Stack-of-stars Research Articles

Whole brain multiparametric mapping in two minutes using a dual-flip-angle stack-of-stars blipped multi-gradient-echo acquisition

A new MRI technique is presented for three-dimensional fast simultaneous whole brain mapping of myelin water fraction (MWF), T1, proton density (PD), R2*, magnetic susceptibility (QSM), and B1 transmit field (B1+). Phantom and human (N = 9) datasets were acquired using a dual-flip-angle blipped multi-gradient-echo (DFA-mGRE) sequence with a stack-of-stars (SOS) trajectory. Images were reconstructed using a subspace-based algorithm with a locally low-rank constraint. A novel joint-sparsity-constrained multicomponent T2*-T1 spectrum estimation (JMSE) algorithm is proposed to correct for the T1 saturation effect and B1+/B1− inhomogeneities in the quantification of MWF. A tissue-prior-based B1+ estimation algorithm was adapted for B1 correction in the mapping of T1 and PD. In the phantom study, measurements obtained at an acceleration factor (R) of 12 using prospectively under-sampled SOS showed good consistency (R2 > 0.997) with Cartesian reference for R2*/T1app/M0app. In the in vivo study, results of retrospectively under-sampled SOS with R = 6, 12, 18, showed good quality (structure similarity index measure > 0.95) compared with those of fully-sampled SOS. Besides, results of prospectively under-sampled SOS with R = 12 showed good consistency (intraclass correlation coefficient > 0.91) with Cartesian reference for T1/PD/B1+/MWF/QSM/R2*, and good reproducibility (coefficient of variation < 7.0 %) in the test-retest analysis for T1/PD/B1+/MWF/R2*. This study has demonstrated the feasibility of simultaneous whole brain multiparametric mapping with a two-minute scan using the DFA-mGRE SOS sequence, which may overcome a major obstacle for neurological applications of multiparametric MRI.

T1 mapping for Head and Neck Cancer Patients undergoing Chemoradiotherapy: Feasibility of 3D Stack of Star Imaging

BackgroundMeasuring tissue oxygen concentration is crucial in understanding the pathophysiological process of hypoxia in head and neck cancer (HNC) and its significant role in cancer biology. This study aimed to determine the feasibility of T1 mapping using a variable flip angle (VFA) technique with stack of stars (SOS) trajectory sampling in HNC patients undergoing chemoradiotherapy (CRT). MethodsTo evaluate the ability of SOS acquisition to detect T1, a phantom study was conducted and compared to conventional Cartesian acquisition (CART). Additionally, four newly diagnosed patients were recruited and underwent two scans each at baseline and inter-treatment. The repeatability of SOS and CART acquisitions was assessed by comparing the T1 measurements of CSF from the baseline and intra-treatment MRI studies. The changes in ∆T1 of the tumors during air and oxygen inhalation between baseline and inter-treatment scans were also evaluated. ResultsOur study found that the 3D VFA SOS sequence was effective in reducing motion artifacts compared to the conventional VFA sequence with CART sampling and the same scan time, as demonstrated by the results from the phantom and patient studies. In terms of repeatability, no significant correlation was observed between the variability in ΔT1 measurements of CSF obtained from SOS T1 maps. The SOS ΔT1 measurements showed higher consistency, as evidenced by the ICC values ranging from 0.52 to 0.92. The ∆T1 measurements on the primary tumors increased after the first CRT (p<0.05) for all patients who showed a positive treatment response, except for one patient (0.05<p<0.1) who did not respond to the treatment. ConclusionThe 3D VFA SOS sequence is a feasible and reliable method for T1 mapping in HNC patients undergoing CRT. The use of this technique could potentially aid in the assessment of treatment response and contribute to improving patient outcomes.

Correcting gradient chain induced fat quantification errors in radial multi-echo Dixon imaging using a gradient modulation transfer function

