NRA & CSF Studies with Clinical Applications

As magnetic field strength increase toward higher fields , it allows significant improvements in MRI techniques by enhancing contrast to noise and signal to noise ratio. The use of magnetic resonance angiography (MRA) in ultra high magnetic field to visualize cerebrovascular structure of animals, promote development of early diagnosis and treatment of human neurodegenerative diseases. In this study, an improved contrast-to-noise ratio at 17.6 T imaging contribute to visualization the smaller vessels of the mouse brain. Branches of anterior cerebral artery (ACA)are better depicted on maximum intensity projections(MIP) with 17.6 T imaging than MIPs obtained with 9.4.

The purpose of this study was to evaluate the ability of 2D ToF-MRA to depict cerebral arteries in the canine brain and to compare the results obtained from a high field magnet (3T) with an ultrahigh field magnet (7T). ToF-MRA at high and ultra-high magnetic fields should be included in the MRI imaging protocol of dogs suspected of having cerebrovascular disease. 7T field ToF-MRA allows a better delineation of small vessels in the canine brain than 3T ToF-MRA.

Quantitative dynamic MRI requires knowledge of contrast agent (CA) concentration in blood. Due to the small size of murine vessels, so far an arterial input function (AIF) has only been measured in mouse hearts. Using a novel cryogenic probe at 9.4 T, we measured CA kinetics in intra- and extracranial vessels. Although high inter-individual variations were observed, in average, kinetics of the superficial temporal vein provided good estimates for blood CA concentration. Smaller vessels suffered from partial volume effects but were less prone to inter-individual variations. Whether mouse perfusion studies benefit from vessel-based AIFs, remains to be studied in future.

The purpose of this study was to evaluate the cerebral blood change in one cardiac cycle in different concentration of carbon dioxide inhalation. Using retrospectively gated 2D phase contrast MRI is suitable method for measuring the velocity of cerebral arteries and veins during one hear beat. It is noninvasive modality to quantify the blood flow and blood volume in one heart cycle with high spatial and temporal resolution. By this MR method, we proceeded the experiment that observe the blood flow change during the CO2 concentration change.

Cerebrovascular reserve or the ability to vasodilate under stress may be a crucial physiological mechanism, providing increased arterial flux when necessary. This study quantified flow within the internal carotid artery (ICA) in 14 normal young adults before and after administration of a carbonic anhydrase inhibitor (acetazolamide). Quantitative flow assessment was based on a single-slice, multi-phase, fast-field echo sequence. Data was extracted via ROI analysis. Significant increases in velocity, flux, apparent vessel diameter but not heart rate were observed following acetazolamide. This assessment provides an objective in-vivo marker of the functional reserve of the macrovascular supply system.

TOF MRA highly profits from high fields, however, SAR restrictions limit the use of high-resolution protocols. In particular, venous suppression with saturation pulses is difficult within clinically acceptable measurement times (TA ¡Ü 10min). Using the VERSE algorithm on the excitation pulses as well as on the energy-intensive saturation pulses permits an effective SAR reduction that can be used to shorten the acquisition time. With a modified TOF MRA pulse sequence high resolution intracranial MRA data sets with excellent venous suppression could be acquired in 10 min at 7 Tesla.

Spin-labeling-based FIR-MRA can provide high resolution 3D intracranial MRA. A detailed comparison of FIR-MRA (7.7 min) to standard 3D time-of-flight (TOF) MRA (6.5 min) was performed at 3 Tesla. Superior or equal vessel conspicuity, continuity, and venous suppression were demonstrated in eight normal subjects with FIR-MRA. Three clinical studies were performed. In two patients with coiled aneurysms, FIR-MRA provided superior depiction of aneurysm remnants to TOF. In one arteriovenous malformation (AVM) patient, FIR-MRA provided a clearer depiction of the AVM nidus than TOF and contrast-enhanced MRA, and could differentiate between the arterial and venous components of the AVM.

