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Intravenous contrast material administration at high-pitch dual-source CT pulmonary angiography: Test bolus versus bolus-tracking technique
European Journal of Radiology 81 (2012) 2887–2891
Contents lists available at SciVerse ScienceDirect
European Journal of Radiology journal homepage: www.elsevier.com/locate/ejrad
Intravenous contrast material administration at high-pitch dual-source CT pulmonary angiography: Test bolus versus bolus-tracking technique J. Matthias Kerl ∗,1 , Thomas Lehnert 1 , Boris Schell, Boris Bodelle, Martin Beeres, Volkmar Jacobi, Thomas J. Vogl, Ralf W. Bauer Institute for Diagnostic and Interventional Radiology, Clinic of the Goethe University, Theodor-Stern-Kai 7, 60590 Frankfurt, Germany
a r t i c l e
i n f o
Article history: Received 4 April 2011 Received in revised form 28 September 2011 Accepted 29 September 2011 Keywords: High-pitch CT Pulmonary embolism Contrast material injection Chest CT
a b s t r a c t Purpose: To compare test bolus and bolus tracking for the determination of scan delay of high-pitch dual-source CT pulmonary angiography in patients with suspected pulmonary embolism using 50 ml of contrast material. Materials and methods: Data of 80 consecutive patients referred for CT pulmonary angiography were evaluated. All scans were performed on a 128-channel dual-source CT scanner with a high-pitch protocol (pitch 3.0, 100 kV, 180 mA s). Contrast enhancement was achieved by injecting 50 ml of iomeprol followed by a saline chaser of 50 ml injected at a rate of 4 ml/s. The scan delay was determined using either the test bolus (n = 40) or bolus tracking (n = 40) technique. Test bolus required another 15 ml CM to determine time to peak enhancement of the contrast bolus within the pulmonary trunk. Attenuation profiles in the pulmonary trunk and on segmental level as well as in the ascending aorta were measured to evaluate the timing techniques. Additionally, overall image quality was evaluated. Results: In all patients an adequate and homogeneous contrast enhancement of more than 250 HU was achieved in the pulmonary arteries. No statistically significant difference between test bolus and bolus tracking was found regarding attenuation of the pulmonary arteries or overall image quality. However, using bolus tracking 15 ml CM less was injected. Conclusion: A homogeneous opacification of the pulmonary arteries and sufficient image quality can be achieved with both the bolus tracking and test bolus techniques with significant lower contrast doses compared to conventional contrast material injection protocols. © 2011 Elsevier Ireland Ltd. All rights reserved.
1. Introduction Computed tomographic pulmonary angiography (CTA) is widely used to evaluate patients who are clinically suspected of having pulmonary embolism to either confirm or rule out this diagnosis. Over the last decade advances in multidetector CT have led to improved spatial resolution, detection of small emboli on subsegmental level by enabling delineation of the peripheral pulmonary arteries and therefore increasing sensitivity and specificity in the diagnosis of pulmonary embolism [1,2]. Beside the developments in CT technology considerable effort is being directed at optimizing injection parameters for contrast-enhanced CT applications in general [3,4]
∗ Corresponding author. Tel.: +49 6301 7277; fax: +49 6301 7258. E-mail addresses: [email protected] (J.M. Kerl), [email protected] (T. Lehnert), [email protected] (B. Schell), [email protected] (B. Bodelle), [email protected] (M. Beeres), [email protected] (V. Jacobi), [email protected] (T.J. Vogl), [email protected] (R.W. Bauer). 1 J. Matthias Kerl and Thomas Lehnert contributed equally to this work and would like to share first-authorship. 0720-048X/$ – see front matter © 2011 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.ejrad.2011.09.018
and for the diagnosis of pulmonary embolism (PE) in particular [5,6] in order to ensure high, homogenous and consistent vascular attenuation. Since the introduction of the second generation of dual-source CT (DSCT), a new era in CT acquisition speed has started. Compared with older CT systems, the second generation of DSCT has two detector systems, each acquiring 128 slices [7]. In single-source CT, the pitch factor is limited to a maximum of approximately 1.5 to ensure gapless volume coverage. In the new-generation DSCT system, a high-pitch data acquisition mode allows for pitch values of up to 3.4 resulting in an increased acquisition speed [8]. Therefore it is possible to image the entire thorax within under 1 s [9]. However, beside the advantages of high-pitch CT acquisition an optimization of contrast injection protocols for the evaluation of the pulmonary arteries is needed. As the data acquisition takes only approximately 1 s there is place for a reduced contrast material volume protocol that ensures the bolus timing only in this very moment. Excluding a fixed empirical delay, bolus tracking (BT) and test bolus (TB) are the most frequently used techniques for the determination of scan delay in clinical routine [10].
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Fig. 1. Transverse (A) and coronal (B) CT sections acquired with high-pitch dual source CT to rule out pulmonary embolism. For the estimation of the optimal contrast timing test bolus technique was used. The bolus timing allowed for the diagnosis of a bilateral pulmonary emboli (white arrow). Additionally, sufficient enhancement could be observed in the ascending aorta to rule out aortic dissection.
