Self‐navigated spiral fMRI: Interleaved versus single‐shot

Glover, Gary H.; Lai, Song

doi:10.1002/mrm.1910390305

Cited by 464 publications

(367 citation statements)

References 21 publications

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“…However, the RMS field homogeneity after the slice-by-slice shim correction was typically 5.9 Hz and 8.1 Hz over the head area at 1.5 T and 3.0 T, respectively, both of which values are well below that required for significant blurring and affection of the point spread function (19).…”

Section: Spatial Aspects Of Activated Brainmentioning

confidence: 94%

“…The SNR was calculated as the ratio of the mean value (signal) from a brain region in the sum image and the standard deviation (noise) in the same ROI in the difference image. A more detailed discussion of this method to calculate SNR has been published recently (19). Note that the SNR calculation was based on an ROI encompassing a mixture between white and gray matter and covering major parts of the brain in the section.…”

Section: Signal-to-noise and Physiological Noisementioning

confidence: 99%

“…Beyond that, we employed very similar sampling times at both fields (T s ϭ 40.1 ms and T s ϭ 39.8 ms). At higher fields the shorter T* 2 relaxation time results in an increased broadening of the point-spread-function (19,21), causing more blurring in spiral imaging and distortions in conventional echo-planar imaging (EPI). Additionally, field inhomogeneities scale with B 0 and cause not only further off-resonance blurring but also stronger signal losses in regions affected by magnetic field susceptibilities.…”

Section: Snrmentioning

confidence: 99%

See 2 more Smart Citations

Neuroimaging at 1.5 T and 3.0 T: Comparison of oxygenation‐sensitive magnetic resonance imaging

Krüger

Kastrup

Glover

2001

Magnetic Resonance in Med

Self Cite

312

222

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Noise properties, the signal-to-noise ratio (SNR), contrast-tonoise ratio (CNR), and signal responses were compared during functional activation of the human brain at 1.5 and 3.0 T. At the higher field spiral gradient-echo (GRE) brain images revealed an average gain in SNR of 1.7 in fully relaxed and 2.2 in images with a repetition time (TR) of 1.5 sec. The tempered gain at longer TRs reflects the fact that the physiological noise depends on the signal strength and becomes a larger fraction of the total noise at 3.0 T. Activation of the primary motor and visual cortex resulted in a 36% and 44% increase of "activated pixels" at 3.0 T, which reflects a greater sensitivity for the detection of activated gray matter at the higher field. The gain in the CNR exhibited a dependency on the underlying tissue, i.e., an increase of 1.8؋ in regions of particular high activation-induced signal changes (presumably venous vessels) and of 2.2؋ in the average activated areas. These results demonstrate that 3.0 T provides a clear advantage over MRI modalities are often limited by the signal-to-noise ratio (SNR) and the contrast-to-noise ratio (CNR). Both SNR and CNR have been shown to increase with magnetic field strength B 0 (1,2). Consequently, the "optimal field strength" and the field dependency in blood oxygenation level dependent (BOLD) MRI have been the subject of various investigations (1,3-6). For many MRI applications a magnetic field strength of 1.5 Tesla (T) seems to represent a good compromise. Functional MRI (fMRI), however, is particularly dependent on good SNR and CNR properties, since typically observed BOLD signal changes at 1.5 T are on the order of a few percent and often exceed the intrinsic noise only slightly. Several biophysical models of activation-induced changes of the oxygenation-sensitive MRI signals have proposed that the changes in the relaxation rate ⌬R* 2 and subsequently the BOLD effect are proportional to B 0 for large vessels and proportional to B 0 2 for small vessels and capillaries (7,8). Thus, higher fields may provide an important improvement in fMRI. Indeed, recent investigations have demonstrated a superlinear increase in the BOLD CNR with the field strength (1,4,5), suggesting that high field fMRI methods may be able to resolve oxygenation changes in small vessels and capillaries, which are spatially localized near the origin of the neuronal activity.In the present study, various BOLD-relevant properties were compared at 1.5 T and 3.0 T. In order to establish identical BOLD-sensitivities, we investigated the T* 2 relaxation times for gray matter at each field strength and scaled the corresponding echo time (TE), and the excitation angle at 3.0 T. We compared intrinsic noise contributions and the SNR in gradient-echo (GRE) images and examined activation-induced BOLD responses during visual and motor activation at both fields in terms of spatial extent, the mean z-score, and the CNR of "activated voxels." T* 2 -maps from various brain sections were calculated to investigate spatial aspect...

