True Fast Imaging With Steady-state Precession Research Articles

Role of magnetic resonance imaging in the diagnosis of placenta accreta.

To analyze the value of magnetic resonance imaging (MRI) in suspicious cases for prenatal detection of placenta accreta (PA). A total of 50 placental MRI exams performed on a 1.5T scanner were retrospectively reviewed by two radiologists in consensus.HASTE(half-Fourier acquisition single-shot turbo spin echo)and True-FISP (true fast imaging with steady-state precession) sequences were acquired. Findings from MRI were compared with the final diagnosis, which was determined by clinical findings at delivery and pathological examination of specimens. Of 50 pregnant women in the analysis, 33 required cesarean hysterectomy, and 17 underwent cesarean delivery.MRI signs such as myometrial thinning, loss of T2 hypointense interface(loss of retroplacental clear space on US), heterogenous intraplacental sign, and intraplacental T2 dark bands were more likely to be seen in this group. In this group, the cases that were finally clinically and pathologically confirmed were 12, 16, and 22 cases of placenta accreta vera, placenta increta, and placenta percreta respectively. MRI is particularly useful in cases where US is inconclusive and to assess the extent to which the placenta penetrates the uterine serosa and invades outward into surrounding tissues.MRI has become a routine examination for patients with suspected PA in clinical practice.

Association of MRI Features and Adverse Maternal Outcome in Patients With Placenta Accreta Spectrum Disorders After Abdominal Aortic Balloon Occlusion.

MRI features may be associated with adverse maternal outcome in patients with placenta accreta spectrum (PAS) disorders even with abdominal aortic balloon occlusion (AABO). This study aimed to identify risk factors of MRI for association with adverse maternal outcome in patients with PAS disorders after AABO. Retrospective. Clinical and MRI features of 80 patients were retrospectively reviewed from October 2016 to August 2021. A total of 40 patients had adverse maternal outcomes including intrapartum/peripartum bleeding >1000 mL and/or emergency hysterectomy after AABO. Half-Fourier acquisition single-shot turbo spin echo and gradient echo imaging True fast imaging with steady-state precession (True-FISP) at 1.5T MR scanner. MRI features were evaluated by three radiologists and were tested for any association with adverse maternal outcome. Interobserver agreement was calculated with kappa (k) statistics. Association between MRI features and adverse maternal outcomes were evaluated by univariate and multivariate analyses. A nomogram was constructed based on the logistic regression. The interobserver agreement ranged from fair to substantial (k=0.379-0.783). Multivariate analyses revealed that short cervical length (OR: 4.344), abnormal intraplacental vascularity (OR: 6.005), placental bulge (OR: 9.085), and myometrial interruption (OR: 9.550) were independent risk factors for adverse maternal outcomes. The combination of four risk factors together demonstrated the highest AUC of 0.851 (95% CI 0.769-0.933) with a sensitivity and specificity of 77.5% and 72.5%, respectively and then a nomogram composed of the above four risk factors was constructed to represent the probability of adverse maternal outcome. The nomogram demonstrated the association between MRI features and patient's poor outcome after undergoing AABO and C-section delivery for PAS. 4 TECHNICAL EFFICACY: Stage 3.

Synthetic CT generation for MRI-guided adaptive radiotherapy in prostate cancer.

Current MRI-guided adaptive radiotherapy (MRgART) workflows require fraction-specific electron and/or mass density maps, which are created by deformable image registration (DIR) between the simulation CT images and daily MR images. Manual density overrides may also be needed where DIR-produced results are inaccurate. This approach slows the adaptive radiotherapy workflow and introduces additional dosimetric uncertainties, especially in the presence of the magnetic field. This study investigated a method based on a conditional generative adversarial network (cGAN) with a multi-planar method to generate synthetic CT images from low-field MR images to improve efficiency in MRgART workflows for prostate cancer. Fifty-seven male patients, who received MRI-guided radiation therapy to the pelvis using the ViewRay MRIdian Linac, were selected. Forty-five cases were randomly assigned to the training cohort with the remaining twelve cases assigned to the validation/testing cohort. All patient datasets had a semi-paired DIR-deformed CT-sim image and 0.35T MR image acquired using a true fast imaging with steady-state precession (TrueFISP) sequence. Synthetic CT images were compared with deformed CT images to evaluate image quality and dosimetric accuracy. To evaluate the dosimetric accuracy of this method, clinical plans were recalculated on synthetic CT images in the MRIdian treatment planning system. Dose volume histograms for planning target volumes (PTVs) and organs-at-risk (OARs) and dose distributions using gamma analyses were evaluated. The mean-absolute-errors (MAEs) in CT numbers were 30.1 ± 4.2 HU, 19.6 ± 2.3 HU and 158.5 ± 26.0 HU for the whole pelvis, soft tissue, and bone, respectively. The peak signal-to-noise ratio was 35.2 ± 1.7 and the structural index similarity measure was 0.9758 ± 0.0035. The dosimetric difference was on average less than 1% for all PTV and OAR metrics. Plans showed good agreement with gamma pass rates of 99% and 99.9% for 1%/1 mm and 2%/2 mm, respectively. Our study demonstrates the potential of using synthetic CT images created with a multi-planar cGAN method from 0.35T MRI TrueFISP images for the MRgART treatment of prostate radiotherapy. Future work will validate the method in a large cohort of patients and investigate the limitations of the method in the adaptive workflow.

