In vivo hemodynamic analysis of intracranial aneurysms obtained by magnetic resonance fluid dynamics (MRFD) based on time-resolved three-dimensional phase-contrast MRI.

INTRODUCTION: Hemodynamics is thought to play a very important role in the initiation, growth, and rupture of intracranial aneurysms. The purpose of our study was to perform in vivo hemodynamic analysis of unruptured intracranial aneurysms of magnetic resonance fluid dynamics using time-resolved three-dimensional phase-contrast MRI (4D-Flow) at 1.5 T and to analyze relationships between hemodynamics and wall shear stress (WSS) and oscillatory shear index (OSI). METHODS: This study included nine subjects with 14 unruptured aneurysms. 4D-Flow was performed by a 1.5-T magnetic resonance scanner with a head coil. We calculated in vivo streamlines, WSS, and OSI of intracranial aneurysms based on 4D-Flow with our software. We evaluated the number of spiral flows in the aneurysms and compared the differences in WSS or OSI between the vessel and aneurysm and between whole aneurysm and the apex of the spiral flow. RESULTS: 3D streamlines, WSS, and OSI distribution maps in arbitrary direction during the cardiac phase were obtained for all intracranial aneurysms. Twelve aneurysms had one spiral flow each, and two aneurysms had two spiral flows each. The WSS was lower and the OSI was higher in the aneurysm compared to the vessel. The apex of the spiral flow had a lower WSS and higher OSI relative to the whole aneurysm. CONCLUSION: Each intracranial aneurysm in this study had at least one spiral flow. The WSS was lower and OSI was higher at the apex of the spiral flow than the whole aneurysmal wall.

Metabolite alterations in basal ganglia associated with psychiatric symptoms of abstinent toluene users: a proton MRS study.

Long-term toluene abuse causes a variety of psychiatric symptoms. However, little is known about abnormalities at the neurochemical level in the living human brain after long-term exposure to toluene. To detect neurochemical changes in the basal ganglia of subjects with a history of long-term toluene use, proton magnetic resonance spectroscopy (1H MRS) was performed in 12 abstinent toluene users and 13 healthy comparisons with no history of drug abuse. N-acetylaspartate (NAA), creatine plus phosphocreatine (Cr + PCr), choline-containing compounds (Cho), and myo-inositol (MI) levels were measured in the left and right basal ganglia. The Cho/Cr + PCr ratio, a marker of membrane metabolism, was significantly increased in the basal ganglia of toluene users in comparison to that of the control subjects. Furthermore, the increase in the Cho/Cr + PCr ratio was significantly correlated with the severity of residual psychiatric symptoms. These findings suggest that long-term toluene use causes membrane disturbance in the basal ganglia, which is associated with residual psychiatric symptoms that persist even after long-term abstinence from toluene use.

Preliminary study of tagged MR image velocimetry in a replica of an intracranial aneurysm.

Flow dynamics in intracranial aneurysms and their adjacent parent vessels play important roles in the development and rupture of intracranial aneurysms. Combined with tagged MR imaging and the use of particle image velocimetry software, tagged MR image velocimetry reveals flow vectors, vorticity, and shear strains at each location in the aneurysm replica every 9 milliseconds. This technique is a promising and noninvasive technique for assessing hemodynamics in intracranial aneurysms.

Acoustic noise transfer function in clinical MRI a multicenter analysis.

RATIONALE AND OBJECTIVES: Acoustic noise both in terms of its magnitude and frequency during magnetic resonance imaging (MRI) scan is influenced by imaging parameters and pulse sequences. It varies because of many different factors such as structure, materials, and magnetic field strength. The purpose of our study is to evaluate the characteristics of acoustic noise independent of MRI scan protocol by measuring a gradient-pulse-to-acoustic-noise transfer function (GPAN-TF) at various MRI scanners. MATERIALS AND METHODS: We measured sound pressure levels in the frequency domain in a 0.4-T, seven 1.5-T, and three 3.0-T clinical MRI systems when applying a simple narrower trapezoidal gradient pulse. We calculated a GPAN-TF [µPa/(mT/m)] in each gradient coil (ie, X, Y, and Z-axis) by the deconvolution process. RESULTS: GPAN-TF at a high-frequency range (1000-10,000 Hz) was larger than that at low frequency for all MRI (P<0.01) scanners except for a low static field machine. For high frequency (>1000 Hz), the 3.0-T MRI scanner had a larger GPAN-TF than that of 0.4-T and 1.5-T (P < .01). MR scanner with a vacuum chamber reduced GPAN-TF at a lower frequency (P < .01), but this effect decreased at higher frequency. CONCLUSION: GPAN-TF analysis makes it possible to obtain more detailed information on acoustic noise properties among MRI scanners.

Contrast-enhanced three-dimensional MR angiography with an elliptical centric view for the evaluation of intracranial aneurysms.

The purpose of this study was to assess the feasibility of high spatial resolution, selective arterial phase, 3D contrast-enhanced (CE) MR angiography with first pass bolus, software-trigger, elliptical centric view ordering in the detection of intracranial aneurysms. Our study included nine consecutive patients with ten intracranial aneurysms. 3D TOF MR angiography and 3D CE MR angiography were carried out with a 1.5-T MR scanner. 3D CE MR angiography was performed with an automated bolus detection algorithm and elliptical centric view order using ultrafast SPGR with a spatial resolution of 0.63x0.83x0.5 mm and imaging time of 55 s. Observers detected seven of ten aneurysms on 3D TOF MR angiograms and nine of ten aneurysms on 3D CE MR angiograms. 3D CE MR angiography clearly revealed an IC-PC aneurysm with a relatively smaller neck, a broad-based small aneurysm originating from tortuous and dilated MCA bifurcation, and a residual aneurysm and parent vessels adjacent to metallic aneurysmal clips, which had relatively low signal intensities on 3D TOF MR angiograms. 3D CE MR angiography was found to be a good and promising technique for detecting intracranial aneurysms with small necks and slow flow, vasculature with aneurysmal clips and tortuous vasculature with disturbed flow.

