Axel Bornstedt

Comparison of Magnetic Resonance Real-Time Imaging of Left Ventricular Function With Conventional Magnetic Resonance Imaging and Echocardiography

This study analyzes the accuracy of a new real-time magnetic resonance imaging (MRI) technique (acquisition duration, 62 ms/image) and echocardiography for the determination of left ventricular (LV) end-diastolic volume, end-systolic volume, ejection fraction, and muscle mass when compared with turbo gradient echo imaging as the reference standard. Thirty-four patients were examined with digital echocardiography, standard, and real-time MRI. A close correlation was found between the results of real-time imaging and the reference standard for end-diastolic volume, end-systolic volume, and ejection fraction (r >0.95), with a lower correlation for LV muscle mass (r = 0.81). Correlations between echocardiography and the reference standard were lower for all parameters. Real-time MRI enables the acquisition of high-quality cine loops of the entire heart in minimal time without electrocardiographic triggering or breath holding. Thus, patient setup and scan time can be reduced considerably. Results are similar to the reference standard and superior to echocardiography for determining LV volumes and ejection fraction. This technique is a valid alternative to current approaches and can form the basis of every cardiac MRI examination.

Improved Accuracy of Quantitative Assessment of Left Ventricular Volume and Ejection Fraction by Geometric Models with Steady-State Free Precession

The purpose of this study was to determine whether steady-state free precession (SSFP) could improve accuracy of geometric models for evaluation of left ventricular (LV) function in comparison to turbo gradient echo (TGrE) and thereby reduce the acquisition and post-processing times, which are commonly long by use of the Simpsons Rule. In 25 subjects, cine loops of the complete heart in short and horizontal long-axis planes were acquired using TGrE (TR/TE/flip = 5.0/1.9/25) compared with SSFP (TR/TE/flip = 3.2/1.2/60). LV volumes and EF were measured with various geometric models for TGrE and SSFP. With three-dimensional data, the LV volumes were higher and the resulting EF lower for SSFP in contrast to TGrE (51 +/- 15% vs. 57 +/- 15%, p < 0.001). With SSFP, various geometric models yielded good to excellent correlations for LV volumes and LVEF compared to volumetric data (r = 0.94-0.98, mean relative difference 7.0-11.4%). In contrast, correlations were low using biplane or single-plane ellipsoid models in TGrE (r = 0.71-0.75, mean relative difference 15.9-30.2%). A new combined geometric model, taking all three dimensions into account, yielded the highest accuracy for SSFP in comparison to volumetric data (r = 0.99, mean relative difference 4.7%). Geometric models for assessment of LV volumes and EF yield higher accuracy and reproducibility by use of the SSFP sequence than by standard TGrE. This may increase clinical utility of magnetic resonance by shorter acquisition and processing times.

Performance of a new gadolinium-based intravascular contrast agent in free-breathing inversion-recovery 3D coronary MRA

In three‐dimensional (3D) coronary magnetic resonance angiography (MRA), the in‐flow contrast between the coronary blood and the surrounding myocardium is attenuated as compared to thin‐slab two‐dimensional (2D) techniques. The application of a gadolinium (Gd)‐based intravascular contrast agent may provide an additional source of signal and contrast by reducing T1blood and supporting the visualization of more distal or branching segments of the coronary arterial tree. In six healthy adults, the left coronary artery (LCA) system was imaged pre‐ and postcontrast with a 0.075‐mmol/kg bodyweight dose of the intravascular contrast agent B‐22956. For imaging, an optimized free‐breathing, navigator‐gated and ‐corrected 3D inversion recovery (IR) sequence was used. For comparison, state‐of‐the‐art baseline 3D coronary MRA with T2 preparation for non‐exogenous contrast enhancement was acquired. The combination of IR 3D coronary MRA, sophisticated navigator technology, and B‐22956 allowed for an extensive visualization of the LCA system. Postcontrast, a significant increase in both the signal‐to‐noise ratio (SNR; 46%, P < 0.05) and contrast‐to‐noise ratio (CNR; 160%, P < 0.01) was observed, while vessel sharpness of the left anterior descending (LAD) artery and the left coronary circumflex (LCX) were improved by 20% (P < 0.05) and 18% (P < 0.05), respectively. Magn Reson Med 49:115–121, 2003.

Optimization of realtime adaptive navigator correction for 3D magnetic resonance coronary angiography.

Breathing motion artifacts reduce the quality of MR coronary artery images. Real‐time adaptive navigator correction with different correction factors (0%, 30%, 60%, 80% of diaphragmatic displacement) was used to correct for respiratory motion in 3D coronary artery imaging. Significant improvements of image quality were achieved by adaptive motion correction in comparison with conventional navigator gating. A close correlation between the correction factor, which yielded optimal image quality, and cardiac displacement relative to diaphragmatic displacement was found. The quality of coronary artery imaging can be improved using real‐time adaptive navigator correction. Correction factors have to be adjusted for each segment of the coronary arteries and for each patient. Magn Reson Med 42:408–411, 1999.