Purpose: Multi-echo Stack-of-stars (SoS) radial k-space trajectories with golden angle ordering are becoming popular for free-breathing abdominal Dixon imaging and proton density fat fraction (PDFF) mapping. Gradient chain imperfections including eddy currents and system delays are known to affect the image quality of radial imaging and to confound the estimation of PDFF mapping. This work proposes a retrospective trajectory correction method based on a simple gradient modulation transfer function (GMTF) measurement to predict and correct gradient chain induced k-space trajectory errors.Methods: The GMTF was measured using the standard hardware of a 3 Tesla scanner on a phantom using the thin slice method and was applied to a 3D radial SoS Dixon imaging sequence. The impact of the GMTF-based correction on image reconstruction and PDFF quantification was investigated using numerical simulations and validated on experimental phantom data as well as on in vivo leg and liver data of healthy volunteers.Results: Correcting the k-space trajectories with the measured GMTF during image reconstruction reduced PDFF quantification errors for phantom and in vivo acquisitions. A Bland-Altman comparison of the measured PDFF phantom and reference data confirmed that the GMTF correction narrowed down the limits of agreement (LoA) from 1.3% ± 8.1% (uncorrected) to 1.9% ± 5.4% (GMTF-corrected) over the full PDFF range (0%–100%) and from −0.26% ± 2.8% (uncorrected) to 0.12% ± 1.5% (GMTF-corrected) within the 0%–50% PDFF range. Liver PDFF estimation was improved by reducing the standard deviation of the mean liver PDFF and the bias of the mean liver PDFF for all subjects.Conclusion: The proposed GMTF-based k-space trajectory correction is a fast alternative method for avoiding PDFF quantitation errors caused by gradient-system induced k-space trajectory errors in 3D radial multi-echo gradient-echo acquisitions.

Stochastic optimization of three-dimensional non-Cartesian sampling trajectory.

Optimizing three-dimensional (3D) k-space sampling trajectories is important for efficient MRI yet presents a challenging computational problem. This work proposes a generalized framework for optimizing 3D non-Cartesian sampling patterns via data-driven optimization. We built a differentiable simulation model to enable gradient-based methods for sampling trajectory optimization. The algorithm can simultaneously optimize multiple properties of sampling patterns, including image quality, hardware constraints (maximum slew rate and gradient strength), reduced peripheral nerve stimulation (PNS), and parameter-weighted contrast. The proposed method can either optimize the gradient waveform (spline-based freeform optimization) or optimize properties of given sampling trajectories (such as the rotation angle of radial trajectories). Notably, the method can optimize sampling trajectories synergistically with either model-based or learning-based reconstruction methods. We proposed several strategies to alleviate the severe nonconvexity and huge computation demand posed by the large scale. The corresponding code is available as an open-source toolbox. We applied the optimized trajectory to multiple applications including structural and functional imaging. In the simulation studies, the image quality of a 3D kooshball trajectory was improved from 0.29 to 0.22 (NRMSE) with Stochastic optimization framework for 3D NOn-Cartesian samPling trajectorY (SNOPY) optimization. In the prospective studies, by optimizing the rotation angles of a stack-of-stars (SOS) trajectory, SNOPY reduced the NRMSE of reconstructed images from 1.19 to 0.97 compared to the best empirical method (RSOS-GR). Optimizing the gradient waveform of a rotational EPI trajectory improved participants' rating of the PNS from "strong" to "mild." SNOPY provides an efficient data-driven and optimization-based method to tailor non-Cartesian sampling trajectories.

Quantitative myocardial perfusion with a hybrid 2D simultaneous multi-slice sequence

PurposeTo evaluate a novel 2D simultaneous multi-slice (SMS) myocardial perfusion acquisition and compare directly to a published quantitative 3D stack-of-stars (SoS) acquisition. MethodsA hybrid saturation recovery radial 2D SMS sequence following a single saturation was created for the quantification of myocardial blood flow (MBF). This sequence acquired three slices simultaneously and generated an arterial input function (AIF) using the first 24 rays. Validation was done in a novel way by alternating heartbeats between the hybrid 2D SMS and the 3D SoS acquisitions. Initial studies were done to study the effects of using only every other beat for the 2D SMS in two subjects, and for the 3D SoS in four subjects. The proposed alternating acquisitions were then performed in ten dog studies at rest, four dog studies at adenosine stress, and two human resting studies. Quantitative MBF analysis was performed for 2D SMS and 3D SoS separately, using a compartment model. ResultsAcquiring every-other-beat data resulted in 6 ± 5% (“ideal”) and 11 ± 8% (“practical”) perfusion changes for both 2D SMS and 3D SoS methods. For alternating acquisitions, 2D SMS and 3D SoS quantitative perfusion values were comparable for both the twelve rest studies (2D SMS: 0.69 ± 0.16 vs 3D: 0.69 ± 0.15 ml/g/min, p = 0.55) and the four stress studies (2D SMS: 1.28 ± 0.22 vs 3D: 1.30 ± 0.24 ml/g/min, p = 0.61). ConclusionEvery-other-beat acquisition changed estimated perfusion values relatively little for both sequences. The quantitative hybrid radial 2D SMS myocardial first-pass perfusion imaging sequence gave results similar to 3D perfusion when compared directly with an alternating beat acquisition.

