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Biomedical subjects

C H Lorenz

Publications and source records attributed to C H Lorenz.

At least 19 recordsLinked to original sources
PubMed2003

Differentiation of heart failure related to dilated cardiomyopathy and coronary artery disease using gadolinium-enhanced cardiovascular magnetic resonance.

BACKGROUND: Heart failure treatment depends partly on the underlying cause of the disease. We evaluated cardiovascular magnetic resonance (CMR) for the problem of differentiating dilated cardiomyopathy (DCM) from left ventricular (LV) dysfunction caused by coronary artery disease (CAD). METHODS AND RESULTS: Late gadolinium enhancement with CMR was performed in 90 patients with heart failure and LV systolic dysfunction (63 patients with DCM and unobstructed coronary arteries and 27 with significant CAD at angiography). We also studied 15 control subjects with no coronary risk factors and/or unobstructed coronary arteries. None (0%) of the control subjects had myocardial gadolinium enhancement; however, all patients (100%) with LV dysfunction and CAD had enhancement, which was subendocardial or transmural. In patients with DCM, there were 3 findings: no enhancement (59%); myocardial enhancement indistinguishable from the patients with CAD (13%); and patchy or longitudinal striae of midwall enhancement clearly different from the distribution in patients with CAD (28%). CONCLUSIONS: Gadolinium CMR is a powerful technique to distinguish DCM from LV dysfunction related to CAD and yields new insights in DCM. These data suggest that using the coronary angiogram as the arbiter for the presence of LV dysfunction caused by CAD could have lead to an incorrect assignment of DCM cause in 13% of patients, possibly because of coronary recanalization after infarction. The midwall myocardial enhancement in patients with DCM is similar to the fibrosis found at autopsy; it has not previously been visualized in vivo and warrants further investigation. CMR may become a useful alternative to routine coronary angiography in the diagnostic workup of DCM.

Aged↗
PubMed2001

Evaluation of free-breathing three-dimensional magnetic resonance coronary angiography with hybrid ordered phase encoding (HOPE) for the detection of proximal coronary artery stenosis.

We evaluated free-breathing, prospective navigator-gated, three-dimensional (3D) magnetic resonance coronary angiography (MRCA) with hybrid ordered phase-encoding (HOPE), in the detection of proximal coronary artery stenosis. The coronary arteries were imaged in 46 patients undergoing cardiac catheterization. The mean scan time was 48 minutes. The mean arterial length (mm) visualized was left main stem (LMS) 11.7 (SD 4.5), left anterior descending (LAD) 30.1 (SD 11.1), circumflex (LCx) 15.5 (SD 8.6), and right (RCA) 56.2 (SD 20.8). Twenty-three patients had coronary artery disease with 47 significant stenoses on cardiac catheterization. All LMS were normal on both catheterization and MRCA. MRCA sensitivity was highest for the LAD (89% CI 65%-99%) and RCA (76% CI 50%-93%), but lower for the LCx (50% CI 21%-79%). Specificity ranged from 72%-100%. Improvements in image quality, length of vessel seen, and specific imaging of the LCx are required for MRCA to become an alternative to cardiac catheterization.

Adult↗
PubMed2001

Anomalous coronary arteries: anatomic and functional assessment by coronary and perfusion cardiovascular magnetic resonance in three sisters.

Combined coronary and perfusion cardiovascular magnetic resonance was performed in three sisters with angina and suspected anomalous coronary arteries. Two sisters had anomalous coronary arteries passing between the aorta and right ventricular outflow tract and had abnormal myocardial perfusion. One sister had normal anatomy and perfusion. The combined approach identified the anatomy and functional significance of suspected anomalous coronary arteries.

Adult↗
PubMed2001

Assessment of ventricular contractility during cardiac magnetic resonance imaging examinations using normalized maximal ventricular power.

Normalized maximal ventricular power (nPWRmax) is an index of cardiac function which measures the innate blood pumping ability, or contractility, of the left ventricle (LV), and its noninvasive assessment could prove useful in a variety of patients. nPWRmax is defined as the maximum instantaneous product of LV pressure and the rate of change of LV volume, divided by the end diastolic volume squared. We have quantified nPWRmax noninvasively in humans by pairing magnetic resonance imaging (MRI) LV volume measurements with aortic pressure estimated using radial artery tonometry and a frequency domain transfer function. In healthy volunteers undergoing cardiac MRI we have tested the sensitivity of nPWRmax to LV contractility with dobutamine and to cardiac loading with methoxamine, a vasoconstrictor. We have found that aortic pressures can be reliably estimated using a transfer function, which we generated and validated in a group of patients undergoing cardiac catheterization. Furthermore, we found that nPWRmax was unchanged by methoxamine, yet sensitive to contractility, with a 325% increase at dobutamine levels half that given during routine clinical cardiac stress tests for ischemia. In conclusion, we have shown that ventricular contractility can be assessed independent of cardiac loading in patients during routine noninvasive cardiac imaging examinations.

Adult↗
PubMed2001

Measurement of the gadopentetate dimeglumine partition coefficient in human myocardium in vivo: normal distribution and elevation in acute and chronic infarction.

PURPOSE: To establish a method for measuring the partition coefficient (lambda) of gadopentetate dimeglumine in humans in vivo, evaluate the spatial and intersubject variation in the lambda of normal myocardium, and compare these values on a regional basis with lambda values of acute and chronic infarcted myocardium. MATERIALS AND METHODS: Twelve healthy subjects and patients with acute (n = 5) or chronic (n = 5) myocardial infarction underwent magnetic resonance imaging at 1.5 T. Look-Locker images were acquired at four short-axis levels to measure myocardial and blood longitudinal relaxation time at baseline and after a 30-40-minute infusion of gadopentetate dimeglumine. lambda was calculated as DeltaR1(M)/DeltaR1(B, )where M = myocardium, and B = blood. RESULTS: The magnitude of the estimated lambda in normal myocardium was uniform over the entire myocardium at 0.56 mL/g +/- 0.10 (SD). The lambda values in patients with acute (0.91 mL/g +/- 0.11, P <.001) or chronic (lambda = 0.78 mL/g +/- 0.09, P <.001) infarction were significantly elevated, as compared with those in healthy subjects. A 20% elevation in lambda, as compared with the mean value of a corresponding normal circumferential segment, allowed identification of chronically (sensitivity, 88%; specificity, 96%) or acutely (sensitivity, 100%; specificity, 98%) infarcted segments. CONCLUSION: Quantification of the lambda in vivo allows differentiation between normal and acutely or chronically infarcted myocardium, with high sensitivity and specificity.

Adult↗
PubMed2000

Quantification of left ventricular function with magnetic resonance images acquired in real time.

The application of real-time magnetic resonance imaging (MRI) techniques to cardiac imaging is particularly attractive because current MR examinations of left ventricular (LV) function can be prohibitively long and are dependent on electrocardiographic triggering. We conducted a study of the minimum spatial and temporal resolution requirements necessary for real-time ventricular function MR imaging to quantify LV volumes accurately, both at resting conditions and during cardiac stress tests. In addition, we implemented a real-time segmented echoplanar imaging pulse sequence and used it to quantify LV volume in 10 healthy volunteers. We compared these results with those obtained using conventional gradient-echo cine imaging and found good agreement throughout the cardiac cycle (mean difference -0.8 +/- 10.6 ml). In conclusion, real-time cardiac MR imaging can be used to quantify LV volumes accurately throughout the cardiac cycle, over the physiologic range of heart rates, thereby decreasing the time required for a complete functional cardiac examination. J. Magn. Reson. Imaging 2000;12:430-438.

Adult↗
PubMed2000

Performance of QRS detection for cardiac magnetic resonance imaging with a novel vectorcardiographic triggering method.