Thus, the purpose of our study was to compare both intravenous contrast media administration techniques with regard to pulmonary arterial enhancement and image quality of CTPA with high-pitch. 2. Materials and methods 2.1. Patients The human research committee of our hospital approved this retrospective analysis and waived the need for informed patient consent. We retrospectively analyzed data of 80 patients who had undergone clinically indicated contrast-enhanced multi-detector row CT angiography of the pulmonary arterieson a DSCT scanner of the second generation between August and December 2010. At our institution, CT angiography is the first-line examination for patients suspected of having pulmonary embolism (PE). In group 1 (n = 40) the test-bolus technique was used, while in group 2 (n = 40) bolus tracking for the determination of scan delay was used. 2.2. CT acquisition protocol All CT examinations were performed on the same dualsource CT device of the second generation (Somatom Definition Flash, Siemens Healthcare, Forchheim, Germany) in high-pitch dual-source mode. A tube potential of 100 kV with a reference tube current-time-product of 180 mA s and a collimation of 128mm × 0.6 mm was used on both tube-detector-units. The pitch was set to 3.0 at a gantry rotation time of 0.28 s. By spatial restrictions inside the gantry, the field of view (FOV) of the second detector is limited to 32 cm while the first detector supports a regular FOV of up to 50 cm. All examinations were performed by using the same nonionic low-osmolar contrast material (CM) (iopamidol, Imeron 400, Bracco Imaging, Konstanz, Germany) injected through an intravenous antecubital catheter at a rate of 4 m/s. In group 1, a test bolus (TB) consistent of 15 ml CM followed by a 30 ml saline chaser bolus was used for the evaluation of the scan delay during the acquisition of a series of dynamic low-dose monitoring scans (100 kV, 20 mA s) at the level of the pulmonary trunk. Region of interests (ROIs) were placed within the pulmonary trunk to calculate the enhancement/time curve. Acquisition of the monitoring scans started 5 s after the beginning of the injection. The delay between each monitoring scan was set to 1 s. The peak enhancement during that attenuation curve was assumed to be the
optimal scan delay with an additional delay of 8 s. The actual image acquisition was performed in free breathing using 50 ml CM and a saline chaser bolus of 50 ml. In group 2, the bolus tracking (BT) technique was performed by using dedicated software (CARE bolus, Siemens). 50 ml CM were injected followed by a saline chaser bolus of 50 ml. Realtime low-dose monitoring scans (100 kV, 20 mA s) of the contrast material were performed 5 s after the beginning of the injection. The delay between each monitoring scan was set to 1 s. The ROI was placed within the pulmonary trunk with a trigger threshold of 100 HU above the baseline. The scan was then started with a delay of 8 s. CTPA images were reconstructed at a slice thickness of 1.0 mm with 0.5 mm increment in angiographic window (center: 100 HU; width: 700 HU) with a medium-soft convolution kernel (B26f).
2.3. Image analysis One observer ( with 1 year of experience reading chest CT scans) who was blinded to the scan protocol performed attenuation measurements in regions of interest (ROI) by using transverse sections on a medical workstation (Syngo Multimodality Workplace; Siemens). In each patient and for each target structure, three regions of interest were prescribed on three consecutive transverse sections depicting the respective target structure. For the pulmonary arteries, these measurements were performed in the bifurcation of the pulmonary trunk and in the artery of segments 1 and 10. Region of interest size was adjusted to encompass the entire contrast-enhanced vessel lumen, avoiding the inclusion of the vessel wall or embolus. For the enhancement in the ascending aorta (AA) and superior vena cava (SVC), the level of the aortic root was used. For the enhancement of the subclavianvein (SV), the measurements were performed in the middle part of the vessel. Regions of interest were as large as possible and were placed in such a fashion that soft tissue structures were avoided. The mean attenuation (in Hounsfield Units) ± the standard deviation (SD) in the regions of interests on three consecutive sections was calculated for each target structure (Figs. 1 and 2). Two observers ( with 3 and 5 years of experience reading cardiovascular CT scans, respectively) who were blinded to the scan and injection technique rated separately each scan in random order on a medical workstation (Syngo Multimodality Workplace, Siemens) and assessed image quality according to a 5-point scale: 1 = excellent; 2 = good; 3 = moderate; 4 = fair; 5 = poor.
J.M. Kerl et al. / European Journal of Radiology 81 (2012) 2887–2891
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Fig. 2. Transverse (A) and coronal (B) CT sections acquired with high-pitch dual source CT to rule out pulmonary embolism. For the estimation of the optimal contrast timing bolus tracking technique was used. The bolus timing allowed for ruling out pulmonary embolism (white arrows).
Table 1 Patient characteristics (HTD, horizontal thoracic diameter; VDT, vertical thoracic diameter).
Group 1 Group 2
Sex
Age
HTD
VTD
21 male/19 female 15 male/25 female
62.92 ± 18.33 61.32 ± 18.93
350.12 ± 35.40 346.55 ± 40.40
232.15 ± 45.80 234.37 ± 46.14
2.4. Statistical analysis Analyses were performed computer-based with dedicated software (BiAS 9.02, Epsilon, Frankfurt, Germany). Patient age and attenuation values are expressed as mean values ± standard deviations. We tested continuous variables for normal distribution using the Kolmogorov Smirnov–Lilliefors test, corrected according to Dallal–Wilkinson as appropriate. Weighted kappa statistics were calculated for interobserver agreements for the subjective image quality rating. Statistical significance was investigated with the Student’s t test for unpaired samples, if values followed a normal distribution. Otherwise, we applied the U test according to Wilcoxon–Mann–Whitney. 3. Results All 80 CT examinations were conducted without any problems or side effects from contrast material injection. Patient demographics were not significantly different in both groups in terms of gender, body habitus and age (Table 1). CT pulmonary angiography was diagnostic in all patients and pulmonary embolism was detected in 14 patients (6 in group 1, 8 in group 2). The mean CTDIvol and DLP were 3.9 and 139, respectively. While there were only small differences in vascular attenuation between the two groups within the pulmonary arteries, the attenuation of the ascending aorta reached statistical significance (p < 0.01) (Table 2). Additionally, there was no significant difference in SNR between group 1 and group 2 (Table 2).
