In vivo and ex vivo measurements of the mean ADC values of lipid necrotic core and hemorrhage obtained from diffusion weighted imaging in human atherosclerotic plaques

Purpose:

To determine the apparent diffusion coefficient (ADC) values of lipid and hemorrhage in atherosclerotic plaque in human carotid arteries in vivo and compare the values obtained from ex vivo carotid endarterectomy specimens.

Materials and Methods:

In vivo diffusion‐weighted imaging (DWI) of carotid plaques was performed using a 2D single shot Interleaved Multislice Inner Volume Diffusion Weighted Echo Planar Imaging (2D ss‐IMIV DWEPI) on 8 subjects who subsequently underwent carotid endarterectomy. A total of 32 slices used to construct the ADC maps were reviewed for the measurement of the mean ADC values in vessel wall, hemorrhage, and lipid necrotic core. The 8 endarterectomy specimens were scanned using by three‐dimensional ms‐IV‐DWEPI. After the ADC maps were created, the mean ADC values in the same locations selected for in vivo values were calculated.

Results:

The mean ADC values obtained from in vivo DWI in normal vessel wall, lipid rich core, and hemorrhage were 1.27 ± 0.16, 0.38 ± 0.1, and 0.98 ± 0.25 × 10^?3 mm²/s, respectively. The mean ADC values in ex vivo lipid necrotic core, and hemorrhage were 0.33 ± 0.08, 1.28 ± 0.10 × 10^?3 mm²/s, respectively. These components mean ADC values obtained from in vivo and ex vivo ADC maps were compared.

Conclusion:

ADC values of the carotid plaque components in vivo are consistent with values obtained from ex vivo endarterectomy specimens. The ability to obtain consistent plaque ADC values in vivo indicates that this technique could be an integral part of the basis for plaque component identification in conjunction with other MRI techniques. J. Magn. Reson. Imaging 2011;. © 2011 Wiley Periodicals, Inc.

     

In vivo quantification of murine aortic cyclic strain, motion, and curvature: implications for abdominal aortic aneurysm growth

Purpose

To develop methods to quantify cyclic strain, motion, and curvature of the murine abdominal aorta in vivo.

Materials and Methods

C57BL/6J and apoE^?/? mice underwent three‐dimensional (3D) time‐of‐flight MR angiography to position cardiac‐gated 2D slices at four locations along the abdominal aorta where circumferential cyclic strain and lumen centroid motion were calculated. From the 3D data, a centerline through the aorta was created to quantify geometric curvature at 0.1‐mm intervals. Medial elastin content was quantified with histology postmortem. The location and shape of abdominal aortic aneurysms (AAAs), created from angiotensin II infusion, were evaluated qualitatively.

Results

Strain waveforms were similar at all locations and between groups. Centroid motion was significantly larger and more leftward above the renal vessels than below (P < 0.05). Maximum geometric curvature occurred slightly proximal to the right renal artery. Elastin content was similar around the circumference of the vessel. AAAs developed in the same location as the maximum curvature and grew in the same direction as vessel curvature and motion.

Conclusion

The methods presented provide temporally and spatially resolved data quantifying murine aortic motion and curvature in vivo. This noninvasive methodology will allow serial quantification of how these parameters influence the location and direction of AAA growth. J. Magn. Reson. Imaging 2010;32:847–858. © 2010 Wiley‐Liss, Inc.

     

Estimation of the timing of carotid artery flow using peripheral pulse wave-gated MRI

Purpose:

To investigate the relationship between peripheral pulse wave (PPW)‐gating and the carotid systolic pulse wave in a large clinical patient cohort, and to establish a process for correct estimation of delay time from PPW‐gating to foot (ie, beginning) or peak times of carotid systolic pulse waves.

Materials and Methods:

Subjects comprised 209 patients scanned using 3T magnetic resonance imaging (MRI) for PPW‐gated phase contrast images at the common carotid artery. Stepwise multiple regression analysis was conducted for the relationship between foot or peak times and the following factors after excluding correlated factors with coefficients ≥0.5: pulse rate (PR); systolic blood pressure; diastolic blood pressure; height; body weight; body mass index; Brinkman index; diabetes mellitus; hypertension; and hyperlipidemia.

