Low-dose computed tomography of the lumbar spine: a phantom study on imaging parameters and image quality.
BACKGROUND
Lumbar spine radiography has limited diagnostic value but low radiation dose compared with computed tomography (CT). The average effective radiation dose from lumbar spine radiography is about 1.1 mSv. Low-dose lumbar spine CT may be an alternative to increase the diagnostic value at low radiation dose, around 1 mSv.


OBJECTIVE
To determine the optimal settings for low-dose lumbar spine CT simultaneously aiming for the highest diagnostic image quality possible.


METHODS
An ovine lower thoracic and lumbar spine phantom, with all soft tissues around the vertebrae preserved except the skin, was placed in a 20 L plastic container filled with water. The phantom was scanned repeatedly with various technical settings; different tube potential, reference mAs, and with different convolution filters. Five radiologists evaluated the image quality according to a modification of the European guidelines for multislice computed tomography (MSCT) quality criteria for lumbar spine CT 2004. In a visual comparison the different scans were also ranked subjectively according to perceived image quality. Image noise and contrast were measured.


RESULTS
A tube potential of 120 kV with reference mAs 30 and medium or medium smooth convolution filter gave the best image quality at a sub-millisievert dose level, i.e. with an effective dose comparable to that from lumbar spine radiography.


CONCLUSIONS
Low-dose lumbar spine CT thus opens a possibility to substitute lumbar spine radiography with CT without obvious increase in radiation dose.
Department of Radiology, Örebro University Hospital and Department of Health and Medical Sciences, Örebro University, Sweden muhammed.alshamari@orebroll.se.
Muhammed
M
Alshamari
Center for Medical Imaging and Physiology, Skåne University Hospital, Lund, Lund University, Sweden.
Mats
M
Geijer
Department of Medical Physics, Örebro University Hospital, Sweden.
Eva
E
Norrman
Department of Radiology, Örebro University Hospital and Department of Health and Medical Sciences, Örebro University, Sweden.
Håkan
H
Geijer
D000818:Animals; D006801:Humans; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging*; D015588:Observer Variation; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011835:Radiation Protection / Q000379:methods*; D011856:Radiographic Image Enhancement / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012756:Sheep; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed / Q000295:instrumentation / Q000379:methods*
CT; conventional radiography; spine; structures; techniques