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

Thomas Schlosser; Konstantin Pagonidis; Christoph U. Herborn; Peter Hunold; Kai-Uwe Waltering; Thomas C. Lauenstein; Jörg Barkhausen

Disclosures

Am J Roentgenol. 2005;184(3):765-773. 

In This Article

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, 38–70 years; mean, 57.4 ± 10.2 [SD] years; men: age range, 38–70 years; mean, 57.6 ± 11.1 years; women: age range, 53–60 years; mean, 56.5 ± 4.9 years) who were referred for CT angiography of the coronary arteries because of known ( n = 7) or 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 > 0.05). 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 examinations were performed on a 16-MDCT scanner (Somatom Sensation 16, Siemens Medical Solutions) with a gantry rotation time of 420 msec (collimation, 0.75 mm; table feed, 1.5 mm per rotation; reconstruction increment, 0.5 mm). All 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. Betablockers (Brevibloc [esmolol], Baxter) were injected IV in patients with heart rates exceeding 65 beats per minute.

One hundred twenty milliliters of iodinated contrast agent (Xenetix [iobitridol], Guerbet; 300 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. As soon as the signal intensity in the ROI reached a threshold of 120 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]

After 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 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 50% 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.

MRI 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, 60°). All 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 40 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 (Argus, Siemens) on a standard postprocessing workstation (Leonardo, Siemens). The most basal section was defined according to the previously described criteria.

All 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 Wilcoxon's signed rank test, in which a p value equal to or less than 0.05 was considered statistically significant. CT and MR data were compared using the Bland-Altman approach.

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