Recent work has proposed the use of steady-state free precession (SSFP) as an alternative to the conventional methods for obtaining functional MRI (FMRI) data. The contrast mechanism in SSFP is ...likely to be related to conventional FMRI signals, but the details of the signal changes may differ in important ways. Functional contrast in SSFP has been proposed to result from several different mechanisms, which are likely to contribute in varying degrees depending on the specific parameters used in the experiment. In particular, the signal dynamics are likely to differ depending on whether the sequence is configured to scan in the SSFP transition band or passband. This work describes experiments that explore the source of SSFP FMRI signal changes by comparing SSFP data to conventional gradient-recalled echo (GRE) data. Data were acquired at a range of magnetic field strengths and repetition times, for both transition band and passband methods. The signal properties of SSFP and GRE differ significantly, confirming a different source of functional contrast in SSFP. In addition, the temporal noise properties are significantly different, with important implications for SSFP FMRI sequence optimisation.
The objective of the study was to investigate the feasibility of 7-T shoulder magnetic resonance imaging by developing transmit and receive radiofrequency (RF) coil arrays and exploring RF shim ...methods.
A mechanically flexible 8-channel transmit array and an anatomically conformable 10-channel receive array were designed and implemented. The transmit performance of various RF shim methods was assessed through local flip angle measurements in the right and left shoulders of 6 subjects. The receive performance was assessed through signal-to-noise ratio measurements using the developed 7-T coil and a baseline commercial 3-T coil.
The 7-T transmit array driven with phase-coherent RF shim weights provided adequate B₁⁺ efficiency and uniformity for turbo spin echo shoulder imaging. B₁⁺ twisting that is characteristic of high-field loop coils necessitates distinct RF shim weights in the right and left shoulders. The 7-T receive array provided a 2-fold signal-to-noise ratio improvement over the 3-T array in the deep articular shoulder cartilage.
Shoulder imaging at 7-T is feasible with a custom transmit/receive array either in a single-channel transmit mode with a fixed RF shim or in a parallel transmit mode with a subject-specific RF shim.
Objectives
To evaluate the image quality of T1-weighted fat-suppressed breast MRI at 7 T and to compare 7-T and 3-T images.
Methods
Seventeen subjects were imaged using a 7-T bilateral ...transmit-receive coil and 3D gradient echo sequence with adiabatic inversion-based fat suppression (FS). Images were graded on a five-point scale and quantitatively assessed through signal-to-noise ratio (SNR), fibroglandular/fat contrast and signal uniformity measurements.
Results
Image scores at 7 and 3 T were similar on standard-resolution images (1.1 × 1.1 × 1.1-1.6 mm
3
), indicating that high-quality breast imaging with clinical parameters can be performed at 7 T. The 7-T SNR advantage was underscored on 0.6-mm isotropic images, where image quality was significantly greater than at 3 T (4.2 versus 3.1,
P
≤ 0.0001). Fibroglandular/fat contrast was more than two times higher at 7 T than at 3 T, owing to effective adiabatic inversion-based FS and the inherent 7-T signal advantage. Signal uniformity was comparable at 7 and 3 T (
P
< 0.05). Similar 7-T image quality was observed in all subjects, indicating robustness against anatomical variation.
Conclusion
The 7-T bilateral transmit-receive coil and adiabatic inversion-based FS technique produce image quality that is as good as or better than at 3 T.
Key Points
•
High image quality bilateral breast MRI is achievable with clinical parameters at 7 T.
•
7-T high-resolution imaging improves delineation of subtle soft tissue structures.
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Adiabatic-based fat suppression provides excellent fibroglandular/fat contrast at 7 T.
•
7- and 3-T 3D T1-weighted gradient-echo images have similar signal uniformity.
•
The 7-T dual solenoid coil enables bilateral imaging without compromising uniformity.
