Relationship between low tube voltage (70 kV) and the iodine delivery rate (IDR) in CT angiography: An experimental in-vivo study.
OBJECTIVE
Very short acquisition times and the use of low-kV protocols in CTA demand modifications in the contrast media (CM) injection regimen. The aim of this study was to optimize the use of CM delivery parameters in thoraco-abdominal CTA in a porcine model.


METHODS
Six pigs (55-68 kg) were examined with a dynamic CTA protocol (454 mm scan length, 2.5 s temporal resolution, 70 s total acquisition time). Four CM injection protocols were applied in a randomized order. 120 kV CTA protocol: (A) 300 mg iodine/kg bodyweight (bw), IDR = 1.5 g/s (flow = 5 mL/s), injection time (ti) 12 s (60 kg bw). 70 kV CTA protocols: 150 mg iodine/kg bw: (B) IDR = 0.75 g/s (flow = 2.5 mL/s), ti = 12 s (60 kg bw); (C) IDR = 1.5 g/s (flow = 5 mL/s), ti = 12 s (60 kg bw); (D) IDR = 3.0 g/s (flow = 10 mL/s), ti = 3 s (60 kg bw). The complete CM bolus shape was monitored by creating time attenuation curves (TAC) in different vascular territories. Based on the TAC, the time to peak (TTP) and the peak enhancement were determined. The diagnostic window (relative enhancement > 300 HU), was calculated and compared to visual inspection of the corresponding CTA data sets.


RESULTS
The average relative arterial peak enhancements after baseline correction were 358.6 HU (A), 356.6 HU (B), 464.0 HU (C), and 477.6 HU (D). The TTP decreased with increasing IDR and decreasing ti, protocols A and B did not differ significantly (systemic arteries, p = 0.843; pulmonary arteries, p = 0.183). The delay time for bolus tracking (trigger level 100 HU; target enhancement 300 HU) for single-phase CTA was comparable for protocol A and B (3.9, 4.3 s) and C and D (2.4, 2.0 s). The scan window time frame was comparable for the different protocols by visual inspection of the different CTA data sets and by analyzing the TAC.


CONCLUSIONS
All protocols provided sufficient arterial enhancement. The use of a 70 kV CTA protocol is recommended because of a 50% reduction of total CM volume and a 50% reduced flow rate while maintaining the bolus profile. In contrast to pulmonary arterial enhancement, the systemic arterial enhancement improved only slightly increasing the IDR from 1.5 g/s to 3 g/s because of bolus dispersion of the very short bolus (3s) in the lungs.
Department of Radiology and Nuclear Medicine, Paracelsus Medical University, Nuernberg, Germany.
Michael M
http://orcid.org/0000-0002-4800-4428
MM
Lell
Department of Radiology, Friedrich-Alexander University Erlangen, Erlangen, Germany.
Ulrike
U
Fleischmann
MR and CT Contrast Media Research, Bayer Healthcare, Berlin, Germany.
Hubertus
H
Pietsch
Siemens Healthcare, Forchheim, Germany.
Johannes G
JG
Korporaal
Siemens Healthcare, Forchheim, Germany.
Ulrike
U
Haberland
Department of Radiology, University of Marburg, Marburg, Germany.
Andreas H
AH
Mahnken
Siemens Healthcare, Forchheim, Germany.
Thomas G
TG
Flohr
Department of Radiology and Nuclear Medicine, Paracelsus Medical University, Nuernberg, Germany.|Imaging Science Institute (ISI) Erlangen, Erlangen, Germany.
Michael
M
Uder
MR and CT Contrast Media Research, Bayer Healthcare, Berlin, Germany.
Gregor
G
Jost
D000818:Animals; D000072226:Computed Tomography Angiography / Q000379:methods*; D003287:Contrast Media / Q000008:administration & dosage*; D005260:Female; D007455:Iodine / Q000008:administration & dosage*; D023421:Models, Animal; D034421:Sus scrofa; D013997:Time Factors
D003287:Contrast Media; D007455:Iodine