The human hippocampus at 7 T—In vivo MRI

Theysohn, JM; Kraff, Oliver; Maderwald, Stefan; Schlamann, M; Greiff, Armin de; Forsting, Michael; Ladd, SC; Ladd, Mark E.; Gizewski, Elke R.

doi:10.1002/hipo.20487

Cited by 79 publications

(79 citation statements)

References 31 publications

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“…Indeed, studies in schizophrenia that show a decline in the hippocampal cell viability marker ( N -acetylaspartate) levels ( 24 ) and hypermetabolism without volumetric changes ( 25 ) suggest that sensitivity to preclinical morphology may be key in establishing disease presence, disease progression, and, by implication, treatment response ( 26 ). Early visualization of signal intensity changes that may refl ect disruptions to hippocampal morphology requires high spatial resolution and contrast typically afforded only by 7.0-9.4-T fi eld strengths and high-element-count coil arrays ( 20,27,28 ). Although together these advanced imaging capabilities facilitate approximately 200-m m spatial resolution in 10-20 minutes, neither of two recent studies ( 20,28 ) demonstrated the ability of 7.0-T MR imaging to depict the DGCL.…”

Section: Mr Imagingmentioning

confidence: 99%

Human Hippocampal Subfields in Young Adults at 7.0 T: Feasibility of Imaging

Prudent¹,

Kumar²,

Liu³

et al. 2010

Radiology

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Purpose:To establish an imaging approach to visualize the 100-m mthick hippocampal neuron-generating dentate granule cell layer (DGCL) consistently within a clinically feasible magnetic resonance (MR) imaging duration and to assess its sensitivity by quantifying the likelihood that it will be detected in healthy young adults. Materials and Methods:The study was HIPAA compliant and institutional review board approved. All subjects provided written informed consent. Ten healthy volunteers (fi ve male subjects, fi ve female subjects; mean age , 26 years 6 6 [standard deviation]) were imaged at 7.0 T by using a 24-element head coil array with three-dimensional T1-weighted MR imaging for anatomic reference, followed by T2*-weighted gradient-echo (echo time, 25 msec; repetition time, 944 msec) imaging at 232-m m in-plane resolution (0.05-mm 3 pixels) in coronal and sagittal slabs (17 sections at 1 mm thick) over the hippocampus in 14 minutes. The entire study took 45 minutes. Results:The DGCL was consistently visible in all 10 enrolled subjects. All larger subfi elds were visible in excellent detail and contrast in every subject. Conclusion:The spatial resolution and tissue contrast at high fi eld strength (7.0 T) MR imaging can be used to consistently reveal hippocampal morphology down to 100-m m subfi elds within a clinically acceptable imaging duration. This imaging technique might be used to detect cellular disarray and degenerative changes in this sensitive circuit earlier than at 1.5 T or even 3.0 T.q RSNA, 2010 1

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Section: Mr Imagingmentioning

confidence: 99%

Human Hippocampal Subfields in Young Adults at 7.0 T: Feasibility of Imaging

Prudent¹,

Kumar²,

Liu³

et al. 2010

Radiology

View full text Add to dashboard Cite

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“…Imaging studies have used methods for identifying these hippocampal subfields through unfolding methods in high resolution functional MRI (Zeineh et al, 2000(Zeineh et al, , 2001Ekstrom et al, 2009) and high resolution in vivo (Mueller et al, 2007;Theysohn et al, 2009;Van Leemput et al, 2009) and ex vivo (Yushkevich et al, 2009) structural MRI mapping. These subfields are independent of subregional definitions of the hippocampus along its longitudinal axis (head, body, and tail) that are more readily evaluated in lower resolution imaging studies.…”

Section: Introductionmentioning

confidence: 99%

Hippocampal Subregions are Differentially Affected in the Progression to Alzheimer's Disease

Greene

Killiany

2011

The Anatomical Record

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Atrophy within the hippocampus (HP) as measured by magnetic resonance imaging (MRI) is a promising biomarker for the progression to Alzheimer's disease (AD). Subregions of the HP along the longitudinal axis have been found to demonstrate unique function, as well as undergo differential changes in the progression to AD. Little is known of relationships between such HP subregions and other potential biomarkers, such as neuropsychological (NP), genetic, and cerebral spinal fluid (CSF) beta amyloid and tau measures. The purpose of this study was to subdivide the hippocampus to determine how the head, body, and tail were affected in normal control, mild cognitively impaired, and AD subjects, and investigate relationships with HP subregions and other potential biomarkers. MRI scans of 120 participants of the Alzheimer's Disease Neuroimaging Initiative were processed using FreeSurfer, and the HP was subdivided using 3D Slicer. Each subregion was compared among groups, and correlations were used to determine relationships with NP, genetic, and CSF measures. Results suggest that HP subregions are undergoing differential atrophy in AD, and demonstrate unique relationships with NP and CSF data. Discriminant function analyses revealed that these regions, when combined with NP and CSF measures, were able to classify by diagnostic group, and classify MCI subjects who would and would not progress to AD within 12 months. Anat Rec,

