Breath hold imaging in MRI is a technique with one ore more stoppage of breathing during the sequence and require therefore a short scan time. Breath hold techniques are used with fast gradient echo sequences in thoracic or abdominal regions with much respiratory movement.
Breath hold cine MRI techniques are used in cardiovascular imaging and provide detailed views of the beating heart in different cardiac axes.
Breath hold imaging requires the full cooperation of the patient, caused by usual MRI scan times from 15 to 20 sec.. In some cases breath holding can be practiced outside the MRI scanner to improve patient cooperation with the examination. Shorter scan times e.g. by parallel imaging techniques, or the administration of oxygen can help the patient to hold the breath during the scan.
See also Abdominal Imaging.

(VIBE) A T1 weighted 3D FLASH breath hold technique with fat selective prepulse.
Used for dynamic liver, pancreas, pelvis, thorax, orbita imaging and MR colonoscopy.

Respiratory compensation reduces motion artifacts due to breathing. The approach is to reassign the echoes that are sensitive to respiratory motion in the central region of k-space. The outer lines of phase encoding normally contain the echoes where the motion from expiration is the greatest. The central portion of k-space will have encoded the echoes where inspiration and expiration are minimal. By a bellows device fixed to the abdomen, monitoring of the diaphragm excursion is possible. Respiratory compensation does not increase scan time with most systems.
An advantage of very fast sequences is the possibility of breath holding during the acquisition to eliminate motion artifacts. Breath hold is commonly used on most abdominal studies where images are acquired using gradient echo-based sequences during a brief inspiratory period (20-30 seconds). To enhance the breath holding endurance of the patient, connecting the patient to oxygen at a 1-liter flow rate via a nasal cannula has been shown to be helpful.
Also called PEAR, Respiratory Trigger, Respiratory Gating, PRIZE, FREEZE, Phase Reordering.

See also Phase Encoding Artifact Reduction, Respiratory Ordered Phase Encoding.

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.

(CE MRA) Contrast enhanced MR angiography is based on the T1 values of blood, the surrounding tissue, and paramagnetic contrast agent.
T1-shortening contrast agents reduces the T1 value of the blood (approximately to 50 msec, shorter than that of the surrounding tissues) and allow the visualization of blood vessels, as the images are no longer dependent primarily on the inflow effect of the blood. Contrast enhanced MRA is performed with a short TR to have low signal (due to the longer T1) from the stationary tissue, short scan time to facilitate breath hold imaging, short TE to minimize T2* effects and a bolus injection of a sufficient dose of a gadolinium chelate.
Images of the region of interest are performed with 3D spoiled gradient echo pulse sequences. The enhancement is maximized by timing the contrast agent injection such that the period of maximum arterial concentration corresponds to the k-space acquisition. Different techniques are used to ensure optimal contrast of the arteries e.g., bolus timing, automatic bolus detection, bolus tracking, care bolus. A high resolution with near isotropic voxels and minimal pulsatility and misregistration artifacts should be striven for. The postprocessing with the maximum intensity projection (MIP) enables different views of the 3D data set.
Unlike conventional MRA techniques based on velocity dependent inflow or phase shift techniques, contrast enhanced MRA exploits the gadolinium induced T1-shortening effects. CE MRA reduces or eliminates most of the artifacts of time of flight angiography or phase contrast angiography. Advantages are the possibility of in plane imaging of the blood vessels, which allows to examine large parts in a short time and high resolution scans in one breath hold. CE MRA has found a wide acceptance in the clinical routine, caused by the advantages: