Assessment of Left Ventricular Parameters Using 16-MDCT and New Software for Endocardial and Epicardial Border Delineation

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1 Cardiac Imaging Schlosser et al. CT of Left Ventricular Parameters Downloaded from by on 5/3/18 from IP address Copyright RRS. For personal use only; all rights reserved Thomas Schlosser 1 Konstantin Pagonidis Christoph U. Herborn Peter Hunold Kai-Uwe Waltering Thomas C. Lauenstein Jörg arkhausen Schlosser T, Pagonidis K, Herborn CU, et al. Received May 1, 4; accepted after revision ugust 1, 4. 1 ll authors: Department of Diagnostic and Interventional Radiology, University Hospital Essen, Hufelandstrasse 55, Essen, Germany. ddress correspondence to J. arkhausen (joerg.barkhausen@uni-essen.de). JR 5;184: X/5/ merican Roentgen Ray Society ssessment of Left Ventricular Parameters Using 16-MDCT and New Software for Endocardial and Epicardial order Delineation OJECTIVE. The purpose of our study was to quantify left ventricular function and mass derived from retrospectively ECG-gated 16-MDCT coronary angiography data sets using a new analysis software based on automatic contour detection in comparison to corresponding standard of reference measurements acquired with. SUJECTS ND METHODS. Multiplanar reformations in the short-axis orientation were calculated from axial contrast-enhanced CT images in 18 patients (men, 15; women, three; age range, 38 7 years; mean, 57.4 ± 1.2 [SD] years) who were referred for CT coronary angiography. End-diastolic volume (EDV), end-systolic volume (ESV), ejection fraction (EF), and left ventricular mass (LVM) were analyzed with a recently developed imaging software using an automated contour detection algorithm of left ventricular endo- and epicardial contours and by manual tracing. The data were compared with similar measurements on as the standard of reference. RESULTS. EDV, ESV, EF, and LVM derived from an automated contour detection algorithm were not statistically significantly different from manual tracing (CT auto vs CT manual : EDV = ± 45.7 ml vs ± 39.9 ml, ESV = 58.8 ± 34.2 ml vs 58.1 ± 3.1 ml, EF = 59.2% ± 13.7% vs 58.1% ± 12.%, LVM = 13.9 ± 29.1 g vs ± 33.2 g; p >.5). However, EDV (118.7 ± 43.6 ml), ESV (5.1 ± 33.5 ml), and LVM (142.8 ± 38.4 g) as calculated on MR data sets were statistically significantly different from those calculated on CT (p <.5), whereas -based EF (59.9% ± 14.4%) did not differ statistically significantly from those based on both CT algorithms (p >.5). CONCLUSION. utomatic and manual analysis of data acquired during CT coronary angiography using a 16-MDCT scanner allows a reliable assessment of left ventricular ejection fraction and a rough estimation of left ventricular volumes and mass. eft ventricular volumes and function are predictive markers of a L variety of cardiovascular diseases. Patients with both coronary artery disease and depressed left ventricular function are at high risk for sudden death, and left ventricular hypertrophy is associated with a significant excess of cardiovascular mortality and morbidity independent of the presence of coronary artery disease or arterial hypertension [1, 2]. Therefore, a precise quantitative and qualitative assessment of left ventricular function and mass is indispensable. In clinical practice, echocardiography has been established as the method of choice for determination of ventricular volumes and mass because of its wide availability and relatively short examination times. Considerable drawbacks inherent to echocardiography are operator dependence and rather poor contrast between blood and myocardium. ecause of its multiplanar cross-sectional nature coupled with high spatial and temporal resolution and the different signal intensities between blood and myocardium, has evolved as the standard of reference for quantification of left ventricular function and mass [3 9]. During the past decade, CT scanners with four parallel slices and a gantry rotation time of 5 msec have been introduced clinically. This technique allows for the first time a reliable noninvasive visualization of the coronary artery lumen [1, 11]. Recently published studies have shown that a new generation of MDCT scanners, equipped with more and thinner detector rows, allows reliable noninvasive detection of obstructive coronary artery disease [12] and dysfunctional bypass grafts [13]. nalysis of multiplanar reformations of such retrospectively ECG-gated CT JR:184, March 5 765

2 Schlosser et al. Downloaded from by on 5/3/18 from IP address Copyright RRS. For personal use only; all rights reserved End-Diastolic Volume (ml) CTUTO End-Diastolic Volume (ml) CTMN Fig. 1. Left ventricular end-diastolic volume assessed using and CT. CTUTO = automatic contour detection; CTMN = manual contour tracing coronary angiography data sets also permits the assessment of left ventricular parameters [14, 15]. In this study, using new CT analysis software, we intraindividually compared fully automatically and manually determined left ventricular function and mass measurements derived from retrospectively ECG-gated 16- MDCT coronary angiography examinations with those obtained by. Subjects and Methods The study protocol was approved by the institutional review board, and written informed consent was obtained from all study participants. Eighteen consecutive patients (15 men, three women; age range, 38 7 years; mean, 57.4 ± 1.2 [SD] years; men: age range, 38 7 years; mean, 57.6 ± 11.1 years; women: age range, 53 6 years; mean, 56.5 ± 4.9 years) who were referred for CT angiography of the coronary arteries because of known (n = 7) or 1 End-Diastolic Volume (ml) End-Diastolic Volume (ml) 3 C Fig. 2. land-ltman plots of end-diastolic volume. C, land-ltman plots were assessed using versus CT auto (automated contour detection, ), versus CT manual (manual tracing, ), and CT auto versus CT manual (C). 766 JR:184, March 5

3 CT of Left Ventricular Parameters Downloaded from by on 5/3/18 from IP address Copyright RRS. For personal use only; all rights reserved suspected (n = 11) coronary artery disease were included in the study. The age between both groups was not significantly different (Mann-Whitney U test, p >.5). Only patients with sinus rhythm were included in the study. Patients with renal insufficiency, hyperthyroidism, anamnestic allergy to iodine contrast media, claustrophobia, and metallic implants were excluded from the study. In all patients an additional cardiac MR examination was performed within 48 hr after the CT examination. CT CT examinations were performed on a 16- MDCT scanner (Somatom Sensation 16, Siemens Medical Solutions) with a gantry rotation time of 4 msec (collimation,.75 mm; table feed, 1.5 mm per rotation; reconstruction increment,.5 mm). ll CT scans were obtained in the craniocaudal direction. Image acquisition was performed in inspiratory breath-hold. To familiarize the patient with the protocol, the examination, including breath-holding, was practiced beforehand. etablockers (revibloc [esmolol], axter) were injected IV in patients with heart rates exceeding 65 beats per minute. One hundred twenty milliliters of iodinated contrast agent (Xenetix [iobitridol], Guerbet; 3 mg I/ ml) was continuously injected into the right antecubital vein via an 18-gauge catheter with an infusion rate of 3.5 ml/sec. To assure maximum contrast material concentration in the coronary arteries, a circular region of interest (ROI) was placed in the ascending aorta. s soon as the signal intensity in the ROI reached a threshold of 1 HU, the patient was instructed to maintain an inspiratory breath-hold, and data acquisition was started. The data set covered the entire heart from base to apex as planned on an unenhanced localizer scan. Two separate data sets were reconstructed in end-systole and end-diastole, respectively. Endsystole was defined as maximum contraction and end-diastole as maximum dilation of the left ventricle. End-diastolic and end-systolic reconstruction windows were selected on the basis of axial images reconstructed at mid ventricular level in 5% steps throughout the entire RR interval. End-diastolic and end-systolic phases were identified visually on those images showing the largest and smallest left ventricular cavity areas, respectively [16]. fter reconstruction, CT raw data were transferred to a PC-based workstation (Wizard, Siemens). Multiplanar reformations in the short-axis orientation (slice thickness, 8 mm; no interslice gap) were calculated from the axial images. The end-diastolic volume (EDV), end-systolic volume (ESV), ejection fraction (EF), and