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.

     

Quantifying in vivo hemodynamic response to exercise in patients with intermittent claudication and abdominal aortic aneurysms using cine phase‐contrast MRI

Purpose:

To evaluate rest and exercise hemodynamics in patients with abdominal aortic aneurysms (AAA) and peripheral occlusive disease (claudicants) using phase‐contrast MRI.

Materials and Methods:

Blood velocities were acquired by means of cardiac‐gated cine phase‐contrast in a 0.5 Tesla (T) open MRI. Volumetric flow was calculated at the supraceliac (SC), infrarenal (IR), and mid‐aneurysm (MA) levels during rest and upright cycling exercise using an MR‐compatible exercise cycle.

Results:

Mean blood flow increased during exercise (AAA: 130%, Claudicants: 136% of resting heart rate) at the SC and IR levels for AAA participants (2.6 ± 0.6 versus 5.8 ± 1.6 L/min, P < 0.001 and 0.8 ± 0.4 versus 5.1 ± 1.7 L/min, P < 0.001) and claudicants (2.3 ± 0.5 versus 4.5 ± 0.9 L/min, P < 0.005 and 0.8 ± 0.2 versus 3.3 ± 0.9 L/min, P < 0.005). AAA participants had a significant decrease in renal and digestive blood flow from rest to exercise (1.8 ± 0.7 to 0.7 ± 0.6 L/min, P < 0.01). The decrease in renal and digestive blood flow during exercise correlated with daily activity level for claudicants (R = 0.81).

Conclusion:

Abdominal aortic hemodynamic changes due to lower extremity exercise can be quantified in patients with AAA and claudication using PC‐MRI. The redistribution of blood flow during exercise was significant and different between the two disease states. J. Magn. Reson. Imaging 2010; 31: 425–429. © 2010 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.

     

Phase‐contrast magnetic resonance quantification of normal pulmonary venous return

Purpose

To assess the feasibility of phase‐contrast magnetic resonance (PCMR) in quantifying the pulmonary venous return in normal subjects.

Materials and Methods

PCMR was performed in 12 healthy adult volunteers (mean age 38 years, range 27–60 years; 9 men; body surface area 1.81 ± 0.15 m²) for the ascending and descending aorta, caval veins, main and branch pulmonary arteries, and pulmonary veins. Two readers independently quantified blood flow in all subjects.

Results

Intraobserver differences were ?2.0% (95% confidence interval [CI]: ?9.9% to 5.9%), ?4.5% (95% CI: ?15.6% to 6.5%), and ?0.7% (95% CI: ?4.5% to 3.0%) for all vessels, pulmonary veins, and other great vessels, respectively. Interobserver differences were ?2.0% (95% CI: ?10.6% to 6.6%), ?3.1% (95% CI: ?16.0% to 9.9%), and ?1.4% (95% CI: ?6.4% to 3.5%) for all vessels, pulmonary veins, and other great vessels, respectively. Pulmonary venous flow volume showed high correlations with the volumes of the pulmonary arterial flow, systemic arterial flow, and systemic venous flow (r = 0.76–0.92, P < 0.005).

Conclusion

Flow quantification of normal pulmonary venous return using PCMR is feasible with high reproducibility and accuracy. J. Magn. Reson. Imaging 2009;29:588–594. © 2009 Wiley‐Liss, Inc.

     

Feasibility of FAIR imaging for evaluating tumor perfusion

Purpose:

To evaluate the feasibility of flow‐sensitive alternating inversion recovery (FAIR) for measuring blood flow in tumor models.

Materials and Methods:

In eight mice tumor models, FAIR and dynamic contrast‐enhanced magnetic resonance imaging (DCE‐MRI) was performed. The reliability for measuring blood flow on FAIR was evaluated using the coefficient of variation of blood flow on psoas muscle. Three regions of interest (ROIs) were drawn in the peripheral, intermediate, and central portions within each tumor. The location of ROI was the same on FAIR and DCE‐MR images. The correlation between the blood flow on FAIR and perfusion‐related parameters on DCE‐MRI was evaluated using the Pearson correlation coefficient.

Results:

The coefficient of variation for measuring blood flow was 9.8%. Blood flow on FAIR showed a strong correlation with Kep (r = 0.77), percent relative enhancement (r = 0.73), and percent enhancement ratio (r = 0.81). The mean values of blood flow (mL/100 g/min) (358 vs. 207), Kep (sec^?1) (7.46 vs. 1.31), percent relative enhancement (179% vs. 134%), and percent enhancement ratio (42% vs. 26%) were greater in the peripheral portion than in the central portion (P < 0.01).