4D Free-Breathing Sequence For The Study Of Pancreatic Lesions In MRI 3 Tesla

Pancreatic cancer is the fourth leading cause of cancer death in both the United States and Europe. A fundamental role in the characterization, early diagnosis, and staging of pancreatic cancer is played by Magnetic Resonance. An innovative and recently implemented sequence, the 4D Free-Breathing sequence, is demonstrating remarkable efficiency in the characterization of pancreatic lesions, as it allows to obtain images with high temporal resolution on the arterial phase, maintaining high spatial and temporal resolution, with the patient free breathing and with compensation of respiratory movement artifacts. The aim of this study was to analyze the 4D Free-Breathing sequence technique and to evaluate its advantages in terms of image quality and diagnostic value in the characterization of pancreatic lesions. The 4D Free Breathing sequence replaces the acquisition of the classic arterial post-contrast phase obtained with the 3D-THRIVE sequence: after a first acquisition of the k-space data in the non-contrast phase (lasting 58 seconds), multiple arterial subphases, each one lasting about 5 seconds, will be acquired with a complete coverage of the post-contrast phase of about 90 seconds. This sequence exploits the k-space sampling technique called "Stack of Stars", based on a radial sampling in the XY plane. In detail, along the slice phase-encoding direction (kz), uniform Cartesian-grid sampling is maintained. Within each kz-encoded plane, radial data is collected with consecutive views (1 per sequence repetition time TR) rotated by a golden-angle of 111.25°, allowing the sampling of a complete circle, also determining a considerably reduced presence of breath artifacts.

4D Free-Breathing Sequence For The Study Of Pancreatic Lesions In MRI 3 Tesla

Pancreatic cancer is the fourth leading cause of cancer death in both the United States and Europe. A fundamental rolein the characterization, early diagnosis, and staging of pancreatic cancer is played by Magnetic Resonance. An innovative and recently implemented sequence, the 4D Free-Breathing sequence, is demonstrating remarkable efficiencyin the characterization of pancreatic lesions, as it allows to obtain images with high temporal resolution on the arterial phase, maintaining high spatial and temporal resolution, with the patient free breathing and with compensationof respiratory movement artifacts. The aim of this study was to analyze the 4D Free-Breathing sequence techniqueand to evaluate its advantages in terms of image quality and diagnostic value in the characterization of pancreaticlesions. The 4D Free Breathing sequence replaces the acquisition of the classic arterial post-contrast phase obtainedwith the 3D-THRIVE sequence: after a first acquisition of the k-space data in the non-contrast phase (lasting 58seconds), multiple arterial subphases, each one lasting about 5 seconds, will be acquired with a complete coverageof the post-contrast phase of about 90 seconds. This sequence exploits the k-space sampling technique called “Stackof Stars”, based on a radial sampling in the XY plane. In detail, along the slice phase-encoding direction (kz), uniform Cartesian-grid sampling is maintained. Within each kz-encoded plane, radial data is collected with consecutiveviews (1 per sequence repetition time TR) rotated by a golden-angle of 111.25°, allowing the sampling of a completecircle, also determining a considerably reduced presence of breath artifacts. The inclusion of the 4D Free-Breathingsequence in the MRI study protocol of the pancreas, through the rapid and consequential acquisitions of 18 arterialphases, allows to improve the diagnostic information contained in the arterial phase, with free breathing, also innon-compliant patients and with correction of breath artifacts

Dynamic MRI of swallowing: real-time volumetric imaging at 12 frames per second at 3 T

ObjectiveDysphagia or difficulty in swallowing is a potentially hazardous clinical problem that needs regular monitoring. Real-time 2D MRI of swallowing is a promising radiation-free alternative to the current clinical standard: videofluoroscopy. However, aspiration may be missed if it occurs outside this single imaged slice. We therefore aimed to image swallowing in 3D real time at 12 frames per second (fps).Materials and methodsAt 3 T, three 3D real-time MRI acquisition approaches were compared to the 2D acquisition: an aligned stack-of-stars (SOS), and a rotated SOS with a golden-angle increment and with a tiny golden-angle increment. The optimal 3D acquisition was determined by computer simulations and phantom scans. Subsequently, five healthy volunteers were scanned and swallowing parameters were measured.ResultsAlthough the rotated SOS approaches resulted in better image quality in simulations, in practice, the aligned SOS performed best due to the limited number of slices. The four swallowing phases could be distinguished in 3D real-time MRI, even though the spatial blurring was stronger than in 2D. The swallowing parameters were similar between 2 and 3D.ConclusionAt a spatial resolution of 2-by-2-by-6 mm with seven slices, swallowing can be imaged in 3D real time at a frame rate of 12 fps.