Susceptibility-weighted imaging to evaluate normal and abnormal vertebrae in fetuses: A preliminary study.

To evaluate the performance of susceptibility-weighted imaging (SWI) in visualizing normal and abnormal fetal vertebrae in vivo and in utero. Ninety-seven women with normal fetal vertebrae and 127 women suspected fetal vertebral anomalies on ultrasound were included in our study. SWI, true fast imaging with steady state precession (TrueFISP), and half-Fourier acquisition single-shot turbo spin-echo (HASTE) of the fetal spine were performed on 1.5-T magnetic resonance imaging. The image quality and diagnostic performance between HASTE/TrueFISP and SWI were compared. Pearson correlations to correlate the L1 centrum ossification center (COC) measurements with gestational age (GA) were performed. The visibility of the fetal vertebral structures on the SWI images (3.58±0.69) was significantly greater than those on the HASTE (1.98±0.51, p<0.001) and TrueFISP (2.63±0.52, p<0.001). The diagnostic accuracy of SWI (89.0%) was superior to HASTE/TrueFISP (48.0%) (p<0.001) and the area under the curve for SWI was 0.909 (p<0.001). The height, transverse, sagittal diameter, and area of L1 COC were linearly correlated with GA (all p<0.001). SWI proved to be a reliable method for depicting fetal vertebral structure and growth, which can significantly improve the diagnostic performance of vertebral anomalies in fetuses.

Pre- and Postoperative Ultrasound and MRI Examinations in Assessing Vocal Folds in Patients with Goiter.

Aim of the study: To determine the value of dynamic examinations ultrasound (US) and MRI in the 1.5T field in the assessment of the mobility of vocal folds (VF) in comparison to laryngoscopy in patients with thyroid gland resection. Materials and methods: A total of 44 patients with goiter, before and after thyroidectomy, were subjected to videolaryngoscopy and dynamic examinations of the vocal folds using ultrasound and the following MRI sequences: generic gradient echo (GRE) and true fast imaging with steady-state precession (TRUFI). The qualitative and quantitative data were analyzed, i.e., the angles of deviation from the midline of the vocal folds and the area of the right and left rima glottidis compartments. Results: The analysis of qualitative data showed that the results obtained by laryngoscopy, US and MRI are independent of the diagnostic method used in the group of patients pre and post thyroidectomy. Between the pre- and postoperative examinations in the group of paralyzed vocal folds, statistically significant differences were found in the minimum and maximum values of the angles for the MRI-GRE and MRI-TRUFI sequences and the maximum value of the angles in the US examination, but also in the maximum value of the area of the glottis compartments in both MRI-GRE and MRI-TRUFI dynamic sequences and the minimum value of the area in the sequence MRI-GRE. Statistically significant differences were found in both MRI sequences during phonation, both for the value of the angles and the area of the affected vocal folds. However, no statistically significant differences were found in the values of the angles or the areas in both vocal fold imaging methods without identified mobility abnormalities. Conclusions: Ultrasound and MRI examinations using dynamic sequences have a similar diagnostic value to laryngoscopy in the assessment of vocal fold paralysis in patients with goiter. The GRE sequence seems to be the most reliable one in determining vocal fold paralysis, and the most reliable parameter is the maximum area of the rima glottidis compartment. The inclusion of dynamic short sequences widely available in 1.5T scanners in standard neck examination protocols represents a novelty of the method and a promising diagnostic perspective in the diagnosis of vocal fold paralysis.

SPIO-enhanced 0.35T MRI-guided radiotherapy for liver malignancies: usefulness in tumor visualization.

