Winfried Kessler

Noninvasive detection of coronary artery stenosis using contrast-enhanced three-dimensional breath-hold magnetic resonance coronary angiography

OBJECTIVES The purpose of this study was to evaluate a contrast-enhanced three-dimensional (3D) breath-hold magnetic resonance (MR) technique for detection of coronary artery stenoses. BACKGROUND The accuracy of previously published MR coronary angiography protocols varies widely. Recently, coronary artery imaging using T1-shortening contrast agent has become possible, but so far there are no data concerning its clinical application. METHODS Magnetic resonance coronary angiography was performed in 50 patients with suspected coronary artery disease. Magnetic resonance data acquisition using an ultrafast 3D gradient-echo sequence lasted over 32 heartbeats within one single breath-hold. Twenty milliliters of gadopentetate dimeglumine was injected at a flow rate of 1 ml/s for two successive studies covering the main coronary arteries in single-oblique planes. Stenosis assessment by MR was compared with significant (diameter stenosis > 50%) stenoses on X-ray angiography. Evaluation was limited to the proximal and mid-coronary artery segments. RESULTS Two hundred sixty-eight of 350 artery segments (76.6%) could be evaluated. Left circumflex coronary artery was only evaluable in 50% of cases by MR. In the evaluable segments, 48 of 56 stenoses and 193 of 212 nonstenotic segments were correctly classified by MR. On a patient basis, MR correctly identified 34 of 36 patients with and 8 of 14 patients without significant coronary stenoses as demonstrated by X-ray angiography (sensitivity 94.4%, specificity 57.1%). CONCLUSIONS Oblique projection contrast-enhanced MR coronary angiograms obtained within one single breath-hold permit identification of patients with coronary stenoses in the proximal and mid segments of the major coronary arteries with satisfactory accuracy.

Usefulness of respiratory gated magnetic resonance coronary angiography in assessing narrowings ≥50% in diameter in native coronary arteries and in aortocoronary bypass conduits

Magnetic resonance coronary angiography (MRCA) is a promising method for the assessment of proximal coronary artery stenosis. Conventional 2-dimensional techniques require repetitive breath holds to image multiple sections. This may lead to misregistrations if the respiratory level is not exactly reproduced. In the present study, MRCA was performed using a 3-dimensional approach with navigator echo-based respiratory gating. In 73 patients (55 men and 18 women) who were referred for cardiac catheterization, the assessment of significant stenoses (> or = 50%) was performed in the proximal and midsegments of the coronary arteries after multiplanar reconstruction of the visualized coronary arteries. In addition, in 8 patients with coronary artery bypass grafts the patency of the transplants was evaluated. After withdrawing 8 patients from analysis because of poor image quality, stenosis evaluation was possible in 236 of 455 reviewed coronary segments (52%). In the other 219 cases, either the visualization of the vessel segment was indistinct (30%) or the segment was located outside the imaging volume (18%). In total, 28 of 43 significant coronary stenoses could be correctly identified (65%). Evaluation of bypass graft patency was possible in 7 patients. All 4 occluded and 13 of 15 patent grafts were correctly classified. Thus, respiratory gated MRCA is a feasable method for the assessment of hemodynamically significant coronary stenoses and bypass graft patency. However, technical improvements are mandatory to improve accuracy of the method.

Comparison of contrast-enhanced breath-hold and free-breathing respiratory-gated imaging in three-dimensional magnetic resonance coronary angiography