Table 2 Attenuation values and standard variations at various anatomic levels. Group 1 A. ascendens Tr. Pulmonalis V. cava sup V. subclavia Segment 1 Segment 10
315.27 407.47 808.76 1282.15 410.60 416.18
Group 2 ± ± ± ± ± ±
107.75 102.76 462.17 743.91 29.34 30.30
247.80 408.27 960.86 1380.94 345.38 338.74
± ± ± ± ± ±
71.99 114.15 505.03 697.90 54.89 38.99
p < 0.01 p > 0.73 p > 0.15 p > 0.40 p > 0.45 p > 0.61
However, a significant difference was found for the amount of contrast material injected for the enhancement of the pulmonary arteries (p < 0.01) between group 1 and group 2. However, this difference is due to the amount of contrast material injected for the test bolus in group 1 (Table 2). There was no need to repeat a single examination during clinical routine due to unsatisfying PA enhancement. At study-related subjective image quality rating both observers did not rate image quality worse than score “2”. Average image quality score was 1.35 ± 0.32 for observer 1 and 1.32 ± 0.37 for observer 2. Inter-observer agreement was good with a kappa-value of 0.65. 4. Discussion The introduction of multidetector row CT technology with shorter acquisition times pushed the development of optimized CM protocols in order to obtain consistent vascular enhancement in CTA. Especially in CTA of the pulmonary arteries a high, uniform and consistent vascular attenuation within the vessel lumen is desirable to rule out pulmonary embolism. Additionally, adequate attenuation is a prerequisite for the evaluation of the luminal integrity of the main and subsegmental pulmonary arteries and the use of twoand three-dimensional postprocessing techniques [2,11]. The introduction of the second generation dual-source CT and the ability to use a high-pitch acquisition mode which is capable of covering the whole thorax in less than 1 s a contrast bolus optimization is mandatory. As CT of the pulmonary arteries is nowadays the appropriate test to rule out PE, the optimization of intravenous contrast material injection protocols for appropriate attenuation of the pulmonary arteries becomes a topic of intense investigation [5,6,12,13]. The introduction of dual-syringe power injectors facilitated the approach of “chasing” the main contrast medium bolus with saline [14,15], which had been required careful techniques for layering contrast medium and saline in the same syringe in the era of single-syringe injectors. Flushing with saline solution avoids pooling of contrast material in the injection system and in the arm veins, leading to better contrast material utilization [16] and improved bolus shaping, with more consistent and homogeneous attenuation of target vessels.
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However, with high-pitch acquisition mode minimized contrast material volumes, and sophisticated scan timing techniques has come to a new era as the contrast material needs to guarantee a vascular enhancement in the pulmonary arteries just in 1 s [7]. Due to the reduced scan time in high pitch acquisition a fixed scan delay for contrast material administration might not be sufficient. Therefore, the optimization of bolus timing has prompted us to evaluate the standard bolus timing techniques in CTPA, namely TB and BT, in high-pitch dual-source CT of the pulmonary arteries for vascular enhancement and image quality. Several studies have compared TB and BT in various applications, with mixed results. Cademartiri et al. compared TB and BT for CT coronary angiography and reported that BT yields a more homogeneous enhancement compared to the TB technique [10]. In comparison Johnson et al. found no significant differences between TB and BT for ECG-gated CTA of the chest using single-source CT [17]. Recently Henzler et al. investigated the influence of TB vs. BT for dual-energy CT of the pulmonary arteries and found no significant difference for dual-energy iodine mapping of the lung parenchyma and the pulmonary vessels [18]. However, to our knowledge, no study has compared the techniques for high-pitch-source CTA of the pulmonary arteries. Similar to the results of Henzler et al. and Johnson et al. we found no significant difference between TB and BT for the enhancement of the pulmonary arteries. However, in our clinical routine the BT technique resulted in a lower volume of contrast material, as the initial small CM bolus for the TB is not needed in BT technique. This phenomenon has been reported earlier and is one major advantage of the BT technique. Additionally we found a higher enhancement in the ascending aorta in the TB group, which may be beneficial for “double-rule out” examinations, meaning to rule out pulmonary embolism and a type A dissection of the ascending aorta with the same scan. However, this phenomenon does not mean that if sufficient enhancement in the ascending aorta and the pulmonary arteries are desired a TB approach is mandatory. BT could also be performed by placing a ROI into the pulmonary trunk and the aorta, using the time point at the intersection between both enhancements for sufficient enhancement in both vessels. We additionally evaluated the enhancement in the SVC and the VSC and made the observation, that these veins still were filled with contrast CM. Therefore in further studies it might be interesting to test advanced CM-Injection protocols with less volume of CM. In general, a major point using high-pitch CTA of the pulmonary artery is the fact that high-pitch CTPA results in less volume of contrast media. In this initial investigation a contrast media bolus of 50 ml was used. In comparable studies without the use of highpitch CT around 100 ml of contrast media were injected to obtain sufficient enhancement within the pulmonary vessels [2,19]. This saving of contrast material results in less risk of contrast material induced nephropathy [20,21]. Another benefit of high-pitch CT of the pulmonary arteries might be the improved radiation dose, compared to conventional CT-techniques as reported recently by De Zordo et al. [22]. Although we used unselected, consecutive patient cohorts to analyze attenuation patterns during the evaluation of our clinical injection protocols, our study was limited by its retrospective nature. For this analysis, we were concerned only with the effect of different contrast medium injection protocols in terms of vascular enhancement and image quality, therefore, we did not evaluate the actual diagnostic performance for detection of pulmonary embolism. Although the empirically determined contrast bolus of 50 ml works well in our practice and delivers the desired clinical results, we did not systematically investigate other conceivable contrast material volumes and whether a smaller contrast material bolus would yield comparable results.