The purpose of this study was to investigate the changes of tumor-to-liver signal ratio in a 0.35T MRI-guided radiotherapy system and to evaluate the usefulness and pitfalls of superparamagnetic iron oxide (SPIO) administration for visualization of liver tumors. Forty-two patients treated with MRI-guided stereotactic ablative radiotherapy (SABR) for liver tumors were included in this study. The tumor-to-liver signal ratios before and after SPIO administration were retrospectively assessed and compared on true fast imaging with steady-state precession (FISP). Before SPIO administration, liver tumors were either invisible or barely visible in 15 cases (36%), but all tumors became visible after SPIO administration. The mean values of tumor-to-liver signal ratio before and after SPIO administration were 0.939 ± 0.201 and 1.336 ± 0.300, respectively (mean ± standard deviation, p < 0.001). In six (14%) patients, liver tumors were visible on true FISP imaging before SPIO administration, but became invisible after administration. This study showed that liver tumors that are invisible on true FISP imaging can be made visible by administration of SPIO, and that MRI-guided SABR can be performed accurately. This is the first report to examine the usefulness of liver-specific contrast agent superparamagnetic iron oxides in 0.35T MRI-guided radiation therapy. Liver tumors that are invisible on true fast imaging with steady-state precession can be made visible by administration of superparamagnetic iron oxides.

Technical Note: Effects of rotating gantry on magnetic field and eddy currents in 0.35 T MRI-guided radiotherapy (MR-IGRT) system.

The purpose of this study was to identify the cause of severe image artifacts that occurred during gantry rotation in a 0.35 T MRI-Linac by comparing measurements of eddy currents, center frequency, and field inhomogeneities made with the gantry in motion and stationary. Gradient and B0 eddy currents were calculated from the free induction decays (FIDs) resulting from selective excitation at a temporal resolution of 200ms/measurement. B0 eddy currents were also calculated from FIDs acquired with nonselective excitation at a temporal resolution of 100ms/measurement. Center frequencies and B0 inhomogeneities were measured by acquiring FIDs with a repetition time (TR) of 290ms. Cartesian and radial 2D true fast imaging with steady-state precession (TrueFISP) pulse sequences used in real-time MRI-guided radiation therapy (MR-IGRT) were acquired. To assess artifact severity, the normalized root mean square error (nRMSE) was calculated between a reference MRI (static gantry) and MRIs acquired during gantry rotation for each serial acquisition. Image artifacts were qualitatively graded as nominal, minor, or severe. Measurements were conducted while the gantry was rotated through its entire range for both clockwise and counterclockwise. Measurements during gantry rotation were compared to measurements with a stationary gantry (every 30°). Severe image artifacts were observed 22-35% of the time while the gantry was rotating. Short time constant eddy currents were not affected by gantry rotation. The peak to peak center frequency and FWHM rose by factors of 13.2-14.5 and 1.1-1.6, respectively, for the rotating versus stationary gantry. The magnitude of the center frequency offset and field inhomogeneities depended on the direction of the gantry rotation. Image artifacts during gantry rotation were primarily caused by center frequency variations and field inhomogeneities. Therefore, dynamic B0 compensation techniques should be able to reduce artifacts during gantry rotation.

Effects of B0 eddy currents on imaging isocenter shifts in 0.35‐T MRI‐guided radiotherapy (MR‐IGRT) system

