Introduction 1 4 5 6 7 8 9 10 11 10 Materials and methods Patients One hundred nine consecutive patients [31 women, 78 men; median age 64 (59–67) years] were prospectively enrolled in the trial. The study was approved by the institutional review board, and informed written consent was obtained from every patient prior to the examination. All patients with acute chest pain were eligible for the study if referred by a colleague after initial diagnostic workup including physical examination, ECG and serum levels of creatinine and TSH. Exclusion criteria were positive ECG changes or troponine test, severe ventricular arrhythmia, a history of severe allergoid reaction to iodinated contrast material, renal insufficiency and young age below 30 years. Also, severe dyspnea with inability to hold the breath for at least 15 s was regarded as exclusion criterion. The patients were asked to hold their breath for approximately 15 s prior to the examination. If the breathhold could not be maintained, the patient was excluded from the study, and seven otherwise eligible patients had to be excluded for this reason. Heart rates were 68 ± 14, ranging from 58 to 118 bpm. Beta-blockers were not administered in preparation of the scan. Eighteen patients had known coronary artery disease and 14 were on continuous oral beta blocker medication. One patient had a known chronic aortic dissection. Examination 5 1 Table 1 Body-weight-adapted contrast material injection protocol Weight (kg) Volume (ml) Flow (ml/s) 50 106 3.5 55 111 3.7 60 116 3.9 65 121 4.0 70 125 4.2 75 130 4.3 80 134 4.5 85 138 4.6 90 142 4.7 95 146 4.9 100 150 5.0 105 154 5.1 110 157 5.2 115 161 5.4 120 164 5.5 Image reconstruction Continuous ECG-gated axial slices and coronal images of the whole chest were reconstructed with a temporal resolution of 330 ms using a soft kernel (B30f). Slice thickness of 3 mm and 2.5-mm increment were applied to avoid artificial inhomogenities in the lung parenchyma due to undersampling with gating. Additionally, axial slices of the heart were reconstructed for a limited range from the carina to the diaphragm with a 200-mm field of view, 0.75-mm slice thickness and 0.5-mm increment using a B26f convolution kernel. If stents had been implanted, an additional reconstruction was performed using a B46 kernel to reduce blooming and enhance the depiction of the lumen. For ECG gating, a single segment reconstruction algorithm utilizing quarter scan segments from both detectors was applied to achieve a temporal resolution of 83 ms, and delays were set to 300 ms and 70% of the cardiac cycle for the initial reconstructions. Also, axial slices with 1-mm thickness and increment were reconstructed with a B26f kernel for the whole cardiac cycle at 10% intervals for dynamic evaluation. Diagnostic evaluation 3 4 1 2 1 2 Fig. 1 a b c d  Fig. 2 a b c d e  Indication for invasive angiography was evaluated by a cardiologist based on CT and clinical findings. Invasive angiography was always initiated if significant coronary artery disease could not be reliably excluded in CT and there was no other evident pathology explaining the symptoms. Selective catheterization and coronary angiography were performed by an experienced cardiologist using a transfemoral arterial approach and standard Seldinger technique. At least three standard projections including a 45° left anterior oblique, a 30° right anterior oblique and a 45° left anterior and 30° cranial projection were acquired for both coronary arteries. For quantitative coronary assessment (QCA) analysis, a densitometrical analysis of two projection images was performed using the Quant-Cor QCA software (Siemens, Erlangen). Conventional coronary angiograms of 29 patients were available for correlation. A third reader correlated the findings in the reports to invasive coronary angiography and performed dose calculations, which were based on the dose length product given in the patient protocol of the CT scanner. Also, he reviewed the files of patients with initially negative results for further diagnoses in the subsequent 6 months. The readers of the initial CT images were unaware of any findings from conventional angiography, and most invasive angiographies were performed to further evaluate or treat lesions detected in CT. Thus, the cardiologists performing the coronary angiography were mostly aware of the CT findings. Statistical analysis Continuous variables are given as median and range. Ninety-five percent confidence intervals were calculated using MedCalc software (MedCalc Software, Mariakerke, Belgium). Diagnostic accuracy was calculated as sensitivity, specificity, positive and negative predictive values based on standard contingency tables. Results Technical success The scans were acquired from all 109 patients without severe adverse events. Although previously tested, three patients were unable to hold their breath for the duration of the scan, which resulted in artifacts in the lower part of the chest, rendering the coverage and depiction of the coronary arteries insufficient for diagnostic