Spoiled Gradient Research Articles

Improved detection of molecularly targeted iron oxide particles in mouse brain using B0 field stabilised high resolution MRI

PurposeHigh resolution multi-gradient echo (MGE) scanning is typically used for detection of molecularly targeted iron oxide particles. The images of individual echoes are often combined to generate a composite image with improved SNR from the early echoes and boosted contrast from later echoes. In 3D implementations prolonged scanning at high gradient duty cycles induces a B0 shift that predominantly affects image alignment in the slow phase encoding dimension of 3D MGE images. The effect corrupts the composite echo image and limits the image resolution that is realised. A real-time adaptive B0 stabilisation during respiration gated 3D MGE scanning is shown to reduce image misalignment and improve detection of molecularly targeted iron oxide particles in composite images of the mouse brain. MethodsAn optional B0 measurement block consisting of a 16 μs hard pulse with FA 1°, an acquisition delay of 3.2 ms, followed by gradient spoiling in all three axes was added to a respiration gated 3D MGE scan. During the acquisition delay of each B0 measurement block the NMR signal was routed to a custom built B0 stabilisation unit which mixed the signal to an audio frequency nominally centred around 1000 Hz to enable an Arduino based single channel receiver to measure frequency shifts. The frequency shift was used to effect correction to the main magnetic field via the B0 coil. The efficacy of B0 stabilisation and respiration gating was validated in vivo and used to improve detection of molecularly targeted microparticles of iron oxide (MPIO) in a mouse model of acute neuroinflammation. ResultsWithout B0 stabilisation 3D MGE image data exhibit varying mixtures of translation, scaling and blurring, which compromise the fidelity of the composite image. The real-time adaptive B0 stabilisation minimises corruption of the composite image as the images from the different echoes are properly aligned. The improved detection of molecularly targeted MPIO easily compensates for the scan time penalty of 14% incurred by the B0 stabilisation method employed. Respiration gating of the B0 measurement and the MRI scan was required to preserve high resolution detail, especially towards the back of the brain. ConclusionsHigh resolution imaging for the detection of molecularly targeted iron oxide particles in the mouse brain requires good stabilisation of the main B0 field, and can benefit from a respiration gated image acquisition strategy.

High-Grade Soft-Tissue Sarcomas: Can Optimizing Dynamic Contrast-Enhanced MRI Postprocessing Improve Prognostic Radiomics Models?

Heterogeneity on pretreatment dynamic contrast-enhanced (DCE)-MRI of sarcomas may be prognostic, but the best technique to capture this characteristic remains unknown. To investigate the best method to extract prognostic data from baseline DCE-MRI. Retrospective, single-center. Fifty consecutive uniformly-treated adults with nonmetastatic high-grade sarcomas. 1.5T; T2 -weighted-imaging, fat-suppressed fast spoiled gradient echo DCE-MRI. Ninety-two radiomics features (RFs) were extracted at each DCE-MRI phase (11, from t = 0-88 sec). Relative changes in RFs (rRFs) since the acquisition baseline were calculated (11 × 92 rRFs). Curves of rRF as function of time postinjection were integrated (92 integrated-rRFs [irRFs]). Ktrans and area under the time-intensity curve at 88-sec parametric maps were computed and 2 × 92 parametric-RFs (pRFs) were extracted. Five DCE-MRI-based radiomics models were built on: an RFs subset (32 sec, 64 sec, 88 sec); all rRFs; all irRFs; and all pRFs. Two models were elaborated as reference, on: conventional radiological features; and T2 -WI RFs. A common machine-learning approach was applied to radiomics models. Features with P < 0.05 at univariate analysis were entered in a LASSO-penalized Cox regression including bootstrapped 10-fold cross-validation. The resulting radiomics scores (RScores) were dichotomized per their median and entered in multivariate Cox models for predicting metastatic relapse-free survival. Models were compared with integrative area under the curve (AUC) and concordance index. Only dichotomized RScores from models based on rRFs subset, all rRFS and irRFS correlated with prognostic (P = 0.0107-0.0377). The models including all rRFs and irRFs had the highest c-index (0.83), followed by the radiological model. The radiological model had the highest integrative AUC (0.87), followed by models including all rRFs and irRFs. The radiological and full rRFs models were significantly better than the T2 -based radiomics model (P = 0.02). The initial DCE-MRI of STS contains prognostic information. It seems more relevant to make predictions on rRFs instead of pRFs. Evidence Level: 3 Technical Efficacy: 3 J. Magn. Reson. Imaging 2020;52:282-297.

MRI-based assessment of proximal femur strength compared to mechanical testing.