Conclusion:

As blood flow measurement on FAIR is reliable and closely related with that on DCE‐MR, FAIR is feasible for measuring tumor blood flow. J. Magn. Reson. Imaging 2010;32:738–744. © 2010 Wiley‐Liss, Inc.

     

Improved aortic stiffness assessment in the elderly using a one-dimensional fluid displacement MR method

Purpose

To assess the in vitro accuracy of two rapid projective MR wave velocity measurement sequences, and their relative performance for assessing aortic stiffness in adults of all ages.

Materials and Methods

In vitro testing was performed using latex tube phantoms with precisely‐known flow wave velocities, both in the presence and absence of simulated static tissue. A total of 104 adults representing a large age range (21–83 years) underwent aortic wave velocity (AWV) measurements using multiple trials of each method in a single MR session. The relative agreement between the two AWV results in each tertile of subject age and the coefficient of variation of the AWV data were assessed.

Results

In vitro wave velocities did not differ significantly from the known values for either MR method, with or without simulated static tissue. In vivo, the mean AWVs for the young and middle‐aged cohorts did not differ significantly between the two MR methods. However, in the elderly group, the two methods did not agree, and one sequence was found to be superior in this age cohort.

Conclusion

In elderly individuals, a one‐dimensional MR method for evaluating aortic stiffness based on aortic blood displacement yields a smaller coefficient of variation and superior overall performance than a similar method based on aortic blood velocity. The two methods perform equivalently in young and middle‐aged subjects. J. Magn. Reson. Imaging 2006. © 2006 Wiley‐Liss, Inc.

     

Dynamic physostigmine effects on hippocampus perfusion

Purpose:

To characterize the dynamic response of hippocampus blood flow to physostigmine infusion and to determine an infusion duration sufficiently long for robust detection of effects with arterial spin labeling (ASL) and sufficiently short to avoid peripheral side effects of physostigmine.

Materials and Methods:

Two female (49 ± 15 years) and nine male (53 ± 13 years) subjects were studied to determine the time course of the physostigmine effect on hippocampus blood flow with ASL perfusion imaging during 20 minutes of baseline, 30 minutes of physostigmine infusion at 1.0 mg/hr, and 70 minutes of recovery.

Results:

Hippocampus perfusion decreased steadily over the course of the infusion, with the reduction in flow becoming significant after 20 minutes of infusion, reaching lowest levels near the end of infusion, and remaining significantly low and stable in the 70‐minute recovery period. Percentage changes of hippocampus perfusion were ?13.3%, ?13.4%, and ?13.4% for left, right, and bilateral hippocampus, respectively, at the end of infusion.

Conclusion:

At a dose rate of 1.0 mg/hr it is feasible to use an infusion time as short as 20 minutes, performing perfusion imaging up to an hour after physostigmine infusion is discontinued, to minimize chances for adverse side effects. J. Magn. Reson. Imaging 2012;280‐286. © 2011 Wiley Periodicals, 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.

     

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.

     

Assessment of macrophage infiltration in a Murine model of abdominal aortic aneurysm

Purpose

To evaluate the use of an ultrasmall superparamagnetic iron oxide (USPIO) contrast agent as a marker for the detection of macrophage in a preclinical abdominal aortic aneurysm animal (AAA) model.

Materials and Methods

Osmotic pumps were implanted subcutaneously in apoE^?/? mice for continuous infusion of Angiotensin II (Ang‐II). Weekly bright‐blood gradient echo scans were performed on the suprarenal abdominal aorta to evaluate aneurysm development. Once an AAA was detected, animals were administered 1000 μmol/kg of the USPIO contrast agent ferumoxtran‐10 (Combidex®) followed by in vivo scanning 24 h post‐USPIO administration. After in vivo imaging, aortas were harvested for ex vivo imaging, histology, iron quantification, and gene expression analysis.

Results

Reduced signal intensity was evident in the post‐USPIO transverse images of the abdominal aorta. The areas of reduced signal were primarily along the aneurysm shoulder and outer perianeurysm areas and corresponded to regions of macrophage infiltration and colocalized USPIO determination by means of histological staining. The absolute iron content measured significantly correlated to the area of signal reduction in the ex vivo images (r = 0.9; P < 0.01). In the AAA tissue, the macrophage‐driven cytokine gene expression was up‐regulated along with a matrix metalloproteinase known to mediate extracellular matrix breakdown in this disease model.

