In vivo validation of an in situ calibration bead as a reference for backscatter coefficient calculation
Objectives
The study aims to assess the capability of Quantitative Ul-trasound (QUS) based on the backscatter coefficient (BSC) for classifying disease states, such as breast cancer response to neoadjuvant chemotherapy and quantifying fatty liver disease. We evaluate the effectiveness of anin situtitanium (Ti) bead as a reference target in calibrating the system and mitigating attenuation and transmission loss effects on BSC estimation.
Methods
Traditional BSC estimation methods require external references for calibration, which do not account for ultrasound attenuation or transmis-sion losses through tissues. To address this issue, we use anin situtitanium (Ti) bead as a reference target, because it can be used to calibrate the system and mitigate the attenuation and transmission loss effects on estimation of the BSC. The capabilities of thein situcalibration approach were assessed by quantifying consistency of BSC estimates from rabbit mammary tumors (N = 21). Specifically, mammary tumors were grown in rabbits and when a tumor reached 1 cm or greater in size, a 2-mm Ti bead was implanted into the tumor as a radiological marker and a calibration source for ultrasound. Three days later, the tumors were scanned with a L-14/5 38 array transducer connected to a SonixOne scanner with and without a slab of pork belly placed on top of the tumors. The pork belly acted as an additional source of attenu-ation and transmission loss. QUS parameters, specifically effective scatterer diameter (ESD) and effective acoustic concentration (EAC), were calculated using calibration spectra from both an external reference phantom and the Ti bead.
Results
For ESD estimation, the 95% confidence interval between measure-ments with and without the pork belly layer was (6.0,27.4) using thein situbead and (114, 135.1) with the external reference phantom. For EAC esti-mation, the 95% confidence interval were (−8.1, 0.5) for the bead and (−41.5, −32.2) for the phantom. These results indicate that thein situbead method shows reduced bias in QUS estimates due to intervening tissue losses.
Conclusions
The use of anin situTi bead as a radiological marker not only serves its traditional role but also effectively acts as a calibration target for QUS methods. This approach accounts for attenuation and transmission losses in tissue, resulting in more accurate QUS estimates and offering a promising method for enhanced disease state classification in clinical settings.