Predicting T and N Staging of Resectable Gastric Cancer According to Whole Tumor Histogram Analysis About a Non-Cartesian k-Space Acquisition DCE-MRI: A Feasibility Study.

ObjectiveTo explore the feasibility of the whole tumor histogram analysis parameters derived from dynamic contrast-enhanced MRI (DCE-MRI) based on stack-of stars (StarVIBE) to predict T and N staging of resectable gastric cancer (GC).MethodsEighty-seven patients confirmed as GC by histopathology were enrolled in this prospective study. DCE-MRI were performed before surgery, and quantitative DCE parameters (Ktrans, Kep, Ve) and histogram metrics (Skewness, Kurtosis and Entropy) were measured by Omni-Kinetics software. Intraclass correlation coefficient (ICC) testing was used to determine the consistency of Ktrans, Kep and Ve values and histogram metrics values between two radiologists using Bland–Altman analysis. The quantitative DCE parameters or histogram metrics values between T stage or N stage were compared using ANOVA or Kruskal–Wallis testing. Receiver operating characteristic (ROC) analyses was performed to find out the best parameters for identifying T and N staging.ResultsThere was statistical difference in Ktrans, Kep, Ve and entropy to identify T staging (P=0.015, 0.033, <0.001, and 0.007, respectively), and in pairwise comparisons of Ve values showed statistically difference between T1+2 and T3 group (P<0.001), T1+2 and T4 group (P<0.001). There were statistical differences in Ve to identify N staging (P=0.041). In ROC analysis, Ve was the best parameter for identifying T staging (AUC: 0.788, the sensitivity and specificity was 0.929 and 0.578, respectively) and N staging (AUC: 0.590, the sensitivity and specificity was 0.714 and 0.899, respectively).ConclusionThe whole tumor histogram analysis parameters derived from StarVIBE DCE-MRI may be able to quantitatively evaluate T and N staging of GC, so as to help clinical treatment decision optimization.

Rapid high-resolution volumetric T1 mapping using a highly accelerated stack-of-stars Look Locker technique

PurposeTo develop a fast volumetric T1 mapping technique. Materials and methodsA stack-of-stars (SOS) Look Locker technique based on the acquisition of undersampled radial data (>30× relative to Nyquist) and an efficient multi-slab excitation scheme is presented. A principal-component based reconstruction is used to reconstruct T1 maps. Computer simulations were performed to determine the best choice of partitions per slab and degree of undersampling. The technique was validated in phantoms against reference T1 values measured with a 2D Cartesian inversion-recovery spin-echo technique. The SOS Look Locker technique was tested in brain (n = 4) and prostate (n = 5). Brain T1 mapping was carried out with and without kz acceleration and results between the two approaches were compared. Prostate T1 mapping was compared to standard techniques. A reproducibility study was conducted in brain and prostate. Statistical analyses were performed using linear regression and Bland Altman analysis. ResultsPhantom T1 values showed excellent correlations between SOS Look Locker and the inversion-recovery spin-echo reference (r2 = 0.9965; p < 0.0001) and between SOS Look Locker with slab-selective and non-slab selective inversion pulses (r2 = 0.9999; p < 0.0001). In vivo results showed that full brain T1 mapping (1 mm3) with kz acceleration is achieved in 4 min 21 s. Full prostate T1 mapping (0.9 × 0.9 × 4 mm3) is achieved in 2 min 43 s. T1 values for brain and prostate were in agreement with literature values. A reproducibility study showed coefficients of variation in the range of 0.18–0.2% (brain) and 0.15–0.18% (prostate). ConclusionA rapid volumetric T1 mapping technique was developed. The technique enables high-resolution T1 mapping with adequate anatomical coverage in a clinically acceptable time.

A post-processing method based on interphase motion correction and averaging to improve image quality of 4D magnetic resonance imaging: a clinical feasibility study.