PurposeThe purpose of this study was to measure gantry angle‐related eddy currents in a 0.35‐T MRI‐Linac and determine if B0 (zeroth order) eddy currents are the primary cause of gantry angle‐dependent imaging isocenter shifts vs other potential causes like B0 inhomogeneities and gradient (first order) eddy currents. For conventional Cartesian acquisitions, B0 eddy currents can cause imaging isocenter shifts along both phase encode and readout directions. Gradient eddy currents can cause spatial distortion along both the phase encode and readout directions. Center frequency offsets can cause imaging isocenter shifts along the readout direction that vary with readout gradient polarity.MethodsMRI‐related eddy currents and imaging isocenter shifts were measured on a 0.35‐T MRI‐Linac at gantry angles from 0° to 330° in increments of 30°. All measurements were made after gradient shimming and center frequency tuning at each planned gantry angle. Eddy current and field homogeneity measurements were conducted using a 24‐cm diameter spherical phantom. Gradient and B0 eddy currents were calculated from the free induction decays (FIDs) resulting from selective excitation of slices located ±5 cm from isocenter. B0 eddy currents were also calculated from FIDs acquired with nonselective excitation and compared with B0 eddy current values derived using selective excitation. B0 inhomogeneities and center frequency offsets were measured by acquiring FIDs with nonselective excitation. Imaging isocenter shifts were measured using a 33x33x10.5 cm3 uniformity linearity (grid) phantom and a 3D true fast imaging with steady‐state precession (TrueFISP) sequence used in MRI‐guided radiation therapy. Eddy currents were compared to vendor specifications and correlated with the imaging isocenter shifts. Measurements were conducted before and after the MRI‐Linac’s waveguide was replaced with an updated design to reduce eddy currents.ResultsB0 eddy currents were highly correlated (r = 0.986, P &lt;&lt; 0.001) for measurements made with vs without selective excitation. Transverse (X and Y) axis B0 eddy currents before and after the waveguide upgrade were out of specification (specification: ≤0.1 μT m/mT for delays &lt; 10 ms) for most of the measured gantry angles. Gradient eddy currents before and after the upgrade were within specifications for the measured gantry angles (≤0.1% for delays &lt; 10 ms). B0 eddy currents and imaging isocenter shifts were highly correlated (r = 0.965, P &lt;&lt; 0.001). After the Linac waveguide upgrade, root mean square (RMS) peak B0 and gradient eddy currents dropped 45% and 11%, respectively, for delays &lt;10 ms, while imaging isocenter shifts dropped 53%. Isocenter shifts were observed in both phase encode and readout directions. Center frequency offsets were &lt;26 Hz while B0 inhomogeneities were &lt;33 Hz full width at half maximum (FWHM).ConclusionsImaging isocenter shifts measured in a 0.35‐T MRI‐Linac were highly correlated with B0 eddy currents. The eddy currents and imaging isocenter shifts decreased after the MRI‐Linac’s waveguide was replaced.

The value of 1.5T MRI in the evaluation of vocal fold mobility in patients with goiter

The laryngoscopic examination remains the gold standard in the perioperative evaluation of the mobility of the vocal folds in patients with goiter. During the COVID-19 pandemic, many medical procedures, including laryngoscopy are optimized in terms of epidemiological safety. Therefore, it seems deeply justified to implement methods like i.e. ultrasound or MRI which can provide the diagnostic information usually obtained via laryngoscopic examination. Aim of the studyTo determine the value of dynamic MRI examination in the 1.5 T field in the assessment of the mobility of vocal folds in patients with goiter compared to healthy people and in relation to ultrasound examinations and routine laryngoscopy. Materials and methods35 healthy volunteers and 44 patients with goiter were subjected to videolaryngoscopy, dynamic examinations of the vocal folds during respiration and phonation using ultrasound and the MRI sequences: generic gradient echo (GRE) and true fast imaging with steady-state precession (TRUFI). The qualitative and quantitative data were analyzed, i.e. the angles of deviation from the midline of the vocal folds and the area of the right and left rima glottidis compartments. ResultsNo statistically significant differences were found between the groups of healthy volunteers and patients with goiter in the values of the angles of deviation of the vocal folds with the use of ultrasound and two MRI dynamic sequences - GRE and TRUFI. There were also no statistically significant differences in the areas of the rima glottidis compartments between these two groups with the use of two MRI dynamic sequences - GRE and TRUFI. Among the analyzed parameters, the maximum size of each rima glottidis compartment was the only one to show features of sexual dimorphism and was significantly higher in men (GRE p < 0.001 and TRUFI p = 0.001). There was no correlation between the size of the minimum and maximum rima glottidis compartment and the total volume of the thyroid lobes in patients with goiter for the GRE and TRUFI sequences. ConclusionsMRI is a promising tool for the objective assessment of the mobility of the vocal folds in patients with goiter, as well as for the qualification for treatment and monitoring its effects. It is particularly important during an epidemiological emergency due to its safety compared to laryngoscopy. The presence of the goiter and its volume do not limit the possibility of performing dynamic imaging studies of the vocal folds and do not affect the surface area of the glottis.

Optimization of pulse sequences in ultrafast magnetic resonance imaging for the diagnosis of acute abdominal pain caused by gastrointestinal disease.

