Comparison of four MR carotid surface coils at 3T.
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ABSTRACT:
SUBMITTER: Zhang Q
PROVIDER: S-EPMC6398924 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:The goal of this work was to investigate the effects of MRI surface coils on attenuation-corrected PET emission data. The authors studied the cases where either an MRI or a CT scan would be used to provide PET attenuation correction (AC). Combined MR/PET scanners that use the MRI for PET AC (MR-AC) face the challenge of absent surface coils in MR images and thus cannot directly account for attenuation in the coils. Combining MR and PET images could be achieved by transporting the subject on a stereotactically registered table between independent MRI and PET scanners. In this case, conventional PET CT-AC methods could be used. A challenge here is that high atomic number materials within MR coils cause artifacts in CT images and CT based AC is typically not validated for coil materials.The authors evaluated PET artifacts when MR coils were absent from AC data (MR-AC), or when coil attenuation was measured by CT scanning (CT-AC). They scanned PET phantoms with MR surface coils on a clinical PET/CT system and used CT-AC to reconstruct PET data. The authors then omitted the coil from the CT-AC image to mimic the MR-AC scenario. Images were acquired using cylinder and anthropomorphic phantoms. They evaluated and compared the following five scenarios: (1) A uniform cylinder phantom and head coil scanned and reconstructed using CT-AC; (2) similar emission data (with head coil present) were reconstructed without the head coil in the AC data; (3) the same cylinder scanned without the head coil present (reference scan); (4) a PET torso phantom with a full MR torso coil present in both PET and CT; (5) only half of the separable torso coil present in the PET/CT acquisition. The authors also performed analytic simulations of the first three scenarios.Streak artifacts were present in CT images containing MR surface coils due to metal components. These artifacts persisted after the CT images were converted for PET AC. The artifacts were significantly reduced when half of the separable coil was removed during the scan. CT scans tended to over-estimate the linear attenuation coefficient (micro) of the metal components when using conventional methods for converting from CT number to micro(511 keV). Artifacts were visible outside the phantom in some of the PET emission images, corresponding to the MRI coil geometry. However, only subtle artifacts were apparent in the emission images inside the phantoms. On the other hand, the PET emission image quantitative accuracy was significantly affected: the activity was underestimated by 19% when AC did not include the head coil, and overestimated by 28% when the CT-AC included the head coil.The presence of MR coils during PET or PET/CT scanning can cause subtle artifacts and potentially important quantification errors. Alternative CT techniques that mitigate artifacts should be used to improve AC accuracy. When possible, removing segments of an MR coil prior to the PET/CT exam is recommended. Further, MR coils could be redesigned to reduce artifacts by rearranging placement of the most attenuating materials.
| S-EPMC3117895 | biostudies-other
Project description:PURPOSE:To exploit the long 3.0T relaxation times and low flow velocity of lymphatic fluid to develop a noninvasive 3.0T lymphangiography sequence and evaluate its relevance in patients with lymphedema. MATERIALS AND METHODS:A 3.0T turbo-spin-echo (TSE) pulse train with long echo time (TEeffective ?=?600 msec; shot-duration?=?13.2 msec) and TSE-factor (TSE-factor?=?90) was developed and signal evolution simulated. The method was evaluated in healthy adults (n?=?11) and patients with unilateral breast cancer treatment-related lymphedema (BCRL; n?=?25), with a subgroup (n?=?5) of BCRL participants scanned before and after manual lymphatic drainage (MLD) therapy. Maximal lymphatic vessel cross-sectional area, signal-to-noise-ratio (SNR), and results from a five-point categorical scoring system were recorded. Nonparametric tests were applied to evaluate study parameter differences between controls and patients, as well as between affected and contralateral sides in patients (significance criteria: two-sided P < 0.05). RESULTS:Patient volunteers demonstrated larger lymphatic cross-sectional areas in the affected (arm?=?12.9?±?6.3?mm2 ; torso?=?17.2?±?15.6?mm2 ) vs. contralateral (arm?=?9.4?±?3.9?mm2 ; torso?=?9.1?±?4.6?mm2 ) side; this difference was significant both for the arm (P?=?0.014) and torso (P?=?0.025). Affected (arm: P?=?0.010; torso: P?=?0.016) but not contralateral (arm: P?=?0.42; torso: P?=?0.71) vessel areas were significantly elevated compared with control values. Lymphatic cross-sectional areas reduced following MLD on the affected side (pre-MLD: arm?=?8.8?±?1.8?mm2 ; torso?=?31.4?±?26.0?mm2 ; post-MLD: arm?=?6.6?±?1.8?mm2 ; torso?=?23.1?±?24.3?mm2 ). This change was significant in the torso (P?=?0.036). The categorical scoring was found to be less specific for detecting lateralizing disease compared to lymphatic-vessel areas. CONCLUSION:A 3.0T lymphangiography sequence is proposed, which allows for upper extremity lymph stasis to be detected in ?10 minutes without exogenous contrast agents. LEVEL OF EVIDENCE:1 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2017;46:1349-1360.
