technical properties of a dedicated interventional magnetic resonance (MR) imaging protocol for near-real-time MR fluoroscopy-guided bilateral lumbar facet joint injections. A total of 44 facet joint injections were performed in 22 patients using a C-shaped open 0.2-T MR imaging system (Magnetom Concerto, Siemens Medical Solutions, Erlangen, Germany). A T1/T2-weighted fast-imaging-with-steady-precession (FISP) sequence with an end-to-end latency of 1.2 s facilitated sufficient near real-time MR imaging guidance in all cases. A T1-weighted two dimensional fast-low-angle-shot (FLASH2D) MR sequence identified final needle tip location. Different angles of the needle path had only minimal influence on the appearance of the needle artifact produced by both sequences, resulting in a symmetrical needle tip artifact. The joint cavity was successfully punctured in 79.5% (35/44) of joints, which was followed by intra-articular fluid accumulation in 75% (33/44). Inaccessible joints demonstrated a significantly (p=0.044) higher number of posterior osteophytes (66.7%, 6/9 joints) compared to accessible joints (26%, 9/35 joints). No complications occurred. Table time showed significant shortening over time with average table time of 33 (21-68.5) min. We conclude that MR fluoroscopy-navigated lumbar facet joint injections are feasible and safe.

Motion corrected free‐breathing delayed‐enhancement imaging of myocardial infarction using nonrigid registration

To develop and test an automatic free-breathing, delayed enhancement imaging method with improved image signal-to-noise ratio (SNR). The proposed approach uses free-breathing, inversion-recovery single-shot fast imaging with steady precession (FISP) delayed-enhancement with respiratory motion compensation based on nonrigid image registration. Motion-corrected averaging is used to enhance SNR. Fully automatic, nonrigid registration was compared to previously validated rigid body registration that required user interaction. The performance was measured using the variance of edge positions in intensity profiles through the myocardial infarction (MI) enhanced region and through the right ventricular (RV) wall. Measured variation of the MI edge was 1.16 +/- 0.71 mm (N = 6 patients; mean +/- SD) for rigid body and 1.08 +/- 0.76 mm for nonrigid registration (no significant difference). On the other hand, significant improvement (P < 0.005) was found in the measurements at the RV edge where the SD was 2.06 +/- 0.56 mm for rigid body and 0.59 +/- 0.22 mm for nonrigid registration. The proposed approach achieves delayed enhancement images with high resolution and SNR without requiring a breathhold. Motion correction of free-breathing delayed-enhancement imaging using nonrigid image registration may be implemented in a fully automatic fashion and performs uniformly well across the full field of view (FOV).

Evaluation of normal brain development by prenatal MR imaging

The aim of this study was to describe the normal pattern of development and maturation of the foetal brain with respect to gestational age as assessed with magnetic resonance imaging (MRI) and to provide an overview of the possibilities of the technique. Foetal cerebral MRI was performed on 56 pregnant women between 19 and 37 weeks of gestation. Half-Fourier single-shot turbo spin-echo (HASTE), true fast imaging with steady precession (FISP), T1-weighted fast low angle shot (FLASH) two-dimensional (2D) and diffusion-weighted (DW) sequences with apparent diffusion coefficient (ADC) were obtained. Biometric parameters and developmental areas of the cerebral cortex were correlated to gestational age by using the Spearman rank correlation test. We found a negative correlation between the germinal matrix/biparietal diameter ratio and gestational age and a positive correlation between the germinal and cortical matrix when expressed as external intraocular diameter ratio (R=0.452, p=0.02). The cortical mantle was correlated with biometric parameters, such as the biparietal diameter and the frontooccipital diameter, and with gestational age. The interhemispheric fissure, the parietooccipital fissure and the sylvian fissure were detectable by the 22nd week. In the grey matter, the mean ADC values varied from 1.76 x 10(-3) mm(2)/s (at week 19) to 0.89 x 10(-3) mm(2)/s (at week 37), whereas in the white matter, the values varied from 2.03 x 10(-3) mm(2)/s (at week 19) to 1.25 x 10(-3) mm(2)/s (at week 37). MRI provides a reliable valuation of brain maturation during pregnancy.

