Johannes Georg Korporaal PhD, Presenter: Employee, Siemens AG

Hatem Alkadhi MD, Abstract Co-Author: Nothing to Disclose

Michael Marcus Lell MD, Abstract Co-Author: Research Grant, Siemens AG Speakers Bureau, Siemens AG Research Grant, Bayer AG Speakers Bureau, Bayer AG Research Consultant, Bracco Group

Hubertus Pietsch PhD, Abstract Co-Author: Employee, Bayer AG

Gregor Jost PhD, Abstract Co-Author: Employee, Bayer AG

Bernhard Schmidt PhD, Abstract Co-Author: Employee, Siemens AG

Thomas G. Flohr PhD, Abstract Co-Author: Employee, Siemens AG

Low kV imaging is an emerging trend in clinical CTA and new scanners enable examinations below 100kV also for adults. This gives radiologists the opportunity to reduce the contrast agent dose instead of the radiation dose. This study shows how injection protocols can be adapted for low kV, and what benefits and risks come with it.

With a phantom, the iodine enhancement at 70 and 120kV (reference) was determined. From the relative iodine enhancement at 70kV, the reduction in total iodine dose (TID) was calculated with preservation of the CNR. We used the arterial impulse responses of 72 patients (median age 62y (range 31-81), median body weight 83 kg (range 61-125)) to simulate the contrast enhancements at 70 kV and 120kV. The reference injection protocol at 120kV was 0.3gI per kg body weight, 300mgI/ml and an iodine delivery rate (IDR) of 1.5gI/s. Two alternative injection protocols with lower TID were simulated at 70kV: A) with reduced volume and IDR to obtain the same injection duration, and B) with reduced volume and the initial IDR of 1.5gI/s and thus shorter injection duration.

The TID at 70kV could be reduced by 47.5% resulting in a reduction in volume of 83.3±14.9ml at 120kV to 43.7±7.8ml at 70kV. With protocol A, the IDR was lowered to 0.8gI/s, resulting in the same injection duration of 16.7±3.0s and identical curve shape and amplitude in each patient. With protocol B, the injection duration decreased to 8.7±1.6s and resulted in narrower enhancement curves, indicating that scan timing becomes more critical. Simultaneously, protocol B leads to higher peak enhancement (+44.0±13.2%), indicating even further potential for TID reduction.

The conservative way to adapt injection protocols for low kV imaging is to adapt the TID based on the change in kV, maintain the injection duration of the reference injection protocol and adjust the IDR. Even further TID reduction is possible by using shorter injection times, but scan timing will become more critical.

Lowering the total iodine dose with low kV imaging is important for patients with impaired kidney function – however, injection protocols should be adapted in a structured way as well as scan timing parameters.

Korporaal, J, Alkadhi, H, Lell, M, Pietsch, H, Jost, G, Schmidt, B, Flohr, T, Adapting Injection Protocols for CT Imaging at Low kV: Benefits and Risks.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14017295.html