Dose reduction in spiral CT coronary angiography with dual source  equipment. Part II. Dose surplus due to slope-up and slope-down of  prospective tube current modulation in a phantom model.
OBJECTIVE
This study was undertaken to estimate surplus radiation dose in retrospectively electrocardiography (ECG)-gated dual-source computed tomography coronary angiography (DSCT-CA) due to the slope-up and slope-down of the tube current using prospectively ECG-triggered tube modulation.


METHODS
We used an anthropomorphic phantom with an ECG-gated retrospective protocol and a DSCT scanner (Definition, Siemens). We used four tube current modulation algorithms: narrow pulsing window, with tube current reduction to 20% (A) and 4% (B) of peak current; and wide pulsing window, with tube current reduction to 20% (C) and 4% (D). Each algorithm was applied at five heart rates (HR=45, 60, 75, 90 and 120 bpm) with adaptive pitch values (0.2-0.5). Data sets were reconstructed in 5% increments from 0-95% of the R-R interval. Noise was measured at each R-R step in order to identify low noise (100% dose), medium noise (slope-up/down) and high noise (4/20% dose). Width of the transition window (slope-up/slope-down from 4/20% to 100% dose) was calculated. The surplus dose due to slope-up/slope-down was calculated.


RESULTS
Surplus dose was 19% (A), 34% (B), 14% (C) and 21% (D). The transition window lasted 10%+10% (slope-up + down) for HR <75 bpm and all HR in C (except for 120 bpm; 25%+15%), 15%+15% for HR >90 bpm (A). For C and D, instead, the slope-up increased with progressively higher HR (10%-25% of the R-R interval, except for 90 bpm, 10%), whereas the slope-down remained constant at 5% (except for 120 bpm; 10%).


CONCLUSIONS
The adaptive ECG-pulsing windows produced an increment of the surplus dose with increasing HR. The transition window was a constant source of surplus radiation dose in the range of 14%-34%.
Martini
C
C
Dipartimento di Radiologia e Cardiologia, Azienda Ospedaliero-Universitaria, Parma, Italy.
Palumbo
A
A
Maffei
E
E
Rossi
A
A
Rengo
M
M
Malagò
R
R
Dijkshoorn
M
M
Weustink
A
A
Mollet
N
N
Krestin
G
G
Cademartiri
F
F
D015502:Absorptiometry, Photon; D000465:Algorithms; D017023:Coronary Angiography / Q000295:instrumentation* / Q000379:methods; D004562:Electrocardiography; D004867:Equipment Design; D006321:Heart / Q000000981:diagnostic imaging; D006339:Heart Rate; D006801:Humans; D008962:Models, Theoretical; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013819:Thermoluminescent Dosimetry; D036542:Tomography, Spiral Computed