MRA of the supra-aortic vessels is usually performed in CARE bolus technique, which necessitates high operator experience and interaction with the control panel. TWIST requires less operator experience and interaction. Goal of the present work was to implement an automated and therefore robust protocol for the TWIST angiography of the supra-aortic vessels with high spatial resolution and increased likelihood of optimal arterial contrast by double bolus injection. The new double bolus injection protocol allowed for good separation of arterial vessels at least after one of the two bolus applications.

Intracranial artery imaging is usually done by 2DTSE. However, the technique has long scan time, and has very limited anatomical coverage. We propose here the use of T1w-SPACE, a variant of TSE, for 3D imaging of the intracranial vessels. Using a 32 channel head coil at 3.0T, the technique achieves a spatial resolution of (0.5mm)3, comparable to CT, in less than 11minutes. The technique can cover both sides of the tortuous ICA and MCA in one scan. SNR comparison found that the 3D technique has consistently higher SNR than 2DTSE.

We retrospectively evaluated the utility of susceptibility weighted imaging (SWI) in the detection of arterio-venous shunting (AVS) in 47 patients with 66 brain vascular malformations (BVM) identified on digital subtraction angiography (DSA). AVS was considered to be present if there was hyperintensity in a vein adjacent to the BVM. Overall, SWI had a sensitivity of 93%, specificity of 100% and accuracy of 97% for the detection of AVS. In the 13 BVMs associated with hemorrhage, SWI had sensitivity and specificity of 100%. In the 53 BVMs not associated with hemorrhage, SWI had a sensitivity of 92% and specificity of 100%.

To retrospectively compare 3.0- and 1.5-T magnetic resonance (MR) findings in patients with moyamoya disease (MMD), and assess the relationship and difference between those two modalities in the follow-up of MMD. 60 (120 sides) MMD patients (15 male and 45 female patients, age range: 5 to 60 years, post/pre-operative patients: 44/ 16) were included. We got different upgrading rate among one-year interval follow-up with 1.5- and 3.0-T MR in different orders. Regardless of disease progressing, we should be careful about 1.5-T MR in evaluating steno-occlusive severity of intracranial vessels in MMD for its higher overestimating rate compared with 3.0-T MR.

Complex flow patterns in cerebral aneurysms have been identified by computational fluid dynamics (CFD) studies to potentially be predictive of aneurysm rupture. Here, we quantified the stability of blood flow patterns in cerebral aneurysms in vivo based on flow features in 2D pcMRI images in seven aneurysms. A stability index (SI) defined as the area fraction (in percent) exhibiting sign changes of the through-plane velocity was calculated. Average SI range was 1.3%-20.6%. Average SI and aneurysm size were linearly correlated (R=0.796). Further studies are warranted to explore the potential of the average SI as a marker for aneurysm rupture.

Conventional imaging fails to reveal evidence of damage in mild traumatic brain injury (MTBI) that accounts for its disabling impairments. The purpose of the current study is to examine if perfusion changes in thalamus and basal ganglia can be a possible indicator of pathology in acute MTBI. We have employed segmented True-FISP ASL, which we recently developed to measure perfusion in deep gray matter at high spatial resolution. Results indicate there are significant differences between patients and controls in thalamus and caudate. This suggests these regions may exhibit hypoperfusion in acute MTBI and could be biomarkers of persistent post-concussive syndrome.

To validate 4D blood flow velocity measurements in intracranial aneurysms using phase contrast MRI, a real-size glass phantom of an intracranial aneurysm was created and used for blood flow velocity measurements using PC-MRI and PIV. Resolution of PC-MRI was 0.5x0.5x0.5 mm and took 70 minutes to scan. Both steady and pulsatile flow measurements in MRI and PIV produced similar flow patterns of similar magnitude, although more noise was found in the MR results. Velocity to noise ratio will improve with more accurate velocity encoding settings. More importantly, to be able to apply the PC-MRI scan in patients, scan time needs to be shortened severely, for example by acceleration techniques.