Visualization of hemodynamics in intracranial arteries using time-resolved three-dimensional phase-contrast MRI.

PURPOSE: To visualize the hemodynamics of the intracranial arteries using time-resolved three-dimensional phase-contrast (PC)-MRI (4D-Flow). MATERIALS AND METHODS: MR examinations were performed with a 1.5T MR unit on six healthy volunteers (22-50 years old, average = 30 years). 4D-Flow was based on a radiofrequency (RF)-spoiled gradient-echo sequence, and velocity encoding (VENC) was performed along all three spatial directions. Measurements were retrospectively gated to the electrocardiogram (ECG), and cine series of three-dimensional (3D) data sets were generated. The voxel size was 1 x 1 x 1 mm, and acquisition time was 30-40 minutes. 4D data sets were calculated into time-resolved images of 3D streamlines, 3D particle traces, and 2D velocity vector fields by means of flow visualization software. RESULTS: We were able to see the 3D streamlines from the circle of Willis to the bilateral M2 segment of the middle cerebral arteries (MCAs). Time-resolved images of 3D particle traces also clearly demonstrated intracranial arterial flow dynamics. 2D velocity vector fields on the planes traversing the carotid siphon or the basilar tip were clearly visualized. These results were obtained in all six volunteers. CONCLUSION: 4D-Flow helped to elucidate the in vivo 3D hemodynamics of human intracranial arteries. This method may be a useful noninvasive means of analyzing the hemodynamics of intracranial arteries in vivo.

Visualization of spinal cord motion associated with the cardiac pulse by tagged magnetic resonance imaging with particle image velocimetry software.

OBJECTIVE: The purpose of this study was to evaluate whether or not tagged magnetic resonance (MR) imaging with particle image velocimetry (PIV) software could reveal spinal cord motion clearly. METHODS: Six volunteers were enrolled in this study. Tagged MR imaging using fast spoiled gradient-recalled acquisition in the steady state with spatial modulation of the magnetization technique was performed using a 1.5-T MR system. RESULTS: Sagittal vector maps analyzed by PIV software revealed entire spinal cord motion sequentially during the cardiac cycle. The cervical spinal cord initially moved in a caudal direction and then continually oscillated from a cephalic-to-caudal direction. Each volunteer had a different cycle. In the thoracic spinal area, similar findings were observed, although they were slightly less clear than in the cervical area. CONCLUSION: Tagged MR imaging combined with PIV software, referred to as tagged MR image velocimetry, revealed spinal cord motion associated with the cardiac pulse, especially in the cervical spine.

Tumor enhancement using Mn-metalloporphyrin in mice: magnetic resonance imaging and histopathologic correlation.

PURPOSE: To determine the signal enhancement characteristics of tumors after administration of a metalloporphyrin derivative, HOP-9P (13, 17-bis (1-carboxypropionyl) carbamoylethyl-3, 8-bis (1-phenylpropyloxyethyl)-2, 7, 12, 18-tetramethyl-porphyrinato manganese (III)) and to determine whether HOP-9P is tumor-necrosis specific. MATERIALS AND METHODS: Ten C3H/He mice bearing a SCC VII tumor in the right flank were examined using T1-weighted conventional spin echo magnetic resonance (MR) imaging before contrast injection, and five minutes, one hour, and 24 hours after intravenous administration of 0.1 mmol/kg of HOP-9P. Following the imaging schedule, the mice were sacrificed, and sectioned in the same axial planes as the MR images. Based on an MR imaging-histopathologic correlation, mean signal intensities were measured, and signal-to-noise ratios (SNR) were calculated for both pure viable component and admixture of necrotic and viable component of the tumor. RESULTS: Mean SNR of the pure viable component peaked at one hour (35.0 +/- 3.8) and maintained that level until 24 hours (34.6 +/- 3.6). Mean SNR of the admixture of necrotic and viable component peaked at 24 hours (44.3 +/- 12.1). CONCLUSION: Although different enhancement patterns were seen between the pure viable component and the admixture of necrotic and viable component, HOP-9P enhanced both of the two components.

Assessment of a potential tumor-seeking manganese metalloporphyrin contrast agent in a mouse model.

The performance of a newly developed potential tumor-seeking magnetic resonance (MR) contrast agent alpha-Aqua-13,17-bis(1-carboxypropionyl) carbamoylethyl-3,8-bis(1-phenethyloxyethyl)-beta-hydroxy-2,7,12,18-tetramethyl-porphyrinato manganese (III) (HOP-8P) was tested using a mouse model. Tumor-bearing (SCC-VII) mice were imaged using a 1.5T MR imager before and after intravenous administration of 0.1 mmol/kg of HOP-8P. A biodistribution analysis was performed using an optical emission spectrometer. Significant enhancement of the transplanted tumor was observed in MR images 24 h after intravenous injection of HOP-8P. The biodistribution assessment of manganese also correlated with the results of the imaging study. During the 24-h period following contrast administration, HOP-8P was consistently cleared from the circulation, liver, kidneys, and muscle; however, it was progressively accumulated within the tumor. HOP-8P is a promising tumor-seeking metalloporphyrin MR contrast agent with a wide imaging window.