Aya Kino MD, Presenter: Nothing to Disclose

Jia Wang PhD, Abstract Co-Author: Nothing to Disclose

Beverley Mansfield Newman MD, MBBCh, Abstract Co-Author: Nothing to Disclose

Frandics Pak Chan MD, PhD, Abstract Co-Author: Nothing to Disclose

We conduct a prospective clinical trial to evaluate the minimum radiation dose, in terms of equivalent dose (ED) and organ doses (OD), that can produce diagnostic studies in children who underwent cardiac gated (CG) and high-pitch (HP) CTA. We also examine dose savings from image based iterative reconstruction (SAFIRE).

With IRB approval, pediatric patients referred for thoracic CTA were recruited for a split dose protocol in which a high-dose and a low-dose scans were performed in tandem under a single contrast bolus and breath-hold on a Siemens Flash scanner. The tube current in each scan was adjusted such that the combined CTDI was the same as a routine scan. The percentage of dose split was randomized. Other scan controls, such as CG versus HP mode, tube-voltage, contrast protocol, and scan range were chosen according to the clinical needs. Images were reconstructed at 0.6 mm thickness without SAFIRE and with SAFIRE at all levels (1-5). Two cardiac radiologists categorized these images as diagnostic without SAFIRE, diagnostic with SAFIRE, and non-diagnostic at any SAFIRE level. ED was estimated from patient size and DLP. OD was calculated with an image-based Monte Carlos simulation.

31 patients (age 8 weeks to 7 years old, weight 4 to 74kg) were recruited, producing 62 scans. 48 scans are HP and 14 scans are CG. 44 scans are first-pass contrast bolus studies while 18 scans are delay-phase blood pool studies. For first-pass HP, the average ED is 0.78 mSv, and the OD for lung, bone, liver, and breast are 1.33, 3.13, 1.25, and 1.19 mGy. Dose values for delay-phase HP are similar. For CG, the average ED is 2.41 mSv, and the OD are 7.93, 16.65, 8.53, and 10.2 mGy, respectively. Among diagnostic studies without SAFIRE, the average ED are 0.8-0.9 mSv for first-pass HP, 1.8-2.0 mSv for delay-phase HP and 3.1-4.0 mSv for CG. Nondiagnostic first-pass HP at ED as low as 0.12 mSv are convertable to diagnostic studies with SAFIRE. The highest ED values for unrecoverable studies are 0.55 mSv for delay-phase HP and 0.93 mSv for CG.

With currently technology, we can expect a minimum dose of 0.1 to 0.5 mSv for non-gated CTA and 1 mSv for retrospectively gated CTA.  In routine practice, actual dose will be higher, depending on patient size and protocol.

Pediatric cardiovascular CTA of the chest should aim for less than 1 mSv for non-gated studies and 3 mSv for gated studies.

Kino, A, Wang, J, Newman, B, Chan, F, A Prospective Clinical Trial for the Determination of Minimum Radiation Dose in Pediatric Cardiovascular CTA.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14019086.html