Results:

PR showed significant correlation with foot (r = ?0.86, P < 0.001) and peak (r = ?0.87, P < 0.001) times. The following equations were derived: foot time (msec) = ?8.55 × PR + 993.1 and peak time (msec) = ?9.21 × PR + 1142.3. No other factors showed significant correlations.

Conclusion:

PR was the only factor showing significant relationships to foot and peak times of carotid artery flow. The derived equations will facilitate various kinds of noncontrast MR acquisition with simple PPW‐gating. J. Magn. Reson. Imaging 2012;36:454–458. © 2012 Wiley Periodicals, Inc.

     

Diffusion‐weighted imaging of human carotid artery using 2D single‐shot interleaved multislice inner volume diffusion‐weighted echo planar imaging (2D ss‐IMIV‐DWEPI) at 3T: Diffusion measurement in atherosclerotic plaque

Purpose:

To determine if 2D single‐shot interleaved multislice inner volume diffusion‐weighted echo planar imaging (ss‐IMIV‐DWEPI) can be used to obtain quantitative diffusion measurements that can assist in the identification of plaque components in the cervical carotid artery.

Materials and Methods:

The 2D ss‐DWEPI sequence was combined with interleaved multislice inner volume region localization to obtain diffusion weighted images with 1 mm in‐plane resolution and 2 mm slice thickness. Eleven subjects, six of whom have carotid plaque, were studied with this technique. The apparent diffusion coefficient (ADC) images were calculated using DW images with b = 10 s/mm² and b = 300 s/mm².

Results:

The mean ADC measurement in normal vessel wall of the 11 subjects was 1.28 ± 0.09 × 10^?3 mm²/s. Six of the 11 subjects had carotid plaque and ADC measurements in plaque ranged from 0.29 to 0.87 × 10^?3 mm²/s. Of the 11 common carotid artery walls studied (33 images), at least partial visualization of the wall was obtained in all ADC images, more than 50% visualization in 82% (27/33 images), and full visualization in 18% (6/33 images).

Conclusion:

2D ss‐IMIV‐DWEPI can perform diffusion‐weighted carotid magnetic resonance imaging (MRI) in vivo with reasonably high spatial resolution (1 × 1 × 2 mm³). ADC values of the carotid wall and plaque are consistent with similar values obtained from ex vivo endarterectomy specimens. The spread in ADC values obtained from plaque indicate that this technique could form a basis for plaque component identification in conjunction with other MRI/MRA techniques. J. Magn. Reson. Imaging 2009;30:1068–1077. © 2009 Wiley‐Liss, Inc.

     

3D coronary motion tracking in swine models with MR tracking catheters

Purpose

To develop MR‐tracked catheters to delineate the three‐dimensional motion of coronary arteries at high spatial and temporal resolution.

Materials and Methods

Catheters with three tracking microcoils were placed into nine swine. During breath‐holds, electrocardiographic (ECG)‐synchronized 3D motion was measured at varying vessel depths. 3D motion was measured in American Heart Association left anterior descending (LAD) segments 6–7, left circumflex (LCX) segments 11–15, and right coronary artery (RCA) segments 2–3, at 60–115 beats/min heart rates. Similar‐length cardiac cycles were averaged. Intercoil cross‐correlation identified early systolic phase (ES) and determined segment motion delay.

Results

Translational and rotational motion, as a function of cardiac phase, is shown, with directionality and amplitude varying along the vessel length. Rotation (peak‐to‐peak solid‐angle RCA ≈0.10, LAD ≈0.06, LCX ≈0.18 radian) occurs primarily during fast translational motion and increases distally. LCX displacement increases with heart rate by 18%. Phantom simulations of motion effects on high‐resolution images, using RCA results, show artifacts due to translation and rotation.

