Comparison of Image Quality Between Conventional and Low-Dose Nonenhanced Head CT

• Published in: American journal of neuroradiology : AJNR 2004-04, Vol.25 (4), p.533-538
• Main Authors: Mullins, Mark E, Lev, Michael H, Bove, Peter, O'Reilly, Cara E, Saini, Sanjay, Rhea, James T, Thrall, James H, Hunter, George J, Hamberg, Leena M, Gonzalez, R. Gilberto
• Format: Article
• Language: English
• Subjects: Aged; Biological and medical sciences; Brain; Brain - diagnostic imaging; Brain - radiation effects; Female; Head and Neck Neoplasms - diagnostic imaging; Humans; Investigative techniques, diagnostic techniques (general aspects); Male; Medical sciences; Nervous system; Quality Control; Radiation Dosage; Radiodiagnosis. Nmr imagery. Nmr spectrometry; Radiographic Image Enhancement; Radiographic Magnification - standards; Radiometry - standards; Sensitivity and Specificity; Tomography, Spiral Computed - standards; Tomography, X-Ray Computed - standards
• ISSN: 0195-6108; 1936-959X

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. 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. 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. Although 90-mAs head CT images were moderately noisier than 170-mAs images, they were rated as having acceptable diagnostic quality.