Multi echo imaging sequences use a series of echoes acquired as a train following after a single excitation pulse. Multiple symmetrical or asymmetrical echoes can be acquired, typically T2 weighted. In spin echo imaging, each echo is formed by a 180° pulse, but also a FSE (TSE, RARE) or EPI sequence can be used. As a difference to a normal fast spin echo sequence, in multi echo imaging, separate images are produced from each echo of the train with different T2 weightings. The signal height reduces with transverse relaxation. This drop in signal can be used to calculate a pure T2 image.

See also Fast Spin Echo.

The process of returning out of phase magnetic moments back into phase coherence. Caused either by rapidly reversing a magnetic gradient (Field Echo) or by applying a 180° RF pulse (Spin Echo). In the spin echo pulse sequence this action effectively cancels out the spurious T2* information from the signal.

See also Spin Echo Sequence and Gradient Echo Sequence.

(TE) Time between middle of exciting (e.g., 90°) RF pulse and middle of spin echo production. For multiple echoes, use TE1, TE2, etc. When the RF spin echo and gradient echo are not coincident in time, TE refers to the time of the gradient spin echo. See also Echo Time.

( TIR / TIRM / IR-TSE - Inversion Recovery Turbo Spin Echo / FIR - Fast Inversion Recovery)
A turbo / fast spin echo sequence with long TI for fluid suppression (FLAIR) or with short TI for fat suppression (STIR). This sequence allows for a true inversion recovery display that shows the arithmetic sign of the signal.
TIRM means a turboIR with a magnitude display.

See also Inversion Recovery, Inversion Recovery Sequence and Fast Spin Echo.

General MRI of the abdomen can consist of T1 or T2 weighted spin echo, fast spin echo (FSE, TSE) or gradient echo sequences with fat suppression and contrast enhanced MRI techniques. The examined organs include liver, pancreas, spleen, kidneys, adrenals as well as parts of the stomach and intestine (see also gastrointestinal imaging). Respiratory compensation and breath hold imaging is mandatory for a good image quality.
T1 weighted sequences are more sensitive for lesion detection than T2 weighted sequences at 0.5 T, while higher field strengths (greater than 1.0 T), T2 weighted and spoiled gradient echo sequences are used for focal lesion detection. Gradient echo in phase T1 breath hold can be performed as a dynamic series with the ability to visualize the blood distribution. Phases of contrast enhancement include the capillary or arterial dominant phase for demonstrating hypervascular lesions, in liver imaging the portal venous phase demonstrates the maximum difference between the liver and hypovascular lesions, while the equilibrium phase demonstrates interstitial disbursement for edematous and malignant tissues.
Out of phase gradient echo imaging for the abdomen is a lipid-type tissue sensitive sequence and is useful for the visualization of focal hepatic lesions, fatty liver (see also Dixon), hemochromatosis, adrenal lesions and renal masses. The standards for abdominal MRI vary according to clinical sites based on sequence availability and MRI equipment. Specific abdominal imaging coils and liver-specific contrast agents targeted to the healthy liver tissue improve the detection and localization of lesions.
See also Hepatobiliary Contrast Agents, Reticuloendothelial Contrast Agents, and Oral Contrast Agents.

For Ultrasound Imaging (USI) see Abdominal Ultrasound at Medical-Ultrasound-Imaging.com.