Conclusion

Magnetic resonance imaging (MRI) tracking catheters quantify motion at 20 fps and 1 mm³ resolution at multiple vessel depths, exceeding that available with other techniques. Imaging artifacts due to rotation are demonstrated. Motion‐tracking catheters may provide physiological information during interventions and improve imaging spatial resolution. J. Magn. Reson. Imaging 2009;29:86–98. © 2008 Wiley‐Liss, Inc.

     

Whole‐heart coronary magnetic resonance angiography at 3.0T using short‐TR steady‐state free precession,vastly undersampled isotropic projection reconstruction

Purpose

To evaluate the feasibility of improving 3.0T steady‐state free precession (SSFP) whole‐heart coronary magnetic resonance angiography (MRA) using short‐TR (repetition time) VIPR (vastly undersampled isotropic projection reconstruction).

Materials and Methods

SSFP is highly sensitive to field inhomogeneity. VIPR imaging uses nonselective radiofrequency pulses, allowing short TR and reduced banding artifacts, while achieving isotropic 3D resolution. Coronary artery imaging was performed in nine healthy volunteers using SSFP VIPR. TR was reduced to 3.0 msec with an isotropic spatial resolution of 1.3 × 1.3 × 1.3 mm³. Image quality, vessel sharpness, and lengths of major coronary arteries were measured. Comparison between SSFP using Cartesian trajectory and SSFP using VIPR trajectory was performed in all volunteers.

Results

Short‐TR SSFP VIPR resulted in whole‐heart images without any banding artifacts, leading to excellent coronary artery visualization. The average image quality score for VIPR‐SSFP was 3.12 ± 0.42 out of four while that for Cartesian SSFP was 0.92 ± 0.61. A significant improvement (P < 0.05) in image quality was shown by Wilcoxon comparison. The visualized coronary artery lengths for VIPR‐SSFP were: 10.13 ± 0.79 cm for the left anterior descending artery (LAD), 7.90 ± 0.91 cm for the left circumflex artery (LCX), 7.50 ± 1.65 cm for the right coronary artery (RCA), and 1.84 ± 0.23 cm for the left main artery (LM). The lengths statistics for Cartesian SSFP were 1.57 ± 2.02 cm, 1.54 ± 1.93 cm, 0.94 ± 1.17 cm, 0.46 ± 0.53 cm, respectively. The image sharpness was also increased from 0.61 ± 0.13 (mm^?1) in Cartesian‐SSFP to 0.81 ± 0.11 (mm^?1) in VIPR‐SSFP.

Conclusion

With VIPR trajectory the TR is substantially decreased, reducing the sensitivity of SSFP to field inhomogeneity and resulting in whole‐heart images without banding artifacts at 3.0T. Image quality improved significantly over Cartesian sampling. J. Magn. Reson. Imaging 2010; 31:1230–1235. © 2010 Wiley‐Liss, Inc.

     

Free-breathing 3D whole-heart black-blood imaging with motion sensitized driven equilibrium

Purpose:

To automatically analyze the time course of collateralization in a rat hindlimb ischemia model based on signal intensity distribution (SID).

Materials and Methods:

Time‐of‐flight magnetic resonance angiograms (TOF‐MRA) were acquired in eight rats at 2, 7, and 21 days after unilateral femoral artery ligation. Analysis was performed on maximum intensity projections filtered with multiscale vessel enhancement filter. Differences in SID between ligated limb and a reference region were monitored over time and compared to manual collateral artery identification.

Results:

The differences in SID correlated well with the number of collateral arteries found with manual quantification. The time courses of ultrasmall (diameter ?0.5 mm) and small (diameter ≈0.5 mm) collateral artery development could be differentiated, revealing that maturation of the collaterals and enlargement of their feeding arteries occurred mainly after the first week postligation.

Conclusion:

SID analysis performed on axial maximum intensity projections is easy to implement, fast, and objective and provides more insight in the time course of arteriogenesis than manual identification. J. Magn. Reson. Imaging 2012;379‐386. © 2011 Wiley Periodicals, Inc.

