Robert MacDougall MSc, Presenter: Nothing to Disclose

Edward Yungjae Lee MD, MPH, Abstract Co-Author: Nothing to Disclose

Patricia Louise Kleinman, Abstract Co-Author: Nothing to Disclose

Feasibility of performting pediatric computed tomography angiography (CTA) at 70 kVP.  Low kVP scanning has the potential to allow for reduced patient dose and improved diagnostic quality by virtue of increased contrast enhancement in the vessel.  This phantom study aims to systematically evaluate the potential for dose reduction/improved image quality at 70 kVp in pediatric CTA exams for various patient sizes, contrast concentrations and reconstruction algorithms.

Four anthropomorohic pediatric thoracic phantoms were used (nominal ages: newborn, 1, 5, 10 years).  Phantoms contained holes (1 cm diameter) in the center and periperhy. Rods with iodine concentrations of 0, 3, 6, 8, 10, 15 mg/cc (HU = 0, 85, 170, 230, 290, 450) were manufactured.  Contrast rods were inserted into the phantom center between the lung regions. Each phantom size and concentration was scanned with the clinical CTA protocol (80 kVp) as well as 70, 100, 120 and 140 kVp (Siemens Biograph mCT).  The mA was fixed and adjusted at each kVP to match the CTDI obtained with the 80 kVP clinical protocol.  Images were reconstructed using FBP and Iterative Reconstruction (SAFIRE).  For each image set, the Contrast to Noise Ratio (CNR) was averaged over five images. Using the method of calculating the Relative Dose Factor (RDF) to optimize CNR with noise constraint (Yu, 2009), the RDF was calculated for each image set.  

At conservative levels of noise contraint (< 1.25), there were conditions that resulted in an increased Relative Dose Factor at 70 kVp.  The RDF showed dependence on the noise constraint parameter and iodine concentration.  The RDF was lower at 70 kVp in all phantom sizes for noise contraints > 1.5.

These results challenge conventional wisdom that "if 80 kVp is good, 70 kVp is better".  It is important to understand the factors that potentially allow for reduced dose at 70 kVp. It is accepted that the noise constraint should be lower for children, as children have smaller organs and less adipose tissue.  Under such conditions, 70 kVp scanning provides benefits in a very limited set of clinical situations that depend on patient size and contrast concentration.

We present the specific conditions where 70 kVP is appropriate and warn against scenarios where scanning at 70 kVp is inappropriate.  This information is valuable to end-users designing pediatric CTA protocols on scanners with 70 kVp capability.

MacDougall, R, Lee, E, Kleinman, P, Pediatric Thoracic CT Angiography at 70 kVp: A Phantom Study to Investigate Effects on Diagnostic Quality and Patient Radiation Dose.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14014155.html