Suppression of respiratory motion is one of the major challenges of magnetic resonance (MR) coronary angiography. Two approaches to compensate for respiratory motion have often been proposed: breath-hold (BH) and free-breathing respiratory-gated (FBRG) imaging. So far, however, these approaches have never been directly compared. MR coronary angiography was performed in 32 patients with suspected coronary artery disease. MR data were acquired using contrast-enhanced BH and FBRG 3-dimensional MR coronary angiographic techniques. MR images were compared with regard to image quality using quantitative parameters and with regard to accuracy for stenosis detection in the proximal and mid-coronary segments in comparison to x-ray angiography. With regard to image quality, BH was superior to FBRG. Signal-to-noise ratio was 29.1 +/- 10.7 for BH versus 18.8 +/- 9.7 for FBRG (p <0.05) and contrast-to-noise was 18.0 +/- 7.4 for BH versus 11.3 +/- 7.9 for FBRG (p </=0.05). One hundered seventy-one of 224 coronary artery segments (76%) were evaluable in BH compared with 155 of 224 in FBRG (69%). In the evaluable segments, BH demonstrated a sensitivity of 87% (26 of 30 stenoses detected) and specificity of 92% (129 of 141 nonstenotic segments correctly identified), whereas FBRG showed a sensitivity of 60% (15 of 25) and specificity of 89% (115 of 130). Overall accuracy was 91% (155 of 171) for BH and 84% (130 of 155) for FBRG. Sensitivity was significantly higher for BH (p = 0.0320), whereas specificity and overall accuracy were not significantly different. Thus, contrast-enhanced BH MR coronary angiography compares favorably to FBRG imaging with regard to image quality and detection of coronary stenoses.

A direct comparison of noninvasive coronary angiography by electron beam tomography and navigator-echo-based magnetic resonance imaging for the detection of restenosis following coronary angioplasty.

Ropers D, Regenfus M, Stilianakis N, et al. A direct comparison of noninvasive coronary angiography by electron beam tomography and navigator-echo-based magnetic resonance imaging for the detection of restenosis following coronary angioplasty. Invest Radiol 2002;37:386–392. rationale and objectives. To compare electron beam tomography (EBT) with MR imaging (MRI) for detection of restenosis after coronary angioplasty (PTCA). methods. One hundred eighteen patients after PTCA were investigated. By EBT, 50 axial images were acquired (3-mm slice thickness, 120–160 mL radiographic contrast agent). MRI was performed using respiratory-gated sequences (24–48 cross-sections, 2-mm slice thickness, 20 mL Gd-DTPA). EBT and MRI images were evaluated concerning high-grade post-PTCA restenosis (≥70%) and validated against coronary angiography. results. In EBT, 28 patients and in MRI, 31 patients were not evaluable. In the remaining patients, sensitivity for restenosis detection was 90% in EBT (17/19) and 73% in MRI (11/15;P = 0.370). In EBT, specificity was significantly higher (66% vs. 49%, P = 0.043). Overall accuracy was 71% for EBT and 53% for MRI (P = 0.014). conclusions. For the detection of high-grade restenosis after PTCA, EBT demonstrated significantly higher accuracy than MRI.

Visualization of the coronary arteries in three-dimensional reconstructions using respiratory gated magnetic resonance imaging.

Objective To assess the applicability of respiratorygated magnetic resonance coronary angiography, combined with three-dimensional image reconstruction, for visualizing the coronary arteries.Methods Twenty subjects (three healthy volunteers and 1 7 patients without stenoses detected by coronary angiography) were investigated. Magnetic resonance imaging was performed in a 1.5 T scanner using ECG-tnggered gradient-echo sequences to acquire a volume data set consisting of 24–48 contiguous axial cross-sections of the heart (2 mm slice thickness, 1.17 mm x 1.1 7 mm in-plane resolution). Navigator-echo-based retrospective respiratory gating was used to minimize respiratory motion artifacts. Three-dimensional reconstructions of the heart were rendered using surface-display techniques. The length of the visualized coronary arteries was measured in curved multiplanar reconstructions.Results In the three-dimensional reconstructions, the left main artery (LMA) and left anterior descending artery (LADA) were visualized in 1 7 cases, the left circumflex artery (LCXA ) in 15, and the right coronary artery (RCA) in 16 cases. Vessel continuity was uninterrupted in all 1 7 cases for the LMA, in 14 for the LADA, eight for the LCXA, and 13 for the RCA. The mean lengths of the visualized vessels were 14 ± 7 mm for the LMA, 65 ± 13 mm for the LADA, 45 ± 1 6 mm for the LCXA, and 37 ± 26 mm for the RCA. Reasons for impaired visibility of the LCXA and RCA were poor image quality due to there being a low contrast: noise ratio, motion artifacts, and incomplete coverage by the imaging volume.Conclusions Navigator-echo-based magnetic resonance imaging is a promising technique for investigating the coronary arteries. Acquisition of a volume data set permits three-dimensional displays of the coronary vessels.

