Re-evaluation of body weight as an indicator for contrast material dosage for indirect CT venography

We evaluated body weight as an accurate indicator for determining contrast load using nonionic monomeric contrast material in indirect CT venography.

One hundred and thirty-two patients (mean age 51 years) underwent indirect CT venography to exclude the possibility of DVT. We used 150 ml of isohexol (iodine, 300 mgI/ml) administered at a rate of 3.0 ml/s. Scanning delay was 180 s from the time of initiation of contrast injection. Scans were obtained in a caudal-to-cranial direction starting from the ankle. Hounsfield unit (HU) measurements were recorded at the common femoral and popliteal veins. Using linear regression analysis, we calculated the correlation the coefficient between the CT attenuation and the iodine dose per body weight of each patient. We also recorded the presence of DVT and measured the CT attenuation of the clots.

Average contrast dosage per weight was 765.3 mgI (from 420.5 -1184.2 mgI). Average measurements of HU at the common femoral and popliteal veins were 114.4 ± 17.8 HU and 109.9 ± 21.4 HU, respectively. The regression coefficients were 0.62 and 0.41 for the common femoral and popliteal veins, respectively. DVT was detected in 33 of 132 patients. The average HU of the thrombus was 47.7 ± 13.3 HU.

Indirect CT venography for detecting DVT initiated 180 s after the start of infusion of contrast material (150 ml) and a contrast injection at a rate of 3 ml/s produced high mean levels of venous enhancement. However, correlation between dose of contrast material per patient weight and CT attenuation of veins was fairly low.