Spoiled Gradient Research Articles

Application of radial GRAPPA techniques to single- and multislice dynamic speech MRI using a 16-channel neurovascular coil.

To investigate: (1) the feasibility of using through-time radial GeneRalized Autocalibrating Partially Parallel Acquisitions (rGRAPPA) and hybrid radial GRAPPA (h-rGRAPPA) in single- and multislice dynamic speech MRI; (2) whether single-slice dynamic speech MRI at a rate of 15 frames per second (fps) or higher and with adequate image quality can be achieved using these radial GRAPPA techniques. Seven healthy adult volunteers were imaged at 3T using a 16-channel neurovascular coil and 2 spoiled gradient echo sequences (radial trajectory, field of view = 192 × 192 mm2 , acquired pixel size = 2.4 × 2.4 mm2 ). One sequence imaged a single slice at 16.8 fps, the other imaged 2 interleaved slices at 7.8 fps per slice. Image sets were reconstructed using rGRAPPA and h-rGRAPPA, and their image quality was compared using the root mean square error, structural similarity index, and visual assessments. Image quality deteriorated when fewer than 170 calibration frames were used in the rGRAPPA reconstruction. rGRAPPA image sets demonstrated: (1) in 97% of cases, a similar image quality to h-rGRAPPA image sets reconstructed using a k-space segment size of 4, (2) in 98% of cases, a better image quality than h-rGRAPPA image sets reconstructed using a k-space segment size of 32. This study confirmed: (1) the feasibility of using rGRAPPA and h-rGRAPPA in single- and multislice dynamic speech MRI, (2) that single-slice speech imaging at a frame rate higher than 15 fps and with adequate image quality can be achieved using these radial GRAPPA techniques.

Pelvic muscle size and myosteatosis: Relationship with age, gender, and obesity

Purpose:To evaluate interreader performance in the measurement of the cross-sectional area and myosteatosis of pelvic skeletal muscles using fat quantification magnetic resonance imaging (MRI) and correlate with patient anthropomorphic characteristics.Materials and Methods:A Health Insurance Portability and Accountability Act–compliant retrospective cross-sectional study was performed. Between January and April 2016, 61 patients (26 males and 35 females) underwent a lumbosacral plexus 3T MRI with a modified three-dimensional spoiled gradient echo sequence dedicated to fat quantification (mDixon Quant; Philips Healthcare). Two independent reviewers outlined muscle cross-sectional area on axial images using a freehand region of interest tool and documented proton-density fat fraction (FF) and muscle area (cm2) of the psoas, gluteus medius, gluteus maximus, and rectus femoris muscles on each side. Interreader agreement was assessed by intraclass correlation coefficient (ICC), and correlation between the measurements and subject's age, gender, and body mass index (BMI) was assessed using multiple linear regression analysis.Results:Excellent interreader agreement was obtained (ICC ≥0.74) for all muscle groups except for the left gluteus medius area and right psoas FF which showed good agreement (0.65 and 0.61, respectively). Statistically significant (P ≤ 0.05) positive correlation was seen between the gluteal muscle FF and area with BMI, and rectus muscle FF with age and BMI. Statistically significant negative correlation between the rectus femoris area and age was also observed.Conclusion:Fat quantification MRI is a highly reproducible imaging technique for the assessment of myosteatosis and muscle size. Intramuscular FF and cross-sectional area were correlated with age and BMI across multiple muscle groups.

Free-breathing quantification of regional ventilation derived by phase-resolved functional lung (PREFUL) MRI.

To test the feasibility of regional fully quantitative ventilation measurement in free breathing derived by phase-resolved functional lung (PREFUL) MRI in the supine and prone positions. In addition, the influence of T2 * relaxation time on ventilation quantification is assessed. Twelve healthy volunteers underwent functional MRI at 1.5T using a 2D triple-echo spoiled gradient echo sequence allowing for quantitative measurement of T2 * relaxation time. Minute ventilation (ΔV) was quantified by conventional fractional ventilation (FV) and the newly introduced regional ventilation (VR), which corrects volume errors due to image registration. ΔVFV versus ΔVVR and ΔVVR versus ΔVVR with T2 * correction were compared using Bland-Altman plots and correlation analysis. The repeatability and physiological plausibility of all measurements were tested in the supine and prone positions. On global and regional scales a strong correlation was observed between ΔVFV versus ΔVVR and ΔVVR versus ΔVVRT2* (r>0.93); however, regional Bland-Altman analysis showed systematic differences (p<0.0001). Unlike ΔVVRT2* , ΔVVR and ΔVFV showed expected physiologic anterior-posterior gradients, which decreased in the supine but not in the prone position at second measurement during 3min in the same position. For all quantification methods a moderate repeatability (coefficient of variation <20%) of ventilation was found. A fully quantified regional ventilation measurement using ΔVVR in free breathing is feasible and shows physiologically plausible results. In contrast to conventional ΔVFV, volume errors due to image registration are eliminated with the ΔVVR approach. However, correction for the T2 * effect remains challenging.