Half of the women who sustain a hip fracture would not qualify for osteoporosis treatment based on current DXA-estimated bone mineral density criteria. Therefore, a better approach is needed to determine if an individual is at risk of hip fracture from a fall. The objective of this study was to determine the association between radiation-free MRI-derived bone strength and strain simulations compared to results from direct mechanical testing of cadaveric femora. Imaging was conducted on a 3-Tesla MRI scanner using two sequences: one balanced steady-state free precession sequence with 300μm isotropic voxel size and one spoiled gradient echo with anisotropic voxel size of 234×234×1500μm. Femora were dissected free of soft-tissue and 4350-ohm strain-gauges were securely applied to surfaces at the femoral shaft, inferior neck, greater trochanter, and superior neck. Cadavers were mechanically tested with a hydraulic universal test frame to simulate loading in a sideways fall orientation. Sideways fall forces were simulated on MRI-based finite element meshes and bone stiffness, failure force, and force for plastic deformation were computed. Simulated bone strength metrics from the 300μm isotropic sequence showed strong agreement with experimentally obtained values of bone strength, with stiffness (r=0.88, p=0.0002), plastic deformation point (r=0.89, p<0.0001), and failure force (r=0.92, p<0.0001). The anisotropic sequence showed similar trends for stiffness, plastic deformation point, and failure force (r=0.68, 0.70, 0.84; p=0.02, 0.01, 0.0006, respectively). Surface strain-gauge measurements showed moderate to strong agreement with simulated magnitude strain values at the greater trochanter, superior neck, and inferior neck (r=-0.97, -0.86, 0.80; p≤0.0001, 0.003, 0.03, respectively). The findings from this study support the use of MRI-based FE analysis of the hip to reliably predict the mechanical competence of the human femur in clinical settings.

Evaluation of Long-term Fluctuation of Geometric Distortion in MRI for Radiation Therapy Planning by Using an Automatic Analysis Tool

High tissue contrast in magnetic resonance imaging (MRI) allows better radiotherapy planning. However, geometric distortion in MRI induces inaccuracies affecting such planning, making it necessary to evaluate the characteristics of such geometric distortion. Although many studies have considered geometric distortion, most of these involved measurements performed only a few times. In this study, we evaluated MRI device-specific geometric distortion over long term and measured its variation by using an automatic analysis tool. The result showed that geometric distortion increased with distance from the center along both lateral and longitudinal directions. Specifically, the average distortion rate and average diameter error over the full measurement period increased by up to 1.02% and 1.96 mm, respectively, when using T1 weighted Image (WI) 3D fast spoiled gradient echo (FSPGR) at R15. In the case of T2 WI 2D fast spin echo (FSE) at R15, the standard deviation of the distortion rate and diameter error increased up to 0.38%, 0.72 mm, respectively. We conclude that periodic quality assurance of geometric distortion should be performed in order to maintain geometric distortion within allowable values.

Clinical experience regarding safety and diagnostic value of cardiovascular magnetic resonance in patients with a subcutaneous implanted cardioverter/defibrillator (S-ICD) at 1.5\u2009T

BackgroundCardiovascular magnetic resonance (CMR) studies in patients with implanted cardioverter/defibrillators (ICD) are increasingly required in daily clinical practice. However, the clinical experience regarding the feasibility as well as clinical value of CMR studies in patients with subcutaneous ICD (S-ICD) is still limited. Besides safety issues, image quality and analysis can be impaired primarily due the presence of image artefacts associated with the generator.MethodsTwenty-three patients with an implanted S-ICD (EMBLEM, Boston Scientific, Marlborough, Massachusetts, USA; MR-conditional) with suspected cardiomyopathy and/or myocarditis underwent multi-parametric CMR imaging. Studies were performed on a 1.5 T CMR scanner after device interrogation and comprised standard a) balanced steady state free precession cine, b) T2 weighted-edema, c) velocity-encoded cine flow, d) myocardial perfusion, e) late-gadolinium-enhancement (LGE)-imaging and f) 3D-CMR angiography of the aorta. In case of substantial artefacts, alternative CMR techniques such as spoiled gradient-echo cine-sequences and wide-band inversion-recovery LGE (wb-LGE) sequences were applied.ResultsSuccessful CMR studies could be performed in all patients without any case of unexpected early termination or relevant technical complication other than permanent loss of the S-ICD system beeper volume in 52% of our patients. Assessment of cine-CMR images was predominantly impaired in the left ventricular (LV) anterior, lateral and inferior wall segments and a switch to spoiled gradient echo-based cine-CMR allowed an accurate assessment of cine-images in N = 17 (74%) patients with only limited artefacts. Hyperintensity artefacts in conventional LGE-images were predominantly observed in the LV anterior, lateral and inferior wall segments and image optimisation by use of the wb-LGE was helpful in 15 (65%) cases. Aortic flow measurements and 3D-CMR angiography were assessable in all patients Perfusion imaging artefacts precluded a meaningful assessment in at least one half of the patients. A benefit in clinical-decision making was documented in 17 (74%) patients in the present study.ConclusionSafe 1.5 T CMR imaging was possible in all patients with an S-ICD, though the majority had permanent loss of the S-ICD beeper volume. Achieving good image quality may be challenging in some patients - particularly for perfusion imaging. Using spoiled gradient echo-based cine-sequences and wb-LGE sequences may help to reduce the extent of artefacts, thereby allowing accurate cardiac assessment. Thus, 1.5 T CMR studies should not be withhold in patients with S-ICD for safety concerns and/or fear of extensive imaging artefacts precluding successful image analysis.

