Too Wide for the DXA Table?
Recently, I wrote a blog on solutions for scanning individuals that are too tall for some dual X-ray absorptiometer (DXA) tables. In this blog, I will explore what to do when an individual is too wide for the DXA scanner table. You may never encounter this issue since most DXA scanner tables are wide enough to accommodate most individuals. For example, the Hologic Horizon A DXA scanner table has a width of 28 inches so most individuals will be able to fit on the DXA table. However, it is important to remember that the actual width of the scanning area on a Hologic Horizon A DXA scanner is actually 26 inches. Still, most individuals will still fit into this scanner area; however, some athletes (i.e., football player, Olympic lifters, etc.), who have wide upper bodies as well as very large arms may not be able to fit their entire upper body in the scanning area. Another issue that may arise with scanning these individuals is that by squeezing their body to fit in the scanner area it will be difficult to separate the arms from the upper body when you analyze the scan.
DXA Manufacturers Address the Too Wide Issue
All three of the major DXA manufacturers have addressed this issue in slightly different ways. Norland (Norland at Swissray, Fort Atkinson, WI, USA) made their DXA scanner table wider (54 inches) so being too wide typically is not a problem on their DXA scanner. One downside of this is that a wider DXA table increases the overall scan time since the X-ray beam travels the entire width of this wider table. For the other two manufacturers, GE Healthcare/Lunar and Hologic, they have addressed the issue of being too wide for the DXA scanner a little differently. Both of these DXA manufacturers have developed software that takes the arm that is fully in the scanning area and uses this arm to recreate the other arm. The GE Healthcare Lunar iDXA (GE Healthcare Lunar, Madison, Wisconsin, USA) calls this “mirroring” software while Hologic Horizon A (Hologic Inc., Marlborough, MA, USA) calls this “reflection” software. One downside of this approach is that analyzing software will duplicate the arm that is fully in the scan area and replace the arm that is not fully in the scan area with this information. For all practical purposes, the two arms will have similar composition. In some situations, this may not matter; however, in some sports that predominately use one arm more than the other arm this may be an issue. For example, you may not want to use the same information to construct an arm in a baseball player or shot putter where it is unlikely that the two arms will be symmetrical. However, in a football offensive lineman, this may not be that much of an issue since the two arms will be very similar. In this offensive lineman, you may be more concerned with giving the coach information that reflects a total right and left arm versus information where one arm has complete information and the other arm has only have partial information. The coach may wonder what is wrong with one of their athlete’s arms. Therefore, as a DXA operator, you want to think about what the goal of the scan is and whether or not you want to use this software. When using the GE Healthcare Lunar scanner (Figure 1) or Hologic scanner (Figure 2) the software will first ask you if you want to use the enhanced imaging feature to reconstruct the arm. You can see that in both images there is adequate space to separate the arms from the upper torso in the analysis.
Another thing to consider is that when using a Hologic DXA scanner you will need to have at least a 25% difference between the two arms before the software will ask you if you want to use the enhanced imaging feature. Therefore, if you are using a Hologic DXA scanner and you know that you are going to want to trigger the enhanced imaging software you will need to make sure there is a 25% difference between the two arms. The best way to ensure that is to place the arm in a position that will create a 25% difference. At the end of this blog, you will find a video that will demonstrate how to do this.
Take Home Message
If you are regularly scanning athletes or very large individuals, it is likely that you will come across an individual that is too wide for your DXA scanner. No matter what DXA scanner you are using, this should not limit your ability to scan this individual. The only issue is that if you are using either a GE Healthcare Lunar DXA scanner or Hologic DXA scanner you will need to decide if you want to use that manufacturer’s software to duplicate the arm that is not in the scanner area or just use the partially scanned arm.
Figure 1 – GE Mirror
Figure 2 – Hologic Reflection
About the Author: Donald Dengel, Ph.D., is a Professor in the School of Kinesiology at the University of Minnesota and is a co-founder of Dexalytics. He serves as the Director of the Laboratory of Integrative Human Physiology, which provides clinical vascular, metabolic, exercise and body composition testing for researchers across the University of Minnesota.