left ventricular mass (LVM) of the reformatted images were analyzed using an automated left ventricular endo- and End-Systolic (Volume ml) epicardial contour detection algorithm (CT Mass, MEDIS) and in a separate analysis by manual tracing. The most basal section was defined as the section in which the left ventricular myocardium extended over at least 5% of the circumference on the end-diastolic and end-systolic images. The first slice with a visible lumen was defined as the left ventricular apex. was performed on a 1.5-T whole-body scanner (Magnetom Sonata, Siemens) using contiguous segmented cine steady-state free-precession sequences (TR/TE, 3/1.5; flip angle, 6 ). ll data were collected in inspiratory breath-hold. Slice thickness was 8 mm, and the entire left ventricle was covered without interslice gaps. The true temporal resolution was 4 msec. The phased-array torso coil (2 coil elements) placed anteriorly on the patient and the table-integrated spine coil (2 coil elements) were used for signal reception. EDV, ESV, EF, and LVM were analyzed using commercially available software (rgus, Siemens) on a standard postprocessing workstation (Leonardo, Siemens). The most basal section was defined according to the previously described criteria. Data nalysis ll CT and MR images were analyzed by an experienced radiologist. EDV, ESV, EF, and LVM were expressed as mean values ± SD. The left ventricular parameters of the CT examinations assessed by automated contour detection algorithm and by manual tracing were compared mutually and with MR data. To detect differences between automated and manually calculated data, we performed CTUTO CTMN Fig. 3. Left ventricular end-systolic volume assessed using and CT. CTUTO = automatic contour detection; CTMN = manual contour tracing. Wilcoxon s signed rank test, in which a p value equal to or less than.5 was considered statistically significant. CT and MR data were compared using the land-ltman approach. Results Of 18 patients referred for CT coronary angiography, one had to be excluded from further analysis because of arrhythmias that occurred during data acquisition. This patient did not undergo the examination. In the remaining 17 patients, CT and examinations were successfully accomplished without any complications. The mean heart rate was 58 ± 4 beats per minute during the CT examinations. During, the mean heart rate was 65 ± 8 beats per minute. Five patients had β-blockers in their standard medication, and in four patients β-blockers had to be injected IV before CT. CT and MR image quality was adequate in all patients. The mean duration of analysis using the CT automated contour detection algorithm was 1 min 4 sec ± 21 sec and 3 min 27 sec ± 46 sec for manual tracing, respectively. The mean duration of analysis of MR data was 4 min 1 sec ± 37 sec. End-Diastolic Volume The mean EDV measured on was ± 43.6 ml (range, ml). CT values derived from automated contour detection (CT auto, ± 45.7 ml; range, ml) and from manual tracing (CT manual, ± 39.9 ml; range, ml) were significantly higher than with ( vs CT auto, p <.5; mean difference,.3 ± 15.7 ml; JR:184, March 5 767

4 Schlosser et al. Downloaded from by on 5/3/18 from IP address Copyright RRS. For personal use only; all rights reserved vs CT manual, p <.5; mean difference, 17.2 ± 13.1 ml). EDV derived from both CT algorithms was not significantly different (CT auto vs CT manual, p >.5; mean difference, 3.1 ± 7.1 ml) (Figs. 1 and 2). End-Systolic Volume The mean ESV calculated from the MR data sets was 5.1 ± 33.5 ml (range, ml). ESV values derived from both CT algorithms (CT auto, 58.8 ± 34.2 ml; range, ml; CT manual, 58.1 ± 3.1 ml; range, ml) were significantly higher than with ( vs CT auto, p <.5; mean difference, 9.2 ± 13.9 ml; vs CT manual, p <.5; mean difference, 9.1 ± 1.9 ml). ESV values from the CT examination assessed by automated and manual measurements were not significantly different (CT auto vs CT manual, p >.5; mean difference,.1 ± 7.1 ml) (Figs. 3 and. 4) End-Systolic Volume (ml) Ejection Fraction EF assessed on (59.9% ± 14.4%; range, 18 76%) was slightly higher but not significantly different from CT values derived by automated contour detection (59.2% ± 13.7%; range, 31 85%) and manual tracing (58.1% ± 11.9%; range, 3 73%; vs CT auto, p >.5; mean difference, 1.