STIR

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STIR (Short Tau Inversion Recovery) is a T2-weighted inversion recovery MRI sequence designed to suppress fat signal by applying a short inversion time (TI) that nulls fat.

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It is especially useful in edema detection, tumor imaging, and musculoskeletal studies, offering uniform fat suppression even in the presence of magnetic field inhomogeneities.

Principle

A 180° inversion pulse is followed by a short inversion time (TI).
The TI is chosen such that the longitudinal magnetization of fat is zero when the 90° excitation pulse is applied.
This results in fat appearing black on the image, while fluid and edema (with longer T1) appear bright.

Typical Timing Parameters (at 1.5T)

Parameter	Value Range	Function
TI	~150–180 ms	Nulls fat signal
TR	Long (>3000 ms)	T2-weighting
TE	Long (~60–100 ms)	Emphasizes T2 contrast (fluid appears bright)

Key Features

Feature	STIR
Suppresses	Fat
Imaging contrast	T2-weighted, fluid-sensitive
Field strength dependence	TI must be adjusted for 3T (~210–240 ms)
Compatible with contrast agents	No (STIR nulls gadolinium-enhanced tissues too)
Susceptibility sensitivity	Less than chemical fat sat

Clinical Applications

Musculoskeletal Imaging:

Edema detection: marrow edema, soft tissue injury
Trauma: ligament/tendon tears, contusions
Infection and inflammation: osteomyelitis, myositis
Neoplasms: highlights tumor-associated edema