Can Diffusion-Weighted Imaging (DWI) be performed on old Magnetic Resonance Imaging (MRI) images stored in Picture Archiving and Communication Systems (PACS)?

From the Guidelines

No, diffusion-weighted imaging (DWI) cannot typically be performed on old MRI images stored in PACS (Picture Archiving and Communication System). DWI requires specific pulse sequences to be acquired during the original MRI scan that measure the random Brownian motion of water molecules in tissue. These specialized sequences must be planned and executed at the time of image acquisition. Once an MRI study is completed and stored in PACS, the raw data needed to generate DWI is not available, only the processed images. This limitation exists because DWI relies on specific gradient pulses and timing parameters that capture the microscopic movement of water molecules, which cannot be retroactively calculated from standard T1 or T2-weighted images.

Key Considerations

• DWI sequences are well established in stroke and tumor imaging but are finding ever-increasing applications in abdominal conditions, in part due to echo planar imaging, which increases the speed of acquisition and reduces motion artifacts 1.
• Adding DWI sequences when performing MRI to diagnose appendicitis in adults has been shown to have specificities and positive predictive values (PPV) of 100% each, and sensitivities and negative predictive values (NPV) between 97% to 99% for qualitative findings made by two experienced observers in high agreement 1.
• If DWI is clinically necessary but was not included in the original protocol, the patient would need to undergo a new MRI examination with the appropriate DWI sequences included, as the technical constraint is fundamental to how MRI physics works, and different tissue properties require specific acquisition techniques to be visualized properly.

Clinical Implications

• The use of DWI in abdominal conditions, such as appendicitis, has been shown to increase diagnostic performance and decrease the dependence on CT 1.
• Abbreviated MR protocols comprising T2 half-Fourier acquisition single-shot turbo spin echo (HASTE) and DWI images have been shown to reduce imaging and interpretation times in diagnosis of appendicitis in emergency department patients with comparable accuracy to full protocol 1.
• DWI may increase the conspicuity of the appendix, increasing the reader’s confidence of visualization, and a combination of DWI sequence and T2-weighted images provided higher accuracy for diagnosing appendicitis 1.

From the Research

Diffusion-Weighted Imaging (DWI) on Old MRI Images

• DWI can be performed on old Magnetic Resonance Imaging (MRI) images stored in Picture Archiving and Communication Systems (PACS) as it is a non-contrast technique that can be integrated into existing imaging protocols 2.
• A study from 2012 demonstrated the feasibility of directly measuring the signal intensity of DWI on PACS monitors for grading gliomas, indicating that DWI can be performed on stored images 3.
• The technique of DWI acquisition and interpretation is widely available and has been applied in various clinical applications, including oncologic evaluation and soft tissue imaging 2, 4, 5.
• DWI has emerging applications for MRI evaluation of the chest, and its quantitative nature and excellent reproducibility make it a valuable tool for tissue characterization and treatment response assessment 4.

Technical Considerations

• DWI acquisition parameters, such as selection of b values, application of parallel imaging, fat saturation, and motion correction techniques, require careful optimization to ensure accurate results 4.
• Artifacts and pitfalls must be considered when interpreting DWI studies, and solutions to existing problems in standard DWI acquisition are being developed 2, 5.
• Quantitative DWI has the potential to assess tumor aggressiveness in prostate cancer, and its application in clinical practice is being evaluated 5.

Clinical Applications

• DWI has been used in clinical practice to enhance lesion conspicability, tissue characterization, and treatment response assessment in various cancers, including gliomas, prostate cancer, and lung cancer 3, 2, 4, 5, 6.
• The apparent diffusion coefficient (ADC) mapping provides a quantitative metric for soft tissue evaluation and has been used to differentiate between benign and malignant lesions 2, 4.