Bernd Ohnesorge

Detection of Coronary Artery Stenoses With Thin-Slice Multi-Detector Row Spiral Computed Tomography and Multiplanar Reconstruction

Background—We analyzed the accuracy of multi-detector row spiral computed tomography (MDCT) using a 16-slice CT scanner with improved spatial and temporal resolution, as well as routine premedication with &bgr;-blockers for detection of coronary stenoses. Methods and Results—Seventy-seven patients with suspected coronary disease were studied by MDCT (12×0.75-mm cross-sections, 420 ms rotation, 100 mL contrast agent IV at 5 mL/s). Patients with a heart rate above 60/min received 50 mg atenolol before the scan. In axial MDCT images and multiplanar reconstructions, all coronary arteries and side branches with a diameter of 1.5 mm or more were assessed for the presence of stenoses exceeding 50% diameter reduction. In comparison to invasive coronary angiography, MDCT correctly classified 35 of 41 patients (85%) as having at least 1 coronary stenosis and correctly detected 57 of 78 coronary lesions (73%). After excluding 38 of 308 coronary arteries (left main, left anterior descending, left circumflex, and right coronary artery in 77 patients) classified as unevaluable by MDCT (12%), 57 of 62 lesions were detected, and absence of stenosis was correctly identified in 194 of 208 arteries (sensitivity: 92%; specificity: 93%; accuracy: 93%; positive and negative predictive values: 79% and 97%). Conclusions—MDCT coronary angiography with improved spatial resolution and premedication with oral &bgr;-blockade permits detection of coronary artery stenoses with high accuracy and a low rate of unevaluable arteries.

Noninvasive detection and evaluation of atherosclerotic coronary plaques with multislice computed tomography

OBJECTIVES The aim of the present study was to evaluate the accuracy in determining coronary lesion configuration by multislice computed tomography (MSCT). The results were compared with the findings of intracoronary ultrasound (ICUS). BACKGROUND The risk of acute coronary syndromes caused by plaque disruption and thrombosis depends on plaque composition rather than stenosis severity. Thus, the reliable noninvasive assessment of plaque configuration would constitute an important step forward for risk stratification in patients with known or suspected coronary artery disease. Just recently, MSCT scanners became available for general purpose scanning. Due to improved spatial and temporal resolution, this new technology holds promise to allow for differentiation of coronary lesion configuration. METHODS The ICUS and MSCT scans (Somatom Volume Zoom, Siemens, Forchheim, Germany) were performed in 15 patients. Plaque composition was analyzed according to ICUS (plaque echogenity: soft, intermediate, calcified) and MSCT criteria (plaque density expressed by Hounsfield units [HU]). RESULTS Thirty-four plaques were analyzed. With ICUS, the plaques were classified as soft (n = 12), intermediate (n = 5) and calcified (n = 17). Using MSCT, soft plaques had a density of 14 +/- 26 HU (range -42 to +47 HU), intermediate plaques of 91 +/- 21 HU (61 to 112 HU) and calcified plaques of 419 +/- 194 HU (126 to 736 HU). Nonparametric Kruskal-Wallis test revealed a significant difference of plaque density among the three groups (p < 0.0001). CONCLUSIONS Our results indicate that coronary lesion configuration might be correctly differentiated by MSCT. Since also rupture-prone soft plaques can be detected by MSCT, this noninvasive method might become an important diagnostic tool for risk stratification in the near future.

Clinical studyNoninvasive detection and evaluation of atherosclerotic coronary plaques with multislice computed tomography1