Current Status of Diagnosis and Management for Functioning Pituitary Tumors: Part I.

Pituitary adenomas (PA) account for approximately 15% of all intracranial neoplasms. Pituitary adenomas can be of different subtypes based on the cell of origin or associated hormone hypersecretion (non-functioning pituitary adenoma, prolactinoma, somatotropinoma, corticotropinoma, thyrotropinoma, and gonadotropinoma). Functioning PAs are associated with relatively higher morbidity and mortality because of associated hormone hypersecretion syndromes. Diagnosis of functioning PA is established by biochemical confirmation of hormone hypersecretion and demonstration of a pituitary lesion on imaging. Trans-sphenoidal surgical resection of tumor represents the first-line treatment for most tumor types, except for prolactinomas where medical therapy with dopamine agonists is preferred. Radiotherapy (RT) and medical therapy are the other options for the management of PA. It is important to individualize treatment options based on tumor type, patient's clinical condition, expertise of surgeon, affordability and patient preferences. In the first part of this series, we review the presentation and management of adrenocorticotropic hormone secreting, gonadotropin secreting and aggressive PA. Despite several recent advances, the diagnosis and management of Cushing's disease is still a challenge. Modifications in magnetic resonance imaging techniques like volume interpolated 3D spoiled gradient echo sequence have improved the sensitivity to detect microcorticotropinomas. Pituitary RT, preferably conventional RT, is a useful second-line therapy for the management of CD. Besides the conventional drugs, few drugs such as pasireotide and osilodrostat have been approved by US FDA recently, whereas several others are in pipeline which provide hope for a better outcome in CD patients. Temozolomide is a useful drug for the management of aggressive PA.

Normal Glenoid Ossification in Pediatric and Adolescent Shoulders Mimics Bankart Lesions: A Magnetic Resonance Imaging–Based Study

The purpose of this descriptive study was to define patterns of ossification and fusion of growth centers around the pediatric and adolescent glenoid as a function of age using 3-dimensional, frequency-selective, fat-suppressed spoiled gradient recalled echo magnetic resonance (MR) imaging sequences, with a particular focus on the anterior glenoid rim because of its clinical relevance as a potential confounder of glenohumeral instability. Picture Archiving and Communication System records at an urban academic tertiary care orthopaedic facility from October 2005 to December 2018 were queried for shoulder MRI in patients aged 9 to 17years. Patients were excluded if they had any diagnoses that could alter glenoid development. All images were independently evaluated by a musculoskeletal fellowship-trained radiologist. Secondary ossification centers were characterized as cartilage anlage, ossified, or fused at 3 anatomic sites: the anterior glenoid rim, coracoid, and superior glenoid rim. A total of 250MR examinations (143 males, 107 females) were assessed in this study. The glenoid develops in a predictably sequential manner with ossification at the anterior glenoid rim lagging behind the coracoid and superior glenoid rim. The earliest age of anterior glenoid rim ossification was 11years for both males (range 11-17) and females (range 11-12). Anterior glenoid rim ossification peaked at age 16 among males (34.8%, 8/23) and age 11 among females (27.3%, 3/11). Glenoid ossification and fusion progress in a predictable and chronological manner. This pattern should be used as a guideline when interpreting pediatric shoulder MRI examinations. In particular, an anterior glenoid ossification center should not be confused with an anterior glenoid injury (e.g., Bankart lesion), particularly in males 11 to 17years old and females 11 to 12years old. IV (case series).

Validation of Automated Perfusion-Weighted Phase-Resolved Functional Lung (PREFUL)-MRI in Patients With Pulmonary Diseases.

