Robert M. Heethaar

Steady-state free precession with myocardial tagging: CSPAMM in a single breathhold

A method is presented that combines steady‐state free precession (SSFP) cine imaging with myocardial tagging. Before the tagging preparation at each ECG‐R wave, the steady‐state magnetization is stored as longitudinal magnetization by an α/2 flip‐back pulse. Imaging is continued immediately after tagging preparation, using linearly increasing startup angles (LISA) with a rampup over 10 pulses. Interleaved segmented k‐space ordering is used to prevent artifacts from the increasing signal during the LISA rampup. First, this LISA‐SSFP method was evaluated regarding ghost artifacts from the steady‐state interruption by comparing LISA with an α/2 startup method. Next, LISA‐SSFP was compared with spoiled gradient echo (SGRE) imaging, regarding tag contrast‐to‐noise ratio and tag persistence. The measurements were performed in phantoms and in six subjects applying breathhold cine imaging with tagging (temporal resolution 51 ms). The results show that ghost artifacts are negligible for the LISA method. Compared to the SGRE reference, LISA‐SSFP was two times faster, with a slightly better tag contrast‐to‐noise. Additionally, the tags persisted 126 ms longer with LISA‐SSFP than with SGRE imaging. The high efficiency of LISA‐SSFP enables the acquisition of complementary tagged (CSPAMM) images in a single breathhold. Magn Reson Med 49:722–730, 2003.

Comparison of 2D and 3D calculation of left ventricular torsion as circumferential-longitudinal shear angle using cardiovascular magnetic resonance tagging

PurposeTo compare left ventricular (LV) torsion represented as the circumferential-longitudinal (CL) shear angle between 2D and 3D quantification, using cardiovascular magnetic resonance (CMR).MethodsCMR tagging was performed in six healthy volunteers. From this, LV torsion was calculated using a 2D and a 3D method. The cross-correlation between both methods was evaluated and comparisons were made using Bland-Altman analysis.ResultsThe cross-correlation between the curves was r2 = 0.97 ± 0.02. No significant time-delay was observed between the curves. Bland-Altman analysis revealed a significant positive linear relationship between the difference and the average value of both analysis methods, with the 2D results showing larger values than the 3D. The difference between both methods can be explained by the definition of the 2D method.ConclusionLV torsion represented as CL shear quantified by the 2D and 3D analysis methods are strongly related. Therefore, it is suggested to use the faster 2D method for torsion calculation.

Nonrandom ventricular rhythm in horses with atrial fibrillation and its significance for patients

RR interval sequences during spontaneous atrial fibrillation in eight horses were analyzed as in previous studies in patients and dogs using histograms and serial auto-correlograms. In patients and dogs with spontaneous atrial fibrillation, ventricular rhythms were always random. In the horses, the histograms were skewed with median RR intervals of approximately 1,000 ms. A striking finding in these animals was the presence of long RR intervals up to 5,000 ms in duration. The shortest RR intervals lasted 400 to 600 ms. In contrast to findings in dogs and patients, the serial autocorrelograms showed periodicity that was reenforced by digitalis (n = 3), but eliminated by quinidine (n = 2) and atropine (n = 2). Quinidine and atropine eliminated the longer RR intervals, whereas digitalis increased the number of long RR intervals. In one horse, it was possible to measure intraarterial pressure, and large fluctuations in pressure were observed as the RR intervals varied from over 3,000 to less than 500 ms. It is postulated that these changes in blood pressure are associated with baroreceptor responses that may alter the electrophysiologic behavior of the atria and atrioventricular node. These changes cause the nonrandom patterns of ventricular rhythm in the horse. Because such very long RR intervals do not occur in human beings or dogs during atrial fibrillation, the random ventricular rhythm in these groups is maintained even during digitalis treatment.

The concept of apparent cardiac arrest as a prerequisite for coronary digital subtraction angiography

This study was undertaken to evaluate the possible use of digital subtraction applied after selective coronary arteriography. An identical position of the objects with and without contrast medium is an absolute requirement for the application of subtraction techniques. Because coronary arteries are in continuous motion, the subtraction technique cannot be applied without certain precautions. In our study, only images from corresponding moments in the cardiac cycle before and after contrast injection were matched for subtraction, that is, the concept of apparent cardiac arrest. To prevent variations in cardiac contractions due to varying RR intervals, heart rate was controlled by regular right atrial stimulation. Moreover, the stimulation rate and cine frequency were in synchrony, which was effected by triggering both on the frequency of the electric main alternating current (50 cycles/s). In this way, each cardiac cycle contains exactly the same number of frames at corresponding moments. A combination of the application of the concept of apparent cardiac arrest with the subtraction technique in 12 patients resulted in good quality images. Furthermore, better visualization of capillary filling with contrast material was obtained than with conventional coronary arteriography.

