Kenneth Alan Fetterly PhD, Presenter: Nothing to Disclose

Shuai Leng PhD, Abstract Co-Author: Nothing to Disclose

Beth A. Schueler PhD, Abstract Co-Author: Nothing to Disclose

Lifeng Yu PhD, Abstract Co-Author: Nothing to Disclose

Methods to optimize cone-beam CT imaging systems for cardiovascular imaging are not well established. This work evaluated the influence of patient (phantom) size on image quality and radiation dose to provide guidance for clinical use.

Cone-beam CT images were acquired using an angiographic x-ray system with a 30x40 cm2 flat panel receptor with 0.144 mm pixel pitch. The system acquired 248 projection images over a 200 degree angular range. In-plane spatial resolution and slice thickness of the reconstructed CT images were measured. Image quality and radiation dose were measured using eight stylized phantoms with average diameter 9.8 to 35 cm. Image contrast (HU difference) and contrast to noise (standard deviation) ratios (CNR) were measured from contrast targets of dilute iodine with concentrations 7.0, 17.5, and 35 mgI/ml. The average and standard deviation of contrast and CNR values were calculated from 50 axial images. Air kerma was measured using a 0.6 cc ionization chamber inserted into the center of the phantoms and four locations which were 1 cm inside the periphery of the phantoms. Absorbed dose was specified using the single center location measurement and using a weighted average (1/3 center + 2/3 periphery) of the five measurements.

Spatial resolution was 6 lp/cm and slice thickness was 1.5 mm. The x-ray peak tube potential was 90 kVp for phantoms in the range 9.8 to 21.3 cm and increased to 125 kVp for the 35 cm phantom. Image contrast of the 7.0 mgI/ml dilution ranged from 289±2 to 120±5 HU for the 9.8 and 35 cm phantoms and CNR ranged from 25.4±1.3 to 3.1±0.2. Contrast and CNR values were increased for the 17.5 and 35 mgI/ml targets. Absorbed dose increased with phantom size and was in the range 2.0 to 12.6 mGy for the center location and 2.5 to 41.8 mGy for the weighted average method.

Image contrast and CNR decreased by 59% and 88%, respectively between the 9.8 and 35 cm phantoms. The center point dose increased by 6.3x and weighted average dose values increased by 16.7x over the range of phantom sizes. The influence of patient size on image quality and dose must be considered during clinical utilization of cone-beam CT systems.

The influence of patient size on image quality and absorbed dose must be considered when determining whether and how to use cone-beam CT for cardiovascular imaging.

Fetterly, K, Leng, S, Schueler, B, Yu, L, Assessment of a Clinical Cone-beam CT System for Cardiovascular Imaging: Influence of Phantom Size on Image Quality and Radiation Dose.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12021873.html