In many cardiac patients, image quality and/or scan efficiency is reduced due to imprecise R-wave ability to trigger the scan due to noise on the electrocardiogram (ECG) caused by the magnetic resonance (MR) environment. We developed a triggering system that uses the spatial information of the vectorcardiogram (VCG) to minimize the effects of MR-related noise on triggering. Fifteen volunteers underwent standard cardiovascular MR exams, and a total of 52,474 R-waves were evaluated with the algorithm, giving a performance index of 99.91%. The mean propagation delay of the system was -10.64 +/- 3.19 msec, which falls within the real-time definition for cardiac MRI triggering. Five patients had arrhythmias consisting of premature ventricular depolarizations (PVDs) and supraventricular extra systoles. For those patients with PVDs, all arrhythmic beats were rejected unless they passed through the algorithm's reference point. The performance index for the arrhythmic patients approached 100%. VCG-based triggering has been demonstrated to provide near 100% triggering performance during cardiac MR examinations.

Adult↗
PubMed2000

Noninvasive modalities. Cardiac MR imaging.

As outlined in this article, the strength of MR imaging is that it can provide flow, function, and in some cases metabolic data in a single examination, independent of patient body habitus. Future prospects for real-time imaging and in vivo mapping of fiber orientation promise further advances in our understanding of the structure-function relationship in diastole. Many of the MR imaging methods that have been developed for cardiovascular imaging are now mature and available on state-of-the-art scanners. Although MR imaging can provide detailed characterization of diastolic function, there is a paucity of clinical results which could lead to use guidelines. When more clinicians have access and become familiar with MR imaging, and the type of information that it can provide, clinical trials will be needed to establish the role of MR imaging for evaluation of diastolic function. In the meantime, MR imaging remains an excellent research tool for this application and will help yield further insights into the pathophysiology of diastolic dysfunction.

Diastole↗
PubMed2000

Left ventricular torsion is equal in mice and humans.

Global cardiac function has been studied in small animals with methods such as echocardiography, cine-magnetic resonance imaging (MRI), and cardiac catheterization. However, these modalities make little impact on delineation of pathophysiology at the tissue level. The advantage of tagged cine-MRI technique is that the twisting motion of the ventricle, referred to as torsion, can be measured noninvasively, reflecting the underlying shearing motion of individual planes of myofibrils that generate wall thickening and ventricular ejection. Thus we sought to determine whether the mechanism of ventricular ejection, as measured by torsion, was the same in both humans and mice. Nine mice and ten healthy humans were studied with tagged cine-MRI. The magnitude and systolic time course of ventricular torsion were equivalent in mouse and humans, when normalized for heart rate and ventricular length. The end-systolic torsion angle was 12.7 +/- 1.7 degrees in humans vs. 2.0 +/- 1.5 degrees in mice unnormalized and 1.9 +/- 0.3 degrees /cm vs. 2.7 +/- 2.3 degrees /cm when normalized for ventricular length). These results support the premise that ventricular torsion may be a uniform measure of normal ventricular ejection across mammalian species and heart sizes.

Adult↗
PubMed2000

Delineation of normal human left ventricular twist throughout systole by tagged cine magnetic resonance imaging.

