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BLACK HOLE ARTIFACTS A New Potential Pitfall
for DXA Interpretation (The Hardest Thing to See
is What You Cant See) S. L. Morgan MD, RD, CCD,
R. Lopez-Ben, MD, CCD, M. Yester Ph.D., N.
Nunnally RT (R), CDT, L .Burroughs RT (R),
CDT The University of Alabama at Birmingham,
Departments of Nutrition Sciences and Medicine
and Radiology, The UAB Osteoporosis Prevention
and Treatment Clinic
BACKGROUND
MATERIALS AND METHODS
DISCUSSION

• Approval was obtained from the UAB Institutional
  Review Board to publish clinical radiographs.
• We stacked ½ x ½ copper squares on top of a
  Hologic spine phantom and scanned them in the
  array mode using 12.17 software on a Hologic
  Discovery W scanner.
• When the pile reached a thickness of 10 mm, the
  opaque/white DXA image began to turn black and
  when the thickness was 13 mm the image was almost
  completely black. (Figures 3A 3D).

Internal metallic objects, like orthopedic
hardware appear white on properly exposed
radiographs or in dual energy x-ray
absorptiometry (DXA) scans, due to the increased
penetration of the x-ray beam. Air within the
lungs is radiolucent and black on images. We
noted a lead bullet within a vertebral body,
where the projectile scanned completely black
(Figure 1).

• The density of lead is 15.7 gm/cm3 and the Z is
  82.
• The density of tantalum is 16.6 gm/cm3 and Z
  73.
• The usual orthopedic hardware consists of
  cobalt-chromium alloys which have lower atomic
  numbers.
• Tantalum, like lead, exhibits a high degree of
  attenuation at both energies and thus the image
  ends up as black on DXA.

Figure 3C Phantom with a 11.5 mm stack of ½
copper squares. Note that the image is becoming
black in the center (arrow).
Figure 1 Lead bullet in L2
Figure 3A Scan of spine phantom with one ½ x
½ copper square on top of L3.
CONCLUSIONS

• When scanning a dense object by DXA, the dual
  energy subtraction may be zero at a certain
  density threshold and the object will appear
  black on the DXA image. The image is visible on
  a single energy scan.
• Unless this phenomenon is understood, small
  black hole artifacts, such as vascular clips
  may be overlooked or misinterpreted as bowel gas
  on PA DXA scans. It is unclear how this artifact
  affects the results of the DXA scan.
• We plan future studies to catalog various types
  of clips and determine whether they appear
  black or white on the DXA scan.
• We also plan to evaluate whether such black
  hole artifacts have a significant effect on BMD.
  

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Figure 3B Phantom with a 10 mm stack of ½
copper squares the image is still white.
Figure 3D Phantom with a 13 mm stack of ½
copper squares. Note that the image has now
become mostly black.
In addition, Weck tantalum vascular clips from an
aorto-bifemoral bypass repair appeared radio
opaque on radiographs and the single energy
vertebral fracture analysis (VFA), while they
scanned black on DXA images. (Figure 2A and 2B)
We placed lead bullets and vascular hemoclips
(Weck) made out of tantalum over the spine
phantom and scanned them in array mode on a
Hologic Discovery W scanner and scanned them in
the array mode using 12.17 software. (Figures
4 and 5A and 5B)
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Figure 5A Spine phantom with a small cassette
of tantalum vascular clips overlying L3
(arrows). It is difficult to see the clip
cassette.
Figure 4 Spine phantom with a .45 caliber lead
bullet overlying L3 the image of the bullet is
black (arrow).
Figure 5B Spine phantom with a large cassette
of tantalum vascular clips overlying L3 (arrows).
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Figure 2B DXA from patient in 2A. Notice the
black areas overlying L2 and L3 (arrow).
Figure 2A- PA and lateral VFA showing vascular
clips anterior to L2 and L3).