Time-optimized 4D phase contrast MRI with real-time convex optimization of gradient waveforms and fast excitation methods.

To shorten 4D flow acquisitions by shortening TRs with fast RF pulses and gradient waveforms. Real-time convex optimization is used to generate these gradients waveforms on the scanner. RF and slab-select waveforms were shortened with a minimum phase SLR excitation and the time-optimal variable-rate selective excitation method. Real-time convex optimization was used to shorten bipolar and spoiler gradients by finding the shortest gradient waveforms that satisfied constraints on scan parameters, gradient hardware, M0 , M1 , and peripheral nerve stimulation. Waveforms were calculated and TE and/or TR values were compared for a range of scan parameters and compared to a conventional 4D flow sequence. The method was tested in flow phantoms, and in the aorta and neurovasculature of volunteers (N = 10). Additionally, eddy current error was measured in a large phantom. TEs and TRs were shortened by 21-32% and 20-34%, respectively, compared to the conventional sequence over a range of scan parameters. Bland-Altman analysis of 2 flow phantom configurations showed flow rate bias of 0.3 mL/s and limits of agreement (LOA) of [-6.9, 7.5] mL/s for a cardiac phantom and a bias of -0.1 mL/s with LOA = [-0.4, 0.2] mL/s for a neuro phantom. Similar agreement was also seen for flow measurements in volunteers (bias = -1.0 and -0.1 mL/s, LOA = [-34.9, 33.0] and [-0.7, 0.6] mL/s). Measured eddy currents were 39% larger with the CVX + mpVERSE method. The real-time optimized 4D flow gradients and fast slab-selection excitation methods produced up to 34% faster TRs with excellent flow measurement agreement compared to a conventional 4D flow sequence.

Steady-state double-angle method for rapid B1 mapping.

To introduce an accurate, rapid, and practical method for active B1 field mapping based on the double-angle method (DAM) in the steady-state (SS) signal regime. We introduced and evaluated the performance of the SS-DAM approach to map the B1 field and compared the results to those calculated from the conventional DAM approach. Similar to DAM, SS-DAM uses the signal intensity ratio of 2 magnitude images acquired with different flip angles using the spoiled gradient recalled echo sequence. However, unlike DAM, in SS-DAM, these 2 spoiled gradient recalled echo images are acquired with very short TR, which allows substantially reduced acquisition time. Numerical, phantom, and in vivo brain imaging analyses, representing a wide range of T1 s and large B1 variation, were conducted. Methods for further accelerating acquisition were also investigated. Our results demonstrate the potential of the SS-DAM approach to be applied widely in the clinical setting. B1 maps derived from SS-DAM were demonstrated to be quantitatively comparable to those derived from DAM but were derived much more rapidly. Large-volume B1 maps were obtained at a field strength of 3 tesla within clinically acceptable acquisition times. SS-DAM permits accurate B1 mapping in the clinical setting, with whole-brain coverage in less than 1 min.

