Wanyong Shin

Glioblastoma: a method for predicting response to antiangiogenic chemotherapy by using MR perfusion imaging--pilot study.

PURPOSE To derive a magnetic resonance (MR)-based imaging metric that reflects local perfusion changes resulting from the administration of angiogenic-inhibiting chemotherapy in patients with recurrent glioblastoma multiforme (GBM). MATERIALS AND METHODS In this retrospective Institutional Review Board-approved HIPAA-compliant study, 16 patients (12 men, four women; mean age, 51.8 years + or - 15.1 [standard deviation]) with recurrent GBM received bevacizumab every 3 weeks (15 mg per kilogram of body weight) as part of a clinical trial. Baseline MR images were acquired, and follow-up images were acquired every 6 weeks thereafter until tumor progression or death. Imaging included perfusion and T1-weighted contrast material-enhanced MR imaging. Perfusion images were analyzed both with and without correction for contrast material leakage. The volumes of interest were selected as enhancing voxels on T1-weighted contrast-enhanced MR images. Relative cerebral blood volume (rCBV) maps were created from analysis of MR perfusion images. The volumes of interest were used to calculate the following parameters: size, mean rCBV, mean leakage coefficient K(2), and hyperperfusion volume (HPV), which is the fraction of the tumor with an rCBV higher than a predetermined threshold. Percent change in each parameter from baseline to first follow-up was compared with time to progression (TTP) by using a Cox proportional hazards model with calculation of hazard ratios. RESULTS The most significant hazard ratio was seen with a DeltaHPV cutoff of rCBV greater than 1.00 (hazard ratio, 1.077; 95% confidence interval: 1.026, 1.130; P = .002). The only significant ratios greater than one were those that resulted from perfusion calculated as mean rCBV and DeltaHPV. The ratios were also higher after correction for leakage. CONCLUSION This pilot study derived an imaging metric (HPV) that reflects local perfusion changes in GBMs. This metric was found to show a significantly improved correlation to TTP as compared with more commonly used metrics.

Quantitative cerebral perfusion using dynamic susceptibility contrast MRI: Evaluation of reproducibility and age- and gender-dependence with fully automatic image postprocessing algorithm

A novel approach for quantifying cerebral blood flow (CBF) is proposed that combines the bookend technique of calculating cerebral perfusion with an automatic postprocessing algorithm. The reproducibility of the quantitative CBF (qCBF) measurement in healthy controls (N = 8) showed a higher intraclass correlation coefficient (ICC) and lower coefficient of variation (COV) when calculated with automatic analysis (ICC/COV = 0.90/0.09) than when compared to conventional manual analysis (ICC/COV = 0.58/0.19). Also, the reproducibility in patients (N = 25) was successfully evaluated with the automatic analysis (ICC/COV = 0.81/0.14). In 175 consecutive clinical scans, we found 3.0% and 7.4% of qCBF decrease per decade in white matter (WM) (21.5 ± 6.66 ml/100 g‐min) and gray matter (GM) (49.6 ± 16.2 ml/100 g‐min), respectively. Cerebral blood volume (CBV) showed a significant 3.7% decrease per decade in GM (3.00 ± 0.94 ml/100 g) but not in WM (1.69 ± 0.40 ml/100 g). Mean transit time (MTT) increased by 1.9% and 3.8% per decade in WM (5.04 ± 0.88 s) and GM (4.14 ± 0.80 s), respectively. qCBF and MTT values between males (N = 85) and females (N = 90) were significantly different in GM. Women showed 11% higher qCBF as well as a higher decrease in qCBF with increasing age than men in the whole brain (WB). Our results supported the notion that population average empirical quantification of cerebral perfusion is subject to individual variation as well as age‐ and gender‐dependent variability. Magn Reson Med, 2007.

Method for Improving the Accuracy of Quantitative Cerebral Perfusion Imaging

To improve the accuracy of dynamic susceptibility contrast (DSC) measurements of cerebral blood flow (CBF) and volume (CBV).

