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J T Marcus

Publications and source records attributed to J T Marcus.

At least 19 recordsLinked to original sources
PubMed2006

NT-proBNP reflects right ventricular structure and function in pulmonary hypertension.

The aim of the current study was to investigate whether alterations in N-terminal pro brain natriuretic peptide (NT-proBNP) reflect changes in right ventricular structure and function in pulmonary hypertension patients during treatment. The study consisted of 30 pulmonary hypertension patients; 15 newly diagnosed and 15 on long-term treatment. NT-proBNP, right heart catheterisation and cardiac magnetic resonance imaging measurements were performed, at baseline and follow-up. There were no significant differences between newly diagnosed patients and those on treatment at baseline or follow-up with respect to NT-proBNP, haemodynamics and right ventricular parameters. Relative changes in NT-proBNP during treatment were correlated to the relative changes in right ventricular end-diastolic volume index (r = 0.59), right ventricular mass index (r = 0.62) and right ventricular ejection fraction (r = -0.81). N-terminal pro brain natriuretic peptide measurements reflect changes in magnetic resonance imaging-measured right ventricular structure and function in pulmonary hypertension patients. An increase in N-terminal pro brain natriuretic peptide over time reflects right ventricular dilatation concomitant to hypertrophy and deterioration of systolic function.

Adult↗
PubMed2005

Noninvasive assessment and monitoring of the pulmonary circulation.

In pulmonary vascular disease, changes in the pulmonary vascular bed will lead to altered pulmonary haemodynamics. This review describes the application of several physiological principles to measure these changes noninvasively by means of novel techniques. Flow characteristics of blood through the pulmonary vascular bed alter in pulmonary vascular disease. Recent developments in magnetic resonance imaging and computed tomography make it possible to visualise and quantify these abnormal flow patterns. Information regarding pulmonary perfusion can also be obtained by measuring the electrical impedance changes in the lung by electrical impedance tomography. A more indirect approach to measure the pulmonary blood flow is the measurement of the absorption of acetylene, a perfusion limited gas. Information on the pulmonary vascular bed can also be obtained by the measurement of exhaled products of the pulmonary vascular endothelium, such as nitric oxide. Although all the techniques described offer new ways to diagnose or monitor pulmonary vascular disease, clinical data on these techniques are limited. Further improvement and evaluation of the clinical value of these techniques are therefore obligatory before they can be used in clinical practice.

Diagnostic Techniques, Cardiovascular↗
PubMed2004

Regional timing of myocardial shortening is related to prestretch from atrial contraction: assessment by high temporal resolution MRI tagging in humans.

Earlier studies have shown substantial nonuniformity in normal left ventricular (LV) myocardial function concerning both the degree of shortening and timing of shortening. We hypothesized that nonuniform LV function may be related to nonuniform prestretch induced by atrial contraction. Eleven healthy human subjects were studied using MRI myocardial tagging and strain analysis. The amount of circumferential prestretch was assessed in 30 LV segments. Prestretch was defined as the difference in strain between end diastole (at ECG R wave) and diastasis. Furthermore, both the degree of shortening (quantified as peak circumferential shortening, peak systolic shortening rate, and amount of postsystolic shortening) and timing of shortening (quantified as the onset time of shortening and time to peak shortening) were assessed. LV prestretch was found to be nonuniform, with the highest values in the lateral wall. The amount of segmental prestretch correlated significantly with peak shortening (r = 0.79), peak shortening rate (r = 0.50), amount of postsystolic shortening (r = 0.67), onset time of shortening (r = -0.57), and time to peak shortening (r = 0.71) (P < 0.001 for each of these relations). These relations may be explained by regional differences in wall stress or by a regional Frank-Starling effect. The correlation between timing of shortening and prestretch demonstrates that mechanical timing is not determined by electrical phenomena alone. In conclusion, regional variation in LV function correlates with the nonuniform prestretch from atrial contraction.

Adult↗
PubMed2004

Timing of cardiac contraction in humans mapped by high-temporal-resolution MRI tagging: early onset and late peak of shortening in lateral wall.

