Patients
A total of 49 consecutively patients (31 men,
18 women; mean age,
69.45 ± 12.45 years,
range 35 – 89 years) who underwent clinically indicated thoracoabdominal CTA between January to July 2013 were included.
The study was approved by the institutional ethics committee,
and written informed consent was obtained from all patients.
The exclusion criteria were nephropathy (serum creatinina > 1.5 mg/dl or glomerular filtration rate < 60 ml/m) and previous reactions to iodinated contrast media.
Patients with irregular or high heart rates were not excluded.
CT Data acquisition
All studies were performed on a second-generation dual-source CT system of 128 detector rows (Somaton Definition Flash,
Siemens Healthcare) using a high pitch protocol (of 3.4).
30 studies were acquired with cardiac synchronization and 19 without it.
Scanning parameters were: slice collimation,
128 x 0.6 mm; gantry rotation time,
280 ms; and temporal resolution,
75 ms.
Attenuation-based tube current modulation was used (CARE dose4D).
The tube voltage (kV) was adapted according to de body mass index,
as [14-16]:
BMI
|
kV
|
≤ de 24,9 Kg/m2
|
80 kV
|
25 - 29,9 Kg/m2
|
100 kV
|
≥ 30 Kg/m2
|
120 kV
|
The scanning range was from thoracic inlet to the ischial tuberosities.
The scanner software automatically calculated the start time of CT acquisition so that acquisition of the heart volume started at 60% of the R-R interval (mid-diastole).
The entire heart volume was acquired in a single beat (Video 5)
No medications for heart rate or rhythm control or vasodilatation were used.
120-ml of contrast material (Iomeprol 350 mg I/ml,
Iomeron,
Bracco SpA,
Milan,
Italia) at a flow rate of 6 ml/s followed by 40-mL of saline solution was used in all patients.
Bolus tracking with the region of interest (ROI) in the ascending aorta was used with and threshold of 100-Hounsfiled unit (HU).
The acquisition was initiated 13 seconds after the threshold was reached.
Postprocessing
Images were reconstructed with a slice thickness of 1.5 mm and an increment of 0.75 mm for the aortic volume,
and a slice thickness of 0.6 mm and an increment of 0.3 mm for the heart volume.
A medium smooth tissue convolution kernel (B26f) was used.
All images were transferred to a workstation (Syngovia,
Siemens Healthcare).
Image Quality Analysis
Two independent radiologists with 4 and 8 years of experience in cardiovascular imaging reviewed all images in axial,
multi-planar and curved multi-planar reformations,
and volume-rendered and maximum intensity projections.
The reviewers were blinded to each other’s findings.
In all studies (with and without ECG-gating) image quality of the aortic valve-root complex (including valve leaflets,
sinuses of Valsalva,
and left and right coronary ostia) and proximal ascending aorta was assessed.
Image quality was subjectively graded according to the following scale:
1: good quality.
Absence of motion artifacts
2: acceptable quality sufficient for diagnosis,
with minor motion artifacts.
3: inadequate quality,
with major motion artifacts impairing diagnosis. (Fig.
1)
In studies with cardiac synchronization image quality of coronary arteries was assessed.
The coronary tree was divided in 18 segments according to the SCCT (Society of Cardiovascular Computer Tomography) coronary segmentation diagram [17] (Fig.
2).
Because of normal anatomic variation,
not all coronary segments were present in all patients.
Image quality of coronary arteries segments was subjectively graded according to the following scale:
1: good quality with absence of motion artifacts and noise-related blurring.
Adequate vessel opacification (Fig.
3).
2: acceptable quality sufficient for diagnosis,
with minor motion artifacts or noise-related blurring.
Adequate vessel opacification (Fig.
4).
3: inadequate quality,
with major motion artifacts or noise-related blurring or fair or lack of vessel opacification impairing diagnosis (Fig.
5).
4: Non-evaluable coronary segment secondary due to severe vessel wall calcifications – blooming artifacts (Fig.
6).
5: Non-evaluable coronary segment secondary due to reduced vessel diameter (luminal diameter < 1 mm) (Fig. 7) [18].
One of the reviewers measured the time used to evaluate coronary arteries,
not only for image quality but also for analysis of coronary artery anatomy and pathology.
Radiation dose:
The effective dose was estimated using the equation E= K x DLP,
proposed by the European guidelines on quality criteria for computed tomography [19],
where K=0.017 mSv/[mGy.cm] [4,11] and the DLP (dose-length product) was generated by the CT system.
Statistical analysis
Statistical analyses were performed using SPSS software (Version 17.0/SPSS Inc.,
Chicago,
IL,
EE.UU.).
Quantitative continuous variables were expressed as means ± SD and categorical variables as frequencies or percentages.
Interobserver agreement on image quality was calculated using kappa statistic.
Fisher’s exact test was used to analyse the influence of heart rate and heart rate variability on image quality.
Analysis of variance test (ANOVA) was used to compare the mean radiation dose in studies with and without cardiac synchronization.
A p value < 0.05 was considered statistically significant.