Conclusion

These results demonstrate the feasibility of using an USPIO contrast agent as a surrogate for detecting the acute inflammatory process involved in the development of abdominal aneurysms. J. Magn. Reson. Imaging 2009;30:455–460. Published by Wiley‐Liss, Inc.

     

Cardiovascular MR dobutamine stress in adult tetralogy of Fallot: disparity between CMR volumetry and flow for cardiovascular function

Purpose:

To evaluate the MR agreement of cardiac function parameters between volumetric (cine SSFP) and phase contrast flow (PC‐flow) assessment in patients with repaired tetralogy of Fallot (r‐TOF) and chronic pulmonary regurgitation (PR) at rest and under dobutamine stress (DS‐MR).

Materials and Methods:

We studied 18 patients with r‐TOF and severe chronic PR (34 ± 12.7 years, PR fraction_[flow] 44 ± 15%) by cardiac MR at rest, 10 and 20 μg/kg/min of dobutamine. We compared analogous functional parameters by volumetry and PC‐flow: (i) Systemic output [left ventricle stroke volume (LV_SV) versus aortic forward flow (AO_FF)], (ii) Pulmonary output [right ventricle stroke volume (RV_SV) versus pulmonary forward flow (PA_FF)], (iii) PR volume [(RV_SV‐LV_SV) versus pulmonary backward flow (PA_BF)], (iv) PR fraction [(RV_SV‐LV_SV/RV_SV) versus (PA_BF/PA_FF)].

Results:

We found excellent Bland‐Altman agreement (mean difference ± limits of agreement, mL/beat/m²) at rest for both the systemic (?0.8 ± 5.7) and pulmonary strokes volumes (?0.1 ± 7.6), which slightly deteriorates during DS‐MR. The PR volume showed acceptable agreement at rest (?3.6 ± 15.1), but also further deteriorated during stress (5.4 ± 24). In contrast, the PR fraction showed poor agreement equally at rest (?5.6 ± 22.8) and DS‐MR (3.2 ± 19.2).

Conclusion:

In r‐TOF with chronic PR, analogous functional parameters should not be used interchangeably between volumetric and PC‐flow assessment during DS‐MR evaluation. J. Magn. Reson. Imaging 2011;33:1341–1350. © 2011 Wiley‐Liss, Inc.

     

Effects of cardiac motion on 3D contrast-enhanced MR angiography of the carotid arteries

Purpose:

To determine the effect of cardiac‐related carotid artery motion on the image quality of 3D contrast‐enhanced MR angiography (CEMRA) in patients presenting with suspected carotid artery disease.

Materials and Methods:

Twenty patients with suspected carotid artery disease underwent cardiac‐gated cinematic steady‐state free precession of the carotid arteries followed by standard 3D CEMRA at 1.5 T. Using postprocessing, computer programs determined the degree of vessel wall dilation and translation across the cardiac cycle from the cinematic exam and related this to vessel wall sharpness in 3D CEMRA, which was determined objectively by computer analysis and subjectively by a panel of expert neuroradiologists.

Results:

In patients, across 40 arteries the average carotid vessel movement due to cardiac pulsation was 0.36 ± 0.17 mm and translation 1.53 ± 0.94 mm. When using computer analysis of sharpness, the mean carotid wall motion had a weak negative correlation with 3D CEMRA vessel sharpness (Pearson's correlation ?0.23, P < 0.01). However, the same trend was not present from the radiological review.

Conclusion:

In standard 3D CEMRA in patients with suspected carotid artery disease, cardiac‐related carotid movement was a statistically significant source of degradation in vessel sharpness, but did not appear to be clinically significant. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.

     

Compliance and pulse wave velocity assessed by MRI detect early aortic impairment in young patients with mutation of the smooth muscle myosin heavy chain

Purpose

To evaluate aortic elasticity with MRI on young asymptomatic individuals with mutation of the smooth muscle myosin heavy chain in whom aortic enlargement is not present.

Materials and Methods

Aortic compliance, aortic distensibility, and pulse wave velocity (PWV) were semiautomatically measured from MRI in 8 asymptomatic subjects having a mutation of the MYH11 gene (M+) and 21 nonmutated relatives (M?) of similar age, sex, and blood pressure characteristics.

Results

Despite a similar aortic diameter in both groups, the aortic compliance and distensibility were significantly lower in M+ subjects compared with M? (0.84 ± 0.33 versus 2.03 ± 0.54 mm²/mmHg, 1.18 ± 0.62 10^?3 versus 5.11 ± 1.58 10^?3 mmHg^?1, respectively), and PWV was significantly higher (5.35 ± 1.53 versus 3.60 ± 0.64 m.s^?1). A threshold aortic compliance value of 1.3 mm²/mmHg separated the two groups. The receiver operating characteristics curve analysis indicated an optimal threshold of 2.9 10^?3 mmHg^?1 for aortic distensibility (sensitivity: 87.5%, specificity: 90%), and of 4.4 m.s^?1 for PWV (sensitivity: 75%, specificity: 100%).

Conclusion

Young asymptomatic adults with MYH11 mutation have an aortic compliance impairment which is not detectable by the sole measurement of the aortic size. Aortic compliance measurement might be part of routine examination in patients suspected of inherited aortic disease even with a normal aortic diameter. J. Magn. Reson. Imaging 2008;28:1180–1187. © 2008 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 blood flow on diffusion coefficients of the human kidney: A time‐resolved ECG‐triggered diffusion‐tensor imaging (DTI) study at 3T

Purpose:

To evaluate the impact of renal blood flow on apparent diffusion coefficients (ADC) and fractional anisotropy (FA) using time‐resolved electrocardiogram (ECG)‐triggered diffusion‐tensor imaging (DTI) of the human kidneys.

Materials and Methods:

DTI was performed in eight healthy volunteers (mean age 29.1 ± 3.2) using a single slice coronal echoplanar imaging (EPI) sequence (3 b‐values: 0, 50, and 300 s/mm²) at the timepoint of minimum (20 msec after R wave) and maximum renal blood flow (200 msec after R wave) at 3T. Following 2D motion correction, region of interest (ROI)‐based analysis of cortical and medullary ADC‐ and FA‐values was performed.

Results:

ADC‐values of the renal cortex at maximum blood flow (2.6 ± 0.19 × 10^?3 mm²/s) were significantly higher than at minimum blood flow (2.2 ± 0.11 × 10^?3 mm²/s) (P < 0.001), while medullary ADC‐values did not differ significantly (maximum blood flow: 2.2 ± 0.18 × 10^?3 mm²/s; minimum blood flow: 2.15 ± 0.14 × 10^?3 mm²/s). FA‐values of the renal medulla were significantly greater at maximal blood (0.53 ± 0.05) than at minimal blood flow (0.47 ± 0.05) (P < 0.01). In contrast, cortical FA‐values were comparable at different timepoints of the cardiac cycle.

Conclusion:

ADC‐values in the renal cortex as well as FA‐values in the renal medulla are influenced by renal blood flow. This impact has to be considered when interpreting renal ADC‐ and FA‐values. J. Magn. Reson. Imaging 2013;37:233–236. © 2012 Wiley Periodicals, Inc.

     

Relationship between sodium intensity and perfusion deficits in acute ischemic stroke

Purpose

To assess the relationship between sodium signal intensity changes and oligemia, measured with perfusion‐weighted imaging (PWI), in ischemic stroke patients.

Materials and Methods

Nine ischemic stroke patients (55 ± 13 years), four with follow‐up scans, underwent sodium and proton imaging 4–32 hours after symptom onset. Relative sodium intensity was calculated as the ratio of signal intensities in core (identified as hypertintense lesions on diffusion‐weighted imaging [DWI]) or putative penumbra (PWI‐DWI mismatch) to contralateral homologous regions.

Results

Sodium intensity increases in the core were not correlated with the severity of hypoperfusion, measured with either cerebral blood flow (rho = 0.157; P = 0.61) or cerebral blood volume (rho = ?0.234; P = 0.44). In contrast, relative sodium intensity was not elevated (4–7 hours 0.96 ± 0.07; 17–32 hours 1.00 ± 0.07) in PWI‐DWI mismatch regions.

Conclusion

Sodium signal intensity cannot be predicted by the degree of hypoperfusion acutely. Sodium intensity also remains unchanged in PWI‐DWI mismatch tissue, indicating preservation of ionic homeostasis. Sodium magnetic resonance imaging (MRI), in conjunction with PWI and DWI, may permit identification of patients with viable tissue, despite an unknown symptom onset time. J. Magn. Reson. Imaging 2011;33:41–47. © 2010 Wiley‐Liss, Inc.

     

Cine cerebrospinal fluid imaging in multiple sclerosis

Purpose:

To investigate cerebrospinal fluid (CSF) dynamics in the aqueduct of Sylvius in multiple sclerosis (MS) patients and healthy controls (HC) using cine phase contrast imaging.

