Automated Attenuation-Based Kilovoltage Selection: Preliminary Observations in Patients After Endovascular Aneurysm Repair of the Abdominal Aorta

OBJECTIVE. The objective of our study was to assess prospectively the impact of automated attenuation-based kilovoltage selection on image quality and radiation dose in patients undergoing body CT angiography (CTA) after endovascular aneurysm repair (EVAR) of the abdominal aorta. SUBJECTS AND METHODS. Thirty-five patients (five women, 30 men; mean age +/- SD, 69 +/- 13 years; mean body mass index +/- SD, 27.3 +/- 4.5 kg/m(2)) underwent 64-MDCT angiography of the thoracoabdominal aorta using a fixed 120-kVp protocol (scan A: 120 mAs [reference]; rotation time, 0.33 second; pitch, 1.2) and, within a median time interval of 224 days, using a protocol with automated kilovoltage selection (scan B: tube voltage, 80-140 kVp). Subjective image quality (5-point scale: 1 [excellent] to 5 [nondiagnostic]) and objective image quality (aortic attenuation at four locations of the aortoiliac system, noise, contrast-to-noise ratio [CNR]) were assessed independently by two blinded radiologists. The volume CT dose index (CTDIvol) was compared between scans A and B. RESULTS. The subjective image quality of scans A and B was similar (median score for both, 1; range, 1-4; p = 0.74), with all datasets being of diagnostic quality. Automated attenuation-based kilovoltage selection led to a reduction to 80 kVp in one patient (2.9%) and 100 kVp in 18 patients (51.4%). Fifteen of 35 patients (42.9%) were scanned at 120 kVp, whereas in one patient (2.9%) the kilovoltage setting increased to 140 kVp. Image noise (scan A vs scan B: mean +/- SD, 12.8 +/- 2.3 vs 13.7 +/- 2.9 HU, respectively) was significantly (p < 0.05) higher in scan B than in scan A, whereas CNR was similar among scans (A vs B: mean +/- SD, 15.7 +/- 7.0 vs 16.9 +/- 9.7; p = 0.43). The CTDIvol was significantly lower in scan B (mean +/- SD, 8.9 +/- 2.9 mGy; scan A, 10.6 +/- 1.5 mGy; average reduction, 16%; p = 0.002) despite a higher tube current-exposure time product (B vs A: mean +/- SD, 152 +/- 27 vs 141 +/- 29 mAs; p = 0.01). CONCLUSION. In patients undergoing follow-up after EVAR of the abdominal aorta, body CTA using automated attenuation-based kilovoltage selection yields similar subjective image quality and CNR at a significantly reduced dose compared with a protocol that uses 120 kVp.