Noninvasive determination of coronary blood flow velocity with magnetic resonance imaging: comparison of breath-hold and navigator techniques with intravascular ultrasound.

The aim of this study was to evaluate two different magnetic resonance (MR) techniques for the noninvasive assessment of intracoronary blood flow. Coronary blood flow velocities were measured invasively in 26 angiographically normal segments of 12 patients. Noninvasive measurements were performed in identical segments with two MR techniques using a 1.5 T MR tomograph (ACS NT, Philips). A single breath‐hold technique (temporal resolution: 140 msec) and a similar non‐breath‐hold technique with prospective navigator correction and improved temporal resolution (45 msec) were used. Maximal coronary flow velocities determined by MR correlated closely with invasive measurements (breath‐hold: r = 0.70; navigator: r = 0.86); however, a significant underestimation of the MR measurements was found (slope = 0.33 and 0.37). The relative difference from the invasive method was lower for the navigator technique compared with the breath‐hold technique (P < 0.02). Both MR techniques allow the determination of coronary blood flow velocities. The higher temporal resolution and shorter acquisition window of navigator‐corrected non‐breath‐hold techniques lead to increased accuracy. This approach is a further step toward the diagnostic use of MR flow measurements in coronary artery disease. Magn Reson Med 41:544–549, 1999.

Feasibility of ultra-short echo time (UTE) magnetic resonance imaging for identification of carious lesions.

The objective of this study was to investigate the potential of ultra short echo time imaging for the assessment of caries lesions and early demineralization. 12 patients with suspected caries lesions underwent a dental magnetic resonance imaging investigation comprising ultra short echo time imaging (echo time = 50 μs) and spin echo imaging. Before the dental magnetic resonance imaging, all patients underwent a conventional clinical dental investigation including visual assessment of the teeth as well as dental x‐ray imaging. All lesions identifiable in the x‐ray could be clearly identified in the ultra short echo time images, but only about 19% of the lesions were visible in the spin echo images. In 19% of all lesions, the lesions could be more clearly delineated in the ultra short echo time images than in the x‐ray images. This was especially the case for secondary lesions. In direct comparison with the x‐ray images, all lesions appeared substantially larger in the dental magnetic resonance imaging data. The presented data provide evidence that caries lesions can be identified in ultra short echo time magnetic resonance imaging with high sensitivity. The apparent larger volume of the lesions in dental magnetic resonance imaging may be attributed to fluid accumulation in demineralized areas without substantial breakdown of mineral structures. Magn Reson Med, 2011.

Vergleich verschiedener Parameter zur Bestimmung eines Index der myokardialen Perfusionsreserve zur Erkennung von Koronarstenosen mit kardiovaskulärer Magnetresonanztomographie