Perfusion-weighted (Qw) noncontrast-enhanced proton lung MRI is a promising technique for assessment of pulmonary perfusion, but still requires validation. To improve perfusion-weighted phase-resolved functional lung (PREFUL)-MRI, to validate PREFUL with perfusion single photon emission computed tomography (SPECT) as a gold standard, and to compare PREFUL with dynamic contrast-enhanced (DCE)-MRI as a reference. Retrospective. Twenty patients with chronic obstructive pulmonary disease (COPD), 14 patients with cystic fibrosis (CF), and 21 patients with chronic thromboembolic pulmonary hypertension (CTEPH) were included. For PREFUL-MRI, a spoiled gradient echo sequence and for DCE-MRI a 3D time-resolved angiography with stochastic trajectories sequence were used at 1.5T. PREFUL-MRI coronal slices were acquired in free-breathing. DCE-MRI was performed in breath-hold with injection of 0.03 mmol/kg bodyweight of gadoteric acid at a rate of 4 cc/s. Perfusion SPECT images were obtained for six CTEPH patients. Images were coregistered. An algorithm to define the appropriate PREFUL perfusion phase was developed using perfusion SPECT data. Perfusion defect percentages (QDP) and Qw-values were calculated for all methods. For PREFUL quantitative perfusion values (PREFULQ ) and for DCE pulmonary blood flow (PBF) was calculated. Obtained parameters were assessed using Pearson correlation and Bland-Altman analysis. Qw-SPECT correlated with Qw-DCE (r = 0.50, P < 0.01) and Qw-PREFUL (r = 0.47, P < 0.01). Spatial overlap of QDP maps showed an agreement ≥67.7% comparing SPECT and DCE, ≥64.1% for SPECT and PREFUL, and ≥60.2% comparing DCE and PREFUL. Significant correlations of Qw-PREFUL and Qw-DCE were found (COPD: r = 0.79, P < 0.01; CF: r = 0.77, P < 0.01; CTEPH: r = 0.73, P < 0.01). PREFULQ /PBF correlations were similar/lower (CF, CTEPH: P > 0.12; COPD: P < 0.01) compared to Qw-PREFUL/DCE correlations. PREFULQ -values were higher/similar compared to PBF-values (COPD, CF: P < 0.01; CTEPH: P = 0.026). The automated PREFUL algorithm may allow for noncontrast-enhanced pulmonary perfusion assessment in COPD, CF, and CTEPH patients comparable to DCE-MRI. Level of Evidence 3 Technical Efficacy Stage 2 J. Magn. Reson. Imaging 2020;52:103-114.

Across-vendor standardization of semi-LASER for single-voxel MRS at 3T.

The semi-adiabatic localization by adiabatic selective refocusing (sLASER) sequence provides single-shot full intensity signal with clean localization and minimal chemical shift displacement error and was recommended by the international MRS Consensus Group as the preferred localization sequence at high- and ultra-high fields. Across-vendor standardization of the sLASER sequence at 3 tesla has been challenging due to the B1 requirements of the adiabatic inversion pulses and maximum B1 limitations on some platforms. The aims of this study were to design a short-echo sLASER sequence that can be executed within a B1 limit of 15 μT by taking advantage of gradient-modulated RF pulses, to implement it on three major platforms and to evaluate the between-vendor reproducibility of its perfomance with phantoms and in vivo. In addition, voxel-based first and second order B0 shimming and voxel-based B1 adjustments of RF pulses were implemented on all platforms. Amongst the gradient-modulated pulses considered (GOIA, FOCI and BASSI), GOIA-WURST was identified as the optimal refocusing pulse that provides good voxel selection within a maximum B1 of 15 μT based on localization efficiency, contamination error and ripple artifacts of the inversion profile. An sLASER sequence (30 ms echo time) that incorporates VAPOR water suppression and 3D outer volume suppression was implemented with identical parameters (RF pulse type and duration, spoiler gradients and inter-pulse delays) on GE, Philips and Siemens and generated identical spectra on the GE 'Braino' phantom between vendors. High-quality spectra were consistently obtained in multiple regions (cerebellar white matter, hippocampus, pons, posterior cingulate cortex and putamen) in the human brain across vendors (5 subjects scanned per vendor per region; mean signal-to-noise ratio > 33; mean water linewidth between 6.5 Hz to 11.4 Hz). The harmonized sLASER protocol is expected to produce high reproducibility of MRS across sites thereby allowing large multi-site studies with clinical cohorts.

Balanced steady-state free precession thoracic imaging with half-radial dual-echo readout on smoothly interleaved archimedean spirals.

To investigate the prospects of a minimal-TR half-radial dual-echo balanced steady-state free precession (bSSFP) acquisition for high-resolution and artifact-free thoracic imaging at 1.5T. Feasibility of bSSFP imaging using isotropic half-radial dual-echo (hr-de) projections with TE1 /TE2 /TR of 0.12/1.18/1.39 ms acquired along Archimedean spiral trajectories was demonstrated for phantoms and in vivo thorax scans at 1.5T. The centered-out projection offers an ultra-short echo (UTE) comparable to contemporary spoiled gradient echo (SPGR) UTE radial acquisitions used for the assessment of chest morphology. Signal intensities of hr-de-bSSFP were measured and compared to UTE-SPGR in a phantom and for parenchyma and blood in vivo and compared to theory. For the lung parenchyma and the blood, hr-de-bSSFP provided more than 4 times higher signal intensity than contemporary UTE-SPGR imaging. The measured hr-de-bSSFP and UTE-SPGR signal ratios were in the agreement with theoretically simulated values. Overall, the very short TR of hr-de-bSSFP successfully mitigated off-resonance artifacts offering high-quality breath-hold thoracic imaging at isotropic resolution of 1.7 mm. The application of a smooth interleaved spiral trajectory for half-radial readouts improved the robustness of hr-de-bSSFP to cardiac motion. Thoracic hr-de-bSSFP offers artifact-free chest images with considerably improved signal intensity as compared to contemporary UTE-SPGR imaging at 1.5T.