MRI of articular cartilage in OA: novel pulse sequences and compositional/functional markers

Osteoarthritis (OA) is a leading cause of disability worldwide. Magnetic resonance imaging (MRI), with its unique ability to image and characterize soft tissue non-invasively, has proven valuable in assessing cartilage in OA. The development of new, fast imaging methods with high contrast show promise to improve the magnetic resonance (MR) evaluation of this disease. In addition to morphologic MRI methods, MRI contrast mechanisms under development may reveal detailed information about the physiology of cartilage. It is anticipated that these and other MRI techniques will play an increasingly important role in assessing the success or failure of therapies for OA. On December 5 and 6, 2002, OMERACT (Outcome Measures in Rheumatology Clinical Trials) and OARSI (Osteoarthritis Research Society International) held a workshop in Bethesda, MD aiming at providing a state-of-the-art review of imaging outcome measures for OA of the knee to help guide scientists and pharmaceutical companies in the use of MRI in multi-site studies of OA. Applications of MRI were initially reviewed by a multidisciplinary, international panel of expert scientists and physicians from academia, the pharmaceutical industry and regulatory agencies. The findings of the panel were then presented to a wider group of participants for open discussion. The following report summarizes the results of these discussions with respect to novel MRI pulse sequences for evaluating articular cartilage of the knee in OA and notes any additional advances that have been made since.

Comparison of MR imaging sequences for liver and head and neck interventions: Is there a single optimal sequence for all purposes? 1

Rationale and objectives To compare the appropriate pulse sequences for interventional device guidance during magnetic resonance (MR) imaging at 0.2 T and to evaluate the dependence of sequence selection on the anatomic region of the procedure. Materials and methods Using a C-arm 0.2 T system, four interventional MR sequences were applied in 23 liver cases and during MR-guided neck interventions in 13 patients. The imaging protocol consisted of: multislice turbo spin echo (TSE) T 2w, sequential-slice fast imaging with steady precession (FISP), a time-reversed version of FISP (PSIF), and FISP with balanced gradients in all spatial directions (True-FISP) sequences. Vessel conspicuity was rated and contrast-to-noise ratio (CNR) was calculated for each sequence and a differential receiver operating characteristic was performed. Results Liver findings were detected in 96% using the TSE sequence. PSIF, FISP, and True-FISP imaging showed lesions in 91%, 61%, and 65%, respectively. The TSE sequence offered the best CNR, followed by PSIF imaging. Differential receiver operating characteristic analysis also rated TSE and PSIF to be the superior sequences. Lesions in the head and neck were detected in all cases by TSE and FISP, in 92% using True-FISP, and in 84% using PSIF. True-FISP offered the best CNR, followed by TSE imaging. Vessels appeared bright on FISP and True-FISP imaging and dark on the other sequences. Conclusion In interventional MR imaging, no single sequence fits all purposes. Image guidance for interventional MR during liver procedures is best achieved by PSIF or TSE, whereas biopsies in the head and neck are best performed using FISP or True-FISP sequences.

MR lung imaging at 0.2 T with T1‐weighted true FISP: Native and oxygen‐enhanced

An inversion recovery true fast imaging with steady precession (FISP) pulse sequence was developed to carry out fast imaging of the lungs at 0.2 T. Using this sequence, oxygen-enhanced magnetic resonance (MR) lung imaging was performed on healthy volunteers. The lungs showed signal enhancement (11.7% +/- 3.8%) when breathing 100% oxygen. Using inversion recovery, true FISP at low field may prove promising for MR lung imaging.

Human articular cartilage: in vitro correlation of MRI and histologic findings.

The aim of our study was to correlate MRI with histologic findings in normal and degenerative cartilage. Twenty-two human knees derived from patients undergoing amputation were examined with 1.0- and 1. 5-T MR imaging units. Firstly, we optimized two fat-suppressed 3D gradient-echo sequences. In this pilot study two knees were examined with fast imaging with steady precession (FISP) sequences and fast low-angle shot (FLASH, SPGR) sequence by varying the flip angles (40, 60, 90 degrees) and combining each flip angle with different echo time (7, 10 or 11, 20 ms). We chose the sequences with the best visual contrast between the cartilage layers and the best measured contrast-to-noise ratio between cartilage and bone marrow. Therefore, we used a 3D FLASH fat-saturated sequence (TR/TE/flip angle = 50/11 ms/40 degrees) and a 3D FISP fat-saturated sequence (TR/TE/flip angle = 40/10 ms/40 degrees) for cartilage imaging in 22 human knees. The images were obtained at various angles of the patellar cartilage in relation to the main magnetic field (0, 55, 90 degrees). The MR appearances were classified into five categories: normal, intracartilaginous signal changes, diffuse thinning (cartilage thickness < 3 mm), superficial erosions, and cartilage ulcers. After imaging, the knees were examined macroscopically and photographed. In addition, we performed histologic studies using light microscopy with several different stainings, polarization, and dark field microscopy as well as electron microscopy. The structural characteristics with the cartilage lesions were correlated with the MR findings. We identified a hyperintense superficial zone in the MR image which did not correlate to the histologically identifiable superficial zone. The second lamina was hypointense on MRI and correlated to the bulk of the radial zone. The third (or deep) cartilage lamina in the MR image seemed to represent the combination of the lowest portion of the radial zone and the calcified cartilage. The width of the hypointense second zone correlated weakly to the accumulation of proteoglycans in the radial zone. The trilaminar MRI appearance of the cartilage was only visible when the cartilage was thicker than 2 mm. In cartilage degeneration, we found either a diffuse thinning of all layers or circumscribed lesions ("cartilage ulcer") of these cartilage layers in the MR images. Early cartilage degeneration was indicated by a signal loss in the superficial zone, correlating to the histologically proven damage of proteoglycans in the transitional and radial zone along with destruction of the superficial zone. We found a strong effect of cartilage rotation in the main magnetic field, too. A rotation of the cartilage structures caused considerable variation in the signal intensity of the second lamina. Cartilage segments in a 55 degreesangle to the magnetic main field had a homogeneous appearance, not a trilaminar appearance. The signal behavior of hyaline articular cartilage does not reflect the laminar histologic structure. Osteoarthrosis and cartilage degeneration are visible on MR images as intracartilaginous signal changes, superficial erosions, diffuse cartilage thinning, and cartilage ulceration.