Loss of opposite left ventricular basal and apical rotation predicts acute response to cardiac resynchronization therapy and is associated with long-term reversed remodeling

BACKGROUNDnNormal left ventricular (LV) torsion is caused by opposite basal and apical rotation. Opposite rotation can be lost in heart failure, but might be restored by pacing; therefore, the predictive value of the loss of opposite base-apex rotation in heart failure patients for the response to cardiac resynchronization therapy (CRT) was studied.nnnMETHODS AND RESULTSnIn 34 CRT candidates and 12 controls, basal and apical LV rotations were calculated using magnetic resonance image tagging. Loss of opposite rotation was quantified by the correlation between both rotation curves: a negative correlation indicates normal, opposite rotation and a positive correlation indicates that base and apex rotate in the same direction. In patients, LV pressure was measured invasively during biventricular stimulation. Acute response to CRT was defined by >10% increase in dP/dt(max) relative to baseline. LV volume was determined at baseline and 8 months follow-up using echocardiography. The base-apex rotation correlation (BARC) was significantly higher in acute responders (n=22) than in nonresponders (n=12) and controls (0.64+/-0.51, -0.23+/-0.67, and -0.68+/-0.22, respectively; P=.001). The sensitivity and specificity for prediction of acute response were 82% and 83%, respectively, at a cutoff value of 0.5. At follow-up, volumes could be analyzed in 18 patients. In the group with BARC >0.5, end-diastolic volume decreased by 7% (NS), end-systolic volume by 16%, and ejection fraction increased by 28% (both P=.02), whereas in the group with BARC <0.5, no significant changes were observed.nnnCONCLUSIONSnThe loss of opposite base-apex rotation in patients eligible for CRT is an excellent predictor of acute response and is associated with LV reverse remodeling.

Improved Correction of Spatial Inhomogeneities of Surface Coils in Quantitative Analysis of First-Pass Myocardial Perfusion Imaging

To test whether image normalization using either a separate 3D proton‐density (PD)‐weighted prescan, or 2D PD‐weighted images prior to the perfusion series, improves correction of differences in spatial sensitivity induced by radiofrequency (RF) surface receiver coils. Originally, this correction was applied using the baseline signal in the myocardium before arrival of the contrast agent. This is of importance, as quantitative analysis of magnetic resonance (MR) myocardial perfusion using deconvolution with the arterial input assumes equal signal sensitivity over the heart.

Assessment of the opening angle of implanted Björk-Shiley prosthetic valves.

A method has been developed in which cineradiography is used for the assessment of the opening angle of implanted Bjork-Shiley prosthetic valves. The method is based on the fact that the ring and the disc, which are known to be circular, appear to be elliptical on x-ray films. The spatial position of the valve can be retrieved from the characteristics of these ellipses when vectoranalysis is applied. The methods accuracy does not depend on the position of the patient with respect to the direction of the x-ray beam. The accuracy of the method was demonstrated with the use of a phantom valve. The difference between the measured and the real opening angle was -0.7 +/- 1.8 degrees (mean +/- SD). Results were reproducible in patients to within -0.1 +/- 1.8 degrees. In 18 patients with normally functioning valves it could be demonstrated with frame-by-frame analysis (interval between frames 20 msec) that the valves opened very rapidly up to about 60 degrees. Closing patterns varied. In one of our patients with valvular thrombosis insufficient valvular opening could be demonstrated by our method before the patients complaints drew attention to the valvular dysfunction.

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° each, approximately 65% of the total variance in εr and εc was due to intersubject variability, the remaining 35% was due to measurement error. With 12 sectors of 30° each, the intersubject variability and measurement error both contributed 50% to the total variance. With 18 sectors of 20° 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.

Comparison of Time Parameters Derived from Myocardial Time-Density Curves in Patients before and after Percutaneous Transluminal Coronary Angioplasty

Much uncertainty exists about the pathophysiological significance of narrowings in the coronary arteries, especially those of moderate degree, as well as about the importance of diffuse coronary artery disease. Analysis of the contrast dynamics in the myocardium may provide pathophysiological information with which these problems can be solved or at least approached in a quantitative manner.

Determination of coronary artery diameter and contrast medium concentration from angiograms - possibilities and limitations.

The quantification of coronary arterial stenosis is a great clinical importance. The coronarograms obtained with the usual X-ray systems are severely distorted. The principal effects, underlying this distortion are the focal spot dimensions, blurring due to object movements and noise due to individual X-ray photons. Some general assessment, as well as a simplified procedure are given. Under the assumptions of a cylindrical artery and a Gaussian curve for its density graph, a relation can be derived to calculate the artery diameter. Application to test objects show that this is a practicable method.