Last, although we have shown that both our investigated protocols work well in clinical practice and may decrease the amount of contrast material, these protocols still represent a standardized approach. While this works well for clinical practice, future research ought to be directed at individualized, patient based injection protocols to ensure that the minimum amount of contrast material is injected for achieving the desired contrast material attenuation throughout the target anatomic structures. In conclusion, a homogeneous vascular enhancement of the pulmonary arteries as well as a sufficient image quality can be achieved with both, the TB and the BT technique. However, the results of our study suggest that the adoption of a BT injection protocol for high-pitch CT angiography of the pulmonary arteries preserves the desired attenuation of the pulmonary arteries with less contrast material in comparison to the TB technique. Conflict of interest J. Matthias Kerl and Ralf W. Bauer are medical consultants for Siemens AG. References [1] Raptopoulos V, Boiselle PM. Multi-detector row spiral CT pulmonary angiography: comparison with single-detector row spiral CT. Radiology 2001;221(3):606–13. [2] Schoepf UJ, Holzknecht N, Helmberger TK, Crispin A, Hong C, Becker CR, et al. Subsegmental pulmonary emboli: improved detection with thin-collimation multi-detector row spiral CT. Radiology 2002;222(2):483–90. [3] Bae KT, Heiken JP, Brink JA. Aortic and hepatic peak enhancement at CT: effect of contrast medium injection rate—pharmacokinetic analysis and experimental porcine model. Radiology 1998;206(2):455–64. [4] Fleischmann D, Rubin GD, Bankier AA, Hittmair K. Improved uniformity of aortic enhancement with customized contrast medium injection protocols at CT angiography. Radiology 2000;214(2):363–71. [5] Yankelevitz DF, Shaham D, Shah A, Rademacker J, Henschke CI. Optimization of contrast delivery for pulmonary CT angiography. Clin Imaging 1998;22(6):398–403. [6] Hopper KD, Mosher TJ, Kasales CJ, TenHave TR, Tully DA, Weaver JS. Thoracic spiral CT: delivery of contrast material pushed with injectable saline solution in a power injector. Radiology 1997;205(1):269–71. [7] Petersilka M, Bruder H, Krauss B, Stierstorfer K, Flohr TG. Technical principles of dual source CT. Eur J Radiol 2008;68(3):362–8. [8] Achenbach S, Marwan M, Schepis T, Pflederer T, Bruder H, Allmendinger T, et al. High-pitch spiral acquisition: a new scan mode for coronary CT angiography. J Cardiovasc Comput Tomogr 2009;3(2):117–21. [9] Bamberg F, Marcus R, Sommer W, Schwarz F, Nikolaou K, Becker CR, et al. Diagnostic image quality of a comprehensive high-pitch dual-spiral cardiothoracic CT protocol in patients with undifferentiated acute chest pain. Eur J Radiol 2010;(December) [Epub ahead of print]. [10] Cademartiri F, Nieman K, van der Lugt A, Raaijmakers RH, Mollet N, Pattynama PM, et al. Intravenous contrast material administration at 16-detector row helical CT coronary angiography: test bolus versus bolus-tracking technique. Radiology 2004;233(3):817–23. [11] Coche E, Pawlak S, Dechambre S, Maldague B. Peripheral pulmonary arteries: identification at multi-slice spiral CT with 3D reconstruction. Eur Radiol 2003;13(4):815–22. [12] Hartmann IJ, Lo RT, Bakker J, de Monyé W, van Waes PF, Pattynama PM. Optimal scan delay in spiral CT for the diagnosis of acute pulmonary embolism. J Comput Assist Tomogr 2002;26(1):21–5. [13] Bae KT, Tran HQ, Heiken JP. Multiphasic injection method for uniform prolonged vascular enhancement at CT angiography: pharmacokinetic analysis and experimental porcine model. Radiology 2000;216(3): 872–80. [14] Kerl JM, Bauer RW, Renker M, Weber E, Weisser P, Korkusuz H, et al. Triphasic contrast injection improves evaluation of dual energy lung perfusion in pulmonary CT angiography. Eur J Radiol 2010;(October) [Epub ahead of print]. [15] Haage P, Schmitz-Rode T, Hübner D, Piroth W, Günther RW. Reduction of contrast material dose and artifacts by a saline flush using a double power injector in helical CT of the thorax. AJR Am J Roentgenol 2000;174(4):1049–53. [16] Schoellnast H, Tillich M, Deutschmann HA, Stessel U, Deutschmann MJ, Schaffler GJ, et al. Improvement of parenchymal and vascular enhancement using saline flush and power injection for multiple-detector-row abdominal CT. Eur Radiol 2004;14(4):659–64. [17] Johnson TR, Nikolaou K, Wintersperger BJ, Fink C, Rist C, Leber AW, et al. Optimization of contrast material administration for electrocardiogram-gated computed tomographic angiography of the chest. J Comput Assist Tomogr 2007;31(2):265–71.
J.M. Kerl et al. / European Journal of Radiology 81 (2012) 2887–2891 [18] Henzler T, Meyer M, Reichert M, Krissak R, Nance Jr JW, Haneder S, et al. Dualenergy CT angiography of the lungs: comparison of test bolus and bolus tracking techniques for the determination of scan delay. Eur J Radiol 2010;(July) [Epub ahead of print]. [19] Henzler T, Diehl S, Jochum S, Sueselbeck T, Schoenberg SO, Fink C. Dual energy computed tomography angiography of a pulmonary embolized port catheter fragment. J Cardiovasc Med (Hagerstown) 2011;12(1):62–3. [20] Morcos SK, Thomsen HS, Webb JA. Contrast-media-induced nephrotoxicity: a consensus report. Contrast Media Safety Committee, European Society of Urogenital Radiology (ESUR). Eur Radiol 1999;9(8):1602–13.