     

Single breathhold cardiac CINE imaging with multi‐echo three‐dimensional hybrid radial SSFP acquisition

Purpose:

To achieve single breathhold whole heart cardiac CINE imaging with improved spatial resolution and temporal resolution by using a multi‐echo three‐dimensional (3D) hybrid radial SSFP acquisition.

Materials and Methods:

Multi‐echo 3D hybrid radial SSFP acquisitions were used to acquire cardiac CINE imaging within a single breathhold. An optimized interleaving scheme was developed for view ordering throughout the cardiac cycle.

Results:

Whole heart short axis views were acquired with a spatial resolution of 1.3 × 1.3 × 8.0 mm³ and temporal resolution of 45 ms, within a single 17 s breathhold. The technique was validated on eight healthy volunteers by measuring the left ventricular volume throughout the cardiac cycle and comparing with the conventional 2D multiple breathhold technique. The left ventricle functional measurement bias of our proposed 3D technique from the conventional 2D technique: end diastolic volume ?3.3 mL ± 13.7 mL, end systolic volume 1.4 mL ± 6.1 mL, and ejection fraction ?1.7% ± 4.3%, with high correlations 0.94, 0.97, and 0.91, accordingly.

Conclusion:

A multi‐echo 3D hybrid radial SSFP acquisition was developed to allow for a whole heart cardiac CINE exam in a single breathhold. Cardiac function measurements in volunteers compared favorably with the standard multiple breathhold exams. J. Magn. Reson. Imaging 2010;32:434–440. © 2010 Wiley‐Liss, Inc.

     

Utility of phase contrast MR imaging for assessment of pulmonary flow and pressure estimation in patients with pulmonary hypertension: Comparison with right heart catheterization and echocardiography

Purpose:

To compare the utility of phase contrast MR imaging (PC‐MRI) for assessment of pulmonary flow and pressure estimation with that of right heart catheterization and echocardiography (cardiac US) in patients with pulmonary arterial hypertension (PAH).

Materials and Methods:

Twenty consecutive patients with suspected PAH underwent PC‐MRI, cardiac US, and right heart catheterization. In each patient, PC‐MRI was acquired by cine 2D‐PC method on a 1.5 Tesla scanner, and stroke volume (SV) and pulmonary arterial systolic pressure (PASP) were assessed by using the modified Bernoulli's equation. To evaluate the agreements of SV and PASP among the three methods, correlations and limits of agreement among the three methods were statistically assessed by using the Bland‐Altman's analyses.

Results:

The correlations and limits of agreement for SV and PASP between PC‐MRI and catheterization (r = 0.96, r² = 0.94, 1.1 ± 6.9 mL and r = 0.94, r² = 0.88, ?3.2 ± 14.5 mmHg, respectively) were better than between cardiac US and catheterization (r = 0.01, r² < 0.01, 8.9 ± 42.1 mL and r = 0.86, r² = 0.72, ?5.9 ± 27.7 mmHg, respectively).

Conclusion:

PC‐MRI is more compatible with right heart catheterization than cardiac US in pulmonary flow and pressure estimation. J. Magn. Reson. Imaging 2009;30:973–980. © 2009 Wiley‐Liss, Inc.

     

Reliability in detection of hemorrhage in acute stroke by a new three-dimensional gradient recalled echo susceptibility-weighted imaging technique compared to computed tomography: a retrospective study

Purpose

To compare the sensitivity of magnetic resonance (MR) susceptibility‐weighted imaging (SWI) with conventional MR sequences and computed tomography (CT) in the detection of hemorrhage in an acute infarct.

Materials and Methods

A series of 84 patients suspected of having acute strokes had both CT and MR imaging (MRI) scans with diffusion‐weighted imaging (DWI) and SWI. The SWI sequence is a new high‐resolution three‐dimensional (3D) imaging technique that amplifies phase to enhance the magnitude contrast.

