Neck MRA (blood vessel MRI, with and without contrast)

What it is

When a carotid artery is narrowed, the decision about whether to operate turns on how narrow it actually is. That makes measurement, rather than detection, the job of this study — and measurement is where unenhanced technique is weakest. Blood squeezing through a tight point becomes turbulent, its signal drops, and the gap on the picture can look longer than the real disease. Contrast removes that dependence: the dye is imaged as a column filling the vessel, so the narrowing is rendered as it is rather than as the flow pattern implies.

Acquiring both sets in one sitting gives the radiologist a direct comparison and a baseline for anything that appears bright after the injection. The timing is the technically demanding part — the images have to be captured in the seconds when the contrast is in the arteries and has not yet filled the veins beside them.

Why it is done

• To grade the severity of a carotid narrowing precisely enough to inform a decision about surgery or stenting
• To resolve a neck study or ultrasound that was equivocal or contradicted another test
• To examine the vessels along their whole length, including the portion near the chest that unenhanced technique covers poorly
• To assess a suspected tear in an artery wall where the unenhanced images did not settle the question
• To look at the neck vessels after a stent or previous surgery
• To investigate an abnormal tangle of vessels or an unusual vascular mass in the neck

What to expect

You are screened for metal implants and devices before going anywhere near the scanner, and asked about kidney function and prior contrast reactions. An intravenous line is placed in the arm. The unenhanced series is acquired first; then the dye is injected by pump through the line while you lie still, and a rapid set of images is taken as it passes. You may be asked to hold a breath on cue. Because two acquisitions are involved, expect an appointment closer to an hour, longer if the head is being imaged in the same slot. Some people notice a cool feeling in the arm during the injection. There is no recovery period.

Questions worth asking

• This is the most expensive of the three neck MRA codes. Ask explicitly which of the three was ordered and get the estimate against that code.
• Ask whether the contrast agent, the injector and the scan are billed as one line or three.
• Carotid duplex ultrasound and CT angiography answer a similar question at different prices and with different trade-offs. Ask what each costs here and why this one was chosen.
• If both neck and head vessels are on the order, that is two codes. Ask for the estimate itemized by region.
• If this is a pre-operative study, ask whether the surgeon's team will accept an outside facility's images — having the scan where it is cheapest only helps if the images will be used.