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Section: Spatial Aspects Of Activated Brainmentioning

confidence: 94%

Section: Signal-to-noise and Physiological Noisementioning

confidence: 99%

Section: Snrmentioning

confidence: 99%

See 1 more Smart Citation

Neuroimaging at 1.5 T and 3.0 T: Comparison of oxygenation‐sensitive magnetic resonance imaging

Krüger

Kastrup

Glover

2001

Magnetic Resonance in Med

Self Cite

312

222

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“…The SPGR data were aligned such that adjacent pairs of 1.25-mm thick SPGR slices subtended each 2.5-mm thick FSE and DTI slice using custom scanner prescription software, which computed precise slice locations. The data from the spiral acquisition for each echo were gridded and Fourier transformed, and a fieldmap was estimated from a complex difference image between the two echoes (Glover and Lai, 1998;Pfeuffer et al, 2002). The 1.5 T structural data used for this analysis were coronally-acquired FSE images (FOV = 24 cm, T r = 7500 ms TE = 14/98 ms, ETL = 8, thick = 4.0 mm, skip = 0 mm, slices = 47, and echo-train flip angle = 180°).…”

Section: Mri and Dti Acquisition Protocolmentioning

confidence: 99%

Diffusion tensor imaging of deep gray matter brain structures: Effects of age and iron concentration

Pfefferbaum

Adalsteinsson

Rohlfing

et al. 2010

Neurobiology of Aging

167

169

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Diffusion tensor imaging (DTI) of the brain has become a mainstay in the study of normal aging of white matter, and only recently has attention turned to the use of DTI to examine aging effects in gray matter structures. Of the many changes in the brain that occur with advancing age is increased presence of iron, notable in selective deep gray matter structures. In vivo detection and measurement of iron deposition is possible with magnetic resonance imaging (MRI) because of iron's effect on signal intensity. In the process of a DTI study, a series of diffusion-weighted images (DWI) is collected, and while not normally considered as a major dependent variable in research studies, they are used clinically and they reveal striking conspicuity of the globus pallidus and putamen caused by signal loss in these structures, presumably due to iron accumulation with age. These iron deposits may in turn influence DTI metrics, especially of deep gray matter structures. The combined imaging modality approach has not been previously used in the study of normal aging. The present study used legacy DTI data collected in 10 younger (22-37 years) and 10 older (65-79 years) men and women at 3.0 T and fast spin-echo (FSE) data collected at 1.5 T and 3.0 T to derive an estimate of the fielddependent relaxation rate increase (the "FDRI estimate") in the putamen, caudate nucleus, globus pallidus, thalamus, and a frontal white matter sample comparison region. The effect of age on the diffusion measures in the deep gray matter structures was distinctly different from that reported in white matter. In contrast to lower anisotropy and higher diffusivity typical in white matter of older relative to younger adults observed with DTI, both anisotropy and diffusivity were higher in the older than younger group in the caudate nucleus and putamen; the thalamus showed little effect of age on anisotropy or diffusivity. Signal intensity measured with DWI was lower in the putamen of elderly than young adults, whereas the opposite was observed for the white matter region and thalamus. As a retrospective study based on legacy data, the FDRI estimates were based on FSE sequences, which underestimated the classical FDRI index of brain iron. Nonetheless, the differential effects of age on DTI metrics in subcortical gray matter structures compared with white matter tracts appears to be related, at least in part, to local iron content, which in the elderly of the present study was prominent