OBJECTIVES The aim of the present study was to evaluate the accuracy in determining coronary lesion configuration by multislice computed tomography (MSCT). The results were compared with the findings of intracoronary ultrasound (ICUS). BACKGROUND The risk of acute coronary syndromes caused by plaque disruption and thrombosis depends on plaque composition rather than stenosis severity. Thus, the reliable noninvasive assessment of plaque configuration would constitute an important step forward for risk stratification in patients with known or suspected coronary artery disease. Just recently, MSCT scanners became available for general purpose scanning. Due to improved spatial and temporal resolution, this new technology holds promise to allow for differentiation of coronary lesion configuration. METHODS The ICUS and MSCT scans (Somatom Volume Zoom, Siemens, Forchheim, Germany) were performed in 15 patients. Plaque composition was analyzed according to ICUS (plaque echogenity: soft, intermediate, calcified) and MSCT criteria (plaque density expressed by Hounsfield units [HU]). RESULTS Thirty-four plaques were analyzed. With ICUS, the plaques were classified as soft (n = 12), intermediate (n = 5) and calcified (n = 17). Using MSCT, soft plaques had a density of 14 +/- 26 HU (range -42 to +47 HU), intermediate plaques of 91 +/- 21 HU (61 to 112 HU) and calcified plaques of 419 +/- 194 HU (126 to 736 HU). Nonparametric Kruskal-Wallis test revealed a significant difference of plaque density among the three groups (p < 0.0001). CONCLUSIONS Our results indicate that coronary lesion configuration might be correctly differentiated by MSCT. Since also rupture-prone soft plaques can be detected by MSCT, this noninvasive method might become an important diagnostic tool for risk stratification in the near future.

Subsecond multi-slice computed tomography: basics and applications

The recent advent of multislice-scanning is the first real quantum leap in computed tomography since the introduction of spiral CT in the early 90s. We discuss basic theoretical considerations important for the design of multislice scanners. Then, specific issues, like the design of the detector and spiral interpolation schemes are addressed briefly for the SOMATOM PLUS 4 Volume Zoom. The theoretical concepts are validated with phantom measurements. We finally show the large potential of the new technology for clinical applications. The concurrent acquisition of multiple slices results in a dramatic reduction of scan time for a given scan technique. This allows scanning volumes previously inaccessible. Similarly, given volumes can be scanned at narrower collimation, i.e. higher axial resolution in a given time. From data acquired at narrow collimation, both high-resolution studies and standard images can be reconstructed in the so-called Combi-Mode. This on the one hand reduces dose exposure to the patient because repeated scanning of a patient is no longer required. On the other hand, standard reconstructions benefit from narrow collimation as Partial Volume Artifacts are drastically suppressed. The rotational speed of 0.5 s of the SOMATOM PLUS 4 Volume Zoom furthermore opens up a whole range of new applications in cardiac CT. For the first time, virtually motion-free images can be acquired even for large volumes in a single breathhold by the combination of fast rotation and ECG triggering, respectively gating. We explain the underlying concepts and present initial results. The paper concludes with a brief discussion of the impact of the new technique on image display and postprocessing.

Heart rate adaptive optimization of spatial and temporal resolution for electrocardiogram-gated multislice spiral CT of the heart.

Purpose We introduce a reconstruction method for electrocardiogram (ECG)-gated multislice spiral computed tomography (CT) examinations of the heart [adaptive cardio volume (ACV) reconstruction]. It is evaluated for a four-slice CT system (Siemens Somatom VolumeZoom). Method State-of-the-art reconstruction techniques for ECG-gated multislice spiral CT use scan data from N consecutive heart cycles for image reconstruction. With increased N, the temporal resolution improves up to t rot /(2 N) (t rot is the 360° rotation time of the scanner) but at the expense of insufficient volume coverage or loss of longitudinal resolution, especially at low heart rates. With the ACV technique, the number N of consecutive heart cycles used for image reconstruction is automatically adapted to the momentary heart rate of the patient, ranging from N = 1 at very low heart rates up to N = 3 at high heart rates, to maintain both high z resolution (reconstructed slice width close to the collimated slice width) and adequate temporal resolution. We evaluated slice sensitivity profiles and investigated 10 patients with different heart rates ranging from 55 to 110 beats/min for CT angiography (CTA) studies of the coronary arteries and compared the results with those from a reconstruction with fixed N (N = 1 and N = 2). Axial images as well as multiplanar reformations were used for an evaluation of image quality. Results With the ACV approach, the complete heart may be scanned at 1 mm slice width within 25–35 s. A narrow slice sensitivity profile (full width at half-maximum of approximately 1.3 mm) is maintained for all heart rates. Diagnostic results can be obtained for heart rates up to about 95 beats/min by individual patient optimization of the ECG gating parameters. Improved temporal resolution at the expense of reduced longitudinal resolution may degrade the image quality of CTA studies at low heart rates by blurring plaques and stenoses. Conclusion The results indicate the potential of the ACV reconstruction technique for high-resolution coronary CTA in a wide range of heart rates.

