Author: Paul Deak, Yang Li, Mark Pankuch, Yanling Qu, Maggie Stauffer, Hazel Wang 👨🔬
Affiliation: Northwestern Medicine Proton Center, GE, Northwestern Medicine 🌍
Purpose: The objective is to evaluate Relative Stopping Power(RSP) accuracy of ultra-fast switching KV Dual-Energy CT(DECT) in animal tissue and compare it to the RSP converted from Single Energy CT(SECT). While RSP can be directly measured in homogeneous material, it is not straightforward to determine in heterogeneous tissues. Proton CT(pCT) RSP can be directly measured and a comparison can then be made with derived DECT and converted SECT RSP values.
Methods: RSP of tissue-mimicking cylindrical plugs were obtained using MLIC measurements. They were placed in a cylindrical phantom and scanned using a phase-II pCT. RSP accuracy between MLIC and pCT was verified. DECT and SECT of the phantom were also taken. A fresh, post-mortem lamb head was immobilized inside a wax container and scanned upright on the pCT. Immediately afterwards, DECT and SECT were taken in the same orientation. The container was rotated 90degrees and rescanned using DECT and SECT to mimic supine orientation. This process was repeated with a post-mortem lamb shank. DECT, SECT and pCT scans were registered and ROIs for different tissues were contoured. The percentage difference of derived RSP obtained with DECT, SECT and pCT was calculated.
Results: MAPE of pCT compared to the MLIC was 1.64%±1.80%. The largest noise in the pCT existed at the center. Excluding the central and lung plug, pCT MAPE is 0.83%±0.54%. MAPE of DECT compared to MLIC was 0.61%±0.55%. For live tissue evaluation between pCT and DECT, the largest percent difference was seen in enamel(30.73%). MAPE of DECT excluding enamel is 1.46±1.22%. DECT performed better than SECT in tissue-mimicking phantoms by demonstrating RSP accuracy up to 2%. In live tissues, DECT was accurate to 2.7% while SECT was accurate up to 5.2%.
Conclusion: Fast Switching KV DECT has the potential to reduce uncertainty in RSP compared with SECT in tissue.