Purpose:To improve the accuracy of dynamic susceptibility contrast (DSC) measurements of cerebral blood flow (CBF) and volume (CBV). Materials and Methods:In eight volunteers, steady-state CBV (CBV SS ) was measured using TrueFISP readout of inversion recovery (IR) before and after injection of a bolus of contrast. A standard DSC (STD) perfusion measurement was performed by echo-planar imaging (EPI) during passage of the bolus and subsequently used to calculate the CBF (CBF DSC ) and CBV (CBV DSC ). The ratio of CBV SS to CBV DSC was used to calibrate measurements of CBV and CBF on a subject-by-subject basis. Results:Agreement of values of CBV (1.77 Ϯ 0.27 mL/100 g in white matter (WM), 3.65 Ϯ 1.04 mL/100 g in gray matter (GM)), and CBF (23.6 Ϯ 2.4 mL/(100 g min) in WM, 57.3 Ϯ 18.2 mL/(100 g min) in GM) with published goldstandard values shows improvement after calibration. An F-test comparison of the coefficients of variation of the CBV and CBF showed a significant reduction, with calibration, of the variability of CBV in WM (P Ͻ 0.001) and GM (P Ͻ 0.03), and of CBF in WM (P Ͻ 0.0001). Conclusion:The addition of a CBV SS measurement to an STD measurement of cerebral perfusion improves the accuracy of CBV and CBF measurements. The method may prove useful for assessing patients suffering from acute stroke.
The steady-state (SS) approach has been proposed to measure quantitative cerebral blood volume (CBV). However, it is known that the CBV value in SS (CBV SS ) is subject to error resulting from the effects of water diffusion from the intra-to extravascular space. CBV SS measurements were simulated in both fastand no-water-exchange limits, and compared with measured CBV SS values to determine which limiting case is appropriate. Twenty-eight patients were scanned with a segmented LookLocker echo-planar imaging (LL-EPI) sequence before and after the injection of 0.1 mmol/kg of a T 1 -shortening contrast agent. Signal changes and T 1 values of brain parenchyma and the blood pool were measured pre-and postcontrast. These signal changes and T 1 values, in combination with the simulated results, were used to estimate water-exchange rates. We found that the intra-to extravascular water-exchange rates in white matter (WM) and gray matter (GM) were 0.9 and 1.6 s -1 , respectively. With these water-exchange rates, the fast-water-ex- In recent years MRI techniques have been developed to quantify a variety of physiologic parameters that reflect pathology. Parameters related to tissue perfusion have been shown to reflect underlying pathophysiology in a variety of diseases of the central nervous system, including ischemic stroke, tumor neovascularity, neoplasia, and Alzheimer's disease (1-5). Imaging techniques to measure relative cerebral blood volume (CBV), cerebral blood flow (CBF), and mean transit time (MTT) have been established (6). However, reliable quantification of these parameters has been elusive.When the blood-brain barrier (BBB) is intact, one can measure CBV values using contrast-enhanced MRI by comparing T 1 maps or T 1 -weighted images measured before and after the intravascular injection of a T 1 -shortening contrast agent (7,8). This approach is conventionally referred to as the steady-state CBV (CBV SS ) measurement. However, quantification of CBV SS has been problematic due to under-or overestimation resulting from the continual exchange of water from the intravascular space (9). The effect of water exchange has been extensively modeled (10), and there are predictable trends that depend on the approximations of the exchange rate. There are two limiting cases-the "fast-exchange" and "no-exchange" limits-that require different approaches to calculate CBV SS .We attempted to determine which limiting case of the exchange rate is valid in healthy tissue by performing direct measurements in humans. First we simulated CBV measurement in both fast-and no-water-exchange limits to determine the behavior in the range of values relevant to normal white matter (WM) and gray matter (GM). We then compared these simulated results with data acquired in patients. Then we used in vivo data to determine which limiting case is valid, and to determine the intravascular (to extravascular) and extravascular (to intravascular) water-exchange rates. Finally, with the optimum values for exchange rate determined, we developed a techni...
A method is presented for high spatial and temporal resolution 3D contrast-enhanced magnetic resonance angiography. The overall technique involves a set of interrelated components suited to high-frame-rate angiography, including 3D cylindrical k-space sampling, angular undersampling, asymmetric sampling, sliding window reconstruction, pseudorandom view ordering, and a sliding subtraction mask.
BACKGROUND AND PURPOSE:Spinal arteriovenous shunts usually require digital subtraction angiography (DSA) for evaluation. We report a unique time-resolved spinal MR angiographic (TRSMRA) technique with a temporal resolution of 3-6 seconds and spatial resolution of approximately 1 mm
Sufficient temporal resolution is required to image the dynamics of blood flow, which may be critical for accurate diagnosis and treatment of various intracranial vascular diseases, such as arteriovenous malformations (AVMs) and aneurysms. Highlyconstrained projection reconstruction (HYPR) has recently become a technique of interest for high-speed contrast-enhanced magnetic resonance angiography (CE-MRA). HYPR provides high frame rates by preferential weighting of radial projections while maintaining signal-to-noise ratio (SNR) by using a high SNR composite. An analysis was done to quantify the effects of HYPR on SNR, contrast-to-noise ratio (CNR), and temporal blur compared to the previously developed radial sliding-window technique using standard filtered backprojection or regridding methods. Computer simulations were performed to study the effects of HYPR processing on image error and the temporal information. Additionally, in vivo imaging was done on patients with angiographically confirmed AVMs to measure the effects of alteration of various HYPR parameters on SNR as well as the fidelity of the temporal information. The images were scored by an interventional radiologist in a blinded read and were compared with X-ray digital subtraction angiography (DSA). It was found that with the right choice of parameters, modest improvements in both SNR and dynamic information can be achieved as compared to radial sliding-window MRA. Magn
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