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[21] Cochran ST, Wong WS, Roe DJ. Predicting angiography-induced acute renal function impairment: clinical risk model. AJR Am J Roentgenol 1983;141(5):1027–33. [22] De Zordo T, von Lutterotti K, Dejaco C, Soegner PF, Frank R, Aigner F, et al. Comparison of image quality and radiation dose of different pulmonary CTA protocols on a 128-slice CT: high-pitch dual source CT, dual energy CT and conventional spiral CT. Eur Radiol 2011;(August) [Epub ahead of print].
Contents lists available at SciVerse ScienceDirect
European Journal of Radiology journal homepage: www.elsevier.com/locate/ejrad
Intravenous contrast material administration at high-pitch dual-source CT pulmonary angiography: Test bolus versus bolus-tracking technique J. Matthias Kerl ∗,1 , Thomas Lehnert 1 , Boris Schell, Boris Bodelle, Martin Beeres, Volkmar Jacobi, Thomas J. Vogl, Ralf W. Bauer Institute for Diagnostic and Interventional Radiology, Clinic of the Goethe University, Theodor-Stern-Kai 7, 60590 Frankfurt, Germany
a r t i c l e
i n f o
Article history: Received 4 April 2011 Received in revised form 28 September 2011 Accepted 29 September 2011 Keywords: High-pitch CT Pulmonary embolism Contrast material injection Chest CT
a b s t r a c t Purpose: To compare test bolus and bolus tracking for the determination of scan delay of high-pitch dual-source CT pulmonary angiography in patients with suspected pulmonary embolism using 50 ml of contrast material. Materials and methods: Data of 80 consecutive patients referred for CT pulmonary angiography were evaluated. All scans were performed on a 128-channel dual-source CT scanner with a high-pitch protocol (pitch 3.0, 100 kV, 180 mA s). Contrast enhancement was achieved by injecting 50 ml of iomeprol followed by a saline chaser of 50 ml injected at a rate of 4 ml/s. The scan delay was determined using either the test bolus (n = 40) or bolus tracking (n = 40) technique. Test bolus required another 15 ml CM to determine time to peak enhancement of the contrast bolus within the pulmonary trunk. Attenuation profiles in the pulmonary trunk and on segmental level as well as in the ascending aorta were measured to evaluate the timing techniques. Additionally, overall image quality was evaluated. Results: In all patients an adequate and homogeneous contrast enhancement of more than 250 HU was achieved in the pulmonary arteries. No statistically significant difference between test bolus and bolus tracking was found regarding attenuation of the pulmonary arteries or overall image quality. However, using bolus tracking 15 ml CM less was injected. Conclusion: A homogeneous opacification of the pulmonary arteries and sufficient image quality can be achieved with both the bolus tracking and test bolus techniques with significant lower contrast doses compared to conventional contrast material injection protocols. © 2011 Elsevier Ireland Ltd. All rights reserved.
1. Introduction Computed tomographic pulmonary angiography (CTA) is widely used to evaluate patients who are clinically suspected of having pulmonary embolism to either confirm or rule out this diagnosis. Over the last decade advances in multidetector CT have led to improved spatial resolution, detection of small emboli on subsegmental level by enabling delineation of the peripheral pulmonary arteries and therefore increasing sensitivity and specificity in the diagnosis of pulmonary embolism [1,2]. Beside the developments in CT technology considerable effort is being directed at optimizing injection parameters for contrast-enhanced CT applications in general [3,4]
∗ Corresponding author. Tel.: +49 6301 7277; fax: +49 6301 7258. E-mail addresses: [email protected] (J.M. Kerl), [email protected] (T. Lehnert), [email protected] (B. Schell), [email protected] (B. Bodelle), [email protected] (M. Beeres), [email protected] (V. Jacobi), [email protected] (T.J. Vogl), [email protected] (R.W. Bauer). 1 J. Matthias Kerl and Thomas Lehnert contributed equally to this work and would like to share first-authorship. 0720-048X/$ – see front matter © 2011 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.ejrad.2011.09.018
and for the diagnosis of pulmonary embolism (PE) in particular [5,6] in order to ensure high, homogenous and consistent vascular attenuation. Since the introduction of the second generation of dual-source CT (DSCT), a new era in CT acquisition speed has started. Compared with older CT systems, the second generation of DSCT has two detector systems, each acquiring 128 slices [7]. In single-source CT, the pitch factor is limited to a maximum of approximately 1.5 to ensure gapless volume coverage. In the new-generation DSCT system, a high-pitch data acquisition mode allows for pitch values of up to 3.4 resulting in an increased acquisition speed [8]. Therefore it is possible to image the entire thorax within under 1 s [9]. However, beside the advantages of high-pitch CT acquisition an optimization of contrast injection protocols for the evaluation of the pulmonary arteries is needed. As the data acquisition takes only approximately 1 s there is place for a reduced contrast material volume protocol that ensures the bolus timing only in this very moment. Excluding a fixed empirical delay, bolus tracking (BT) and test bolus (TB) are the most frequently used techniques for the determination of scan delay in clinical routine [10].
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J.M. Kerl et al. / European Journal of Radiology 81 (2012) 2887–2891
Fig. 1. Transverse (A) and coronal (B) CT sections acquired with high-pitch dual source CT to rule out pulmonary embolism. For the estimation of the optimal contrast timing test bolus technique was used. The bolus timing allowed for the diagnosis of a bilateral pulmonary emboli (white arrow). Additionally, sufficient enhancement could be observed in the ascending aorta to rule out aortic dissection.