| S-EPMC5573666 | biostudies-literature
Project description:PurposeTo demonstrate the capability of insertable inductively coupled volumetric coils for MR microscopy in a human 7T MR system.MethodsInsertable inductively coupled volume coils with diameters of 26 and 64 mm (D26 and D64 coils) targeted for monkey and mouse brain specimen sizes were designed and fabricated. These coils were placed inside the imaging volume of a transmit/receive knee coil without wired connections to the main system. Signal-to-noise ratio (SNR) evaluations were conducted with and without the insertable coils, and the g-factor maps of parallel imaging (PI) were also calculated for the D64 coil. Brain specimens were imaged using 3D T2∗ -weighted images with spatial resolution of isotropic 50 and 160 μm using D26 and D64 coils, respectively.ResultsRelative average (SD) SNRs compared with knee coil alone were 12.54 (0.30) and 2.37 (0.05) at the center for the D26 and D64 coils, respectively. The mean g-factors of PI with the D64 coil for the factor of 2 were less than 1.1 in the left-right and anterior-posterior directions, and around 1.5 in the superior-inferior direction or when the PI factor of 3 was used. Acceleration in two directions showed lower g-factors but suffered from intrinsic low SNR. Representative T2∗ -weighted images of the specimen showed structural details.ConclusionInductively coupled small diameter coils insertable to the knee coil demonstrated high SNR and modest PI capability. The concept was successfully used to visualize fine structures of the brain specimen. The insertable coils are easy to handle and enable MR microscopy in a human whole-body 7T MRI system.
| S-EPMC9297907 | biostudies-literature
Project description:Background and purposeImproved MR imaging at higher field strengths enables more detailed imaging of cranial nerves. The aim of this study was to assess the identifiability of the NI in the CPA and IAC by using high-resolution 3T MR imaging.Materials and methodsTwenty-seven healthy volunteers (13 men and 14 women; mean age, 33 years) underwent 3T MR imaging of the CPA. The section thicknesses of the CISS sequence was 0.4 mm (TR, 12.18 ms; TE, 6.09 ms) using a 12-channel head coil. Evaluation was performed by using MPR mode. Image quality and identifiability of the NI were rated independently by 2 observers according to predefined criteria on an ordinal scale. Interobserver agreement was assessed by κ statistics.ResultsFifty-four NIs were evaluated. Both observers were able to identify the NI in nearly 60% of cases. It was possible to indentify at least 1 NI in 70% of all volunteers in the CPA and/or IAC. Image quality ratings showed a substantial agreement (κ = 0.65) and identifiability ratings an almost perfect (κ = 0.83) agreement.ConclusionsCareful evaluation of all nervous and vascular structures in the CPA and IAC at high-resolution 3T MR imaging allows reliable depiction of the NI.
