Purpose: The aim of this study was to optimize acquisition data during multislice multiphasic CT examination of the renal excretory system in order to reduce patient effective dose without deterioration of the imaging quality.
Materials and methods: With the aid of two dedicated software programmes we evaluated the patient effective dose during both multislice multiphasic CT examination of the renal excretory system and excretory urography. With the CT acquisition protocol, images of a test object (Helical CT phantom, CIRS) were examined by two expert radiologists to assess the number of visible inserted test images. Other scans of the test object were then obtained utilizing decreased tube current intensity; among these that with minor information loss was identified. Patient effective dose was measured utilizing correspondent acquisition data.
Results: Patient effective dose during multiphasic multislice CT examination before optimization (280 mA tube current intensity) was 22.9 mSv for males and 31.1 mSv for females; after optimization it was 19.6 mSv and 26.7 mSv, respectively, with a 14% decrease. Patient effective dose during CT direct phase before optimization was 8.9 mSv for males and 12.8 mSv for females, after optimization 7.6 mSv and 11 mSv with a 15% decrease. The absorbed dose for males is lower because the females gonads are completely included in the primary CT beam, whereas the testicles are hit by diffuse radiation only.
Discussion and conclusions: During CT direct phase the patient absorbed dose is 1.45 for males and 1.9 for females (1.2 and 1.6 respectively after optimization) higher than that absorbed during intravenous pyelography; the absorbed dose of a complete multiphasic CT examination is 3.7 for males and 4.6 for females (3.2 and 3.9 respectively after optimization) higher than that absorbed during intravenous pyelography. Such dosimetric data may be justified by diagnostic advantages in stone assessment, especially in males, and by the fact that multislice CT may unify different diagnostic tools such as intravenous pyelography, axial CT and angiography, thereby simplifying the entire diagnostic protocol. As far as exposure is concerned radiologists should follow the optimizing principle referred to each clinical query, bearing in mind that diagnostic accuracy is more important than the simple iconographic aspect.