Keywords:
Quality assurance, Dosimetric comparison, Developmental disease, Technical aspects, Radiation safety, Imaging sequences, CT, Conventional radiography, Musculoskeletal system, Musculoskeletal joint, Musculoskeletal bone
Authors:
M. A. Shah1, C. Skiada2, M. Siebachmeyer1, M. Njunge1, H. Patel1, G. Nandra1, M. Carpenter1, J. Hutt1, N. Papadakos1; 1London/UK, 2Athens/GR
DOI:
10.1594/essr2017/P-0217
Conclusion
CT permits better assessment of femoroacetabular morphology compared to plain film imaging and is useful in directing surgical intervention where this is being considered (1).
However,
it is important that strategies to ensure as low as reasonably practicable radiation doses are employed since FAI is typically seen in the young population.
In our study the average patient was 35 years old.
At our institution,
practice has been modified so that rather than whole pelvic CT,
the scan range is restricted to the region of interest i.e.
anterior inferior iliac spine to just distal to the greater trochanter.
Additionally,
mAs is limited so that,
despite a potential image quality penalty,
adequate anatomical data for surgical planning is obtained.
Figures 1-3 show typical images from the previously employed standard pelvic CT protocol.
In comparison,
figures 4-6 demonstrate images from a low dose study and the typical reconstructions used to aid diagnosis.
This study demonstrates that large dose reductions can be achieved,
75% in our case,
by actively restricting the scan range and optimising exposure factors.
In our study the highest dose from the new protocol overlapped with the lowest dose from the older protocol.
This was due to inadequate scan range restriction and consequently skewed results.
Nevertheless,
the 1.4 mSv mean effective dose achieved in low dose studies compares favourably with the estimated 1mSv delivered by plain film radiography.
It should be noted that the estimated plain film effective dose is the sum of standard anteroposterior pelvic and lateral femoral radiographs but does not include additional ‘special’ femoral neck views and therefore likely underestimates overall dose.
It is possible that with further careful CT optimisation,
doses equivalent or lower than plain film imaging can be consistently achieved and work in this area is ongoing at our institution.
Additionally,
views of the femoral condyles are now being included to evaluate femoral torsion and the impact on the effective dose is being evaluated.
Learning point
Dose optimisation is an important consideration in the typical young,
mobile patient presenting with features of FAI.
We illustrate a low dose CT technique that,
through reducing the scan range to just the region of interest and limiting mAs,
reduces the effective dose by 75% compared to standard pelvic CT and brings doses closer to plain film radiography levels.