| S-EPMC8013097 | biostudies-literature
Project description:Current risk stratification for stroke is still based upon percentage of carotid stenosis, despite this measure providing minimal patient-specific information on the actual risk of stroke for both symptomatic individuals without significant carotid artery stenosis as well as asymptomatic carotid stenosis patients. A continuously growing body of literature suggests that the identification and quantification of certain carotid plaque characteristics, including lipid-rich necrotic core (LRNC), thin/ruptured fibrous cap (FC), and intraplaque hemorrhage (IPH), provide a superior means of predicting future stroke. These characteristics are identifiable via magnetic resonance imaging (MRI), with most features detectable using commercially available coils and sequences utilized in routine clinical practice in as little as 4 minutes. The presence of LRNC, a thin/ruptured FC, and IPH is associated with increased risk of future stroke or TIA. Plaques with greater than 40% LRNC with a thin overlying FC are prone to rupture. LRNC is T2 hypointense and lacks enhancement on contrast enhanced T1 weighted images. Increasing LRNC size is associated with the development of new ulceration, FC rupture, increasing plaque burden, as well as fatal and nonfatal myocardial infarction, ischemic stroke, hospitalization for acute coronary syndrome (ACS), and symptom-driven revascularization, allowing for MR biomarkers of carotid plaque vulnerability to be utilized for systemic athero-thrombotic risk and not just stroke/TIA. LRNC typically shrinks with appropriate statin therapy, with PCSK9 inhibitors possibly playing a role in patients with inadequate response. Carotid plaques with IPH represent a more advanced stage of atherosclerotic disease. IPH is detectable with field strengths of both 3.0 T and 1.5 T and will demonstrate high signal on all T1 weighted imaging sequences. The presence of IPH increases the risk of future stroke in both symptomatic and asymptomatic patients, with multivariate analysis identifying IPH as a predictor of stroke, independent of percent stenosis, with no statistical difference in men vs. women, demonstrating that simple carotid stenosis measurements and traditional risk factor analysis may be inadequate in identifying patients at the highest risk for adverse cerebrovascular events. In the evaluation for recurrent stroke in recently symptomatic patients with >50% carotid stenosis, the estimated annual stroke risk is 23.2% in IPH+ patients and only 0.6% in IPH- patients, calling into question the current risk-benefit assessment for CEA. Additionally, a recent meta-analysis suggests that IPH+ plaque in patients with symptomatic <50% stenosis may be the etiology of embolic strokes previously labeled as "embolic stroke of undetermined source" (ESUS). There are no prospective drug trials testing the ability of any lipid-lowering therapies to decrease IPH and/or total plaque volume (TPV). Given the continuously increasing evidence of IPH as a significant predictor of carotid plaque progression and future adverse vascular events, trials aimed at targeted therapy for IPH represents a significant need.
| S-EPMC7487401 | biostudies-literature
Project description:The characterization of peripheral nerve sheath tumors is challenging. The purpose here was to investigate the diagnostic value of quantitative proton MR spectroscopy at 3T for the characterization of peripheral nerve sheath tumors as benign or malignant, compared with PET.Twenty participants with 24 peripheral nerve sheath tumors underwent MR spectroscopy by use of a point-resolved sequence (TE, 135 ms). Six voxels were placed in 4 histologically proven malignant peripheral nerve sheath tumors and 22 voxels in 20 benign peripheral nerve sheath tumors (9 histologically proven, 11 with documented stability). The presence or absence of a trimethylamine signal was evaluated, the trimethylamine concentration estimated by use of phantom replacement methodology, and the trimethylamine fraction relative to Cr measured. MR spectroscopy results for benign and malignant peripheral nerve sheath tumors were compared by use of a Mann-Whitney test, and concordance or discordance with PET findings was recorded.In all malignant tumors and in 9 of 18 benign peripheral nerve sheath tumors, a trimethylamine peak was detected, offering the presence of trimethylamine as a sensitive (100%), but not specific (50%), marker of malignant disease. Trimethylamine concentrations (2.2 ± 2.8 vs 6.6 ± 5.8 institutional units; P < .049) and the trimethylamine fraction (27 ± 42 vs 88 ± 22%; P < .012) were lower in benign than malignant peripheral nerve sheath tumors. A trimethylamine fraction threshold of 50% resulted in 100% sensitivity (95% CI, 58.0%-100%) and 72.2% (95% CI, 59.5%-75%) specificity for distinguishing benign from malignant disease. MR spectroscopy and PET results were concordant in 12 of 16 cases, (2 false-positive results for MR spectroscopy and PET each).Quantitative measurement of trimethylamine concentration by use of MR spectroscopy is feasible in peripheral nerve sheath tumors and shows promise as a method for the differentiation of benign and malignant lesions. Trimethylamine presence within a peripheral nerve sheath tumor is a sensitive marker of malignant disease, but quantitative measurement of trimethylamine content is required to improve specificity.