Nine patients (seven pancreas, one liver, and one lung) were recruited. 4D-MRI was performed using two prototype k-space sorted techniques, stack-of-stars (SOS) and koosh-ball (KB) acquisitions. Post-processing using MoCoAve was implemented for both methods. Image quality score, apparent SNR (aSNR), sharpness, motion trajectory and standard deviation (σ_GTV) of the gross tumor volumes were compared between original and MoCoAve image sets. All subjects successfully underwent 4D-MRI scans and MoCoAve was performed on all data sets. Significantly higher image quality scores (2.64 ± 0.39 vs 1.18 ± 0.34, p = 0.001) and aSNR (37.6 ± 15.3 vs 18.1 ± 5.7, p = 0.001) was observed in the MoCoAve images when compared to the original images. High correlation in tumor motion trajectories in the superoinferior direction (SI: 0.91 ± 0.08) and weaker in the anteroposterior (AP: 0.51 ± 0.44) and mediolateral (ML: 0.37 ± 0.23) directions, similar image sharpness (0.367 ± 0.068 vs 0.369 ± 0.072, p = 0.805), and minimal average absolute difference (0.47 ± 0.34 mm) of the motion trajectory profiles was found between the two image sets. The σ_GTV in pancreas patients was significantly (p = 0.039) lower in MoCoAve images (1.48 ± 1.35 cm3) than in the original images (2.17 ± 1.31 cm3). MoCoAve using interphase motion correction and averaging has shown promise as a post-processing method for improving k-space sorted (SOS and KB) 4D-MRI image quality in thoracic and abdominal cancer patients. The proposed method is an image based post-processing method that could be applied to many k-space sorted 4D-MRI methods for improved image quality and signal-to-noise ratio while preserving image sharpness and respiratory motion fidelity. It is a useful technique for the radiotherapy planning community who are interested in using 4D-MRI but aren't satisfied with their current MR image quality.

Reconstruction of undersampled radial free-breathing 3D abdominal MRI using stacked convolutional auto-encoders.

Free-breathing three-dimensional (3D) abdominal imaging is a challenging task for MRI, as respiratory motion severely degrades image quality. One of the most promising self-navigation techniques is the 3D golden-angle radial stack-of-stars (SOS) sequence, which has advantages in terms of speed, resolution, and allowing free breathing. However, streaking artifacts are still clearly observed in reconstructed images when undersampling is applied. This work presents a novel reconstruction approach based on a stacked convolutional auto-encoder (SCAE) network to solve this problem. Thirty healthy volunteers participated in our experiment. To build the dataset, reference and artifact-affected images were reconstructed using 451 golden-angle spokes and the first 20, 40, or 90 golden-angle spokes corresponding to acceleration rates of 31.4, 15.7, and 6.98, respectively. In the training step, we trained the SCAE by feeding it with patches from artifact-affected images. The SCAE outputs patches in the corresponding reference images. In the testing step, we applied the trained SCAE to map each input artifact-affected patch to the corresponding reference image patch. The SCAE-based reconstruction images with acceleration rates of 6.98 and 15.7 show nearly similar quality as the reference images. Additionally, the calculation time is below 1 s. Moreover, the proposed approach preserves important features, such as lesions not presented in the training set. The preliminary results demonstrate the feasibility of the proposed SCAE-based strategy for correcting the streaking artifacts of undersampled free-breathing 3D abdominal MRI with a negligible reconstruction time.

Noncontrast-enhanced time-resolved 4D dynamic intracranial MR angiography at 7T: A feasibility study.

Arterial spin labeling (ASL) based-noncontrast-enhanced 4D MR angiography (NCE 4D MRA) shows potential in characterizing cerebrovascular hemodynamics in cerebrovascular disorders. Ultrahigh-field theoretically benefits ASL signal with increased inherent signal-to-noise ratio (SNR) and prolonged blood T1 , which may provide improved delineation of vasculature in 4D MRA. To investigate the feasibility of NCE 4D MRA using 3D Cartesian trajectory and stack-of-stars (SOS) golden angle radial trajectory at 7T. A prospective study. Six normal volunteers and eight patients with arteriovenous malformation (AVM). NCE 4D MRA with Cartesian and radial trajectories were performed at 3T and 7T. Subjective image quality of 4D MRA was evaluated using a 4-point scale by two experienced neuroradiologists. The characterization of AVM components with 4D MRA and DSA was also graded using the Spetzler-Martin grading scale. Cohen's kappa coefficient was calculated to evaluate the agreement between two readers within each 4D MRA technique (Cartesian and Radial). A Wilcoxon signed-rank test was performed to compare the subjective image quality scores of 4D MRA between Cartesian and radial trajectories, and between 7T and 3T, respectively. Good-to-excellent image quality was achieved in 4D MRA with both Cartesian (3.83 ± 0.41) and radial (3.42 ± 0.49) acquisitions in healthy volunteers at 7T. However, markedly reduced scan time was needed with radial acquisition. 4D MRA at 7T (3.31 ± 0.59) shows better delineation of AVM lesion features, especially the vein drainage, compared with that of 3T (2.83 ± 0.75), although no statistical significance was achieved (P = 0.180). The feasibility of ASL based 4D MRA at 7T with Cartesian and SOS golden angle radial acquisition was demonstrated. The clinical evaluation of 4D MRA in AVMs between 3T and 7T suggested 7T 4D MRA images acquired with radial acquisition demonstrate excellent delineation of AVM features, especially the draining veins. 2 Technical Efficacy Stage 2 J. Magn. Reson. Imaging 2017.