Spectrum of Magnetic Resonance imaging in Afebrile Pediatric Epilepsy

Background: Pediatric neurological disorders are commonly encountered. Epilepsy is one of the most common neurological disorder in childhood. Clinically diagnosis is established by two or more unprovoked seizures at least 24 hours apart. It has got considerable importance due to fact that it can cause anxiety in parents. Cortical malformations characterized by abnormal structure of cerebral cortex are one of the major cause for epilepsy. Magnetic resonance imaging is the modality of choice to evaluate the structural anomaly, the cause of seizure disorder and to assess the potential need for surgery. In this study, we tried to evaluate the spectrum of MRI imaging to evaluate afebrile pediatric epilepsy. Subjects and Methods: The study was retrospective cross sectional study. We collected data of 400 patients of pediatric epilepsy who underwent non contrast MRI evaluation during June 2017 to January 2019 at department of Radio-diagnosis at GCS Medical college, Hospital and Research Center. Exclusion criteria consist of a recent history of fever and clinical laboratory parameters of any infective cause. MRI was done using 1.5 Tesla equipment. Sequences included Sagittal T1-weighted spin echo (SE), Axial T2-weighted fast spin echo (FSE), Coronal oblique fast fluid attenuated inversion recovery (FLAIR), Axial diffusion weighted single-shot spin-echo echoplanar, Axial 3D inversion recovery prepped fast SPGR (spoiled gradient recalled). Results: The most common detected changes were unilateral and bilateral mesial temporal sclerosis (21% & 9% respectively), cortical dysplasia (1.5%), migrational anomalies, neurocutaneous syndromes and few cortical neoplasms (0.5 to 1%). Conclusion: MRI in today's world plays a deciding role in diagnostic work-up of a child with epilepsy.

Accuracy of computed tomography: magnetic resonance imaging image fusion using a phantom for skull base surgery.

The aim of this study is to assess the positional accuracy of image fusions of the skull base region using different magnetic resonance imaging (MRI) and computed tomography (CT) image pairs. An image set of 3D fast imaging employing steady-state acquisition-C (FIESTA-C) was used as the base image set. Image fusions were performed using an image set with different fields of view (FOVs): one with different matrix size, one with a different sequence of 3D spoiled gradient recalled acquisition, and one with different modality (CT), using a phantom including multi columnar objects. Position of columns at the center, and 4 and 8 cm from the center were measured. The displacements between the base image set and fused image set were measured. For slices with different z-positions, the displacement of the 8-cm column was assessed. For 20 clinical MRI cases, the distance between the dorsum sellae and the cranial nerves was measured. No significant differences were found between the different FOVs or image sequences. However, with the different matrix sizes and modalities, significant displacements were observed, although they were all within 0.5 mm. Similar displacements were observed in the slices at different z-positions. All cranial nerves were located within 40 mm of the dorsum sellae. The displacements following image fusion were within approximately 0.5 mm, even at 8 cm from the center. This suggests that the region where the cranial nerves are located, within 40 mm of the dorsum sellae, had no risk of positional error following image fusion.

Associations between vertebral body fat fraction and intervertebral disc biochemical composition as assessed by quantitative MRI.

There is an interplay between the intervertebral disc (IVD) and the adjacent bone marrow that may play a role in the development of IVD degeneration and might influence chronic lower back pain (CLBP). To apply novel quantitative MRI techniques to assess the relationship between vertebral bone marrow fat (BMF) and biochemical changes in the adjacent IVD. Prospective. Forty-six subjects (26 female and 20 male) with a mean age of 47.3 ± 12.0 years. 3 T MRI; a combined T1ρ and T2 mapping pulse sequence and a 3D spoiled gradient recalled sequence with six echoes and iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) reconstruction algorithm. Using quantitative MRI, the vertebral BMF fraction was measured as well as the biochemical composition (proteoglycan and collagen content) of the IVD. Furthermore, clinical Pfirrmann grading, Oswestry disability index (ODI), and visual analog scale (VAS) was assessed. Mixed random effects models accounting for multiple measurements per subject were used to assess the relationships between disc measurements and BMF. The relationships between BMF (mean) and T1ρ /T2 (mean and SD) were significant, with P < 0.05. Significant associations (P < 0.001) were found between clinical scores (Pfirrmann, ODI, and VAS) with T1ρ /T2 (mean and SD). BMF mean was significantly related to ODI (P = 0.037) and VAS (P = 0.043), but not with Pfirrmann (P = 0.451). In contrast, BMF SD was significantly related to Pfirrmann (P = 0.000) but not to ODI (P = 0.064) and VAS (P = 0.13). Our study demonstrates significant associations between BMF and biochemical changes in the adjacent IVD, both assessed by quantitative MRI; this may suggest that the conversion of hematopoietic bone marrow to fatty bone marrow impairs the supply of available nutrients to cells in the IVD and may thereby accelerate disc degeneration. 2 Technical Efficacy Stage: 3 J. Magn. Reson. Imaging 2019;50:1219-1226.

