Tag Archives: radiation

Imaging

Arms Up or Arms Down In Torso CT Scans?

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CT scan is a valuable tool for initial screening and diagnosis of trauma patients. However, more attention is being paid to radiation exposure and dosing. Besides selecting patients carefully and striving for ALARA radiation dosing (as low as reasonably achievable) by adjusting technique, what else can be done? Obviously, shielding parts of the body that do not need imaging is simple and effective. But what about simply changing body position?

One simple item to consider is arm positioning in torso scanning. There are no consistent recommendations for use in trauma scanning. Patients with arm and shoulder injuries generally keep the affected upper extremity at their side. Radiologists prefer to have the arms up if possible to reduce scatter and provide clearer imaging.

A recently published article looked at arm positioning and its effect on radiation dose. A retrospective review of 690 patients used dose information computed by the CT software and displayed on the console. Radiation exposure was estimated using this data and was stratified by arm positioning. Even though there are some issues with study design, the results were impressive.

The dose results were as follows:

  • Both arms up: 19.2 mSv (p<0.0000001)
  • Left arm up: 22.5 mSv
  • Right arm up: 23.5 mSv
  • Arms down: 24.7 mSv

Bottom line: Do everything you can to reduce radiation exposure:

  1. Be selective with your imaging. Do you really need it?
  2. Work with your radiologists and physicists to use techniques that reduce dose yet retain image quality
  3. Shield everything that’s not being imaged.
  4. Think hard about getting CT scans in children
  5. Raise both arms up during torso scanning unless injuries preclude it.

Reference: Influence of arm positioning on radiation dose for whole body computed tomography in trauma patients. J Trauma 70(4):900-905, 2011.

General

Radiation Exposure in Pediatric Trauma

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The use of radiographic imaging in trauma patients has exploded over the past decade. A growing amount of research is looking at adult patients, but what about children?

Johns Hopkins did a one year retrospective review of radiographic imaging in kids age 14 and below. The studies performed and the estimated radiation dose was calculated for each child. A total of 719 children were studied and they underwent a total of 4603 studies:

  • CT scans – 1457 (32%)
  • Plain radiographs – 3097 (67%)
  • Fluoroscopy – 49 (1%)

CT accounted for only 32% of studies but delivered 91% of the total radiation dose. Children involved in car crashes received the highest dose of radiation (18mSv) versus burned children, who had the lowest dose (1.2 mSv). Radiation exposure increased as the injury severity increased. The average age was 8 years, which means that these children have a long time until possible side-effects emerge.

What to do? First, seriously weigh the risks and benefits of every radiographic study before you order it. If CT is not essential, do something else. The ALARA concept is key (as low as reasonably achievable):

  • Use weight-based CT protocols in order to deliver the minimum amount of radiation needed to get decent images
  • Shield all sensitive areas that are not being imaged
  • Use focused studies
  • Avoid repeat exams
  • Become knowledgeable about the effects of radiation exposure
  • Ask yourself: “What if this were my child?”

Reference: Brown, et al. Diagnostic radiation exposure in pediatric trauma patients. J Trauma 2010, ahead of print. 

General

How Much Radiation is the Trauma Team Really Exposed To?

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Okay, so you’ve seen “other people” wearing perfectly good lead aprons lifting them up to their chin during portable xrays in the trauma bay. Is that really necessary, or is it just an urban legend?

After hitting the medical radiation physics books (really light reading, I must say), I’ve finally got an answer. Let’s say that the xray is taken in the “usual fashion”:

  • Tube is approximately 5 feet above the xray plate
  • Typical chest settings of 85kVp, 2mAs, 3mm Al filtration
  • Xray plate is 35x43cm

The calculated exposure to the patient is 52 microGrays. Most of the radiation goes through the patient onto the plate. A very small amount reflects off their bones and the table itself. This is the scatter we worry about.

So let’s assume that the closest person to the patient is 3 feet away. Remember that radiation intensity diminishes as the square of the distance. So if the distance doubles, the intensity decreases to one fourth. By calculating the intensity of the small amount of scatter at 3 feet from the patient, we come up with a whopping 0.2 microGrays. Since most people are even further away, the dose is much, much less for them.

Let’s put it perspective now. The background radiation we are exposed to every day (from cosmic rays, brick buildings, etc) amounts to about 2400 microGrays per year. So 0.2 microGrays from chest xray scatter is less than the radiation we are exposed to naturally every hour!

The bottom line: unless you need to work out you shoulders and pecs, don’t bother to lift your lead apron every time the portable xray unit beeps. It’s a waste of time and effort!

General

Repeated Head CT Scans: Are They Really Necessary?

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There is an increasing public interest regarding exposure to medical radiation. It represents the major exposure source for the population at large. There may be a presumption on the part of medical providers that “what you can’t see can’t hurt you” but this is just not the case.

A number of studies have shown that there is risk association with repeated exposure to xray. This risk is particularly important when dealing with pediatric patients. It’s time to start critically looking at our imaging practices and to start critically thinking about every one that we order.

One common source of repeat radiation is the repetitive CT scans of the head that patients who suffer TBI undergo. Frequently, there is little rhyme or reason to the patter of these scans. Should we repeat in 6 hours? 24 hours? When any lesions finish evolving?

It turns out that there is a reasonable amount of guidance in the brain literature. For the most part, they suggest that patients who are not in an ICU only need a repeat CT if their mental status changes. Any others obtained did not result in any management change. The first 6 papers listed below agree with this.

However, number 7 is interesting. It was published in the Journal of the American College of Surgeons and was a retrospective study of patients seen at a Level I Trauma Center. All patients had a lesion seen on initial scan, and underwent repeat scanning. The authors found that 6% of their patients underwent a surgical or medical “intervention” based on changes on the repeat head CT. What troubled them the most was that 21 of these 51 patients did not have any substantial neurologic change. They conclude that routine repeat head CT is very useful.

It’s not clear why their results are so disparate from the others. It is retrospective, and the authors do not state what the interventions exactly are. Nor do they speculate on why their results are so different from others. Nor do they show any difference in outcomes.

The bottom line: Repeat head CT is probably not needed in patients with mild TBI who are not on anti-coagulants or anti-platelet agents. However, regular mental status checks and GCS measurements must be taken.

References:

  1. Is repeated head computed tomography necessary for traumatic intracranial hemorrhage? American Surgeon 2005 Sep;71(9):701-4.
  2. Routine repeat head CT for minimal head injury is unnecessary. J Trauma 2006, Mar;60(3):494-9.
  3. A prospective evaluation of the value of repeat cranial computed tomography in patients with minimal head injury and an intracranial bleed. J Trauma 2006 Oct;61(4):862-7.
  4. Indications for routine repeat head computed tomography (CT) stratified by severity of traumatic brain injury. J Trauma 2007 Jun;62(6):1339-44.
  5. The role of early follow-up computed tomography imaging in the management of traumatic brain injury patients with intracranial hemorrhage. J Trauma 2007 Jul;63(1):75-82.
  6. Value of repeat cranial computed tomography in pediatric patients sustaining moderate to severe traumatic brain injury. J Trauma 2008 Dec;65(6):1293-7.
  7. Schedule repeat CT scanning for traumatic brain injury remains important in assessing head injury progression. J Amer Coll Surgeons 2010 May;210:824-32.