Protocol optimization for quantitative MRI studies in radiation oncology: II. Diffusion MRI.

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Radiotherapy
• Biomedical Engineering

Background:

• Diffusion-weighted MRI (DWI) is widely used in radiation therapy for gross target volume (GTV) delineation and treatment response assessment.
• Quantitative accuracy of apparent diffusion coefficient (ADC) maps is critical but often compromised by suboptimal scanning and simplified diffusion models.
• Discrepancies in published ADC maps highlight the need for improved quality assurance (QA) and fitting models in clinical DWI.

Purpose of the Study:

• To address the discrepancies in quantitative ADC maps derived from diffusion-weighted MRI (DWI) in radiation therapy.
• To emphasize the importance of robust quality assurance (QA) and appropriate diffusion models for accurate quantitative DWI.
• To discuss common pitfalls and methodological errors in clinical DWI studies.

Main Methods:

• Review and discussion of various quality assurance (QA) methods for clinical DWI.
• Analysis of deviations from the mono-exponential diffusion model, including diffusion time and directional dependence in human tissues.
• Illustration of how organ motion can compromise quantitative parametric diffusion maps.

Main Results:

• Standard commercial QA phantoms may not detect all methodological errors in quantitative DWI.
• Significant deviations from the mono-exponential diffusion model are observed in human tissues.
• Organ motion can introduce substantial, often unrecognized, artifacts in quantitative diffusion parametric maps.

Conclusions:

• Robust QA protocols and advanced diffusion models are essential for accurate quantitative DWI in radiation therapy.
• Oversimplified diffusion models and inadequate QA can lead to unreliable ADC measurements.
• Awareness of potential artifacts, such as those caused by organ motion, is crucial for accurate interpretation of quantitative DWI data.