% ± 9.%; vs CT manual, p >.5; mean difference, 2.6% ± 7.3%). EF derived from both CT algorithms was not significantly different (CT auto vs CT manual, p >.5; mean difference, 1.5% ± 4.4%) (Figs. 5 and 6). Left Ventricular Mass The highest mean LVM was assessed using (142.7 ± 38.4 g; range, g). These data were significantly different from CT values derived by automated contour detection (13.9 ± 29.1 g; range, g) and manual tracing (133.7 ± 33.2 g; range, g; vs CT auto, p <.5; mean difference, 11.7 ± 15.9 g; vs CT manual, p <.5; mean difference, 8.3 ± 12.4 g). LVM measurements derived from both CT algorithms were not significantly different (CT auto vs CT manual, p >.5; mean difference, 3.3 ± 7. g) (Figs. 7 and 8). Examples of end-diastolic and end-systolic MR and CT images and automatic detected and manually traced endo- and epicardial contours are displayed in Figure 9. Discussion In this study we evaluated the ability of the newest generation of CT scanners to assess left ventricular parameters. This study carries four major findings we believe are important: First, EDV and ESV values calculated on MR data sets are statistically significantly lower compared End-Systolic Volume (ml) End-Systolic Volume (ml) C Fig. 4. land-ltman plots of end-systolic volume. C, land-ltman plots were assessed using versus CT auto (automated contour detection, ), versus CT manual (manual tracing, ), and CT auto versus CT manual (C). 768 JR:184, March 5

5 CT of Left Ventricular Parameters Downloaded from by on 5/3/18 from IP address Copyright RRS. For personal use only; all rights reserved Ejection Fraction (%) CTUTO CTMN Fig. 5. Ejection fraction assessed using and CT. CTUTO = automatic contour detection; CTMN = manual contour tracing Ejection Fraction (%) with automated and manual measurements derived from 16-MDCT examinations. Second, LVM measurements on MR data sets resulted in statistically significantly higher values compared with automated and manual measurements derived from 16-MDCT examinations. Third, EF measurements are not statistically significantly different among all techniques. Fourth, values from the automated contour detection algorithm using the new software CT Mass are not significantly different compared with manual tracing. Cine has been established as the most accurate clinical method for assessing ventricular volumes [17 19] and mass [, 21]. In particular, steady-state free-precession cine is the technique of choice because of its excellent contrast between the bloodfilled cavities and the surrounding myocardium. In this setting, automatic segmentation provides accurate volumetric data [8] Ejection Fraction (%) Fig. 6. land-ltman plots of ejection fraction. C, land-ltman plots were assessed using versus CT auto (automated contour detection, ), versus CT manual (manual tracing, ), and CT auto versus CT manual (C) Ejection Fraction (%) C JR:184, March 5 769

6 Schlosser et al. Downloaded from by on 5/3/18 from IP address Copyright RRS. For personal use only; all rights reserved Left Ventricular Mass (g) CTUTO CTMN Fig. 7. Left ventricular mass assessed using and CT. CTUTO = automatic contour detection; CTMN = manual contour tracing Left Ventricular Mass (g) Left Ventricular Mass (g) 225 C In contrast to conventional angiographic volumetric analysis, the cross-sectional nature of makes it independent of geometric assumptions. In addition, noninvasiveness, the lack of ionizing radiation, and the excellent soft-tissue contrast without IV contrast material injection render highly attractive for patients with various cardiac diseases with compromised left ventricular function. In contrast to 3D echocardiography, is operator-independent and permits a far better distinction between myocardium and the ventricular cavity. However, cardiac is still limited with regard to restricted scanner availability, relatively high costs, and generally long examination times. Several studies have shown the ability of electron beam CT and MDCT to assess left ventricular function and mass by multiplanar reformation algorithms using short-axis images [14, 15, 22]. ecause of the retrospective Left Ventricular Mass (g) 225 Fig. 8. land-ltman plots of left ventricular mass. C, land-ltman plots were assessed using versus CT auto (automated contour detection, ), versus CT manual (manual tracing, ), and CT auto versus CT manual (C). 77 JR:184, March 5