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“…BOLD imaging was performed with the use of a gradient-echo sequence (10 6-mm-thick slices, FOV ϭ 16 cm, TE/TR ϭ 40/1500 msec, NEX ϭ 2, ␣ ϭ 90°, bandwidth (BW) ϭ 100 kHz) with a spiral readout (4096 points per spiral) (6). A total of 180 temporal points were collected during which the subjects periodically inhaled 100% O 2 (four cycles of 90 seconds of normoxia, each followed by 45 seconds of 100% O 2 at 22 L/minute).…”

Section: Scanningmentioning

confidence: 99%

Vasomodulation of skeletal muscle BOLD signal

Bulte

Alfonsi

Bells

et al. 2006

Magnetic Resonance Imaging

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Purpose: To evaluate whether the BOLD signal from skeletal muscle can be modulated by exercise and ingestion of vasoactive substances. Materials and Methods:The right calf muscles of healthy adult volunteers were imaged using a GE 1.5-Tesla scanner and a gradient-echo sequence with spiral readout. Timevarying changes in the BOLD signal were induced through cyclic phases of normoxia (90 seconds of 20.8% O 2 ) and hyperoxia (45 seconds of 100% O 2 at 22 L/minute). Superimposed on this paradigm were pre-and post-exercise regimes, with and without ingestion of caffeine (100 mg) or antihistamine (4 mg chlorpheniramine). The numbers of voxels within slow-twitch (soleus) and fast-twitch (gastrocnemius) muscles that significantly responded to the paradigms were scored and compared using the AFNI software (NIMH).Results: Cycling-inspired O 2 produced a corresponding BOLD modulation that increased in magnitude with exercise. Chlorpheniramine significantly (P Ͻ 0.01) prevented the overall increase in exercise-induced soleus muscle BOLD signal, while caffeine accentuated the increase (P Ͻ 0.05) in the gastrocnemius relative to control (no vasomodulator) conditions. Conclusion:BOLD signal changes with exercise can be modulated by standard doses of chlorpheniramine (antihistamine) and caffeine. We suggest that chlorpheniramine may act detrimentally on slow-twitch muscle contractility, while caffeine appears to improve fast-twitch muscle function. THE BLOOD OXYGEN LEVEL-DEPENDENT (BOLD) signal in MRI, which was first described by Ogawa et al (1) in 1990, is attributed to a change in the blood ratio of oxyhemoglobin (oxyHb) to deoxyhemoglobin (deoxyHb). This signal modulation is the basis for functional MRI (fMRI) studies of brain activation, in which increased local metabolism disproportionately drives increased blood flow and volume, resulting in elevated oxyHb/deoxyHb and BOLD signal enhancement. Recently the BOLD signal has been applied to the study of other tissues, including muscle (2) and tumors (3), and BOLD signal changes have been observed with inspiration of 100% O 2 . In addition, the potential for MR to characterize myocardial perfusion reserve, as indexed by the BOLD response to maximal pharmacological vasodilation, has been documented (4,5).Even though the blood volume of the brain is fairly low (on the order of 4%), BOLD signal changes with activation are still visible. Skeletal muscle at rest has a comparable blood volume; however, activation (through exercise) results in comparatively larger increases in blood flow and volume. In a previous report (2) we demonstrated that cycling inspired gas between hyperoxia (100% O 2 ) and air (20.8% O 2 ) resulted in a time-varying BOLD signal in the lower human leg that was analyzable with routine "block design" fMRI-based methods and software. Using this method we showed clear differences between the soleus (slow-twitch oxidative muscle) and gastrocnemius (fast-twitch anaerobic/glycolytic muscle), which were hypothesized to be due largely to the comparatively greater mic...

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Self‐navigated spiral fMRI: Interleaved versus single‐shot

Cited by 464 publications

References 21 publications

Neuroimaging at 1.5 T and 3.0 T: Comparison of oxygenation‐sensitive magnetic resonance imaging

Neuroimaging at 1.5 T and 3.0 T: Comparison of oxygenation‐sensitive magnetic resonance imaging

Diffusion tensor imaging of deep gray matter brain structures: Effects of age and iron concentration

Vasomodulation of skeletal muscle BOLD signal

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