Assessment of myocardial perfusion and viability from routine contrast-enhanced 16-detector-row computed tomography of the heart: preliminary results

To assess the diagnostic accuracy of 16-detector-row computed tomography (16DCT) of the heart in the assessment of myocardial perfusion and viability in comparison to stress perfusion magnetic resonance imaging (SP-MRI) and delayed-enhancement magnetic resonance imaging (DE-MRI). A number of 30 patients underwent both 16DCT and MRI of the heart. Contrast-enhanced 16DCT data sets were reviewed for areas of myocardium with reduced attenuation. Both CT and MRI data were examined by independent reviewers for the presence of myocardial perfusion defects or myocardial infarctions (MI). Volumetric analysis of the hypoperfusion areas in CT and the infarct sizes in DE-MRI were performed. According to MRI, myocardial infarctions were detected in 11 of 30 cases, and perfusion defects not corresponding to an MI were detected in six of 30 patients. CTA was able to detect ten of 11 MI correctly (sensitivity 91%, specificity 79%, accuracy 83%), and detected three of six hypoperfusions correctly (sensitivity 50%, specificity 92%, accuracy 79%). Assessing the volume of perfusion defects correlating to history of MI on the CT images, a systematic underestimation of the true infarct size as compared to the results of DE-MRI was found (P<0.01). Routine, contrast-enhanced 16-detector row CT of the heart can detect chronic myocardial infarctions in the majority of cases, but ischemic perfusion defects are not reliably detected under resting conditions.

A retrospectively ECG-gated multislice spiral CT scan and reconstruction technique with suppression of heart pulsation artifacts for cardio-thoracic imaging with extended volume coverage

Abstract. A method for cardio-thoracic multislice spiral CT imaging with ECG gating for suppression of heart pulsation artifacts is introduced. The proposed technique offers extended volume coverage compared with standard ECG-gated spiral scan and reconstruction approaches for cardiac applications: Thin-slice data of the entire thorax can be acquired within one breath-hold period using a four-slice CT system. The extended volume coverage is enabled by a modified approach for ECG-gated image reconstruction. For a CT system with 0.5-s gantry rotation time, images are reconstructed with 250-ms image temporal resolution. Instead of selecting scan data acquired in exactly the same phase of the cardiac cycle for each image as in standard ECG-gated reconstruction techniques, the patients ECG signal is used to omit scan data acquired during the systolic phase of highest cardiac motion. With this approach cardiac pulsation artifacts in CT studies of the aorta, of paracardiac lung segments, and of coronary bypass grafts can be effectively reduced.

Accuracy of Density measurements within plaques located in artificial coronary arteries by X-ray multislice CT: Results of a phantom study

Purpose Clinical studies indicate that coronary plaque morphology might be differentiated noninvasively using multislice CT by determining tissue density within the lesions. The aim of the present experimental study was to evaluate factors that influence density measurements within small vessels. Method A coronary phantom model was developed, consisting of silicon tubes (lumen diameter 4 mm) with two plaques of known density inside, simulating soft and intermediate lesions (Plaque 1: −39 HU; Plaque 2: 72 HU). Density measurement were conducted in three different contrast medium concentrations (1:30, 1:40, 1:50) and two different slice widths (4 × 2.5 mm, 4 × 1 mm). All scans were performed on a Somatom Volume Zoom (Siemens, Forchheim, Germany). Experimental results were compared with calculated data based on computer simulation. Results The two plaques could be clearly differentiated from each other on both collimations (4 × 2.5 mm: Plaque 1, 85 ± 61 HU vs. Plaque 2, 119 ± 26 HU, p < 0.0001; 4 × 1 mm: Plaque 1, 50 ± 54 HU vs. Plaque 2, 91 ± 17 HU, p < 0.0001). Significantly lower and more accurate results were achieved with 1.0 mm collimation (p < 0.0001). Contrast medium concentration contributed significantly to the measurements (p < 0.001). The experimental findings were confirmed by computer simulation, which revealed even more accurate results when using a 0.5 mm collimation (Plaque 1, 0.5 mm: −9 HU vs. 4 × 1 mm: 14 HU, Plaque 2, 4 × 0.5 mm: 83 HU vs. 4 × 1 mm: 93 HU). Conclusion Density measurements were found to be highly dependent on slice width and surrounding contrast enhancement. Our results indicate that standardization of methodology is required before the noninvasive differentiation of human plaque morphology by multislice CT can be applied in the clinical setting as a screening test for coronary soft plaques.