Resting-State Functional MRI Study: Connection Strength of Brain Networks in DR Patients.

PurposeTo explore the functional connection strength (FCS) changes of brain networks in diabetic retinopathy (DR) patients and uncover the underlying mechanism.Methods and MaterialsTwenty-one patients with DR and 21 age- and sex-matched healthy controls were enrolled from August 2012 to September 2014. Subjects were scanned using 3T MR with blood-oxygen-level dependent (BOLD) and 3-dimension fast spoiled gradient echo (3D-FSPGR) sequences. MR data was analyzed via preprocessing and functional network construction. After a group comparison, components of brain networks with significant group differences were extracted and the FCS of the brain network was evaluated. The brain areas were compared between patients and controls. P-values less than 0.05 were considered statistically significant. Connection strength was evaluated with alphasim, P<0.01.ResultsThe component maps of altered brain networks with quantified FCS were obtained in DR patients, demonstrating more disconnections mainly in the bilateral Heschl's gyrus, left cuneus, left occipital lobe, bilateral amygdala, left parahippocampal, bilateral fusiform, and left superior parietal in the patients group compared to the healthy controls (P<0.01), while compensations may occur in the frontal-cingulum region, as well as among the right caudate, left thalamus, left inferior temporal lobe, and middle orbital frontal lobe.ConclusionBrain network connections, decreased in the brain areas of which in charging with cognition and visual function, suggests that DR patients might have cognitive decline and visual function loss. However, there might be a frontal compensatory circle in patients with DR.

Utility of dynamic MRA in the evaluation of male erectile dysfunction.

To assess the efficacy of time-resolved MR angiography (MRA) in evaluating penile vasculature in patients with clinically suspected vascular anomalies contributing to their erectile dysfunction correlating with penile doppler ultrasound (PDUS) findings and clinical outcomes after surgical intervention. Men (n = 26) with signs of early vascular shunting on PDUS underwent time-resolved, contrast-enhanced (0.1mMol/kg gadobutrol at 1ml/s followed by saline flush) 3-dimensional spoiled gradient echo T1-weighted MRA sequence performed over 3min with 4.6s frame rate after intracavernosal injection of an erectogenic agent. Additional T1- and T2-weighted sequences were performed for anatomic co-localization and tissue characterization. MRA images were evaluated for early filling of draining veins as well as arteriovenous malformations and fistulas and correlated with findings at surgery. 29 MRA examinations on 26 patients (mean age 39years) demonstrated abnormal early venous drainage (n = 22) as well as diminutive/delayed cavernosal enhancement (n = 3), incomplete tumescence (n = 2), and combined arterial inflow/venous outflow disease (n = 1). The MRA had a concordance of 85.2% at determining the presence, or lack thereof of a shunt/AVM when compared to PDUS. Time-resolved MRA allows for both temporal and spatial resolution with visualization of both arterial and venous abnormalities which may be suggested with a screening PDUS examination. This technique allows us to provide detailed anatomic information prior to any surgical intervention.

Unipolar MR elastography: Theory, numerical analysis and implementation.

In MR elastography (MRE), zeroth moment balanced motion‐encoding gradients (MEGs) are incorporated into MRI sequences to induce a phase shift proportional to the local displacement caused by external actuation. To maximize the signal‐to‐noise ratio (SNR), fractional encoding is employed, i.e., the MEG duration is reduced below the wave period. Here, gradients encode primarily the velocity of the motion‐reducing encoding efficiency. Thus, in GRE‐MRE, T2* decay and motion sensitivity have to be balanced, imposing a lower limit on repetition times (TRs).We propose to use a single trapezoidal gradient, a “unipolar gradient”, to directly encode spin displacement. Such gradients cannot be used in conventional sequences as they exhibit a large zeroth moment and dephase magnetization. By time‐reversing a spoiled SSFP sequence, the spoiling gradient becomes an efficient unipolar MEG. The proposed “unipolar MRE” technique benefits from this approach in three ways: first, displacement encoding is split over multiple TRs increasing motion sensitivity; second, spoiler and MEG coincide, allowing a reduction in TR; third, motion sensitivity of a typical unipolar lobe is of an order of magnitude higher than a bipolar MEG of equal duration.In this work, motion encoding using unipolar MRE is analyzed using the extended phase graph (EPG) formalism with a periodic motion propagator. As an approximation, the two‐transverse TR approximation for diffusion‐weighted SSFP is extended to incorporate cyclic motion. A complex encoding efficiency metric is introduced to compare the displacement fields of unipolar and conventional GRE‐MRE sequences in both magnitude and phase. The derived theoretical encoding equations are used to characterize the proposed sequence using an extensive parameter study. Unipolar MRE is validated against conventional GRE‐MRE in a phantom study showing excellent agreement between measured displacement fields. In addition, unipolar MRE yields significantly increased octahedral shear strain‐SNR relative to conventional GRE‐MRE and allows for the recovery of high stiffness inclusions, where conventional GRE‐MRE fails.

