This prospective study was approved by the institutional review board and informed consent was obtained from all patients.
90 consecutive patients with clinically indicated CTA were enrolled in the study and randomized into three groups based on CTA protocols: first (120kV 200mAs),
second (80kV 200mAs) and third (120 kV 50mAs).
Exclusion criteria were renal dysfunction and allergy to iodine.
All had suspected lesions of aorta and peripheral vessels.
Examination protocols
CTA examinations were performed on a 256-MDCT (Brilliance iCT,
Philips Healthcare,
Cleveland,
OH).
First group (n=30) was examined with following parameters: tube potential 120 kV,
tube current 200 mAs,
collimation was decreased up to 64x0,625 for optimization of scan time,
rotation time 0,5 s; pitch 0,98.
Second group of patients (n=30) was examined with tube potential 80 kW,
tube current 200 mAs.
Tube potential in third group was 120 kV,
but the tube potential was 50mAs.
All patients received 80 ml of contrast media (350mg/ml) at a flow rate 5 ml/s.
Bolus of CM followed by 30 ml of saline bolus.
Synchronization between the bolus of CM and CT acquisition was achieved using a bolus-tracking system.
Monitoring of bolus was performed on the level of abdominal aorta.
The trigger threshold was set at 100 HU,
delay before acquisition start was 8 sec.
CT Data were reconstructed with 0,9 mm slice thickness and 0,45 reconstruction interval.
CT images in all groups were reconstructed from raw data only with the filtered back projection (FBP).
To evaluate objective image quality the mean intraarterial attenuation and image noise were measured in main three segments: aorto-iliac,
femoropopliteal and lower leg.
Attenuation levels of right and left segments were averaged.
The density and the noise within the psoas major was measured to calculate contrast-to-noise ratio (CNR).
Radiation doses were also compared among the groups.
We recorded the scanner-generated CTDI volume (CTDIvol),
dose length product (DLP).
Effective dose (ED) was calculated using weighted coefficient 0,015.
For visual evaluation axial images,
thin-slab maximum intensity projections and volume rendered images were used.
All data sets were interpreted by two radiologists with 5 and 12 years of experience. Radiologists were blinded to protocols used. They visually evaluated all data by consensus using 3 point scale.
Images were classified so that
3 (excellent) = excellent visualization of arteries with no or minimal streak artifacts,
no image noise with preserved spatial resolution,
grade of the stenosis could be easily evaluated;
2 (fair) = acceptable visualization of arteries with artifacts,
image noise is high, the lumen contour is partially obscured due to image noise and impaired spatial resolution,
but the grade of the stenosis can be assessed still.
1 (poor) =insufficient visualization,
noise is very high,
spatial resolution is impaired,
stenosis could not be evaluated.
All data were reported as the mean±SD.
Two-tailed (paired and unpaired) Student’s t-test was performed for analysis of continuous variables with normal distributions.
The Mann- Whitney U-test was used to compare visual scores.
We used a statistical software package (SPSS 21,
version 21.0.0.0; SPSS,
Chicago,
IL).
Two-tailed p<0.05 was considered statistically significant.