A Phantom Study for Attenuation Change and Detection of Calcification in Lung Nodules According to Variation of Examination Techniques in Low Dose CT

Abstract

Purpose : To evaluate the attenuation change of hyperdense lung nodule and diagnostic performance of visual assessment according to various tube voltage and current setting in low-dose CT comparing with standard-dose CT.

Material and Methods : A chest phantom containing artificial nodules was scanned with 64-detector-row and 128-detector-row CT scanners using a standard and various low-dose settings with iterative reconstruction. Mean attenuation of nodules and image noise were compared between the standard-dose and low-dose images. Diagnostic accuracy of visual assessment by two readers for discrimination of hyperdense nodule was analyzed using CT images of standard and 5 selected low-dose settings.

Results : Mean CT attenuation of nodules was increased with low tube voltage and image noise was increased with low tube voltage and current in both CT scanners. Mean attenuation of some nodules below hyperdense criteria (200 HU) on standard-dose CT was changed to considerably above 200 HU on low tube current and voltage setting. Diagnostic accuracy for discrimination of hyperdense nodule by visual assessment was not different between standard-dose and low-dose CT scans. Inter-observer agreement for grading of hyperdense nodule showed better agreement in higher radiation-dose scans.

Conclusion : Low-dose CT maintains the diagnostic accuracy in visual assessment of hyperdense lung nodule despite increased image noise and higher attenuation criteria will be necessary for determining hyperdense nodule using CT densitometry in low-dose setting.