Comparison of image quality between conventional and low-dose nonenhanced head CT.
OBJECTIVE
Increasing use of CT for evaluating neurologic disease may expose patients to considerable levels of ionizing radiation. We compared the image quality of low-mAs head CT scans with that of conventional nonenhanced scans.


METHODS
Conventional head CT scans were obtained in 20 patients (all >65 years with history of non-CNS malignancy) by using a multidetector technique: 170 mA and 1-second scanning time (ie, 170 mAs), 140 kVp, table speed of 7.5 mm per rotation, pitch of 0.75, section thickness of 5 mm, and field of view of 25 mm. A limited volume helical data acquisition covering four 5-mm-thick images was obtained by using 90 mAs but otherwise the same parameters. Three neuroradiologists visually rated the resulting images for quality in a blinded comparison. Representative 1- to 4-mm(2) regions of interest were chosen in gray matter and white matter locations. Conspicuity and the contrast-to-noise ratio were analyzed. Statistical comparisons were done by using the Student t test.


RESULTS
Mean gray matter conspicuity was not significantly different between the 170- and 90-mAs groups (0.39 +/- 0.19 vs 0.41 +/- 0.03, P =.32). Mean gray matter contrast-to-noise ratio was approximately 22% higher with 170 mAs than with 90 mAs (1.77 +/- 0.52 vs 1.39 +/- 0.38, P =.005). All 90-mAs images were rated as having slightly greater image noise than the 170-mAs scans but with sufficient perceived resolution.


CONCLUSIONS
Although 90-mAs head CT images were moderately noisier than 170-mAs images, they were rated as having acceptable diagnostic quality.
Mullins
Mark E
ME
Neuroradiology Division, Massachusetts General Hospital and the Harvard Medical School, Boston, MA, USA.
Lev
Michael H
MH
Bove
Peter
P
O'Reilly
Cara E
CE
Saini
Sanjay
S
Rhea
James T
JT
Thrall
James H
JH
Hunter
George J
GJ
Hamberg
Leena M
LM
Gonzalez
R Gilberto
RG
D000368:Aged; D016477:Artifacts; D001921:Brain / Q000000981:diagnostic imaging* / Q000528:radiation effects; D005260:Female; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging*; D006801:Humans; D008297:Male; D011786:Quality Control; D011829:Radiation Dosage; D011856:Radiographic Image Enhancement; D011858:Radiographic Magnification / Q000592:standards; D011874:Radiometry / Q000592:standards*; D012680:Sensitivity and Specificity; D036542:Tomography, Spiral Computed / Q000592:standards*; D014057:Tomography, X-Ray Computed / Q000592:standards*