Results

Thirty‐eight of 84 cases showed abnormal DWI consistent with acute infarct. Of the 38, SWI showed evidence of hemorrhage in 16 cases, compared to eight cases with spin echo (SE) T2, seven cases with fluid attentuated inversion recovery (FLAIR), and only five cases with CT. In a subset of 17 cases of acute infarct who had both two‐dimensional gradient recalled echo (2D‐GRE) T2*‐weighted imaging and SWI, in addition to conventional MRI, evidence of hemorrhage was seen in 10 cases using SWI, compared to seven cases with 2D‐GRE T2*.

Conclusion

SWI proved to be a powerful new approach for visualizing hemorrhage in acute stroke compared to CT and conventional MRI methods. J. Magn. Reson. Imaging 2004;20:372–377. © 2004 Wiley‐Liss, Inc.

     

Automated ischemic lesion detection in a neonatal model of hypoxic ischemic injury

Purpose:

To develop and compare an automated detection system for ischemic lesions in a neonatal model of bilateral carotid artery occlusion with hypoxia (BCAO‐H) from T2 weighted MRI (T2WI) to the currently used “gold standard” of manual segmentation.

Materials and Methods:

Forty‐three P10 BCAO‐H rat pups and 8 controls underwent T2WI at 1 day and 28 days. A computational imaging method, Hierarchical Region Splitting (HRS), was developed to automatically and rapidly detect and quantify 3D lesion and normal appearing brain matter (NABM) volumes.

Results:

HRS quantified lesion and NABM volumes within 15 s in comparison to 3 h for its manual counterpart, with a high correlation for injury (r² = 0. 95; P = 8.6 × 10^?7) and NABM (r² = 0. 92; P = 1.4 × 10^?22). Average lesion volumes for mild, moderate, and severe injuries were 3.85%, 28.85%, and 52.98% for HRS and 0.51%, 24.22%, and 48.74% for manual detection. Lesion volumes and locations were similar for both methods (sensitivity: 0.82, specificity: 0.86, and similarity: 1.47).

Conclusion:

HRS is an accurate, objective, and rapid method to quantify injury evolution in neonatal hypoxic ischemic injury models. J. Magn. Reson. Imaging 2011;33:772–781. © 2011 Wiley‐Liss, Inc.

     

Coronary artery wall imaging: initial experience at 3 Tesla

Purpose

To assess the feasibility of black‐blood turbo spin‐echo imaging of the left anterior descending coronary artery wall at 3 Tesla under free‐breathing and breath‐hold conditions.

Materials and Methods

Proton density‐weighted black‐blood turbo spin‐echo imaging of the left anterior descending coronary artery was performed on 15 volunteers on a 3 T whole body scanner with an eight channel phased array coil. Volunteers were imaged during free‐breathing (with navigators, N = 5), or with breath‐hold (N = 5), or both (N = 2). Imaging was not possible in three volunteers due to either gradient or radiofrequency (RF) coupling with the electrocardiogram (ECG). Images were analyzed to determine coronary artery wall thickness, wall area, lumen diameter, and lumen area. Signal‐to‐noise and contrast‐to‐noise ratios were calculated.

Results

Coronary artery wall thickness, wall area, lumen diameter, and lumen area measurements were consistent with previous magnetic resonance (MR) measurements of the coronary wall at 1.5 Tesla.

Conclusion

Coronary wall imaging using free‐breathing and breath‐hold two‐dimensional black‐blood TSE is feasible at 3 T. Further improvement in resolution and image quality is required to detect and characterize coronary plaque. J. Magn. Reson. Imaging 2005;21:128–132. © 2005 Wiley‐Liss, Inc.

     

Transmural heterogeneity of left ventricular myocardium remodeling in postinfarct porcine model revealed by MR diffusion tensor imaging

Purpose:

To investigate the transmural heterogeneity of left ventricular myocardium structural remodeling.