Optimization of steady-state pulsed CEST imaging for amide proton transfer at 3T MRI.

To optimize a steady-state imaging sequence for maximizing the amide proton transfer effects in pulsed-CEST (pCEST) imaging. The steady-state pCEST (SS-pCEST) sequence is a fast CEST imaging scheme that applies repetitive short RF pulses for generating CEST and acquiring MR imaging signal alternately. To maximize the obtainable amide proton transfer effects, the SS-pCEST scheme is analyzed and optimized with respect to not only the imaging parameters but also the imaging schemes of the signal acquisition part. Three imaging parameters such as the flip angle and RF power for saturation and the flip angle for imaging are selected as factors affecting the obtainable CEST effects; and 2 imaging schemes, namely, SSFP and spoiled gradient echo sequences, are analyzed and compared for numerical simulations and MRI experiments at 3 tesla. SS-pCEST combined with SSFP could provide higher amide proton transfer effects than that with spoiled gradient echo. Furthermore, in the proposed SS-pCEST imaging with SSFP, 3 imaging parameters can be independently optimized so that the optimization complexities can be reduced. We optimized the SS-pCEST imaging method with SSFP to maximize the amide proton transfer effects. In addition, our analysis showed the SSFP sequence was more efficient than the spoiled gradient echo sequence for SS-pCEST imaging.

Brain Morphometry and Longitudinal Relaxation Time of Spontaneously Hypertensive Rats (SHRs) in Early and Intermediate Stages of Hypertension Investigated by 3D VFA-SPGR MRI

Cerebral small vessel disease(s) (SVD) results from pathological changes of the small blood vessels in the brain and is common in older people. The diagnostic features by which SVD manifests in brain includes white matter hyperintensities, lacunes, dilated perivascular spaces, microbleeds, and atrophy. In the present study, we use in vivo magnetic resonance imaging (MRI) to characterize brain morphometry and longitudinal relaxation time (T1) of spontaneously hypertensive rats (SHRs) to study the contribution of chronic hypertension to SVD relevant pathology. Male SHR and Wistar-Kyoto (WKY) rats underwent 3D variable flip angle spoiled gradient echo brain MRI at 9.4 T at early (seven weeks old) and established (19 weeks old) stages of hypertension. The derived proton density weighted and T1 images were utilized for morphometry and to characterize T1 properties in gray matter (GM), white matter (WM) and cerebrospinal fluid (CSF). Custom tissue probability maps were constructed for accurate computerized whole brain tissue segmentations and voxel-wise analyses. Characteristic morphological differences between the two strains included enlarged ventricles, smaller corpus callosum (CC) volumes and general ‘thinning’ of CC in SHR compared to WKY rats at both age groups. While we did not observe parenchymal T1 differences, the T1 of CSF was elevated in SHR compared to controls. Collectively these findings indicate that SHRs develop WM atrophy which is a clinically robust MRI biomarker associated with WM degeneration.

Improved repeatability of dynamic contrast-enhanced MRI using the complex MRI signal to derive arterial input functions: a test-retest study in prostate cancer patients.

PurposeThe arterial input function (AIF) is a major source of uncertainty in tracer kinetic (TK) analysis of dynamic contrast‐enhanced (DCE)‐MRI data. The aim of this study was to investigate the repeatability of AIFs extracted from the complex signal and of the resulting TK parameters in prostate cancer patients.MethodsTwenty‐two patients with biopsy‐proven prostate cancer underwent a 3T MRI exam twice. DCE‐MRI data were acquired with a 3D spoiled gradient echo sequence. AIFs were extracted from the magnitude of the signal (AIFMAGN), phase (AIFPHASE), and complex signal (AIFCOMPLEX). The Tofts model was applied to extract Ktrans, kep and ve. Repeatability of AIF curve characteristics and TK parameters was assessed with the within‐subject coefficient of variation (wCV).ResultsThe wCV for peak height and full width at half maximum for AIFCOMPLEX (7% and 8%) indicated an improved repeatability compared to AIFMAGN (12% and 12%) and AIFPHASE (12% and 7%). This translated in lower wCV values for Ktrans (11%) with AIFCOMPLEX in comparison to AIFMAGN (24%) and AIFPHASE (15%). For kep, the wCV was 16% with AIFMAGN, 13% with AIFPHASE, and 13% with AIFCOMPLEX.ConclusionRepeatability of AIFPHASE and AIFCOMPLEX is higher than for AIFMAGN, resulting in a better repeatability of TK parameters. Thus, use of either AIFPHASE or AIFCOMPLEX improves the robustness of quantitative analysis of DCE‐MRI in prostate cancer.