For patients with a symptomatic internal carotid artery (ICA) stenosis, it is often difficult to identify the symptomatic artery for treatment due to the variability in perfusion territories of the major cerebral arteries. For the basal ganglia, this imposes an even greater difficulty. Using selective arterial spin-labeling MRI, this study found the nucleus caudatus in patients with a symptomatic ICA stenosis was more often fed by the contralateral ICA compared to healthy control subjects (p=0.03). This was accompanied by reversed blood flow through the ipsilateral anterior part of the circle of Willis (p<0.01).

Cerebral arteriovenous malformations are congenital vascular lesions with dilated feeding arteries and draining veins without an intervening capillary bed. Treatment is recommended for most patients because of the risk of hemorrhage, which largely dependent on the imaging information available before treatment. Three-dimensional contrasted-enhanced MR angiography combined with MRI, as a noninvasive technique with the advantages of arterial angiography, can depict the feeding arteries, venous drainage pattern, nidus, and provide more accurate localization of the nidus, adjacent brain anatomy. These data are important for the planning of surgical resection, endovascular embolization and radiotherapy.

Susceptibility-weighted imaging (SWI) is sensitive to venous vasculature and is a powerful tool for evaluating vascular malformations such as venous angiomas. To enhance the visibility of small vascular structures, especially at 1,5T systems, a flow-sensitive black-blood (FS-BB) has been recently developed; The purpose of this study is to evaluate the utility of the FS-BB sequence in various intracranial lesions apart from vascular malformations.

In-vivo 3T MR and CTA images were acquired of symptomatic stroke patients. These images show that most of the patients presented high degrees of atherosclerotic carotid plaque. To help to identify unstable and vulnerable plaques, segmentation of the different plaque components was carried out by using a semiautomatic thresholding method. Half of the patients underwent surgical excision of the carotid plaque. The specimens obtained were imaged in a 7T scanner. The specimens were sectioned and stained with heamatoxylin-eosin and Elastin van Gieson. Correlation of the MRI datasets and Histology was carried out.

Vessel wall enhancement may serve as a potential marker for identification of high-risk atherosclerotic plaques. 3D-MRA and plaque enhancement at the level of the carotid bifurcation were assessed after application of the blood pool contrast agent gadofosveset trisodium and Gd-DTPA at 3.0 Tesla. 24h after injection of Gd-DTPA, no remaining vessel wall enhancement was observed, whereas remaining vessel wall enhancement (10% in atherosclerotic plaque and 2% in non-diseased vessel walls) was observed after injection of Gadofosveset Trisodium. Residual vessel wall enhancement 24h after injection of gadofosveset trisodium may reflect neo-vessel density and be a predictor for future ischemic events.

We evaluated the stenotic degree of arteries at the skull base level which are demonstrated on both 3D-TOF MRA and CE-MRA in 139 cases (659 vessels ). The discrepancy between these two technique in grading steotic degree occurred in 80 arteries. The stenotic grading were more severely estimated with CE MRA than with TOF MRA.We also performed phantom study. TOF-MRA tended to demonstrate the phantom more accurately than CE-MRA. On TOF-MRA with 1.6mm slice thickness, diameters were most accurately demonstrated. In CE-MRA, diameters of the tube were significantly more accurate with parallel imaging than with ZIP.

Diversion of excessive CSF from hydrocephalic brains by shunting is, in many cases, a life saving procedure. The down side of shunting is high failure rate. Consequently, about 40% of the shunting procedures performed annually in the US are for shunt replacement. The decision for shunt replacement is challenging as there is no reliable noninvasive test for shunt function. We present the first direct visualization and quantitation of CSF flow in ventricular shunts using high temporal and spatial resolution cine phase contrast MR and automated flow quantitation technique. Volumetric flow rate through in patent shunts were on the order of the CSF production rate.