BackgroundMagnetic resonance imaging (MRI) is widely used to diagnose acute abdominal pain; however, it remains unclear which pulse sequence has priority in acute abdominal pain.PurposeTo investigate the diagnostic accuracy of MRI and to assess the conspicuity of each pulse sequence for the diagnosis of acute abdominal pain due to gastrointestinal diseasesMaterial and MethodsWe retrospectively enrolled 60 patients with acute abdominal pain who underwent MRI for axial and coronal T2-weighted (T2W) imaging, fat-suppressed (FS)-T2W imaging, and true-fast imaging with steady-state precession (True-FISP) and axial T1-weighted (T1W) imaging and investigated the diagnosis with endoscopy, surgery, histopathology, computed tomography, and clinical follow-up as standard references. Two radiologists determined the diagnosis with MRI and rated scores of the respective sequences in assessing intraluminal, intramural, and extramural abnormality using a 5-point scale after one month. Diagnostic accuracy was calculated and scores were compared by Wilcoxon-signed rank test with Bonferroni correction.ResultsDiagnostic accuracy was 90.0% and 93.3% for readers 1 and 2, respectively. Regarding intraluminal abnormality, T2W, FS-T2W, and True-FISP imaging were superior to T1W imaging in both readers. FS-T2W imaging was superior to True-FISP in reader 2 (P < 0.0083). For intramural findings, there was no significant difference in reader 1, whereas T2W, FS-T2W, and True-FISP imaging were superior to T1W imaging in reader 2 (P < 0.0083). For extramural findings, FS-T2W imaging was superior to T2W, T1W, and True-FISP imaging in both readers (P < 0.0083).ConclusionT2W and FS-T2W imaging are pivotal pulse sequences and should be obtained before T1W and True-FISP imaging.

23 Na-T1 quantification with saturation recovery TrueFISP and variable flip angle GRE at 3T: A phantom study.

The aim of the current study was to compare the reproducibility of sodium (23 Na)-T1 estimation using a centric-reordered saturation recovery (SR) true fast imaging with steady-state precession (TrueFISP) and a variable flip angle (VFA) spoiled gradient echo (GRE). Additionally, we evaluated the effect of spatial averaging on 23 Na-T1 estimation by the two methods. Measurements were performed in the phantom, consisting of 10 dm3 volume rectangular polyethylene container filled with distilled water solution of 0.6% NaCl+0.004% CuSO4 , using a dual-tunable 23 Na/1 H coil at 3 Tesla. 23 Na images were acquired for FOV=384×384mm2 and voxel size=6×6×6mm3 using: (1) TrueFISP: TR/TE=900/1.5ms, flip angle=90°, bandwidth=450Hz/px, and (2) GRE: TR/TE=30/1.5ms, bandwidth=350Hz/px. 23 Na-T1 weightings were obtained with nonselective saturation prepulses delayed from the center of the k-space acquisition by 25/40/60/130/280ms (SR-TrueFISP) and by applying different nominal flip angles: 10°/30°/50°/70°/90° (VFA-GRE). Both sequences were acquired twice, applying 20 and 30 spatial averages. The resulting images were B1 -corrected with a double-angle GRE method. Image acquisition varied from 5:41 to 9:37 for TrueFISP and from 12:48 to 19:12min for GRE using 20 and 30 spatial averages, respectively. Higher averaging increased the acquisition time by 53% and mean SNR at scan < 10%, without an effect on 23 Na-T1 estimations with both methods (SR-Truefisp |Δ|=1.58ms, VFA-GRE |Δ|=0.53ms; for SNR P<.001). Overall, mean±SD of 23 Na-T1 was found as 51±3ms with SR-TrueFISP and 53±2ms with VFA-GRE. Both SR-TrueFISP and VFA-GRE provided similar 23 Na-T1 estimates based on the phantom measurements with isotropic resolution.

Quantification of sodium T1 in abdominal tissues at 3T.

Although relevant for assessment of sodium in multiple endocrine pathways, 23Na-T1 quantification is challenging due to technical limitations (SAR, B1 inhomogeneity) or influence of tissue's local molecular dynamics. Hereby, we propose T1 quantification of 23Na-MRI signal acquired over the abdomen using a centric-reordered saturation-recovery (SR) true fast imaging with steady state precession (TrueFISP) sequence. Measurements were performed at 3T using a dual-tunable 23Na/1H coil in 7 healthy volunteers (TR/TE = 858-928/1.57 ms; flip angle = 90°; bandwidth = 450 Hz/px; voxel size = 5×5×10mm3). Variable T1-weighting was achieved applying non-selective saturation pre-pulses delayed from the centre of the k-space acquisition by 25, 40, 60, 120 and 250 ms. T1-curve fitting was performed slice-wise, separately for average intensity values from the manually segmented areas of the renal parenchyma and spinal canal, over the increasing SR times- assuming monoexponential signal pattern. Mean ± standard deviation of 23Na-T1 was found as 29 ± 10 ms and 35 ± 8 ms for the renal parenchyma and the spinal canal, respectively. 23Na-T1 quantification using a SR-TrueFISP is feasible in clinical settings, in the images constrained by clinically applicable acquisition time of reduced spatial resolution or averages.