Thus, the purpose of our study was to compare both intravenous contrast media administration techniques with regard to pulmonary arterial enhancement and image quality of CTPA with high-pitch. 2. Materials and methods 2.1. Patients The human research committee of our hospital approved this retrospective analysis and waived the need for informed patient consent. We retrospectively analyzed data of 80 patients who had undergone clinically indicated contrast-enhanced multi-detector row CT angiography of the pulmonary arterieson a DSCT scanner of the second generation between August and December 2010. At our institution, CT angiography is the first-line examination for patients suspected of having pulmonary embolism (PE). In group 1 (n = 40) the test-bolus technique was used, while in group 2 (n = 40) bolus tracking for the determination of scan delay was used. 2.2. CT acquisition protocol All CT examinations were performed on the same dualsource CT device of the second generation (Somatom Definition Flash, Siemens Healthcare, Forchheim, Germany) in high-pitch dual-source mode. A tube potential of 100 kV with a reference tube current-time-product of 180 mA s and a collimation of 128mm × 0.6 mm was used on both tube-detector-units. The pitch was set to 3.0 at a gantry rotation time of 0.28 s. By spatial restrictions inside the gantry, the field of view (FOV) of the second detector is limited to 32 cm while the first detector supports a regular FOV of up to 50 cm. All examinations were performed by using the same nonionic low-osmolar contrast material (CM) (iopamidol, Imeron 400, Bracco Imaging, Konstanz, Germany) injected through an intravenous antecubital catheter at a rate of 4 m/s. In group 1, a test bolus (TB) consistent of 15 ml CM followed by a 30 ml saline chaser bolus was used for the evaluation of the scan delay during the acquisition of a series of dynamic low-dose monitoring scans (100 kV, 20 mA s) at the level of the pulmonary trunk. Region of interests (ROIs) were placed within the pulmonary trunk to calculate the enhancement/time curve. Acquisition of the monitoring scans started 5 s after the beginning of the injection. The delay between each monitoring scan was set to 1 s. The peak enhancement during that attenuation curve was assumed to be the
optimal scan delay with an additional delay of 8 s. The actual image acquisition was performed in free breathing using 50 ml CM and a saline chaser bolus of 50 ml. In group 2, the bolus tracking (BT) technique was performed by using dedicated software (CARE bolus, Siemens). 50 ml CM were injected followed by a saline chaser bolus of 50 ml. Realtime low-dose monitoring scans (100 kV, 20 mA s) of the contrast material were performed 5 s after the beginning of the injection. The delay between each monitoring scan was set to 1 s. The ROI was placed within the pulmonary trunk with a trigger threshold of 100 HU above the baseline. The scan was then started with a delay of 8 s. CTPA images were reconstructed at a slice thickness of 1.0 mm with 0.5 mm increment in angiographic window (center: 100 HU; width: 700 HU) with a medium-soft convolution kernel (B26f).
2.3. Image analysis One observer ( with 1 year of experience reading chest CT scans) who was blinded to the scan protocol performed attenuation measurements in regions of interest (ROI) by using transverse sections on a medical workstation (Syngo Multimodality Workplace; Siemens). In each patient and for each target structure, three regions of interest were prescribed on three consecutive transverse sections depicting the respective target structure. For the pulmonary arteries, these measurements were performed in the bifurcation of the pulmonary trunk and in the artery of segments 1 and 10. Region of interest size was adjusted to encompass the entire contrast-enhanced vessel lumen, avoiding the inclusion of the vessel wall or embolus. For the enhancement in the ascending aorta (AA) and superior vena cava (SVC), the level of the aortic root was used. For the enhancement of the subclavianvein (SV), the measurements were performed in the middle part of the vessel. Regions of interest were as large as possible and were placed in such a fashion that soft tissue structures were avoided. The mean attenuation (in Hounsfield Units) ± the standard deviation (SD) in the regions of interests on three consecutive sections was calculated for each target structure (Figs. 1 and 2). Two observers ( with 3 and 5 years of experience reading cardiovascular CT scans, respectively) who were blinded to the scan and injection technique rated separately each scan in random order on a medical workstation (Syngo Multimodality Workplace, Siemens) and assessed image quality according to a 5-point scale: 1 = excellent; 2 = good; 3 = moderate; 4 = fair; 5 = poor.
J.M. Kerl et al. / European Journal of Radiology 81 (2012) 2887–2891
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Fig. 2. Transverse (A) and coronal (B) CT sections acquired with high-pitch dual source CT to rule out pulmonary embolism. For the estimation of the optimal contrast timing bolus tracking technique was used. The bolus timing allowed for ruling out pulmonary embolism (white arrows).
Table 1 Patient characteristics (HTD, horizontal thoracic diameter; VDT, vertical thoracic diameter).
Group 1 Group 2
Sex
Age
HTD
VTD
21 male/19 female 15 male/25 female
62.92 ± 18.33 61.32 ± 18.93
350.12 ± 35.40 346.55 ± 40.40
232.15 ± 45.80 234.37 ± 46.14
2.4. Statistical analysis Analyses were performed computer-based with dedicated software (BiAS 9.02, Epsilon, Frankfurt, Germany). Patient age and attenuation values are expressed as mean values ± standard deviations. We tested continuous variables for normal distribution using the Kolmogorov Smirnov–Lilliefors test, corrected according to Dallal–Wilkinson as appropriate. Weighted kappa statistics were calculated for interobserver agreements for the subjective image quality rating. Statistical significance was investigated with the Student’s t test for unpaired samples, if values followed a normal distribution. Otherwise, we applied the U test according to Wilcoxon–Mann–Whitney. 3. Results All 80 CT examinations were conducted without any problems or side effects from contrast material injection. Patient demographics were not significantly different in both groups in terms of gender, body habitus and age (Table 1). CT pulmonary angiography was diagnostic in all patients and pulmonary embolism was detected in 14 patients (6 in group 1, 8 in group 2). The mean CTDIvol and DLP were 3.9 and 139, respectively. While there were only small differences in vascular attenuation between the two groups within the pulmonary arteries, the attenuation of the ascending aorta reached statistical significance (p < 0.01) (Table 2). Additionally, there was no significant difference in SNR between group 1 and group 2 (Table 2).