Combined gadoxetic acid and gadobenate dimeglumine enhanced liver MRI: a parameter optimization study.

To demonstrate the feasibility of combined delayed-phase gadoxetic acid (GA) and gadobenate dimeglumine (GD) enhanced liver MRI for improved detection of liver metastases, and to optimize contrast agent dose, timing, and flip angle (FA). Fourteen healthy volunteers underwent liver MRI at 3.0T at two visits during which they received two consecutive injections: 1. GA (Visit1 = 0.025mmol/kg; Visit 2 = 0.05mmol/kg) and 2. GD (both visits = 0.1mmol/kg) 20min after GA administration. Two sub-studies were performed: Experiment-1 Eight subjects underwent multi-phase breath-held 3D-fat-saturated T1-weighted spoiled gradient echo (SGRE) imaging to determine the optimal imaging window for the combined GA + GD protocol to create a homogeneously hyperintense liver and vasculature ("plain-white-liver") with maximum contrast to muscle which served as a surrogate for metastatic lesions in both experiments. Experiment-2 Six subjects underwent breath-held 3D-fat-saturated T1-weighted SGRE imaging at three different FA to determine the optimal FA for best image contrast. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were evaluated. Experiment-1 The combined GA + GD protocol created a homogeneously hyperintense liver and vasculature with maximum CNR liver/muscle at approximately 60-120s after automatic GD-bolus detection. Experiment-2 Flip angles between 25° and 35° at a dose of 0.025mmol/kg GA provided the best combination that minimized liver/vasculature CNR, while maximizing liver/muscle CNR. CNR performance to achieve a "plain-white-liver" was superior with 0.025mmol/kg GA compared to 0.05mmol/kg. Combined GA + GD enhanced T1-weighted MRI is feasible to achieve a homogeneously "plain-white-liver". Future studies need to confirm that this protocol can improve sensitivity of liver lesion detection in patients with metastatic liver disease.

Comparative evaluation of dural venous sinuses and cerebral veins using contrast-enhanced spoiled gradient recalled echo and time-of-flight magnetic resonance venography

AbstractBackground/Aims:In the present study, dural venous sinuses and cerebral veins were examined using 3D SPGR MRV and 2D TOF MRV. These methods were compared in terms of detectability of venous structures and their diameters. Methods:A total of 110 patients(66 female and 44 male) who had contrast-enhanced 3D SPGR MRV and 2D TOF MRV examinations using a 1.5 T MRI machine in May 2008-June 2011 period were included in the present study. Diameters of dural venous sinuses and veins were measured at three different planes at a position 1cm distal to the site they drained into, and average values were used. Both MRV methods were compared to reveal whether the diameters calculated were different in age groups and between genders.Results:SSS, bilateral TS’s, right sigmoid sinus, Galen vein and bilateral ICV’s all could be determined using 3D SPGR MRV. Not all dural venous sinuses and veins other than right sigmoid sinus could be visualized in all patients using 2D TOF MRV.There were significant differences between the two examinations for SSS and ISS, bilateral TS and sigmoid sinuses, SS, bilateral Labbe and ICV and Galen vein diameters(p&amp;lt;0.05) Diameters of dural venous sinuses and cortical veins were generally measured larger by 3D SPGR MRV compared to 2D TOF MRV.Conclusions:In conclusion, differences could be observed between the two MRV examinations for detectability and diameters of intracranial venous structures. Evaluation of intracranial venous structures should not be carried out using only 2D TOF MRV.

Steady‐state imaging with inhomogeneous magnetization transfer contrast using multiband radiofrequency pulses

PurposeInhomogeneous magnetization transfer (ihMT) is an emerging form of MRI contrast that may offer high specificity for myelinated tissue. Existing ihMT and pulsed MT sequences often use separate radiofrequency pulses for saturation and signal excitation. This study investigates the use of nonselective multiband radiofrequency pulses for simultaneous off‐resonance saturation and on‐resonance excitation specifically for generation of ihMT contrast within rapid steady‐state pulse sequences.Theory and MethodsA matrix‐based signal modeling approach was developed and applied for both balanced steady state free precession and spoiled gradient echo sequences, accounting specifically for multiband pulses. Phantom experiments were performed using a combination of balanced steady state free precession and spoiled gradient echo sequences, and compared with model fits. A human brain imaging exam was performed using balanced steady state free precession sequences to demonstrate the achieved contrast.ResultsA simple signal model derived assuming instantaneous radiofrequency pulses was shown to agree well with full integration of the governing equations and provided fits to phantom data for materials with strong ihMT contrast (PL161 root mean square error = 0.9%, and hair conditioner root mean square error = 2.4%). In vivo ihMT ratio images showed the expected white matter contrast that has been seen by other ihMT investigations, and the observed ihMT ratios corresponded well with predictions.ConclusionsihMT contrast can be generated by integrating multiband radiofrequency pulses directly into both spoiled gradient echo and balanced steady state free precession sequences, and the presented signal modeling approach can be used to understand the acquired signals.