True FISP Cardiac Gated CSF Flow Dynamic Imaging of Chiari Malformation

Abstract INTRODUCTION Brain pulsation and related CSF dynamics is a well-known intraoperative characteristic, but methods for its visualization on magnetic resonance imaging (MRI) have until now been very limited. Best characterized techniques including phase-contrast MRI and cine echo-planar imaging, although of significant value, lack a detailed spatial and temporal resolution needed to investigate CSF and structural dynamics in an adequate manner to address preoperative decision making. Electrocardiographic (ECG)-gated true fast imaging with steady-state precession (FISP) sequences has been widely used to investigate cardiac motion and is capable of demonstrating brain pulsations and movements of intracranial structures surrounded by CSF with high temporal and spatial precision. We feature here the application of true FISP cardiac-gated imaging to the management of 2 patients with Chiari Malformation Type 1 and associated syringohydromyelia. METHODS Two children with Chiari Malformation Type 1 and concurrent syringohydromyelia underwent true FISP cardiac-gated imaging at our institution. RESULTS While conventional imaging studies such as T1 and phase-contrast cine MRI appeared to demonstrate obstruction of CSF flow secondary to tonsillar herniation, true FISP showed patent peritonsillar CSF flow and the presence of a pulsatile arachnoid veil. Subsequently, open surgery confirmed the presence of an arachnoid veil, and postoperative true FISP imaging revealed restoration of CSF flow following arachnoid veil fenestration. CONCLUSION We demonstrated 2 patients who presented with Chiari 1 malformation, where true FISP cardiac imaging was very instructive in visualizing dynamic images of an arachnoid veil and its possible role in the development of syringomyelia without a significant obstruction of outflow by cerebellar tonsils at the foramen of Magendie. We advocate use of this technology will aid in pre and post-surgical decision making, providing a more representative image of posterior fossa pathology in patients with Chiari 1 malformation.

Magnetic resonance field fingerprinting.

To develop and evaluate the magnetic resonance field fingerprinting method that simultaneously generates T1 , T2 , B0 , and maps from a single continuous measurement. An encoding pattern was designed to integrate true fast imaging with steady-state precession (TrueFISP), fast imaging with steady-state precession (FISP), and fast low-angle shot (FLASH) sequence segments with varying flip angles, radio frequency (RF) phases, TEs, and gradient moments in a continuous acquisition. A multistep matching process was introduced that includes steps for integrated spiral deblurring and the correction of intravoxel phase dispersion. The method was evaluated in phantoms as well as in vivo studies in brain and lower abdomen. Simultaneous measurement of T1 , T2 , B0 , and is achieved with T1 and T2 subsequently being less afflicted by B0 and variations. Phantom results demonstrate the stability of generated parameter maps. Higher undersampling factors and spatial resolution can be achieved with the proposed method as compared with solely FISP-based magnetic resonance fingerprinting. High-resolution B0 maps can potentially be further used as diagnostic information. The proposed magnetic resonance field fingerprinting method can estimate T1 , T2 , B0 , and maps accurately in phantoms, in the brain, and in the lower abdomen.

Abstract 2111: The tumor microenvironment of preclinical tumor models may have an impact on the therapeutic index of nanotherapeutics

Abstract Rapid development in nanotechnology allows the incorporation of multiple therapeutic agents (e.g. liposomes) into nanoparticle with a size range from 1 to 1000 nm. These nanocarrier systems provide new approaches to treat aggressive malignancy. Nano-based delivery systems hold an advantage over traditional small molecule therapy in that they can deliver drugs preferentially to tumors due to the enhanced permeability and retention (EPR) effect. On one hand, high permeability of the tumor vessels and a lack of functional lymphatic vessels results in the EPR effect, driving nanoparticle extravasation. On the other hand, these phenomena lead to high interstitial fluid pressure (IFP), limiting nanoparticle extravasation. In this study, we have used dynamic-contrast enhanced (DCE) MRI with small (Dotarem, 5 nm) and large (Vistarem, 25 nm) contrast agents (CAs) to examine tumor vessel permeability in SJSA-1 osteosarcoma tumor-bearing rats. An inversion-recovery true fast imaging with steady state precession (TrueFISP) was employed to determine the transfer constant Ktrans in subcutaneous and intra-tibia tumor models. When the tumor cells were injected in both niches within the same animal, Ktrans was significantly lower in intra-tibia tumors with both CAs, and blood vessels significantly less and larger compared to subcutaneous tumors. Moreover, Ktrans negatively correlated with tumor bioluminescence for the intra-tibia model, suggesting that EPR decreased inversely with tumor size, while the opposite was noticed for the subcutaneous tumors. These data demonstrate for the first time that the EPR of tumors with a similar size within the same animal can be influenced by the microenvironment. Moreover, they show that the therapeutic index of a nanotherapeutics may be different if it's determined with either an orthotopic or ectopic model. Citation Format: Stephane Ferretti, Nicolau Beckmann, laura Holzer, Michael Obrecht, Marjorie Berger, Michael Rugaard Jensen. The tumor microenvironment of preclinical tumor models may have an impact on the therapeutic index of nanotherapeutics [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2111.