evaluation. All examinations showed an adequate contrast enhancement of the pulmonary arteries, the coronary arteries and the aorta except for six examinations. In two, the bolus was too short due to hemodynamic parameters, making the assessment of pulmonary embolism only possible in the central arteries. In three examinations an erroneous administration of a smaller volume of contrast material caused a weak opacification of the pulmonary arteries, and in one examination overall opacification was too weak (220–245 HU) for coronary artery assessment. Patient findings 2 3 1 2 4 5 Fig. 3 Curved multiplanar reconstruction of the lower lobe pulmonary arteries showing emboli in the lobar and segmental arteries  Fig. 4 a b  Fig. 5 a b  Table 2 Diagnoses found in the study population Territory Type Diagnosis n Pulmonary 19% Vascular 62% Embolism 77% 10 Pulmonary hypertension 23% 3 Non-vascular 38% Pneumonia 50% 4 Edema 50% 4 Cardiac 40% Coronary 84% Atherosclerosis 100% 37 Relevant stenosis 57% 21 Occlusion 8% 3 Bypass grafts 18% Patent 75% 15 Occluded 25% 5 Non-coronary 13% Valvular 50% 7 Myocardial 50% 7 Aortic 13%   Aneurysm 50% 7 Dissection 43% 6 Rupture 7% 1 Other 7% Vascular variants 25%   2 Neoplastic 75%   6 Negative 24%     26 Sum of patients 100%     109 Correlation to invasive angiography The 29 conventional coronary angiograms that were available for correlation of the coronary findings were evaluated in a segment-based and a patient-based analysis. Thirty-two coronary artery segments (7%) of these patients were excluded from analysis due to small size or insufficient visualization in CT. Of the 29 patients, 25 had evidence of coronary atherosclerosis in CT. Nineteen stenoses were rated as potentially hemodynamically relevant with more than 50% stenosis in CTA, but invasive angiography confirmed only 15 of those, whereas the other 4 were overrated. There were no false-negative results, i.e., all the stenoses had been cited in CTA, although it has to be taken into account that the indication for invasive angiography was frequently derived from CTA findings. Thus, sensitivity, specificity, positive and negative predictive value amounted to 100%, 99%, 79% and 100%, respectively, in the segment-based analysis. In the patient-based analysis, all 13 patients with significant stenoses were identified. There were two patients with completely negative CTA and symptoms very suggestive of coronary ischemia who had additional invasive angiography, and both of them remained negative. The overrated stenoses occurred in patients with other, significant stenoses. Thus, CTA achieved full diagnostic accuracy in correlation to invasive angiography for this patient-based analysis. The database of the coronary angiography laboratory was screened for those patients who had not initially been examined invasively, and there were no readmissions for angiography within 6 months after inclusion of the last patient. Radiation exposure As the patient protocols had not been archived in all patients, there were only 51 dose-length products available for calculation. Based on a conversion factor of 0.012 for chest exams, the estimated equivalent dose ranged between 9.2 mSv in low heart rates with strict dose modulation to 19.5 mSv in tall patients with heart rates around 70–80 bpm, which resulted in a wide pulsing interval of 30–70% with a still quite low pitch below 0.3. Overall, the median radiation exposure was 15.1 mSv (95% CI 9.9–18.8). Discussion 12 2 4 12 1 3 10 11 1 13 11 9 14 15 16 17 8 1 18 19 20 Several limitations of this study have to be acknowledged. One limitation is the exclusion of patients with the evidence of an acute coronary syndrome based on ECG or serum markers, which causes a bias in the assessment of the diagnostic accuracy of coronary CTA. Another limitation is the lacking correlation to other diagnostic approaches in the evaluation of pulmonary embolism and aortic disease. Of course, additional ventilation/perfusion scintigraphy and aortic MRI would be desirable for study purposes, but cannot be justified considering the necessary time and the encroachment of acutely ill patients and the involved radiation exposure. Also, additional invasive coronary angiography of the patients without coronary findings would be helpful to assess the actual negative predictive value, but the application of this invasive procedure involving radiation exposure to patients with other pathologies would of course not be acceptable. The follow-up of the coronary angiography database that showed no readmissions at least confirms the unlikelihood of relevant coronary artery stenoses in these patients. The fact that immediately therapy-relevant findings in all vascular districts were represented and quite evenly distributed in our patient population emphasizes that a combined protocol can be a valuable tool for diagnostic workup of acute, unclear chest pain. In conclusion, the specific dual-source CT protocol for chest pain assessment proved to be a very helpful tool offering a fast diagnostic workup and patient triage.