7 CT of Left Ventricular Parameters Downloaded from by on 5/3/18 from IP address Copyright RRS. For personal use only; all rights reserved Fig. 9. Examples of end-diastolic and end-systolic MR and CT images., End-diastolic MR (top row) and CT images and automatically detected (center row) and manually traced (bottom row) endo- and epicardial contours. Only each second short-axis slice is displayed. See next page for end-systolic images. (Fig. 9 continues on next page) gating used for cardiac MDCT, all data for the analysis of left ventricular parameters can be calculated from a standard CT coronary angiography data set without any additional radiation exposure. ecause of the introduction of the new generation of MDCT scanners that allow the reliable detection of significant coronary stenoses and calcified plaque, the number of cardiac CT investigations has increased. With regard to time constraints in clinical practice, an automatic postprocessing tool allowing fast and reliable assessment of left ventricular volumes and masses is a prerequisite for a more widespread use of left ventricular measurements based on CT data sets. The results of our study show that automatic contour detection is feasible for CT data sets and results in fast and reliable measurements without significant differences compared with manual contour tracing. However, a drawback of CT measurements in general is the overestimation of EDV and ESV compared with as the standard of reference. Regarding ESV, this overestimation might be explained by the relatively low temporal resolution, even of the latest 16-MDCT scanners, of about 21 msec compared with cine (4 msec) and the inability to acquire the maximum systolic contraction. For this reason, an underestimation of the EDV might be plausible. However, in our study, CT measurements overestimated EDV in the same dimension as ESV. One reason might be that the two techniques do not display identical slices, and variations of the most basal slice thickness may result in a difference of up to 27 ml, as determined in our study. Left ventricular EF estimated on CT with both manual and fully automated contour determination was almost identical to measurements using, indicating a reliable estimation of the global left ventricular function using the former technique. Using the CT Mass software, automated analysis of left ventricular parameters was significantly quicker than manual drawing, indicating a potential improvement in workflow and data analysis. The data provided in this study need to be interpreted critically. First, only a small group of patients were examined; the data need to be validated by larger patient cohorts. Furthermore, the influence of β-blocker administration before CT has not been assessed. For functional analysis it is crucial that no medication influencing the patient s heart rate or myocardial contractility be applied. Therefore, the administration of β- blockers in some patients before CT is not only a limitation of this study but also a general limitation of the method. However, the major advantage of 16- MDCT regarding estimation of left ventricular parameters is the shorter examination time per patient. However, as a result of lower temporal resolution, the need of nephrotoxic contrast material, and substantial radiation doses up to 13 msv delivered during a single CT scan [23], CT can hardly be considered a method of choice for the determination of left ventricular parameters in clinical practice. Nevertheless these parameters are most likely to be seen as additional information in patients undergoing CT coronary angiography. In conclusion, fully automated analysis of data acquired during CT coronary angiography using a 16-MDCT scanner allows fast JR:184, March 5 771

