3D bSSFP Research Articles

Fast volumetric spatial-spectral MR imaging of hyperpolarized 13C-labeled compounds using multiple echo 3D bSSFP.

The goal of this work was to develop a fast 3D chemical shift imaging technique for the noninvasive measurement of hyperpolarized (13)C-labeled substrates and metabolic products at low concentration. Multiple echo 3D balanced steady state magnetic resonance imaging (ME-3DbSSFP) was performed in vitro on a syringe containing hyperpolarized [1,3,3-2H3; 1-(13)C]2-hydroxyethylpropionate (HEP) adjacent to a (13)C-enriched acetate phantom, and in vivo on a rat before and after intravenous injection of hyperpolarized HEP at 1.5 T. Chemical shift images of the hyperpolarized HEP were derived from the multiple echo data by Fourier transformation along the echoes on a voxel by voxel basis for each slice of the 3D data set. ME-3DbSSFP imaging was able to provide chemical shift images of hyperpolarized HEP in vitro, and in a rat with isotropic 7-mm spatial resolution, 93 Hz spectral resolution and 16-s temporal resolution for a period greater than 45 s. Multiple echo 3D bSSFP imaging can provide chemical shift images of hyperpolarized (13)C-labeled compounds in vivo with relatively high spatial resolution and moderate spectral resolution. The increased signal-to-noise ratio of this 3D technique will enable the detection of hyperpolarized (13)C-labeled metabolites at lower concentrations as compared to a 2D technique.

MRI-guided robotic system for transperineal prostate interventions: proof of principle

In this study, we demonstrate the proof of principle of the University Medical Center Utrecht (UMCU) robot dedicated to magnetic resonance imaging (MRI)-guided interventions in patients. The UMCU robot consists of polymers and non-ferromagnetic materials. For transperineal prostate interventions, it can be placed between the patient's legs inside a closed bore 1.5T MR scanner. The robot can manually be translated and rotated resulting in five degrees of freedom. It contains a pneumatically driven tapping device to automatically insert a needle stepwise into the prostate using a controller unit outside the scanning room. To define the target positions and to verify the needle insertion point and the needle trajectory, a high-resolution 3D balanced steady state free precession (bSSFP) scan that provides a T2/T1-weighted contrast is acquired. During the needle insertion fast 2D bSSFP images are generated to track the needle on-line. When the target position is reached, the radiation oncologist manually places a fiducial gold marker (small seed) at this location. In total two needle trajectories are used to place all markers. Afterwards, a high-resolution 3D bSSFP scan is acquired to visualize the fiducial gold markers. Four fiducial gold markers were placed transperineally into the prostate of a patient with a clinical stage T3 prostate cancer. In the generated scans, it was possible to discriminate the patient's anatomy, the needle and the markers. All markers were delivered inside the prostate. The procedure time was 1.5 h. This study proves that MRI-guided needle placement and seed delivery in the prostate with the UMCU robot are feasible.

3D nongadolinium-enhanced mra using flow-sensitive dephasing (fsd) prepared balanced ssfp: identification of the optimal first-order gradient moment

Introduction A noncontrast MRA technique using ECG-triggered 3D bSSFP with FSD preparation has recently been developed (Fig. 1) [1]. The angiographic quality relies on the blood signal suppression by FSD preparation, which is in turn determined by FSD's first-order gradient moment, m1. A suboptimal m1 may result in venous contamination or incomplete arterial delineation. This work aimed to develop an m1-scout approach to rapidly identify the optimal m1-value.

Modulated repetition time look‐locker (MORTLL): A method for rapid high resolution three‐dimensional T1 mapping

To demonstrate a modification of the Look-Locker (LL) technique that enables rapid high resolution T1 mapping over the physiologic range of intracranial T1 values, ranging from white matter to cerebrospinal fluid (CSF). This is achieved by use of a three-dimensional (3D) balanced steady-state free precession (b-SSFP) acquisition (for high signal-to-noise and resolution) along with variable repetition time to allow effective full recovery of longitudinal magnetization. Two modifications to the Look-Locker technique were made to realize high resolution imaging in a clinically reasonable scan time. The 3D b-SSFP acquisition after an initial inversion pulse was followed by a variable repetition time. This technique makes it possible to image a volume of thin contiguous slices with high resolution and accuracy using a simple fitting procedure and is particularly useful for imaging long T1 species such as CSF. The total scan time is directly proportional to the number of slices to be acquired. The scan time was reduced by almost half when the repetition time was modified using a predesigned smooth function. Phantoms and volunteers were imaged at different resolutions on a 3 Tesla scanner. Results were compared with other accepted techniques. T1 values in the brain corresponded well with full repetition time imaging as well as inversion recovery spin echo imaging. T1 values for white matter, gray matter, and CSF were measured to be 755 +/- 10 ms, 1202 +/- 9 ms, and 4482 +/- 71 ms, respectively. Scan times were reduced by approximately half over full repetition time measurements. High resolution T1 maps can be obtained rapidly and with a relatively simple postprocessing method. The technique is particularly well suited for long T1 species. For example, changes in the composition of proteins in CSF are linked to various pathologies. The T1 values showed excellent agreement with values obtained from inversion recovery spin-echo imaging.

Improved SNR in linear reordered 2D bSSFP imaging using variable flip angles

This article presents a variable flip-angle approach for balanced steady-state free precession (bSSFP) imaging, which allows increases in signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) while keeping specific absorption rate (SAR) constant or reduces SAR for given CNR and SNR. The gain in SNR is achieved by utilizing the higher signal in the transient phase. Flip-angle variation during the echo train is realized using a trigonometric function with M steps (ramp length). Variation is combined with a linear k-space reordering such that outer parts of k-space are sampled using a lower flip angle alpha(min), while the central part of k-space is acquired with a higher flip angle alpha(max). No additional preparation or dummy cycles are applied prior to data acquisition. Several variation schemes with different starting flip angles alpha(min) and ramp length M are considered. For example, using alpha(min)=1 degrees and M=96, alpha(max) can be set to 47 degrees without exceeding SAR limits at 3 T and gaining up to 50% in SNR, while, conventionally, alpha=34 degrees is the maximal possible flip angle. Resolution seems unaffected in volunteer imaging. In all cases, no transient artifacts due to flip-angle variation were observed. This article demonstrates the use of flip-angle variations in bSSFP to increase SNR and CNR while keeping SAR constant, which is especially important at higher field strengths. Flip-angle variation can also be combined with other methods such as parallel imaging techniques for further SAR reduction.