Kenneth A. Kraft

Angle independent doppler color imaging: Determination of accuracy and a method of display

A multiple beam technique was utilized to obtain angle independent Doppler color images (AIDCI) using an ultrasonic scanner with a linear transducer. A quantitative study using steady flow models has been performed to evaluate the accuracy of this method in velocity measurements. The results show that the velocity amplitudes measured with this method correlated with those calculated from the measured flow rates (r = 0.95-0.98). The flow angles obtained with this method also correlated with those calculated from the coordinates of the tube image (r = 0.93-0.96). To improve the interpretation of the angle independent results, a method for visualizing two-dimensional flow fields is presented and compared with two existing methods.

Rapid measurement of aortic wave velocity: in vivo evaluation.

A 1D MR sequence has been developed for determining aortic flow wave velocity (WV), a metric of arterial compliance, within a single cardiac cycle. Studies were carried out on the thoracic aortas of 10 normal volunteers. Correlative WV data were also acquired from each subject using a conventional phase‐velocity 2D mapping technique. Aortic WV in this cohort was found to range from 411 to 714 cm/s and was highly correlated (R = 0.95) between the two methods. Peak blood velocity was also measured using both methods and found to agree closely. The reproducibility of WV measurements using the rapid 1D method averaged 7.6%, which is comparable or better than that achieved using existing noninvasive techniques. Magn Reson Med 46:95–102, 2001.

Quantitative phase‐velocity MR imaging of in‐plane laminar flow: Effect of fluid velocity, vessel diameter, and slice thickness

Quantitative MR phase imaging is frequently used to measure spin velocities. A potential difficulty may arise, however, when in-plane phase images are acquired of a vessel carrying laminar flow, for which the fluid velocity profile is parabolic. In that case, depending on the flow velocity (v), the vessel diameter (D), and the chosen MR slice thickness (ST), a spin velocity gradient will be present to some extent within each intraluminal voxel. The resulting intravoxel phase dispersion may be expected to affect the net pixel phase value, and hence compromise the assumed linear correlation between phase shift and velocity. In this study, the effects of alterations of v, D, and ST on the apparent image phase are investigated for the case of laminar flow directed parallel to the sequence read gradient. A theoretical model is developed and the conclusions experimentally tested using a flow phantom. The data demonstrate that when quantitating inplane phase-flow images, significant velocity underestimations may occur when the net flow-induced phase shifts are small and the MR slice thickness is an appreciable fraction of the vessel diameter.

The relationship between C-reactive protein and other cardiovascular risk factors in men and women.

INTRODUCTION C-reactive protein (CRP) has emerged as an important indicator of risk for cardiovascular disease. The impact of gender on the relationship between CRP and other cardiovascular risk factors, however, has not been thoroughly investigated. METHODS Ninety men and 75 women participated in this study. Age, resting systolic and diastolic blood pressure, resting heart rate, body mass index, total cholesterol, high-density lipoprotein, low-density lipoprotein, triglycerides, and hs-CRP were ascertained. Maximal oxygen consumption was obtained via treadmill testing, and aortic stiffness was measured using magnetic resonance imaging. RESULTS Log hs-CRP level was significantly higher in the female subjects compared with the males subjects (0.86 +/- 0.67 mg/L vs 0.63 +/- 0.44 mg/L, respectively; P = .003). In the male group, Pearson product moment correlation analysis showed that log hs-CRP was not significantly correlated (P > .10) with any of the other variables of interest. In the female group, however, log hs-CRP was significantly correlated (P < .05) with total cholesterol (r = 0.30), low-density lipoprotein (r = 0.27), tryglycerides (r = 0.51), and body mass index (r = 0.36). Linear regression analysis determined that triglycerides and body mass index explained 30% of the variability in log hs-CRP. CONCLUSIONS These results indicate that the relationship between CRP and other cardiac risk factors is different between apparently healthy men and women. The prognostic characteristics of CRP and the impact of statin therapy on CRP may therefore differ between men and women. Future research should be directed toward resolving this issue.