Myofibril shortening and the oblique fiber orientation of the left ventricular myocardium results in a twisting motion of the left ventricle. Advances in cardiac magnetic resonance imaging (MRI) have made it possible to label the myocardium noninvasively and track this motion (twist) through the cardiac cycle, but little data exist on its complete systolic time course. The purpose of this study was to delineate the normal human systolic time course of ventricular twist using tagged cine-MRI. Tagged cine-MRI was performed in 10 healthy subjects. The mean systolic twist angle relative to the short axis centroid for the 10 volunteers was calculated. Interstudy and intra- and interobserver variability were assessed. During isovolumic contraction, all ventricular twist was counterclockwise. Later in systole, the basal segments changed direction and rotated in a clockwise direction, whereas the apical segments continued counterclockwise rotation. The midpoint for rotation was 45+/-8% of ventricular length. The mean short axis net ventricular twist (apex-base) at 80% systole was 12.6+/-1.5 degrees. The four wall segments showed heterogeneity in twist (lateral wall, 20.6+/-1.7 degrees; anterior wall, 17.5+/-5.1 degrees; inferior wall, 8.8+/-4.9 degrees; septum, 3.5+/-2.4 degrees). The anterior and lateral walls demonstrated significantly higher twist than the other walls (p < 0.01). Torsion increased steadily throughout systole after isovolumic contraction, whereas twist displayed rate changes. The mean interstudy and intra- and interobserver differences were less than 2.1 degrees. The close similarity in twist between subjects and the low interstudy and inter/intraobserver variation indicates that twist is a robust parameter of myocardial function. Torsion varies smoothly during systole, which may play a role in minimizing oxygen consumption. These data can serve as a baseline from which to compare alterations in regional myocardial function in disease.

Adult↗
PubMed1999

Benefit of T1 reduction for magnetic resonance coronary angiography: a numerical simulation and phantom study.

Contrast agents have dramatically improved magnetic resonance angiography (MRA) of the abdominal and peripheral arteries. The imaging technique for these applications is usually a steady-state acquisition, for which the relationship between T1 in blood and the MR signal is well known. However, in electrocardiography-triggered angiography with limited acquisition windows, this relationship is more complex. Therefore the purpose of this work is to define the relationship between the T1 in blood and the MR signal amplitude in three-dimensional magnetic resonance coronary angiography (3D-MRCA). Simulations were performed using equations describing the MR signal in both steady-state and triggered acquisition schemes. Triggered acquisition schemes use flip-angle sweeps to maintain a constant signal during the acquisition. In this study, the effect of the flip angle sweep was calculated as a function of T1. The results show that the effect of T1 shortening in contrast-enhanced 3D-MRCA differs substantially from that in conventional contrast-enhanced MRA. The triggered acquisition allows unsaturated blood to enter the volume between the acquisitions and thereby gives a much higher signal at long T1s than does steady-state acquisition. Therefore, to gain a benefit in signal amplitude with contrast agents for 3D-MRCA using gradient-echo sequences, the T1 in blood may have to be as low as 50 msec. In addition, when using a prepulse to null myocardium, the results indicate the need for a large difference in T1 between blood and myocardium to avoid signal loss in blood.

Computer Simulation↗
PubMed1999

Contrast-enhanced coronary MRA.

Coronary angiography with magnetic resonance imaging (MRI) has long been a goal for bringing cardiac MRI into clinical use for diagnosis of coronary artery disease. In this paper, the fundamental problems of respiratory and cardiac motion, signal-to-noise ratio, and contrast-to-noise ratio are discussed in reference to implications for coronary imaging strategies. Various methods that have been proposed to improve signal-to-noise and contrast-to-noise ratios in MR coronary imaging are presented with an emphasis on the role of T1-shortening contrast agents, both extracellular and intravascular. Although much progress has been made in recent years in techniques for imaging the coronary arteries, ultimate clinical success remains unproved. Success will depend on synergistic developments in MR acquisition techniques, respiratory compensation methods, post-processing techniques, and contrast agents to develop a workable solution for reliable coronary imaging across a wide range of patients. J. Magn. Reson. Imaging 1999;10:703-708.

Animals↗
PubMed1999

Characterization of t1 relaxation and blood-myocardial contrast enhancement of NC100150 injection in cardiac MRI.

A new ultrasmall superparamagnetic iron oxide (Clariscan; NC100150 Injection) was studied in domestic farm pigs. The T1 effects were characterized for blood and myocardium and the blood-myocardial contrast was measured in T1-weighted cine images. The contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) were measured at baseline and contrast doses of 1 and 5 mg Fe/kg body weight (bw) at end diastole and late systole. The T1 values for blood and myocardium were reduced by 97 and 43%, respectively, from baseline to 5 mg Fe/kg bw. The CNR was significantly improved with contrast at end diastole and late systole. The maximum improvement shown was 202% at 5 mg Fe/kg bw in late systole. The percent SNR enhancement was significantly higher in blood than myocardium at late systole. NC100150 Injection is an effective T1 shortening agent and can be used to improve blood-myocardial contrast in cine images of the heart. J. Magn. Reson. Imaging 1999;10:784-789.