Mechanical asynchrony is an important parameter in predicting the response to cardiac resynchronization therapy, but detailed knowledge of cardiac contraction timing in healthy persons is scarce. In this work, timing of cardiac contraction was mapped in 17 healthy subjects with high-temporal-resolution (14 ms) MRI myocardial tagging and strain analysis. Both the onset time of circumferential shortening (T(onset)) in early systole and the time of peak circumferential shortening (T(peak)) at end systole were determined. The onset of shortening width (time needed for 20-90% of the left ventricle to start shortening) was small (35 +/- 9 ms). A distinct spatial pattern for T(onset) was found, with earliest onset in the lateral wall and latest onset in the septum (P = 0.001). Compared with T(onset), T(peak) had a larger width (121 +/- 22 ms) and an opposite spatial pattern, with peak shortening occurring earlier in the septum than in the lateral wall (P < 0.001). Postsystolic shortening (T(peak) later than aortic valve closure; P < 0.05) was observed in 13 of the 30 cardiac segments, mainly in the lateral and basal segments. Shortening in these segments continued 58 +/- 14 ms after aortic valve closure, during which circumferential shortening increased from 16.9 +/- 1.2% to 20.0 +/- 1.5%. Maps of the timing of contraction in normal subjects may serve as a reference in detecting mechanical asynchrony due to intraventricular conduction defects or ischemia.

Adult↗
PubMed2002

Aortic aneurysm pulsatile wall motion imaged by cine MRI: a tool to evaluate efficacy of endovascular aneurysm repair?

OBJECTIVES: to evaluate cine MRI as a means of determining the two-dimensional pulsatile wall motion (2D-PWM) of abdominal aortic aneurysm (AAA). DESIGN: prospective study of 21 patients with AAA. 2D-PWM was defined as change in cross-sectional area. RESULTS: the median diastolic area was 28 cm(2) (intraquartile range, IQR, 22-31 cm(2)) and the median (IQR) 2D-PWM was 0.25 (0.10-0.40) cm(2). Assuming that the AAA is circular in cross-section this represents a median (IQR) diameter increase of 0.3 (0.1-0.4) mm. However, local wall displacements up to 2 mm were present in varying directions, without significant change in surface area. CONCLUSION: AAA PWM is negligible and may not therefore be a potential tool to assess efficacy of endovascular aneurysm exclusion.

Aged↗
PubMed2002

Imaging of thoracic blood volume changes during the heart cycle with electrical impedance using a linear spot-electrode array.

Electrical impedance (EI) measurements conducted on the thorax contain useful information about the changes in blood volume that occur in the thorax during the heart cycle. The aim of this paper is to present a new (tomographic-like) method to obtain this relevant information with electrical impedance measurements, using a linear electrode array. This method is tested on three subjects and the results are compared with results, obtained from magnetic resonance cine-images showing the cross-sectional surface area changes of the aorta, the vena cava, the carotid arteries, and the heart. This paper shows that the different sources of the thoracic EI waveform may be separated in time and location on the thoracic surface and that aortic volume changes may be estimated accurately.

Adult↗
PubMed2001

Quantification of regional contractile function after infarction: strain analysis superior to wall thickening analysis in discriminating infarct from remote myocardium.

OBJECTIVES: Using two-dimensional wall thickening (WT) (expressed as percentage) and strain analysis, regional contractile myocardial function was quantified and compared in 13 control subjects and 13 patients with a first myocardial infarction (MI). The findings in the patient group were related to global ventricular function and infarct size. BACKGROUND: In patients with coronary artery disease, regions with dysfunctional myocardium cannot be differentiated easily from regions with normal function by planar WT analysis. Physiologic factors, in combination with limitations of conventional imaging techniques, affect the calculation of WT. Quantitative assessment of contractile function by magnetic resonance (MR) tissue tagging and strain analysis may be less affected by these factors. METHODS: Two-dimensional regional WT and strain were calculated in three short-axis MR cine and tagged images, respectively. Left ventricular volumes and ejection fraction (EF) were obtained from a series of contiguous short-axis cine images. RESULTS: In patients with infarct-related ventricles, WT and strain analysis both revealed reduced myocardial function, as compared with control subjects (p < 0.005 and p < 0.001, respectively). However, WT analysis yielded no significant regional differences in function between infarct-related and remote myocardium (p = 0.064), whereas strain analysis did (p < 0.005). For detecting dysfunctional myocardium of electrocardiographically and angiographically defined infarct areas, WT analysis had a sensitivity of 69% and a specificity of 92%, whereas strain analysis demonstrated a sensitivity of 92% and a specificity of 99%. The EF correlated with WT (r = 0.76, p < 0.005) and strain (r = 0.89, p < 0.001). CONCLUSIONS: Two-dimensional strain analysis is more accurate than planar WT analysis in discriminating dysfunctional from functional myocardium, and it provides a strong correlation between regional myocardial and global ventricular function.

