Tag Archives: xray

General

Final Answer: What The Heck Is It #1

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Alright, here’s the final answer to the xray I posted last Friday. This patient was using a ThermaCare Menstrual HeatWrap by Pfizer. It was applied to her back, though, for relief from back pain. It was not apparent during the trauma activation exam, even with clothes off, until we logrolled her to examine her back.

Each pocket in the wrap contains a granular mixture of activated carbon, iron powder, salt and a few other ingredients. When the wrap is removed from its vacuum pouch it heats up to 104F (40C) and stays hot for up to 8 hours. The iron shows up on xrays. The regular pattern is a giveaway that this is not some other problem (stones, drug pouches in the colon).

Bottom line: Remember, conventional xrays collapse a 3D space onto a 2D image, so you can’t tell how deep objects are (anterior to posterior). This is another reminder to be thorough when examining your patient. They can hide things anywhere!

Disclaimer: I do not have any financial or other interest in Pfizer Inc.

What The Heck Final Answer

General

How Often Are Imaging Studies Repeated After Trauma Transfers?

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Smaller trauma hospitals, both designated and undesignated, are the front line for the initial care of the majority of trauma patients. Many patients can be evaluated and sent home or admitted to the initial hospital. More severely injured patients are commonly transferred to the nearest Level I or Level II trauma center for care of injuries requiring specialists.

Imaging studies such as conventional xray and CT scan are a necessary part of the initial trauma evaluation. But is it necessary to do a full radiographic evaluation, even when it is known that the patient will have to be transferred?

Researchers at Dartmouth Hitchcock Medical Center examined the issue of repeat imaging at their Level I center. They looked at 138 patients that were transferred to them from other rural hospitals. They found that 75% underwent CT scanning prior to transfer, and 58% underwent repeat scanning upon arriving at Dartmouth.

The authors discovered the following:

  • Head CTs were repeated 52% of the time, primarily due to clinical indications
  • Spine reconstructions were repeated 33-50% of the time due to inadequate reconstruction technique
  • Chest (31%) and abdomen (20%) were repeated due to inappropriate use of IV contrast
  • 13% of image disks used incompatible software
  • 7% of images were not sent with the patient

Here are my recommendations for imaging by hospitals that refer patients to Level I or II trauma center:

  • Obtain the essential plain films recommended by ATLS (chest, pelvis)
  • If an obvious injury requiring transfer is found on exam (e.g. open fracture) do no further studies
  • Obtain any imaging studies needed to decide if you can admit the patient to your own hospital (example: abdominal CT for abdominal pain and negative FAST. Keep if no injury, transfer if solid organ injury)
  • As soon as an injury is identified that mandates transfer, do no further studies
  • Always send image disks with the patient
  • Work with your referral trauma center to obtain a copy of their CT imaging protocols so if you do need to perform a study you can duplicate their technique

Reference: Gupta et al. Inefficiencies in a Rural Trauma System: The Burden of Repeat Imaging in Interfacility Transfers. J Trauma 69(2):253-255, 2010.

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!