Differential impact of hyponatremia and hepatic encephalopathy on health-related quality of life and brain metabolite abnormalities in cirrhosis

BACKGROUND & AIMS Hyponatremia (HN) and hepatic encephalopathy (HE) together can impair health-related quality of life (HRQOL) and cognition in cirrhosis. We aimed at studying the effect of hyponatremia on cognition, HRQOL, and brain MR spectroscopy (MRS) independent of HE. METHODS Four cirrhotic groups (no HE/HN, HE alone, HN alone (sodium <130 mEq/L), HE+HN) underwent cognitive testing, HRQOL using Sickness Impact Profile (SIP: higher score is worse; has psychosocial and physical sub-scores) and brain MRS (myoinositol (mI) and glutamate+glutamine (Glx)), which were compared across groups. A subset underwent HRQOL testing before/after diuretic withdrawal. RESULTS 82 cirrhotics (30 no HE/HN, 25 HE, 17 HE+HN, and 10 HN, MELD 12, 63% hepatitis C) were included. Cirrhotics with HN alone and without HE/HN had better cognition compared to HE groups (median abnormal tests no-HE/HN: 3, HN: 3.5, HE: 6.5, HE+HN: 7, p=0.008). Despite better cognition, HN only patients had worse HRQOL in total and psychosocial SIP while both HN groups (with/without HE) had a significantly worse physical SIP (p<0.0001, all comparisons). Brain MRS showed the lowest Glx in HN and the highest in HE groups (p<0.02). mI levels were comparably decreased in the three affected (HE, HE+HN, and HN) groups compared to no HE/HN and were associated with poor HRQOL. Six HE+HN cirrhotics underwent diuretic withdrawal which improved serum sodium and total/psychosocial SIP scores. CONCLUSIONS Hyponatremic cirrhotics without HE have poor HRQOL despite better cognition than those with concomitant HE. Glx levels were lowest in HN without HE but mI was similar across affected groups. HRQOL improved after diuretic withdrawal. Hyponatremia has a complex, non-linear relationship with brain Glx and mI, cognition and HRQOL.

Rapid measurement of pulse wave velocity via multisite flow displacement.

A MR method is presented for measuring pulse wave velocity (PWV) and its application to assessing stiffness in the human thoracic aorta. This one‐dimensional (1D) flow displacement method applies a single RF comb excitation to the vessel, followed by an oscillating frequency encoding gradient, each oscillation providing a 1D projection of the vessel, enabling one to track fluid motion. The currently implemented sequence excites nine slices within a 20‐cm length of vessel and has a temporal resolution of 2.03 msec and a total acquisition time of 140 msec. Offline‐reconstructed position‐versus‐time plots show curvilinear flow displacement trajectories corresponding to fluid motion at each of the excitation positions. The PWV can be reliably calculated by curve‐fitting these trajectories to a model. In vitro studies using compliant tubes demonstrate no significant difference between results obtained using this method and those directly obtained using pressure transducers. Compared to another MR method previously developed in our laboratory, the proposed method displays improved temporal resolution and enhanced ability to extract PWV from vessels exhibiting low peak flow velocity. Preliminary data suggest that this method is feasible for in vivo application and may provide a more accurate estimation of aortic wave velocity among subjects exhibiting low peak flow velocity, such as the elderly or those with impaired cardiac function. Magn Reson Med 52:1351–1357, 2004.

MR imaging of model fluid velocity profiles

A projection MR technique for imaging the velocity profiles of moving fluids has been applied to various steady flow models designed to simulate a variety of flow conditions. From such profiles can be readily deduced peak velocities, volume flow rates, information concerning the degree of flow development, features such as flow separation, and estimates shear stresses at the vessel wall.