Do segmented reconstruction algorithms for cardiac multi-slice computed tomography improve image quality?

Purpose: To evaluate segmented reconstruction algorithms for spiral multi-slice computed tomography (MSCT) that use data from two cardiac cycles to improve temporal resolution (τ) for imaging of the heart. Materials and Methods: An initial group of 78 cardiac patients (heart rates [HR] = 63–167 beats per minute [bpm]) were imaged on a 4-slice, 500 ms gantry rotation time scanner (scanner 1). Images were reconstructed with a single-segment algorithm using data from one cardiac cycle with a reconstruction window of fixed length (τ = 250 ms). Images were also reconstructed with two variants of a multi-segment algorithm using data from two cardiac cycles where only one end of the reconstruction window was fixed and the other end was freely moveable to allow adjustment of τ according to HR: (1) “2-segment fixed start” with fixed start of reconstruction, (2) “2-segment fixed end” with fixed end of reconstruction (for both, τ = 125–250 ms). The resulting image sets were ranked from best to worst (1–3, respectively) in a side-by-side, blinded comparison by two independent readers. A second group of 26 patients (HR = 74–90 bpm) were imaged on a 12-slice, 420 ms gantry rotation time scanner (scanner 2). Data were reconstructed with a single-segment algorithm (τ = 210 ms) and a “2-segment fixed start” algorithm (τ = 105–210 ms) and image sets were ranked from best to worst (1–2, respectively). Results: There was no clear evidence that any one technique is superior for imaging on scanner 1. Reader 1 ranked single-segment images the highest for all HRs, but statistically significant differences among the three algorithms were only found for the lowest HRs (< 80 bpm), where reader 1 preferred singlesegment over “2-segment fixed end” techniques (p = 0.048). The highest rankings given by reader 2 varied according to HR: single-segment images were superior for lowest HRs, while “2-segment fixed start” images were superior for HRs > 80 bpm; none of these comparisons reached statistical significance. Improved performance of 2-segment reconstruction was found with scanner 2. Both readers ranked “2-segment fixed start” images the highest (p < 0.01). Conclusions: The added value of 2-segment cardiac reconstruction algorithms for spiral MSCT was not demonstrated for a 4-slice, 500 ms gantry rotation time scanner but shown to be beneficial for a 12-slice, 420 ms gantry rotation time scanner in the crucial HR range of 74–90 bpm.Hintergrund und Ziel: Die im Vergleich zu Elektronenstrahl-Computertomographie, Magnetresonanztomographie, Fluoroskopie und Ultraschall relativ geringe zeitliche Auflösung (τ) und entsprechend längere Bildakquisitionszeit gegenwärtiger Mehrschicht-Computertomographie-(MSCT-)Systeme sind ein wichtiger limitierender Faktor für kardiovaskuläre Untersuchungen. Mehrere spezielle Rekonstruktionsalgorithmen wurden mit dem Ziel entwickelt, die zeitliche Auflösung (τ) für kardiovaskuläre MSCT-Untersuchungen zu verbessern. Bei Einzelsegment-Rekonstruktionsalgorithmen stammt die gesamte Bildinformation jedes Schnittbildes aus einem einzelnen Herzzyklus, und die zeitliche Auflösung (τ) entspricht der Gantry-Rotationszeit (trot)/2. Mehrsegment-Rekonstruktionsalgorithmen werden für Patienten mit hoher Herzfrequenz (HR) empfohlen (HR > 65–70 Schläge/min, abhängig vom benutzten System und Algorithmus), um die effektive zeitliche Auflösung im Vergleich zu Einzelsegmentalgorithmen zu erhöhen. Mehrsegmentalgorithmen reduzieren das Aufnahmezeitintervall, das durch Nutzung der Bildinformation aus derselben Phase von n aufeinander folgenden Herzzyklen zu jedem Schnittbild beiträgt. Mehrsegmentrekonstruktion erreicht eine zeitliche Auflösung zwischen trot/2n und trot/2, abhängig von der Herzfrequenz (Abbildungen 1 und 2). Das Ziel dieser Studie war zu untersuchen, ob Mehrsegment Rekonstruktionsalgorithmen die Bildqualität tatsächlich verbessern. Die Bildqualität von 4- und 12-Schicht-Systemen wurde in Einzel- und Mehrsegmentrekonstruktionen mit n = 2 Herzzyklen verglichen. Material und Methodik: Eine Gruppe von 78 Patienten (HR = 63–167 Schläge/min) wurde mit einem 4-Schicht-System mit 500 ms Gantry-Rotationszeit (SOMATOM Sensation 4, Siemens Medical Solutions, Erlangen; Scanner 