Comparison of 3D MR imaging sequences in knee articular cartilage at 1.5 T

Purpose: To compare 3D high-resolution MRI sequences in term of contrast, Signal to Noise Ratio (SNR), artefacts and cartilage thickness in knee articular cartilage at 1.5 T. Materials and Methods: Fourteen healthy volunteers and seven patients underwent articular knee cartilage exam. The 3D sequences were VOLUME Imaging with Body Enhancement (VIBE), True Fast Imaging with Steady-state Precession (TRUEFISP), Dual Echo Steady State (DESS), Multi Echo Data Image Combination (MEDIC) and Sampling Perfection with Application optimized Contrasts using different flip angle Evolutions (SPACE). For all 3D sequences, we measured contrast ratio between cartilage-bone and cartilage-meniscus, SNR and cartilage thickness. In addition, we quantified magnetic susceptibility and flow artifacts. Statistical analyses were performed using the t-test and P<0.005 was considered statistically significant. Results: Statistical results were significantly different (p>0.05). MEDIC and VIBE sequences showed the best contrast ratio between cartilage-meniscus (0.40 ± 0.14, p=0.000) and cartilage-bone (0.75 ± 0.4, p=0.022), respectively. TRUEFISP sequence showed the highest SNR (28.04 ± 14.05, p=0.000) whereas DESS sequence showed the lowest SNR (11.62 ± 3.99, p=0.000). VIBE sequence provided the highest cartilage thickness measurement compared to the remaining 3D sequences (2.0 ± 0.4 cm, IRR=75.33%, ICC=0.96). The quantification of magnetic susceptibility and flow artifacts revealed that TRUEFISP (IRR=59%, ICC=0.92) and SPACE (IRR=59%, ICC=0.96) sequences presented the highest artifacts compared to the others sequences. Conclusion: 3D high-resolution sequences provide knee articular cartilage imaging with high image quality in relatively short acquisition time. MEDIC and VIBE sequences showed the best contrast and the lowest magnetic susceptibility and flow artifacts, TRUEFISP and SPACE sequence showed the highest SNR but they are more sensitive to artifacts, DESS sequence showed medium contrast and VIBE sequence provided the highest cartilage thickness.

Fast, precise, and accurate myocardial T1 mapping using a radial MOLLI sequence with FLASH readout.

Quantitative cardiac MRI, and more particularly T1 mapping, has become a most important modality to characterize myocardial tissue. In this work, the value of a radial variant of the conventional modified Look-Locker inversion recovery sequence (raMOLLI) is demonstrated. The raMOLLI acquisition scheme consisted of five radial echo trains of 80 spokes acquired using either a fast low-angle shot (FLASH) or a true fast imaging with steady-state-precession (TrueFISP) readout at different time points after a single magnetization inversion. View sharing combined with a compressed sensing algorithm allowed the reconstruction of 50 images along the T1 relaxation recovery curve, to which a dictionary-fitting approach was applied to estimate T1 . The sequence was validated on a nine-vial phantom, on 19 healthy subjects, and one patient suffering from dilated cardiomyopathy. The raMOLLI sequence allowed a significant decrease of myocardial T1 map acquisition time down to five heartbeats, while exhibiting a higher degree of accuracy and a comparable precision on T1 value estimation than the conventional modified Look-Locker inversion recovery sequence. The FLASH readout demonstrated a better robustness to B0 inhomogeneities than TrueFISP, and was therefore preferred for in vivo acquisitions. This sequence represents a good candidate for ultrafast acquisition of myocardial T1 maps. Magn Reson Med 79:1387-1398, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Magnetic Resonance Imaging of Pulmonary Embolism: Diagnostic Accuracy of Unenhanced MR and Influence in Mortality Rates.

