Needles and Radiology Procedures

For some tests in radiology—for example, those that require intravenous contrast dye—the radiologist, technologist, or radiology nurse must use a needle. Needles can be painful and/or problematic for some patients.

The vein located at inside of the elbow (anticubital fossa) usually is the best place as far as the pain is concerned—sometimes the patient doesn't even feel it. However, the problem with that location is that when the arm bends, the IV is at risk of infiltrating. A successful procedure requires the contrast to flow from the syringe into the needle, which is safely ensconced in the vein, directly into the bloodstream. It isn't desirable for the dye to escape from the vein into the soft tissues at the site of injection. If the needle or catheter is not cleanly inserted, it may puncture the walls of the vein so that, even though most of the dye flows where it should, some gets into the soft tissues (called extravasation).

Today, extravasations in the era of low osmolarity contrast agents (LOCA) are minor problems. LOCA seems to be much less toxic to the soft tissues than high osmolarity contrast agents (HOCA) used in the past. The severe pain that some patients had with HOCA extravasations does not occur with LOCA. Still, with skilled administrations, most extravasations can be avoided.

To improve the inside of the elbow location for IVs, flexible needles—made of plastic and not metal—are now used. The so-called angiocatheters, which are simply metal needles, are fitted with a plastic catheter. Once in the vein, the metal needle is slowly withdrawn while the plastic catheter is advanced further into the vessel and left in place.

What about using the hand for an IV? While almost everyone has a decent hand vein or two, the back of the hand doesn't bend, and the physician, nurse, or technologist can actually see them better than in the inside of the elbow, this area hurts more than the inside of the elbow. Also, because there is so little space available, extravasations and black-and-blue marks are more obvious and uncomfortable in the hands. In some cases, radiologists inject contrast agents into veins in the foot and ankle.

About needles

Metal needles have a shaft with a sharp bezel at one end, and a hub that could fit onto the end of syringes at the other end. The thickness or thinness of the needle shaft is described by gauge numbers. The lower the gauge, the thicker the needle; the higher the gauge, the thinner the needle.

A 25-gauge needle is so thin that patients often don't even know when the needle is going in. To draw blood, the technicians in the lab use 19- or 20-gauge needles attached to a tube system. When you donate blood, a 16 gauge needle is used. Stereotactic breast biopsies are done with 11-/or 14-gauge needles, which are large enough to produce a core of tissue.

The problem with using just a needle in an IV is that they are difficult to immobilize. So today, the hub of the needle is encompassed into a plastic apparatus (sometimes called a "butterfly") that can easily be attached to the skin surface with tape. The metal shaft of a certain gauge needle with a sharp bezel is joined to a hub for connection to a syringe and attached to a plastic harness and immobilized to the skin with tape.

The less rigid catheter that is left in place will endure much more motion than the inflexible metal needle, but may cause a little more pain. Adding plastic also makes the needle thicker by a gauge or two and may cause a reaction in some people.

A plastic catheter with a bevel at its tip surrounding a withdrawable metal needle is called an intercath, angiocath, etc. depending on styles and brands. They come in all sizes, gauges, and models, but basically allow the injector to insert a flexible catheter into a vein.

Updated by Remedy Health Media

Publication Review By: the Editorial Staff at

Published: 01 May 2000

Last Modified: 23 Mar 2015