Diagnostics for Bone Mineralization Assessment

I recently read a couple of articles on pediatric skeletal health, and wanted to share my notes regarding patient dose. One of the roles that a Radiologic Technologist fills is that of gatekeeper regarding radiation exposure, especially when it has been determined that radiation dose is considered to be cumulative. This is particularly important when caring for our pediatric patients, as they are undergoing rapid physiological changes heightening radiation sensitivity.

Reminding ourselves of the American Registry of Radiologic Technologists (ARRT) code of ethics, which forms the first part of the ARRT standards of ethics, helps us stay aware that we are mandated to protect our patients from unnecessary radiation exposure, and that as Radiologic Technologists, we are at the forefront of patient safety and quality. These standards do empower us to advise ordering providers, perhaps suggesting alternative diagnostic imaging studies and methods.

There are a number of modalities used to determine BMD (Bone Mineral Density), a measure of bone density, reflecting the strength of bones as represented by calcium content.

DXA (dual-energy x-ray absorptiometry)

QUS (quantitative ultrasound)

mQUS (multisite quantitative ultrasound)

pQCT (peripheral quantitative computed tomography)

DXA is the most common method, using 2 levels of x-ray photons produced with either a fan beam or a pencil beam. FAN BEAM IS QUCKER BUT HAS MORE EXPOSURE DOSE. When utilizing DXA, a conscientious clinician will be aware of the type of beam that is available at the imaging facilities being utilized.

DXA has a relatively low radiation dose of 0.013 mSv. The yearly exposure limit for pediatrics is 5 mSv. DXA is also widely available.

pQCT dose is 0.03-0.3 mSv, 3-30 times more dose than DXA.

QUS has no radiation dose, working with sound waves instead of x-ray. QUS can be performed using a portable scanner.

Multisite Quantitative Ultrasound is coming up as a viable alternative. In a study published March 2016, comparing Speed of Sound (SOS) measures assessed by mQUS to BMD assessed by DXA had findings consistent with using mQUS as an alternative to DXA when DXA is not readily available. The multisite portion where QUS measurements obtained, are at the distal radius, tibia, and phalanx sites, and “provides an estimate of bone stiffness, expressed as speed of sound (SOS, in m/s) These SOS values can then be compared with normative mQUS values, that have been published for both women and men, allowing for the identification of individuals at increased risk for fracture.” The study concludes that “mQUS SOS values were found to be largely independent from DXA BMD measures. mQUS SOS measures have been previously demonstrated by” the study group “to be able to prospectively predict fragility fracture either when used as a solitary risk factor or when added to the variables included in 10-year fracture risk assessment models”. “Thus, in areas with no or limited access to DXA, the mQUS may act as a valuable tool to assess fracture risk”. (Olszynski)

Ultimately the choice is up to the ordering clinician. Quality of results must be considered in the decision making process. Consideration must also be given to exposing young patients to ionizing radiation unnecessarily. The risk of long term risk of radiation is linear, so doubling the exposure is doubling the risk. It is also known that there is no minimum safe dose of radiation, so all involved must be alert to alternative means of diagnostics.

As an alternative, multifocal quantitative ultrasound for the assessment of pediatric patient’s bone structure, should continue to be explored as a possible gold standard. This will save dose for any needed diagnostics needed when patients are into their adult years. Quantitative ultrasound is economical, and widely available. It can be performed portably and insures zero radiation exposure.