Asymmetric dimethylarginine is strongly associated with cognitive dysfunction and brain MR spectroscopic abnormalities in cirrhosis

BACKGROUND & AIMS Asymmetric dimethylarginine (ADMA) is an inhibitor of nitric oxide synthase that accumulates in liver disease and may contribute to hepatic encephalopathy (HE). We aimed at evaluating the association of ADMA with cognition and brain MR spectroscopy (MRS) in cirrhosis. METHODS Cirrhotic patients with/without prior HE and non-cirrhotic controls underwent cognitive testing and ADMA determination. A subgroup underwent brain MRS [glutamine/glutamate (Glx), myoinositol (mI), N-acetyl-aspartate (NAA) in parietal white, occipital gray, and anterior cingulated (ACC)]. Cognition and ADMA in a cirrhotic subgroup before and one month after transjugular intrahepatic portosystemic shunting (TIPS) were also tested. Cognition and MRS values were correlated with ADMA and compared between groups using multivariable regression. ADMA levels were compared between those who did/did not develop post-TIPS HE. RESULTS Ninety cirrhotics (MELD 13, 54 prior HE) and 16 controls were included. Controls had better cognition and lower ADMA, Glx, and higher mI compared to cirrhotics. Prior HE patients had worse cognition, higher ADMA and Glx and lower mI compared to non-HE cirrhotics. ADMA was positively correlated with MELD (r=0.58, p<0.0001), abnormal cognitive test number (r=0.66, p<0.0001), and Glx and NAAA (white matter, ACC) and negatively with mI. On regression, ADMA predicted number of abnormal tests and mean Z-score independent of prior HE and MELD. Twelve patients underwent TIPS; 7 developed HE post-TIPS. ADMA increased post-TIPS in patients who developed HE (p=0.019) but not in others (p=0.89). CONCLUSIONS A strong association of ADMA with cognition and prior HE was found independent of the MELD score in cirrhosis.

The influence of sex on the relationship between heart rate recovery and other cardiovascular risk factors in apparently healthy subjects

Heart rate recovery (HRR) is an important indicator of cardiovascular health. The purpose of the present investigation is to examine the influence of sex on the relationship between HRR and other markers of cardiovascular health. Two hundred and seventy‐five apparently healthy subjects participated in this study. Subjects underwent cardiopulmonary exercise testing (outcome measures: VO2max and HRR 1 and 2 min into recovery), lipid analysis, measurement of resting systolic and diastolic blood pressure and measurement of aortic wave velocity (AWV in m/s) via magnetic resonance. HRR both at 1 min (HRR1) and at 2 min (HRR2) were higher in males. In general, the correlation between HRR1 and other measures of interest was weaker than that found with HRR2 in both male and female subjects. With respect to HRR2, the relationship with other measures of interest was stronger in the female subgroup. Specific to arterial stiffness, the correlation between HRR2 and AWV was −0.33 and −0.46 (P<0.001 for both) in male and female subgroups, respectively. The results of the present study indicate that both gender and the timing of HRR measurement influence its relationship with other important cardiovascular risk factors.

Maximal Aerobic Capacity and the Oxygen Uptake Efficiency Slope as Predictors of Large Artery Stiffness in Apparently Healthy Subjects

PURPOSE Large artery stiffness is now recognized as an important marker of cardiovascular health. The purpose of the present investigation was to assess the relationship between large artery stiffness and the oxygen uptake efficiency slope (OUES) and to determine whether the OUES is a viable surrogate for maximal oxygen uptake (&OV0312;O2max) in a multivariate regression analysis developed to estimate large artery stiffness. METHODS Two hundred seventy-five apparently healthy subjects (149 men; age = 48.1 ± 15.8 years/126 women; age = 47.0 ± 15.3 years) participated in this study. Subjects underwent maximal cardiopulmonary exercise testing to determine &OV0312;O2max and the OUES. The OUES was calculated using 50% and 100% of the exercise data. Measurement of aortic wave velocity (AWV in meters/second) was obtained via magnetic resonance imaging. RESULTS Pearson product-moment correlation analysis revealed that &OV0312;O2max (r = −0.49, P < .001), the OUES calculation using 50% of exercise data (r = −0.25, P < .001), and the OUES calculation using 100% of exercise data (r = −0.34, P < .001) were all significantly related to AWV. However, only &OV0312;O2max was retained in a linear regression (also including age and resting systolic blood pressure) used to predict AWV. discusSION Previous research has demonstrated a relationship between &OV0312;O2max and AWV, which was also found in the present study. While the OUES was significantly correlated with AWV, it does not appear to be an adequate replacement for &OV0312;O2max when attempting to gauge large artery compliance.