Automated attenuation-based kilovoltage selection: preliminary observations in patients after endovascular aneurysm repair of the abdominal aorta.

ABSTRACT

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 (CTDI(vol)) 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 CTDI(vol) 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.