Table 2 Attenuation values and standard variations at various anatomic levels. Group 1 A. ascendens Tr. Pulmonalis V. cava sup V. subclavia Segment 1 Segment 10
315.27 407.47 808.76 1282.15 410.60 416.18
Group 2 ± ± ± ± ± ±
107.75 102.76 462.17 743.91 29.34 30.30
247.80 408.27 960.86 1380.94 345.38 338.74
± ± ± ± ± ±
71.99 114.15 505.03 697.90 54.89 38.99
p < 0.01 p > 0.73 p > 0.15 p > 0.40 p > 0.45 p > 0.61
However, a significant difference was found for the amount of contrast material injected for the enhancement of the pulmonary arteries (p < 0.01) between group 1 and group 2. However, this difference is due to the amount of contrast material injected for the test bolus in group 1 (Table 2). There was no need to repeat a single examination during clinical routine due to unsatisfying PA enhancement. At study-related subjective image quality rating both observers did not rate image quality worse than score “2”. Average image quality score was 1.35 ± 0.32 for observer 1 and 1.32 ± 0.37 for observer 2. Inter-observer agreement was good with a kappa-value of 0.65. 4. Discussion The introduction of multidetector row CT technology with shorter acquisition times pushed the development of optimized CM protocols in order to obtain consistent vascular enhancement in CTA. Especially in CTA of the pulmonary arteries a high, uniform and consistent vascular attenuation within the vessel lumen is desirable to rule out pulmonary embolism. Additionally, adequate attenuation is a prerequisite for the evaluation of the luminal integrity of the main and subsegmental pulmonary arteries and the use of twoand three-dimensional postprocessing techniques [2,11]. The introduction of the second generation dual-source CT and the ability to use a high-pitch acquisition mode which is capable of covering the whole thorax in less than 1 s a contrast bolus optimization is mandatory. As CT of the pulmonary arteries is nowadays the appropriate test to rule out PE, the optimization of intravenous contrast material injection protocols for appropriate attenuation of the pulmonary arteries becomes a topic of intense investigation [5,6,12,13]. The introduction of dual-syringe power injectors facilitated the approach of “chasing” the main contrast medium bolus with saline [14,15], which had been required careful techniques for layering contrast medium and saline in the same syringe in the era of single-syringe injectors. Flushing with saline solution avoids pooling of contrast material in the injection system and in the arm veins, leading to better contrast material utilization [16] and improved bolus shaping, with more consistent and homogeneous attenuation of target vessels.
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However, with high-pitch acquisition mode minimized contrast material volumes, and sophisticated scan timing techniques has come to a new era as the contrast material needs to guarantee a vascular enhancement in the pulmonary arteries just in 1 s [7]. Due to the reduced scan time in high pitch acquisition a fixed scan delay for contrast material administration might not be sufficient. Therefore, the optimization of bolus timing has prompted us to evaluate the standard bolus timing techniques in CTPA, namely TB and BT, in high-pitch dual-source CT of the pulmonary arteries for vascular enhancement and image quality. Several studies have compared TB and BT in various applications, with mixed results. Cademartiri et al. compared TB and BT for CT coronary angiography and reported that BT yields a more homogeneous enhancement compared to the TB technique [10]. In comparison Johnson et al. found no significant differences between TB and BT for ECG-gated CTA of the chest using single-source CT [17]. Recently Henzler et al. investigated the influence of TB vs. BT for dual-energy CT of the pulmonary arteries and found no significant difference for dual-energy iodine mapping of the lung parenchyma and the pulmonary vessels [18]. However, to our knowledge, no study has compared the techniques for high-pitch-source CTA of the pulmonary arteries. Similar to the results of Henzler et al. and Johnson et al. we found no significant difference between TB and BT for the enhancement of the pulmonary arteries. However, in our clinical routine the BT technique resulted in a lower volume of contrast material, as the initial small CM bolus for the TB is not needed in BT technique. This phenomenon has been reported earlier and is one major advantage of the BT technique. Additionally we found a higher enhancement in the ascending aorta in the TB group, which may be beneficial for “double-rule out” examinations, meaning to rule out pulmonary embolism and a type A dissection of the ascending aorta with the same scan. However, this phenomenon does not mean that if sufficient enhancement in the ascending aorta and the pulmonary arteries are desired a TB approach is mandatory. BT could also be performed by placing a ROI into the pulmonary trunk and the aorta, using the time point at the intersection between both enhancements for sufficient enhancement in both vessels. We additionally evaluated the enhancement in the SVC and the VSC and made the observation, that these veins still were filled with contrast CM. Therefore in further studies it might be interesting to test advanced CM-Injection protocols with less volume of CM. In general, a major point using high-pitch CTA of the pulmonary artery is the fact that high-pitch CTPA results in less volume of contrast media. In this initial investigation a contrast media bolus of 50 ml was used. In comparable studies without the use of highpitch CT around 100 ml of contrast media were injected to obtain sufficient enhancement within the pulmonary vessels [2,19]. This saving of contrast material results in less risk of contrast material induced nephropathy [20,21]. Another benefit of high-pitch CT of the pulmonary arteries might be the improved radiation dose, compared to conventional CT-techniques as reported recently by De Zordo et al. [22]. Although we used unselected, consecutive patient cohorts to analyze attenuation patterns during the evaluation of our clinical injection protocols, our study was limited by its retrospective nature. For this analysis, we were concerned only with the effect of different contrast medium injection protocols in terms of vascular enhancement and image quality, therefore, we did not evaluate the actual diagnostic performance for detection of pulmonary embolism. Although the empirically determined contrast bolus of 50 ml works well in our practice and delivers the desired clinical results, we did not systematically investigate other conceivable contrast material volumes and whether a smaller contrast material bolus would yield comparable results.