Materials and Methods:

Ex vivo diffusion tensor imaging (DTI) was performed in six adult porcine heart samples with apical septum infarction collected 13 weeks after permanent left anterior descending coronary artery ligation and six age‐matched intact controls. Alterations in diffusion indices and myocardial fiber orientation, including fractional anisotropy (FA), mean apparent diffusion coefficient (mean ADC), axial diffusivity (λ_∥), radial diffusivity (λ_?), and fiber helix angle were investigated at five transmural zones across myocardium wall in regions adjacent and remote to the infarct.

Results:

In both adjacent and remote regions of infarcted hearts, FA showed no significant alteration across transmural zones compared to controls. However, mean ADC, λ_∥, and λ_? exhibited significant decreases at endocardium zones but not epicardium zones. Moreover, myocardial fiber helix angle shifted towards left‐handed orientation at all transmural zones, especially in regions adjacent to the infarct, becoming more aligned with the epicardium fiber orientation.

Conclusion:

These experimental DTI findings indicate that the endocardium was more vulnerable to infarction, leading to more pronounced microstructural changes during remodeling. The current DTI approach reveals additional information in delineating postinfarct remodeling process, which may provide insights into cardiac mechanics and clinical assessment of cardiac diseases. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.

     

Real‐time flow with fast GPU reconstruction for continuous assessment of cardiac output

Purpose:

To demonstrate the feasibility of real‐time phase contrast magnetic resonance (PCMR) assessment of continuous cardiac output with a heterogeneous (CPU/GPU) system for online image reconstruction.

Materials and Methods:

Twenty healthy volunteers underwent aortic flow examination during exercise using a real‐time spiral PCMR sequence. Acquired data were reconstructed in online fashion using an iterative sensitivity encoding (SENSE) algorithm implemented on an external computer equipped with a GPU card. Importantly, data were sent back to the scanner console for viewing. A multithreaded CPU implementation of the real‐time PCMR reconstruction was used as a reference point for the online GPU reconstruction assessment and validation. A semiautomated segmentation and registration algorithm was applied for flow data analysis.

Results:

There was good agreement between the GPU and CPU reconstruction (?0.4 ± 0.8 mL). There was a significant speed‐up compared to the CPU reconstruction (15×). This translated into the flow data being available on the scanner console ≈9 seconds after acquisition finished. This compares to an estimated time using the CPU implementation of 83 minutes.

Conclusion:

Our heterogeneous image reconstruction system provides a base for translation of complex MRI algorithms into clinical workflow. We demonstrated its feasibility using real‐time PCMR assessment of continuous cardiac output as an example. J. Magn. Reson. Imaging 2012; 36:1477–1482. © 2012 Wiley Periodicals, Inc.

     

Clinical evaluation of aortic coarctation with 4D flow MR imaging

Purpose:

To show that 4D Flow is a clinically viable tool for evaluation of collateral blood flow and demonstration of distorted blood flow patterns in patients with treated and untreated aortic coarctation.

Materials and Methods:

Time‐resolved, 3D phase contrast magnetic resonance imaging (MRI) (4D Flow) was used to assess blood flow in the thoracic aorta of 34 individuals: 26 patients with coarctation (22 after surgery or stent placement) and eight healthy volunteers.

Results:

Direct comparison of blood flow calculated with 2D and 4D phase contrast data at standard levels for analysis in coarctation patients showed good correlation and agreement (correlation coefficient r = 0.99, limits of agreement = ?20% to 20% for collateral blood flow calculations). Abnormal blood flow patterns were demonstrated at peak systole with 4D Flow visualization techniques in the descending thoracic aorta of patients but not volunteers. Marked helical flow was seen in 9 of 13 patients with angulated aortic arch geometries after coarctation repair. Vortical flow was seen in regions of poststenotic dilation.

Conclusion:

4D Flow is a fast and reliable means of evaluating collateral blood flow in patients with aortic coarctation in order to establish hemodynamic significance. It also can detect distorted blood flow patterns in the descending aorta after coarctation repair. J. Magn. Reson. Imaging 2010;31:711–718. © 2010 Wiley‐Liss, Inc.

