scholarly journals Dynamic Imaging of Perfusion and Oxygenation by Functional Magnetic Resonance Imaging

2004 ◽  
Vol 24 (12) ◽  
pp. 1369-1381 ◽  
Author(s):  
Kida Ikuhiro ◽  
K. Maciejewski Paul ◽  
Fahmeed Hyder
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Functional Mri ◽  
Dynamic Imaging ◽  
Flip Angle ◽  
Image Contrast ◽  
Laser Doppler ◽  
Resonance Imaging ◽  
Tissue Water ◽  
Dynamic Changes

Cerebral blood flow can be measured with magnetic resonance imaging (MRI) by arterial spin labeling techniques, where magnetic labeling of flowing spins in arterial blood water functions as the endogenous tracer upon mixing with the unlabeled stationary spins of tissue water. The consequence is that the apparent longitudinal relaxation time (T1) of tissue water is attenuated. A modified functional MRI scheme for dynamic CBF measurement is proposed that depends on extraction of T1 weighting from the blood oxygenation level–dependent (BOLD) image contrast, because the functional MRI signal also has an intrinsic T1 weighting that can be altered by variations of the excitation flip angle. In the α-chloralose-anesthetized rat model at 7T, the authors show that the stimulation-induced BOLD signal change measured with two different flip angles can be combined to obtain a T1-weighted MRI signal, reflecting the magnitude of the CBF change, which can be deconvolved to obtain dynamic changes in CBF. The deconvolution of the T1-weighted MRI signal, which is a necessary step for accurate reflection of the dynamic changes in CBF, was made possible by a transfer function obtained from parallel laser-Doppler flowmetry experiments. For all stimulus durations (ranging from 4 to 32 seconds), the peak CBF response measured by MRI after the deconvolution was reached at 4.5 ± 1.0 seconds, which is in good agreement with (present and prior) laser-Doppler measurements. Because the low flip angle data can also provide dynamic changes of the conventional BOLD image contrast, this method can be used for simultaneous imaging of CBF and BOLD dynamics.

scholarly journals Optimization of the Image Contrast for the Developing Fetal Brain using 3D Radial VIBE Sequence in 3T Magnetic Resonance Imaging

2021 ◽  
Author(s):  
Yi Liao ◽  
Xuesheng Li ◽  
Fenglin Jia ◽  
Zhijun Ye ◽  
Gang Ning ◽  
...  
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Image Quality ◽  
Gray Matter ◽  
Interobserver Reliability ◽  
Fetal Brain ◽  
Flip Angle ◽  
Image Contrast ◽  
Resonance Imaging ◽  
Radial Vibe

Abstract Background: Faster and motion robust magnetic resonance imaging (MRI) sequences are desirable in fetal brain MRI. T1-weighted images are essential for evaluating fetal brain development. We optimized the radial volumetric interpolated breath-hold examination (VIBE) sequence for qualitative T1-weighted images of the fetal brain with improved image contrast and reduced motion sensitivity. Materials and Methods: This was an institutional review board-approved prospective study. Thirty-two pregnant subjects underwent fetal brain scan at 3 Tesla MRI. T1-weighted images were acquired using a 3D radial VIBE sequence with flip angles of 6º, 9º, 12º, and 15º and turbo FLASH (TFL) sequence. Qualitative assessments including image quality and motion artifact severity were evaluated. The image contrast ratio between gray and white matter were measured. Interobserver reliability and intraobserver repeatability were assessed using intraclass correlation coefficient (ICC).Results: Interobserver reliability and intraobserver repeatability universally revealed almost perfect agreement (ICC > 0.800). Significant differences in image quality were detected in basal ganglia (P < 0.001), central sulcus (P = 0.005), myelination (P < 0.001), lateral fissure (P = 0.008), optic chiasm (P < 0.001), and gray matter (P < 0.001) among radial VIBE with flip angles 6º, 9º, 12º, 15º and TFL groups. Image quality at the 9º flip angle in radial VIBE was generally better than TFL. Radial VIBE sequence with 9º flip angle of gray matter was significantly different by gestational age (GA) before and after 28 weeks (P = 0.036). Quantified image contrast was significantly different among protocols, consistent with qualitative analysis of image quality.Conclusions: Three-dimensional radial VIBE with 9º flip angle provides optimal, stable T1-weighted images of the fetal brain. Fetal brain structure and development can be evaluated using high-quality images obtained using this angle.

scholarly journals Three-Tesla Magnetic Resonance Imaging of Patients With Deep Brain Stimulators: Results From a Phantom Study and a Pilot Study in Patients

Neurosurgery ◽  
2020 ◽  
Author(s):  
Benjamin Davidson ◽  
Fred Tam ◽  
Benson Yang ◽  
Ying Meng ◽  
Clement Hamani ◽  
...  
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Functional Mri ◽  
Phantom Study ◽  
Voltage Amplitude ◽  
Resonance Imaging ◽  
Safety Testing ◽  
3T Mri ◽  
Activated State ◽  
Deep Brain

