Category: Central DXA: (DXA, TBS)

36 - Impact of Very Dense Artifacts on Hologic and GE Lunar Densitometers

Introduction: 
Black hole-type artifacts have been described on Hologic densitometers from materials such as tantalum clips and lead bullets. Whether such artifacts occur on GE Healthcare scanners has not been reported. We hypothesized that black hole-type artifacts are specific to Hologic instruments.

Materials and
Methods:
Lead bullets (a spent .22, intact .38 special and .45 caliber) were placed overlying L3 on an anthropometric Hologic spine phantom and an encapsulated aluminum GE spine phantom. The phantoms were scanned 3 times on each instrument without a projectile and with each of the bullets placed over L3 in standard mode on a GE Healthcare iDXA and Prodigy.


Results:
Published data demonstrate that very dense metal objects such as a .45 caliber bullet can increase BMD of acrylic phantoms from 13% at the L1-L4 spine to 48% at one vertebral body (L3) on Hologic instruments. In constrast, data collected on these GE instruments found the BMD numerically decreased at L1-4 and L3, with greater effect as the bullet size increased (i.e. least change with the .22 and greatest with .45). These trends were observed using both phantoms and both instruments (Tables 1 & 2). Prodigy and iDXA BMD change ranged from 0.019 – 0.065; 0.002 – 0.039 g/cm2 respectively at L3 and 0.004 – 0.013; 0.000 – 0.008 g/cm2 at L1-4. L1-4 BMD decreased < 1%. At L3, the BMD decrease with Prodigy ranged from 2.0-5.5%; with iDXA the change was less than 1% except when using a .45 on the Hologic phantom (3.5%).


Discussion:


Technological differences exist between densitometry manufacturers. For example, Kev peaks, edge detection algorithms and shape of the region of interest at the proximal femur differ between Hologic and GE Healthcare. Therefore, confounders can be instrument specific, for example, due to differences in radiation detection, radioisotopes generally don't interfere with Hologic instruments, while these increase BMD on GE Lunar instruments. We report another difference between technologies; that measurement of highly dense materials, such as lead, have differing effects on BMD. A potential explanation is it leads to complete attenuation of both Kev peaks on Hologic, therefore the difference between the energies approaches zero and the image appears black. However, on GE Lunar instruments, there is not complete attenuation, so by subtraction, the image is still a positive. An additional difference is that GE software automatically excludes the associated BMC and area covered by the artifact, therefore minimizing the impact on BMD, as demonstrated here. In conclusion, to ensure high quality DXA acquisition and interpretation, it is important to understand the confounders of these technologies and how they impact BMD results.

Neil Binkley

Professor of Medicine
University of Wisconsin School of Medicine and Public Health
Madison, Wisconsin

Leandria Burroughs

Certified Bone Density Technologist
Kirklin Clinic of UAB Hospital
Birmingham, Alabama

Diane Krueger

Research Program Manager
University of Wisconsin Osteoporosis Clinical Research Program
Madison, Wisconsin

Diane Krueger received her Bachelor of Science degree at the University of Wisconsin-Madison. She is an ISCD-certified clinical densitometrist and a certified clinical research coordinator through the Association of Clinical Research Professionals. She has been program manager of the University of Wisconsin Osteoporosis Clinical Research Program since its inception in 1993. Ms. Krueger has extensive clinical research experience in osteoporosis and bone densitometry, having coordinated multiple industry and investigator-initiated studies. In collaboration with the UW Osteoporosis Program, she has published over 70 manuscripts and authored or presented over 100 abstracts. Her service with ISCD has included chairing the Technologist Bone Densitometry Update and Annual Meeting Committees, participating on the Education Council, serving on the Executive Committee and Board as member and officer (Secretary and four Presidential seats). She has been Technologist Bone Densitometry Course faculty since 2006.

Sarah L. Morgan

Professor, Medical Director UAB Osteoporosis Clinic and DXA Facility University of Alabama at Birmingham
University of Alabama at Birmingham
BIrmingham , Alabama

Sarah L Morgan, MD, MS, RD, FADA, FACP, CCD

Dr. Morgan is the Medical Director of the University of Alabama at Birmingham Osteoporosis Prevention and Treatment Clinic and the UAB Bone Densitometry (DXA) Service. The UAB DXA service is accredited by the International Society for Clinical Densitometry. She received degrees in Food and Nutrition and Dietetics and Food and Nutrition and Related Sciences at Iowa State University and completed medical school and an internal medicine internship and residency at the University of Iowa. She completed a Clinical Nutrition fellowship and a master’s degree in Clinical Nutrition at the University of Alabama at Birmingham. She currently is a Professor of Medicine and Nutrition Sciences in the Division of Clinical Immunology and Rheumatology. Dr. Morgan’s research interests are in the areas of folate and methotrexate metabolism in rheumatoid arthritis and bone densitometry and she participates in osteoporosis and DXA clinical trials in the UAB Osteoporosis Clinic. Dr. Morgan is s past President of the International Society for Clinical Densitometry and a past chair of the ISCD Education Council.