ACR CT QC Manual – Measuring Beam Slice Width

In December 2013, facilities that are currently ACR accredited in CT will have to maintain a CT QC program that follows the current ACR CT QC Manual.  In addition, the frequency of specific checks will have to follow the periodicity stated in the ACR manual.  One of these checks, measuring CT slice width, can be cumbersome and expensive to perform routinely.

Typically Gafchromic film is used to measure the beam slice width of a CT scanner.  This film is one time use only, and is quite expensive.  Checking several slice width configurations for each scanner in a facility with several CT scanners will become costly.  An alternative technique for measuring the CT slice width utilizes a phosphorescent screen to temporarily record the slice width.  A nicely designed and useful phosphorescent screen is made by RTI electronics, and is called the Visi-X radiation and light field analyzer.  RTI also manufactures the popular Piranha x-ray measuring device used by many service engineers, technologists, and medical physics personnel.

RTI Visi-X Phosphorescent Screen Test Tool

The Visi-X tool is typically used for checking the light field and X-ray field alignment on a regular radiographic or fluoroscopic machine.  However, it can also be used to measure the slice width of a CT scanner.

ACR accreditation CT slice width toolThe cassette-shaped tool has a built-in scale and visible light screen to prevent phosphoresnce under normal room lighting.  From experience, it’s best to make the exposure and read the screen while the room is as dark as possible.  Even a small amount of ambient light will flood the phosphorescent screen.  This will make reading the exposed area difficult, if not impossible.  The tool can be used repeatedly, as the phosphorescent screen lifetime is not affected by the energy or number of exposures.

ACR Accreditation CT Beam Slice Width

The current ACR CT QC Manual specifies measurement of radiation beam width annually or after relevant service.  The Visi-X can be used to measure the slice width by placing it so that the center of the flat test tool is at isocenter in the scanner.  Through careful alignment the tool can be scanned at various beam widths and then immediately ‘read’ to verify slice width accuracy.

As ACR accreditation requirements for CT become more cumbersome, one must look for ways to efficiently and effectively meet the expectations of the ACR CT accreditation program.  A copy of the ACR Accreditation CT QC Manual may be downloaded for $40 from the ACR website.

Proposed License Fee Increase for IEMA Radioactive Material Licensees

Illinois radioactive material licensees look to face an increase in their annual IEMA license fee due to a recently proposed amendment to 32 Illinois Administrative Code Part 331. The proposed amendment was printed in the Illinois Register August 23, 2013, and there will be a comment period extending 45 days from the above date.  To view the proposed increase in fees for your specific license, visit the IEMA Proposed Regulations website and scroll down to page 13682.  At a glance, the fee increase looks to be 30% across the board from the 2012 rates.

Radiographic Imaging of Pregnant or Potentially Pregnant Women

The best guidance I have found regarding the imaging of pregnant or potentially pregnant women with x-rays is from this ACR Practice Guideline.

From the Guideline:

“If a patient can reliably answer that 1) she cannot be pregnant (for example, she is not sexually active, or she is using an effective form of birth control, or she is biologically incapable of conceiving) and that 2) she had a recent complete menstrual period, then it is reasonable to proceed with a medically indicated diagnostic X-ray test of the abdomen or pelvis.”


Two sample forms are included at the bottom of the ACR guidance.  These forms could be used to draft facility-specific consent forms.  The first could be used to document a negative response to pregnancy, the second for performing procedures on known pregnant women.


Update on Radon Levels – Post Mitigation System Install

A month ago I wrote about the installation of a radon mitigation system in my home.  Before the install, the level in the basement measured 12.1 pCi/L , while the level on the first floor measured 6.0 pCi/L.

After the installation of the active mitigation system, the level on the first floor of the house was reduced to 2.6 pCi/L, as measured with a charcoal detector made by Air Chek.  I haven’t rechecked the basement yet.

In addition to the lower radon reading, I’ve noticed that the basement humidity averages about 65%, and doesn’t rise much even after a good rain.  That might make for the most useful result: no more soggy cardboard storage boxes.

New Study Published on Prolonged Low Dose-Rate Radiation Exposure and Cell Repair

Researchers at MIT recently published a study on the effects of low dose-rate radiation on cell repair mechanisms.

One of the more interesting quotes in the story, suggesting that the human body already possesses substantial radiation repair capability: “DNA damage occurs spontaneously even at background radiation levels, conservatively at a rate of about 10,000 changes per cell per day.”