     

4D time-resolved magnetic resonance angiography for noninvasive assessment of pulmonary arteriovenous malformations patency

Purpose

To assess the capability of four‐dimensional (4D) time‐resolved magnetic resonance angiography (MRA) to assess pulmonary arteriovenous malformations (PAVMs) patency by analyzing pulmonary arterial and venous enhancement kinetics.

Materials and Methods

Seven patients with eight documented patent PAVMs underwent a 4D‐MRA with keyhole and viewsharing compression at 3T with the following parameters: spatial resolution 0.87 × 0.87 × 1.4 mm³; field of view 500 × 350 × 238 mm³; dynamic scan time (temporal resolution) 1.2 seconds; total acquisition time 18.1 seconds for six dynamic datasets (6 × 1.2 sec + reference scan: 10.9 sec). All images were reviewed by two experienced radiologists. Image quality was rated on a qualitative 5‐point scale (1: not assessable to 5: excellent). Signal value was measured on cross‐sectional planes for the afferent arteries and efferent veins of the PAVM, and for normal reference healthy arteries and veins. The difference in time to peak for each coupled artery/vein (dTTPav) was calculated and compared with a Mann–Whitney test between PAVMs and reference vessels.

Results

Mean image quality was 3.2 ± 0.9. dTTPav was significantly smaller in PAVMs (0.15 ± 0.76 sec) than in reference vessels (3.75 ± 1.62 sec), P < 0.001.

Conclusion

4D‐MRA is a promising tool for noninvasive assessment of PAVM patency. J. Magn. Reson. Imaging 2010;32:1110–1116. © 2010 Wiley‐Liss, Inc.

     

Vascular space occupancy (VASO) cerebral blood volume‐weighted MRI identifies hemodynamic impairment in patients with carotid artery disease

Purpose

To assess the role of vascular space occupancy (VASO) magnetic resonance imaging (MRI), a noninvasive cerebral blood volume (CBV)‐weighted technique, for evaluating CBV reactivity in patients with internal carotid artery (ICA) stenosis.

Materials and Methods

VASO reactivity, defined as a signal change in response to hypercapnic stimulus (4‐second exhale, 14‐second breath‐hold), was measured in the left and right ICA flow territories in patients (n = 10) with varying degrees of unilateral and bilateral ICA stenosis and in healthy volunteers (n = 10).

Results

Percent VASO reactivity was more negative (P < 0.01) bilaterally in patients (ipsilateral: ?3.6 ± 1.5%; contralateral: ?3.4 ± 1.2%) compared with age‐matched controls (left: ?1.9 ± 0.6%; right: ?1.9 ± 0.8%). Owing to the nature of the VASO contrast mechanism, this more negative VASO reactivity was attributed to autoregulatory CBV effects in patients. A postbreath‐hold overshoot, which was absent in healthy volunteers, was observed unilaterally in a subset of patients.

Conclusion

More negative VASO reactivity was observed in patients with ICA stenosis and may be a marker of autoregulatory effects. Furthermore, the postbreath‐hold overshoot observed in patients is consistent with compensatory microvascular vasoconstriction and may be a marker of hemodynamic impairment. Based on the results of this feasibility study, VASO should be useful for identifying CBV adjustments in patients with steno‐occlusive disease of the ICA. J. Magn. Reson. Imaging 2009;29:718–724. © 2009 Wiley‐Liss, Inc.

     

Optimum fuzzy filters for phase‐contrast magnetic resonance imaging segmentation

Purpose

To develop and validate a multidimensional segmentation and filtering methodology for accurate blood flow velocity field reconstruction from phase‐contrast magnetic resonance imaging (PC MRI).

Materials and Methods

The proposed technique consists of two steps: (1) the boundary of the vessel is automatically segmented using the active contour approach; and (2) the noise embedded within the segmented vector field is selectively removed using a novel fuzzy adaptive vector median filtering (FAVMF) technique. This two‐step segmentation process was tested and validated on 111 synthetically generated PC MRI slices and on 10 patients with congenital heart disease.

