Sarvenaz Pourjabbar MD, Presenter: Nothing to Disclose

Sarabjeet Singh MD, Abstract Co-Author: Research Grant, Siemens AG Research Grant, Toshiba Corporation Research Grant, General Electric Company Research Grant, Koninklijke Philips NV

Michael Austin Blake MBBCh, Abstract Co-Author: Editor with royalties, Springer Science+Business Media Deutschland GmbH

Diego Alfonso Lira MD, Abstract Co-Author: Nothing to Disclose

Atul Padole MD, Abstract Co-Author: Nothing to Disclose

Mannudeep K. S. Kalra MD, Abstract Co-Author: Nothing to Disclose

Ranish Deedar Ali Khawaja MD, Abstract Co-Author: Nothing to Disclose

Roberto Lo Gullo MD, Abstract Co-Author: Nothing to Disclose

Alexi Otrakji MD, Abstract Co-Author: Nothing to Disclose

To assess feasibility of abdominal CT scan acquired at CTDIvol of 1.4mGy (less than 1mSv) & reconstructed with filtered back projection(FBP) and two iterative reconstruction(IR) techniques.

In an IRB approved prospective study, 25 patients (58.8 ±12.5years, M:F 15:10) undergoing standard of care(SOC) abdominal CT on 128-MDC (Definition FLASH, Siemens) gave written informed consent for acquisition of an extra series low dose CT scan(LD, lower reference mAs).The LD images were reconstructed with SafeCT(A1,A2,A3 settings; MedicVision) and SAFIRE(S3, S4, S5). Two radiologists evaluated LD images for lesion detection and contour delineation including liver (parenchyma, margins),adrenal (nodule detection), pancreas(duct), kidney(parenchyma & stones),bowel (wall, abnormalities) & lymph nodes. All structures were evaluated on a 5-point scale in comparison to SOC-FBP(1=supra-clinical diagnostic performance, 5=unacceptable clinical diagnostic performance).Objective noise was measured in liver & spleen.Modal scores and inter-observer agreement (kappa) were calculated for subjective quality.

Average CTDIvol for SOC-FBP and LD were 9±5mGy(6±4mSv) & 1.4±0.2mGy(0.9±0.05mSv),respectively. Inter-observer agreement was good (κ= 0.65). LD-FBP were suboptima(14/25) or unacceptable(11/25). SafeCT showed improvement in diagnostic performance as acceptable(7/25),limited (11/25) and suboptimal(7/25) with A2 setting. Evaluation of the SAFIRE also showed improvement in diagnostic performance, as acceptable (9/25), limited (9/25) & suboptimal(7/25) with S5.Patients with limited and suboptimal diagnostic performance had significantly higher BMI (S5: 34.0 ±7.5 kg/m2 and A2: 32 ± 9.2 kg/m2) as compared to acceptable performance(S5: 22.2 ± 6 kg/m2 and A2: 23.4 ± 5.4 kg/m2),(p =0.000). In patients with BMI< 23, liver parenchyma and liver margin on LD images were not significantly different from SOC-FBP(p = 0.17-0.3). A2(28 ± 14) and S5(23 ± 11) settings showed similar objective noise as for the SOC-FBP abdominal CT(23 ± 7).

Both of the iterative reconstruction techniques (SafeCT and SAFIRE) improve diagnostic performance of low dose abdominal CT as opposed to FBP. However, it is crucial to select the optimal settings of the IR techniques to achieve a desirable image quality.

It is feasible to lower the radiation dose of abdominal CT in small patients (BMI<23 kg/m2) by use of iterative reconstruction techniques.

Pourjabbar, S, Singh, S, Blake, M, Lira, D, Padole, A, Kalra, M, Khawaja, R, Lo Gullo, R, Otrakji, A, Feasibility of Abdominal CT Scan at Sub Milli-Sievert Doses with Two Iterative Reconstruction Techniques: A Prospective Study.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14011334.html