To quantitatively assess the effect of slice thickness on Agatston Score, calcium mass and volume score in coronary screening using a 16-slice multidetector-row CT (MDCT).

First, a non-moving anthropomorphic thorax-phantom with calcium cylinders of different sizes and densities was scanned twenty times with a standardized examination protocol (collimation of 12x0.75mm, tube voltage 120KV and effective tube current time-product of 133mAseff). Second 38 patients (21 male; age 63.1±6.9 years; heart rate 73.1±15.3 bpm) underwent non-enhanced retrospectively ECG-gated MDCT (Sensation 16; Siemens, Forchheim, Germany) using the same scan protocol. Image reconstruction was performed at 60% of the RR-interval with an effective slice thickness of 3mm (increment of 2mm) and 1mm (increment 0.6mm). A dedicated convolution kernel (B35f) was applied and Agatston score, calcium mass, volume score and number of lesions were calculated using thresholds of 130HU and 350HU. Mean CT-value in a water syringe fixed to the patients chest was measured with image noise assigned to the standard deviation of these measurements.

Due to increased image noise in the thinner 1mm-slices (noise level in 3mm-slices: 16HU, in 1mm-slices: 26.1HU) these images could only be scored accurately with a scoring threshold of 350HU. Therefore only images with a scoring threshold of 350HU could be compared.
In the phantom study comparison of scoring values of 1mm and 3mm slices showed higher values for thinner slices. There was an increase of the Agatston score of 7.2%, mass of 9.5%, volume score of 9.1% and number of lesions of 13.7%.
In the patient study 29 patients (76,3%) showed coronary calcifications. Comparing scoring values of 1mm and 3mm slices also higher values were observed for the thinner slices. There was an increase of the Agatston score of 30.4%, mass of 47%, volume score of 46.6% and number of lesions of 48.9%.

In MDCT coronary calcium scoring of 1mm slice thickness leads to increased values for Agatston score, calcium mass, volume score and number of lesions in vitro and in vivo when compared to a slice thickness of 3mm.

T.F.: Works for Siemens Medical Solutions, Germany