Biomedical subjects

J P Kuijer

Publications and source records attributed to J P Kuijer.

8 recordsLinked to original sources

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↗

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↗

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↗

PubMed1997

Myocardial function in infarcted and remote regions early after infarction in man: assessment by magnetic resonance tagging and strain analysis.

Early after infarction in the perfusion bed of the left anterior descending coronary artery, cine MRI with spatial modulation of magnetization (SPAMM) tagging (7-mm grid) was used for short- and long-axis cardiac imaging. Two-dimensional strain analysis of triangular finite elements was performed between end-diastole and end-systole. Patients (n = 10) were compared with age-matched healthy subjects (n = 8). The anteroseptal region at midventricular level was considered representative for "infarcted" and the posterolateral region at basal level was considered "remote". The left ventricular end-diastolic volume index was larger in the patients (69 +/- 15 ml/m2 versus 56 +/- 4 ml/m2, P < 0.05). Short-axis images showed in the infarcted region a decrease of first principal strain (greatest systolic lengthening: 1.10 +/- .06 versus 1.27 +/- 0.04, P < 0.0001), and in the remote region an increase (1.48 +/- 0.11 versus 1.36 +/- 0.07, P < 0.025). The lateral and inferior ventricular regions at mid- and basal levels were found to function normally. Long-axis images yielded similar results. Early after infarction, regions with dysfunction, normal function, and hyperfunction can be delineated with MR tagging. The compensatory increased contraction in the remote region is possibly triggered by the Frank-Starling mechanism.

Case-Control Studies↗

PubMed1995

Performance evaluation of annular arrays in practice: the measurement of phase and amplitude patterns of radio-frequency deep body applicators.

An approach to a solution of two major problems in operating Annular Phased Arrays in deep body hyperthermia is presented: an E-field sensor capable of measuring phase and amplitude at 70 MHz and the concept of a power transmission factor to determine the effective amplitude of each applicator. In the four-waveguide Phased Array operating at 70 MHz, which is in clinical use at the department of Radiotherapy of the Academic Medical Center (AMC), the incident fields of the waveguides were scanned in phase and amplitude over the complete aperture midplane, inside an elliptical and a square phantom filled with saline. As a check on the application of the superposition principle, superpositions of the incident fields were compared with the electric field in the measured interference set-ups. With all four applicators radiating at equal amplitude and in phase, the maximum difference over the complete midplane of the phantom between superimposed and measured interference scans was 20% and 10 degrees in the elliptical phantom, and 20% and 30 degrees in the square phantom. After having determined nominal amplitude and phase patterns by a vector probe, any interference set-up can be superimposed from measurement of the actual incident field of each applicator. Therefore, the availability of a vector sensor as described here will contribute to solve a problem of hyperthermia quality assurance: the performance evaluation of Phased Arrays.

Humans↗

PubMedDate not supplied

Flow profiles in the left anterior descending and the right coronary artery assessed by MR velocity quantification: effects of through-plane and in-plane motion of the heart.

PURPOSE: The purpose of this work was to compare the temporal profiles of volume flow in the left anterior descending artery (LAD) and the right coronary artery (RCA) and to assess the effect of through-plane and in-plane myocardial motion. METHOD: In eight healthy volunteers, MR phase-difference velocity quantification was applied with prospective ECG triggering, pixel size of 1.16 x 0.98 mm2 (LAD) or 1.25 x 0.98 mm2 (RCA), velocity sensitivity of 40 cm/s, and data acquisition time window of 64 ms for LAD (3 ky lines per heartbeat) and 24 ms for RCA. In-plane motion was measured from the magnitude images. RESULTS: In the LAD, systolic peak and mean flow values were 0.94+/-0.28 and 0.30 +/-0.22 ml/s, respectively. Diastolic peak and mean flows were 2.42+/-0.56 and 1.38+/-0.43 ml/s. The systolic to diastolic ratio was 0.37+/-0.12 for peak flow and 0.22+/-0.15 for mean flow. Mean flow through the cardiac cycle was 59.1+/-15.0 ml/min. In the RCA, systolic peak and mean flow values were 1.96+/-0.69 and 0.74+/-0.31 ml/s, respectively. Diastolic peak and mean flows were 1.80+/-0.53 and 0.83+/-0.20 ml/s. The systolic to diastolic ratio was 0.97+/-0.58 for peak flow and 0.85+/-0.39 for mean flow. Mean flow through the cardiac cycle was 38.4+/-10.8 ml/min. The in-plane velocity of the coronary artery cross-section was 6.4+/-1.8 cm/s for the LAD and 14.9 +/-4.0 cm/s for the RCA (given by peak values in diastole). CONCLUSION: It is confirmed noninvasively with MR that the LAD shows a predominantly diastolic flow, whereas the RCA shows about equal flow values in systole and diastole. Through-plane motion correction is required for assessing the true flow patterns. The in-plane velocities of the coronary artery cross-sections imply a maximum data acquisition time window, estimated at 58 ms for the LAD and at 23 ms for the RCA.

Adult↗