Purpose: The CT angiography (CTA) spot sign is a strong predictor of hematoma expansion in intracerebral hemorrhage (ICH). However, CTA parameters vary widely across centers and may negatively impact spot sign accuracy in predicting ICH expansion. We developed a CT iodine calibration phantom that was scanned at different institutions in a large multicenter ICH clinical trial to determine the effect of image standardization on spot sign detection and performance. Methods: A custom phantom containing known concentrations of iodine was designed and scanned using the stroke CT protocol at each institution. Custom software was developed to read the CT volume datasets and calculate the Hounsfield unit as a function of iodine concentration for each phantom scan. CTA images obtained within 8 h from symptom onset were analyzed by two trained readers comparing the calibrated vs. uncalibrated density cutoffs for spot sign identification. ICH expansion was defined as hematoma volume growth >33%. Results: A total of 90 subjects qualified for the study, of whom 17/83 (20.5%) experienced ICH expansion. The number of spot sign positive scans was higher in the calibrated analysis (67.8 vs 38.9% p < 0.001). All spot signs identified in the non-calibrated analysis remained positive after calibration. Calibrated CTA images had higher sensitivity for ICH expansion (76 vs 52%) but inferior specificity (35 vs 63%) compared with uncalibrated images. Conclusion: Normalization of CTA images using phantom data is a feasible strategy to obtain consistent image quantification for spot sign analysis across different sites and may improve sensitivity for identification of ICH expansion.
Bibliographical noteFunding Information:
JR receives research funding from the NIH. JG receives research funding from the NIH, Boehringer Ingelheim, Pfizer and Portola, and consults for Bristol Myers Squibb. TAB receives funding from the NIH, the Minnesota State and Spinal Cord Injury and Traumatic Brain Injury Grant and Vertex Pharmaceuticals. CL receives research funding from the NIH.
This study was funded by the following award from the National Institute of Neurological Disorders and Stroke: R01NS073344.
© 2017, Springer-Verlag Berlin Heidelberg.
- CT angiography
- Intracerebral hemorrhage
- Phantom standardization
- Spot sign