8 Schlosser et al. Downloaded from by on 5/3/18 from IP address Copyright RRS. For personal use only; all rights reserved Fig. 9. (continued) Examples of end-diastolic and end-systolic MR and CT images., End-systolic MR (top row) and CT images and automatically detected (center row) and manually traced (bottom row) endo- and epicardial contours. Only each second short-axis slice is displayed. See previous page for end-diastolic images. and reliable assessment of left ventricular EF and a rough estimation of left ventricular volumes and mass. References 1. Levy D, Garrison RJ, Savage DD, Kannel W, Castelli WP. Prognostic implications of echocardiographically determined left ventricular mass in the Framingham Heart Study. N Engl J Med 199;322: Ghali JK, Liao Y, Simmons, Castaner, Cao G, Cooper RS. The prognostic role of left ventricular hypertrophy in patients with or without coronary artery disease. nn Intern Med 1992;117: Keller M, Peshock RM, Malloy CR, et al. In vivo measurement of myocardial mass using nuclear magnetic resonance imaging. J m Coll Cardiol 1986;8: Florentine MS, Grosskreutz CL, Chang W, et al. Measurement of left ventricular mass in vivo using gated nuclear magnetic resonance imaging. J m Coll Cardiol 1986;8: Katz J, Milliken MC, Stray-Gundersen J, et al. Estimation of human myocardial mass with MR imaging. Radiology 1988;169: Sakuma H, Fujita N, Foo TK, et al. Evaluation of left ventricular volume and mass with breathhold cine MR imaging. Radiology 1993;188: Sandstede J, Lipke C, eer M, et al. ge- and gender-specific differences in left and right ventricular cardiac function and mass determined by cine magnetic resonance imaging. Eur Radiol ;1: arkhausen J, Ruehm SG, Goyen M, uck T, Laub G, Debatin JF. MR evaluation of ventricular function: true fast imaging with steady-state precession versus fast low-angle shot cine MR imaging feasibility study. Radiology 1; 219: arkhausen J, Goyen M, Ruhm SG, Eggebrecht H, Debatin JF, Ladd ME. ssessment of ventricular function with single breath-hold real-time steady-state free precession cine MR imaging. JR 2;178: chenbach S, Ulzheimer S, aum U, et al. Noninvasive coronary angiography by retrospectively ECG-gated multislice spiral CT. Circulation ;12: chenbach S, Giesler T, Ropers D, et al. Detection of coronary artery stenoses by contrast-enhanced, retrospectively electrocardiographicallygated, multislice spiral computed tomography. Circulation 1;13: Nieman K, Cademartiri F, Lemos P, Raaijmakers R, Pattynama PM, de Feyter PJ. Reliable noninvasive coronary angiography with fast submillimeter multislice spiral computed tomography. Circulation 2;16: Schlosser T, Konorza T, Hunold P, Kuhl H, Schmermund, arkhausen J. Noninvasive visualization of coronary artery bypass grafts using 16 detector-row- CT. J m Coll Cardiol 4;44: Mahnken H, Spuentrup E, Niethammer M, et al. Quantitative and qualitative assessment of left ventricular volume with ECG-gated multislice spiral CT: value of different image reconstruction algorithms in comparison to. cta Radiol 3;44: JR:184, March 5

9 CT of Left Ventricular Parameters Downloaded from by on 5/3/18 from IP address Copyright RRS. For personal use only; all rights reserved 15. Heuschmid M, Kuttner, Schroder S, et al. Left ventricular functional parameters using ECGgated multidetector spiral CT in comparison with invasive ventriculography [in German]. Rofo Fortschr Geb Rontgenstr Neuen ildgeb Verfahr 3;175: Juergens KU, Grude M, Maintz D, et al. Multidetector row CT of left ventricular function with dedicated analysis software versus MR imaging: initial experience. Radiology 4;23: Higgins C. Which standard has the gold? J m Coll Cardiol 1992;19: Debatin JF, Nadel SN, Paolini JF, et al. Cardiac ejection fraction: phantom study comparing cine MR imaging, radionuclide blood pool imaging, and ventriculography. J Magn Reson Imaging 1992;2: Heusch, Koch J, Krogmann ON, Korbmacher, ourgeois M. Volumetric analysis of the right and left ventricle in a porcine heart model: comparison of three-dimensional echocardiography, magnetic resonance imaging and angiocardiography. Eur J Ultrasound 1999;9: Myerson SG, ellenger NG, Pennell DJ. ssessment of left ventricular mass by cardiovascular magnetic resonance. Hypertension 2;39: Myerson SG, Montgomery HE, World MJ, Pennell DJ. Left ventricular mass: reliability of M- mode and 2-dimensional echocardiographic formulas. Hypertension 2;4: Mousseaux E, eygui F, Fornes P, et al. Determination of left ventricular mass with electron beam computed tomography in deformed, hypertrophic human hearts. Eur Heart J 1994;15: Hunold P, Vogt FM, Schmermund, et al. Radiation exposure during cardiac CT: effective doses at multi-detector row CT and electron-beam CT. Radiology 3;226: JR:184, March 5 773