Altered functional connectivity of the marginal division in Parkinson's disease with mild cognitive impairment: A pilot resting-state fMRI study.

The marginal division (MrD) is an important subcortical center involved in learning and memory. Mild cognitive impairment (MCI) is commonly seen in patients with Parkinson's disease (PD), but the neurobiological basis is yet to be elucidated. To use resting-state functional magnetic resonance imaging (rs-fMRI) to explore the altered functional connectivity (FC) of the MrD in patients with PD-MCI. Prospective pilot study. Twenty-five patients with PD-MCI; 25 PD patients and no cognitive impairment (PD-NCI); and 25 healthy control (HC) participants. 3.0 T GE Healthcare MRI scanner; three-dimensional T1 -weighted fast spoiled gradient recalled echo (3D T1 -FSPGR); rs-fMRI. The MrD was defined using manual delineation, which was the seed point to compute the FC to examine correlations between low-frequency fMRI signal fluctuations in MrD and the whole brain. Between-group comparisons of the rs-fMRI data were computed using two-sample t-tests in a voxelwise manner after controlling for age and sex, to determine the brain regions that showed significant differences in FC with the bilateral MrDs. Correlation analyses were performed for FC values and cognitive abilities in patients with PD. In the PD-MCI group, compared with the PD-NCI group, we observed lesser FC between the MrD bilaterally and right putamen, left insula, left cerebellum, and left thalamus; greater FC between the MrD bilaterally and left middle cingulate cortex, left middle frontal gyrus, left superior frontal gyrus, left supplementary motor area, and left middle/inferior occipital gyrus. Moreover, the strength of FC between the MrD and regions that showed differences between the PD-MCI and PD-NCI groups was significantly correlated with neuropsychological scores in patients with PD. The current study suggests that MrD dysfunction may contribute to MCI in PD. However, the mechanisms underlying this process require further investigation. Level of Evidence 1. Technical Efficacy Stage 2. J. Magn. Reson. Imaging 2019;50:183-192.

Diagnostic value of T1ρ and T2 mapping sequences of 3D fat-suppressed spoiled gradient (FS SPGR-3D) 3.0-T magnetic resonance imaging for osteoarthritis

Three-dimensional fat-suppressed spoiled gradient magnetic resonance imaging can be used to observe cartilages with high resolution.To quantify and compare the T1ρ and T2 relaxation times of the knee articular cartilage between healthy asymptomatic adults and patients with osteoarthritis (OA).This was a retrospective study of 53 patients with symptomatic OA (6 males and 47 females; aged 57.6 ± 10.0 years) and 26 healthy adults (11 males and 15 females; aged 31.7 ± 12.2 years) from the Ruijin Hospital. T1ρ and T2 relaxation times of knee cartilage were quantified using sagittal multi-echo T1ρ and T2 mapping sequences (3.0-T scanner) and analyzed by receiver operating characteristic (ROC) curve.T1ρ and T2 relaxation times in the OA group were higher than in controls (both P < .01). The sensitivity, specificity, and critical value for differentiating normal from OA cartilage were respectively 92%, 85.6%, and 45.90 ms for T1ρ, and 93.6%, 93.3%, and 50.42 ms for T2. T2 mapping sequence showed a higher area under the ROC curve (AUC) than T1ρ (0.965 vs 0.927, P = .02). The AUC for differentiating normal from Noyes IIA cartilage was 0.922 for T1ρ (cut-off: 46.0; sensitivity: 87.7%; specificity: 89.7%) and 0.954 for T2 (cut-off: 49.5; sensitivity: 91.2%; specificity: 92.3%), with no significant difference between them (P = .08).Both T1ρ and T2 mapping sequences could be used to assess OA cartilage lesions, with T2 mapping sequence demonstrating significant sensitivity for cartilage degeneration. These 2 sequences could also identify early-stage OA cartilage.