Diagnostic value of maximum intensity projections versus source images for assessment of contrast-enhanced three-dimensional breath-hold magnetic resonance coronary angiography.

Regenfus M, Ropers D, Achenbach S, et al. Diagnostic value of maximum intensity projections versus source images for assessment of contrast-enhanced three-dimensional breath-hold magnetic resonance coronary angiography. Invest Radiol 2003;38:200–206. Rationale and Objectives.We compared maximum intensity projections (MIP) versus original source images (SI) in respect to detection of coronary artery stenoses by means of magnetic resonance (MR) coronary angiography. Methods.MR coronary angiography was performed on 61 patients. MIP and SI were independently evaluated as to presence of significant stenoses in the proximal and midcoronary segments and compared with x-ray angiography. Results.A total of 315 of 427 (74%) coronary artery segments could be evaluated in MIP and 328 of 427 (77%) in SI. In segments able to be evaluated, MIP images demonstrated 84% (54/64) sensitivity and 87% (219/251) specificity, whereas SI images showed 85% (58/68) sensitivity and 90% (235/260) specificity. Overall accuracy was 87% (273/310) for MIP and 89% (293/328) for SI. There was no statistically significant difference between both modalities. Conclusions.The MIP reconstructions showed comparable accuracy to unprocessed SI. However, MIP postprocessing is compromised by a higher number of images that were unable to be evaluated due to overlap of coronary arteries with adjacent cardiac structures.

Beurteilung von Koronararterienstenosen mittels atemkontrollierter NMR-Angiographie

Die atemkontrollierte NMR-Angiographie ist eine neue Abbildungstechnik in der Kernspintomographie, die es erlaubt, einen dreidimensionalen Bilddatensatz des Herzens zu akquirieren und hieraus einzelne Koronararterien zu rekonstruieren. In dieser Studie sollte die Beurteilbarkeit von signifikanten Koronararterienstenosen (≥ 50%) mittels atemkontrollierter NMR-Angiographie untersucht werden. Die NMR-Untersuchung erfolgte bei 68 Patienten (50 Männer, 18 Frauen), bei denen aufgrund einer vermuteten oder bekannten koronaren Herzerkrankung eine Herzkatheteruntersuchung durchgeführt wurde. Die Stenosebeurteilung erfolgte nach multiplanarer Gefäßrekonstruktion im proximalen, mittleren und distalen Koronarsegment ohne Kenntnis des tatsächlichen angiographischen Befundes. 275 von 680 Koronarsegmenten (40%) lagen außerhalb des Abbildungsvolumens und wurden von der Auswertung ausgeschlossen. Die Sensivität für die Erkennung signifikanter Stenosen lag im proximalen Verlauf des Ramus interventricularis anterior (RIVA) mit 75% und der rechten Koronararterie (RCA) mit 71% am höchsten. Die Gesamtsensitivität war allerdings mit 48% niedrig bei einer Spezifität von 92%. Der positive und negative Vorhersagewert lag bei 67% und 85%. Diese Studie zeigt, daß signifikante Koronararterienstenosen, insbesondere des proximalen RIVA und der RCA, mittels atemkontrollierter NMR-Angiographie erkannt werden können. Weitere technische Verbesserungen sind notwendig, um die Methode in der klinischen Routinediagnostik zuverlässig einsetzen zu können. Respiratory gated MR coronary angiography is a new MR imaging technique which permits reconstruction of the coronary arteries from a three-dimensional data set obtained from contiguous parallel sections. In this study, respiratory gated MR angiography was applied to assess significant coronary artery stenoses (≥ 50%). MR imaging was performed in 68 patients (50 men, 18 women) who had been referred to cardiac catheterization because of suspected or known coronary artery disease. The evaluation of coronary artery stenoses was performed in a blindes manner in the proximal, middle, and distal vessel segments after multiplanar coronary reconstruction of the MR images. Of the 680 coronary segments, 275 (40%) were located outside the imaging volume and were, therefore, excluded from further analysis. The highest sensitivity for stenosis detection was found in the proximal left anterior descending (LAD) and right coronary artery (RCA) with 75% and 71%, respectively. The overall sensitivity, however, was low with 48%. The overall specificity was 92%. The positive and negative predictive values were 67% and 85%, respectively. This study shows that significant coronary artery stenoses, especially in the proximal LAD and RCA, can be correctly identified using respiratory gated MR angiography. However, further technical improvements are necessary before this method may become a reliable diagnostic tool in clinical practice.