Aged↗
PubMed2001

Improved harmonic phase myocardial strain maps.

Magnetic resonance tagging has proven a valuable tool in the quantification of myocardial deformation. However, time-consuming postprocessing has discouraged the use of this technique in clinical routine. Recently, the harmonic phase (HARP) technique was introduced for automatic calculation of myocardial strain maps from tagged images. In this study, a comparison was made between HARP instantaneous strain maps calculated from single tagged images (SPAMM) and those calculated from subtracted tagged images (CSPAMM). The performance was quantified using simulated images of an incompressible cylinder in the 'end-systolic' state with realistic image contrast and noise. The error in the second principal stretch ratio was 0.009 +/- 0.032 (mean +/- SD) for the SPAMM acquisition, and 0.007 +/- 0.016 for CSPAMM at identical contrast-to-noise ratio. Furthermore, differences between the methods were illustrated with in vivo strain maps. Those calculated from CSPAMM images showed fewer artifacts and were less sensitive to the choice of cut-off frequencies in the HARP band-pass filter. A prerequisite for the method to become practical is that the CSPAMM images should be acquired in a single breathhold.

Heart↗
PubMed2001

Variance components of two-dimensional strain parameters in the left-ventricular heart wall obtained by magnetic resonance tagging.

This study quantifies variance components of two-dimensional strains in the left-ventricular heart wall assessed by magnetic resonance (MR) tagging in 18 healthy xxvolunteers. For a 7-mm tagging grid and homogeneous strain analysis, the intersubject variability and measurement error were estimated, as well as the intra- and interobserver variability. The variance components were calculated for the mean strain of a circumferential sector. The results show that the measurement error was almost equal to the intra-observer variability. With four circumferential sectors of 90 degrees each, approximately 65% of the total variance in epsilonr and epsilonc was due to intersubject variability, the remaining 35% was due to measurement error. With 12 sectors of 30 degrees each, the intersubject variability and measurement error both contributed 50% to the total variance. With 18 sectors of 20 degrees each, only 40% of the total variance was due to intersubject variability. The total variability increased with the number of sectors and therefore the number of sectors used in a study will be a trade-off between segment size (defining spatial resolution) and variability.

Analysis of Variance↗
PubMed2001

Impaired left ventricular filling due to right ventricular pressure overload in primary pulmonary hypertension: noninvasive monitoring using MRI.

OBJECTIVE: To analyze the effect of primary pulmonary hypertension (PPH) on cardiac function using MRI. METHODS: In 12 patients (9 women; age range, 30 to 56 years), the diagnosis of PPH had been established by catheterization (mean +/- SD pulmonary artery pressure [PAP] was 56 +/- 8 mm Hg). With breath-hold cine MRI, a series of short-axis images was acquired covering the whole left ventricle (LV) and right ventricle (RV). The curvature, defined as 1 divided by the radius of curvature in centimeters, was calculated for the septum and the LV free wall in early diastole. Leftward ventricular septal bowing (LVSB) is denoted by a negative curvature. For the LV and the RV, the end-diastolic volume (EDV), stroke volume (SV), and volumetric filling rate were calculated. The control subjects were all healthy (n = 14; 11 women; age range, 20 to 57 years). RESULTS: In the patients, LVSB was quantified in early diastole by the septal curvature of - 0.14 +/- 0.07 cm(-1), and the septal to free-wall curvature ratio of - 0.42 +/- 0.21. LV EDV and LV SV correlated negatively with diastolic PAP (p = 0.004 and p = 0.04, respectively). In patients vs control subjects, RV SV was reduced (52 +/- 12 mL vs 82 +/- 11 mL, p < 0.0001); LV peak filling rate was smaller (2.2 +/- 0.7 EDV/s vs 3.3 +/- 0.5 EDV/s, p < 0.001); LV EDV was smaller (81 +/- 23 mL vs 117 +/- 19 mL, p = 0.001); and LV SV was smaller (49 +/- 18 mL vs 83 +/- 13 mL, p < 0.0001). CONCLUSION: In PPH, RV pressure overload leads to LVSB and reduced RV output. By decreased blood delivery, LV filling is reduced, which results in decreased LV SV by the Frank-Starling mechanism.