Last, although we have shown that both our investigated protocols work well in clinical practice and may decrease the amount of contrast material, these protocols still represent a standardized approach. While this works well for clinical practice, future research ought to be directed at individualized, patient based injection protocols to ensure that the minimum amount of contrast material is injected for achieving the desired contrast material attenuation throughout the target anatomic structures. In conclusion, a homogeneous vascular enhancement of the pulmonary arteries as well as a sufficient image quality can be achieved with both, the TB and the BT technique. However, the results of our study suggest that the adoption of a BT injection protocol for high-pitch CT angiography of the pulmonary arteries preserves the desired attenuation of the pulmonary arteries with less contrast material in comparison to the TB technique. Conflict of interest J. Matthias Kerl and Ralf W. Bauer are medical consultants for Siemens AG. References [1] Raptopoulos V, Boiselle PM. Multi-detector row spiral CT pulmonary angiography: comparison with single-detector row spiral CT. Radiology 2001;221(3):606–13. [2] Schoepf UJ, Holzknecht N, Helmberger TK, Crispin A, Hong C, Becker CR, et al. Subsegmental pulmonary emboli: improved detection with thin-collimation multi-detector row spiral CT. Radiology 2002;222(2):483–90. [3] Bae KT, Heiken JP, Brink JA. Aortic and hepatic peak enhancement at CT: effect of contrast medium injection rate—pharmacokinetic analysis and experimental porcine model. Radiology 1998;206(2):455–64. [4] Fleischmann D, Rubin GD, Bankier AA, Hittmair K. Improved uniformity of aortic enhancement with customized contrast medium injection protocols at CT angiography. Radiology 2000;214(2):363–71. [5] Yankelevitz DF, Shaham D, Shah A, Rademacker J, Henschke CI. Optimization of contrast delivery for pulmonary CT angiography. Clin Imaging 1998;22(6):398–403. [6] Hopper KD, Mosher TJ, Kasales CJ, TenHave TR, Tully DA, Weaver JS. Thoracic spiral CT: delivery of contrast material pushed with injectable saline solution in a power injector. Radiology 1997;205(1):269–71. [7] Petersilka M, Bruder H, Krauss B, Stierstorfer K, Flohr TG. Technical principles of dual source CT. Eur J Radiol 2008;68(3):362–8. [8] Achenbach S, Marwan M, Schepis T, Pflederer T, Bruder H, Allmendinger T, et al. High-pitch spiral acquisition: a new scan mode for coronary CT angiography. J Cardiovasc Comput Tomogr 2009;3(2):117–21. [9] Bamberg F, Marcus R, Sommer W, Schwarz F, Nikolaou K, Becker CR, et al. Diagnostic image quality of a comprehensive high-pitch dual-spiral cardiothoracic CT protocol in patients with undifferentiated acute chest pain. Eur J Radiol 2010;(December) [Epub ahead of print]. [10] Cademartiri F, Nieman K, van der Lugt A, Raaijmakers RH, Mollet N, Pattynama PM, et al. Intravenous contrast material administration at 16-detector row helical CT coronary angiography: test bolus versus bolus-tracking technique. Radiology 2004;233(3):817–23. [11] Coche E, Pawlak S, Dechambre S, Maldague B. Peripheral pulmonary arteries: identification at multi-slice spiral CT with 3D reconstruction. Eur Radiol 2003;13(4):815–22. [12] Hartmann IJ, Lo RT, Bakker J, de Monyé W, van Waes PF, Pattynama PM. Optimal scan delay in spiral CT for the diagnosis of acute pulmonary embolism. J Comput Assist Tomogr 2002;26(1):21–5. [13] Bae KT, Tran HQ, Heiken JP. Multiphasic injection method for uniform prolonged vascular enhancement at CT angiography: pharmacokinetic analysis and experimental porcine model. Radiology 2000;216(3): 872–80. [14] Kerl JM, Bauer RW, Renker M, Weber E, Weisser P, Korkusuz H, et al. Triphasic contrast injection improves evaluation of dual energy lung perfusion in pulmonary CT angiography. Eur J Radiol 2010;(October) [Epub ahead of print]. [15] Haage P, Schmitz-Rode T, Hübner D, Piroth W, Günther RW. Reduction of contrast material dose and artifacts by a saline flush using a double power injector in helical CT of the thorax. AJR Am J Roentgenol 2000;174(4):1049–53. [16] Schoellnast H, Tillich M, Deutschmann HA, Stessel U, Deutschmann MJ, Schaffler GJ, et al. Improvement of parenchymal and vascular enhancement using saline flush and power injection for multiple-detector-row abdominal CT. Eur Radiol 2004;14(4):659–64. [17] Johnson TR, Nikolaou K, Wintersperger BJ, Fink C, Rist C, Leber AW, et al. Optimization of contrast material administration for electrocardiogram-gated computed tomographic angiography of the chest. J Comput Assist Tomogr 2007;31(2):265–71.
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