DEAR DR. DONOHUE: I have noticed several articles in the paper about the risks of radiation from medical procedures. One said to limit your exposure to no more than 50 millisieverts in one year. In the past year I have had a spine and hip X-ray, two CT scans and an MRI on my neck. I am scheduled for an injection into the neck, which will also involve an X-ray. I also have had a colonoscopy. I am scheduled for a bone density scan, which I have had every two years for the past 10 years.

Will you elaborate on the amount of radiation these procedures produce? Should I postpone the bone density test this year? I am worried. — P.H.

ANSWER: It’s good to be cautious about the amount of radiation you receive yearly, and it’s very good to keep a record of it. It’s not good to become so concerned that you refuse tests needed to keep you in good health. You have had more than your share of imaging procedures, and are justifiably concerned.

A chest X-ray serves as a frame of reference. It delivers 0.02 to 0.06 millisieverts, mSv, of radiation, not much. A yearly dose of less than 3 mSv is considered a low dose; of 3 to 20, a moderate dose; of 20 to 50, a high dose; and of more than 50, a very high dose. Theoretically, you could have 50 to 150 chest X-rays in a year and still be classified as having a low dose of radiation.

Your spine X-ray gave you 0.16 to 2.4 mSv; your hip X-ray, 0.6. The planned neck X-ray will give you another 0.6.

The amount of radiation from CT scans is much higher, and depends on what kind of scan and where it is given. A CT scan of the chest gives off 7 mSv; of the abdomen, 8; of the lower spine, 6.

MRI scans give off no radiation. Most colonoscopies are done without any radiation. The bone density scan (DEXA, dual-energy X-ray absorptiometry) for osteoporosis testing emits very little radiation, 0.0001 mSv.

Even though I had to guess about your CT scans, your total radiation is less than 20 mSv, a “low dose.” You can have the bone density scan this year without significantly adding to your radiation exposure.

DEAR DR. DONOHUE: My husband has been advised by his doctor that he might be a candidate for an InterStim procedure for urinary incontinence. Please tell me about this. — J.L.

ANSWER: The InterStim device was designed for control of urge incontinence, urine loss because of strong, involuntary contractions of the bladder muscles. These contractions send a person dashing to the bathroom many times during the day and night. Urge incontinence also is called overactive bladder.

InterStim delivers a harmless and painless electric current to nerves controlling bladder muscles. It’s a bit like a heart pacemaker, only smaller. It’s effective for people who don’t respond to bladder retraining or bladder medicines. The actual device isn’t implanted until a trial run with an external unit shows it will work. I am in favor of it for people with otherwise uncontrollable overactive bladder.

DEAR DR. DONOHUE: For the past several days, my left eyelid has been twitching. There’s no pain. It does not affect my vision. Does it mean anything? — T.P.

ANSWER: Not usually. Eyelid twitches result from spasms of muscles controlling eyelid movement. It’s intermittent and lasts for a few days, at most. Fatigue, stress and caffeine have been implicated as causes. I have had such twitching, at times when I was neither tired nor stressed nor drinking caffeine.

If the twitching is bothersome, soak a washcloth in warm water and apply it to the closed eyelid.

If twitching lasts longer than a week or two, see the family doctor.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475. Readers may also order health newsletters from www.rbmamall.com.

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