Vascular Application Tips: Upper Extremity And Hand MRA

Clinical indications for the detailed evaluation of the arteries of the upper extremity and hand are diverse. Most commonly, patients are referred for the evaluation of acute or chronic ischemia caused by atherosclerotic disease, thrombotic and embolic disease, vasculitis, vasospasm, and iatrogenic complications. In cases of trauma and in patients with arteriovenous malformations, hand angiography can provide diagnostic evaluation and aid in presurgical planning.

Magnetic resonance angiography (MRA), unlike conventional angiography, is noninvasive, does not require ionizing radiation, and has minimal associated risk of contrast agent reaction and renal injury. The technique is based on the principle of shortening the T1 relaxation time of blood by injecting paramagnetic contrast material, e.g. gadolinium chelate. This results in an increased signal intensity of the blood within vessels in comparison to surrounding stationary tissue on heavily T1-weighted arterial phase images. Over the years, as a noninvasive approach for assessing the aorta, its branch vessels, and the lower extremity, MRA has been established as a preferred method for initial screening and follow-up in certain patients. Today, MRA techniques prove useful in the evaluation of the vessels of the upper extremities, including the wrists and hands, where the challenge of visualizing small, fine vessels is especially great.

The patient is put in a prone position with arms extended above the head (�superman position�). If only the hand is to be imaged, use two 6-element phased array coils positioned over and under the hand respectively. No other coils are necessary. After a general scout is performed, a coronal 3D slab is positioned to cover the hand of interest. The effective thickness is about 1-1.2 mm. The field of view (FOV) is about 250 mm, with matrix of 320. With the combination of parallel acquisition technique (PAT), this data set can be acquired within 7-8 seconds. Ten to fifteen consecutive 3D CE-MRA data sets are initiated as contrast medium is injected. No timing run is necessary. Automatic inline subtraction of the first (nonenhanced) 3D volume from the subsequent identical 3D volumes obtained during and after contrast administration is performed. Automatic coronal and sagittal maximal intensity projections (MIPs) are also performed.

If both arm and hand are to be imaged, this can be done as a two-station study. The patient can be put in supine position with arms by the side of the body, using one 6-element phased array coil to cover the upper arm and another 6-element phased array coil to cover the lower arm and hand. The posterior spinal coil elements also need to be turned on. However, if high-resolution images of the hands are desired, the patient may need to be put in the �superman position� for the distal station first, and then changed to supine position for the upper station. A time-resolved 3D CE-MRA of the distal station is performed first, using a protocol similar to that is described above, except that the FOV needs to be larger and therefore the resolution lower than that of the focused hand MRA. Then the timing run is performed at the level of the aortic arch (1cc of contrast is used). Subsequently a pre-contrast 3D acquisition is planned (slab sized and positioned, coils selected, etc.) and run in the upper station. Then, during contrast injection, the prescribed slab is re-run. Image postprocessing, including subtraction and multiplanar reconstructions, is then performed.