Purpose. To illustrate image quality issues that may impact quantitative measurements used to assess treatment response in a multi-site clinical trial.
Background. Quantitative longitudinal measurements on breast MRI are used to assess patient response to neoadjuvant treatment in the multi-site I-SPY 2 TRIAL. A standardized MR protocol is distributed to sites prior to site initiation. Previous work presented image quality issues1, which may affect measurements that rely on automated computerized methods. Functional tumor volume (FTV), a primary imaging biomarker monitoring treatment response, was more predictive of pathological complete response for protocol adherent exams compared to non-adherent exams2. Image quality may also impact background parenchymal enhancement (enhancement level of normal fibroglandular tissue), which is being investigated as a secondary imaging biomarker. This presentation will show example images demonstrating the challenges of quantitative MR analysis in a multi-site clinical trial.
Image quality issues include:. Motion. Motion due to patient movement during the MRI may result in skin, fat, and breast tissue being poorly defined and blurry. Mis-registration between pre- and post-contrast can cause errors in measurements. Threshold variation. For image processing, two signal intensity thresholds are applied to pixels within the region of interest (ROI), which may be adjusted when less than 50% of the tumor is segmented. The percent enhancement threshold is lowered when poorly enhancing areas of tumor are not segmented. The background threshold is lowered when a bright pixel within the ROI of the pre-contrast images causes relatively darker areas of the tumor to be poorly segmented. Scan duration variation. Scan duration is the time required to scan each T1-weighted acquisition phase. Scan duration variations occur if scan duration is outside the specified protocol range or differs from the scan duration of the patient’s baseline MRI. Longer scan duration may result in overestimation of FTV. Field of View. Field of view (FOV) is the anatomical area being imaged and is directly related to spatial resolution, which plays a key role in the FTV measurement. Incorrect FTV monitoring can occur if FOV is inconsistent between visits, outside the specified protocol range, or is overlarge for the patient.
Discussion. The image quality required for measurements used to assess treatment response in I-SPY 2 differs from the image quality that is acceptable for diagnostic evaluation, including BIRADS category, longest diameter measurements, and visual assessment of washout characteristics. In I-SPY 2, 21 sites use a variety of MRI platforms. Since quantitative measurements are increasingly used to monitor treatment response and guide clinical decision-making, high quality images are essential. Strategies must be implemented to minimize imaging issues and further refine the quantitative measurements. Ongoing studies are examining the impact of image quality factors on accuracy of treatment response prediction.
References. 1.Gibbs J et al. Abstract PS11-08: Operational standardization and quality assurance yield high acceptance rate for breast MRI in the I-SPY 2 TRIAL.