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“…SAR mitigation strategies such as RF pulse elongation and bandwidth reduction provide modest power savings and can be applied to high-resolution imaging, but are, in general, of limited versatility and are insufficient to compensate for power levels at very high field. Limited reports from 7 T have presented 2D FSE images of the human head (7,8), but at the expense of the number of slices and with excess delay time for SAR reduction.Previous works have shown that reducing, and often modulating, the refocusing angles of the FSE echo train is a viable means of RF power reduction, contrast manipulation, and point spread function modification. A favorable nonlinear relationship between echo amplitude and refocusing angle (9) permits drastic power reductions with relatively minor signal penalties.…”

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confidence: 99%

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Time‐efficient fast spin echo imaging at 4.7 T with low refocusing angles

Wilman

2009

Magnetic Resonance in Med

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An implementation of fast spin echo at 4.7 T designed for versatile and time-efficient T 2 -weighted imaging of the human brain is presented. Reduced refocusing angles (␣ < 180°) were employed to overcome specific absorption rate (SAR) constraints and their effects on image quality assessed. Image intensity and tissue contrast variations from heterogeneous RF transmit fields and incidental magnetization transfer effects were investigated at reduced refocusing angles. We found that intraslice signal variations are minimized with refocusing angles near 180°, but apparent gray/white matter contrast is independent of refocusing angle. Incidental magnetization transfer effects from multislice acquisitions were shown to attenuate white matter intensity by 25% and gray matter intensity by 15% at 180°; less than 5% attenuation was seen in all tissues at flip angles below 60°. We present multislice images acquired without excess delay time for SAR mitigation using a variety of protocols. Fast spin echo (FSE) imaging, also known as RARE (1) and TSE, is a robust imaging sequence with numerous clinical and research applications. Prototypical FSE uses a 90°e xcitation pulse and a train of 180°refocusing pulses repeated every TR to form a single image. These refocusing pulses render FSE largely insensitive to static field inhomogeneities. High-field imaging systems-loosely defined here as those exceeding 3 T-promise exceptional capabilities including faster or higher-resolution imaging with altered, and possibly enhanced, tissue contrast mechanisms. Unfortunately, there are impediments to high-field imaging (2): First, static magnetic field heterogeneities scale linearly with main field strength and exacerbate signal losses and geometric distortions. Second, short RF wavelengths cause nonuniform sensitivity profiles for excitation and reception (3). Third, RF power deposition scales approximately quadratically with static field strength (4); patient safety requirements can limit successive high flip angle pulses, as required by FSE.Nevertheless, high-resolution FSE images of the human brain have previously been obtained at 4.7 T (5,6) using long interecho spacings (22 ms) to reduce the temporal density of RF pulses, short echo trains (eight refocusing pulses), slightly reduced refocusing flip angles (162°), and likely also long RF pulses, to constrain specific absorption rate (SAR) within safety regulations (4 W/kg for short exposure times). These works demonstrate that FSE and high field are not mutually exclusive; however, this implementation is ill-suited for variants, such as half Fourier acquisition single-shot turbo spin echo (HASTE), where short echo spacings and long echo trains are required and would produce extreme SAR levels due to a large number of brief, high-angle pulses per unit time. SAR mitigation strategies such as RF pulse elongation and bandwidth reduction provide modest power savings and can be applied to high-resolution imaging, but are, in general, of limited versatility and are insufficient to compensa...

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The human hippocampus at 7 T—In vivo MRI

Cited by 79 publications

References 31 publications

Human Hippocampal Subfields in Young Adults at 7.0 T: Feasibility of Imaging

Human Hippocampal Subfields in Young Adults at 7.0 T: Feasibility of Imaging

Hippocampal Subregions are Differentially Affected in the Progression to Alzheimer's Disease

Time‐efficient fast spin echo imaging at 4.7 T with low refocusing angles

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