Abstract BACKGROUND Deep brain stimulation (DBS) is a standard of care treatment for multiple neurologic disorders. Although 3-tesla (3T) magnetic resonance imaging (MRI) has become the gold-standard modality for structural and functional imaging, most centers refrain from 3T imaging in patients with DBS devices in place because of safety concerns. 3T MRI could be used not only for structural imaging, but also for functional MRI to study the effects of DBS on neurocircuitry and optimize programming. OBJECTIVE To use an anthropomorphic phantom design to perform temperature and voltage safety testing on an activated DBS device during 3T imaging. METHODS An anthropomorphic 3D-printed human phantom was constructed and used to perform temperature and voltage testing on a DBS device during 3T MRI. Based on the phantom assessment, a cohort study was conducted in which 6 human patients underwent MRI with their DBS device in an activated (ON) state. RESULTS During the phantom study, temperature rises were under 2°C during all sequences, with the DBS in both the deactivated and activated states. Radiofrequency pulses from the MRI appeared to modulate the electrical discharge from the DBS, resulting in slight fluctuations of voltage amplitude. Six human subjects underwent MRI with their DBS in an activated state without any serious adverse events. One patient experienced stimulation-related side effects during T1-MPRAGE scanning with the DBS in an ON state because of radiofrequency-induced modulation of voltage amplitude. CONCLUSION Following careful phantom-based safety testing, 3T structural and functional MRI can be safely performed in subjects with activated deep brain stimulators.

scholarly journals Diagnostic value of four-dimensional computed tomography and four-dimensional magnetic resonance imaging in primary hyperparathyroidism when first-line imaging was inadequate

2020 ◽  
Vol 102 (4) ◽  
pp. 294-299
Author(s):  
N Acar ◽  
M Haciyanli ◽  
M Coskun ◽  
NK Erdogan ◽  
SC Celik ◽  
...  
Keyword(s):  
Magnetic Resonance Imaging ◽  
Computed Tomography ◽  
Magnetic Resonance ◽  
Primary Hyperparathyroidism ◽  
Dynamic Imaging ◽  
Successful Outcome ◽  
Preoperative Imaging ◽  
Resonance Imaging ◽  
First Line ◽  
Line Imaging

Introduction Accurate localisation of the abnormal hyperfunctioning gland with preoperative imaging has a critical role in parathyroid surgery to obtain a successful outcome. This study aimed to evaluate the diagnostic performance of second-line imaging and their contribution to the treatment success in primary hyperparathyroidism when the first-line methods were negative or discordant. Methods Among the patients who underwent parathyroidectomy due to primary hyperparathyroidism, 33 who underwent four-dimensional computed tomography and/or four-dimensional magnetic resonance imaging because of negative or discordant first-line imaging results were included. Persistent and recurrent cases were excluded. Results The majority of the patients were female (84.8%) and the mean age was 59.2 years. Seventeen patients had four-dimensional computed tomography and 25 had four-dimensional magnetic resonance imaging, respectively. Four-dimensional computed tomography and four-dimensional magnetic resonance imaging localised the culprit gland successfully in 52.9% and 84%, respectively. Twenty-five patients in whom single adenoma was detected underwent focused parathyroidectomy. The culprit gland was solitary in 32 cases and one patient had double adenoma. Normocalcaemia was achieved in all cases. Among the 29 patients who completed their postoperative sixth month success rate was 100%. Conclusion Four-dimensional magnetic resonance imaging had high accuracy with fast dynamic imaging in detecting parathyroid adenomas. When the first-line imaging methods were negative or inconclusive, four-dimensional magnetic resonance imaging should be considered primarily since it is cost effective in Turkey and emits no radiation.

In Vivo MR Studies of Dynamic Changes in the Interosseous Membrane of the Forearm During Rotation

1999 ◽  
Vol 24 (2) ◽  
pp. 245-248 ◽  
Author(s):  
T. NAKAMURA ◽  
Y. YABE ◽  
Y. HORIUCHI
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Interosseous Membrane ◽  
Resonance Imaging ◽  
Forearm Rotation ◽  
Dynamic Changes ◽  
Magnetic Resonance Imaging Mri ◽  
Membranous Part ◽  
The Right

In vivo dynamic changes in the interosseous membrane (IOM) during forearm rotation were studied using magnetic resonance imaging (MRI). The right forearms of 20 healthy volunteers were examined in five different rotational positions. Axial slices were obtained at the proximal quarter, the middle and the distal quarter of the forearm. The changes in shape of the IOM during rotation were observed in an axial MR plane. For each image, we measured the interosseous distance and the length of the interosseous membrane. Images of the tendinous and membranous parts of the IOM could be differentiated by thickness. There were minimal dynamic changes in the tendinous part on the MRI while the membranous part showed numerous changes during rotation. The interosseous distance and the length of the interosseous membrane were maximum from a neutral to a slightly supinated position. The tendinous part is considered to be taut during rotation to provide stability between the radius and the ulna, but the membranous part which is soft, thin and elastic, allows smooth rotation.

High Resolution Magnetic Resonance Imaging of Excised Atherosclerotic Carotid Tissue: The Effects of Specimen Temperature on Image Contrast

2007 ◽  
Vol 9 (6) ◽  
pp. 915-920 ◽  
Author(s):  
Laura Rhodes ◽  
Cedric Abbott ◽  
Graham Fisher ◽  
David Russell ◽  
Demosthenes Dellagrammaticas ◽  
...  
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
High Resolution ◽  
Image Contrast ◽  
Resonance Imaging ◽  
Specimen Temperature
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