| S-EPMC4086645 | biostudies-literature
Project description:BackgroundThe interest in MR-only workflows is growing with the introduction of artificial intelligence in the synthetic CT generators converting MR images into CT images. The aim of this study was to evaluate several commercially available sCT generators for two anatomical localizations.MethodsFour sCT generators were evaluated: one based on the bulk density method and three based on deep learning methods. The comparison was performed on large patient cohorts (brain: 42 patients and pelvis: 52 patients). It included geometric accuracy with the evaluation of Hounsfield Units (HU) mean error (ME) for several structures like the body, bones and soft tissues. Dose evaluation included metrics like the Dmean ME for bone structures (skull or femoral heads), PTV and soft tissues (brain or bladder or rectum). A 1%/1 mm gamma analysis was also performed.ResultsHU ME in the body were similar to those reported in the literature. Dmean ME were smaller than 2% for all structures. Mean gamma pass rate down to 78% were observed for the bulk density method in the brain. Performances of the bulk density generator were generally worse than the artificial intelligence generators for the brain but similar for the pelvis. None of the generators performed best in all the metrics studied.ConclusionsAll four generators can be used in clinical practice to implement a MR-only workflow but the bulk density method clearly performed worst in the brain.
| S-EPMC10478301 | biostudies-literature
Project description:BACKGROUND AND PURPOSE:Intracranial vessel wall MR imaging plays an increasing role in diagnosing intracranial vascular diseases. For a complete assessment, pre- and postcontrast sequences are required, and including other sequences, these result in a long scan duration. Ideally, the scan time of the vessel wall sequence should be reduced. The purpose of this study was to evaluate different intracranial vessel wall sequence variants to reduce scan duration, provided an acceptable image quality can be maintained. MATERIALS AND METHODS:Starting from the vessel wall sequence that we use clinically (6:42 minutes), 6 scan variants were tested (scan duration ranging between 4:39 and 8:24 minutes), creating various trade-offs among spatial resolution, SNR, and contrast-to-noise ratio. In total, 15 subjects were scanned on a 3T MR imaging scanner: In 5 subjects, all 7 variants were performed precontrast-only, and in 10 other subjects, the fastest variant (4:39 minutes) and our clinically used variant (6:42 minutes) were performed pre- and postcontrast. RESULTS:The fastest variant (4:39 minutes) had higher or comparable SNRs/contrast-to-noise ratios of the intracranial vessel walls compared with the reference sequence (6:42 minutes). Qualitative assessment showed that the contrast-to-noise ratio was most suppressed in the fastest variant of 4:39 minutes and the variant of 6:42 minutes pre- and postcontrast. SNRs/contrast-to-noise ratios of the fastest variant were all, except one, higher compared with the variant of 6:42 minutes (P < .008). Furthermore, the fastest variant (4:39 minutes) detected all vessel wall lesions identified on the 6:42-minute variant. CONCLUSIONS:A 30% faster vessel wall sequence was developed with high SNRs/contrast-to-noise ratios that resulted in good visibility of the intracranial vessel wall.