Imaging of the coronary arteries using magnetic resonance angiography

Die Darstellung der Koronararterien mittels Kernspintomographie wird durch ihren geringen Durchmesser, den stark geschlängelten Verlauf und die schnelle Bewegung der Koronargefäße erschwert. Initiale Ergebnisse zweidimensionaler Gradienten-Echosequenzen, die die Abbildung der Koronararterien in wiederholtem inspiratorischem Atemstillstand gestatteten, waren ermutigend. Aufgrund der eingeschränkten Qualität der Datensätze, vor allem bedingt durch inkongruente Atemlage wiederholter Akquisitionen, war das Verfahren jedoch klinisch nur bedingt einsetzbar. Ein großer Fortschritt ließ sich durch dreidimensionale Sequenzen erreichen, bei denen während freier Atmung ein kongruenter Volumendatensatz aus etwa 24 axialen Schnittbildern akquiriert wird. Die kontinuierliche Registrierung der Zwerchfellposition über Navigator-Echos gestattet hierbei ein retrospektives Atemgating, um Artefakte durch die Atembewegung zu reduzieren. Mit diesen Sequenzen konnten mehrere Gruppen bei einer Ortsauflösung von etwa 1,2 × 1,2 × 2 mm und einer Zeitauflösung von ca. 126 ms Sensitivitäten von etwa 70–80% und Spezifitäten von etwa 90% für den Nachweis von Koronararterienstenosen erreichen. Ein weiterer Fortschritt ist durch die Entwicklung neuer, intravaskulär verbleibender Kontrastmittel und durch ultraschnelle Sequenzen, welche die Akquisition eines Volumendatensatzes während eines Atemstillstands gestatten, zu erwarten. Magnetic resonance imaging of the coronary arteries is difficult due to the tortuous course of these vessels, their small diameter, and their rapid movement caused by respiration and cardiac contraction. Initial investigations could demonstrate the feasability of non-invasive magnetic resonance coronary angiography using 2-dimensional turbo-FLASH gradient-echo sequences in repeated breathholds of approximately 16 heart beats duration. Further developments, especially the design of navigator-echo-based respiratory gated 3-dimensional imaging sequences, permitted the acquisition of contiguous volume data sets of the heart which eliminated many limitations of 2-dimensional repeated breathhold sequences. With a spatial resolution of approximately 1.2 × 1.2 × 2 mm and a temporal resolution of approximately 126 ms, several authors reported sensitivities of 70–80% and specificities of approximately 90% for the detection of coronary artery stenoses. Further improvements can be expected from new, intravascular contrast agents and from ultrafast sequences which permit acquisition of a sufficiently large imaging volume within one single breathhold.