Feasibility of free breathing Lung MRI for Radiotherapy using non-Cartesian k-space acquisition schemes.

To test a free-breathing MRI protocol for anatomical and functional assessment during lung cancer radiotherapy by assessing two non-Cartesian acquisition schemes based on T1 weighted 3D gradient recall echo sequence: (i) stack-of stars (StarVIBE) and (ii) spiral (SpiralVIBE) trajectories. MR images on five healthy volunteers were acquired on a wide bore 3T scanner (MAGNETOM Skyra, Siemens Healthcare, Erlangen, Germany). Anatomical image quality was assessed on: (1) free breathing (StarVIBE), (2) the standard clinical sequence (volumetric interpolated breath-hold examination, VIBE) acquired in a 20 second (s) compliant breath-hold and (3) 20 s non-compliant breath-hold. For functional assessment, StarVIBE and the current standard breath-hold time-resolved angiography with stochastic trajectories (TWIST) sequence were run as multiphase acquisitions to replicate dynamic contrast enhancement (DCE) in one healthy volunteer. The potential application of the SpiralVIBE sequence for lung parenchymal imaging was assessed on one healthy volunteer. Ten patients with lung cancer were subsequently imaged with the StarVIBE and SpiralVIBE sequences for anatomical and structural assessment. For functional assessment, free-breathing StarVIBE DCE protocol was compared with breath-hold TWIST sequences on four prior lung cancer patients with similar tumour locations. Image quality was evaluated independently and blinded to sequence information by an experienced thoracic radiologist. For anatomical assessment, the compliant breath-hold VIBE sequence was better than free-breathing StarVIBE. However, in the presence of a non-compliant breath-hold, StarVIBE was superior. For functional assessment, StarVIBE outperformed the standard sequence and was shown to provide robust DCE data in the presence of motion. The ultrashort echo of the SpiralVIBE sequence enabled visualisation of lung parenchyma. The two non-Cartesian acquisition sequences, StarVIBE and SpiralVIBE, provide a free-breathing imaging protocol of the lung with sufficient image quality to permit anatomical, structural and functional assessment during radiotherapy. Advances in knowledge: Novel application of non-Cartesian MRI sequences for lung cancer imaging for radiotherapy. Illustration of SpiralVIBE UTE sequence as a promising sequence for lung structural imaging during lung radiotherapy.

Multiecho pseudo-golden angle stack of stars thermometry with high spatial and temporal resolution using k-space weighted image contrast.

Implement and evaluate a 3D MRI method to measure temperature changes with high spatial and temporal resolution and large field of view. A multiecho pseudo-golden angle stack-of-stars (SOS) sequence with k-space weighted image contrast (KWIC) reconstruction was implemented to simultaneously measure multiple quantities, including temperature, initial signal magnitude M(0), transverse relaxation time ( T2*), and water/fat images. Respiration artifacts were corrected using self-navigation. KWIC artifacts were removed using a multi-baseline library. The phases of the multiple echo images were combined to improve proton resonance frequency precision. Temperature precision was tested through in vivo breast imaging (N = 5 healthy volunteers) using both coronal and sagittal orientations and with focused ultrasound (FUS) heating in a pork phantom using a breast specific MR-guided FUS system. Temperature measurement precision was significantly improved after echo combination when compared with the no echo combination case (spatial average of the standard deviation through time of 0.3-1.0 and 0.7-1.9°C, respectively). Temperature measurement accuracy during heating was comparable to a 3D seg-EPI sequence. M(0) and T2* values showed temperature dependence during heating in pork adipose tissue. A self-navigated 3D multiecho SOS sequence with dynamic KWIC reconstruction is a promising thermometry method that provides multiple temperature sensitive quantitative values. Magn Reson Med 79:1407-1419, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Motion-insensitive carotid intraplaque hemorrhage imaging using 3D inversion recovery preparation stack of stars (IR-prep SOS) technique.