| S-EPMC6004122 | biostudies-literature
Project description:Background and purposeIntracranial atherosclerosis is a common cause of ischemic stroke. Intracranial stenosis is most commonly quantified by the Warfarin-Aspirin Symptomatic Intracranial Disease method, which involves calculating a ratio of luminal diameter measurements on conventional angiography. Our purpose was to determine whether a single linear measurement of the narrowest caliber of the intracranial ICA on MRA can accurately predict Warfarin-Aspirin Symptomatic Intracranial Disease stenosis measurements.Materials and methodsWe identified patients from a prospective stroke registry who had undergone head MRAs to quantitatively evaluate the degree of Warfarin-Aspirin Symptomatic Intracranial Disease-derived stenosis in each intracranial ICA. We also made a single linear millimeter measurement at the site of maximal narrowing of the ICA. We calculated a correlation coefficient between the lumen diameter in millimeters and percentage Warfarin-Aspirin Symptomatic Intracranial Disease stenosis. We performed receiver operating characteristic analysis to determine optimal luminal diameter cutoff values.ResultsIn 386 unique intracranial ICAs, we found a strong linear relationship between single lumen measurements and Warfarin-Aspirin Symptomatic Intracranial Disease-style stenosis measurements (R = -0.84, P < .0001). We found that ICA lumen diameters of ≤2.1 and ≤1.3 mm were optimal cutoffs for identifying patients with ≥50% stenosis and ≥70% stenosis, respectively (area under the curve = 0.96 and 0.99, respectively).ConclusionsThere is a strong linear relationship between the narrowest lumen diameter of the intracranial ICA and percentage stenosis. Our results suggest that a single lumen diameter measurement on MRA allows accurate estimation of Warfarin-Aspirin Symptomatic Intracranial Disease stenosis, which may affect risk stratification and treatment decisions.
| S-EPMC5433892 | biostudies-literature
Project description:PURPOSE:This study is to compare the accuracy of four different black-blood T2 mapping sequences in carotid vessel wall. METHODS:Four different black-blood T2 mapping sequences were developed and tested through phantom experiments and 17 healthy volunteers. The four sequences were: 1) double inversion-recovery (DIR) prepared 2D multi-echo spin-echo (MESE); 2) DIR-prepared 2D multi-echo fast spin-echo (MEFSE); 3) improved motion-sensitized driven-equilibrium (iMSDE) prepared 3D FSE and 4) iMSDE prepared 3D fast spoiled gradient echo (FSPGR). The concordance correlation coefficient and Bland-Altman statistics were used to compare the sequences with a gold-standard 2D MESE, without blood suppression in phantom studies. The volunteers were scanned twice to test the repeatability. Mean and standard deviation of vessel wall T2, signal-to-noise (SNR), the coefficient of variance and interclass coefficient (ICC) of the two scans were compared. RESULTS:The phantom study demonstrated that T2 measurements had high concordance with respect to the gold-standard (all r values >0.9). In the volunteer study, the DIR 2D MEFSE had significantly higher T2 values than the other three sequences (P < 0.01). There was no difference in T2 measurements obtained using the other three sequences (P > 0.05). iMSDE 3D FSE had the highest SNR (P < 0.05) compared with the other three sequences. The 2D DIR MESE has the highest repeatability (ICC: 0.96, [95% CI: 0.88-0.99]). CONCLUSION:Although accurate T2 measurements can be achieved in phantom by the four sequences, in vivo vessel wall T2 quantification shows significant differences. The in vivo images can be influenced by multiple factors including black-blood preparation and acquisition method. Therefore, a careful choice of acquisition methods and analysis of the confounding factors are required for accurate in vivo carotid vessel wall T2 measurements. From the settings in this study, the iMSDE prepared 3D FSE is preferred for the future volunteer/patient scans.
| S-EPMC6326764 | biostudies-other