Optimising contrast-enhanced cranial CT for detection of brain metastases

In order to optimise contrast-enhanced CT in the detection of brain metastases, we investigated how sensitivity was affected by an increase in contrast medium dose and a reduction in slice thickness.

A total of 198 cases of known primary malignancy with suspected brain metastases were investigated in three consecutive contrast-enhanced CT examinations. The first was a standard CT examination with an injection of 100 ml contrast medium (300 mg I/ml) and a slice thickness of 10 mm. A further 100 ml contrast medium was given and the second examination was performed immediately afterwards with the same slice thickness as the first. This was followed by the third examination, which used a slice thickness of 5 mm. The standard contrast-enhanced CT images were compared with the double-dose images and with the images of reduced slice thickness (5 mm instead of 10 mm).

The double-dose images demonstrated an 8-18% increase in the number of brain metastases detected compared to the standard contrast-enhanced CT; the images of the 5-mm-thick slices showed a further 22-33% increase. The comparison between the standard contrast-enhanced CT images and the images with both thinner slices and the double dose of contrast medium demonstrated a 32-55% increase in the number of metastases detected.

A considerable increase in sensitivity (32-55%) in contrast-enhanced CT can be obtained by reducing the slice thickness and increasing the contrast medium dose. This optimised technique should be the method of choice in patients with known primary malignancy and suspected brain metastases.