Effect of intravenously injected gadolinium-based contrast agents on functional lung parameters derived by PREFUL MRI.

To evaluate the influence of intravenously administered gadolinium-based contrast agents on functional ventilation and perfusion parameters derived by phase-resolved functional lung (PREFUL) MRI. Fourteen participants underwent functional MRI at 1.5T using a 2D spoiled gradient echo sequence during free breathing. Three data sets of PREFUL images were obtained-the 1st data set was acquired in mean 33:46 min (SD = 6:20 min) prior, the 2nd and 3rd data sets 43 and 91 s (both SD = 1.9 s), respectively, after i.v. application of gadobutrol. Full respiratory and cardiac cycles were reconstructed and functional parameters of regional ventilation (RV), perfusion (Q), and quantified perfusion (QQuant ) together with perfusion-defected percentages (QDP), ventilation-defected percentages (VDP), and ventilation-perfusion match (VQM) were calculated and compared for systematic differences between the acquired data sets. RV- and Q-values presented no significant alteration after gadobutrol administration. Consequently, QDP, VDP, and VQ maps were not significantly different. Sørensen-Dice coefficients of QDP and VDP maps between the different series varied up to ±9%. QQuant was significantly increased after the application of gadobutrol (1st vs. 2nd series, P = 0.0021; 1st vs. 3rd, P = 0.0188), which can be explained by the velocity-dependent signal in the completely blood-filled voxel (ROI of the aorta) after shortening of T1 relaxation time (1st vs. 2nd series, P = 0.0003; 1st vs. 3rd series, P = 0.0008). Except for quantified perfusion, all evaluated functional parameters including ventilation- and perfusion-weighted maps derived by PREFUL MRI were independent of gadolinium-based contrast agents, which is important for the design of MRI protocols in future studies.

A Novel 3D-Printed Patient Positioning Platform to Accommodate Curved Couch of MR Scanner Optimizes Precision Treatment Planning Workflow for Abdominal Radiotherapy.

Magnetic Resonance Imaging (MR) is increasingly used in treatment planning (TP) owing to superior soft tissue contrast versus computed tomography (CT). Organ deformation in patient positioning on a curved MR couch versus a flat CT couch causes registration difficulties. This may lead to contour errors and tumor volume misjudgment, particularly in organs poorly visualized on CT (i.e. liver). MR-based simulation systems (MR-BSS) address this issue but are not widely available. In this study, we fabricated a 3D-printed platform (3D-PP) adapted to the MR couch and body array to enable scans in the TP position and optimize MR-guided TP in the absence of a dedicated MR-BSS. We demonstrate that a 3D-PP is low cost, does not interfere with image quality, and is easily implemented by radiology staff. The 3D-PP was drafted with computer-aided design to fit the table arc and 12 channel body array coil of a 1.5 T, 70 cm wide bore, MR scanner. The 3D-PP creates a flat surface to position an immobilization vacuum bag typically used in treatment. The 3D-PP consists of ¼” thick deck and 3/32” thick alignment wings mounted on ten risers. The deck and alignment wings are polyoxymethylene homopolymer laser-cut with a contact-free CO2 beam. Risers are fabricated from polylactide in a thermoplastic 3D printer. A urethane immobilization vacuum cushion (88 x 55 cm, 15 L fill) was fabricated for an 8-channel upper annular MR phantom. CT was acquired in an 85 cm bore simulation CT (120kVp, 512x512 in-plane dimensions, 0.11cm x 0.11cm pixel size, 2mm thickness). Standard body MR sequences were done including single shot fast spin echo (SS-FSE), 3D fast spoiled gradient echo with fat suppression(FSPGR FS), T2 fat suppression(T2 FS), balanced steady-state free precession (BSSFP), dual echo fast spin echo(DE FSE), and diffusion weight imaging (DWI). MR and CT scans were exported to a treatment planning system and fused using a local correlation algorithm capable of both rigid and deformable registration. An anthropomorphic phantom and quality control devices were employed for MR scans. SS-FSE, FSPGR, FSPGR FS, T2 FS, BSSFP, DEFSE, and DWI were analyzed to determine the effect of any artifacts contributed by the 3D-PP. Neither appreciable signal loss nor artifact were observed on any scan. Each MR-CT fusion required negligible computation time (< 2 seconds). In-plane registration was within sub-pixel accuracy for every slice in each sequence. We report a new, low cost approach to optimize MR-guided TP. A 3D-PP enables MR scans in the simulated TP position without appreciable loss of image quality or interruption of radiology workflow. A 3D-PP in a 70 cm wide bore MR system accommodates most treatment positions, including wing board. We are implementing this process into our abdominal SBRT workflow. The 3D-PP design and fabrication can be modified for the workflow of most clinics.