Adult↗
PubMed2000

Three-dimensional myocardial strain analysis based on short- and long-axis magnetic resonance tagged images using a 1D displacement field.

A robust algorithm to estimate three-dimensional strain in the left-ventricular heart wall, based on magnetic resonance (MR) grid-tagging in two sets of orthogonal image planes, is presented. Starting-point of this study was to minimize global interpolation and smoothing. Only the longitudinal displacement was interpolated between long-axis images. Homogeneous strain analysis was performed using small tetrahedrons. The method was tested using a stack of short-axis images and three long-axis images in six healthy volunteers. In addition, the method was subjected to an analytical test case, in which the effect of noise in tag point position on the observed strains was explored for normally distributed noise (0.5 mm RMS). In volunteers, the error in the longitudinal displacement due to interpolation between the long-axis image planes was -0.10 +/- 0. 48 mm (mean +/- SD). The resulting error in the longitudinal strain epsilon(l) was -0.003 +/- 0.02. The analytical test case was used to quantify the effects of three sources of errors on the observed strain. The SD of the difference between homogeneous strain and true strain was 0.06 for epsilon(r.) The error due to the 3-D reconstruction was 0.004 for epsilon(r.) The error in epsilon(r) resulting from simulated noise in the tag point position was 0.10. Equivalent results were obtained for all other strain parameters; thus, the error resulting from noise in the tag point position dominates the error introduced by approximations in the method. Because the proposed method uses a minimum of global interpolation and smoothing, it offers the prospect to detect small regions of aberrant contraction.

Adult↗
PubMed2000

Determination of stroke volume by means of electrical impedance tomography.

ECG-gated electrical impedance tomography (EIT) is a non-invasive imaging technique, developed to monitor blood volume changes. This study is the first in comparing this non-invasive technique in measuring stroke volume with established techniques. The objective of this study was to validate EIT variables derived from the EIT images with paired obtained stroke volume measurements by thermodilution and MRI. After right cardiac catheterization, EIT measurements were performed in 25 patients. Regression analysis was used to analyse the relation between the EIT results and stroke volume determined by thermodilution. From the regression line an equation was derived to estimate stroke volume (in ml) by EIT. A strong correlation was found between EIT and stroke volume measured by the thermodilution method (r = 0.86). In a group of 11 healthy subjects this equation was validated to MRI. The mean and standard deviation of the difference between EIT and MRI was 0.7 ml and 5.4 ml respectively. These data indicate that EIT is a valid and reproducible method for the assessment of stroke volume.

Aged↗
PubMed1999

Simultaneous MRI tagging and through-plane velocity quantification: a three-dimensional myocardial motion tracking algorithm.

A tracking algorithm was developed for calculation of three-dimensional point-specific myocardial motion. The algorithm was designed for images acquired with simultaneous magnetic resonance imaging (MRI) grid tagging and through-plane velocity quantification. The tagging grid provided the in-plane motion while the velocity quantification measured the through-plane motion. In four healthy volunteers, the in vivo performance was evaluated by comparing the systolic through-plane displacement with the displacement of tagging-grid intersections in long-axis images. The correlation coefficient was 0.93 (P < 0.001, N = 183). A t-test for paired samples revealed a small underestimation of the through-plane displacement by 0.04 +/- 0.09 cm (mean +/- SD, P < 0.001) on an average displacement of 0.77 +/- 0.23 cm toward the apex. The authors conclude that three-dimensional point-specific motion tracking based on simultaneous tagging and velocity quantification is competitive with other methods such as tagging in mutually orthogonal image planes or quantification of three orthogonal velocity components.

Algorithms↗
PubMed1999

Recognition of infarct localization by specific changes in intramural myocardial mechanics.