Animals↗
PubMed1999

Blood pool agent strongly improves 3D magnetic resonance coronary angiography using an inversion pre-pulse.

The ability of a blood pool contrast agent to enhance MR coronary angiography was defined. The proximal coronary vessels of pigs were imaged before and after administration of Gd-DTPA bound covalently to bovine serum albumin (0.2 mmol/ kg). The contrast agent resulted in a reduction of the blood T1 value to 33+/-5 msec, as determined in vivo with a Look-Locker technique. Both 2D and 3D imaging techniques were performed. An inversion pulse suppressed the signal of nonblood tissue postcontrast. After contrast agent administration, in the 3D data set the signal-to-noise ratio (SNR) of blood and contrast-to-noise ratio (CNR) of blood to myocardium were improved by factors of 2.0+/-0.2 and 15+/-8, respectively (P < 0.05). Postcontrast, the 3D acquisition was superior to the 2D technique in terms of spatial resolution, SNR of blood, and CNR of blood to myocardium. The high contrast of the 3D data set allowed for direct and rapid display of coronary arteries using a "closest vessel projection."

Animals↗
PubMed1999

Novel real-time R-wave detection algorithm based on the vectorcardiogram for accurate gated magnetic resonance acquisitions.

Electrocardiograph (ECG) triggered or gated magnetic resonance methods are used in many imaging applications. Therefore, a reliable trigger signal derived from to the R-wave of the ECG is essential, especially in cardiac imaging. However, currently available methods often fail mainly due to the artifacts in the ECG generated by the MR scanner itself, such as the magnetohydrodynamic effect and gradient switching noise. The purpose this study was to characterize the accuracy of selected R-wave detection algorithms in an MR environment, and to develop novel approaches to eliminate imprecise triggering. Vectorcardiograms (VCG) in 12 healthy volunteers exposed to 1.5 T magnetic field were digitized and used as a reference data set including manually corrected onsets of R-waves. To define the magnetohydrodynamic effect, the VCGs were characterized in time, frequency, and spatial domains. The selected real-time R-wave detection algorithms, and a new "target-distance" VCG-based algorithm were applied either to standard surface leads calculated from the recorded VCG or to the VCG directly. The flow related artifact was higher in amplitude than the R-wave in 28% of the investigated VCGs which yielded up to 9-16%false positive detected QRS complexes for traditional algorithms. The "target-distance" R-wave detection algorithm yielded a score of 100% for detection with 0.2% false positives and was superior to all the other selected methods. Thus, the VCG of subjects exposed to a strong magnetic field can be use to separate the magnetohydrodynamic artifact and the actual R-wave, and markedly improves the trigger accuracy in gated magnetic resonance scans. Magn Reson Med 42:361-370, 1999.

Adult↗
PubMed1999

Normal human right and left ventricular mass, systolic function, and gender differences by cine magnetic resonance imaging.

Our objective was to establish normal ranges of left and right ventricular mass and function with cine magnetic resonance imaging (MRI) and to determine gender differences. Seventy-five healthy subjects (age range 8-55, mean 28 yr) were studied with cine MRI. Ten dogs were imaged for autopsy validation with a mean difference between actual and MRI-determined mass of 0.2 A +/- 8.4 g. Intraobserver and interobserver variability and interstudy variability were 5-6%. All parameters were significantly different between males and females except ejection fraction and the left ventricular mass to end-diastolic volume ratio. Agreement with published autopsy series, including gender differences, was excellent. This study presents normative MRI data that can be used for comparing individual patients and for further study of right and left ventricular interaction.

Adolescent↗