Apparent Diffusion Coefficient (ADC) is an emerging quantitative imaging biomarker in oncology obtained from MR imaging. This index might predict tumor aggressiveness and therapy response at baseline. The Quantitative Imaging Biomarkers Alliance (QIBA) published a guideline to assess the reliability of ADC. Our study aims at testing the implementation of QIBA guidelines and confirm the expected results. This is a first step before assessing response thresholds of ADC for patient monitoring.
An ice–water phantom was scanned on an Optima MR 450W 1,5T (GE) following the QIBA quality control protocol. The diffusion weighted MRI images were obtained using a multislice SS-EPI sequence with b-values 0, 100, 600 and 800 s/mm2. Mean ADC and standard deviation ADC were measured over a spherical volume of interest (diameter: 4cm) placed at the center of the 0°C water cylinder (Diameter: 5 cm). To assess the spatial dependence, another acquisition was performed with the phantom in a different orientation. ADC bias error, ADC random error, ADC b-value dependence, ADC signal to noise ratio and ADC spatial dependence were assessed as defined into the QIBA guideline and were compared to the QIBA tolerances, respectively 10%, 5%, 2%, 75:1 and 5%.
The ADC bias error was about 6%, meaning the ADC measured is close to the theoretical value of 1.1*10−3 mm2/s for the 0°C water. ADC b-value dependence and ADC spatial dependence were respectively 0.5% and 3% and passed the test. With about 10%, the random error was out of the tolerance. The ADC signal to noise ratio was about 2:1, below QIBA expectations.
The obtained results do not perfectly fit with the QIBA expectations. Therefore, these data deserve further analysis and the QIBA guidelines likely to be discussed. Even if the clinical value of ADC has been put in evidence by several groups, the process of qualification of the biomarker and its performances need to be more documented.
Clinical trial identification
Legal entity responsible for the study
Centre Antoine Lacassagne, Nice, FRANCE
All authors have declared no conflicts of interest.