1) untersucht. Die Untersuchungen wurden nach Kontrastmittelgabe in retrospektiv EKG-getriggerter Spiraltechnik durchgeführt. Die Bildrekonstruktion erfolgte mit einem Einzelsegmentalgorithmus der Bildinformation aus einem einzelnen Herzzyklus mit einem Rekonstruktionsfenster konstanter Länge (τ = 250 ms; Abbildung 3a). Darüber hinaus wurde die Bildrekonstruktion mit zwei verschiedenen Mehrsegmentalgorithmen durchgeführt. Diese Mehrsegmentalgorithmen nutzten die Bildinformation aus zwei Herzzyklen, wobei ein Ende des Rekonstruktionsfenster fixiert war und das andere Ende verschoben werden konnte mit dem Ziel, die zeitliche Auflösung (τ) der jeweiligen Herzfrequenz anzupassen. Die beiden Varianten wurden beschrieben als 1. “2-segment fixed start” mit festgelegtem Ausgangspunkt der Rekonstruktion (Abbildung 3b) und 2. “2-segment fixed end” mit festgelegtem Endpunkt der Rekonstruktion (für beide Varianten: τ = 125–250 ms; Abbildung 3c). Die Bildqualität der entsprechenden Bildsätze wurde auf einer Skala von 1 (höchste Qualität) bis 3 (niedrigste Qualität) mit einem “side-by-side” verblindeten Vergleich von zwei Untersuchern bewertet. Eine zweite Gruppe von Patienten mit Herzfrequenzen zwischen 74 und 90 Schlägen/min wurde mit einen 12-Schicht-System mit 420 ms Gantry-Rotationszeit (SOMATOM Sensation 16, Siemens Medical Solutions, Erlangen; Scanner 2) untersucht. Die Untersuchungen wurden nach Kontrastmittelgabe in retrospektiv EKG-getriggerter Spiraltechnik durchgeführt. Die Bildrekonstruktion erfolgte mit einem Einzelsegmentalgorithmus (τ = 210 ms) und einem “2-segment fixed start”-Algorithmus (τ = 105–210 ms). Die Bildqualität der entsprechenden Bildsätze wurde auf einer Skala von 1 (höchste Qualität) bis 2 (niedrigste Qualität) von zwei Untersuchern gewertet. Ergebnisse: Die Mittelwerte (“mean rank”) der Bildqualität für die drei Bildsätze der mit Scanner 1 untersuchten Patienten sind in Tabelle 1 für zwei Untersucher zusammengefasst. Die Mittelwerte (“mean rank”) der Bildqualität für die drei Bildsätze in Abhängigkeit von der Herzfrequenz zeigt Tabelle 2. Die Bewertung der verschiedenen Rekonstruktionstechniken mit Scanner 1 war untersucherabhängig (Abbildung 4). Untersucher 1 bewertete die Bildqualität der Einzelsegmentrekonstruktion für alle Herzfrequenzen höher, signifikante Unterschiede zwischen den drei Rekonstruktionsalgorithmen wurden jedoch nur für niedrige Herzfrequenzen (HR < 80 Schläge/min) gefunden. Für diese Herzfrequenzen bewertete Untersucher 1 Einzelsegment- höher als “2-segment fixed end”-Techniken (p = 0,048). Die Bewertung der Bildqualität durch Untersucher 2 hing von der Herzfrequenz ab: Die Bildqualität von Einzelsegmentrekonstruktionen war für niedrigere Herzfrequenzen höher, während die Bildqualität von “2-segment fixed start”-Rekonstruktionen für Herzfrequenzen > 80 Schläge/min höher bewertet wurde. Allerdings erreichten diese Unterschiede für Untersucher 2 in keinem der Vergleiche statistische Signifikanz. Insgesamt zeigten die Ergebnisse der mit dem 4-Schicht-System untersuchten Patienten, dass Einzelsegmentalgorithmen für Herzfrequenzen zwischen 63 and 80 Schlägen/min bevorzugt wurden und dass die “2-segment fixed end”-Algorithmen für alle Herzfrequenzen keinen Vorteil aufwiesen. Allerdings erreichten die Unterschiede zwischen den verschiedenen Rekonstruktionstechniken mit Scanner 1 keine statistische Signifikanz. Die Mittelwerte (“mean rank”) der Bildqualität für die Bildsätze der mit Scanner 2 untersuchten Patienten sind in Tabelle 3 für zwei Untersucher zusammengefasst. 2-Segment-Rekonstruktionen hatten bei Untersuchungen mit dem 12-Schicht-System einen größeren Einfluss (Abbildung 5). Beide Untersucher bewerteten die Bildqualität mit “2-segment fixed start”-Rekonstruktionen höher (p < 0,01). Schlussfolgerung: Beim Einsatz von 4-Schicht-MSCT-Systemen mit 500 ms Gantry-Rotationszeit führte die höhere effektive zeitliche Auflösung (τ) mit 2-Segment-Rekonstruktion kardiovaskulärer Untersuchungen nicht zu einer verbesserten Bildqualität (Abbildung 6). Im Gegensatz dazu konnten bei Verwendung von “state-of-the-art” 12-Schicht-Systemen mit 420 ms Gantry-Rotationszeit Verbesserungen der Bildqualität mit 2-Segment-Rekonstruktion im Vergleich zu Einzelsegmentrekonstruktion für Herzfrequenzen zwischen 74 und 90 Schlägen/min erreicht werden.

