Low-dose CT for patients with clinically suspected acute appendicitis: optimal strength of sinogram affirmed iterative reconstruction for image quality and diagnostic performance

Abstract

Background As there is increased concern over the radiation exposure particularly in adolescents and young adults, computed tomography (CT) dose reduction is needed in the diagnosis of acute appendicitis. Purpose To evaluate the optimal strength of sinogram affirmed iterative reconstruction (SAFIRE) to obtain the best image quality on a 30-mAs applied low-dose CT (LDCT30mAs) and to compare the diagnostic performances of the LDCT30mAs with different SAFIRE strengths with that of the 100-mAs applied LDCT (LDCT100mAs) for the diagnosis of acute appendicitis. Material and Methods A total of 102 consecutive patients (47 men, 55 women; mean age, 41.2 years; range, 15–82 years) with right lower quadrant pain underwent abdominal-pelvic CT, consisting of arterial phase LDCT100mAs and portal venous phase LDCT30mAs under a fixed 120 kV. LDCT30mAs images were reconstructed separately with five strength levels (S1–S5). Two blinded radiologists recorded scores for the subjective image quality of the LDCT30mAs dataset (S0–S5) and confidence scores for the diagnosis of acute appendicitis on each dataset and LDCT100mAs. CT image noise was measured for each set. Results The study population consisted of 58 patients with confirmed appendicitis and 44 without appendicitis. There was no significant difference in diagnostic performance between LDCT100mAs and LDCT30mAs with any strength for both readers (AUC for reader 1, LDCT30mAs with S0–S5 = 0.97, LDCT100mAs = 0.93, P = 0.0936; for reader 2, LDCT30mAs with S0–S5 = 0.96, LDCT100mAs = 0.97, P = 0.128). The measured noise decreased as the strength increased from S0 to S5 (mean, 20.8 > 17.7 > 15.6 > 13.5 > 11.5 > 9.5, P < 0.0001). However, overall subjective image quality on S3 was better than the other strengths for both readers (S0 < S1 < S2 < S3 > S4 > S5, P < 0.0001). Conclusion Although measured noise declined as SAFIRE strength increased, S3 seems optimal for the best subjective image quality on LDCT30mAs. The diagnostic performance of LDCT30mAs with any strength is comparable to that of LDCT100mAs for the diagnosis of acute appendicitis.