Diffusion-weighted imaging measures the movement of water within tissue and is an important part of many whole-body oncology MRI protocols.
What is diffusion-weighted imaging?
Diffusion-weighted imaging, or DWI, is an MRI technique that is sensitive to the microscopic movement of water molecules. In many cancers, cells are more tightly packed than surrounding tissue. This can restrict water movement and create a bright signal on high diffusion-weighted images.
DWIBS means diffusion-weighted imaging with background body signal suppression. It is designed to make areas of restricted diffusion more conspicuous across a large field of view.
Why is diffusion included?
Diffusion imaging can help identify and monitor abnormalities in organs, lymph nodes, soft tissues and bone marrow. It may reveal disease that is less obvious on some anatomical sequences and can be useful for treatment-response assessment.
However, a bright area on DWI is not automatically cancer. Infection, inflammation, normal organs and technical artefact can also appear bright.
Why anatomical images are still essential
Diffusion images must be interpreted with anatomical MRI sequences. The radiologist needs to locate the signal precisely, assess its structure and compare it with other sequences and previous studies.
Distortion, patient movement and incomplete background suppression can reduce confidence. The value of DWI therefore depends on acquisition quality, correction methods and experienced interpretation.
What diffusion cannot do by itself
- It cannot provide a tissue diagnosis or replace biopsy when pathology is required.
- It cannot reliably distinguish every benign process from cancer.
- It cannot replace dedicated imaging of the breast, lung, bowel, prostate or other organs when a specific question requires it.
- It cannot guarantee detection of very small or low-cellularity tumours.
What patients need to do
Diffusion imaging is sensitive to motion. Lying still and following breath-hold instructions helps reduce artefact. The sequence may make different sounds from the rest of the scan, but you will not feel the diffusion measurement itself.
Related Patient Guides
- PG1001 – MRI Scan: What to Expect Before, During and After Your Appointment
- PG1002 – What Does 3T MRI Mean? Why Protocol Design Still Matters
- PG1003 – MRI Safety with Implants, Devices, Metal and Body Piercings
- PG1004 – Claustrophobia and Anxiety During MRI
- PG1005 – MRI Contrast: Gadolinium Explained
- PG1006 – Whole-Body MRI for Cancer Staging, Surveillance and Selected Screening
We have more information on Why Not All Whole Body MRIs are the Same and other more detailed information on our Insights page
Frequently Asked Questions
For other FAQs please visit our FAQs page
Does a bright spot on DWI mean cancer?
No. It is a signal that must be correlated with anatomy, clinical information and sometimes another test.
Is diffusion imaging safe?
Yes. It is an MRI sequence and does not use ionising radiation.
Why do different whole-body MRI scans look different?
The scanner, b-values, distortion correction, coverage, resolution and supporting anatomical sequences vary between protocols.
| Important: Diffusion imaging supports diagnosis; it does not replace anatomical imaging, clinical assessment or pathology. |
PATIENT GUIDE • PG-1007 [Patient information: Diffusion-weighted imaging measures the movement of water within tissue and is an important part of many whole-body oncology MRI protocols.]