Results

The active contour technique was effective for segmenting blood vessels having a sensitivity and specificity of 93.1% and 92.1% using manual segmentation as a reference standard. FAVMF was the superior technique in filtering out noise vectors, when compared with other commonly used filters in PC MRI (P < 0.05). The peak wall shear rate calculated from the PC MRI data (248 ± 39 sec^?1), was significantly decreased to (146 ± 26 sec^?1) after the filtering process.

Conclusion

The proposed two‐step segmentation and filtering methodology is more accurate compared to a single‐step segmentation process for post‐processing of PC MRI data. J. Magn. Reson. Imaging 2009;29:155–165. © 2008 Wiley‐Liss, Inc.

     

Impact of motion on T1 mapping acquired with inversion recovery fast spin echo and rapid spoiled gradient recalled‐echo pulse sequences for delayed gadolinium‐enhanced MRI of cartilage (dGEMRIC) in volunteers

Purpose:

To evaluate the impact of motion on T1 values acquired by using either inversion‐recovery fast spin echo (IR‐FSE) or three‐dimensional (3D) spoiled gradient recalled‐echo (SPGR) sequences for delayed gadolinium‐enhanced magnetic resonance imaging of cartilage (dGEMRIC) in volunteers.

Materials and Methods:

Single‐slice IR‐FSE and 3D SPGR sequences were applied to perform dGEMRIC in five healthy volunteers. A mutual information‐based approach was used to correct for image misregistration. Displacements were expressed as averaged Euclidean distances and angles. Averages of differences in goodness of fit (Δχ²) tests and averages of relative differences in T1 values (ΔT1) before and after motion correction were computed.

Results:

Maximum Euclidean distance was 3.5 mm and 1.2 mm for IR‐FSE and SPGR respectively. Mean ± SD of Δχ² were 10.18 ± 8.4 for IR‐FSE and ?1.37 ± 5.5 for SPGR. Mean ± SD of ΔT1 were 0.008 ± 0.0048 for IR‐FSE and ?0.002 ± 0.019 for FSPGR. Pairwise comparison of Δχ² values showed a significant difference for IR‐FSE, but not for 3D‐SPGR. Significantly greater variability in T1 values was also noted for IR‐FSE than for 3D‐SPGR.

Conclusion:

Involuntary motion has a significant influence on T1 values acquired with IR‐FSE, but not with 3D‐SPGR in healthy volunteers. J. Magn. Reson. Imaging 2010;32:394–398. © 2010 Wiley‐Liss, Inc.

     

Local flip angle correction for improved volume T1‐quantification in three‐dimensional dGEMRIC using the look‐locker technique

Purpose

To present an evaluation method for three‐dimensional Look‐Locker (3D‐LL) based T1 quantification, calculating correct T1 values independent of local flip angle (FA) variations. The method was evaluated both in phantoms and in vivo in a delayed Gadolinium Enhanced MRI of Cartilage (dGEMRIC) study with 33 subjects.

Materials and Methods

T1 was measured with 3D‐LL, using both local FA correction and a precalculated FA slice profile, and compared with standard constant FA correction, for all slices in phantoms and in both femur condyles in vivo. T1 measured using two‐dimensional Inversion Recovery (2D‐IR) was used as gold standard.

Results

Due to the FA being slice dependent, the standard constant FA correction results in erroneous T1 (systematic error = 109.1 ms in vivo), especially in the outer slices. With local FA correction, the calculated T1 is excellent for all slices in phantoms (<5% deviation from 2D‐IR). In vivo the performance is lower (systematic error = ?57.5 ms), probably due to imperfect inversion. With precalculated FA correction the performance is very good also in vivo (systematic error = 13.3 ms).

Conclusion

With the precalculated FA correction method, the 3D‐LL sequence is robust enough for in vivo dGEMRIC, even outside the centermost slices. J. Magn. Reson. Imaging 2009;30:834–841. © 2009 Wiley‐Liss, Inc.