Carotid artery imaging is important in the clinical management of patients at risk for stroke. Carotid intraplaque hemorrhage (IPH) presents an important diagnostic challenge. 3D magnetization prepared rapid acquisition gradient echo (MPRAGE) has been shown to accurately image carotid IPH; however, this sequence can be limited due to motion- and flow-related artifact. The purpose of this work was to develop and evaluate an improved 3D carotid MPRAGE sequence for IPH detection. We hypothesized that a radial-based k-space trajectory sequence such as "Stack of Stars" (SOS) incorporated with inversion recovery preparation would offer reduced motion sensitivity and more robust flow suppression by oversampling of central k-space. A total of 31 patients with carotid disease (62 carotid arteries) were imaged at 3T magnetic resonance imaging (MRI) with 3D IR-prep Cartesian and SOS sequences. Image quality was determined between SOS and Cartesian MPRAGE in 62 carotid arteries using t-tests and multivariable linear regression. Kappa analysis was used to determine interrater reliability. In all, 25 among 62 carotid plaques had carotid IPH by consensus from the reviewers on SOS compared to 24 on Cartesian sequence. Image quality was significantly higher with SOS compared to Cartesian (mean 3.74 vs. 3.11, P < 0.001). SOS acquisition yielded sharper image features with less motion (19.4% vs. 45.2%, P < 0.002) and flow artifact (27.4% vs. 41.9%, P < 0.089). There was also excellent interrater reliability with SOS (kappa = 0.89), higher than that of Cartesian (kappa = 0.84). By minimizing flow and motion artifacts and retaining high interrater reliability, the SOS MPRAGE has important advantages over Cartesian MPRAGE in carotid IPH detection. 1 J. Magn. Reson. Imaging 2017;45:410-417.

TH‐EF‐BRA‐07: Evaluation of Internal Target Volume Derived From a Prototype 4D‐MRI Sequence with 3D Radial Stack‐Of‐Stars Trajectory and K‐Space Self‐Gating

Purpose:4D‐MRI based on resorting of 2D‐cine‐MRI images shows great potential to assess tumor motion more accurately compared to 4D‐CT, however, it suffers from low through‐plane resolution and stitching artifacts. 4D‐MRI based on 3D acquisition results in stitching‐artifact‐free images with high in‐plane and through‐plane resolutions. In this study, we report our early clinical experience of a prototype 4D‐MRI sequence with 3D stack‐of‐stars (SOS) trajectory for internal target volume (ITV) definition.Methods:Ten patients with 13 total lesions (7 pancreatic, 1 lung with 2 lesions, 1 liver with 3 lesions and 1 esophagus) were recruited. 4D‐MRI used in‐plane radial and through‐plane Cartesian sampling. Two imaging orientations, i.e. axial slab (A) and coronal slab (B), were compared. ITVs were derived from 3‐bin (ITV3), 5‐bin (ITV5) and 10‐bin (ITV10) reconstruction protocols. ITV5 was set as standard and minimum expansion of ITV3 needed to encompass ITV5 was derived. Similarity index was calculated from ITV3 and ITV5 (SI3/5), and ITV10 and ITV5 (SI10/5). Imaging noise was calculated for both method A and B. Wilcoxon‐rank‐sum test was performed with a p value &lt;0.05 deemed as significant.Results:No significant difference (p=0.34) was observed from method A and B, indicating a uniform imaging noise distribution from 3D acquisition. Imaging noise and artifacts were visually different from different binning protocols, with more bins resulting in more noise, more artifacts and larger ITV. On average, ITV differs by 7% (1%–19%) comparing ITV3 with ITV5 for the patient cohort. For the pancreas sub‐group, ITV differs by 4% (1%–6%). An average of 2.3mm (2mm‐3mm) expansion was needed for ITV3 to encompass ITV5. SI10/5 was 0.93±0.03 (mean±σ) and SI3/5 was 0.95±0.03.Conclusion:4D‐MRI with 3D SOS trajectory was evaluated on 10 patients. Significant difference in ITV was observed with different binning protocols. Imaging noise was similar irrespective of the imaging orientations.This work is partially supported by NIH R03CA173273 and CTSI core voucher award.

USPIO-enhanced 3D-cine self-gated cardiac MRI based on a stack-of-stars golden angle short echo time sequence: Application on mice with acute myocardial infarction.