BACKGROUND: After transmural myocardial infarction (MI), changes occur in intramural myocardial function. This has been described in anterior MI only. The aim of this study was to determine the relation between variable infarct locations and intramural deformation in patients with a first MI. METHODS: Forty patients (33 men and 7 women aged 57 +/- 11 years) with different infarct-related coronary arteries (25 left anterior descending, 7 circumflex, and 8 right coronary) were studied 6 +/- 3 days after infarction with magnetic resonance tissue tagging and 2-dimensional finite element analysis of myocardial deformation. Short-axis tagged images were acquired at base, mid, and apical level. Intramural deformation was measured in 6 circumferential segments per level. Results were compared with 9 age-matched healthy controls. RESULTS: Each infarct area demonstrated a significant reduction of intramural deformation. At mid-ventricular level, segments with maximum impaired intramural function were the anteroseptal segment for left anterior descending-related MI (stretch: 16% vs 33% for controls, P <.001), the posterolateral segment for related MI (stretch: 20% vs 34%, P <. 01); and the inferior segment for right coronary artery related MI (stretch: 18% vs 25%, P =.082). In these infarct segments, the intramural regional systolic stretch was more circumferentially oriented compared with radially oriented stretch in the same segments in controls (P <.05). CONCLUSION: The infarct area can be recognized by a specific spatial pattern of intramural deformation. In infarcted compared with noninfarcted myocardium, deformation is significantly reduced and systolic stretch deviates from the radial direction. Left anterior descending related infarcts were found to have larger regional differences in intramural deformation than circumflex or right coronary artery related MI of enzymatically the same size.

Aged↗
PubMed1999

MRI-derived left ventricular function parameters and mass in healthy young adults: relation with gender and body size.

PURPOSE: To obtain normal values of left ventricular (LV) end-diastolic volume (EDV), stroke volume (SV), cardiac output (CO) and LV mass, in relation to gender, weight (W), length (L) and body surface area (BSA). METHODS: Sixty-one healthy volunteers (32 male, 22.4 +/- 2.2 years) were examined, weight was 70.9 +/- 12.2 kg, length was 1.78 +/- 0.09 m, BSA was 1.88 +/- 0.19 m2. Segmented k-space breathhold cine MRI was used to obtain a stack of parallel short-axis images, from which LV volumes and end-diastolic mass were derived by slice summation. Four different body size indices were studied: W, L, L2 and BSA. RESULTS: After indexing for L, L2 and BSA, the gender differences in all LV parameters are still persisting. After indexing for W, gender differences persist for EDV and EDM, but are no longer observed for SV and CO. Separate regression analyses for males and females were performed. EDV, SV, CO and EDM correlated significantly with each body size index, both in males and in females. L or BSA were in general better predictors for LV parameters than W. Linear regression equations of EDV (ml) vs. L(m) were for males: EDV = 275 x L - 359 and for females: EDV = 190 x L - 215. Equations of SV(ml) vs. L were for males: SV = 186 x L - 237 and for females: SV = 118 x L - 121. Equations of LV mass(g) vs. L were for males: Mass = 175 x L - 179 and for females: Mass = 65.8 x L - 10.9. CONCLUSION: Most gender differences in LV parameters remain even after correction for body size indices. Normal reference values for LV parameters are given in relation to body size indices, by calculating regression coefficients separately for males and females. These normal values serve to obtain more accurate reference values for a patient with given gender, weight and length, and thus to improve the differentiation between normal and abnormal LV parameters.

Adult↗
PubMed1999

The influence of through-plane motion on left ventricular volumes measured by magnetic resonance imaging: implications for image acquisition and analysis.

In the evaluation of the left ventricular (LV) function using magnetic resonance imaging (MRI), a stack of parallel short-axis (SA) cine images is acquired that covers the whole LV. The aim of this study is to quantify the contribution to the LV volume parameters, provided by the most basal image plane that shows the LV wall only in end diastole (ED) but not in end systole (ES). In 57 healthy volunteers (31 men, mean body surface area 1.87 m2), a complete set of parallel SA images was acquired (10-mm slice distance) by breathhold segmented k-space cine MRI (7 ky lines per beat). The LV end-diastolic volume (EDV), stroke volume (SV), ejection fraction (EF), and cardiac output (CO) were determined by slice summation. Calculations were performed both with and without inclusion of the most basal slice. With inclusion of the most basal slice, all parameters were significantly (p < 0.001) larger compared with the values obtained by excluding this slice. EDV was 134 +/- 29 ml versus 113 +/- 26 ml; SV was 93 +/- 18 ml versus 72 +/- 16 ml; EF was 70 +/- 4% versus 64 +/- 4%; and CO was 5.3 +/- 1.4 l/min versus 4.1 +/- 1.1 l/min. The inclusion of the most basal slice leads to significantly larger values of LV volume parameters. Thus, this most basal SA image slice should be included in calculating the EDV. Whether or not this basal SA slice also contributes to the ES volume should be decided by using anatomical criteria on the ES image. The projection line onto the ES image of a long-axis view provides an additional criterion.

Adult↗