For the assessment of myocardial perfusion with cardiac magnetic resonance imaging, different semiquantitative parameters of the first pass signal intensity time curves can be calculated and myocardial perfusion reserve indices can be determined. In this study we evaluated the feasibility of different perfusion parameters and their perfusion reserve indices for the detection of significant coronary artery stenosis.¶u2002u2009u2009The signal intensity time curves of the first pass of a gadolinium-DTPA bolus injected via a central vein catheter before and after dipyridamole infusion were investigated in 15 patients with single vessel (stenosis ≥75% area reduction) and five patients without significant coronary artery disease. For the distinction of ischemic and nonischemic myocardial segments, semiquantitative parameters, such as maximal signal intensity, contrast appearance time, time to maximal signal intensity and the steepness of the signal intensity curve‘s upslope determined by a linear fit, were assessed after correction for the input function. For each parameter a myocardial perfusion reserve index was calculated and cut off values for the detection of significant coronary stenosis were defined. The diagnostic accuracy of each parameter was then examined prospectively in 36 patients with coronary artery disease and compared with coronary angiography.¶u2002u2009u2009Where as a distinction of ischemic and normal myocardium was possible with myocardial perfusion reserve indices, semiquantitative parameters at rest or after vasodilation alone did not allow such a distinction. The perfusion reserve index calculated from the upslope showed the most significant difference between ischemic and nonischemic myocardial segments (1.19±0.4 and 2.38±0.45, p<0.001) followed by maximum signal intensity, time to maximum signal intensity and contrast appearance time. Sensitivity, specificity and diagnostic accuracy was 87, 82 and 85% for the detection of hypoperfusion induced by significant coronary artery stenoses using the perfusion reserve index calculated from the upslope.¶u2002u2009u2009The steepness of the first pass signal intensity curve‘s upslope, determined by a linear fit, is a feasible parameter for the detection of significant coronary artery disease with MR. Based on a myocardial perfusion reserve index of this parameter, ischemic myocardium can be identified with high diagnostic accuracy. Zur Beurteilung der myokardialen Perfusion mit Magnetresonanztomographie können verschiedene Parameter der Signalintensitätskurven evaluiert, sowie ein Index zur Erkennung der Auswirkungen von Koronararterienstenosen ermittelt werden.¶u2002u2009u2009An 15 Patienten mit koronarer Eingefäßerkrankung (≥75%) und 5 Patienten ohne signifikante Koronararterienstenose wurden die first pass Signalintensitäts-Kurven eines zentralvenös injizierten Gadolinium DTPA-Bolus vor und nach Dipyridamolinfusion untersucht. Die zur Eingangsfunktion normalisierten Parameter maximale Signalintensität, Kontrastmittelankunftzeit, Einwaschzeit und die Anstiegssteilheit wurden ermittelt und ein Perfusionsreserve-Index für die einzelnen Parameter errechnet. Für jeden Parameter wurden Grenzwerte zur Unterscheidung ischämischer und nicht ischämischer Myokardareale definiert. Die diagnostische Genauigkeit der errechneten Grenzwerte zur Erkennung von Koronarstenosen (≥75%) wurden prospektiv an 36 Patienten untersucht und die Ergebnisse mit der Koronarangiographie verglichen.¶u2002u2009u2009Der aus der Anstiegssteilheit berechnete Perfusionsreserveindex (Grenzwert 1,5) ergab die beste diagnostische Genauigkeit zur Unterscheidung von ischämischen und nicht ischämischen Myokardarealen (1,19±0,4 und 2,38±0,45, p<0,001). Die Sensitivität, Spezifität und diagnostische Genauigkeit zur Erkennung von Koronarstenosen waren 87, 82 und 85%. Die Beurteilung der Werte nur in Ruhe oder nach Vasodilatation erlaubt keine sichere Erkennung von Koronarstenosen.¶u2002u2009u2009Die Anstiegssteilheit der first pass Signalintensitätskurve, ermittelt durch einen linearen Fit, ist der geeignetste Parameter zur Beurteilung der myokardialen Perfusionsreserve mit MRT. Ischämische Myokardareale können mit hoher diagnostischer Genauigkeit erfasst werden.

Dobutamine Induced Myocardial Perfusion Reserve Index with Cardiovascular MR in Patients with Coronary Artery Disease

Currently, adenosine or dipyridamole is commonly used for the assessment of perfusion reserve. With intolerance to these agents, dobutamine can be used alternatively or it can be used for a combined examination of wall motion and perfusion. The aim of the study was to analyze the feasibility of cardiovascular magnetic resonance (CMR) to assess perfusion reserve with dobutamine. Alterations of myocardial perfusion were noninvasively assessed in 23 patients with and 4 without significant coronary artery disease by calculation of a myocardial perfusion reserve index from the upslope of the signal intensity curves of a first pass gadolinium bolus before and during dobutamine infusion (20 micrograms/min/kg). An ischemic threshold value of perfusion reserve index was determined from patients without significant coronary artery disease. Significant differences were found between ischemic and remote to ischemic segments in patients with single vessel disease (0.90 +/- 0.18 vs. 1.73 +/- 0.32, p < 0.0001). Differences between nonischemic segments in patients without and ischemic segments in patients with coronary artery disease were significant (2.0 +/- 0.39 vs. 0.97 +/- 0.20, p < 0.001). A cut-off value for myocardial perfusion reserve index of 1.22 for the detection of significant coronary artery stenosis yielded a sensitivity, specificity, and diagnostic accuracy of 81, 73, and 77%, respectively. Dobutamine MR is feasible in the evaluation of myocardial perfusion and can be used for the detection of myocardial ischemia alternatively to adenosine or dipyridamole in patients with coronary artery disease.

The intravascular contrast agent Clariscan™ (NC 100150 injection) for 3D MR coronary angiography in patients with coronary artery disease

4. ConclusionIn our experience ClariscanTM improves image quality, thus, increasing the visual length and improving the actual visible dimensions of the coronary arteries. Distal segments improved to a higher extent than the proximal parts. In that way sensitivity and specificity for the detection of significant coronary artery disease could be improved. Better SNR and CNR can be used to improve spatial resolution or to reduce scan time by techniques like SENSE or SMASH [14,15].

Multi‐slice dynamic imaging: Complete functional cardiac MR examination within 15 seconds

A new magnetic resonance (MR) sequence was developed to acquire real‐time images in a multi‐slice dynamic imaging mode to cover the complete heart in 15 seconds without the need for electrocardiogram (ECG) triggering and multiple breath holds. In 34 patients, left ventricular function was assessed with the new technique and a standard technique. The new technique proved to be feasible and accurate for functional cardiac examinations. J. Magn. Reson. Imaging 2001;14:300–305.