We evaluated the diagnostic value for pulmonary embolism (PE) of the True fast imaging with steady-state precession (TrueFISP) MRI, a method that allows the visualization of pulmonary vasculature without breath holding or intravenous contrast. This is a prospective investigation including 93 patients with suspected PE. All patients underwent TrueFISP MRI after undergoing CT pulmonary angiography (CTPA). Two independent readers evaluated each MR study, and consensus was obtained. CTPA results were analysed by a third independent reviewer and these results served as the reference standard. A fourth radiologist was responsible for evaluating if lesions found on MRI for both analysis were the same and if these were the correspondent lesions on the CTPA. Sensitivity, specificity, predictive values and accuracy were calculated. Evidence for death from PE within the 1-year follow-up was also assessed. Two patients could not undergo the real-time MRI and were excluded from the study. PE prevalence was 22%. During the 1-year follow-up period, eight patients died, whereas PE was responsible for 12.5% of cases. Between patients who developed PE, only 5% died due to this condition. There were no differences between MR and CT embolism detection in these subjects. MR sequences had a sensitivity of 85%, specificity was 98.6% and accuracy was 95.6%. Agreement between readers was high (κ= 0.87). Compared with contrast-enhanced CT, unenhanced MR sequences demonstrate good accuracy and no differences in the mortality rates in 1 year were detected.

Unenhanced respiratory-navigated NATIVE® TrueFISP magnetic resonance angiography in the evaluation of renal arteries: Comparison with contrast-enhanced magnetic resonance angiography.

To compare unenhanced three-dimensional (3D) NATIVE® true fast imaging with steady-state precession (TrueFISP) magnetic resonance (MR) angiography with the more conventional MR angiography technique obtained after intravenous administration of a gadolinium chelate in the evaluation of renal arteries and their branches in patients with suspected renal artery stenosis. A total of 39patients (25men, 14women) with a mean age of 51.4±17.5years (SD) (range: 10-82years) were included in the study. All patients with suspected renal artery stenosis underwent unenhanced 3D NATIVE® TrueFISP MR angiography and contrast-enhanced MR angiography. The two MR angiography methods were compared by two independent readers for image quality using a four-point scale, diagnostic performance and grading of renal artery stenosis on a total of 78renal arteries. For both readers image quality of unenhanced 3D NATIVE® TrueFISP MR angiography (3.12 to 3.63) was greater than that of contrast-enhanced MR angiography (1.94 to 2.71) for renal artery ostium-trunk and the left renal artery segmental branches. The sensitivity of 3D NATIVE® TrueFISP MR angiography for the diagnosis of renal artery stenosis was 100% for both readers for the right renal artery and 66% and 80% for the left renal artery for reader 1 and reader 2, respectively. Agreement between 3D NATIVE® TrueFISP MR angiography and CE-MR angiography was 95% (74/78) for reader 1 and 92% (72/78) for reader 2. Unenhanced NATIVE® TrueFISP magnetic resonance angiography can play an additional role in the evaluation of renal arteries in patients with hypertension, especially in subjects at risk of nephrogenic systemic fibrosis.

Non-enhanced magnetic resonance imaging of the small bowel at 7 Tesla in comparison to 1.5 Tesla: First steps towards clinical application

ObjectiveTo perform non-enhanced (NE) magnetic resonance imaging (MRI) of the small bowel at 7 Tesla (7T) and to compare it with 1.5 Tesla (1.5T). Material and methodsTwelve healthy subjects were prospectively examined using a 1.5T and 7T MRI system. Coronal and axial true fast imaging with steady-state precession (TrueFISP) imaging and a coronal T2-weighted (T2w) half-Fourier acquisition single-shot turbo spin-echo (HASTE) sequence were acquired. Image analysis was performed by 1) visual evaluation of tissue contrast and detail detectability, 2) measurement and calculation of contrast ratios and 3) assessment of artifacts. ResultsNE MRI of the small bowel at 7T was technically feasible. In the vast majority of the cases, tissue contrast and image details were equivalent at both field strengths. At 7T, two cases revealed better detail detectability in the TrueFISP, and better contrast in the HASTE. Susceptibility artifacts and B1 inhomogeneities were significantly increased at 7T. ConclusionThis study provides first insights into NE ultra-high field MRI of the small bowel and may be considered an important step towards high quality T2w abdominal imaging at 7T MRI.