Feasibility Study of Simultaneous MR and 4D Ultrasound Imaging for IGRT

This work aimed to assess the feasibility of simultaneous MR and ultrasound image acquisition of healthy volunteers as part of a cost-effective and non-invasive real-time motion management solution for liver image-guided radiotherapy (IGRT). Pre-treatment simultaneous ultrasound and MR image datasets will be used to characterize respiratory motion states of salient features during free-breathing image acquisitions. These features will be tracked during treatment using ultrasound and mapped to the pre-treatment dataset to provide real-time motion management. While other motion management solutions exist, many have one or more drawbacks such as employing a high cost system, requiring invasive implants for imaging, adding dose to the patient, or potentially compromising on accuracy by utilizing optical tracking of external motion. Nine healthy volunteers were included in this study. For this IGRT project, we developed the first hands-free, MR-compatible, and real-time e4D ultrasound probe. The maximum depth is 18 cm with 2 mm lateral resolution at 7 cm depth. In 3D mode at 18 cm depth, the frame rate is 4 fps. The ultrasound was positioned either sub- or intercostally in order to view vasculature in the liver and a strap technique was utilized for probe stabilization. For this study, the harmonic mode (1.7/3.3 MHz) was employed. A fast spoiled gradient echo sequence (FSPGR) was used to obtain multi-phase 2D sagittal image slices. Nine consecutive sagittal slices were acquired for each volunteer. During acquisition, both datasets were streamed to an external machine for processing and analysis. After the scan, the data was synchronized using temporal image information. The image data was then analyzed using ITK-Snap and DICOM Slicer. Simultaneous ultrasound and MR images were successfully acquired and synchronized from nine volunteers. There were no major artifacts in either the ultrasound or MR images. Minor low level susceptibility artifacts within 1-2 cm of the ultrasound probe position were visible in the MR for some of the images acquired; such artifacts have not inhibited image analysis nor have they impacted overall image quality. Preliminary analyses do not provide evidence of drift over the course of ultrasound data acquisition, implying the position of the ultrasound is stable over the course of imaging. Limitations with internal over-heating of the ultrasound were experienced. We found that heating is mediated by lowering the acoustic power and allowing cooling time between slices of MR data. This study demonstrates the feasibility of simultaneous ultrasound and MR image acquisition using a hands-free, MR-compatible, 4D ultrasound transducer. While the current project looks to apply this technology specifically to liver IGRT, there may be opportunities for more broad application in IGRT as well as other image guidance procedures.

18F]‐Sodium Fluoride PET/MR Imaging for Bone–Cartilage Interactions in Hip Osteoarthritis: A Feasibility Study

ABSTRACTThis study characterized the distribution of [18F]‐sodium fluoride (NaF) uptake and blood flow in the femur and acetabulum in hip osteoarthritis (OA) patients to find associations between bone remodeling and cartilage composition in the presence of morphological abnormalities using simultaneous positron emission tomography and magnetic resonance imaging (PET/MR), quantitative magnetic resonance imaging (MRI) and femur shape modeling. Ten patients underwent a [18F]‐NaF PET/MR dynamic scan of the hip simultaneously with: (i) fast spin‐echo CUBE for morphology grading and (ii) T 1ρ/T 2 magnetization‐prepared angle‐modulated partitioned k‐space spoiled gradient echo snapshots for cartilage, bone segmentation, bone shape modeling, and T 1ρ/T 2 quantification. The standardized uptake values (SUVs) and Patlak kinetic parameter (K pat) were calculated for each patient as PET outcomes, using an automated post‐processing pipeline. Shape modeling was performed to extract the variations in bone shapes in the patients. Pearson's correlation coefficients were used to study the associations between bone shapes, PET outcomes, and patient reported pain. Direct associations between quantitative MR and PET evidence of bone remodeling were established in the acetabulum and femur. Associations of shaft thickness with SUV in the femur (p = 0.07) and K pat in the acetabulum (p = 0.02), cam deformity with acetabular score (p = 0.09), osteophytic growth on the femur head with K pat (p = 0.01) were observed. Pain had increased correlations with SUV in the acetabulum (p = 0.14) and femur (p = 0.09) when shaft thickness was accounted for. This study demonstrated the ability of [18F]‐NaF PET‐MRI, 3D shape modeling, and quantitative MRI to investigate cartilage‐bone interactions and bone shape features in hip OA, providing potential investigative tools to diagnose OA. © 2019 The Authors. Journal of Orthopaedic Research ® published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society J Orthop Res 37:2671–2680, 2019