245. A protocol set-up for fast brain T1 mapping of subcortical tissues

PurposeThis work is part of a larger cohort study aimed at investigating the long term effects of exposure to manganese [1]. In this study we set up a protocol for brain fast T1 mapping and segmentation of subcortical tissues, in particular globus pallidus (GP), that is reported to be a target tissue for manganese deposition in brain. MethodsThe variable flip angle model was used for T1 mapping. Acquisition protocol, set up on a 3T Siemens Skyra MR system, includes 10 RF spoiled 3D gradient echoes (VIBE) with flip angles from 2° to 30° and a reduced scanned volume to cover GP in the shortest possible time, an extra 30° VIBE covering the whole brain (WB- VIBE), two fast acquisitions with different TEs for B1 map calculation, used to correct nominal flip angles, and a 3D-MPRAGE acquisition of the whole brain with the same WB-WIBE geometry. T1 and error maps were calculated offline with a bespoke Matlab script, checking accuracy with calibrated gels. The most efficient pipeline for post-processing, shown in Fig. 1, is as follows: T1 map calculation of the reduced volume, and zero padding of the missing slices to get the same WB-VIBE volume (WB-T1MAP); 3D-MPRAGE and WB-T1MAP coregistration using the WB-VIBE to 3D transformation matrix (WB-T1MAP-COR); GP automatic segmentation of the 3D-MPRAGE and, with the output mask, GP statistics calculation of the WB-T1MAP-COR. In order to cancel possible partial volume effects, segmented regions were eroded by 1 pixels and T1 results were compared. The protocol was checked on a group of 10 adolescents that were exposed to Mn during childhood. ResultsT1 accuracy was 4.3% (median) and within 13.8% (interquartile distance). GP-T1 average values were 1314,65 ms and 1302,92 ms after erosion, close to the values reported in other papers, with a coefficient of variation respectively decreased from 6.8%, to 5.6%. ConclusionsWe set up a fast and automated T1 mapping protocol with good accuracy and optimised data variability in vivo.

Commissioning of a 4D MRI phantom for use in MR-guided radiotherapy.

Systems for integrated magnetic resonance guided radiation therapy (MRgRT) provide real-time and online MRI guidance for unequaled targeting performance of moving tumors and organs at risk. The clinical introduction of such systems requires dedicated methods for commissioning and routine machine quality assurance (QA). The aim of the study was to develop a commissioning protocol and method for automatic quantification of target motion and geometric accuracy using a 4D MRI motion phantom. The commissioning was performed on a clinically used 3T MR scanner. The phantom was positioned on a flat tabletop overlay using an in-house constructed base plate for a quick and reproducible setup. The torso-shaped phantom body, which was filled with mineral oil as signal generating medium, included a 3D grid structure for image distortion analysis and a cylindrical thru-hole in which a software-controlled moving rod with a hypo-intense background gel and a decentralized hyper-intense target simulated 3D organ motion patterns. To allow for sequence optimization, MR relaxometry was performed to determine the longitudinal T1 and transverse T2 relaxation times of both target and background gel in the movable cylinder. The geometric image distortion was determined as the mean and maximum 3D Euclidean distance (Δmean , Δmax ) of grid points determined by nonrigid registration of a 3D spoiled gradient echo MRI scan and a CT scan. Sinusoidal 1D/2D/3D motion trajectories, varying in amplitude and frequency, as well as an exemplary 1D MR navigator diaphragm motion pattern extracted from a healthy volunteer scan, were scanned by means of 2D cine MRI and 4D MRI. Target positions were automatically extracted from 2D cine MRI using an in-house developed software tool. The base plate enabled a reproducible setup with a deviation of <1mm in all directions. Relaxometry yielded T1 /T2 values for target and background gel of 208.1±2.8/30.5±4.7ms and 871±36/13.4 ± 1.3ms, respectively. The 3D geometric image distortion increased with distance from the magnetic isocenter, with Δmean =0.58±0.30mm and Δmax =1.31mm. The frequencies of the reconstructed motion patterns agreed with the preset values within 0.5%, whereas the reconstructed amplitudes showed a maximum deviation to the preset amplitudes of <0.5mm in AP/LR direction and <0.3mm in IS direction. A method and protocol for commissioning of a 4D MRI motion phantom on a 3T MR scanner for MRgRT was developed. High-contrast and geometrically reliable 2D cine MR images of the phantom's moving target could be obtained. The preset motion parameters could be extracted with sufficient spatio-temporal accuracy from 2D cine MRI in all motion directions. The overall 3D geometric image distortion of <1.31mm within the phantom grid confirms geometric accuracy of the clinically utilized 3D spoiled gradient echo sequence. The method developed can be used for routine QA tests of spatio-temporally resolved MRI data in MRgRT.