Improving diagnostic accuracy of MDCT coronary angiography in patients with mild heart rhythm irregularities using ECG editing.

OBJECTIVE The objective of our study was to compare diagnostic accuracy of MDCT coronary angiography in a population of patients with mild heart rhythm irregularities before and after editing the ECG. SUBJECTS AND METHODS Thirty-eight patients who underwent MDCT coronary angiography and conventional coronary angiography were enrolled in the study. The inclusion criterion was the presence of mild heart rhythm irregularities (i.e., premature beats; atrial fibrillation; mistriggering; or low heart rate, defined as 40 beats per minute or less) during the scan. All patients underwent MDCT with the following parameters: 16 detectors; collimation, 0.75 mm; gantry rotation time, 375 msec; 120 kV; and effective milliampere-second setting, 500-600. Images were reconstructed in two settings: before ECG editing and after ECG editing (i.e., arbitrary modification of temporal windows within the cardiac cycle at the site of mild heart rhythm irregularities). Data sets were scored for the presence of significant stenoses (> or = 50% lumen reduction) in coronary segments > or = 2 mm diameter. The results of the two groups were compared with a McNemar test, and a p value of less than 0.05 was considered significant. RESULTS The sensitivity, specificity, and negative and positive predictive values of MDCT coronary angiography for the detection of significant stenoses before and after ECG editing were 63% (41/65) and 92% (78/85); 97% (251/260) and 96% (305/317); 87% (62/71) and 87% (81/93); 91% (251/275) and 97% (305/313), respectively (p < 0.05). The proportion of nonassessable segments was reduced from 17% (70/416) before ECG editing to 2% (10/416) after. CONCLUSION ECG editing significantly improves diagnostic accuracy in a selected population of patients with mild heart rate irregularities.