The hippocampus is central to the pathophysiology of schizophrenia. Histology shows abnormalities in the dentate granule cell layer (DGCL), but its small size (~100μm thickness) has precluded in vivo ...human studies. We used ultra high field magnetic resonance imaging (MRI) to compare DGCL morphology of schizophrenic patients to matched controls.
Bilateral hippocampi of 16 schizophrenia patients (10 male) 40.7±10.6years old (mean±standard deviation) were imaged at 7Tesla MRI with heavily T2⁎-weighted gradient-echo sequence at 232μm in-plane resolution (0.08μL image voxels). Fifteen matched controls (8 male, 35.6±9.4years old) and one ex vivo post mortem hippocampus (that also underwent histopathology) were scanned with same protocol. Three blinded neuroradiologists rated each DGCL on a qualitative scale of 1 to 6 (from “not discernible” to “easily visible, appearing dark gray or black”) and mean left and right DGCL scores were compared using a non-parametric Mann–Whitney test.
MRI identification of the DGCL was validated with histopathology. Mean right and left DGCL ratings in patients (3.2±1.0 and 3.5±1.2) were not statistically different from those of controls (3.9±1.1 and 3.8±0.8), but patients had a trend for lower right DGCL score (p=0.07), which was significantly associated with patient diagnosis (p=0.05). The optimal 48% sensitivity and 80% specificity for schizophrenia were achieved with a DGCL rating of ≤2.
Decreased contrast in the right DGCL in schizophrenia was predictive of schizophrenia diagnosis. Better utility of this metric as a schizophrenia biomarker may be achieved in future studies of patients with homogeneous disease subtypes and progression rates.
Abstract Purpose The hippocampus is central to the pathophysiology of schizophrenia. Histology shows abnormalities in the dentate granule cell layer (DGCL), but its small size (~ 100 μm thickness) ...has precluded in vivo human studies. We used ultra high field magnetic resonance imaging (MRI) to compare DGCL morphology of schizophrenic patients to matched controls. Method Bilateral hippocampi of 16 schizophrenia patients (10 male) 40.7 ± 10.6 years old (mean ± standard deviation) were imaged at 7 Tesla MRI with heavily T2⁎ -weighted gradient-echo sequence at 232 μm in-plane resolution (0.08 μL image voxels). Fifteen matched controls (8 male, 35.6 ± 9.4 years old) and one ex vivo post mortem hippocampus (that also underwent histopathology) were scanned with same protocol. Three blinded neuroradiologists rated each DGCL on a qualitative scale of 1 to 6 (from “not discernible” to “easily visible, appearing dark gray or black”) and mean left and right DGCL scores were compared using a non-parametric Mann–Whitney test. Results MRI identification of the DGCL was validated with histopathology. Mean right and left DGCL ratings in patients (3.2 ± 1.0 and 3.5 ± 1.2) were not statistically different from those of controls (3.9 ± 1.1 and 3.8 ± 0.8), but patients had a trend for lower right DGCL score ( p = 0.07), which was significantly associated with patient diagnosis ( p = 0.05). The optimal 48% sensitivity and 80% specificity for schizophrenia were achieved with a DGCL rating of ≤ 2. Conclusion Decreased contrast in the right DGCL in schizophrenia was predictive of schizophrenia diagnosis. Better utility of this metric as a schizophrenia biomarker may be achieved in future studies of patients with homogeneous disease subtypes and progression rates.
Entorhinal cortex (EC) is a medial temporal lobe area critical to memory formation and spatial navigation that is among the earliest parts of the brain affected by Alzheimer's disease (AD). Accurate ...localization of EC would thus greatly facilitate early detection and diagnosis of AD. In this study, we used ultra-high resolution ex vivo MRI to directly visualize the architectonic features that define EC rostrocaudally and mediolaterally, then applied surface-based registration techniques to quantify the variability of EC with respect to cortical geometry, and made predictions of its location on in vivo scans. The results indicate that EC can be localized quite accurately based on cortical folding patterns, within 3 mm in vivo, a significant step forward in our ability to detect the earliest effects of AD when clinical intervention is most likely to be effective.
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