Simultaneous estimation of PD, T1 , T2 , T2* , and ∆B0 using magnetic resonance fingerprinting with background gradient compensation.

This study aims to estimate PD, T1 , T2 , T2* , and B0 simultaneously using magnetic resonance fingerprinting (MRF) with compensation of the linearly varying background field. MRF based on fast imaging with steady-state precession (FISP) and multi-echo spoiled gradient (SPGR) schemes are alternatively used, which encode T2 and T2* , respectively. Simulations are performed to determine the appropriate ratio of the FISP and SPGR sections with respect to the T2 and T2* accuracy. Additionally, background field inhomogeneity (Gz ) compensation using z-shim gradients are incorporated into the SPGR section and the dictionary. The background field compensation is tested in the phantom experiment under well-shimmed and poor-shimmed conditions. An in vivo experiment is performed and the estimated parameters are compared before and after Gz compensation. The T1 , T2 , and T2* values from the phantom results are in good agreement with the reference methods under well-shimmed condition. The underestimated T2 and T2* values under poor-shimmed condition are recovered by Gz compensation and the parameters are also in good agreement with the reference methods. In the human brain, T2 and T2* values are restored by Gz compensation in regions where the magnetic field is particularly inhomogeneous, such as near the sinus and ear canals. The proposed FISP and SPGR combined MRF provides a simultaneous estimation of PD, T1 , T2 , T2* , and B0 . By incorporating field inhomogeneity as a gradient term into both the sequence and dictionary, T2 and T2* values can be restored where field inhomogeneity exists.

A three‐dimensional free‐breathing sequence for simultaneous myocardial T1 and T2 mapping

The aim of this study was to develop, test and validate a 3D free-breathing technique for simultaneous measurement of native myocardial T1 and T2 . The proposed 3D technique acquires five fat-suppressed electrocardiogram-triggered respiratory navigator-gated spoiled gradient echo volumes in an interleaved manner. Four volumes are prepared using a combination of nonselective saturation and T2 preparation. One volume is acquired with fully recovered longitudinal magnetization for accuracy during parametric fitting. Performance of the technique was validated through numerical simulations, phantom experiments and in vivo experiments in 15 healthy human subjects. Simulations and phantom experiments show that the measured T1 and T2 are largely insensitive to heart rate. In vivo whole-heart maps with a voxel size of 1.5×1.5×16 mm3 were acquired without parallel imaging within~8 min including respiratory gating efficiency. The in vivo parametric maps were homogeneous (coefficients of variation of left ventricle myocardium were 6.0%±0.8% and 10.2%±3.4% for T1 and T2 maps, respectively), with an average T1 value of 1470±59.2ms and T2 value of 41.6±1.8ms CONCLUSIONS: The proposed 3D technique allows for measurement of whole-heart T1 and T2 with preserved accuracy and precision in a single scan.

In vitro distinction between proinflammatory and antiinflammatory macrophages with gadolinium-liposomes and ultrasmall superparamagnetic iron oxide particles at 3.0T.

Inflammation involves a heterogeneous macrophage population, for which there is no readily available MR assessment method. To assess the feasibility of distinguishing proinflammatory M1 and antiinflammatory M2 macrophages at MRI enhanced with gadolinium liposomes or ultrasmall superparamagnetic iron oxide particles. In vitro. We employed cultured RAW macrophages. M0 macrophages were polarized with lipopolysaccharide (LPS) or interleukin-4 (IL-4), resulting in M1 or M2 macrophages. The macrophages were incubated with gadolinium (±rhodamine) liposomes or iron oxide particles and cell pellets were prepared for MRI. Transverse relaxation rates and quantitative susceptibility were obtained at 3.0T with multiecho turbo spin echo and spoiled gradient echo sequences. MRI results were compared with confocal microscopy, flow cytometry, and expression of endocytosis, M1 and M2 genes. Mann-Whitney and Kruskal-Wallis tests were performed. Higher transverse relaxation rates and susceptibility were observed in M1 than in M2 and M0 macrophages (P < 0.01 both with liposomes and USPIO) and significantly different susceptibility in M2 and M0 macrophages (P < 0.01 both with liposomes and USPIO). These MRI results were confirmed at confocal microscopy and flow cytometry. LPS macrophages displayed M1 gene expression, whereas IL-4 macrophages showed M2 polarization and lower endocytosis gene expression rates. These in vitro results show that it is feasible to distinguish between proinflammatory M1 and antiinflammatory M2 macrophages according to their level of contrast agent uptake at MRI. 1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;49:1166-1173.