To develop and assess a 3D-cine self-gated method for cardiac imaging of murine models. A 3D stack-of-stars (SOS) short echo time (STE) sequence with a navigator echo was performed at 7T on healthy mice (n = 4) and mice with acute myocardial infarction (MI) (n = 4) injected with ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles. In all, 402 spokes were acquired per stack with the incremental or the golden angle method using an angle increment of (360/402)° or 222.48°, respectively. A cylindrical k-space was filled and repeated with a maximum number of repetitions (NR) of 10. 3D cine cardiac images at 156 μm resolution were reconstructed retrospectively and compared for the two methods in terms of contrast-to-noise ratio (CNR). The golden angle images were also reconstructed with NR = 10, 6, and 3, to assess cardiac functional parameters (ejection fraction, EF) on both animal models. The combination of 3D SOS-STE and USPIO injection allowed us to optimize the identification of cardiac peaks on navigator signal and generate high CNR between blood and myocardium (15.3 ± 1.0). The golden angle method resulted in a more homogeneous distribution of the spokes inside a stack (P < 0.05), enabling reducing the acquisition time to 15 minutes. EF was significantly different between healthy and MI mice (P < 0.05). The method proposed here showed that 3D-cine images could be obtained without electrocardiogram or respiratory gating in mice. It allows precise measurement of cardiac functional parameters even on MI mice. J. Magn. Reson. Imaging 2016;44:355-365.

Sodium (23Na) ultra-short echo time imaging in the human brain using a 3D-Cones trajectory

ObjectSodium magnetic resonance imaging (23Na-MRI) of the brain has shown changes in 23Na signal as a hallmark of various neurological diseases such as stroke, Alzheimer’s disease, Multiple Sclerosis and Huntington’s disease. To improve scan times and image quality, we have implemented the 3D-Cones (CN) sequence for in vivo 23Na brain MRI.Materials and methodsUsing signal-to-noise (SNR) as a measurement of sequence performance, CN is compared against more established 3D-radial k-space sampling schemes featuring cylindrical stack-of-stars (SOS) and 3D-spokes kooshball (KB) trajectories, on five healthy volunteers in a clinical setting. Resolution was evaluated by simulating the point-spread-functions (PSFs) and experimental measures on a phantom.ResultsAll sequences were shown to have a similar SNR arbitrary units (AU) of 6–6.5 in brain white matter, 7–9 in gray matter and 17–18 AU in cerebrospinal fluid. SNR between white and gray matter were significantly different for KB and CN (p = 0.046 and <0.001 respectively), but not for SOS (p = 0.1). Group mean standard deviations were significantly smaller for CN (p = 0.016). Theoretical full-width at half-maximum linewidth of the PSF for CN is broadened by only 0.1, compared to 0.3 and 0.8 pixels for SOS and KB respectively. Actual image resolution is estimated as 8, 9 and 6.3 mm for SOS, KB and CN respectively.ConclusionThe CN sequence provides stronger tissue contrast than both SOS and KB, with more reproducible SNR measurements compared to KB. For CN, a higher true resolution in the same amount of time with no significant trade-off in SNR is achieved. CN is therefore more suitable for 23Na-MRI in the brain.

High resolution three‐dimensional cine phase contrast MRI of small intracranial aneurysms using a stack of stars k‐space trajectory

AbstractPurpose:To develop a method for targeted volumetric, three directional cine phase contrast (PC) imaging with high spatial resolution in clinically feasible scan times.Materials and Methods:A hybrid radial‐Cartesian k‐space trajectory is used for cardiac gated, volumetric imaging with three directional velocity encoding. Imaging times are reduced by radial undersampling and temporal viewsharing. Phase contrast angiograms are displayed in a new approach that addresses the concern of signal drop out in regions of slow flow. The feasibility of the PC stack of stars (SOS) trajectory was demonstrated with an in vivo study capturing 14 small intracranial aneurysms (2–10 mm). Aneurysm measures from six aneurysms also imaged with digital subtraction angiography (DSA) were compared with linear regression with those from the PC SOS images.Results:All aneurysms were identified on the phase contrast angiograms. The geometric measures from PC SOS and DSA were in good agreement (linear regression: slope = 0.89, intercept = 0.35, R∧2 = 0.88).Conclusion:PC SOS is a promising method for obtaining volumetric angiograms and cine phase contrast velocity measurements in three dimensions. Acquired spatial resolutions of 0.4 × 0.4 × (0.7–1.0) mm make this method especially promising for studying flow in small intracranial aneurysms. J. Magn. Reson. Imaging 2012. © 2012 Wiley Periodicals, Inc.