Three-dimensional reconstructed MR imaging of the inner ear.

The three-dimensional Fourier transform fast imaging with steady precession (FISP) technique was used to obtain high-resolution magnetic resonance (MR) images of the temporal bone region and to generate three-dimensional reconstructed images of the inner ear. The three-dimensional reconstructed images of the inner ear were directly synthesized from two-dimensional images of the temporal bone region by means of an external processing computer. With use of three-dimensional reconstructed images and stereoscopic observations, structures inside the temporal bone region and the positional relationship among them were easily recognized. These structures are difficult to demonstrate with two-dimensional images. This three-dimensional method was also shown to be useful for recognition of disease and anatomic malformations in the temporal bone region.

Intracranial circulation: preliminary clinical results with three-dimensional (volume) MR angiography.

The authors assessed the clinical utility of a magnetic resonance angiography technique in the evaluation of intracranial circulation. Eighteen patients with a low likelihood of cerebrovascular disease (control group) and 40 patients with suspected cerebrovascular disease were imaged with a FISP (fast imaging with steady precession) sequence (repetition time of 50 msec, echo time of 15 msec, velocity compensation in the read and section-select directions with acceleration compensation in the read direction, 15 degrees anisotropic volume, and a 1.25-mm partition thickness). Ninety-four percent of images in the control group and 72% of images in the group with cerebrovascular disease were considered useful for diagnosis. This technique can provide accurate images of intracranial circulation and can be performed in conjunction with two-dimensional spin-echo or gradient-echo imaging. It was most useful in the evaluation of patent intracranial aneurysms, vessel displacement, and large-vessel occlusive disease. Disadvantages included limited field of view, persistent signal voids, limited spatial resolution, and inadequate depiction of lesions with slow flow.

Intracranial circulation: pulse-sequence considerations in three-dimensional (volume) MR angiography.

The technique and feasibility of magnetic resonance (MR) angiography of intracranial vessels were studied in 35 healthy volunteers. Variations in image orientation, repetition time (TR), and flip angle were evaluated to determine their effects on flow-related enhancement. Gradient modifications--including echo time (TE), motion compensation, bandwidth, and field of view--were also studied in an effort to reduce motion-induced phase shifts. Results indicated that a FISP (fast imaging with steady precession) sequence with a TR of 50 msec, TE of 15 msec, velocity compensation in the read and section-select directions, acceleration compensation in the read direction, anisotropic volume, and a 1.25-mm partition thickness produced three-dimensional angiographic MR images that were accurate and reproducible in the depiction of the major intracranial vessels. Difficulties with field of view, persistent signal void secondary to higher-order motion, and spatial resolution remain major problems requiring additional study.

A comparison of fast spin echo and gradient field echo sequences

Optimal angle, fast repeat time, gradient field echo imaging techniques such as FISP (Fast Imaging with Steady Precession) and FLASH (Fast Low Angle Shot) often fail to discriminate disease from healthy tissue for two main reasons. First, T 1 and T 2 of the affected tissue may increase such that the ratio of T 1 to T 2 remains nearly unchanged, hence there is no contrast change with FISP. Second, T 2 weighted gradient field echo images suffer severely from T 2 ∗ signal and resolution loss leading to a reduction in C N . Although FLASH imaging with two separate angles can, in principle, extract the longer T 1 tumors, contrast is often not good. To overcome the inhomogeneity and contrast problems, we have implemented a FAst optimal angle spin-echo sequence with a short TE(FATE). For the first echo, FATE has the same contrast properties as FLASH with a slight decrease in signal intensity. The advantage is that the intensity of the signal does not suffer from T 2 ∗ signal decay, hence improved contrast and disease detection via T 2 weighted FATE images is possible. Contrast-to-noise in lesion detection is also considered for CE FAST (Contrast Enhanced Fast), a T 2-weighted version of FISP, and HYBRID.