Optimization of steady-state free precession MRI for lung ventilation imaging with 19 F C3 F8 at 1.5T and 3T.

Purpose:To optimize 19F imaging pulse sequences for perfluoropropane (C3F8) gas human lung ventilation MRI considering intrinsic in vivo relaxation parameters at both 1.5T and 3T.Methods:Optimization of the imaging parameters for both 3D spoiled gradient (SPGR) and steady‐state free precession (SSFP) 19F imaging sequences with inhaled 79% C3F8% and 21% oxygen was performed. Phantom measurements were used to validate simulations of SNR. In vivo parameter mapping and sequence optimization and comparison was performed by imaging the lungs of a healthy adult volunteer. T1 and T2 * mapping was performed in vivo to optimize sequence parameters for in vivo lung MRI. The performance of SSFP and SPGR was then evaluated in vivo at 1.5T and 3T.Results:The in vivo T2 * of C3F8 was shown to be dependent upon lung inflation level (2.04 ms ± 36% for residual volume and 3.14 ms ± 28% for total lung capacity measured at 3T), with lower T2 * observed near the susceptibility interfaces of the diaphragm and around pulmonary blood vessels. Simulation and phantom measurements indicate that a factor of ~2‐3 higher SNR can be achieved with SSFP when compared with optimized SPGR. In vivo lung imaging showed a 1.7 factor of improvement in SNR achieved at 1.5T, while the theoretical improvement at 3T was not attained due to experimental SAR constraints, shorter in vivo T1, and B0 inhomogeneity.Conclusion:SSFP imaging provides increased SNR in lung ventilation imaging of C3F8 demonstrated at 1.5T with optimized SSFP similar to the SNR that can be obtained at 3T with optimized SPGR.

Functional lung imaging with transient spoiled gradient echo.

To introduce an alternative framework for perfusion and ventilation lung imaging at 3T using transient spoiled gradient echo (tSPGR) acquisitions. Sets of coronal 2D time-resolved lung image series were acquired in 5 healthy volunteers using tSPGR and compared with contemporary SPGR and ultrafast balanced SSFP (uf-bSSFP) implementations at 1.5T and 3T. Sequence parameters and view ordering were optimized for tSPGR to yield maximum signal intensity in the lung tissue. Signal-to-noise ratio and contrast-to-noise ratio analyses were performed in all acquired tSPGR, SPGR, and uf-bSSFP data sets. Matrix pencil decomposition was applied to generate functional parameter maps, including fractional ventilation, relative perfusion, and blood arrival time. For the lung, the signal intensity of tSPGR imaging was maximal for minimal TR and TE settings of 0.99ms and 0.43ms, respectively. Moreover, low RF spoiling increments in combination with a centric view ordering resulted in a further signal-to-noise ratio increase of about 30% to 40%. The average signal-to-noise ratio in the lung parenchyma was 73.3 for uf-bSSFP, 38.1 for tSPGR, 20.7 for SPGR at 1.5T, and 31.2 for uf-bSSFP, 35.6 for tSPGR, and 21.3 for SPGR at 3T. The average ventilation and perfusion contrast-to-noise ratio was 33.2 and 36.2 for uf-bSSFP, 15.4 and 12.5 for tSPGR, 13.5 and 4.1 for SPGR at 1.5T, and 16.5 and 11.3 for uf-bSSFP, 29.7 and 50.8 for tSPGR, and 22.4 and 16.5 for SPGR at 3T, respectively. At 3T, application of balanced SSFP is limited, so tSPGR offers an alternative framework for successful lung function assessment using matrix pencil MRI.