Materials and Methods:

In all, 67 MS patients (48 relapsing‐remitting [RR] and 19 secondary‐progressive [SP]), nine patients with clinically isolated syndrome (CIS), and 35 age‐ and sex‐matched HC were examined. CSF flow and velocity measures were quantified using a semiautomated method and compared with clinical and magnetic resonance imaging (MRI) disease outcomes.

Results:

Significantly decreased CSF net flow was detected in MS patients compared to HC (?3.7 vs. ?7.1 μL/beat, P = 0.005). There was a trend for increased net positive flow between SP, RR, and CIS patients. Altered CSF flow and velocity measures were associated with more severe T1 and T2 lesion volumes, lateral and fourth ventricular volumes, and third ventricular width in MS and CIS patients (P < 0.01 for all). In CIS patients, conversion to clinically definite MS in the following year was related to decreased CSF net flow (P = 0.007). There was a trend between increased annual relapse rate and altered CSF flow/velocity measures in RRMS patients (P < 0.05).

Conclusion:

CSF flow dynamics are altered in MS patients. More severe clinical and MRI outcomes in RRMS and CIS patients relate to altered CSF flow and velocity measures. J. Magn. Reson. Imaging 2012;36:825–834. © 2012 Wiley Periodicals, 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.

     

Value of quantitative MRI biomarkers (Evans' index,aqueductal flow rate,and apparent diffusion coefficient) in idiopathic normal pressure hydrocephalus

Purpose

To define the value of Evans' index (EI), aqueductal flow rate (FR), and apparent diffusion coefficient (ADC) in the diagnosis of normal pressure hydrocephalus (NPH) and to assess the ability of these markers preoperatively to predict shunt response. To shed some light as to the mechanisms responsible for the symptoms of NPH.

Materials and Methods

Preoperative EI, FR, and ADC readings in nine cases of clinically diagnosed NPH were compared with those of age‐ and gender‐matched controls. Similar pre‐ and postoperative readings of responders and nonresponders were subsequently compared.

Results

Compared with the controls, all measurements were statistically significant except for peak systolic flow rate (pSfr), which was near statistical significance. Comparison of pre‐ and postoperative readings of responders and nonresponders revealed a decrease in ADC in all responders (P = 0.032). Subdural hemorrhage was found in all nonresponders (P = 0.012).

Conclusion

For patients presenting with signs and symptoms of NPH, readings on MRI greater than 0.3, 10 mL/min, ?9.0 mL/min, and 10.65 × 10^?4 mm²/s for EI, peak diastolic flow rate (pDfr), pSfr, and ADC, respectively, add further weight to the diagnosis. The strong correlation between shunt response and ADC decline support our hypothesis that water accumulation in the cerebrum is the major cause for the symptoms of NPH. The presence of subdural hemorrhage in all nonresponders raises suspicion of decreased compliance as the other major cause. J. Magn. Reson. Imaging 2009;30:708–715. © 2009 Wiley‐Liss, Inc.

     

Left ventricle segmentation using graph searching on intensity and gradient and a priori knowledge (lvGIGA) for short‐axis cardiac magnetic resonance imaging

Purpose

To develop and evaluate an automated left ventricle (LV) segmentation algorithm using Graph searching based on Intensity and Gradient information and A priori knowledge (lvGIGA).

Materials and Methods

The lvGIGA algorithm was implemented with coil sensitivity correction and polar coordinate transformation. Graph searching and expansion were applied for extracting myocardial endocardial and epicardial borders. LV blood and myocardium intensities were estimated for accurate partial volume calculation of blood volume and myocardial mass. Cardiac cine SSFP images were acquired from 38 patients. The lvGIGA algorithm was used to measure blood volume, myocardial mass, and ejection fraction, and compared with clinical manual tracing and the commercial MASS software.

Results

The success rate for segmenting both endocardial and epicardial borders was 95.6% slices for lvGIGA and 37.8% for MASS (excluding basal slices that required manual enclosure of ventricle blood). The lvGIGA segmentation result agreed well with manual tracing, within ?2.9 ± 4.4 mL, 2.1 ± 2.2%, and ?9.6 ± 13.0 g, for blood volume, ejection fraction, and myocardial mass, respectively.

Conclusion

The lvGIGA algorithm substantially improves the robustness of LV segmentation automation over the commercial MASS software, agrees well with clinical manual tracing, and may be a useful tool for clinical practice. J. Magn. Reson. Imaging 2008;28:1393–1401. © 2008 Wiley‐Liss, Inc.