The Impacts of Vertical Off-Centring, Localiser Direction, Phantom Positioning and Tube Voltage on CT Number Accuracy: An Experimental Study

• Published in: Journal of imaging Vol. 8; no. 7; p. 175
• Main Authors: Al-Hayek, Yazan, Spuur, Kelly, Davidson, Rob, Hayre, Christopher, Zheng, Xiaoming
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 21-06-2022; MDPI
• Subjects: Abdomen; Accuracy; Computed tomography; CT number accuracy; Cysts; Electric potential; Image acquisition; localizer direction; phantom positioning; Prone position; Radiation; Radiation dosage; radiation dose; Statistical analysis; Supine position; Thorax; tube voltage; Variance analysis; vertical off-centring; Vertical orientation; Voltage; tube voltage; phantom positioning; radiation dose; CT number accuracy; localizer direction; vertical off-centring
• ISSN: 2313-433X; 2313-433X
• DOI: 10.3390/jimaging8070175

Background: This study investigates the effects of vertical off-centring, localiser direction, tube voltage, and phantom positioning (supine and prone) on computed tomography (CT) numbers and radiation dose. Methods: An anthropomorphic phantom was scanned using a Discovery CT750 HD—128 slice (GE Healthcare) scanner at different tube voltages (80, 120, and 140 kVp). Images employing 0° and 180° localisers were acquired in supine and prone positions for each vertical off-centring (±100, ±60, and ±30 mm from the iso-centre). CT numbers and displayed volume CT dose index (CTDIvol) were recorded. The relationship between dose variation and CT number was investigated. Results: The maximum changes in CT number between the two phantom positions as a function of vertical-off-centring were for the upper thorax 34 HU (0° localiser, 120 kVp), mid thorax 43 HU (180° localiser, 80 kVp), and for the abdominal section 31 HU (0° localiser, 80 kVp) in the prone position. A strong positive correlation was reported between the variation in dose and CT number (r = 0.969, p < 0.001); 95% CI (0.93, 0.99). Conclusions: Patient positioning demands an approach with a high degree of accuracy, especially in cases where clinical decisions depend on CT number accuracy for tissue lesion characterisation.