Quantitative CBV measurement from static T1 changes in tissue and correction for intravascular water exchange

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 (CBVSS) is subject to error resulting from the effects of water diffusion from the intra‐ to extravascular space. CBVSS measurements were simulated in both fast‐ and no‐water‐exchange limits, and compared with measured CBVSS values to determine which limiting case is appropriate. Twenty‐eight patients were scanned with a segmented Look‐Locker echo‐planar imaging (LL‐EPI) sequence before and after the injection of 0.1 mmol/kg of a T1‐shortening contrast agent. Signal changes and T1 values of brain parenchyma and the blood pool were measured pre‐ and postcontrast. These signal changes and T1 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‐exchange limit of the CBV values showed good agreement with the simulation (r = 0.86 in WM, and 0.78 in GM). The CBV values with the correction for water‐exchange effects were recalculated as 2.73 ± 0.44 and 5.81 ± 1.12 of quantitative cerebral blood water volume (%) in WM and GM, respectively. Magn Reson Med, 2006.

4D radial contrast-enhanced MR angiography with sliding subtraction

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. Computer simulations and volunteer studies demonstrated the utility of each component of the technique. Angiograms of one hemisphere of the intracranial vasculature were acquired with a pixel size of 1.1 × 1.1 × 2.8 mm and a frame rate of 0.35 sec based on a temporal resolution of 3.5 sec. Such a 3D time‐resolved, or “4D,” technique has the potential to noninvasively acquire diagnostic quality images of certain anatomic regions with a frame rate fast enough to not only ensure the capture of an uncontaminated arterial phase, but even demonstrate contrast bolus flow dynamics. Clinical applications include noninvasive imaging of arteriovenous shunting, which is demonstrated with a patient study. Magn Reson Med 58:962–972, 2007.

Quantitative cerebral MR perfusion imaging: Preliminary results in stroke

To evaluate quantitative cerebral blood flow (qCBF) with traditional time‐based measurements or metrics of cerebral perfusion: time to peak (Tmax) and mean transit time (MTT) in stroke patients.

Comparison of Intraarterial MR Angiography at 3.0 T with X-ray Digital Subtraction Angiography for Detection of Renal Artery Stenosis in Swine

PURPOSE To compare the accuracy of catheter-directed intraarterial (IA) magnetic resonance (MR) angiography at 3.0 T with that of x-ray digital subtraction angiography (DSA) for the measurement of renal artery stenosis (RAS) in swine. MATERIALS AND METHODS Unilateral hemodynamically significant RAS (>50%) was induced surgically in six pigs with use of reverse cable ties. One to two weeks after surgery, each pig underwent x-ray DSA and MR angiography before and after percutaneous transluminal balloon angioplasty (PTA). X-ray DSA was performed before and after PTA of RAS by injection of iodinated contrast agent through a 5-F multiple-side hole angiographic catheter placed in the abdominal aorta under fluoroscopic guidance. MR angiography of RAS was performed before and after PTA of RAS on a 3.0-T clinical MR imager with use of gadolinium-based contrast agent. MR angiography and DSA images were analyzed with the full width at half maximum method. Percent stenosis measurements between x-ray DSA and MR angiography were compared with a paired t test and were correlated with linear regression and Bland Altman analysis (alpha = 0.05). RESULTS Six cases of RAS were induced and imaged successfully with DSA and MR angiography techniques before and after PTA. On x-ray DSA, median stenoses was 64% (95% CI 57%-80%) before PTA and 20% (95% CI 5%-32%) after PTA. Corresponding MR angiography median stenosis measurement was 69% (95% CI 58%-80%) before PTA and 26% (95% CI 16%-36%) after PTA. A paired t test comparison did not show a difference between DSA and MR angiography (P = .16). RAS measurements on MR angiography correlated closely (P < .01) with DSA measurements (r(2) = 0.92). CONCLUSION In swine, the accuracy of catheter-directed IA MR angiography with use of a clinical 3.0-T MR imaging unit for the measurement of RAS was similar to that of conventional x-ray DSA.

Method for Rapid Calculation of Quantitative Cerebral Perfusion

To evaluate an algorithm based on algebraic estimation of T1 values (three‐point estimation) in comparison with computational curve‐fitting for the postprocessing of quantitative cerebral perfusion scans.