Window, level, and LUT

Window/level (VOI) means choosing width and center to map raw intensities to display gray levels. LUT (lookup table) recolors the grayscale to pseudo color (hot, spectrum, or inverted) for emphasis or education—use selectively in clinical work.

Window/level in practice

• Width (W) is the range of values shown; Center (C) is the midpoint. A wider window shows more anatomy but with less contrast between tissues. A narrow window boosts contrast in a small intensity band.

Use cases

• Lung parenchyma (CT): wide window, lower center; tiny nodules stand out in air.
• Soft tissue (CT): mid-width around water density; good for solid organs and nodes.
• Bone (CT): very wide and high to include cortical and trabecular detail.

Presets in Prism

• Modality-aware auto — a starting point for many stacks when you first open. Always verify for finding-specific windows.
• CT named presets (examples) — soft tissue, lung, bone, brain are common radiology shortcuts. They translate to a window width/center pattern suited to the task.

Use case: initial read on CT CAP—start soft for abdomen, one click to lung for a lung window pass, then return to soft for nodes.

Use case: missed fracture query—bone to evaluate cortical break lines; if subtle marrow edema is on an MR, those controls live on the MR set with different VOI tools.

LUT (color) presets

• grayscale — default diagnostic viewing for most.
• inverted — sometimes preferred for CXR-like feel or to highlight a narrow band.
• hot / hsv / rainbow — use for conspicuity in teaching or to separate overlapping intensity bands. Avoid over-reliance: perceptual color scales can hide true attenuation or signal differences.

Use case: PET-CT fusion in some products benefits from a hot look on the PET stack while CT stays grayscale (availability depends on study mix).

Use case: functional CTP maps may be delivered as secondary captures; a rainbow LUT is educational but not a substitute for numeric perfusion on the workstation that generated it.

Interaction pattern

• Use W/L tool in the Navigate group, then drag in the active viewport. Vertical vs horizontal drags are mapped to W/L in the same style as DICOM readers expect (if unsure, do small moves and undo with reset—see Viewports and layouts).

• With Synchronization VOI on, changing one pane can push to others—handy for matched comparison, a distraction for mixed-phase reads.

Related

• Navigation and cine — after W/L, scroll through the stack.