DWI, the ADC map and T2 shine-through
Bright on DWI does not always mean restricted diffusion. The ADC map settles it.
DWI and ADC map
DWI bright with ADC dark: water cannot move freely (restricted diffusion). DWI bright with ADC bright: T2 shine-through.
Acute infarct within minutes, abscess, epidermoid, highly cellular tumours (lymphoma, many metastases, prostate cancer). In the body it finds lesions and lymph nodes quickly.
Never read DWI without the ADC map. EPI distorts near air and metal. Blood products can be dark on both (T2 blackout).
Diffusion, ADC and shine-through
Water molecules wander. Two matching gradient pulses are applied: molecules that stayed in place are restored by the second pulse and keep their signal; molecules that moved are not, and lose signal. Tissue where water is trapped (swollen cells, pus, packed tumour cells) stays bright. But DWI is built on a T2 image, so very T2-bright tissue can look bright without any restriction.
The ADC map removes the T2 part. True restriction: bright on DWI, dark on ADC. Shine-through: bright on both.
This page is one entry from the MRI Technologist Reference
The full reference has 31 protocols, 9 dynamic study timelines, 19 artifacts, 16 scanner problems and 15 safety topics, as a PDF in English and Arabic plus an interactive tool.
Educational reference. It does not replace your site protocols, the radiologist's instructions, the MR safety officer, or the manufacturer's instructions for any implant, device or contrast agent. Parameter values are typical starting points at 1.5 T and must be adapted to the scanner, coil and patient.