Abstract
ObjectiveVery 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.Materials and methodsSix 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.ResultsThe 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.ConclusionsAll 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.
Highlights
State-of-the-art multidetector-row computed tomography (MDCT) with large detector panels and dual source technology with high-pitch scan modes have dramatically shortened data acquisition times
The time to peak (TTP) decreased with increasing iodine delivery rate (IDR) and decreasing ti, protocols A and B did not differ significantly
The scan window time frame was comparable for the different protocols by visual inspection of the different Computed tomography angiography (CTA) data sets and by analyzing the time attenuation curves (TAC)
Summary
State-of-the-art multidetector-row computed tomography (MDCT) with large detector panels (up to 16 cm in the z-axis) and dual source technology with high-pitch scan modes have dramatically shortened data acquisition times. When the scan time of a body CTA is on the order of 5 s or less, the traditional CM injection protocols need to be reconsidered and short and compact injection protocols should be preferred to those protocols that are optimized to provide a long and stable plateau phase of enhancement [10]. High peak enhancement with low CM volume can be achieved with monophasic injection protocols and a high iodine delivery rate (IDR) [11, 12], and it has been demonstrated, that even very high flow rates can safely injected with special i.v. lines [13]
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